Abstract
Constructed wetlands (CWs) provide favorable conditions for removing nitrate from polluted agricultural runoff via heterotrophic denitrification. Although the general operability of CWs has been shown in previous studies, the suitability of peat soils as a bed medium for a vertical flow through a system for nitrate attenuation has not been proven to date. In this study, a mesocosm experiment was conducted under continuous flow with conditions aiming to quantify nitrate (NO3−) removal efficiency in degraded peat soils. Input solution of NO3− was supplied at three different concentrations (65, 100, and 150 mg/L). Pore water samples were collected at different depths and analyzed for NO3−, pH, and dissolved N2O concentrations. The redox potential (Eh) was registered at different depths. The results showed that the median NO3-N removal rate was 1.20 g/(m2·day) and the median removal efficiency was calculated as 63.5%. The nitrate removal efficiency was affected by the NO3− supply load, flow rate, and environmental boundary conditions. A higher NO3− removal efficiency was observed at an input NO3− concentration of 100 mg/L, a lower flow rate, and higher temperature. The results of pore water pH and NO3− and N2O levels from the bottom of the mesocosm suggest that N2 is the dominant denitrification product. Thus, degraded peat soils showed the potential to serve as a substrate for the clean-up of nitrate-laden agricultural runoff.
Highlights
Nitrogen (N) is an important nutrient in terrestrial and aquatic ecosystems
Three nitrate concentrations (N65, NO3 − concentrations of 100 mg/L (N100), and N150 ) were supplied into the mesocosm, there was no significant difference in nitrate removal rate between NO3 − concentration of 65 mg/L (N65), N100, and N150, whereas significances in nitrate load, NO3 -N removal efficiency, and ∆C
With decreases in the applied nitrate concentration to N100 and N65, the nitrate removal efficiency increased to 83.0% and 72.7%, respectively
Summary
Nitrogen (N) is an important nutrient in terrestrial and aquatic ecosystems. Around 120 million tons of nitrogen gases (N2 ) per year are converted worldwide from the atmosphere into reactive nitrogen forms such as ammonium and nitrate by mineral fertilizer production and N-fixation by leguminous crops [1]. Most of the nitrogen reaching the terrestrial environment (directly or indirectly) is dissolved in surface runoff and infiltrating water. Regardless of the environmental compartment into which reactive N is released, much of the transported load ends up as NO3 -N in the aquatic environment [2]. In lowland catchments with intensive agriculture, NO3 -N loads from agricultural fields may exceed 2000 kg/(km2 ·year), impacting drinking water quality [3]. In the German lowlands, the average NO3 -N losses from tile-drained field sites were found to vary between
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