Effectiveness of Man-Made Wetland Systems in Filtering Contaminants from Urban Runoff in Milledgeville, Georgia.

Abstract

A wetland system made up of linked basins was investigated to determine its role in local flood control and contaminant filtration. The study focused on a wetland basin that is dominated by the Celtis laevigata plant and is underlain by clay, with a small sandy layer approximately 1 m below surface. Field and laboratory data were collected to understand the transport and filtration of phosphate, iron, and nitrate. Field results showed the wetland to effectively reduce iron and phosphates from runoff via groundwater flow. These results also showed an increase in the phosphate concentration of surface water while within the basin, resulting from agitation of wetland sediments. Laboratory column experiments showed more than 90% reduction in phosphorus and iron while nitrate concentrations increased above the input concentration. Phosphate and iron were high in wetland water immediately after a rain event. Nitrate concentrations increased as the water filtered through the sediments due to desorption of previously adsorbed nitrates. This wetland could potentially act as a temporal hot spot and rain events as hot moments for these substances. Therefore, the best flood control measure for this site would be to increase residence time in the wetland. This would help to better manage/control the concentration of phosphate, iron and nitrate pollution in surface waters.