Abstract
Excess nitrogen (N) from agricultural runoff is a cause of pollution in aquatic ecosystems. Created free water surface (FWS) wetlands can be used as buffering systems to lower the impacts of nutrients from agricultural runoff. The purpose of this paper was to evaluate critical factors for N removal in FWS wetlands receiving high nitrate (NO3−) loads from agriculture. The study was performed in 12 experimental FWS wetlands in southern Sweden, receiving drainage water from an agricultural field area. The effects of water depth (mean depth of 0.4 m and 0.6 m, respectively) and phosphorus (P) availability (with or without additional P load) were investigated from July to October. The experiment was performed in a two-way design, with three wetlands of each combination of depth and P availability. The effects of P availability on the removal of NO3− and total N were strongly significant, with higher absolute N removal rates per wetland area (g m−2 day−1) as well as temperature-adjusted first-order area-based removal rate coefficients (Kat) in wetlands with external P addition compared to wetlands with no addition. Further, higher N removal in deep compared to shallow wetlands was indicated by statistically significant differences in Kat. The results show that low P availability may limit N removal in wetlands receiving agricultural drainage water. Furthermore, the results support that not only wetland area but also wetland volume may be important for N removal. The results have implications for the planning, location, and design of created wetlands in agricultural areas.
Highlights
The use of nitrogen (N) fertilizers in agriculture has increased dramatically during the last century and is expected to continue to increase in most future scenarios [1]
The aim of this paper was to evaluate the effects of water depth and P availability on N removal in free water surface (FWS) wetlands receiving N largely as NO3 −
There was no significant interaction between the two treatments (P addition and water depth), indicating that the effect of one treatment was not affected by the other treatment
Summary
The use of nitrogen (N) fertilizers in agriculture has increased dramatically during the last century and is expected to continue to increase in most future scenarios [1]. Agricultural runoff, which is rich in nutrients, is a source of diffuse pollution and contributes to eutrophication [2,3]. Wetlands have been created for the remediation of runoff from agriculture and are used to reduce. The application of agricultural treatment wetlands has been reported in several countries worldwide. From 1996 to 2008, over 2400 wetlands were created in Sweden with support from different national programs, with the aim of remediating runoff from agriculture and decreasing N transport to the eutrophicated Baltic Sea [5]. In the US, the ongoing restoration and creation of wetlands along the Missouri River is part of a strategy to decrease N loads to the Mississippi
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