PREWET Version 2.3

A screening-level, analytical model was developed that can be rapidly applied with minimal input data for estimating the amount of water quality improvement provided by wetlands. Given basic characteristics about the wetland, pollutant removal efficiency (RE) can be computed for total suspended solids, total coliform bacteria, biochemical oxygen demand, total nitrogen, total phosphorus, and contaminants (e.g., organic chemicals and trace metals). The RE depends on the wetland detention time and the removal rate, K (day-1), for the constituent. The removal rates depend on a number of processes, such as microbial metabolism, adsorption, volatilization, denitrification, settling, etc., and ambient conditions, such as water temperature. The model was focused on the dominant long-term removal mechanisms, making use of literature values or mathematical formulations for those mechanisms when possible. A report documents the analytical model formulations for predicting pollutant RE provided by wetlands. These formulations have been programmed into an interactive, user-friendly, PC-based computer program, which is also described in the report. Predicted RE's for total suspended solids, total nitrogen, and total phosphorus are compared to observed RE's at the Cache River Wetland, Arkansas.