U.S. Wetlands Outside of CEAP Wetlands Assessment Regions

Constructed wetlands are gaining increased attention for treatment of nonpoint sources of water pollution. Although constructed wetlands have been utilized for wastewater treatment in warm climates, their performance in cold climates has been questioned. A surface-flow wetland, designed to treat 2.65 m super(3) d super(-1) of milkhouse wastewater, was constructed on the University of Connecticut's Storrs campus in 1994. The purpose of the project was to determine the efficiency of the system in reducing nitrogen, phosphorus, five-day biochemical oxygen demand (BOD sub(5)), total suspended solids (TSS), and fecal coliform bacteria (FC). The wetland was designed to process an estimated BOD sub(5) loading rate of 7.3 g m super(-2) d super(-1), which was less than half of the average actual loading rate. The overall percentage of mass retention was 94, 85, 68, 60 and 53% for TSS, BOD sub(5), total phosphorus, nitratenitrite and total Kjeldahl-nitrogen, respectively. Although the wetland became a net source of ammonia nitrogen (NH sub(3)-N) following plant die back in fall 1994, NH sub(3)-N outflow concentrations have gradually declined over time. Wetlands in Agricultural Landscapes 370 Mass retention was significantly greater (P < 0.05) during the summer than during the winter for all variables except FC. Denitrification rates measured using the acetylene block method have shown denitrification to be a minor removal mechanism (<1%) for nitrogen in this wetland. The mass balance indicated that settling and increased storage was the largest removal mechanism. The treatment of wastewater in this wetland did not meet design outflow concentration criteria, most likely due to BOD sub(5) overloading. © CSA