The Natural Functions of Headwater Drainage Features: A ... · The Natural Functions of Headwater Drainage Features: A Literature Review March 2007 With over 50 years of experience,

The Natural Functions of Headwater Drainage Features:

A Literature Review March 2007

With over 50 years of experience, Toronto and Region Conservation (TRCA) helps people understand, enjoy and look after the natural environment. Our vision is for The Living City®—a cleaner, greener and healthier place to live, for you today and for your children tomorrow. For more information, call 416-661-6600 or visit us at www.trca.on.ca

The Natural Functions of Headwater Drainage Features March 2007

Toronto and Region Conservation Authority

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©2007 Toronto and Region Conservation Authority, 5 Shoreham Drive, Downsview, ON M3N 1S4. All rights reserved. The Living City is a trademark of the Toronto and Region Conservation Authority (TRCA). All other brands, logos, products or company names are trademarks or registered trademarks of their respective companies. Although every effort has been made to ensure accuracy, TRCA assumes no liability for errors or omissions. The Great Lakes Sustainability Fund is a component of the Federal Government’s Great Lakes Program. The Sustainability Fund provides resources to demonstrate and implement technologies and techniques to assist in the remediation of Areas of Concern and other priority areas in the Great Lakes. The report that follows was supported in part by the Great Lakes Sustainability Fund and addresses fish habitat and sediment issues in the Toronto Area of Concern in the Greater Toronto Area, Ontario. Although the report was subject to technical review, it does not necessarily reflect the views of the Sustainability Fund or the Government of Canada.”



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ACKNOWLEDGEMENTS

Project Manager: Laura Del Giudice Toronto and Region Conservation Authority Steering Committee: Lori Cook Toronto and Region Conservation Authority Ewa Downarowicz Toronto and Region Conservation Authority Noah Gaetz Toronto and Region Conservation Authority Scott Jarvie Toronto and Region Conservation Authority David Lawrie Toronto and Region Conservation Authority Dena Lewis Toronto and Region Conservation Authority Deborah Martin-Downs Toronto and Region Conservation Authority Maria Parish Toronto and Region Conservation Authority Leslie Piercey Toronto and Region Conservation Authority Tim Rance Toronto and Region Conservation Authority Lisa Roberti Toronto and Region Conservation Authority Brad Stephens Toronto and Region Conservation Authority Christine Tu Toronto and Region Conservation Authority Susan Jorgenson Credit Valley Conservation Karen Chisholme Halton Region Conservation Authority Sherwin Watson-Leung Halton Region Conservation Authority Jeff Anderson Lake Simcoe Region Conservation Authority Jason Barnucz Central Lake Ontario Conservation Authority Ian Kelsey Central Lake Ontario Conservation Authority Les Stanfield University of Toronto/Ontario Ministry of Natural Resources Lisa Fowler Fisheries and Oceans Canada John Pisapio Ontario Ministry of Natural Resources Mark Heaton Ontario Ministry of Natural Resources Researchers: Sonia Hugh Toronto and Region Conservation Authority Rita Barbosa Toronto and Region Conservation Authority



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TABLE OF CONTENTS 1. INTRODUCTION .............................................................................................................................................................1

1.1. PURPOSE OF THE PROJECT......................................................................................................................................1 1.2. OBJECTIVE QUESTIONS ............................................................................................................................................2

2. HEADWATER SYSTEMS: RELEVANT TERMS AND CONCEPTS ......................................................................3 2.1 FISH HABITAT............................................................................................................................................................3

2.1.1 WHAT IS FISH HABITAT?.......................................................................................................................................3 2.1.2 WHAT IS INDIRECT FISH HABITAT? .......................................................................................................................4

2.2 DEFINITION OF A ‘WATERCOURSE’ ..........................................................................................................................4 2.3 HOW DOES THE LITERATURE DEFINE WHAT IS A HEADWATER STREAM?..............................................................5 2.4 TYPES OF HEADWATER FEATURES ..........................................................................................................................5

2.4.1 According to Flow Permanence ......................................................................................................................5 2.4.2 According to Stream Order ..............................................................................................................................6

2.5 HEADWATER TERMINOLOGY WITHIN THIS CONTEXT ..............................................................................................8 2.6 ISSUES WITH CLASSIFYING HEADWATER SYSTEMS..............................................................................................10

3. THE SOUTHERN ONTARIO CONTEXT...................................................................................................................12 AGRICULTURAL SETTING .................................................................................................................................................12 4. EXPLORING FUNCTIONS OF HEADWATERS AND HEADWATER DRAINAGE FEATURES ....................13

4.1 ECOSYSTEM SERVICES...........................................................................................................................................13 4.1.1 HYDROLOGY ......................................................................................................................................................14

4.1.1.1 Streamflow Generation........................................................................................................................................... 14 4.1.1.2 Natural Flow Regime ............................................................................................................................................. 15 4.1.1.3 Flood Control ........................................................................................................................................................... 18

4.1.2 WATER QUALITY ................................................................................................................................................19 4.1.3 EROSION AND SEDIMENT CONTROL ..................................................................................................................22

4.2 BIOLOGICAL FUNCTIONS........................................................................................................................................23 4.2.1 THE RIVER CONTINUUM CONCEPT ....................................................................................................................23 4.2.2 AQUATIC FUNCTIONS ........................................................................................................................................25

4.2.2.1 Groundwater Functions and the Hyporheic Zone............................................................................................... 25 4.2.2.2 Contributions of Detritus and Invertebrates to Downstream Habitats.............................................................. 28 4.2.2.3 Woody material and Leaf Litter Contributions ..................................................................................................... 31 4.2.2.4 Organic Debris Dams ............................................................................................................................................. 32 4.2.2.5 Riparian Shading..................................................................................................................................................... 33 4.2.2.6 Direct Fish Habitat................................................................................................................................................... 33 4.2.2.7 Mussels..................................................................................................................................................................... 34 4.2.2.8 Impacts of Urbanization on Aquatic Systems...................................................................................................... 35

4.2.3 TERRESTRIAL FUNCTIONS.................................................................................................................................38 4.2.3.1 HABITAT FOR TERRESTRIAL FLORA AND FAUNA......................................................................................................... 38

4.2.4 AQUATIC-TERRESTRIAL RECIPROCAL RELATIONSHIPS...................................................................................40 5 CONCLUSION AND RECOMMENDATIONS...........................................................................................................42 6 GLOSSARY ...................................................................................................................................................................46 7 REFERENCES ..............................................................................................................................................................49



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LIST OF TABLES Table 1: Five essential components needed for successful fish habitat ________________________ 3 Table 2: Stream classification systems based on different stream characteristics. _____________ 7 Table 3: Taxonomic composition of invertebrates from headwater habitats in southeastern

Alaska _________________________________________________________________________________ 29 Table 4: Summary of headwater drainage feature functions and their benefits to downstream

channels and whether the function is supported in the literature______________________ 43



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LIST OF FIGURES Figure 1: Systems of stream ordering. Channel segments ordered by the Horton system___8 Figure 2: Conceptual view of dynamic, hydrologically active areas in headwaters_________15 Figure 3: Flow Data From the Duffins Creek Gauging Station at Pickering_______________16 Figure 4: Strategies for freshwater protection against land-use disturbances_____________17 Figure 5: A general River Continuum Concept diagram depicting upstream-downstream

linkages___________________________________________________________24 Figure 6: The hyporheic zone shown at three spatial scales__________________________27 Figure 7: Annual litter input (direct fall) as a function of stream order for rivers in eastern

Quebec___________________________________________________________32 Figure 8: Sediment removed from stripped soils during rainstorms enters streams and harms

fish habitat_________________________________________________________36 Figure 9: Contrast in seasonal dynamics of allochthonus prey contributions to forest birds and

stream fishes_______________________________________________________41 Figure 10: Food web linkage across a forest-stream interface representing predator subsidies

by allochthonus, invertebrate prey flux___________________________________42



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1. INTRODUCTION

1.1. PURPOSE OF THE PROJECT Historically, much of the early urban development within the Greater Toronto Area was concentrated in areas closest to Lake Ontario and other major lakes. As populations grew, development radiated away from the lake but remained within large “tailwater” systems (Scheckenberger, et al., 2004). Currently, development is at or approaching the headwaters of these larger systems, which could have broad implications for water quality and quantity, recharge/infiltration, and the overall health of downstream habitats. There is a need for a better understanding of headwater drainage features (HDF) to determine if and/or how development will impair the functioning of our watersheds as urban development continues to advance to the upper parts of our catchments throughout Southern Ontario. The spatial extent of headwater drainage features accounts for the majority of the total catchment area (70% to 80%) within a watershed (Gomi, et al., 2002). It has been suggested that 90% of a river’s flow may be derived from catchment headwaters (Kirby 1978). Because of this, headwater systems are thought to be important sources of sediment, water, nutrients, and organic matter for downstream reaches. However, due to their small size and because these functions are poorly understood and typically underestimated, headwater drainage features can be vulnerable to impacts resulting from agricultural and urban land uses, such as tile drainage, channel lowering, relocation, and enclosure (i.e. piping). Many Conservation Authorities have legal agreements with the Fisheries and Oceans Canada (DFO) to review development and permitting applications for potential impacts to fish habitat. When reviewing these applications, staff at Conservation Authorities is often challenged on the importance of intermittent and ephemeral streams to fish habitat and how these small features contribute to the overall health of a watershed either directly or indirectly. Practitioners in general may also find it difficult to ascertain the importance of smaller drainage features because of the lack of a standardized and consistent approach. There is a lack of clarity around how Conservation Authorities (CAs) should be treating small drainage features through planning and permitting processes in order to properly protect ecological functions and contributions to watershed health. These features may constitute direct or indirect fish habitat, both of which are included in the definition of fish habitat under the Federal Fisheries Act. Some headwater systems will support fish year-round because there is a permanent supply of water. In these types of features it is relatively simple to confirm fish presence. However, some features with intermittent or ephemeral flow may not provide direct fish habitat, but may provide indirect fish habitat via the contribution of flow, detritus, and invertebrates, others will provide seasonal fish habitat when the water table within the feature is seasonally high or provide refugia. The agreements Conservation Authorities have with DFO are to review projects for any potential harmful alteration, disruption or destruction (HADD) of fish habitat, under Section 35 of the Federal Fisheries Act. Depending on the level of agreement (Level I, II, and III require differing levels of review), Conservation Authorities may need to determine if a HADD is likely to occur. For example, CAs that have Level II and III agreements would determine whether a



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project would likely result in a HADD, and if the CA has a Level III agreement, it would negotiate compensation and forward the application to DFO to authorize the works. There is currently no DFO policy document currently available that provides specific detail and guidance to CAs as to what constitutes indirect fish habitat when making a management decision regarding headwater drainage features. Where an HDF constitutes a “watercourse,” it is subject to the Generic Regulation 166/06 under the Conservation Authorities Act. The definition for watercourses used by Conservation Authorities has changed since the recent adoption of the Generic Regulation approved in May 2006. The Generic Regulation brought all 36 Conservation Authorities’ regulations into conformity with one regulation. This new definition may provide more flexibility in interpreting which drainage features qualify as a “watercourse” subject to the regulation, thereby requiring applicants to obtain approval from Conservation Authorities prior to interference with these features. This review will ultimately contribute to the development of an in-field assessment tool for determining the management objectives of HDFs via both the Federal Fisheries Act and the new Generic Regulation. By summarizing the scientific findings relating to the ecological functions of HDFs, it is intended that this review will provide recommendations for future research efforts in order to fill any gaps in the available science, as well as management direction provided through an interim guideline.

1.2. OBJECTIVE QUESTIONS The objective questions of this literature review are broad, but are intended to assist with the development of a comprehensive understanding of headwater features and their functions. This will facilitate the development of a management tool for these resources. The objectives are to answer the following questions;

1) What are the ecological functions provided to fish and aquatic communities by headwater drainage features (e.g. surface and groundwater contribution, flow attenuation, natural nutrient and detritus provision, contaminant removal, invertebrate production, seasonal habitat, and woody material, etc.)?

2) How is/should indirect fish habitat be defined? What are the important ecological

attributes of indirect fish habitat?

3) What other important hydrologic, hydrogeologic, geomorphologic, and water quality functions do headwater drainage features provide? For instance, how is the hyporheic zone linked to water quality in HDFs? How much recharge contribution do headwaters cumulatively provide in a watershed? How do HDFs contribute to sediment regulation?

4) What are the ecological, hydrological, and fluvial geomorphological impacts of enclosing

headwater drainage features on both in-situ direct and indirect fish habitat and downstream fisheries?

5) Do open headwater drainage features in urbanized areas function in the same manner

as streams in agricultural or forested areas?



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6) What engineering, drainage or mitigation measures and guidelines/evaluation criteria are required to properly protect the ecological functions of headwaters in urbanizing areas? Can the functions of headwater drainage features be adequately replicated by stormwater management?

7) What are the terrestrial functions that are offered by headwater streams?

2. HEADWATER SYSTEMS: RELEVANT TERMS AND CONCEPTS

2.1 FISH HABITAT

2.1.1 WHAT IS FISH HABITAT? Fish habitat is any constituent of an aquatic system that provides cover, food, reproduction, water quality, and migration routes (As seen in table 2) (Fisheries and Oceans Canada 2003). Fish habitat is defined in the Federal Fisheries Act (R.S., c. F-14, s. 34 (1) (e)) as the “spawning grounds and nursery, rearing, food supply and migration areas on which fish depend directly or indirectly in order to carry out their life processes”. The term fish includes “parts of fish; shellfish, crustaceans, marine animals and any parts of shellfish, crustaceans or marine animals, and the eggs, sperm, spawn, larvae, spat and juvenile stages of fish, shellfish, crustaceans and marine animals” (Fisheries Act, R.S., 1985, c. F-14, s. 2 (e)). The function of headwaters as direct fish habitat or habitat for organisms not associated with larger streams is poorly known (Richardson 2000). Table 1: Five essential components needed for successful fish habitat

COMPONENT CHARACTERISTIC Cover Cover exists in many forms including deep pools, rocks, overhanging plants,

substrate, undercut banks and woody materials. Any area that allows for escape from competitors, predators, extreme temperatures and high flow is considered to be cover.

Food Food can range from algae to dragonflies for small fish, and smaller fish to worms for bigger fish. Production of food is dependant on substrate and riparian characteristics. The provision of an adequate food supply is essential to fish survival and reproduction.

Reproduction Most fish have specific spawning, nursery and rearing habitat requirements for reproduction. Substrate, water quality, temperature and velocity are all important factors in successful fish reproduction.

