Published on 05 May 2020
About this good practice
Constructed wetlands are implemented to improve water quality, to offer a habitat for biological diversity support in simplified, uniform areas, and also as water storage for water reuse in dry summers. The pilot object in Latvia was built at the intensively used agricultural area to retain nutrients and suspended solids. Drainage runoff was collected in surface flow constructed wetland to ensure the appropriate conditions for the biological water treatment and retain phosphorous and nitrogen compounds and suspended solids.
The main practical benefits are a nutrient amount retained in artificial water bodies and knowledge-based on scientific studies and monitoring data in pilot sites. The stakeholders including farmers and legal beneficiaries can use good practice advice. The pilot site constructed wetland demonstrated a good example in the reuse of water recourse as providing irrigation from wetland as a water reservoir during dry periods of a year. Wetland capacity served to reduce flooding risks in adjacent areas during spring flood or heavy rains.
Groundwater recharge can be considered as one of the benefits of the practice. As the water treatment plant is designed with an open connection to groundwater, some water amount infiltrates into the upper ground levels depending on the site-specific conditions. The water quality is monitored in terms of the ongoing scientific activities and is acceptable for this initiative.
The main expenses consist of earthworks as an appropriate trench has to be made. The calculations and dimensions are based on the incoming water quality and the catchment area. The average depth of the wetland can vary from 0.3 to 1.5 m.
Evidence of success
The concentrations of NO3-N, NH4-N and TN were reduced on average by 21 %, 35 % and 20 %, respectively for the surface flow constructed wetland. PO4-P and TP concentrations were reduced on average by 31 % and 45 %, respectively for the surface flow constructed wetland. Total suspended solids were reduced by 17% at the outlet of the surface flow constructed wetland. Water from the wetland is reused to irrigate greenhouse plants of 0.5 ha, taking 7- 15 m3 water daily throughout the growing season.
Potential for learning or transfer
The lesson to transfer from the pilot-site constructed wetland in Latvia to the potential future projects is the additional benefits that you can gain. This project was initially implemented as a wastewater treatment method. The monitoring showed good results in water quality improvement and the primary target was achieved. Recreational, social, and economic benefits for the landowner were indicated during the exploitation period. Farmer used the wetland as an open water basin for swimming and fishing. Greenhouse plants were irrigated regularly with water from the wetland, while other watercourses were dry during the vegetation period. Other farmers are using this example to meet water quality requirements and to adapt to the changing climate.