EVALUATION OF US EPA ENVIRONMENTAL MONITORING AND ASSESSMENT PROGRAMS(EMAP)-WETLANDS SAMPLING DESIGN AND CLASSIFICATION

The United States Environmental Protection Agency's Environmental Moni toring and Assessment Program (EMAP) will monitor the nation's resourc es by evaluating the status and trends of selected indicators of condi tion using a probability-based sampling design. The EMAP-Wetlands prog ram will monitor the condition of the nation's wetlands. The EMAP clas sification system is an aggregation of the many subclasses of the US F ish and Wildlife Service's National Wetlands Inventory (NWI) classific ation system. This aggregation results in fewer wetland classes with m ore wetlands per class than the NWI system. Aggregation of the NWI cla ssification was based primarily on dominant vegetation cover, flooding regimes, dominant water source, and adjacency to rivers and lakes. We evaluated the EMAP classification system and sampling design using NW I digital wetlands data for portions of Illinois, Washington, North Da kota, and South Dakota. Relative numbers of wetlands, total areas, ave rage areas, and common versus rare classes were compared between the E MAP and NWI classification systems. As expected, the EMAP classificati on provided fewer wetland polygons, each with larger areas, without al tering total wetland area. Summary statistics comparing sample estimat es to true population parameters (represented by the NWI data) demonst rated the effectiveness of the EMAP sampling design with the exception of rare EMAP classes in the selected regions. Although simple random sampling is inadequate for both targe and small wetlands, the EMAP sam pling design is readily adapted to provide better estimates for these categories. Aggregating the NWI classification to the EMAP classificat ion provides fewer wetland classes, with more wetlands per class, for EMAP's annual reports and statistical summaries.