Water Quality Water quality is an important component due to the specific habitat requirements of most fish. Any changes to the surrounding terrestrial and aquatic systems could alter temperature and introduce sediment, chemicals and other deleterious substances, which can degrade water quality.

Migration Routes Migration routes are the corridors that allow the passage of fish from one part of the watershed to another. Any barriers that block migrant activities like spawning, feeding, and over-wintering can damage fish populations.

(Source: Fisheries and Oceans Canada 2003; Evanitski 2002)



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2.1.2 WHAT IS INDIRECT FISH HABITAT?

Most of the ecological function usually imparted to small streams is the availability of seasonal fish habitat. Seasonal fish habitat clearly constitutes direct fish habitat under the Federal Fisheries Act (FFA). The assessment of this function is usually easy to assess in the field through standard fisheries inventories (i.e. fish are present at some point during the year, usually in spring). The part of the FFA definition of “fish habitat” that we are mostly interested in, in the context of this review, is the concept of indirect fish habitat. This is the part of fish habitat “on which fish depend indirectly” according to the FFA definition. Although DFO has not provided any formal guidelines for assessing what constitutes indirect fish habitat, in practice it is generally considered to be ecological features that do not directly support fish, but supply food, nutrients, flow, and organic material to downstream habitat that contains fish. Wetlands can also be considered indirect fish habitat; however, in this case, we are focusing on wetlands that are hydrologically connected to linear drainage features by a surficial pathway (i.e. riparian wetlands are included, but off-line, non-floodplain wetlands are not included). In order to defensibly constitute indirect fish habitat, a drainage feature generally must satisfy at least one of the components outlined in Table 1 above. In the context of headwater streams, the feature would need to contribute food (detritus or invertebrates), cover (woody material and leaf litter) to downstream habitat, or improve downstream water quality. While this offers a broad sense of what is indirect fish habitat, the intent of this study is to provide further guidance for defining what specifically qualifies as one of these functions, how these functions may translate into on-the-ground features, and how important these features are to fish habitat.

2.2 DEFINITION OF A ‘WATERCOURSE’

Originally, the Conservation Authorities Act did not include a definition of “watercourse.” In order to have a consistent approach to managing and regulating drainage features within the agency, some Conservation Authorities used the Black’s Law Dictionary definition of a watercourse, as follows: Flowing water, though not necessarily continuous, within a defined channel with bed or banks and usually discharges itself into some other stream or body of water The amendments to the Conservation Authorities Act that were approved in 1997 included a definition of “watercourse”; however the adoption of this definition did not legally come into force until the approval of the Generic Regulation in May 2006. The Generic Regulation brought all 36 Conservation Authorities (CAs) different regulations into conformity with one regulation, and finally gave Conservation Authorities an opportunity to apply a consistent “watercourse” definition. The new definition is as follows: An identifiable depression in the ground in which a flow of water regularly or continuously occurs The new definition no longer incorporates the “defined channel with bed or banks” concept within the Black’s Law definition and perhaps provides more flexibility on what features can be regulated. Since a feature that may not have enough regular or continuous flow to form a defined bed or banks is no longer necessarily excluded from the regulation, based on the new



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Generic Regulation, the regulatory boundaries of these features may need to be reexamined. Part of the intent of this literature review is to determine whether there is an ecological and/or hydrological argument for doing this. The term watercourse is considered to be interchangeable with the term stream, since there is no legal definition for the latter.

2.3 HOW DOES THE LITERATURE DEFINE WHAT IS A HEADWATER STREAM?

There are many definitions for headwater streams as described in the literature. Headwater systems, headwater drainage systems, headwater drainage features, small streams, or simply headwaters are all terms that are used. Some refer to the headwater streams as the beginnings from which water originates within a watershed network and may include small swales, creeks and streams (Gomi et al. 2002, Ohio EPA Keyfindings 2003). Meyer et al. (2003) use the term headwaters, to describe the smallest streams in the network. Others suggest that headwater streams represent the beginning of the River Continuum, as described by Vannote et al., in 1980 (Richards 2004). Some exceptions exist, for example, in Ohio, the Environmental Protection Agency (EPA) does not consider grass waterways or other watercourses that do not have a defined bed and bank as primary headwater streams (Ohio EPA Keyfindings 2003). The Ohio EPA (2003) considers headwater streams to be generally small in area and often less than one square mile (2.6 km2 or 260 hectares) in size.

2.4 TYPES OF HEADWATER FEATURES

2.4.1 According to Flow Permanence

Perennial Headwater Stream A perennial stream refers to a watercourse that continuously carries water throughout the year (i.e. is permanently flowing) and is predominantly fed by groundwater (Ohio EPA Keyfindings 2003, Richards 2004, Town of Markham 2004). This type of permanent stream is usually associated with coldwater streams, which have a temperature regime that supports terrestrial and aquatic species adapted to the presence of cool water. Examples of such species include salamanders, certain insect larvae such as mayflies, stoneflies and caddisflies, as well as fish species like brook trout, sculpin, brook lamprey, brown and rainbow trout (Ohio EPA Keyfindings 2003, Town of Markham 2004). We will not be discussing perennial streams in this document as their functions within the watershed are well-documented and well-understood and their ecological validity is typically not questioned. Intermittent Stream Intermittent streams only flow for several months (usually 4-5 months) during the year, most commonly during the wetter periods or seasons, where the streambed is below the water table and water availability is higher (Gomi et al. 2002, Ohio EPA Import 2003, Meyer et al. 2003, Meyer and Wallace 2001, Richards 2005).



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Depending on the amount of flow within these streams, the development of a defined channel bed or banks usually occurs.

Ephemeral Stream Ephemeral streams do not flow throughout the year, but rather flow periodically on an irregular basis, generally in response to a specific rainstorm event (Meyer et al. 2003, Richards 2005) or snowmelt. Hansen (2001) examined the characteristics of stream types within the Chattooga River watershed in the Blue Ridge Mountains of southeastern US (South and North Carolina). He found that the presence of a defined channel was the primary indicator separating perennial and intermittent streams from ephemeral features. Without regular and frequent flow, ephemeral channels are typically ill-defined. In the Greater Toronto Area, such streams are commonly referred to as swales. A swale is a shallow, drainage hollow or depression that collects water (Meyer et al. 2003, Town of Markham 2004) and, in the past, was not typically considered to be a watercourse because it lacks a defined bed or banks. The density of undefined headwater features, or swales, in a watershed is a function of the surficial geology. Areas with a high frequency of swales are typical when the surficial geology consists of fine-sediments with low infiltration and recharge capacities. These systems respond rapidly to rainfall events and are typical of lacustrine deposits such as the Peel plain. When underlying soils are coarser, such as alluvial sands and gravels, recharge rates are higher resulting in a lower drainage density. These systems have a more moderated hydrologic response (Gorenc et al. undated), and are more typical of sediments found on the Oak Ridges Moraine.

Intermittent and ephemeral streams are most commonly associated with warm water streams because they are usually fed by precipitation or snowmelt events, rather than by cooler groundwater. These streams can support species suitable for warm water conditions such as certain amphibians, insect larvae such as dragonflies and damselflies, and some fish species that may include northern pike, basses, darters, and various minnow species (Ohio EPA Keyfindings 2003, Town of Markham 2004). However, seasonal groundwater inputs to intermittent streams can also occur.

2.4.2 According to Stream Order

There are many different ways of classifying stream systems using a number of stream characteristics as shown in Table 2. However, the most common, as found in the literature, was the Horton channel ordering system, which uses numbers to define a stream depending on its location in the network’s branching pattern (Benda et al. 2005, Horton 1945, Meyer et al. 2003, Platts 1979). Headwaters are represented by the lowest ordered streams, which include; zero-, first- and second-order streams (Meyer et al. 2003, and Richards 2004).



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Table 2: Stream classification systems based on different stream characteristics.

CLASSIFICATION SYSTEM/SOURCE

STREAM CHARACTERISTIC USED

Klugh 1923 Water velocity Pearse 1939 Channel substrate

Thompson & Hunt 1930 Size of drainage basin Horton 1945 Stream branching Huet 1959 Stream slope and velocity

Odum 1959 Habitat

Usinger 1963 Temperature, altitude, rainfall, and permanence of water

Platts 1974 Geomorphic conditions

A zero-order stream refers specifically to small, non-permanently flowing intermittent, or ephemeral swales that lack distinct stream banks but still act as conduits of water, sediment, nutrients, and other materials during snowmelt and rainfall (Benda et al. 2005, Gomi et al. 2002, Meyer et al. 2003, Richards 2004). Sometimes zero-order streams are called zero-order basins and the ephemeral or intermittent channels that emerge from these basins are referred as “transitional” channels (Gomi et al. 2002).

First-order streams are the smallest distinct watercourses that are visible on 1:25,000 or 1:50,000 topographic maps and are generally the uppermost, unbranched tributary channels with either perennial flow or sustained intermittent flow (more than 4-5 months during an average year) (Gomi et al. 2002, Meyer et al. 2003, Platts 1979, Richards 2004). Rogers and Singh (1986) proposed that first order streams are streams with no contributing upstream tributaries and that they are formed when the tractive force exerted by surface flow is sufficient to entrain sediment. First-order streams usually have either perennial flow or sustained intermittent flow such that water may enter the stream from a hillside spring or by overland movement (Gomi et al. 2002, Meyer et al. 2003, Richards 2004).

Second-order streams are formed when two first-order streams combine and third-order streams form by the combination of two second-order streams, and so on, according to Horton’s (1945) system as modified by Strahler (1957). The most common practice in deriving these orders is to take the blue-line network at an appropriate map scale (typically 1:25,000) as the initial basis (Knighton, 1998). The ordering system involves the following rules: (i) fingertip tributaries originating at a source are designated order 1; (ii) the junction of two streams of order u forms a downstream channel segment of order u + 1; (iii) the junction of two streams of unequal order u and v, where v>u, creates a downstream segment having an order equal to that of the higher order tributary v (Knighton, 1998; see Figure 1).



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Figure 1: Systems of stream ordering. Channel segments ordered by the Horton system as modified by Strahler (1952). (Source: Knighton, 1998). In Canada, National Topographic System (NTS) of Canada base mapping is at 1:50,000 scale, hence most stream ordering systems are derived at this scale. Second-order streams can also be intermittent (Gomi et al. 2002) depending on the basin characteristics such as precipitation pattern, vegetation, geomorphology, and hydrogeology. Although both first and second-order streams in our regional setting can have permanent flow or have defined bed or banks, there are areas where second-order streams are intermittent, such as where the soils are tight (i.e. Peel Plain). The intermittency of flow is more important in the context of this review than the stream order, since flow permanence is likely more closely tied to function than stream order.

2.5 HEADWATER TERMINOLOGY WITHIN THIS CONTEXT In order to minimize confusion over the types of features we are referring to, it is critical to clarify some key terms. For the purposes of this literature review, it is necessary to distinguish between the broad concept of headwater systems referenced in the literature from the mainly ill-defined, ephemeral and intermittent features with which we are mostly interested. Usually, when headwater streams are referenced in the literature, permanently-flowing streams are implied, but the term can also refer to all features including, catchments, zero-, first- and second-order streams. Henceforth, this broad reference to the permanently and non-permanently flowing features in upper reaches of catchments will be termed headwaters, headwater streams or headwater systems. However, in this review, we are mostly interested in the hydrological drainage features at the very top of catchments that may not have enough continuous flow to form an identifiable bed or banks. We will refer to headwater drainage features (HDFs) when we are specifically discussing ill-defined, non-permanently flowing drainage features that would not qualify as direct fish habitat under the FFA, or as a



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‘watercourse’ under the old Black’s Law Dictionary definition. It is these features that we are mostly interested in, in the context of this review. However, the recommendations that will be developed as an interim management guideline will need to discuss both permanently and non-permanently flowing features. While the majority of the features we are concerned with here will be located at the top end of the watersheds, non-permanently flowing drainage features can also be tributaries to larger streams anywhere within the watershed. We expect that headwater drainage features that drain directly into higher order streams (i.e. third-order or higher) would function similarly to headwater drainage features at the upper end of watersheds. These streams would also be subject to the same debate in terms of their management, and as such, are also of interest in the context of this review. Because the available literature that specifically examines headwater drainage features is scarce, we will be discussing the findings in the science that focus on the broad concept of headwaters and make specific correlations to HDFs where possible. This is important because the functions that can be related to first- and second-order streams may also be true of HDFs; except the science may not be presently available to support this. Understanding the functions of permanently flowing and/or first- and second-order streams may inform the understanding of headwater drainage features and provides a context for the type of functions that may exist. Similarly, while first- and second-order streams may be intermittent or even ephemeral, we draw from literature examining the functions of non-permanently flowing streams in order to understand how flow permanence may affect functionality in the context of headwater drainage features. EXAMPLES OF HEADWATER DRAINAGE FEATURES

(Photo Credit: HRCA) (Photo Credit: HRCA)



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(Photo Credit: HRCA) (Photo Credit: TRCA) EXAMPLE OF A FEATURE NOT CONSIDERED TO BE AN HDF

RILLS OR FURROWS

2.6 ISSUES WITH CLASSIFYING HEADWATER SYSTEMS It is evident from the literature that studies of headwater systems are not given as much attention as larger streams (third-order and larger). This is due to the notion that headwaters can lack obvious resources, such as fish, and most are difficult to access and work in (Benda et al. 2005). When compared to larger downstream systems, the roles and importance of headwater streams are typically underestimated and mismanaged because of their size and



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number (Gomi et al. 2002). However, headwater streams can represent between 70-80% of total catchment area or 50-80% of the total length of the river network (Benda et al. 2005, Beschta and Platts 1986, Gomi et al. 2002, Lowe and Likens 2005, Meyer et al. 2003, Ohio EPA Import 2003, Peterson et al. 2001, Platts 1979, Richards 2004, Richardson 2000, Schlosser 1982, Veliz et al. 2005).

In the United States, a problem with headwaters that is revealed in the literature is that low order streams are not all represented on topographic maps. It is estimated that only about 20% of the headwater stream network is shown on current United States Geological Survey (USGS) maps (Meyer et al. 2003). Intermittent and ephemeral headwater streams become most problematic to define and classify. This is primarily due to the fact that intermittent and ephemeral streams have not been studied or explored for the ecosystem services they provide (Meyer and Wallace 2001). In addition, there are problems classifying streams using Strahler’s (1957) method when stream orders depend on scales of map used; when stream orders change based on topography within the catchment (hills vs. plains); and when stream orders are not suitable for explaining hydrologic, geomorphic, or biological processes (Gomi et al. 2002). Hansen (2001) found that flow duration criteria are difficult to measure and verify across regions. Similarly, Shreve (1965) suggested that the stream ordering as described by Strahler (1957) could change with field verification or mapping, and he reported instances where even one incorrect placement of just one source channel could cause a reordering in each larger downstream reach within the network. Because HDFs cannot typically be interpreted from the scale of maps used to determine stream orders (i.e. 1:50,000), they are frequently omitted from the ordering system. HDFs can also be difficult to sample for fish due to the lack of flow.

