Urban wetland parks in Finland: improving water quality and creating endangered habitats

Abstract

Urbanization changes water balance, degrades water quality and disrupts habitats. Wetlands offer storm water volume and flow control, water pollution mitigation, and rich land-water interphase habitats. In the present case study, urban wetlands were designed and implemented to provide multiple functions, including water quality improvement and the establishment of critically endangered clay stream habitat, along a revived urban stream within the Baltic Sea watershed in Southern Finland. The primary water quality concern in the recipient lake is algal bloom controlling and clay particle-carried phosphorus. Wetlands were monitored for functioning over five calendar years. At a wetland monitored for 5 years, herbaceous vegetation was well self-established in the second year, and reached 102 species, of which 97% were native, in the fifth growing season. Successful breeding of amphibians and water birds occurred right after construction. Continuous water quality monitoring over the fourth year at this wetland, with 0.1% area of its watershed, revealed seasonal and event-based differences: for total phosphorus, an annual 10% average with lower removal rates outside, and up to 71% event reductions during the growing season, while highest load reductions occurred during heavy rain and snowmelt events outside the growing season. The created wetlands provided critical habitat and beneficial functions and thus compensated partly for urbanization.

Ecosystem services of wetlands

“…Ten percent phosphorus retention was realized on average through the wetlands with up to 70% retention during summer storm and winter snowmelt events. Wahlroos et al (2015) also point out, not surprisingly, that the public found the wetland parks appealing because of the plant and animal, especially avian, diversity. The pattern of nutrient retention, a diverse flora and fauna, and public appreciation of a 'wetland park' is similar to the ecosystem services that have been demonstrated over 20 years at the urban Olentangy River Wetland Research Park in Columbus, Ohio, USA (Mitsch et al 1998(Mitsch et al , 2012(Mitsch et al , 2014.…”

“…The authors suggest that soil properties and denitrification should be considered when assessing the effectiveness of restored wetlands at providing ecosystem services, such as nitrogen removal. Wahlroos et al (2015) describe the ecosystem services of two small flow-through wetlands, which were constructed in Baltic Sea catchments in southern Finland over 2010 to 2014. The values described include water pollution mitigation, amphibian and bird population enhancement, and urban enhancement.…”

Indicators for mapping and assessment of ecosystem condition and of the ecosystem service habitat maintenance in support of the EU Biodiversity Strategy to 2020

“…Green and Elmberg (2013) show that wetland habitats for migratory birds are critical as they contribute to other supporting and regulating ecosystem services including nutrient cycling, control and disease surveillance. Moreover, Wahlroos et al (2015) stated that even artificial wetlands in urban landscapes provide critical habitat (successful breeding of amphibians and water birds occurred right after their construction) and beneficial functions. At the same time, the maintenance of habitats is evaluated by Okruszko et al (2011) as the most fragile ecosystem service, amongst other services provided by a sample of 104 wetlands across Europe (i.e.…”

Carbon dioxide and methane fluxes from different surface types in a created urban wetland

“…Herbaceous vegetation has been allowed to fully self-establish after the construction of the wetland. Annual monitoring of vegetation carried out in summers 2010, 2011 and 2012 indicated rapid self-establishment of vegetation which was rich in taxa and dominated by native species (Wahlroos et al, 2015). At frequently-inundated area (elevation levels of 50-50.35 m), vegetation was arranged in dense patches with different dominating wetland plant species: Typha latifolia L., Iris pseudacorus L., Carex spp.…”

“…It is not surprising that the studied ecosystem appeared to CO2 neutral as it was recently constructed. The herbaceous vegetation has been allowed to fully self-establish without human intervention and at the early successional stage, plant diversity and biomass were still increasing each year (Wahlroos, 2019). With the vegetation being more developed, a greater CO2 uptake from the vegetated area can be expected in the following years.…”