Abstract
We compared the nitrate removal efficiency of two constructed wetlands receiving ambient river water to one constructed municipal wastewater treatment wetland over the same 2-year period in central Ohio, USA. The wastewater wetland represents a high-nutrient system, with an average nitrate plus nitrite load of 12.3 kg N ha
-1day
−1 and an average nitrate and nitrite inflow concentration of 12.5 mg N l
−1. The riverine wetland loadings and concentrations were approximately 60% lower (4.6–4.7 kg N ha
−1day
−1 and 4.6 mg N l
−1). Percent nitrate removal by mass ranged from 29% in the wastewater wetland to 37–40% in the riverine wetlands, although differences in retention varied widely by season and were not statistically significant among the wetlands. Retention efficiency was considerably lower in all three wetlands during floods; nitrate outflow was as much as 400% greater than inflow during some flood events. We developed a simple Vollenweider-type model of nitrate retention based on seasonal temperature, hydraulic loading, and nitrate loading. The model is general enough to be useful in describing nitrate retention in both high and low-loaded wetlands and was calibrated and validated with extensive field data. The model was used to predict wetland nitrate removal efficiency as the hydrologic and nutrient conditions change. The ability to make such predictions could be valuable in the design, construction, and management of wetlands for nutrient removal.