In addition, there can be within-catchment differences. For example, Williams and Magnusson (2002) conducted a preliminary review of 1:50,000 topographic maps in southern and central Ontario and estimated that the densities of intermittent streams were 0.08 to 1.08 per km2. On average, 85.3% of all first order streams shown on these maps were marked as being intermittent at their source. However, in heavily forested areas where wetlands provide the water source for many of the streams, this value declines to only 13%.

Therefore, the misrepresentation and misclassification of small streams, coupled with the lack of knowledge of headwater streams have resulted in minimal, if any, protection and conservation concerns from land use changes and development (Benda et al. 2005, Meyer et al. 2003). In the Nairn Creek watershed of the Ausable River Basin in Southern Ontario, Veliz and Richards (2005) identified that 69% of first order and 29% of second order streams had been enclosed to accommodate agricultural activities between 1960 and 1980. Small streams are difficult to identify and classify because they drain a variety of landforms and landuses, and they have been historically altered within the urban and agricultural settings of Southern Ontario.



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3. THE SOUTHERN ONTARIO CONTEXT Agricultural Setting Since European settlement first occurred within Southern Ontario over a hundred years ago, much of the once pristine forested landscape was cleared for agricultural land uses. Today, agriculture is still one of the dominant land uses throughout Southern Ontario. Impacts to streams within the region have extensively occurred since land clearing and agricultural uses began. Although some headwater drainage features remain in a forested setting, these forests are typically relatively small and fragmented. For the most part, we are not dealing with the pristine or near-pristine systems that may be present in other settings where headwater drainage systems have been studied. Potential effects of agriculture on headwaters include inputs of eroded soil, nutrients and pesticides; removal of the riparian canopy; physical disturbance of the channel by grazing sites in agricultural basins; and disruption of the hydrological regime by removal of vegetation and agricultural land use (Barton, 1996). Many small streams and drainageways were also channelized and re-routed to maximize agricultural land use efficiencies. Much of the agricultural lands in Southern Ontario have tile drains which are installed by farmers in order to remove excess water from lands to improve crop yields. Tile drains modify two natural hydrologic functions. First, they intercept the water that would normally infiltrate into the groundwater system, by moving laterally to discharge in a drainage pipe. Secondly, tile drains accelerate the rate at which water flows, which promotes drying of surface soils to allow for cultivation earlier in the year. This drying action also allows for more surface compaction, and reduces the water volume capacity of the field, which then potentially increases runoff rates and decreases baseflow levels. With the conversion from natural landscape to agricultural production, there is generally an increase in peak runoff rates, sediment losses and nutrient losses, although some exceptions occurred as reported by Skaggs et al (1994), Fraser and Fleming (2001), and Richards (2004). In some cases, improved subsurface drainage actually decreased peak flow volumes, surface soil erosion, sediment loss, pollutants (nitrates and soluble salts), but increased other nutrients such as phosphorus and organic nitrogen (Fraser and Fleming 2001, Richards 2004, Skaggs et al. 1994). Urban Setting The impacts on biological communities by agricultural practices and land use are similar to urbanization impacts in some ways. However, while agricultural practices degrade biological communities, the impacts are generally less severe than those from urbanization (Wang et al. 2000; Schueler and Holland 2000). This is primarily because agriculture does not require extensive alterations to hydrologic processes resulting from the introduction of impermeable surfaces. Although stormwater management practices, which are relatively recent phenomena, do help to mitigate some of the impacts of urbanization. As development continues to proceed to the upper portions of our watersheds, agricultural lands that dominate our landscapes are converted to urban uses. These uses introduce a whole new level of impact to the ecology of headwater drainage features and the downstream habitats to which they are connected.



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Most of the literature focused on the general impacts of urbanization to a stream such as increased runoff and other hydrologic changes. Only a limited number of sources were specific to the implications on smaller streams and headwaters. The main direct impacts of urbanization on headwater drainage features include enclosure (i.e. piping), realignment, and feature lowering/deepening. Studies examining the impacts of these activities on headwater drainage features were few for piping and altogether absent for the latter activities. This is not surprising since there were few studies available to support the functions of headwater drainage features in an undisturbed state. Since literature on the effects of enclosing a stream is scarce, we assumed that urbanization implied that drainage pipes, stormwater and sewer outlets would be included in the process of urban land use. Therefore, we could assume that implications of “urbanization” on headwater drainage features would subsequently also include impacts of enclosing these features in pipes. In the context of this review, urbanization is formally defined as, modification of a catchment by clearing vegetation, compacting soil, ditching, draining, piping and ultimately covering land with impermeable surfaces (Booth and Jackson, 1997).

4. EXPLORING FUNCTIONS OF HEADWATERS AND HEADWATER DRAINAGE

FEATURES

4.1 ECOSYSTEM SERVICES

The literature discusses many biological functions of headwaters in their broad sense, however before we discuss these, it is important to outline the physical processes that shape the environments upon which biota depend for habitat, both in headwaters themselves, as well as those downstream habitats that are influenced by headwater processes. Some of these physical processes also provide potential functional benefits to humans. This concept is referred to in the literature as ecosystem services (Daily 1997, Meyer et al. 2003, Meyer et al. 2005, Palmer et al. 2004). Ecosystem services may include providing flood mitigation, maintaining water quantity and quality, recycling nutrients, and preventing sedimentation of downstream channels (Meyer et al. 2003).

These services may also offer many economic benefits. The Ohio EPA (2003) highlights how headwater streams can aid in reducing costs of dredging, water treatment, human health risks, as well as preventing excess erosion. In addition, by providing natural habitat for wildlife, headwater streams can easily increase property values and improve recreational opportunities for hunting and fishing (Ohio EPA Import 2003).

An excerpt from The Rivers Handbook by Burt (1992) states that “the importance of the headwater region is that it determines both the quantity and quality of water received downstream, and as such, may impose important constraints on resource development and hazard control on the main river.” Is this true of the small intermittent and ephemeral drainage features we are interested in as well? We will explore this below.



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4.1.1 HYDROLOGY 4.1.1.1 Streamflow Generation Freeze (1974) summarized research that had been conducted to examine the mechanisms by which water moves from hillslopes into small stream channels in response to storm events in headwater catchments. One conclusion drawn from previous studies was that overland flow does not widely occur in time and space in humid (non-arid) vegetated basins, because vegetative cover protects the soil from raindrop impact, thereby promoting infiltration and preventing flash-flooding. Freeze also discusses the ‘variable source area’ concept of expanding and contracting channel systems, as first described by Hewlett and Nutter (1970), which is as follows: An expanding channel network…[wherein] the channel reaches out to tap the subsurface flow systems which, for whatever reason, have overridden their capacity to transmit water beneath the surface…The rapidly expanding channel allows subsurface flow, even at velocities of only a few feet per day, to reach the channel in time to contribute to and sustain the upland storm hydrograph…[The] expansion is aided by rain falling directly on the wetted areas. More current thinking around this concept supports the idea that saturated overland flow contributes more significantly to this process than subsurface flow (Sidle et al. 2000). Over a large part of the drainage area, including the period during intense and prolonged precipitation, all precipitation enters the soil. After some time passes, infiltration and throughflow cause the shallow water table areas adjacent to streams to rise, and subsequently the lower valley slopes also become saturated. As these surface-saturated areas can no longer store any additional water, excess precipitation flows toward the stream and contributes to streamflow (Ward and Robinson 1990). During very wet conditions, zero-order basins begin contributing surface runoff (Gomi et al. 2002), thereby becoming connected to the stream network (Sidle et al. 2000). When soil conditions are very wet, zero-order basins and preferential flow paths (soil macropores) expand and substantially enhance subsurface flow, and overland flow contributions from the riparian zone become less important (Gomi et al. 2002; Sidle et al. 2000). Burgess et al. (1998) suggest that the temporal and spatial elements of this hydrologic response is “critical to the evaluation of land use within headwater areas” and the resulting peak flow generation and chemical, sediment and biota transport processes. Figure 2 depicts these ’hydrologically active’ areas of headwater regions, which are not simply extensions of the riparian corridors as is suggested by the variable-source area concept. Instead, these zones, becoming activated during wet conditions, are linked hydrogeomorphic components of the basin, and include riparian zones, linear hillslope segments, and geomorphic hollows or zero-order basins. Although these concepts have been developed based on stormflow generation in steep headwater systems, they will likely hold relevance in our geographic setting as well. When land use changes in headwater areas, the natural hydrologic response of streams is altered, and the process of streamflow generation becomes flashier. By controlling flow of water to



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larger streams, headwater drainage features may protect downstream areas from flooding, as well as preventing excess erosion (Ohio EPA Import 2003).

Figure 2: Conceptual view of dynamic, hydrologically active areas in headwaters. For dry conditions, riparian zones and direct precipitation on channels are the only active sites of flow generation. Throughflow from the soil matrix at the foot of hillslopes and riparian areas gradually activates with increasing wetness. Zero-order basins (shaded areas) with relatively shallow soils begin to contribute surface runoff (broad white arrows) during wet conditions, while preferential flow (thin black arrows) from hillslopes contributes less to stream flow. Water begins to flow in transitional channels emerging from zero-order basins. Zero-order basins and preferential flow actively contribute to storm flow during very wet conditions (Source: Gomi et al. 2002). 4.1.1.2 Natural Flow Regime Naturally variable flow regimes create and maintain the dynamics of in-channel and floodplain conditions and habitats that are critical to aquatic life (Poff et al. 1997). The timing, duration, magnitude, frequency, and rate of change (see glossary for definitions) are all critical components of flow (Poff et al. 1997; Saunders et al. 2002; Richter et al. 1997). Together, these components constitute the flow regime or hydrological regime of an area. The critical components for fish communities, including water temperature, dissolved oxygen concentrations, suspended sediment loads, nutrient availability, and physical habitat structure, all vary with hydrological regime (Richter et al. 1997). As such, aquatic communities are vulnerable to changes in the flow regime. Poff et al. (1997) suggest that flow regime is the ‘master variable’ limiting the distribution and abundance of riverine species. Variability in intensity, timing, and duration of precipitation and in the effects of terrain, soil texture, and evapotranspiration on the hydrologic cycle collectively form the local and regional flow pattern. The timing, or predictability, of flow events is of paramount ecological importance because the life cycles of many aquatic or riparian organisms are timed to either avoid or exploit flows of variable magnitudes (Poff et al. 1997). For example, the natural timing of high or low streamflows is a trigger for the initiation of life cycle processes, such as spawning, egg



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hatching, rearing, movement onto floodplain for feeding or reproduction, or migration upstream or downstream (Poff et al. 1997). Figure 3 shows the natural variability in the flow regime for Duffins Creek Watershed (Durham Region), and spawning of some fish species coincides with the higher flows occurring during the spring. Urbanization can impact the natural flow regime by altering the hydrologic components (Poff et al. 1997; Saunders et al. 2002).

Figure 3: Flow Data From the Duffins Creek Gauging Station at Pickering (Source: Toronto and Region Conservation 2004). When urbanization occurs in any watershed, it increases the area of impervious surfaces (Paul and Meyer 2001, White et al. 2006). The general implications of increasing impervious areas in a watershed are the increase of runoff into surrounding streams and the decrease of the amount of precipitation that infiltrates into the soil as groundwater recharge (Blackport et al. 1995, Burns et al. 2005). This creates the characteristic ‘flashy’, urban stream flow regime as predicted by the urban stream syndrome. More specifically, urban development and its associated impervious surfaces and storm drains disrupt the natural flow regime of a stream by: decreasing baseflow and groundwater recharge; increasing surface runoff in annual streamflow; increasing the magnitude of peak runoff; decreasing the lag time between rainfall and runoff response; increasing the rate of hydrograph rise and recession; and decreasing mean residence time of streamflow (Burns et al. 2005, Hirsch et al. 1990, McCuen 1998, Rose and Peters 2001). Stormwater management (SWM) facilities, such as ponds, have been used in recent years in an effort to mitigate the symptoms of ‘flashy’ urban systems. An example of this problem in the Toronto and Region Conservation Authority jurisdiction is the case of Highland Creek. Urbanization spread into the upper reaches of the Highland Creek Watershed in the late 1960s and 1970s, prior to the implementation of SWM measures. Headwater creeks were channelized to facilitate development and to efficiently convey stormwater away from urbanized areas. As development continued, flows within the creek became flashier, with very high flows during rain events, and very low flows during dry periods. The unnaturally high flows were quickly conveyed through the system of pipes and concrete



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channels. The energy from the resulting flows has resulted in severe erosion downstream, especially along the sandy banks of the lower Highland on the Lake Iroquois plain. The large volumes of water have resulted in an unnaturally wide channel, which causes the watercourse to flow as a thin layer over a broad area, resulting in greater solar heating, higher temperatures, and impacts to sensitive fish species (City of Toronto and TRCA, 1999). The City spends an incredible amount of money dealing with erosion problems associated with this. The cost to repair the erosion damage caused by one storm event in 2000 alone was over $3 million (City of Toronto 2007). As a result of these high storm flows, the City of Toronto was compelled to develop the Wet Weather Flow Management Master Plan (WWFMMP) in order to strategically address erosion problems in the city. The implementation of the WWFMMP will be a substantial long-term budgetary commitment. The full implementation of the strategy may take 75-100 years and is expected to cost in the order of $12-16 billion (City of Toronto 2006). Saunders et al. (2002) present strategies for conserving freshwater habitat and suggest that one highly recommended option is to use the river-continuum concept (for further information see Section 4.2.1 below) to determine which portions of the catchment are the highest priority areas for protection. They suggest that this concept supports concentrating protection efforts on headwater areas because downstream processes depend primarily on terrestrial production occurring in headwater regions. They state that because more than 90% of a river’s flow may be derived from catchment headwaters, efforts to maintain or restore natural flow regimes should focus most intensely on these areas. Where efforts to conserve the entire catchment are constrained, this approach will benefit both upstream and downstream habitats; see Figure 4(C) below.

Figure 4: Strategies for freshwater protection against land-use disturbances: (a) whole catchment management, (b) multiple-use modules (c) river continuum concept, and (d) vegetated buffer strips (Source: Saunders et al. 2002).



