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Cluster Analysis of Great Basin Ecoregions Using REMAP Stream Data

Robert K. Hall 1, James Omernik 2, Allan Woods 3, Sandy Bryce 4, and Daniel Heggem 5

1 USEPA Region IX, WTR2, 75 Hawthorne St., San Francisco, CA 94105
2 USGS, c/o USEPA, 200 SW 35th St., Corvallis, OR 97333
3 Department of Geosciences, Oregon State University, Corvallis, OR 97333
4 Dynamac Co., 200 SW 35th St., Corvallis, OR 97333
5 USEPA ORD Environmental Science Division, Landscape Ecology Branch, Reno, NV 89557

Ecological regions (ecoregions) are defined as areas of relative homogeneity in ecosystem type, quality and quantity of environmental resources. Ecoregions are identified by analyzing biotic and abiotic geographic patterns, which are natural and human related. Parameters used in classifying these spatial patterns are climate, physiography, geology, soil, vegetation and land use (i.e. human influences). Human influences will accelerate changes in the ecosystem character. Over time ecoregions will develop patterns characteristic of human disturbance and alterations. The objective of this study is to test the viability of ecoregions using environmental data from the U.S. EPA Region IX Regional Environmental Monitoring and Assessment Program (R-EMAP) project in the Humboldt Basin, Nevada, to define areas impacted by human activity. Group averaging cluster analysis of environmental data indicates increasing nutrients and metal concentrations towards the basins as a result of upstream land use (extensive grazing, agricultural pressure, mining). Phosphorus, arsenic and sulfate concentrations are indicative of the general geology, and the spatial distribution of land cover and land use (mining and agriculture) patterns. Variability, of water and sediment chemistry and benthic invertebrate community, within an ecoregion is associated with land use characteristics.

Keywords: Ecoregion, nutrients, arsenic, sulfate, benthic invertebrates, water chemistry, sediment chemistry, land use

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