Nitrogen and Phosphorus Gradients from a Working Farm through Wetlands to Streams in the Georgia Piedmont, USA

We quantified nutrient concentrations and water quality parameters in soils and water from a working farm (in operation for over 100 years), through contrasting agricultural wetlands, to their receiving waters. Contrasting wetlands were a forested alluvial swamp and a ditched wetland swale. Our objective was to determine if nutrients diminished in concentration or changed in form as water moved through wetlands below the farm. Soils were collected from around the farm and receiving wetlands and were analyzed for nitrate, ammonium, and phosphorus. Water samples, collected from shallow piezometers and surface waters were analyzed for nitrate + nitrite, and total phosphorus. Nitrate in groundwater and surface water in the alluvial swamp were much lower than concentrations measured in flows from farmlands. Nitrogen in upland water was dominated by nitrate, but ammonium dominated in the swamp. Phosphorus was low in wetland soils and also diminished through the swamp. Despite receiving agricultural run-off for many decades, the natural alluvial swamp still provided an effective environment for water quality mitigation of nitrate and phosphorus. The ditched wetland swale did not significantly reduce nitrate but appeared to provide some phosphorus mitigation. Agricultural wetland conservation is an especially effective, low cost tool for water quality management.