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4.1.1.3 Flood Control Some literature suggests that headwater streams and wetlands are important in controlling water flow to larger streams (Ohio EPA Import 2003). In their natural setting, streambeds are generally rough and irregular. Rocks, leaf litter, twigs or vegetation in the channel provide roughness on the streambed, and the friction that is produced decreases the velocity of water flowing over these materials (Mayer et al. 2003, Richards 2004). By slowing down the flow of water in headwater streams, the water has a greater probability of seeping into the stream channel or banks, contributing to groundwater recharge (Meyer et al. 2003), or evaporating/evapotranspirating instead of flooding downstream areas. In zero-order streams, the roughness on the streambed due to in-channel vegetation will likely be high. Low channel gradients of zero-order streams may also play a role in reducing velocities and attenuating flooding. Precipitation is the most important factor that initiates a flooding event; however the physical characteristics of the drainage basin, surficial geology, hydrology, and geomorphology of the stream-floodplain ecosystem are the primary factors controlling the concentration, spatial distribution, and dispersal rate of floodwaters (Brooks et al. 2005). Finkenbine et al. 2000 suggest that when imperviousness is more than 40%, summer baseflow was uniformly low in a low-order stream in British Columbia, 20 years after initial urbanization. Increases in impervious surfaces will deliver water from the headwater basin to downstream channels much more rapidly and increase the number of floods (Meyer and Wallace 2001). The Ohio EPA (1999) suggests that in order to reduce the overall impact of traditional urban development on receiving watercourses, the objective should be to try to mimic the predevelopment hydrology as closely as possible. One method of achieving this is to maintain open drainage systems (swales) wherever possible instead of more conventional storm drain systems as a means of conveying surface runoff between lots and along roadways. Much of the literature on swales focuses on the use of vegetated swales for stormwater management. These swales are usually broad, shallow, earthen channels designed to slow runoff, promote infiltration, and filter pollutants and sediments in the process of conveying runoff (Ontario Ministry of Environment, 2003). Li et al (1998) suggest that end-of-pipe controls such as SWM ponds, though they mitigate increased flood peaks after urbanization, may not meet other SWM objectives. Efforts to store, treat, and dispose of runoff closer to the source (i.e. where precipitation falls) are now being recognized as effective techniques for reducing runoff volume, improving water quality and groundwater recharge. They also propose that properly designed grass swales are the most environmentally sound road and lot drainage technique because the vegetation within the swales can trap sediment, slow flow velocities, and promote infiltration. Li et al. encourage the use of grassed swales instead of or in conjunction with standard curb-and-gutter systems because of the environmental benefits that these measures provide. Although grassed swales or ditches are not exactly the same as natural swales and headwater drainage features, open drainage systems may mimic the functions of natural flow paths such as those provided by headwater drainage systems. Based on the above, there does seem to be some evidence to suggest that these facilities would alleviate flooding problems by



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providing storage and by promoting infiltration instead of promoting runoff, particularly if examined on a cumulative basis. Given the surfacing inadequacies that end-of-pipe controls have with respect to maintaining natural hydrologic functions, Gorenc et al. (undated) propose “drainage density” as an alternative approach to SWM controls at a watershed or sub-watershed scale. Drainage density is the ratio of the total length of all watercourses in a drainage basin to the total basin area. This approach encourages the protection of natural streams in the post-development scenario. However, if the features themselves cannot be achieved in the desired urban form, other measures, such as the provision of open conveyance features, are required to meet the pre-development drainage density targets. As a component of their work, Gorenc et al. has conducted some preliminary hydrologic modeling (using SWMHYMO) to determine numerically how this approach would fair with respect to flow attenuation. Results show that when headwater swales are maintained, a significant attenuation of peak flows (2-30%) and a minor reduction in quantity storage (1-4%) were evident. While SWM ponds may not be entirely effective at addressing all stormwater-related impacts of urban development, they will likely continue to be required to meet water quality, peak flood control and erosion mitigation objectives. However, using natural swales and open drainage features in the landscape may be used supplement SWM ponds.

4.1.2 WATER QUALITY

Urbanization and agricultural land uses often introduce non-point source pollutants into stream systems, such as nutrients (nitrogen and phosphorus), and pesticides, herbicides, salt, and sediments through surface water. These pollutants enter the stream as stormwater runs off lawns, farms and roads and can alter downstream water quality for biota and can impact recreation opportunities, increase water treatment costs and human health risks, and degrade downstream waters.

Clinton and Vose (2006) suggest that one of the most important functions that is attributed to headwater streams is its role in naturally improving water quality in undisturbed sites. Because small streams are generally shallow and have more water in physical contact with the stream channel, the distance by which a particle can travel before being removed from the water column is shorter than in larger streams (Meyer et al. 2003).

Nutrient enrichment of nitrogen and phosphorus from agricultural and urban uses has been shown to change the assemblage of benthic algae from diatoms, the preferred source of food for many invertebrates, to the filamentous green and blue-green algae that detrivores tend to avoid consuming (Hart and Robinson 1990). Excess nutrients results in an overabundance of these green and blue-green algae and causes eutrophication within wetlands and streams. This can be a significant stressor in tributary watersheds as decomposition of these algae reduces the availability of oxygen for aquatic organisms. These changes usually lead to highly productive, but taxonomically and trophically simple biological communities (Brooks et al. 2005).



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First-order streams were found to have higher mean Phosphorus (P) concentrations than (approximately twice) that of larger order streams. P adsorbs to soil particles, which are transported from uplands to streams and wetlands through surface water. As a result, the most effective method of removing phosphorus (and metals) from the water column is to allow the settling of particles and adsorption to organic matter and clay (Brooks et al. 2005). Hence, storage of sediments in small streams can be effective in trapping phosphorus. The Ohio EPA (2001) has found that primary headwater streams (defined as having a drainage area <2.6 km2 that have a defined bed and bank, and therefore likely has permanent flow) and riparian areas can efficiently retain many forms of nutrients, especially phosphorus, before they reach the stream. We did not find many published papers that specifically examined the function of phosphorus and nitrogen removal by headwater drainage features, however, some general findings may be applicable in these systems. For example, as long as there is adequate time for transported material to come into contact with roots, buried leaves and sediment, riparian vegetation can be effective in retaining sediments and nutrients, which is a function that can likely be attributed to headwater drainage features with intact riparian zones. This perhaps lends support for the protection of undisturbed headwater drainage features and the restoration of features that have unvegetated riparian zones. However, as discharge increases, removal rates decline because of the difficultly in settling out finer sediment particles where phosphorus may be adsorbed. In contrast to phosphorus which primarily moves through surface water, nitrogen moves through ground water as dissolved nitrate, ammonia or organic nitrogen (Peterjohn and Correl 1984, 1986). Most nitrogen is removed from subsurface water through denitrification by soil microbes within wetlands and riparian soils (Davidsson and Stahl 2000). Research indicates that riparian forests can retain upwards of 89% of nitrogen loads as compared to 8% for cropland. The nitrogen uptake by the forest was mainly through groundwater processes (Peterjohn and Correll 1984, Gilliam 1994, Jordan et al. 1997). However, as with sediments and phosphorus, retention of nitrogen is more efficient at low discharge (Schnabel 1986). When flows are high, relatively more of the discharge reaching streams arrives as surface flow thereby permitting less time for vegetative uptake and microbial transformation of nutrients (Pionke et al. 1986). Gilliam (1994) found that there was a 90% or more reduction in nitrate

concentrations in water as it flows through riparian areas. Organic matter is also important in providing a substrate necessary for microbes to perform the process of denitrification. Plant uptake is an additional means of nitrogen removal from the system. Peterson et al. (2001) and Starry et al. (2005) reported that small streams were found to have the most rapid uptake and transformation of inorganic nitrogen. However, the drainage features that were examined were larger than those in which we are interested here. Peterson et al. (2001) considered small streams to have widths less than 10 m, and Starry et al. (2005) examined second-order permanently flowing streams with an average annual discharge of 19.6 L/s. Alexander et al (2000) examined the rate of N loss as stream order increased. Small streams that had flows <28 m3/s (28,000 L/s) lost approximately half of their N load per day, while larger streams lost only 5-10%. The largest rivers lost less than 1% of their N load daily. This suggests that nitrogen uptake in smaller streams is more efficient than uptake in larger streams, particularly when streams are forested.



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When headwater drainage features are eliminated or altered, they may not process or retain nutrient inputs as quickly or at all, due to increased stream flow from runoff, and therefore reduced ability of the stream network to provide the ecosystem service of natural recycling (Meyer and Wallace 2001). By enclosing a stream with pipe or storm drain, the stream water is no longer in contact with the streambed, and consequently blocks any interactions with groundwater and the hyporheic zone (Town of Markham 2004). Paving over good recharge areas within headwaters also reduces stream discharge, which in turn, reduces stream dilution capacity for pollutants (van Seeters, 2006). This has substantial implications on water quality and temperature of streams during low flows. Enclosing a stream will reduce its ability to remove nutrients; however, it may also reduce the streams exposure to nutrient sources when agricultural uses are converted to urban uses. The hyporheic zone is part of the streambed, and is the site of groundwater-surface water interactions (Morrice et al. 1997). Removal of nutrients from the water column is highly dependent on exchanges with this zone (Meyer and Wallace 2001). However, no literature was found that definitively linked drainage feature piping with loss of hyporheic zone functioning. There is, however, literature available that supports the pollutant removal function of swales and drainage features specifically designed for stormwater management purposes (Dorman et al. 1989; Yu et al. 1993). Horner et al. (1988) examined the pollutant removal performance of a typical biofilter (grassed swale) in the City of Mountlake Terrace in Washington. Based on the monitoring, they determined that a 5-10 minute residence time in a minimum 100-foot (30.5 m) long biofilter would result in reliable pollutant removal, especially for storms with significant rainfall peaks. Harper (1988) examined runoff and groundwater dynamics of two swales in Florida. He found that although the two swales functioned at opposite ends of the continuum of infiltration conditions (one dry swale with high infiltration and one wet swale with low/no infiltration), both swales performed moderately well in removing pollutants in urban stormwater. The wet swale functioned more like a wetland feature and removed 40, 19 and 30-90% of total nitrogen, total phosphorus and most trace metals, respectively. The dry swale performed much better with mass reduction rates of 70% or greater for all sampled parameters, and the key pollutant removal process was infiltration of runoff into the ground. However the wet swale outperformed the dry swale in reducing the concentration of pollutants, and in contrast to the dry swale, settling and vegetative filtering were the main processes operating to remove pollutants. In comparison, review of the monitoring results of six different stormwater management facilities in the Greater Toronto Area (SWAMP, 2005) revealed that effluent concentrations of phosphorus, copper and bacteria consistently exceeded water quality guidelines. This was true even for facilities that had very long settling times. In addition, because the surface area of stream water in contact with the hyporheic zone is relatively larger in smaller streams the exchange may have important implications for nutrient cycling. Given the geographical extent of headwater drainage features, the cumulative effect of maintaining open headwater drainage features could have beneficial implications on water quality. This would be an important consideration for future research efforts. While current-practice SWM facilities may be able to at least partially replicate some of the potential hydrological functions of headwater drainage features, there is no evidence to suggest that SWM facilities could replicate any biological functions.



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4.1.3 EROSION AND SEDIMENT CONTROL Water quality impairment can also result from an increase in sediment transport. If natural vegetation and soil cover are disturbed by activities such as urbanization, an increase in sediment transport levels could be delivered to larger channels downstream. Increased sediment supplies decreases water quality, increases dredging costs, and degrades aquatic habitats downstream (Meyer et al. 2003). Higher sediment levels can also impair fish habitat by covering spawning beds and by suffocating fish as particles become trapped in fish gills. Channel erosion of the streambed and banks also increases the amount of sediment in the stream channel and causes further disturbances downstream (Meyer et al. 2003). Some literature suggests that because of the ability of headwater drainage features to slow down water flow, they can trap or delay the delivery of excess sediment to larger downstream habitats (Meyer et al. 2003). Benda et al. (2005) suggests that small streams act as sediment reservoirs that can retain sediment for long periods of time from decades to centuries. Meyer et al. (2003) reported that in the headwater streams of Oregon’s Rock Creek basin, sediment could be stored for 114 years. However, other studies suggest that headwater areas are sources of sediment (e.g. Gomi et al. 2002). Presumably, the sediment supply to downstream reaches from headwater drainage features will be largely controlled by slope, catchment area, climate, soil type, and vegetative cover. For example, high gradient streams tend to flush, rather than store fine sediments when compared with low gradient streams (Welsh, et al. 2005). While some biological processes intuitively would not be possible once a drainage feature is enclosed, other functions that could be imparted to headwater drainage features may be replicated by standard engineering practices, or conversely, the functions imparted to engineered swales may also be true of HDFs. Sediment, erosion and flood control have traditionally been mitigated through the use of stormwater management (SWM) facilities. Monitoring of five pond and wetland facilities by SWAMP (SWAMP 2005) has shown that they helped to control flooding and downstream channel erosion by significantly reducing peak flows. The average peak flow reduction rate was 77% and ranges varied between 40 and 95%. Additionally, load-based total suspended solids (TSS) removal rates for the facilities exceeded their respective design targets by 10-21%. Similarly, Winer (2000) reported that open channels (grassed swales and ditches) used for stormwater management purposes removed an average of 81% of total suspended solids. Although current SWM ponds are designed to settle out sediments that are entrained during and after development and to control stream erosion by reducing peak flows, they may not effectively replicate natural conditions. According to Schumm (1977), undisturbed headwater regions are also areas of sediment production. Under natural conditions, this sediment production is necessary to feed downstream geomorphic processes (Gorenc et al. undated). The stability of a creek is dependent on its ability to maintain a balance between channel form, flow and sediment load (Town of Markham 2005). Any increase or decrease in the mean supply rate of mobile sediment would result in aggradation (deposition) or degradation (erosion) of the channel in an attempt to restore a balance by respectively decreasing or increasing relative roughness (Knighton 1998). Aggradation and degradation are signs of channel instability as the channel attempts to restore balance through adjustment (Town of Markham 2005).



