Constructed Wetlands vs. Retention Pond BMPs: Mesocosm Studies for Improved Pollutant Management in Urban Stormwater Treatment

Abstract

Increased urbanization has increased the amount of impervious area resulting in larger quantities of stormwater runoff. This runoff can contribute significant amounts of debris and pollutants to receiving waters. Urban watershed managers often incorporate best management practices (BMPs) to treat these pollutants. Although many studies have evaluated the capabilities of two popular treatment methods — retention ponds and constructed wetlands — to reduce pollutant concentration and load in stormwater, few have focused on the internal mechanisms controlling the efficacy of these stormwater BMPs. Experimental mesocosms were constructed in Edison, NJ to simulate retention pond and wetland BMPs and to evaluate, describe, and model key processes that occur within these treatment systems. Understanding the hydrologic character of the mesocosms, and BMPs in general, is necessary to model the performance of these systems. Preliminary data suggest constructed wetland mesocosms outperformed retention pond mesocosms for removal of total suspended solids and total Kjeldahl nitrogen. However, retention pond mesocosms were the most effective at treating dissolved nitrates. Complete data that includes hydraulic modeling, multiple nutrient parameters, microbial indicators and metals will provide more information on the mechanisms controlling BMP effectiveness. A primary goal is developing models for constructed wetland and retention pond BMPs that will allow for better stormwater BMP design leading to overall improvements in receiving water quality to meet state and federal water quality standards.