Abstract
Diffuse agricultural pollution degrades water quality and is one of the main causes of eutrophication; therefore, it is important to reduce it. Constructed wetlands (CW) can be used as an effective measure for water quality improvement. There are two possible ways to establish surface flow CWs, in-stream and off-stream. We studied treatment efficiency of the in-stream free surface flow (FSW) Vända CW in southern Estonia from March 2017 until July 2018. The CW consists of two shallow-water parts planted with cattail (Typha latifolia). According to our analyses, the CW reduced total phosphorus (TP) and phosphate (PO4-P) by 20.5% and 16.3%, respectively, however, in summer, phosphorus removal was twice as high. We saw significant logarithmic correlation between flow rates and log TP and log PO4-P removal efficiency (rs = 0.53, rs = 0.63, p < 0.01 respectively). Yearly reduction of total organic carbon was 12.4% while total inorganic carbon increased by 9.7% due to groundwater seepage. Groundwater inflow also increased the concentration of total nitrogen in the outlet by 27.7% and nitrate concentration by 31.6%. In-stream FWS CWs are a promising measure to reduce diffuse pollution from agriculture; however, our experience and literature data prove that there are several factors that can influence CWs’ treatment efficiency.
Highlights
The growing population demands food, which in turn, affects agriculture and other land management
Our results show higher phosphorus removal efficiency with lower oxygen concentration in the water, which suggests that the wetland soil is in an oxic state and acts as a sink of phosphorus
Junean2018 revealed concentration was in thegroundwater range of 0.6–21 mg·Lof−1around with an90average flow rate with average flowthat rateTN
Summary
The growing population demands food, which in turn, affects agriculture and other land management. This causes land use changes and intensifies fertilizer use, which increases the impact of diffuse pollution on water quality [1]. Nutrient runoff from intensively managed agricultural land causes water quality degradation, increases plant growth, loss of biodiversity, and other problems related to eutrophication [2,3]. Several legal regulations have been created, but nutrients still transfer to water bodies [4]. It is necessary to use measures for diffuse pollution reduction, such as creating surface-flow constructed wetlands
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