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Gorenc et al. (undated) propose in an unpublished document that SWM ponds and pipes eliminate the natural levels of sediment from the system and effectively “starve” the fluvial network downstream. SWM ponds dampen the flow regime of a system by enhancing low flows and reducing peak flows through attenuation, and therefore do not necessarily replicate the function of natural streams. As a result of this, Gorenc et al. state that some practitioners have recognized the need to incorporate headwater features (swales) into urban form to maintain the form, habitat and sediment delivery aspects of the fluvial network. Gorenc et al. have initiated a sediment transport modeling exercise, similar to the hydrologic assessment component of their study discussed in Section 4.1.1.3 above. They will utilize the HEC_RAS SIAM model to assess sediment budgets, balances, and energy-transport relationships on an annual basis. This modeling will facilitate the comparison in annual sediment transport between scenarios with and without headwater swales. The Town of Markham (2005) initiated a study that examined the effectiveness of alternative stormwater management scenarios with respect to erosion control in Burndenet Creek, which is a first to second order stream located within the town limits and is a tributary of the Rouge River. The alternatives examined included three varying designs of SWM ponds, including standard design, standard design with distributed runoff control, and standard design with 50% oversizing of future SWM facilities. Their study findings confirmed the statements made by Gorenc et al. (undated), as they reported that although peak flow rates for individual events were regulated, the volume of runoff increased substantially when compared to baseline conditions. The Town concluded the study by stating that implementing traditional measures would not be adequate to prevent in-stream adjustments and that evapotranspiration and/or infiltration measures would be needed to ensure that no runoff occurs for the first 10-12 mm of a rain event. Maintaining open headwater drainage features could increase infiltration and evapotranspiration to ameliorate this erosion problem. As a result of this, Gorenc et al. (undated) have proposed a study to test whether “protection of headwater swales is beneficial to the sustainability of stream-based ecosystems” and whether “replication of headwater swale functions through conventional stormwater management is not always effective.” Particularly given the Southern Ontario context within which this study will take place, the findings of this work will be of great interest to us.

4.2 BIOLOGICAL FUNCTIONS

4.2.1 THE RIVER CONTINUUM CONCEPT

Vannote et al. (1980) developed the “River Continuum Concept” to describe the structure and function of communities along a river system (see Figure 5). It suggests that biological strategies and dynamics are related to the physical factors generated by the drainage network. The physical structure along with the hydrological cycle form a continuous gradient for biological responses, which results in a consistent pattern of community structure and function, as well as organic matter loading, transport, utilization, and storage along the length of a river (Vannote et al. 1980).



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Figure 5: A general River Continuum Concept diagram depicting upstream-downstream linkages. (Source: http://www.oxbowriver.com/Web_Images/Stream_Ecology_Images/RCC/OEPA-RCCpsd.jpg)



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It begins at the headwaters of a stream, where productivity is dependent on riparian vegetation. As you go further downstream, the stream size increases and energy derived from primary productivity becomes just as important as energy derived from allochthonous inputs. This shift is thought to be generally reflected by a change in the ratio of gross primary productivity to community respiration (P/R). Larger order streams receive fine particulate organic matter (FPOM) from upstream, but energy is not significantly derived from primary producers (Vannote et al. 1980).

Aquatic invertebrates reflect these shifts in productivity by the types and locations of food resources, with respect to stream size. In headwater streams, shredder communities that consume coarse particulate organic matter (CPOM) dominate. Further downstream, there is a shift in dominance to grazer communities where sunlight plays an important role in the production of algae growth that the grazer community consumes. In the larger ordered streams, grazer communities decrease in dominance and collector communities that consume FPOM dominate. Throughout the continuum, predators are present. Insectivores are predominant in headwaters; mid-sized rivers are piscivorous; and large rivers contain primarily planktivores (Vannote et al. 1980).

The River Continuum Concept illustrates the importance of headwater streams (orders 1-3, including headwater seeps) to downstream systems. Small streams at the tips of catchments constitute a significant portion of a watershed and provide valuable resources and habitat. This concept shows how greatly dependent the whole river network is on the individual and cumulative impacts occurring in the many small streams making up the headwaters. However, it is unclear whether the theory includes HDFs as zero-order and/or non-permanently flowing streams are not specifically referenced, although features as small as groundwater seeps are included. Thus, although this concept is important in setting the stage for what functions could be supported by the streams in question, the importance of intermittent and ephemeral headwater drainage features must be further explored.

4.2.2 AQUATIC FUNCTIONS

4.2.2.1 Groundwater Functions and the Hyporheic Zone

It has been suggested that headwater streams, including wetlands and intermittent streams, play a critical role in providing a continuous flow of water to downstream ecosystems (Meyer et al. 2003, MMM 2005). Groundwater recharge is important in maintaining a continuous water source and occurs when water from precipitation, snow accumulation, or runoff processes, infiltrate or percolate into the ground until it reaches the water table (Blackport et al. 1995). Precipitation and snow accumulation are generally greater at higher positions in catchments areas, where headwater streams tend to be situated. Because headwater streams cover a majority of the total catchment area, they provide the greatest chance for groundwater recharge in these areas (Gomi et al. 2002, Meyer et al. 2003).

It has been suggested that intermittent streams also have a major influence on the amount of water supplied to downstream channels (Reid and Ziemer 1994). Baseflow, which is derived from groundwater supplies, maintains streamflow when there is no precipitation, and tends to increase downstream as more headwater streams contribute to the watercourse (Richards



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2004). Ohio EPA (2003) also suggests that headwater streams may be beneficial in maintaining baseflow levels in larger streams in times of drought.

Groundwater has an important moderating influence on stream temperature, especially in headwater streams because they can be frequent receptors of significant amounts of groundwater discharge or upwelling if they are permanently flowing. Since groundwater travels much slower than surface water, it tends to cool as it moves through the ground. This results in groundwater having the same mean annual temperature of soil. In southern Ontario, the normal temperature for groundwater is between 7-10ºC (Blackport et al. 1995). In HDFs, which usually have little groundwater influence, diurnal variations in stream temperatures of 6ºC or more have been documented. This is due to daytime temperatures warming surface water and a decrease in evapotranspiration overnight (Blackport et al. 1995). The inflow or upwelling of cool groundwater could help to moderate this diurnal fluctuation. There were no papers that specifically examined the moderating role of intermittent drainage features on downstream communities. However, intermittent streams are typically dry when the stream moderation function is most important (i.e. summer), hence it is uncertain whether this function is relevant for HDFs. The area of saturated sediments beneath and beside a watercourse, known as the hyporheic zone (See Figure 6), plays a key role in water, nutrient, and organic matter exchange in streams between surface and groundwater (Boulton et al. 1998, Hill and Lymburner 1998, Richards 2004). These exchanges are a result of variations in discharge and bed topography and porosity and are important to ecological processes within streams. The hyporheic zone is considered to be defined as the subsurface water adjacent to the channel that contains greater than 10% advected channel water (Triska et al. 1989). Upwelling from groundwater towards the stream provides stream biota with nutrients while downwelling stream water offers dissolved oxygen and organic matter to the microorganisms and invertebrates that inhabit the hyporheic zone (Boulton et al. 1998). Many of the organisms within the hyporheic zone are also found in the stream proper; however, some are unique forms that are adapted to living in subsurface interstitial spaces (Jones and Holmes, 1996). Downwelling water from the stream to the hyporheic zone also supplies fish eggs within the subsurface sediments with a source of dissolved oxygen. Beneath the hyporheic zone is the groundwater zone where the water chemistry is not influenced by the channel water (Patschke, 1996). Headwater hyporheic zones are smaller, and their nutrient exchange is less than in downstream reaches in an absolute sense (Stanford and Ward 1993), and conceptual models have suggested that there would be little, if any hyporheic development in headwaters (White 1993). However, there is empirical evidence to support that hyporheic exchange can be ecologically important in first-order streams. D'Angelo et al. (1993) proposed that solute storage within first-order streams is relatively greater than higher order streams because of the presence of debris dams, boulders and a relatively large and porous hyporheic zone. The first-order streams examined had the largest As/A (transient storage zone cross-sectional area/stream cross-sectional area) relative to higher stream orders. This suggests a high potential for temporary storage of materials during downstream transport, which permits solutes to be retained within the stream for a longer period and promotes biological, chemical and physical interactions. The surface area of stream water in contact with the hyporheic zone is relatively larger in small streams, hence the



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exchange may have important implications for nutrient cycling. As a result, there is greater contact between dissolved nutrients and subsurface sediments than in larger stream systems. The first order streams examined in this study had flows varying from 0.5-5.0 L/s and drained mountainous mixed hardwood or white pine forests. Since these streams had continuous flow during the summer months, they would likely be permanently flowing streams. The streambed contains irregularities, small pore space, deposits of organic matter and anoxic and hypoxic pockets. The hyporheic zone influences stream chemistry as a result of storage and retention via groundwater and surface water exchanges, and biogeochemical transformations (Hill and Lymburner 1998). A study performed in Duffins Creek in Toronto, Ontario, found evidence that suggests the hyporheic zone influences stream nutrient retention. Nutrient retention is determined by the extent of surface-groundwater exchange and subsurface chemical transformation rates (Hill and Lymburner 1998). This area of exchange between surface water and ground water is the prime zone for N chemical reactions like ammonification, nitrification and denitrification. These processes are controlled by oxygen availability. Second and third-order permanently flowing streams were examined in the study. Most of the studies discussed above were conducted in temperate bioregions in permanently-flowing mountainous streams. Studies that examined hyporheic exchange in intermittent streams were largely in arid or semi-arid regions (Jones et al. 1995; Valett. et al.1990; Cooling and Boulton 1993; Butturini et al. 2002; Robson et al. 2005; Sanzone et al. 2003; Moyle and Nichols 1973) or draining karst catchments (Chafiq et al. 1999) with climates very different from Southern Ontario. We did not locate any studies that specifically examined the hyporheic functions of non-permanently flowing streams in temperate regions similar to our regional setting.

Figure 6: The hyporheic zone shown at three spatial scales. At the catchment-scale (a), the reach-scale (b), and at the sediment scale (c). The hyporheic zone is an active ecotone between the surface stream and groundwater. (Source: Boulton et al. 1998)



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4.2.2.2 Contributions of Detritus and Invertebrates to Downstream Habitats

and Invertebrate Diversity

In headwaters, allochthonous inputs are much greater than autochthonous energy sources. This organic matter accumulates and becomes an important source of food and habitat for macroinvertebrates and microbial decomposers (Lecerf et al. 2005, Gomi et al. 2002, Richardson, 2000, Vannote et al. 1980). Shredders are the dominant functional group of macroinvertebrates in headwater streams and convert coarse particulate organic matter (CPOM) into smaller particles. Abelho and Graca (1998) examined the importance of organic matter inputs in forested streams in a first-order stream in Portugal. Mean discharge was 23 L/s (range: 5-68 L/s), and hence was permanently flowing. They found that litter production was 715 g m-2 y-1 and dependent on seasonal changes (73% of the annual total occurring during autumn, October-December).

Seasonal duration of flow in a stream influences the life cycle and community structure of invertebrates in headwater systems. When flow duration is greater than 4-5 months, streams tend to have similar invertebrate assemblages. Intermittent streams with less than 3 months of flow, on the other hand, have altered macroinvertebrate life cycles (Gomi et al. 2002), whereby aquatic insects move to hyporheic zones, remnant wetted pools, and permanently flowing channels during drier periods (Williams and Hynes 1977). Dieterich and Anderson (2000) examined the invertebrate communities in summer-dry streams in western Oregon and found 202 aquatic and semi-aquatic species. More than 125 species were recorded in temporary forest streams whereas only 100 species were found in a permanent headwater stream. Species richness in ephemeral streams was less than 35 species (Dieterich and Anderson 2000). The main factors influencing community composition both between and within stream types were duration of flow, exposure (shaded or open), riffle-pool structure and summer drought conditions. They concluded that the invertebrate habitat function of summer-dry streams is highly underestimated. Flow within some headwater systems may not be of sufficient duration to support aquatic invertebrates, in which case terrestrial invertebrates will be the primary functional group present (Gomi et al. 2002). Despite this, terrestrial invertebrates have been shown to be important for aquatic biota in both warmwater and coldwater systems (Wipfli 1997; Garman 1991; Nakano et al. 1999; Edwards and Huryn 1996; Angermeier 1982). Wipfli (1997) found that diets of salmonid (juvenile salmon, char, and trout) often consist of 50% terrestrial invertebrates. Similarly, Garman (1991) reported that terrestrial prey dominated the diet of the major cyprinid fish (Notropsis ardens) during August despite the fact that terrestrial prey availability sharply declined throughout the summer. Diets of salmonid (juvenile salmon, char, and trout) diets often consist of 50% terrestrial invertebrates (Wipfli 1997). Wipfli (2005) reported that in a study on fishless headwater streams in Alaska, these headwater streams may be important food sources for downstream foodwebs because of their ability to potentially produce and deliver food to downstream consumers. Although all streams tested contained some surface flow (mean 2.7 L/s) during sampling, some streams had neglible flow during dry periods (<0.1 L/s), suggesting that these streams were nearly intermittent. Table 3 depicts that up to 35% of the taxomonic composition transported from these headwater habitats is terrestrial and probably contributes to whole-



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catchment energy budgets. The fish communities present in the downstream reaches consisted of family groups similar to those found in Southern Ontario, such as salmonids (including rainbow trout), sculpin (Cottus spp.) found in coldwater and coolwater streams, and stickleback (Gasterosteus spp.) in warmwater systems. Table 3: Taxonomic composition of invertebrates from headwater habitats in southeastern Alaska (Source: Wiplfi, 2005).

In Alaska, Wipfli and Gregovich (2002) studied the fluvial transport of invertebrates and coarse organic detritus from headwaters to aquatic stream habitats downstream. Again, small, fishless, nearly intermittent (during dry periods, some streams had discharges during sampling as low as 0.008 L/s) streams were tested. Invertebrates and detritus were exported from the headwater streams throughout the year with a mean of 163 mg invertebrate dry mass stream-1 day-1 and 10.4 g detritus stream-1 day-1, respectively. As a result of this transport, Wipfli and Gregovich estimated that every kilometer of salmonid-bearing stream could receive enough energy from fishless headwaters to support 100-2000 young-of-the-year salmonids, based on the frequency of headwater streams in the watersheds studied and the average amount of food delivered to downstream habitats by these streams.

Although stream order was not reported, these Alaskan studies do support the notion that the transport of energy (food and detritus) from headwater systems could also be an important function of these types of streams in a Southern Ontario setting. This function alone would be sufficient to warrant protection of these headwater drainage features by virtue of contributing to the productive capacity of fish habitat according to Table 1 above, thereby constituting indirect fish habitat. However, having been conducted in Alaska, the study sites are very different from Southern Ontario landscapes because of higher gradients, more heavily forested catchments, higher rainfall, cooler climates, and shallower soils. The ecological function may be more pronounced in that type of setting than it is in our regional context. In addition, the sampled streams were permanent (always contained some flow, although negligible at times).



