NUTRIENT RETENTION IN SURFACE FLOW CONSTRUCTED WETLAND IN AGRICULTURAL LAND IN LATVIA

Abstract

The research site consists of a pilot-scale surface flow constructed wetland at the farm Mezaciruli located in Zalenieki County, Jelgava Region, in the middle part of Latvia. The constructed wetland was installed in June 2014 to improve water quality in agricultural catchment and examine nutrient retention at the constructed wetland receiving surface and drainage runoff. The constructed wetland’s surface area of 0.37 ha corresponds to 0.5 % of the total catchment area. During the observation period of 32 months (2014-2017) water quality parameters such as total suspended solids (TSS), nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), total nitrogen (TN), orthophosphate-phosphorus (PO4-P), and total phosphorus (TP) were monitored twice a month using a grab sample approach. Retention efficiency for monitored water quality parameters was calculated based on their concentrations at the inlet and outlet. The monitoring results obtained during this study showed a reduction within the constructed wetland for all examined parameters. The concentrations of NO3-N, NH4-N and TN were reduced on average by 13 %, 15 % and 16 %, respectively. PO4-P and TP concentrations were reduced on average by 38 % and 36 %, respectively. Total suspended solids were reduced by 31% at the outlet of the constructed wetland. However, in some cases, an increase in nutrient concentrations in water leaving the constructed wetland was observed. Therefore, there is a need for further research to investigate causes of such increase.