The Hydrologic Budget of WetlandsJason HallRobert LomaxLisa Thatcher

November 4, 2003

OverviewInformation on hydrology budgets of wetlandsCase study of hydrology in a Carolina bay wetlandJason - watershed hydrology of coastal forested wetland of the southern USLisa - hydrology of a constructed wetland in south Florida, peatland in Wisconsin, and conclusion

Hydrology BudgetHydrology is probably the single most important determinant of the establishment and maintenance of specific types of wetlands and wetland processes. (Mitsch and Gosselink 1993)Hydrology describes all inflows and outflows of water, soil contours of the wetland, and subsurface conditions

Hydrology BudgetHydrologic conditions directly modify or change chemical and physical properties such as nutrient availability, degree of soil anoxia, soil salinity, sediment properties, and pH. These are major factors in the ultimate classification of the wetland itself as well as the selection of biota.Small changes in hydrology can result in significant biotic changes.

Hydrology BudgetThree main characteristics: (1) the balance btwn inflows and outflows. (2) surface contours of landscape. (3) subsurface soil, geology, and groundwater conditionsBudget usually described in terms of depth per unit time, e.g., cm/yr or in volume per unit time, e.g., m/day

animation

V/t = Pn + Si + Gi ET- So Go TV = volume of water storage in wetlandV/t = change in volume of water per unit timePn = net precipitationSi = surface inflows, including floodingGi = ground water inflows ET = evapotranspirationSo = surface outflowsGo = groundwater outflowsT = tidal inflow(+) or outflow(-)

Mitsch and Gosselink 1993

Mitsch and Gosselink 1993

PrecipitationWetlands favor areas where precipitation rates typically exceed evapotranspiration ratesPn = TF + SF

Surface InflowsOverland flow: nonchannelized sheet flow, occurs during and immediately following rainfall, spring thaw, or as tides rise.Stream flow: channelized flow from drainage basin, difficult to determine, often the most important source of water in hydrology budget

Surface OutflowsEither channelized or overland sheet flow

GroundwaterGroundwater inflows and outflows occur when surface water level of wetland is lower hydrologically than the water table of the surrounding landDifferent ways this occursDescribed by Darcys Law G = k a sG = flow rate of groundwaterK = hydraulic conductivity or permeabilityA = groundwater cross-sectional area perpendicular to flowS = hydraulic gradient ( peizometeric surface )

Mitsch and Gosselink 1998

GroundwaterGroundwater flows are important source of nutrients and dissolved minerals.Partly responsible for species diversity and richnessGroundwater hydraulics, despite their obvious importance, are still poorly understood

Mitsch and Gosselink 1993

EvapotranspirationWater that vaporizes from water or soil in wetlands (evaporation), combined with moisture that passes through vascular plants to the atmosphere (transpiration).Rate of evapotranspiration is proportional to the difference btwn vapor pressure at water surface (or leaf surface) and vapor pressure in overlying air

EvapotranspirationEnhanced by solar radiation and surface temperature which increase value of vapor pressure at evaporative surface or by reduced humidity and increased wind speed which decrease vapor pressure.If water is limited, evapotranspiration limited Transpiration can be limited physiologically by certain plants

EvapotranspirationFour equations used to describe the rate of evapotranspiration although none entirely satisfactory.Mainly because climatic conditions as well as vegetation vary btwn wetlands

TidesPredictable and periodic tidal inundations of coastal salt marshes, mangroves, and freshwater tidal marshes are major hydrologic feature of these wetlandsSalinity, duration and flooding frequency in part determine the abiotic and biotic components of the system

Principles underscoring the importance of hydrology in wetlandsHydrology leads to unique vegetation composition but can limit or enhance species richnessPrimary productivity and other functions enhanced by flowing conditions and pulsing hydroperiodsAccumulation of organic material controlled by hydrology through influence on primary productivity, decomposition, and export of POMNutrient cycling and availability are both significantly influenced by hydrologic conditions.