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One study conducted by Feminella (1996) examined the differences in benthic invertebrate assemblages in small intermittent first-order streams along a gradient of flow permanence in Alabama. Two of the six streams studied were normally intermittent (i.e. riffles ceased flowing in normal rainfall years), 3 streams were occasionally intermittent (i.e. riffles ceased flowing during dry years), and 1 stream was rarely intermittent (i.e. normally perennial). Flow permanence was widely varying between the streams, however invertebrate assemblages among streams were similar as 75% of the species were ubiquitously found in all 6 streams. Surprisingly, the stream with the highest total richness (93 taxa) for any date of the study was the stream with the lowest permanence score (i.e. longest intermittency) during the summer months (i.e. when flow had ceased) of a normal rainfall year. Although no surface flow was evident during this time, the streams remained moist and contained small isolated pools (< 1 cm depth). In addition, Feminella found that 7% of the total macroinvertebrates collected only occurred in the normally intermittent streams, suggesting that these streams may be important habitat niches for certain temporary specialist species with tolerance of or preference for non-flowing conditions (Williams and Hynes 1977). Stout and Wallace (2003) examined the macroinvertebrate diversity of 34 unmapped intermittent streams from February through April, 2000 in southern West Virginia and Kentucky. Intermittent streams were sampled at distances upstream from the confluence of permanent streams or from where streams were mapped as blueline permanent streams. Results of the sampling indicated a significant increased in Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa richness as streams became more intermittent (i.e. further away from permanently-flowing sections), and included over 86 insect genera of 47 families. EPT and other taxa were observed despite that these intermittent were streams, and some of the streams had catchments as small as 4 ha. Fritz and Dodds (2004) studied the resistence and resilience of aquatic macroinvertebrate assemblages to drying in intermittent tallgrass prairie streams in Kansas. Although macroinvertebrates in temporary habitats can be resistant to drying due to aestivation and diapause characteristics, they found that macroinvertebrate resistance to seasonal drying (~9 mo.) was low at their site. They theorized that this was due to the long duration of drying relative to that studied elsewhere. In addition, invertebrates would not have been able to depend on an extensive hyporheic zone for refugia as this was not present in the streambed sediments. In addition, recovery following drying in the intermittent streams occurred as quickly as that studied at perennial streams, and invertebrate densities recovered within about 30 days. Based on this finding, one could argue that provided that flow permanency of a drainage feature exceeds that of the invertebrate recovery period (in this case 30 days), there would be sufficient flow to provide productive habitat for aquatic invertebrate export. However, this would need to be confirmed in our regional setting. Feature enclosure is expected to have impacts on the potential HDF function of contributing invertebrate and detritus to downstream habitats. Although no literature focused on the impacts of altering the stream morphology by enclosing a stream, intuitively it eliminates all channel characteristics. By replacing the natural stream bed channel with pipe, it eliminates stream morphology features such as micro-pools and riffles that may assist in providing refugia for macroinvertebrates, flow storage and attenuation, and sediment trapping. Piping streams also eliminates contact of water with stream substrate, which would potentially alter infiltration, groundwater discharge, and reduce hyporheic zone functioning.



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4.2.2.3 Woody material and Leaf Litter Contributions

Riparian vegetation provides the source of large woody material in headwaters. The vegetative composition of the riparian zone dictates the size, quality and quantity of wood entering the stream system. Once in the stream, this wood can trap fine sediment, retain spawning gravels in downstream habitats, form pools, and provide cover and nutrients (Fox 2004). Woody material enhances organic matter and nutrient retention, as well as provides the in-stream structure to dissipate energy and reduce downcutting (Meyer and Wallace 2001).

Decay rates are also higher in headwaters. A study by Melillo et al. (1983) found that woody materials decayed more rapidly in a first-order stream than in larger streams in eastern Quebec, however the reason and relevance of this was not given. We presume that higher decay rates allow faster uptake of nutrients by biota, and may be a result of more frequent wetting and drying cycles and exposure to oxygen and frost. The smallest streams studied in all of the literature examined, with respect to woody material and leaf litter contributions, were first-order streams. Most were permanently flowing (e.g. Reeves et al. 2003) or the flow period was unreported (e.g. Richardson 1999). For example, mean annual discharge and mean wetted width is reported, but not flow permanence or flow range. One paper by Reid and Zeimer (2006) specifically examined the ecological functions of intermittent streams in the Pacific northwest. They suggested that productivity of perennial channels is heavily reliant on the transport of materials from intermittent channels on a seasonal basis. However, this finding was not based on published scientific data and appeared to be derived from anecdotal evidence. Hence, it remains unclear whether woody and leaf material contributions to downstream habitats from headwater features are significant or not. A study conducted by Conners and Naiman (1984) examined the relationships between allochthonous inputs and stream order in an undisturbed watershed in Eastern Quebec. They found that headwater streams (orders 1-3) each contributed about 22% of total allochthonous loading to the watershed income. In addition, their data supported the idea that the relative contribution of organic matter (leaves and twigs) from the riparian zone decreases downstream once the data are corrected for unit stream length, although they offer the caveat that the results were influenced by local factors. Again, the streams tested were likely all permanently-flowing (although not reported as such) first- to sixth-order streams. Interestingly though, because the relationship between annual litterfall and stream order is exponential and inversely related, when the data presented in Figure 7 are extrapolated to zero-order streams, they suggest that it is possible inputs from these smaller streams are even higher than larger streams. A separate study would be required to confirm this assumption.



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Figure 7: Annual litter input (direct fall) as a function of stream order for rivers in eastern Quebec. Broken lines indicate exponential regressions for data points from the individual years for 1980-1981 (r2=0.99) and for 1981-1982 (r2=0.99). The solid line indicates the regression using combined year data (r2=0.98). (Source: Conners and Naiman 1984).

4.2.2.4 Organic Debris Dams

Some headwater streams located in forested areas are heavily reliant on input of organic material as an energy source from the surrounding terrestrial system. In particular, the accumulation of organic matter across a stream channel, also known as an organic debris dam, was found to be one of the most important structural components of small stream ecosystems and an important mechanism in retaining organic carbon within the system (Bilby and Likens 1980). Organic debris dams catch and retain leaf-sized organic matter within smaller first-order streams, then allows trapped material to be processed into finer size portions before being carried downstream to larger reaches. This is significant because a slower release of carbon can supply food resources to downstream aquatic communities more evenly, and for a longer period of time (Meyer et al. 2003). In addition, the input of large organic pieces such as leaves and woody material, often enter headwater streams in large amounts and cannot be easily carried downstream and therefore block passage of materials (Meyer et al. 2003). These types of structures also become important for sediment trapping, as some form pools on the upstream side and catch larger materials (Bilby and Likens 1980). In their study conducted in a forested mountainous region of New Hampshire, Bilby and Likens (1980) found that in first-order streams, debris dams contain nearly 75% of the standing stock of organic matter. This declines to only 58% and 20% in second-order and third-order streams, respectively. They compare removal of organic debris dams within small streams to stream piping, whereby organic inputs are rapidly flushed from the system, reducing the energy base of the stream system. The authors did not specifically report whether flow was permanent or intermittent, however, some of the data presented included zero or nearly-zero flow discharges.

Small streams within our Southern Ontario setting are typically disturbed in some way (i.e. through agricultural or urban uses) and cannot always be compared to the forested



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catchments examined above. Many headwater drainage features in Southern Ontario do not have forest cover, but may have herbaceous riparian cover, which may limit the relevance of organic debris dams within our regional setting. However, if the importance of organic debris dams can be proven for intermittent and ephemeral streams in this area, both protection and restoration of these headwater drainage features to forest cover would be an important consideration.

4.2.2.5 Riparian Shading

Another function of the intact headwaters and their riparian zones is shading, as a control on stream temperature. Temperature is one of the most important controlling factors of in-stream processes and aquatic ecosystem dynamics, such as metabolism, organic matter decomposition, and gas solubility (Caissie et al. 1998, Johnson 2004). However, again, all of the emphasis in the literature is on permanently-flowing first and second-order streams. There is literature that both contests (Larson and Larson 1996, Larson et al. 2002) and supports (Rutherford et al. 2004, Johnson 2004, Poole and Berman 2001) the idea that shade will influence stream temperature. Incoming solar radiation is accepted to be the major source of thermal energy in stream waters, but some literature suggests that groundwater inputs, air temperature, substrate type and shading may also influence water temperatures in small streams (Blackport et al. 1995, Caissie et al. 1998, Johnson 2004, Rutherford et al. 2004). Smaller permanently flowing streams have a substantially lower volume of water and are relatively shallow in depth, in comparison to the higher order reaches (Caissie et al. 1998). Consequently, there is some evidence to support that headwater streams are more susceptible to receiving the suns rays and are more sensitive to changes in shade. The primary mechanism by which riparian vegetation controls temperature is through insulation, where the vegetation not only shades but traps the air next to the stream surface (Poole 2001). Rutherford et al. (2004) studied five second-order streams and found that patches of dense riparian shade and unshaded reaches, 500-1000m long, resulted in water temperature changes of 4-5°C. There was a strong linear relationship between the rate of change of daily maximum temperature and the changes of shade, such that a 100% change in shade downstream resulted in a heating/cooling rate of ±4°C h-1 and ±10°Ckm-1 respectively. Johnson (2004) found that maximum water temperature declined significantly in the shaded second-order reach being evaluated. Stream temperature is not only controlled by shading, but also elevation and interannual climate variation (Meyer et al. 2005b). Headwater areas may also be important contributors of seed supply to downstream riparian habitats following disturbances, such as floods (Gomi et al., 2002). This could be an important pathway contributing to the recolonization of riparian vegetation within these downstream habitats following such disturbances.

4.2.2.6 Direct Fish Habitat

Headwaters play a crucial role for a variety of fish at different stages of their life. For certain species like brook and brown trout, permanently flowing headwaters provide the right habitat conditions to live exclusively in the system. Typical headwater species are primarily insectivore-piscivores and generalized insectivores (Schlosser, 1982, Paller, 1994).



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Headwaters can contain a unique species assemblage, which can make a significant contribution to regional fish diversity (Meyer et al. submitted ms). They can also act as refugia for riverine species during specific life-history stages and critical periods of the year (Lowe and Likens, 2005). Adult coho salmon (Oncorhynchus kisutch) use the lower headwaters as spawning grounds and some of the resulting juveniles use these areas as refugia during high flows (Gomi et al. 2002). Erman and Hawthorne (1976) reported that approximately 39-47% of the adult rainbow trout in a creek in California spawned in an intermittent stream, while only 10-15% of the trout run were attracted to several permanently-flowing tributaries. They presumed that the main factor for this was that the intermittent tributary drained a south-facing slope that had early peak runoff following spring snow melt. In addition, this tributary’s importance to rainbow trout was also attributed to low competition from brook trout (Salvelinus fontinalis), which were unable to spawn in the drier autumn months. Another species that is known to use these systems for spawning during times of higher flows, is the northern pike (Esox lucius). Spawning occurs in the early spring, immediately after ice melts in April to early May, when temperatures range between 4.4-11.1ºC. This species spawns on the heavily vegetated floodplains of rivers, marshes, and bays of larger lakes (Scott and Crossman 1985), where, ideally, dense vegetation obscures 40-90% of the bottom, with an optimum at 60% (Casselman and Lewis 1996). They swim through and over the vegetation in water that is often very shallow, <200 mm (Scott and Crossman 1985), that could be associated with the riparian zones of HDFs. Ideal habitat suitability criteria include areas where vegetation provides extensive surface area to which eggs can adhere, such as flooded sedge or grass meadow, typical of zero-order swales. Eggs usually hatch in 12-14 days, the young remain inactive for another 6-10 days as the yolk is absorbed (Scott and Crossman 1985), and fry usually move out of nursery habitats after approximately 6-8 weeks (Casselman and Lewis 1996). Rivulets that permit easy movement of spawners into spawning habitat and allow fry to move out with receding water are important habitat criteria (Casselman and Lewis 1996). When pike are known to be present within downstream systems and suitable spawning and nursery habitat are available within the HDF, these sites may be critical habitats for the northern pike. Despite the above, it is critical to note that any streams that offer direct fish habitat, even seasonally, are not of particular interest in the context of this review as this would not constitute indirect fish habitat. Nevertheless, it is important to note the fish species that could use these systems seasonally.

4.2.2.7 Mussels

Mussels qualify as ‘fish’ under the definition provided in the Federal Fisheries Act. As such, we searched the literature to determine whether headwater drainage features provide specialized habitats for certain mussel species. From the literature that we reviewed, it was clear that most mussel species are not known to be resistant to extended periods of drought (Johnson et al. 2001), as will likely be experienced in intermittent and ephemeral systems. In fact, it appears, from the available science, that prolonged drought is detrimental to most mussels due to greater predation pressures, hypoxia (low levels of dissolved oxygen in water,



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i.e. <5 mg/L), increased water temperature, and eventually, anoxia (no dissolved oxygen in water) or emersion (stranding out of water and exposure to air). However, one mussel family, Unionidae, has evolved several mechanisms for tolerating drought-related environmental change. Some of these mechanisms include: lowering metabolic activity; producing metabolic oxygen in sufficient amounts to survive anoxic environments; respiring through “mantle exposure behaviour;” switching from aerobic to anaerobic respiration; and migrating to deeper sediment to avoid emersion. Johnson et al. (2001) examined unionid survivorship during a drought that occurred during 2000, which caused perennial second and third-order streams in Georgia, U.S.A., to become intermittent between the months of July and October. The species with the highest tolerance for drought conditions were common, abundant, and widespread species (particularly Elliptio complanata/icterina, Villosa vibex, V. lienosa, and Uniomerous carolinianus), and were typical in highly degraded, intermittent or headwater streams. Intolerance to hypoxia may be the reason for some species preferences for larger stream bodies and increased mussel diversity with increasing stream size (Johnson et al. 2001). While this suggests that specialized mussel habitat may not be provided by headwater drainage features, some mussel species may be able to tolerate the intermittent flow conditions that may be present in HDFs. If this is the case, these features would provide direct fish habitat.

