Nutrient Removal in a Constructed Wetland, and Impact on Water Quality in a Downstream Pond

Abstract

Research was conducted on Dick's Pond in Columbiana County, OH. The pond has been affected by high concentrations of nutrients entering the pond, causing heavy growth of algae and duckweed. A constructed wetland was built to remove nutrients from the pond inflow in order to make the pond less productive and more aesthetically appealing. A preliminary monitoring program was conducted to measure the water quality and trophic condition of the pond before wetland construction. Post-construction monitoring was performed to evaluate changes in the pond's water quality after wetland construction and nutrient removal at several points within the wetland. Data were analyzed using statistics, the Student's t-test, and a mathematical model of phosphorus removal in the wetland. Nutrient and chlorophyll a measurements indicate that the pond is highly eutrophic. Concentrations were highly variable, depending on season and runoff from the watershed. The mean total and soluble phosphorus concentrations after wetland construction were well below the levels observed before construction in the pond's water column. The Student's t-test indicated a high probability that the decrease in phosphorus was due to real changes in the system. A settling pond and wetland cell #1 appear to be removing phosphorus, but not nitrate, from the inflow, while data on the performance of wetland cell #2 are inconclusive. The calculated removal rate constant for phosphorus in wetland cell #1 was much greater than values reported for studies on natural wetlands.