Hydrologic conditionsUsed by scientists to classify these ecosystemsClassification and mapping of wetlands based on biotic features (dominant vegetation) often matches the hydrologic conditions of different wetlands

HYDROLOGY, COMMUNITY STRUCTURE, AND PRODUCTIVITY PATTERNS OF A DYSTROPHIC CAROLINA BAY WETLAND

Thunder Bay Upper coastal plane in SE corner of the 750 - km Savannah River Plant in Barnwell County, South Carolina.US Dept. of Energy radioisotope production facility.Occurs in Lower Three Runs Creek watershed, tributary of Savannah River

Study SiteSchalles et. al. 1988

Thunder BayShallow 5.4 ha dystrophic Carolina bay wetlandStagnant hydrology, dilute/acidic chemistryLow primary production / low biomassSharitz 1994

Thunder BayAverage rainfall over the four year study period was 122.25 cmAir temperature averaged 18.3C (8.8C in Jan. and 27.5C in Jul)Growing season is approx. 245 d.At intermediate water stage, surface elevation was 61 m NGVD (National Geodetic Vertical Datum)Little to no surface inflows or outflows

Thunder BaySoil dark sandy loamUnderlying clay lensSurface water extremely dilute (16.7 S)

Thunder Bay HydrologyStaff gauge used to take water levels Surface water level taken with Stevens Type F recorderBehavior of adjacent, near-surface aquifer monitored with four wells using Type F recordersWells CB-1 and CB-3 on south and northeast sides respectively, just outside of bay margin

HydrologyCB-2 located 360 m southwest and downslope of CB-1CB-4 located 270 m northeast and upslope of CB-3

ResultsWater levels dynamic and responsiveGeneral absence of peat, periodic pond drawdown and oxidation of exposed soilSurface water levels varied from 61.30 to 61.85 m NGVD largely due to rainfall.Avg. surface rate loss varied from 0.12 cm/d in Jan. to 0.76 cm/d in July.Monthly water loss and surface water temp. had a strong correlation(r = 0.93)

Strong relationship between precipitation and water level.Amount of rain necessary to offset loss rates was 62 cm/6 mon period(x-axis intercept of regression line in Fig. 4)Schalles et. al. 1998

This strong correlation btwn surface water levels and precipitation and net water-loss rates and temperature suggests a perched conditionDilute chemistry of Thunder Bay suggests subsurface hydrologic exchange must exist to maintain long-term chemical equilibrium

Schalles et. al. 1998

Thunder Bay occurs within a persistent groundwater gradientUpslope CB-4 always had higher water levels than the pond (63.0 64.1 m NGVD) and downslope CB-2 lower water levels than the pond(55.7 57.7 m NGVD)Comparisons surface groundwater levels exhibit connections shown in Fig. 5Elevated ground-water levels in winter and spring resulted from increased rain and decreased evapotranspiration.

Schalles et.al. 1998

Groundwater exchange primarily lateral as opposed to vertical due to a clay lens below the wetland Lateral exchanges may be lost as subsurface and surface levels decline below the contact zoneTotal system surface water loss from the Y-axis intercept from Fig. 4 is 80 cm net loss for a precipitation-free, 6-mon period.Thus total system loss (160 cm/yr) equilibrium precipitation (124 cm/yr) yields 36 cm/yr which may represent net surface gain from groundwater

ReferencesMitsch W. J., and Gosselink J. G., Wetlands 2nd ed., 1993, pp 67-113.Schalles J.F., and Shure D. J., Hydrology, Community Structure, and Productivity Patterns of a Dystrophic Carolina Bay Wetland. Ecological Monographs, 59(4), 1989, pp 365-385.Sharitz A. B.,1994, University of Georgia., www.uga.edu/srel/ESSite/Sharitz.htm.

A comparison of the watershed hydrology of coastal forested wetlands and the mountainous uplands in the Southern US

CASE STUDY AREAS:BRADFORD FOREST WATERSHED OF NORTHERN FLORIDACARTERET 7 WATERSHED OF SE NORTH CAROLINACOWEETA 14 WATERSHED OF WESTERN NORTH CAROLINA

