Full ecoregional plan - Conservation Gateway

The classification provides an apriori hypotheses regarding how large-scale suites ofenvironmental features directly or indirectly influence aquatic biota. When watersheds of similarsize occur under similar climatic and zoogeographic conditions and share a similar set ofphysical features such as elevation zones, geology, landforms, gradients and drainage patterns,they may be reasonably expected to contain similar aquatic biodiversity patterns (Tonn 1990,Jackson and Harvey 1989, Hudson et al. 1992, Maxwell et al. 1995, Angermeier and Winston1998, Pflieger 1989, Burnett et al. 1998, Van Sickle and Hughes 2000, Oswood et al 2000, Waiteet al. 2000, Sandin and Johnson 2000, Rabeni and Doisy 2000, Marchant et al 2000, Feminella2000, Gerritsen et al 2000, Hawkins and Vinson 2000, Johnson 2000, Pan et al 2000). Thephysical landscape classification variables in this analysis were chosen because they 1) displayedlow spatial and temporal variation at the given watershed scale under consideration and 2) havebeen shown to strongly affect the form, function, and evolution of aquatic ecosystems andecological processes at the considered scales (Frisell 1986).Classification watershed scale variables included watershed size, elevation, bedrock, surficialgeology, and landform. Stream watershed area was used as a proxy for stream size. Watershedarea is correlated with local scale measures of stream width, depth, flow velocity and alsoinfluences flow rate, velocity, regime, and channel morphology. Elevation was used to representlocal climate variation which limits some aquatic species distributions, influences forest type andorganic input to rivers, stream temperature, and flow regime due to differences in snow melt andprecipitation. Bedrock and surficial geology were used due to their control of water chemistry,stability of flow, and sedimentation which influence the hydrologic character and habitat ofstreams. For example sediment texture and cohesion impacts the stability of flow as sedimentswith higher porosity (coarse grained sandy surficial sediments, acidicsedimentary/metasedimentary bedrocks, calcareous bedrocks) are likely to have more stablegroundwater dominated flows as precipitation in these landscapes is more likely to percolate intothe groundwater than to runoff overland into streams. Less porous sediments (fine grained claysurficial, acidic granitic bedrock, other crystalline bedrocks) are likely to have more flashyhydrologic regimes as surface water flows predominate unless the watersheds contain sufficientmultiple fracture/fault zones for groundwater recharge. Gradient and landform were usedbecause they influence stream morphology (confined/meandering), flow velocity, substratecomposition, and habitat types due to differences in soil type, flow velocity, moisture, nutrients,and disturbance history. For example, the morphology of valley floors differs substantiallybetween mountains and lowland areas due to contrast in the degree of landform controls onstream meandering. Likewise, lower gradient streams in New England typically have sand, siltand clay substrates while high gradient streams typically have cobble, boulder, and rocksubstrates (Argent et al 2002).The classification used WWF Fish Zoogeographic Ecoregions and Ecological Drainage Units toplace the physical watershed and reach classification within the context of its regionalgeoclimate and zoogeographic setting. Large-scale geologic and climate factors constrain thedevelopment of both physical habitat and biological structure of smaller spatial scales throughtheir large-scale controls on temperature, chemistry, hydrology, stream morphology, nutrient andsediment delivery, and on patterns of disturbance (flood, fires, hurricanes, major geologic events)that operate over this scale (Frisell 1986, Poff and Allan 1995, Hawkins et al. 2000). Geoclimatesettings also influence zoogeographic distributions of aquatic biota as the current and historicalpattern of linked aquatic networks has influenced isolation, dispersion, and speciation. Analysisof the physical characteristics and fish and mussel distributions between Ecological DrainageREVISED 6/2003AQUA-RESULTS-23