Effects of Water Depth and Phosphorus Availability on Nitrogen Removal in Agricultural Wetlands

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 (NO 3 − ) 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 NO 3 − 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 (K at ) 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 K at . 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.

Performance of a full scale constructed wetland as ecological practice for agricultural drainage water treatment in Northern Italy

“…Nevertheless, the agricultural drainage water can be a source of diffuse pollution in aquatic ecosystems due to high concentrations of nitrate, certain salts, phosphorus, organic nitrogen, pesticides and sediments (Woltemade, 2000;Haverstock et al 2017), as confirmed by the authors from different parts of the world (Tanner and Kadlec, 2013;Darwiche-Criado et al 2017;Mendes et al 2018a;Song et al 2019). Particularly, P enrichment in runoff leads to eutrophication harmful to plants growth (Johannesson et al 2017;Lavrnić et al 2018), and it can even result in toxic algae blooms and loss of biodiversity (Reinhardt et al 2005).…”

“…SFCW systems are designed using parameters like water depth, size, substrate, plant, etc., and implemented under various requirements (e.g. flow rate, feeding mode) (Headley et al 2013;Morató et al 2014;Herrera-Melián et al 2018;Song et al 2019). However, factors like seasonal and annual variation, the aging of CW systems or other internal/external conditions have a possibility to negatively affect the treatment performance of CWs, particularly over the longer time periods.…”

“…It was reported that SFCWs can be an inexpensive and efficient nature-based solution for the reduction of non-point source pollution, especially for nitrogen and phosphorus (Tolomio et al 2019, Pugliese et al 2020, and they were used for that purpose in different countries (Song et al 2019). Nitrogen removal/retention in SFCWs mainly depends on the biological and physico-chemical mechanisms (e.g.…”

“…Nitrogen removal/retention in SFCWs mainly depends on the biological and physico-chemical mechanisms (e.g. nitrification/denitrification, plant uptake, biomass assimilation and volatilization) (Billy et al 2013;Song et al 2019), while the mechanisms for phosphorus removal include soil accretion, adsorption, microbial/plant uptake and precipitation (Vymazal, 2007). On the other hand, scientific research on the effect that CWs can have on agricultural pollution abatement is still limited, especially the one considering seasonal and long-term hydro-meteorological variations (Ulén et al 2019).…”

“…On the other hand, scientific research on the effect that CWs can have on agricultural pollution abatement is still limited, especially the one considering seasonal and long-term hydro-meteorological variations (Ulén et al 2019). Moreover, since the expansion of SFCWs for agricultural drainage water treatment started a few decades ago (Song et al 2019), it is important to understand their behaviour and performance once they reach the mature stage.…”