WATERSHED LOCATIONS

SITE DESCRIPTIONSBRADFORD FOREST WATERSHEDREPRESENTS A MIXTURE OF ECOSYSTEMS: CYPRESS WETLANDS & SLASH PINE UPLANDSUPLANDS ARE FLAT & CLOSE IN ELEVATION TO ADJACENT WETLANDS (>1M DIFFERENCE)UPLANDS: RELATIVELY DRY DUE TO WELL DRAINED SANDY SOILSCYPRESS WETLANDS: SURFACE WATER IS PRESENT 9 MONTH OF THE YEAR, UNDERLINED BY IMPERMEABLE CLAY LAYERS 3M BELOW GROUND SURFACE

CARTERET 7 WATERSHED

ARTIFICIALLY DELINATED WITH ROADS AND PARALLEL DITCHES

LOW ELEVATION AND TOPOGRAPHY

CLASSIFIED AS POORLY DRAINED WITH HYDRIC SOILS DOMINATED BY FINE SANDY LOAM

WATERSHED 14 AT COWEETAREPRESENTS AN UPLAND WATERSHEDCLEAR CUT IN 1962 LOCATED IN SOUTHERN APPALACHIAN MOUNTAINSWHICH ARE DOMINATED NATIVE HARDWOODS

*** THESE THREE WATERSHEDS HAVE THE LONGEST CONTINUOUS RECORDS OF HYDRLOGIC RESEARCH IN THE S.E. UNITED STATES

FUNCTIONS WITHIN THE FORESTED WETLANDG.Sun and S.G. McNulty (2002)

KEY FACTORS EFFECTING HYDROLOGIC BUDGETEVAPOTRANSPIRATIONGROUNDWATER INFLOWS AND OUTFLOWSVOLUME OF WATER STORAGESURFACE INFLOWS & OUTFLOWSNET PRECIPITATIONTIDAL INFLOW & OUTFLOW

QUESTIONS ADDRESSED BY THIS STUDY1. Is actual evapotranspiration (AET) from pine flatwoods close or equal to potential forest evapotranspiration (PET) in the long-term? And, is upland forest AET is far less than PET?

2. In the long-term, what caused the hydrologic differences (streamflow/precipitation ratio) among the wetland and upland watersheds, topographical features or climate?

POTENTIAL FOREST EVAPOTRANSPIRATION (PET)

The total maximum possible water loss from a forest ecosystem through evApotranspiration.(PET) IS DETERMINED BY TEMPERATURE, DAY TIME HOURS AND SATURATED VAPOR PRESSURE.HAMONS METHOD (PET=0.1651XDAYLXRHOSATXKPEC)ACTUAL WATER LOSS THROUGH INTERCEPTION AND TRANSPIRATION WAS LESS THAN (PET) UNDER WATER STRESS CONDITIONS DURING THE GROWING SEASON.ACTUAL EVAPOTRANSPIRATION (AET)DIFFERENCE BETWEEN MEASURED AVERAGE ANNUAL PRECIPITATION AND STREAM FLOW FOR EACH WATERSHED.

DATA COLLECTION

DAILY STREAM FLOW TEMPERATURERAINFALL DATAUSED TO DETERMINE FLOW PATTERNS, PET AND ANNUAL WATER BUDGET.

FLOW PATTERNSOUTFLOW FROM BRADFORD FOREST WATERSHED (FL) AND CARTERET WATERSHED(NC) STOPPED DURING SPRING AND SUMMER MONTHS WHEN PET AND AET INCREASED.WETLAND STREAM FLOW PATTERNS WERE CONTROLLED BY GROUND WATER STORAGE THAT WAS THE NET RESULT OF RAINFALL AND AET.HIGH RAINFALL INPUT AND LOW PET AT CARTERET WATERSHED SUSTAINED BASE FLOW DURING NON RAIN EVENTS.DEEP SOILS AT COWEETA STORED LARGE VOLUMES OF WATER WHICH MAINTAINED A CONSTANT WATER RELEASE THROUGHOUT THE YEAR.OVER 75 % OF THE ANNUAL PRECEPITATION RETURNED TO THE ATMOSPHERE AS ET, WHILE STREAM FLOW DECREASED IN THE DRY SEASON AND FLOODED THE ENTIRE WATERSHED DURING THE WET SEASON.

