RIVER ECOLOGY in the - Fraser Cascade Mountain School River Ecology--Background... · Page 3 Skagit River Ecology Riparian Zones A riparian zone is defined as the strip of vegetation

Aquatic Food WebsRiparian ZonesRiver Habitat

Aquatic AnimalsWatersheds

in theUpper Skagit

Watershed

RIVERECOLOGY

RIVERECOLOGY

Acknowledgements

This booklet is a joint project of Fraser Cascade-Mountain School and

Hope Mountain Centre, Hope BC

The project is funded through a grant from the Skagit Environmental Endowment Commission (SEEC)

January, 2008

For copies, contact Fraser-Cascade Mountain School at 604-869-2411

Table of Contents

THE SKAGIT RIVER ....................................................................1

AQUATIC FOOD WEBS..................................................................2

Primary producers, herbivores, carnivores..................................................................2

RIPARIAN ZONES .......................................................................3

Riparian Forests ..........................................................................................................3

Riparian Animals .........................................................................................................3

RIVER HABITAT .........................................................................4

In-Stream Boulders .....................................................................................................4

Slimy Rocks.................................................................................................................4

Clean Gravel ...............................................................................................................4

Overhanging Banks.....................................................................................................4

Large Organic Debris ..................................................................................................5

Gravel Bar Formation ..................................................................................................5

Log Jams ....................................................................................................................5

Side Channels .............................................................................................................5

APPENDIX ................................................................................6

GLOSSARY OF TERMS ..................................................................6

Skagit River EcologyPage 1

The Skagit River

The Skagit River begins as little more than a stream near Allison Pass in Manning Provincial Park. From its origin, the Skagit flows northwest until, at the Skagit Bluffs, it meets the Sumallo River and turns southwest into a narrow V-shaped valley. About 10 kilometres later, it veers to the southeast and spills into a broad, U-shaped valley averaging about 2 km in width. About 16 km later it empties into Ross Lake, a reservoir created by the Ross Dam.

Along its course, the Skagit is fed by numerous small streams from the bordering mountains. Like all BC rivers, the Skagit has an enormous seasonal variation in flow. During the peak of June runoff, the rate may exceed 300 cubic metres per second. In September the flow may be 1/100 of this rate.

The Skagit runs along bedrock for it upper portion, and is therefore tightly constrained. But in the wider valley below 26-Mile Bridge, the river flows over glacial till and has room to migrate laterally across the broad valley floor, forming a classic “meandering” river pattern. Wide, meandering river valleys are relatively rare in Southwestern British Columbia, where most valleys are typically V-shaped and granitic. In the lower valley, log jams, beaver dams, and gravel bars have created numerous side channels, ponds, and ox-bow lakes. This relatively calm water supports additional aquatic communities not found in fast-flowing rivers.

In other ways, the Skagit is a prototypic British Columbian river: fast-flowing, cold, highly oxygenated, and productive for aquatic insects, fish, and the birds that feed on them.

The only lake of any size is artificially-created Ross Lake. At full pool, the reservoir is 120 metres deep and 35 km long, however, because of winter draw downs to supply power, the lake may shrink to just 15 km in length, and a few metres in depth.

The Skagit River is renowned for its fishing opportunities. Fishers come from all over to test their skills against

the Dolly Varden, Bull Trout and Rainbow Trout found in the river and its tributaries.

The photo at right shows the wide, meandering river as it appears in the lower valley, between

26-Mile Bridge and Ross Lake Reservoir.

Fraser-Cascade Mountain SchoolHope Mountain Centre


Aquatic Food Webs

Rivers and wetlands are some of the most productive ecosystems in the world, due to the abundance of life-sustaining water As with terrestrial ecosystems, aquatic food webs are supported by a foundation of primary producers — plants that capture solar energy and convert it into chemical forms that are consumed by animals.

Primary Producers

Herbivores

Carnivores/Omnivores

Top Carnivores

Includes microscopic Zooplankton, insects, and large mammals.

Largely microscopic algae and diatoms, but also larger vascular plants.

