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Eutrophication is the state with high nutrient concentration, which can cause plant growth including algae blooms. Nutrients drain into the Baltic Sea from agricultural lands and drainage systems, from weak or insufficient wastewater treatment, from contaminated industrial waste water, and even from the rain water, if it contains dust, unburnt oil from the roads and parking areas or other pollutants washed from hard coverings or accumulated in the air. High nutrient level into the natural waters affects the human economic activity. An inexpensive way to reduce nutrient load to water objects from agricultural lands is formation of constructed wetlands or restoration of natural wetlands. The main tasks of this study were to describe the processes in constructed wetlands, the conditions of construction and to analyze the capacity of constructed wetlands to reduce nutrients and suspended particles inflow to open waters. Another task was to determine nutrient retention efficiency in the Mežacīruļi constructed wetland in Latvia by the descriptive methods of mathematical statistics and Wilcoxon T test method and to compare the obtained results with ones from Bergaholm constructed wetland in Sweden. In the end of this article, the evaluation of efficient theoretical design parameters for constructed wetlands in Latvia is made. The research results indicate that the Mežacīruļi constructed wetland does not provide the sufficient nutrient retention. To improve the nutrient retention efficiency, it would be necessary to develop it, e.g., to increase the amount of vegetation, such as planting Typha spp. or to make a small constructed wetland extension to a depth of 0.3 m for Carex spp. to stabilize the sediments. [ABSTRACT FROM AUTHOR]

A pilot-scale horizontal subsurface flow constructed wetland was installed at the farm Mezaciruli, Zalenieki county, Jelgava region, in the middle part of Latvia, in August 2014 to improve stormwater quality collected from the farmyard and demonstrate applicability of constructed wetland as a convenient treatment option for contaminated surface runoff. The examined water treatment system consists of a sedimentation pond as a pretreatment plant, a water pump, a water distribution well, and a horizontal subsurface flow constructed wetland with the surface area of 160 m². During the observation period of 27 months (2014 - 2016) 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 and nutrient removal efficiency of the system was examined. Water samples collected at the inlet and outlet were compared. Monitoring results obtained during this study show that on average concentrations of TN and TP were reduced by 22% and 80%, respectively. However, nitrate - nitrogen concentrations on average increased by 10%, as during the time period from June, 2015 to March, 2016 reduction in NO3-N concentrations was not observed. [ABSTRACT FROM AUTHOR]

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 out let. 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. [ABSTRACT FROM AUTHOR]