WATER BUDGET FOR BRADFORD FORESTG.Sun and S.G. McNulty (2002)

WATER BUDGET FOR CARTERET 7 WATERSHED G.Sun and S.G. McNulty (2002)

WATER BUDGET FOR COWEETA WATERSHED 14 G.Sun and S.G. McNulty (2002)

CARTERET 7 WATERSHED G.Sun and S.G. McNulty (2002)

COWEETA WATERSHED G.Sun and S.G. McNulty (2002)

COMPARISON: LONG TERM RUNOFF & PRECIPATATIONBRADFORD WATERSHED (FL) G.Sun and S.G. McNulty (2002)

RUNOFF AND PRECIPITATION RATIOSCOWEETA (0.53/0.092)-LOWEST

CARTERET (0.30/0.079)

FLORIDA (0.13/0.079)-HIGHEST

CONTRIBUTING FACTORSANNUAL PETTOPOGRAPHYSOILSDIFFERENT TREE SPECIESCLIMATE

BRADFORD WATERSHED (FL)AET/PET RATIO (0.75)LOW AET/PET RATIO IS DUE TO HIGH PET VALUESWELL DRAINED WATER SHED (SANDY SOILS & LOW WATER HOLDING CAPACITY)SEASONAL SHIFTSSPRING & SUMMER EVAPOTRANSPIRATION DEFECITS OCCUR (PET >P)FALL & WINTER PRECIPITATION EXCEEDS PET & AET

BRADFORD WATERSHED (FL)AET/PET (CONT.)ANNUAL PET>ANNUAL PRECEPITATIONRESULTING IN EXCESS WATERPROMOTING CYPRESS WETLAND DEVELOPMENTCOMPARED TO THE OTHER SITESLOW P/PET RATIO IS RESPONSIBLE FOR A LOW AET/PET

COWEETA WATERSHED (NC)AET/PET RATIO (0.84)

DECIDUOUS FOREST USE 20% LESS WATER THAN CONIFERS DUE DUE TO LOWER CANOPY INTERCEPTION LOSSAET/PET WAS RATIO MODERATE DUE TO THE LOWER PET IN THE MOUTAINS WITH LOWER AIR TEMPERATURES.

CARTERET WATERSHED (NC)AET/PET RATIO (0.92)P>PET>AETNOT A WATER LIMITED SYSTEM MOST OF THE YEAR.POORLY DRAINED DUE TO FLAT TOPOGRAPHY.LOW HYDRAULIC CONDUCTIVITY OF FINE SANDY LOAM SOILS PROVIDING SOIL MOISTURE FOR TREE USE.

RESULTSUPLAND WATERSHED COWEETA WATERSHED HAD THE HIGHEST PRECIPITATION AND P/PET RATIO, WITH A MODERATE AET/PET RATIO. THESE FACTORS ARE RESPONSIBLE FOR A HIGHER WATER YIELD INSTEAD OF STEEP TERRAIN.WETLAND WATERSHEDS R/P RATIO FOR BRADFORD IS LESS THAN HALF THAT OF CARTERET EVEN THOUGH BRADFORD IS ON A HIGHER TOPOGRAPHIC RELIEF WITH BETTER DRAINAGE.

RESULTS(CONT.)HIGHER P/PET RATIO AT THE CARTERET SITE IS RESPONSIBLE FOR THE HIGHER FLOW RATES.THIS SUGGEST TOPOGRAPHY IS NOT FULLY RESPONSIBLE FOR THE LONG TERM HYDROLOGIC BALANCE OF THE TWO WATERSHEDS.THIS ANALSIS SUGGESTS THAT CLIMATE DICTATES WATER YIELD FROM THE THREE WATER SHEDS.

CONCLUSIONLONG-TERM ANNUAL WATER BALANCES FOR THREE WATER SHEDS IN THE SOUTHERN US WERE CONSTRUTED.THE WATERSHEDS CONSISTED OF SLASH PINE-CYPRESS WETLAND, LOBOLLY PINE PLANTATION, AND SOUTHERN HARDWOODS.DATA CONCLUDED CLIMATE IS THE MOST IMPORTANT FACTOR IN DETERMINING LONG TERM WATER BALANCE OF A FORESTED WATERSHED.TOPOGRAPY IS THE KEY FACTOR IN CONTROLLING WETLAND FORMATION, DEVELOPMENT AND FUNCTION.LONG TERM WETLAND WATERSHED AET MAY BE LESS THAN PET.