Food Pyramids:Notice that the number of organisms near the top of the pyramid is less than thebottom. This is due to the 90% Loss rulewhich states that at each food level(called a “trophiclevel”), there is anenergy loss of 90%.The energy is lostas heat during ananimal’s metabolicprocesses. Hence, only 10% of the energyconsumed at one levelis passed up to the next level above.



Riparian Zones

A riparian zone is defined as the strip of vegetation growing on either side of a stream or lake, influenced by the abundance of water. This zone is extremely productive for plants and attracts a great diversity of animals. Riparian vegetation also plays a key role in stabilizing streams and supporting aquatic organisms.

Riparian Forests

Riparian zones differ dramatically from thedrier forest around them. BC forests are typically dominated by a climax community of evergreen trees, due to their drought resistance and longer growing season. But in riparian zones, deciduous trees andshrubs are the dominant plants.

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Big leaf maple, black cottonwood, alder, red osier dogwood, willow — these plants dominate because they are pioneers. A pioneer plantis sun-loving, fast-growing, and adept at establishing itself after a disturbance. riparian zones are routinely disturbed by flood events that carry debris down river andscour the vegetation and soil on either side.Riparian pioneers recover quickly from these events, and trees such as alder have anitrogen-fixing capacity in their roots that allows them to overcome poor, sandy soil.

Riparian Animals

Riparian zones contain the greatest diversity and numberof animals in a typical BC mountain valley. This is due towealth of habitat — water, food, and shelter — providedby the river and its riparianvegetation. Many animalslive here, or use river corridorsas their preferred route of travel.

Riparian vegetation is very productive, thanks to thepresence of water close to the soil surface near lakesand rivers.

Riparian forests are dominated by fast-growing, sun-loving deciduous trees.

Osprey build their nests on tree snags inriparian zones, to be close to their

main food source — fish.

Wildlife as diverse as deer, insects, bears, and bats are attracted to riparian zones for the food, shelter and water they provide.


River Habitat

Rivers and their adjacent banks provide avariety of physical structures that are usedby plants and wildlife.

In-Stream Boulders

Fish use the downstream eddies behindlarge boulders to rest and feed. They are soimportant, that fish aggressively protect theiraccess to preferred rocks in a river. From the vantage point of a big boulder, a fishcan conserve energy while waiting for the“conveyer belt of bugs” to deliver food.

Slimy Rocks

Clean Gravel

Overhanging Banks

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Gravel and boulders on the river bottom area substrate on which algae can grow. Aquatic insect herbivores such as mayflies will graze on the algae, and inturn, those insects are eaten by fish, water shrews, and harlequin ducks. There is also a community of aquatic insect carnivores who prey upon the grazers.

The eggs of trout and salmon need clean gravel, washed over by clean, well-oxygenated water to incubate successfully. Fine dirt and silt will smotherthe eggs, depriving them of oxygen. Suddenfloods and debris flows will scour the riverbottom, killing eggs directly or exposing them to predators. The other extreme — drought— will dry the gravel beds and expose theeggs to dehydration.

The earthen banks that sometimes overhanga river are important in several ways. Thebanks offer shade and visual cover to fish, which reduces stress on those animals. Overhanging banks are also used by river otters and king fishers to dig underground burrows. A king fisher’s hole will often be excavated several feet into the ground — an amazing feat for a medium-sized bird.


Even in ideal conditions,over 90% of fish eggsare lost to floods, droughts, and predators.

Gravel and boulders onthe river bottom arehome to algae and theinsects that grazeon algae (mayfly adultat right).

River otter



Large Organic Debris

Gravel Bar Formation

Log Jams

Side Channels

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Wind, floods, and old age areconstantly recruiting treesto a river system, and it isnow understood what an important role they play inthe structure of rivers andstreams.

When a large tree travelsdownriver, it may eventually become anchored in theriver bank. When thisoccurs, the river currentis immediately changed.Gravel and sand begin to accumulate on the downstream side of the log, promoting the formation of a new gravel bar. Over time, gravel bar formation will change the force and direction of the river,sending it across the valley in new directions. In this way, large trees play a key rolein the creation of side channels, ox-bow lakes, and the general ‘braiding’ seen in rivers.

