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

Data analyzed at national, multistate or state scales often reveal more serious deterioration of various biological assemblages than that suspected from 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 representativeness, accuracy and precision questionable. In 1989, the United States Environmental Protection Agency (USEPA) began EMAP-Surface Waters (EMAP-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 streams and rivers throughout the U.S.A. in collaboration with State agencies, universities and EPA regional offices. We discuss EMAP's conceptual design, which focuses on biological integrity through use of multiple biological assemblages and includes physical and chemical habitat and landscape characteristics. When coupled with appropriate biological indicators, a probability-based design enabled us to provide accurate, precise and unbiased assessments of biological conditions, along with quantitative estimates of sampling uncertainty. Regional EMAP-SW surveys indicated the importance of assessing multiple biological assemblages because each assemblage was differentially sensitive to different stressors and at different spatial scales. Synthesizing multiple metrics from multiple assemblages allowed us to detect the effects of multiple anthropogenic disturbances. We also illustrate the value of using historical reconstruction and paleolimnological data for determining reference conditions where disturbance is extensive. We conclude that an EMAP approach to sampling design and indicators (recognizing natural ecoregional differences) has distinct advantages for monitoring and assessments that may be applicable to European Communities seeking to assess the ecological integrity of waters.