Biodiversity Guide - The Intertwine

egional conservation strategybiodiversity guideChapter 3 Major Habitat Types of the Regionate influences include water depth, flow, temperature,substrate materials such as sand and gravel,bank conditions, and the presence or absence offloating and submerged logs and debris. Seasonalfluctuations of water level, temperature, and floware important in all of the region’s waters but havebeen significantly modified in many areas by surfaceand groundwater withdrawals, dams, dikes,and other water control structures. In rivers andsloughs, upstream flow regulation has reducedthe impact of spring freshets and winter floodsand severed or undermined connections betweenopen-water habitats and surrounding ecosystems.Other human-caused disturbances includeimpacts associated with stormwater runoff, filland channelization, toxic and nutrient pollution,erosion and sedimentation, removal of riparianvegetation, alteration of banks and shorelines,and the creation of barriers to fish and wildlifemovement. Natural processes that influence thedevelopment of streams, rivers, and open-waterhabitats include flooding, drought, accretion,siltation, and tidal influence.Historical and Current OccurrenceThe amount of open-water habitat in the greaterPortland-Vancouver region has declined by morethan 49 percent since 1806. Several lakes in theregion were drained or filled decades ago fordevelopment and agriculture, and most remainingopen-water habitat has been significantlyaltered. Dams have altered stream and river flowpatterns, reducing peak flows and moderatingseasonal fluctuations. Levees, dikes, and pumpshave disconnected streams and rivers from theirassociated floodplains and wetlands. The proliferationof roads, buildings, and other impervioussurfaces has radically transformed stream hydrology,increasing pollution and the frequency andseverity of winter scouring flows.Many streams, particularly in the urban area,have been put into underground pipes. Roadsthat crisscross drainage networks create numerousculvert barriers to fish and wildlife movement,and they alter the delivery of large woodand sediment to receiving waters downstream.Removal of riparian vegetation has resulted inhigher water temperatures and reduced inputs oflarge woody debris and organic matter—materialsthat are critical for stream health. Revetments forflood protection along shorelines have eliminatedrefugia for young fish, amphibians, and turtlesand diminished habitat values for many otherspecies. Salmon, lamprey, and sturgeon speciesare among the casualties of the degradation of theregion’s rivers, streams, and open waters.River, stream, and open-water habitats in theregion include the following:n The Columbia, Willamette, Clackamas, Tualatin,Lewis, Washougal, Sandy, and Molalla rivers,as well as many smaller tributary rivers, streamsand sloughsn Lakes and permanent large wetlands, includingSturgeon Lake and other lakes on Sauvie Island,Smith and Bybee Wetlands Natural Area, BlueLake, Fairview Lake, Vancouver Lake, Hagg Lake,Oswego Lake, and Force Laken Crystal Springs and several other permanentspring-fed streams, ponds, and wetlandsn Scappoose Bayn Numerous ponds, including natural and smallfarm ponds, stormwater ponds, impoundmentsbehind weirs and dams, and golf course waterhazardsn Sloughs, including Multnomah Channel andColumbia SloughRiver, Stream, and Open-water SpeciesThe Pacific Northwest’s salmon and steelhead arethe iconic residents of the region’s water bodies,along with sturgeon, lamprey, and various smallernative fish, mollusks, turtles, amphibians, andgarter snakes. However, a majority of the region’swildlife species spend at least part of their lives inor near rivers, streams, or open water, and purplemartins, swallows, and other birds and bats feedon insects above these habitats. Many birds, suchas gulls, cormorants, osprey, bald eagles, kingfishers,and white pelicans, feed on fish and aquaticinvertebrates in the region’s streams, rivers andopen waters.Because the greater Portland-Vancouverregion is part of the Pacific Flyway, legions ofgeese, ducks, loons, grebes, and swans winter onlocal waters, while other birds stop over as theymigrate through. Eagles migrate and winter inthe region, and more eagles are staying throughthe summer to nest. Wood ducks and mergansersalso nest in the region, using both the waters andthe snags and cavities in adjacent riparian habitat.River otters, mink, muskrats, and beavers livetheir lives in and near water bodies. Beavers actuallycreate ponds and other habitats characterizedby slow-moving water. Two species of nativeturtles, several species of frogs, freshwater mussels,and pond-breeding newts and salamandersuse quiet open waters. Other amphibians, such astorrent salamanders and tailed frogs, rely moreon the region’s clear, cold-water streams.Plants are less abundant in streams and largeopen rivers than in shallower bodies of water, butwapato, plantago, duckweed, polygonums, andother floating plants are present in quiet waters.Threats Specific to Rivers, Streams,and Open WatersHumans have profoundly influenced the region’sbodies of water. Some threats to this habitat areresidual from a more cavalier era when peopledid not understand the consequences of theiractions and land use regulations were less protectiveof aquatic resources, but many threats areongoing.Approximately 80 percent of stream milesin the lower Willamette subbasin are severelydisturbed, primarily from urban and agriculturalland uses. Streams that originate in forestlandsshow significantly less instream and riparianhabitat degradation than streams whose headwatersare not within forestland. Stream temperatureand disturbance of streamside vegetationare the most prevalent stressors, affecting 75 to90 percent of all stream miles. Other importantstream health stressors include fine sediment,streambed stability, nutrient impairment, and lowdissolved oxygen, which the Oregon Departmentof Environmental Quality estimates affect 30 to60 percent of stream miles in certain watersheds.The following actions degrade, diminish, oreliminate the region’s aquatic habitats:n Draining and filling lakes and pondsn Alteration of natural flow and water level fluctuationsthrough dam operation and stormwaterrunoffn Surface and groundwater withdrawal, whichlowers water tables and diminishes stream flowsn Channelization, hardening, and other alterationsof banks and shorelinesn Small “check-dams” and artificial farm ponds,which impede fish passage and diminish waterqualityn Erosion of banks from removal of vegetationn Dredgingn Construction of water crossings, which impedefish and wildlife movements and disrupt deliveryof sediment and large wood, which are essentialfor healthy habitat2627