Treatment Efficiency of Diffuse Agricultural Pollution in a Constructed Wetland Impacted by Groundwater Seepage

• Main Authors: Keit Kill, Jaan Pärn, Rauno Lust, Ülo Mander, Kuno Kasak
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Water
• Subjects: constructed in-stream wetland; groundwater inflow; nitrate; non-point pollution; nutrient reduction; phosphate
• Online Access: https://www.mdpi.com/2073-4441/10/11/1601

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) V&#228;nda CW in southern Estonia from March 2017 until July 2018. The CW consists of two shallow-water parts planted with cattail (<i>Typha latifolia</i>). 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 (r_s = 0.53, r_s = 0.63, <i>p</i> &lt; 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&#8217; treatment efficiency.