Other fallen trees become caught up in log jams. Log jams help to moderate water velocities during high water events, and tend to force water laterally during those events, thus contributing to side channel formation and other changes in river direction. In calmer flows, log jams provide excellent shade and visual cover for fish.

Side channels are critical to the health of river wildlife. They provide calmer water during peak flows, giving fish a safe place to shelter. As well, they give animals such as beaver the calmer water they need for food gathering and lodge construction.

A new tree is recruited to the river system. The branches and root wad onthis cedar will help to anchor the tree in a new location downriver. Large trees such as this can influence the structure of a river for many years.

Students investigate river habitat at Strawberry Bar Day-Use Area in Skagit Valley Provincial Park.The Skagit River provides an exciting outdoor classroom to learn about the value of healthy rivers.



APPENDIX

Glossary of Termso

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WatershedA natural drainage basin comprised of streams and lakes that feed a common river system.

EcosystemA community of organisms and the environment in which they live. This includes the interactions between organisms, and between organisms and their environment. Includes all living and non-living components.

EcologyThe scientific study of ecosystems, with special focus on the interactions and relationships between living and non-living components of the ecosystem. Term “Ecology” derives from the Greek word “Oikos”, meaning “house” or “place to live”.

OrganismAny living thing. All organisms fall within one of FIVE KINGDOMS OF LIFE — Animals, Plants, Fungi, Protista, and Monera. Protista and Monera include largely simple, single-celled organisms such as algae and bacteria.

SpeciesThe most detailed or “specific” term used in Taxonomy — the naming and categorizing of organisms. Organisms of a particular species share physical characteristics and a genetic makeup that is distinct from organisms of another species. Typically (but not always), an organism can only reproduce successfully with others of its own species. “Subspecies” are variations within a species, usually geographically separate and physically different, but still capable of reproducing with the original species.

BiodiversityA term used to describe the species richness of a region or ecosystem.

HabitatAn organism's surroundings, including four major components required for survival;Food, water, shelter, and space. Habitat changes through time, affecting the population of many different organisms.

AquaticA term referring to any water-based organism or ecosystem.

TerrestrialA term referring to any land-based organism or ecosystem.

Evergreen — plants that keep their needles or leaves alive all year long.

Deciduous — plants that drop their needles/leaves during fall and winter.



Riparian ZoneThe strip of vegetation on either side of a stream or lake, influenced by the abundance of water. This zone is extremely productive for plants and attracts a great diversity of animals. Riparian vegetation is also important in stabilizing streams and supporting aquatic organisms.

HerbivoreAny animal that eats only plants in its diet (Example: Beaver, Deer, Aphid).

CarnivoreAny animal that eats only animals in its diet (Example: Cougar, Salamander, Owl, Dragonfly).

OmnivoreAny animal that eats both plants and animals in its diet (Example: Bear, Gray Jay, Human).

ExtinctionThe permanent loss of a species, with no living examples left on earth. May be caused by habitat loss, climate change, predation, disease, or competition from other species.

ExterpationA “local extinction”, when a species disappears from a geographical area. For example, Grizzly Bears have been exterpated from the Fraser Valley, but they are still found in BC.

Endangered SpeciesA species that has been designated by the Provincial or Federal Government as being dangerously close to extinction. For example, there are less than 100 Spotted Owls left in BC, and their numbers continue to drop. A “recovery plan” is usually prepared by government biologists, to try and reverse the trend. Historically, several major species such as Beavers, Trumpeter Swans, and Peregrine Falcons have been saved from extinction by urgent conservation efforts enacted by governments and citizens.

Threatened SpeciesA species that is one step away from the “endangered” list due to declining populations. Both Endangered and Threatened species are often referred to as “Red Listed Species”.

Species of Special ConcernA species designated by the Provincial Government as requiring special management to prevent decline toward “endangered” and “threatened” status. Often referred to as “Blue Listed Species”.

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Documents

RIVER ECOLOGY in the - Fraser Cascade Mountain School River Ecology--Background... · Page 3 Skagit River Ecology Riparian Zones A riparian zone is defined as the strip of vegetation