The use of terrestrial ecoregions as a regional-scale screen for selecting representative reference sites for water quality monitoring

A process has been developed to select watersheds that are representative of terrestrial ecoregions and that are relatively undisturbed by human activity. Using an existing land classification system at two hierarchical levels of resolution, representative subsets (ecodistricts) of large-scale ecoregions were selected, on the basis of their physiographic, biological, and climatological attributes, to represent the ecoregions. This was achieved using a frequency distribution analysis of existing attribute data and choosing the ecodistrict most closely resembling the most common set of conditions for that ecoregion. Within each ecodistrict, river basins were selected through a best-judgement evaluation of land use, coupled with an assessment of the size and location of each river basin, in order to meet the condition of minimal human impact. Preliminary assessment of water quality data collected from six watersheds selected in this way suggests that the process is effective in targeting regional scale river basins exhibiting the desired characteristics.