EMAP-Surface Waters: a multiassemblage, probability survey of ecological integrity in the USA

Data analyzed at national, multistate or state scales often reveal more ser ious deterioration of various biological assemblages than that suspected fr om site specific studies simply because the impacts are observed regionally rather than locally. Unfortunately many regional assessments are based on data collected with differing sampling designs and methods, making their re presentativeness, accuracy and precision questionable. In 1989, the United States Environmental Protection Agency (USEPA) began EMAP-Surface Waters (E MAP-SW), a program for developing methods to monitor and assess status and trends in the nation's lakes and rivers in a statistically and ecologically rigorous manner. EMAP-SW has now conducted regional multistate pilots in s treams and rivers throughout the U.S.A. in collaboration with State agencie s, universities and EPA regional offices. We discuss EMAP's conceptual desi gn, which focuses on biological integrity through use of multiple biologica l assemblages and includes physical and chemical habitat and landscape char acteristics. When coupled with appropriate biological indicators, a probabi lity-based design enabled us to provide accurate, precise and unbiased asse ssments of biological conditions, along with quantitative estimates of samp ling uncertainty. Regional EMAP-SW surveys indicated the importance of asse ssing multiple biological assemblages because each assemblage was different ially sensitive to different stressors and at different spatial scales. Syn thesizing multiple metrics from multiple assemblages allowed us to detect t he effects of multiple anthropogenic disturbances. We also illustrate the v alue of using historical reconstruction and paleolimnological data for dete rmining reference conditions where disturbance is extensive. We conclude th at an EMAP approach to sampling design and indicators (recognizing natural ecoregional differences) has distinct advantages for monitoring and assessm ents that may be applicable to European Communities seeking to assess the e cological integrity of waters.