Hydrologic and Water Quality Assessment of Constructed Wetlands on a Coastal Plains Golf Course

Abstract

Golf courses have come under considerable scrutiny in recent years due to the large amount of chemicals and nutrients associated with their intensive management. Drainage water from the Chowan Golf and Country club in eastern North Carolina drained directly into the nutrient sensitive Albemarle Sound. Stormwater wetlands were constructed on the golf course as part of a vegetative treatment network to reduce nutrients in stormwater runoff, reduce ponding on the course, and provide additional water storage for irrigation. The wetlands were monitored for three years to evaluate the performance of the Best Management Practices (BMPs) established. Precipitation and weather data were used with stage-discharge and outflow to compute water balances for each wetland in the vegetative treatment network. Throughout the three year study period, wetlands temporarily stored between 5% and 85% of the water which entered the wetlands. During a period of drought, all wetlands stored a larger percentage of influent water than during normal rainfall periods. Peak flow rates were reduced by 7% to 92% and time to peak was delayed by 10 to 46 hours. Residence times were evaluated for wetlands with small (1:40 (2.5%)), medium (1:23 (4.5%)), and large (1:11 (9.0%)) wetland:watershed area ratios. On average, residence times were more than five days 6% of the time in the wetland with the small wetland:watershed area ratio, 45% of the time in the wetland with the medium wetland:watershed area ratio, and 66% of the time in the wetland with the large wetland:watershed area ratio. Five day residence times are generally considered the minimum residence time for effective settling of sediment, and treatment of nitrogen and phosphorus. This study demonstrates that stormwater wetlands can be utilized to reduce outflow volume and peak discharge rates in areas where drainage discharge is a concern of receiving waters. Influent and effluent concentration data was collected and combined with water balances for each wetland over a three year period. Influent concentrations from runoff had an average of 3.65 mg/L Total Kjeldahl Nitrogen (TKN), 0.15 mg/L nitrate-nitrogen (NO3-N), 0.30 mg/L ammonia-nitrogen (NH4-N) 3.82 mg/L total nitrogen (TN), 1.61 mg/L ortho-phosphate (PO4-P), and 2.06 mg/L total phosphorus (TP). Effluent water had mean concentrations of 2.06 mg/L TKN, 0.06 mg/L NO3-N, 0.14 mg/L NH4-N, 2.07 mg/L TN, 0.60 mg/L PO4-P, and 1.62 mg/L TP. Runoff water carried a mean of 12.80 kg/ha/yr TKN, 0.57 kg/ha/yr NO3-N, 1.30 kg/ha/yr NH4-N, 13.32 kg/ha/yr TN, 5.62 kg/ha/yr PO4-P, and 7.17 kg/ha/yr TP. The wetlands removed an average of 29% TKN, 67% NH4-N, 51% TN, 70% PO4-P, and 64% TP on a mass basis. Removal efficiencies for wetlands with small (1:40), medium (1:23), and large (1:11) wetland:watershed areas were compared in detail. At loading rates above 1.0 kg/ha/d TN, an increase wetland:watershed area ratio was shown to increase removal rate. An increase in wetland:watershed area ratio also increased TP removal rate. On average, the wetland with the small ratio reduced TN and TP loads by 45%. The wetland with the medium ratio reduced TN loads by 49% and TP loads by 83%. The wetland with the large ratio reduced TN load 84% and TP loads by 88%.