CONCLUSION (CONT.)HIGHER HYDROLOGIC RESPONSES IN UPLANDS ARE DUE TO HIGHER P/PET AND STREAMFLOW/P RATIOS.FOR WETLAND WATERSHEDS REDUCTION OF TRANSPIRATION OF TRESS MAY COMPENSATED BY AN INCREASE IN SOIL EVAPORATION.OVER 75 % OF THE ANNUAL PRECEPITATION RETURNED TO THE ATMOSPHERE AS ET, WHILE STREAM FLOW DECREASED IN THE DRY SEASON AND FLOODED THE ENTIRE WATERSHED DURING THE WET SEASON.

REFERENCESG.SUN et al.,2002 G.Sun, S.G. McNulty, D.M. Amatya, R.W. Skaggs, L.W. Swift,Jr., J.P. Shepard and H. RiekerK, A comparison of the watershed hydrology of coastal forested wetlands and the mountainous uplands in the Southern US. J. Hydrol. 263(2002), PP. 92-104. Mitsch and Goselink, 1986. W.J. Mitsch and J.G. Goselink Wetlands, Van Nostrand Reinhold Co, New York (1986)

OverviewIntroduction to hydrologic budgetWisconsin sitePollution in the watershed Wisconsin natural urban wetland budgetEverglades sitePollution in the watershedEverglades constructed wetland budgetSummary

Hydrologic BudgetHydrology is one of primary controlling factors in wetlandsI O = VClosely related to nutrient budget since inputs and outputs of nutrients are mainly through hydrologic pathways http://www.groundwater.org/GWBasics/hydro.htm

Where is Wisconsin?http://alabamamaps.ua.edu/world/usa/usa1.jpg

Wisconsin Wetland Case StudyPollution in watershedWetland typeSite descriptionMethodsResultsConclusion

http://www.co.dane.wi.us/landconservation/widanepg.htm

Pollution in WatershedPoor habitat for fish and aquatic insectsNuisance algae and weed growthOver 60% of watershed is urban and pollution problems originate from various sources

Case StudyTitle: Water budget and flow patterns in an urban wetland by Catherine R. OwenGoal of project: Quantify relationships of wetland to groundwater and surface water, particularly as are affected by human activities in watershed

Study Site92 ha urban peatland in city of Monona, Dane County, WisconsinCalled Monona Wetlands ConservancyWetland is stream-side graminoid-dominated urban peatland in S-C WIEastern border YaharaSouthern border railroad and channelized Nine Springs Creek

Vegetation in SiteWetland dominated by four vegetation associationsReed Canary Grass Meadow: Phalaris arundinadeaSedge Meadow: Carex lacustisBluejoint Grass Meadow: Calamagrostis canadensis Cattail-giant Reed Marsh: Typha latifolia

MethodsMass balance approach used to describe and quantify wetland: Change in storage = Inputs Outputs errorInputs to wetland: Precipitation, Surface Inflow, Groundwater InflowOutputs: Evapotranspiration, Surface Outflow, Groundwater Outflow12 piezometer nests and 27 gages installed in wetland, 3 nests installed in upland

MethodsWater levels monitored weekly from June 21 to Nov. 14, 1990, and from Mar. 27 to Oct. 29, 1991Change in storage calc. using water level readings and estimates of specific yield and above ground storagePrecipitation meas. using automated tipping rain bucket

Surface flow est. using rainfall-runoff method and stage gagesGroundwater flow calc. from piezo readings and hydraulic conductiv. est. using Darcys Law. Horizontal component meas. using flownetsEvapotranspiration (ET) calc. using mass balance approach based on water table hydrograph

Hydro Budget ResultsPrecipitation dominated both years, comprising 94% and 83% of inputsRemainder of input came from surface runoff from uplandsVery little groundwater flow. Wetland recharged aquifer belowAlmost all water that came in lost as ETChange in storage was variableLarge range of error in estimatesFlow patterns characterized

ConclusionPotential for filtering all pollutants from runoff since water retainedHowever, past impacts (e.g. channelization) have decreased ability of wetland to perform many of its natural functionsMost water from precipitation and surface inflow from uplandsWetland retained virtually all water from inputs would be classified as a bogMay provide critical protection of WQ in Yahara RiverNine Springs Creek

