Freshwater Ecological Drainage Units

Ecological Drainage Units (EDUs) group together large watersheds that share a common zoogeographic history, physiographic and climatic characteristics, and therefore are likely to have a distinct set of freshwater assemblages and habitats. EDUs are hypothesized to account for the variability within a large freshwater ecoregion (e.g. North Atlantic Drainages) due to major drainage basin boundaries and physiography. EDUs were qualitatively defined by the The Nature Conservancy (TNC) using primarily fish zoogeographic ecoregions and subregions, terrestrial ecoregions and subregions and subsections, and major drainage divisions.

EDUs are an important regional stratification unit used in TNC Aquatic Ecoregional Planning. They are used within a freshwater ecoregion to ensure that conservation elements (species as well as coarse filter Aquatic Ecological Systems or community units) are represented across major regional-scale environmental gradients. This type of regional stratification is critical in conservation planning, the hypothesis being that genetic and ecological variability occurs within species, communities and ecosystems across their spatial and environmental ranges. Conservation planning can account for these differences in the spatial organization of ecological communities by using multiple hierarchical levels of classification stratifications nested within a freshwater ecoregion.

For more information on The Nature Conservancy's The Northern Appalachian Ecoregional Plan Aquatic Assessment, please see http://www.conservationgateway.org