4.2.2.8 Impacts of Urbanization on Aquatic Systems

One unifying theme found throughout the literature was the use of catchment imperviousness or total impervious area (TIA) as a general environmental indicator for the management of urban catchments (Arnold and Gibbons 1996; Finkenbine et al. 2000; Schueler 1994; Schueler and Claytor 1997; Walsh et al. 2001; Paul and Meyer 2001; Stanfield and Kilgour 2006). Stanfield and Kilgour (2006) found that once percent impervious cover in a watershed reaches a threshold of about 10%, regardless of the presence/absence of stormwater management measures, more sensitive aquatic species, such as salmonids, are lost from the system. Not surprisingly, similar imperviousness thresholds are also reported in the literature to mark the onset of instream adjustments (Booth and Jackson 1997; Dunne and Leopold 1978; Morisawa and LaFlure 1979). Booth and Jackson (1997) found that channels begin widening at 6% catchment imperviousness, and channels become unstable above 10% imperviousness. This shows a clear link between the quality of in-stream fish habitat and the quality of fish communities. A number of studies examined the impacts of enclosing headwater streams. In each case, streams had the potential to provide habitat to fish, although water quality impairments may have negated this function. As such, these examples cannot necessarily provide direct correlations to the impacts that would result from piping features further upstream where direct fish habitat is absent, however we present them here for information purposes. Although the first case study was conducted on a fish-bearing stream that likely would automatically be subject to the Federal Fisheries Act, it demonstrates that piping can have a detrimental impact on aquatic macroinvertebrates that can also be found in fishless streams. It examined small headwater trout streams in Georgia, USA, on natural and piped sections of the channel. Insect drift samples of three natural headwater streams resulted in 10-14 taxa in the



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EPT group, indicating the quality of the water was high. However, drift samples collected downstream of the piped section obtained only one EPT individual and 89% of the collected organisms were aquatic worms, which are indicators of poor or low water quality (Meyer et al. 2005b).

The second case study focused on the current state and the aquatic community restoration potential for a small first-order tributary, Fort Chaplin, which drains to the Anacostia River in Washington, D.C. The tributary system is composed of both perennial and intermittent streams with ~2900 feet [~880 m] of open channels and ~6900 feet [~2100 m] of piped section. Water samples collected found that the majority of organisms present were those of pollution tolerant groups, and only extremely low numbers of EPT taxa remained in the stream (Trieu et al. 2004). In addition, increased stormflow levels of sediment resulted, which had many impacts on water quality, streambed stability and physical aquatic quality. Enclosing a headwater stream due to urban land use and development, reduces the retention of sediments and leads to excess sediment transport downstream. This sediment accumulation in larger streams will affect fish spawning success (Kentuckians for the Commonwealth 2006, Waters 1995). When sediment is flushed out of the headwater system at a fast rate, it can impart physical injury to fish, such as their eyes and gills, as well as cover larger materials in the substrate (MMM 2005). This is particularly pronounced during the development construction stage when much of the vegetation on construction sites leave soils exposed and vulnerable to erosion (see Figure 8).

Figure 8: Sediment removed from stripped soils during rainstorms enters streams and harms fish habitat. (Photo credit: Derek Smith) All literature reviewed focused on general fish habitat/health implications due to effects from urbanization, but not specifically from enclosed streams. Although, one would assume that poor water quality flows downstream and subsequently affects fish habitat due to existing upstream-downstream linkages. There clearly is a need for additional research on the impacts of enclosing, lowering, and realigning headwater drainage features; however, we have provided a short discussion of



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possible correlations between these features and lost functions, based on some findings in the literature. There is some evidence to suggest that organic debris dams in headwater systems could provide functions such as sediment retention, and providing important habitat structure for invertebrates (Kentuckians for the Commonwealth 2006, Steinhart et al. 2000) in headwater drainage features. When a feature is piped, organic inputs are likely rapidly flushed from the system (Bilby and Likens 1980), or there may no longer be a source of organic inputs because the riparian vegetation would be absent (Richardson 2000). However, many of the headwater drainage features in our setting are located in agricultural situations, with little to no riparian cover. While these organic inputs may be minimal, it is important to understand how the role of organic matter inputs to downstream reaches would change in a post-development scenario. Sponseller and Benfield (2001) found that in some headwater streams, increased sediment inputs resulting from development in riparian corridors may limit the distribution of shredders and in-stream processing. Riparian cover influences stream temperature by shading from solar radiation and minimizing temperature fluctuations. Once the vegetation is removed, the stream temperatures usually become warmer. A study by Meyer et al. (2005b), found stream temperatures got warmer with decreasing vegetation. Excess sediment inputs from riparian loss can also become a problem because the fine sediments enter the stream network. Fine sediments supplied to the stream by the process of bank erosion smother coarse substrate habitats (Meyer et al. 2005b) Organic inputs are integral to the stream detrital food web, and once a headwater is enclosed there will be no more riparian vegetation, thus no large organic inputs of leaf litter, woody material and allochthonous inputs (i.e. carcasses, dissolved organic matter from groundwater). A study performed by Wallace et al. (1997), found that the exclusion of terrestrial litter inputs from a fishless first-order Appalachian headwater stream (avg Q=2.39 L s-1) will cause major changes in the abundance, biomass and production of invertebrate fauna. Headwaters could no longer store and process the organic matter and there would be no modulation of the release of carbon to downstream reaches. Any organics entering the system would automatically be flushed downstream causing a glut of decomposing material which could deplete oxygen stores (Meyer et al. 2001). The removal of headwater drainage features also represents a potential threat to biodiversity, since there may be species found in these systems that have not yet been identified. Given the evident lack of knowledge of these systems and the transitional habitat they may provide, these systems may be important habitat niches for certain drought-resistant or terrestrial invertebrates. Many threatened insect species have been located in small headwater streams in other regions. A study Morse et al. (1997), found the southern Appalachians had a vast amount of aquatic insect diversity, however, a total of 91 species were reported as being rated vulnerable to extirpated. Muchow and Richardson (2000) investigated macroinvertebrate assemblages in small, zero-order channels. They found that species richness in intermittent streams and continuous streams are approximately equal, however intermittent streams appeared to produce twice the number of adult stoneflies than continuous streams. The study indicated that intermittent streams harbor aquatic fauna and potential unknown species. Intermittent streams make a unique habitat that contributes to the watershed ecosystem. If



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removed, unique populations of stream invertebrates could be eliminated including species that have yet to be discovered.

4.2.3 TERRESTRIAL FUNCTIONS

4.2.3.1 HABITAT FOR TERRESTRIAL FLORA AND FAUNA

It is suggested that headwaters offer a diverse array of habitats for plants, animals and microbial life (Meyer et al. 2003). Some references claim that small streams and their riparian zones offer unique habitats that, for some, can be found nowhere else in the stream network. There is variation in habitat due to regional differences in climate, geology, land-use and biology, which can change throughout the stream network. Despite these statements, there was limited empirical support for this in the literature. Meyer et al. (2003) completed a comprehensive paper that summarized many ecological and environmental functions in support of protecting small streams. They claimed that many of the typical headwater species, including bacteria, fungi, algae, higher plants, invertebrates, amphibians, birds and mammals, are headwater specialists and are most abundant in, or endemic to, headwaters. The following claims were also made by Meyer et al. (2003):

• intermittent streams are said to be generally predator-free, so species like salamanders and crayfish are more abundant; headwaters act as refugia for a variety of organisms. A number of these ephemeral and intermittent streams are small fishless zones. With low to no predator numbers there is a higher diversity of aquatic insects, higher biomass in emerging insects, and a change in crayfish abundance patterns;

• these streams can be a refuge from temperature, competitors and alien species; specialists to headwaters have a small geographic range because of their limited ability to move, which can help repopulate a stressed population or even produce a different species in adjacent headwater systems;

• and finally, in some areas, riparian headwaters can have a closed canopy with some different structural features than those found along larger streams. For organisms like salamanders, frogs, salmonids, snails and birds, the riparian zone creates a habitat with a rich resource base.

However, none of the references were provided in the body of the text to support particular statements. Only one reference appeared to be directly dealing with terrestrial functions and headwater streams. This is discussed below. A study by Stoddard et al. (2004) has placed a conservation priority on headwater streams with northeasterly aspects because Pacific giant salamanders (Dicamptodon tenebrosus) and tailed frog (Ascaphus truei) tadpoles inhabit these areas. These species were positively correlated with the presence of a 46 m band of forested habitat on each side of the stream. A similar study by Hayes et al. (2003) examined Pacific tailed frog distribution during the low flow period between August and October in non-fish bearing streams in southwestern Washington. Their study showed a seasonal connection between various life stages of frogs with flow duration of streams. Adult frogs were typically found further upstream (above the origin of surface flow) than younger stages, but then returned downstream to lay eggs. They believe



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that the frogs probably lay eggs in areas far enough downstream to prevent desiccation, but far enough upstream to avoid fish-bearing reaches (i.e. predators), thereby suggesting a reliance on intermittent streams. Similarly, Welsh et al. (2005) examined the species distribution of herpetofauna of a northern California watershed in permanent and intermittent streams. They defined an intermittent reach as “containing flowing or standing water interspersed between segments of dry channel.” Although they found that overall there was higher species richness near perennial streams in comparison to intermittent reaches, two salamander species were significantly more abundant in the intermittent streams than in the perennial streams. The authors suggest that coastal giant salamander (Dicamptodon tenebrosus) and black salamander (Aneides flavipunctatus) were more plentiful along intermittent reaches because these streams play an important role in some key aspects of their natural history, in particular for breeding and nursery habitat. They theorize that although black salamanders are terrestrial and usually not associated with flowing water, juveniles may migrate to intermittent reaches or adults lay eggs near intermittent reaches to avoid dessication. Female coastal giant salamanders may seek out headwater areas because of reduced predation from other species and from larger individuals of this highly cannibalistic species. Dry channel segments associated with intermittent reaches may prevent the immigration of aquatic predators such as fishes and larger aquatic salamanders, thereby limiting egg and larvae predation. Reid and Ziemer (1994) reported that young salamanders may rear in intermittent streams and then move into more permanent streams once they are large enough to defend themselves against predators. This finding was based on the results of unpublished data from the USDA Forest Service. Waterhouse et al. (2002) examined the use of riparian habitats associated with small streams (<10 m wide, including seeps with surface water) by winter wren in coastal forests of British Columbia. The objective was to determine whether riparian habitats of small streams are selected for territories by males over adjacent upslope habitats because of the provision of differing available resources. All streams were located on what the authors consider to be gentle slopes, with gradients less than 11.5°. There were two classes of streams examined in the study, including streams 5-10 m wide that contained water throughout the breeding season, and stream channels <5 m wide that were typically seasonally dry by late May to June. They found that winter wrens chose habitats close to these small streams for nest building (within 5 m), as well as for song perches. However, they concluded that the structure provided by vegetation and topographic qualities of streams 5-10 m (more permanent) wide may offer more potential opportunities for this species than do streams <5 m wide (more intermittent). The authors also concluded that this preference for small streams may also be attributed to higher forage quality and thermoregulation, which may be positively influenced by riparian habitats. Although not many birds within North America are known to actually nest in or close to small streams, many species depend on headwaters for other life cycle functions (i.e. feeding, drinking, habitat, movement). For example, small headwater streams are the preferred habitat for Louisiana and northern water thrushes (Seiurus noveboracensis and S. motacilla) (Meyer et al. 2007). The abundance of aquatic insects that emerge from small streams provides feeding opportunities for many species, such as flycatchers, which are known to be abundant



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around headwaters (Murray and Stauffer 1995). In addition, overall bird abundance has been found to be elevated in areas close to headwater streams (Wiebe and Martin 1998). There is also some evidence that mammals use headwater streams for habitat. The imperiled star-nosed mole (Condylura cristata) is known to dig tunnels that lead to small streams (Harvey and Clark, 1997), and headwaters are also disproportionately utilized by mink, beaver, and otter in relation to their areal extent on the landscape (Kruuk et al. 1998). In the Pacific Northwest, a number of mammal species are characteristic of headwater systems including Sorex bendirii, S. palustris, S. pacificus, Microtus richardsoni and M. longicaudus (Meyer et al. 2007). Some of these species are obligate headwater species whereas others are widespread but more abundant in headwaters (Richardson et al., 2005). Seidman and Zabel (2001) examined the use of varying sizes of intermittent streams by bats in northwestern California to determine whether the well established use of permanent streams by bats could be extended to non-permanently flowing streams as well. They found that although streams that were wider than 1.8 m had significantly more bat activity than both upland sites and streams smaller than 1.2 m, streams that had any water at all (even small pools) had much higher bat activity than dry channels or upland sites. Bats use riparian areas for drinking and foraging. Different bat species use varying sizes of streams depending on their aerial maneuverability. Smaller more maneuverable bats can drink from very small pools of standing water that can often be found in intermittent streams. This study was conducted in high quality old-growth forests in California, and we, being agencies with little monitoring in this field, know very little about bat ecology in Southern Ontario. However, this indicates that these small streams may be important for bats in our area.

4.2.4 AQUATIC-TERRESTRIAL RECIPROCAL RELATIONSHIPS

There is literature that supports the idea of strong ecological connections between terrestrial and aquatic ecosystems. Nakano and Murakami (2001) studied the dynamic interdependence between terrestrial and aquatic food webs in a small cold-spring-fed stream in northern Japan (temperate bioregion). Characteristics of the stream included a drainage area of 15.4 km2, 14 km length, 2-5 m width, stable 0.25 m2s-1 average discharge (likely permanently flowing), and 97% of the entire width of the study reach had forested canopy cover during the leaf-out period. The allochthonous prey supply within both the stream and the forest changed substantially on a seasonal basis. The forest exhibited higher terrestrial prey biomass during the growing season, peaking in August, than during the defoliation period, and was nearly zero during winter (December to March). Conversely, aquatic prey biomass was higher during the defoliation period, peaking in spring, than that during the growing season (see Figure 9). This seasonal dynamic provided significant aquatic prey subsidies to forest birds when terrestrial invertebrates were lowest (during the spring), as well as terrestrial prey subsidies to stream fishes when aquatic invertebrates were lowest (during late summer).



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Figure 9: Contrast in seasonal dynamics of allochthonus prey contributions to forest birds and stream fishes. (A) Proportion by frequency of aquatic prey foraging to the total observations in each forest bird species. The contribution of aquatic prey differed significantly both among months and species in both year-round and summer-resident birds (P<0.01 for all by Friedman test). GT, great tit; MT, marsh tit; NH, nuthatch; PWP, pygmy woodpecker; BRF, brown flycatcher; NF, narcissus flycatcher; PWW, pale-legged willow warbler; CW, crowned willow warbler; BB, black-faced bunting; WR, wren. Black and white horizontal bars at the bottom of the figure indicate observation periods for winter and summer birds, respectively. (B) Proportion by dry mass of terrestrial prey to the total diets in stream fish species. The proportion differed significantly among both seasons and species (P<0.0001 for both by Friedman test). RBT, rainbow trout; WSC, white-spotted char; DV, Dolly Varden; MS, masu salmon; SC, freshwater sculpin. Black and white portions of horizontal bars at bottom of figure indicate leafing and defoliation periods. (Source: Nakano and Murakami, 2001).