Everglades Case StudyPollution in watershedENR ProjectSite descriptionPlantsLocationMethods/ResultsConclusionhttp://www.cnn.com/2000/NATURE/11/03/everglades.reut/florida.everglades.map.jpg

Pollution in WatershedHealth of Everglades has declined due to factors such as channelization and eutrophication.Eutrophication in Lake Okeechobee and marsh conversionMercury contamination in ecosystemDeclining population of commercially, recreationally, and ecologically important fish

ENR ProjectImplementation of the Everglades ProgramMajor component is Everglades Construction ProjectHas 6 stormwater treatment areas (STA) constructed wetlands that receive runoff from Everglades Agricultural AreaFirst STA is Everglades Nutrient Removal Project

ENR ProjectTo assess how the ENR was working, a hydrologic budget had to be constructed.

Case study: Hydrologic balance for a subtropical treatment wetland constructed for nutrient removal by Mariano Guardo (SFWMD)

ENR Site DescriptionLocated in Palm Beach County, FL, adjacent to Arthur R. Marshall Loxahatchee National Wildlife Refugehttp://loxahatchee.fws.gov/Biology/research.asp

Site DescriptionConverted farmland into biological nutrient removal systemContains buffer cell and 4 treatment cells separated by leveesSite underlain by ~2 m organic soils over limestone

Site DescriptionCells 1 and 2 flow way cellsvegetated by emergent aquatic plants (primarily cattails)Cells 3 and 4 polishing cells Cell 3 mixed-species emergent macrophyte marshCell 4 submerged macrophyte/algal-based systemAlso have levees, canals, pump stations, hydraulic structures

MethodsWater budget:Positive inflow sources pumped water, precipitation, groundwater inflow, seepageNegative outflow sources pumped water, evapotranspiration, seepage, aquifer rechargeDifficult to measure some parameters

Methods/ResultsPump flows calc. from rating curvesChange in storage predicted by stage-storage curveNet seepage /groundwater had major unknown components

Methods/ResultsRainfall est. from areal daily avg. of precipitationET est. from daily measurements from lysimeters and vegetation coverageSeepage most difficult to evaluate, function of seepage canal to recirculate seepage back into project

ResultsRepresents integration of all inflow and outflow components of budgetAffected by natural factors such as topography, geology, groundwater, soils, weather, and unnatural factors from human influence HydroperiodExhibits seasonal variation of wetland 365 days w/ surf. water

ResultsAverage water inputs:86.2% from inflow pumps11.2% from rainfall 2 yr period was relatively wet compared to historic flow2.6% from emerging seepageAverage outputs:85.1% from outflow pumps8.9% from ET6.0% from seepage/groundwaterStage- and depth-duration curves developed also

ConclusionStudy considered ENR Project as a wholeNecessary to analyze each cell independently in future (each has different treatment characteristics)ENR produced excellent results in removal of phosphorus from the system

SummaryWhat is hydrologic budgetWisconsin siteEverglades siteImportance of hydrologic budgethttp://imnh.isu.edu/digitalatlas/hydr/basics/main/imgs/1comp.jpg

ReferencesDepartment of Environmental Protection. 2003. Available: http://www.dep.state.fl.us/secretary/everglades/about.htm. Digital Atlas of Idaho. 2003. http://imnh.isu.edu/digitalatlas/hydr/basics/main/imgs/1comp.jpgGroundwater Foundation. 2003. Available: http://www.groundwater.org/GWBasics/hydro.htm Guardo, M. 1999. Hydrologic balance for a subtropical treatment wetland constructed for nutrient removal. Ecological Engineering 12: 315-337.Land Conservation Department (Dane County, WI). 2003. Available: http://www.co.dane.wi.us/landconservation/programpg.htm.Mitsch, W.J. and J.G. Gosselink. 1986. Wetlands. Van Nostrand Reinhold: New York.Owen, C.R. 1995. Water budget and flow patterns in an urban wetland. Journal of Hydrology 169: 171-187.www.wi-mall.com/images/wisconsin-links-map.jpg