In Finland urban wetlands are being implemented to help improve water quality, absorb storm water volume and flow control, and improve the land-water habitats for urban communities. The wetlands are designed to respond to the needs and negative impacts of urbanization and therefore, public acceptance and multifunctional benefits are central to the design and implementation of the wetlands. The acceptance and understanding of the importance of urban dwellers is important and thus the project sought to demonstrate several benefits of functional wetlands.
Based on Wahlroos et al. (2015): Urban wetland parks in Finland: improving water quality and creating endangered habitats. In: Urban wetland parks in Finland: improving water quality and creating endangered habitats. In: International Journal of Biodiversity Science, Ecosystem Services & Management Volume 11, Issue 1: Pages 46-60
Urbanization is affecting water quality and there is increasing severity of flooding and drought periods in Southern Finland. This is expected to become worse because of climate change. During flooding events, run off from rain and melting snow are quickly carried over urban surfaces and overwhelm receiving streams. Habitat degradation is occurring as harmful water from urban areas is transferred into connected habitats. These urban streams in turn cause flooding and channel erosion. The creation of wetlands is an alternative ecosystem approach to conventional responses that have been to seal natural waterways into culverts or clearing, and stabilization for augmented conveyance and erosion control.
Two urban wetlands, the Nummela Gateway and the Nummela Niittu were designed and implemented. The wetlands are 6ha and 7ha respectively and are within 550 ha of the urbanized Kilsoi stream watershed in the catchment of Lake Enäjärvi, in the Nummela community, Municipality of Vihti, Southern Finland. The lake has poor water quality from algal blooms and fish kills that result from runoff from its catchments and phosphorus load from human activities. The Stream Kilsoi is an inland clay-soil stream that drains into the Baltic Sea. The habitat type and clay-stream is red listed in the Red list Assessment of Finnish habitat types as critically endangered.
The creation of wetlands is an ecosystem approach and replaced hard infrastructure and conventional responses that have previously been implemented in the area to control storm water volume. In the past, the convention has been to seal natural waterways into culverts or clearing, and stabilization for augmented conveyance and erosion control.
The two wetlands, Nummela Gateway and the Nummela Niittu, were established over five years and closely monitored. The ecosystem service that was deemed most important for the wetlands to provide was water quality management. Water treatment by wetlands depends on the plants and their associated microbes. Storm water and flooding events are the main carriers of potential pollutants from urban areas, and thus a high density and diversity of plans and microbes is necessary. In this case, the native origin of the plants was also found to be important to protect urban streams from the erosive effects of storms and snowmelts. Plant self-establishment occurred quickly and construction only required the monitoring of water levels, especially during winter. The existing shoreline and old drainage ditches acted as a seedbank and no maintenance of native plants was necessary.
In addition to improving biodiversity, water quality improvements were also achieved. There was an increase in phosphorus reduction after the third year. Despite that the Gateway wetland is just 0.1% of its 550 ha watershed area, it does achieve an annual 10% for total phosphorus reduction.
The establishment of two wetlands near to an urbanized area was able to mitigate against various challenges stemming from urbanization. The Gateway and Niittu wetlands were successful in creating high biodiversity at the clay-stream habitats and relied on little human maintenance due to the naturally occurring habitat which was conducive to wetland creation and existence.
Some compromises were made in order to ensure the acceptance of the wetlands and their appreciation and support by the community. Both wetlands were designed to accommodate open water areas for recreational purposes and thus do not fulfill the most efficient capacity for pollution removal.
Despite the establishment of the wetlands, they do not address source control directly which remains an issue. If action is taken to reduce pollution at the source, then the wetlands will be more productive in response.
Continued monitoring during and after the establishment of the wetlands allowed for there to be definitive conclusions on the impact of the created wetlands on water pollution mitigation, self establishment of vegetation, and biodiversity development. Water quality improvements were demonstrated with continuous monitoring which would not have been deciphered via discrete water sampling.