Using GIS and Land Use Data to Select Candidate Reference Sites for Stream Bioassessment

GIS was used to select candidate reference sites in Georgia to characterize the reference condition by sub-ecoregion for a rapid bioassessment of streams statewide. Instead of relying on best professional judgment or previous knowledge of a limited number of sites, we performed an objective evaluation of cumulative impact on all catchments using land use data sets. These included road and impoundment data from DLGs and Multi-Resolution Land use Consortium data. Land use impairment was measured as percentages of forest, urban, pasture, row crops, and barren area for both the entire catchment and for 10, 40, and 130-m riparian buffers, road and impoundment density and stream/road crossings. Sites were then ranked by land use impairment, with the least impaired selected as candidate reference sites. The larger buffers, impoundment density, and stream/road crossing criteria were the least able to predict minimal impact, and were weighted less. Water chemistry, benthic macroinvertebrates, and physical habitat results demonstrated that 74% of the sites selected using this method met reference site criteria of other states. These data also demonstrated that these sites were equal to, or better than, sites identified by using best professional judgment. Possible reasons for the misidentification of sites are changes in land use since the data collection and the lack of a direct correlation between moderate human land use and stream habitat impairment