OPTAIN: Dotnuvélè River Basin

In the lower part of the river Stabė, 1.8 km from its mouth, a wetland of 2.38 ha has been installed. The wetland was constructed by artificially flooding the valley. Corrugated metal plating was used at the inlet and outlet of the wetland to protect the stream banks. While most Lithuanian wetlands are peaty, this one is not. Over time, the surface layer of the wetland has been altered by the hydrophytic wetland-specific plants, their species composition, and the degree of decomposition of these plants. Sediments washed down from the fields accumulate here. The organic matter in these sediments creates the typical habitats of saturated organic soils, which are effective in terms of nitrogen - and especially phosphorus - retention.
The wetland has four main sections. The deepest part covers 0.21 ha and is up to 2.0 m deep. Sediments are deposited here. When there is a decrease in flow, these sediments can then be removed mechanically and transported to fertilize the adjacent fields. The next section covers 0.94 ha and its depth is less than 0.5 m. It is covered with wetland vegetation. The third section works as a filter and the water is aerated. It is protected by a dyke, 6 metres in length, perpendicular to the direction of flow. The dyke is formed from soil and pitched with stone and gravel. The maximum depth of the water in this section is 0.1 metres. The fourth and final section is where the surface water is treated by macropytic vegetation. It covers 1.2 ha and is from 0.2 to 0.5 m deep. Barriers help prolong the period that the water is held.
The wetland was designed to retain nutrients in the spring and reduce their concentrations downstream. Through an ongoing research programme, the impact of the wetland has been monitored from the start. In the first year, vegetation had not become established so there were no impacts. However in 2020 and 2021 there were very positive results in terms of nutrient capture.