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Figure 10: Food web linkage across a forest-stream interface representing predator subsidies by allochthonus, invertebrate prey flux. Relative contributions of terrestrial and aquatic prey to the annual total resource budget of each species were represented by line thickness. Annual resource budget of each species was represented as a value proportional to the total assemblage-based budgets, separately for the bird and fish assemblage. (Source: Nakano and Murakami, 2001). When combined, all bird species data suggested that aquatic prey accounted for 25.6% of the annual total energy demand of the bird assemblage (402,607 kJ per 10 ha y-1). Similarly, terrestrial prey contributed 44% of the annual total resource budget of the stream fish assemblage (531,421 kJ per 4,200 m2y-1). The authors suggest that the most important aspect of these reciprocal subsidies, was the asynchrony of allochthonus prey supply on a seasonal basis. The stream provided large energy transfers to the riparian forest, predominantly when terrestrial prey biomass was low. Since birds exploited aquatic prey intensively when terrestrial prey availability was limited, seasonal asynchrony could be the critical factor influencing the subsidy efficiency of aquatic prey flux. This reciprocal prey flux across terrestrial-aquatic ecotones could have substantial implications on food web dynamics (see Figure 10). In particular, understanding these relationships in the Southern Ontario context will be of important considerations as Conservation Authorities (e.g. TRCA) move towards integrating terrestrial and aquatic elements in Natural Heritage Systems. 5 CONCLUSION AND RECOMMENDATIONS Table 4 below summarizes potential benefits that headwater drainage features may contribute to our watersheds. We have also indicated whether there is evidence within the literature to support the notion that intermittent and ephemeral features contribute to the function.



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Table 4: Summary of headwater drainage feature functions and their benefits to downstream channels and whether the function is supported in the literature

FUNCTIONS POTENTIAL BENEFITS FROM HEADWATER DRAINAGE FEATURES

EVIDENCE OF FUNCTION FOUND IN LITERATURE

PHYSICAL/CHEMICAL • maintenance of natural flow regime • support for protecting headwater areas; anecdotal4

support for HDFs2 • increases groundwater infiltration and reduces

peak flows and runoff • growing body of evidence in support of using swales

as at-source control of flooding, preliminary work by Gorenc et al. supports this

• slows flow velocities • anecdotal claims made4

Hydrology

• cumulative water storage and flood control • anecdotal claims made4, some preliminary results support this

• natural level nutrient source • evidence from forested catchments, elevated levels in agricultural land uses

• excess phosphorus trapping by adsorbing to sediment

• some evidence for well-defined streams, indirect evidence1 for HDF2

• excess nitrogen uptake • some evidence for areas with intact riparian zones, some evidence for permanent streams, increasing trend of uptake towards headwaters

Water quality

• pollutant removal • engineered swales are effective at removing most chemical parameters

• sediment trapping • anecdotal claims made, some evidence from mountainous regions

• maintain natural sediment supply to downstream areas

• ongoing work by Gorenc et al. to prove or disprove, will also examine whether HDF2 can be replicated by SWM3

• prevents costly dredging operations • claims made, no direct data

Sediment control

• attenuates impacts to fish and fish habitat • no direct evidence found AQUATIC

• baseflow contribution • anecdotal only • temperature moderation • evidence for permanent streams, little for intermittent

and ephemeral

Groundwater and Hyporheic

• nutrient, water, dissolved organic mater and oxygen exchange

• well documented for permanent streams (largely in mountainous areas), studies on ephemeral and intermittent systems were in arid or semi-arid regions

• allochthonus inputs of detritus • largely theoretical, empirical evidence limited to permanent (nearly intermittent) streams

• unique invertebrate habitats and high species richness

• evidence that intermittent streams can provide unique niches

Subsidies of Detritus and Invertebrates • invertebrate production and export • studies support terrestrial inputs are important to

downstream areas; also support for aquatic invertebrate production can be higher in intermittent than permanent streams; export important from nearly intermittent mountainous forest streams

Woody material and Leaf Litter Contributions

• subsidize downstream productivity • well documented for permanent streams, anecdotal4 for ephemeral and intermittent streams

Organic Debris Dams

• carbon retention • some evidence for higher retention in lower order streams, mountainous regions, flow permanence not reported

Riparian Shading • stream temperature moderation • some conflicting findings, emphasis on permanent streams

Mussel Habitat • unique habitats for mussel species of conservation concern

• evidence that headwaters provide habitat for at risk mussel species in permanent streams only; may provide habitat for more common species tolerant of drought

TERRESTRIAL • unique habitat for terrestrial flora • anecdotal4 only

Habitat Provision • unique habitat for terrestrial fauna • confirmed for bats and amphibians; some evidence for birds and mammals other than bats

TERRESTRIAL-AQUATIC Reciprocal Relationships • asynchronous prey flux provides important food

web subsidies across ecotones • direct evidence of this from a study in Japan, however

not specific to HDFs2 1 indirect evidence suggests that there are indirect correlations made between findings in the literature and their applicability to headwater

drainage features 2 HDF means Headwater Drainage Features 3 SWM means stormwater management 4 anecdotal evidence may also include unpublished or unreported data



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It is clear from the above table that there are many data gaps yet to be filled with respect to confirming functions specific to headwater drainage features. Although there is a growing body of science to support the functions of headwater streams in their broad sense, this is mostly concentrated on permanently flowing streams, first-order streams or higher. Although there are some studies that supported the importance of intermittent streams. Despite some published evidence, anecdotal claims or claims based on unpublished data, there are a limited number of references that specifically addressed headwater drainage features, particularly in a similar regional setting to Southern Ontario. There does appear to be some support for headwaters as sources of food and detritus contributions to downstream fish-bearing habitats, however, few of the studies specifically examined HDFs. In addition, the landscape settings of most of the research were under differing physiographic, climatic and land use conditions. Many studies were conducted in high-gradient forested catchments, which were different from the low-gradient mainly urban and agricultural catchments that are of interest to us. The only real discussion of the aquatic functions of intermittent features was not based on scientifically-defensible empirical data, or the studies were conducted in arid or semi-arid regions. Since, to our knowledge, no other studies have been conducted on Southern Ontario headwater drainage features, further research in our regional context would confirm whether this biological function is relevant within our urban/agricultural setting. There is also a clear need for additional research on the impacts of enclosing, lowering, and realigning headwater drainage features. Terrestrial functions of non-permanent features were substantiated in the literature as they provide habitat for amphibians, birds and mammals. We also know that, locally, Jefferson salamander (Ambystoma maculatum), which is a nationally and provincially threatened species, utilize non-permanently flowing drainage features as breeding habitat (Pisapio, 2007). In addition, HDFs may provide locally unique habitat for certain bat species. However, given our lack of monitoring of this taxum, we are unaware of any local examples. Our original objectives outlined in Section 1.2 have not been adequately answered, however, this provides many opportunities for further research. For instance, the results of ongoing work by Gorenc et al. (undated) will be invaluable in determining whether protection of headwater features is beneficial to stream ecosystems from a hydrologic and sediment transport perspective versus traditional stormwater management approaches, and whether a new “drainage density” approach is warranted. The relevance of this work is heightened by its regional context within Southern Ontario, and as it becomes clearer that traditional end-of-pipe stormwater management techniques do not go far enough in protecting natural hydrologic and sediment transport functions. While proving headwater drainage features serve other functions (flood attenuation, sediment transport, water quality improvement, etc.) would be essential in improving our understanding of the role headwater drainage features play in the ecological health of watersheds, this work would tend to support protection of some sort of open drainage feature on the landscape, and not necessarily insitu natural drainage features. There is a great need to understand when natural features need to be maintained “as is” in the post-development scenario. This will likely be related to a biological or hydrogeological (discharge) function. For example, since alternative open drainage features (as described by Gorenc et al.) may not necessarily be



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designed to maintain biological functions, confirming the importance of invertebrate and detritus export is possibly the easiest way to link the maintenance of downstream productive capacity with the protection and/or enhancement of headwater drainage features as they exist today. A new study examining export in truly intermittent and ephemeral streams is recommended. This would either refute or confirm that these features satisfy the indirect habitat criteria. Nevertheless, Conservation Authorities have enough experience within our watersheds to justify the promotion of a proactive approach to the management of headwater drainage features. While we believe certain research priorities are important in order to define specific functions of headwater drainage features, it is important to use the precautionary principle in developing an interim guideline for HDF management. The interim guideline will outline the protection measures that are required for both permanently flowing and non-permanently flowing headwater features, and should be conservative, until such a time that future research can demonstrate that a less conservative approach is acceptable. If the interim guideline was not conservative, many of these features may be lost during the completion of the additional scientific studies. Future Work Priorities 1. Develop an interim guideline to provide direction on the management of both permanent

and non-permanently flowing headwater drainage features until such time that the science is available to provide further support.

2. Develop a protocol for conducting research on headwater drainage features that can be used for both the interim guideline and for future research.

3. Develop a research design to address the outstanding scientific gaps with regards to headwater drainage features in order to finalize the guideline.

Research Design Priorities 1. Characterizing existing hydrologic conditions and determining how hydrology is

influenced by land use in headwaters. Developing a flow prediction model and/or flow accumulation model to determine, based on catchment characteristics, what is the flow permanence of features being assessed.

2. Examining the cumulative impacts of landscape alteration in headwaters on downstream fisheries.

3. Examining how differences in various vegetated settings (forested, agricultural, and urban) influence the export of detritus and terrestrial and aquatic invertebrates in various HDFs (e.g., how do these differences affect the habitat, water quality, and temperature aspects of aquatic communities?) and how these differences affect the assemblage of aquatic species downstream?

4. Test the similarity between the Interim Guideline and the derived relationships of HDF condition and biota from this research and modify as necessary the management tools.

5. Assessing whether HDFs vary in their importance for maintaining fish communities in watersheds and whether some are more suitable for restoration work.

6. Further examine links between terrestrial fauna species, such as bats, amphibians and birds, and headwater functions. Determine whether there are additional local species that rely specifically on non-permanent streams for their natural histories.



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6 GLOSSARY Aestivation- cessation or slowing of activity during summer, especially the slowing of metabolism of some animals due to hot or dry periods Aggradation – the accumulation of unconsolidated sediments on a surface, thereby resulting in material deposition Allochthonus – not made in situ; applied to material which did not originate in its present position or location Autochthonus – applied to material which originated in its present position or location Baseflow – the sustained or fair-weather runoff Biomass – the total mass of all living organisms (producers, consumers, and decomposers) or of a particular set (e.g. species), present in an ecosystem or at a particular trophic level in a food-chain Degradation – the removal of unconsolidated sediments on a surface, thereby resulting in material erosion Denitrification – the conversion of nitrate to gaseous products, chiefly (N2) and/or nitrous oxide (N2O), by certain types of bacteria. Denitrification occurs mainly under anaerobic or micro-aerobic conditions Detritus – litter formed from fragments of dead organic material. In aquatic habitats, detritus provides habitats equivalent to those which occur in soil humus. Diapause – a period during which growth or development is suspended and physiological activity is diminished, as in certain insects in response to adverse environmental conditions Drainage Density – the ratio of the total length of all watercourses in a drainage basin to the total basin area Duration of Flow – the period of time associated with a specific flow condition Eutrophication – the process of nutrient enrichment (usually by nitrates and phosphates) in aquatic ecosystems, such that the productivity of the system ceases to be limited by the availability of nutrients Exfiltration – the removal of water from the soil at the ground surface, together with the associated unsaturated upward flow Frequency of Flow – how often a flow above a given magnitude recurs over some specified time interval; inversely related to magnitude



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Geomorphology – the study of the origin of landscapes based on a cause and effect relationships. This includes the physical and chemical interactions between the earth’s surface and the natural forces acting on it, such as geology, climate, vegetation and relative base levels Groundwater discharge – the removal of water from the saturated zone within soil across the water table surface, together with the associated flow toward the water table within the saturated zone Headwater - the tributary streams of a river, which flow from the area in which it arises Herpetofauna – reptiles and amphibians Hydrology – the science dealing with the properties, distribution and circulation of water on the surface of the land, in the soil and underlying rocks, and in the atmosphere Hyporheic zone - part of the streambed that is the site of groundwater-surface water interactions. The hyporheic zone is considered to be defined as the subsurface water adjacent to the channel that contains greater than 10% advected channel water Infiltration – the movement of water from the land surface into the soil Insectivores - an organism that feeds primarily on insects Magnitude of flow – the amount of water moving past a fixed location per unit time Piscivore – an organism that feeds primarily on fishes Porosity – the percentage of the total bulk volume of a body of rock or soil that is occupied by pore space Rate of Change of Flow (Flashiness) – how quickly flow changes from one magnitude to another Recharge – the process by which water is added to a zone of saturation, usually by percolation from the soil surface, eg. the recharge of an aquifer Refugium (pl. refugia) - an isolated area where extensive changes, most typically due to changing climate, have not occurred. Plants and animals formerly characteristic of the region in general find refuge from unfavourable conditions in these areas. Riparian – the land, together with the vegetation it supports, immediately in contact with the stream and sufficiently close to have a major influence on the total ecological character and functional process of the stream



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Runoff - the water from rain, snowmelt or irrigation that flows over the land surface and is not absorbed into the ground, instead flowing into streams or other surface waters or land depressions Salmonid - of, belonging to, or characteristic of the family Salmonidae, which includes the salmon, trout, and whitefish Saturated overland flow – when the soil is saturated and the depression storage is filled, and rain continues to fall, the rainfall will immediately produce surface runoff Stream order – a measure of the position of a stream (defined as the reach between successive tributaries) within the hierarchy of the drainage network. A commonly used approach allocates order ‘1’ to unbranched tributaries, ‘2’ to the stream downstream of the junction of two first-order tributaries, and so on Throughflow – water that infiltrates the soil surface and moves laterally through the upper soil horizons towards the stream channels, either as unsaturated flow, or more usually, as shallow perched saturated flow above the main groundwater level. Timing of Flow (Predictability) – the regularity with which a flow of a certain magnitude occurs Trophic levels – any of the feeding levels that energy passes through as it proceeds through the ecosystem. For examples, primary producers form the first level in most ecosystems, followed by primary consumers, and up to the top predator level Watercourse - An identifiable depression in the ground in which a flow of water regularly or continuously occurs



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