Wetlands as a potential multi-functioning tool to mitigate eutrophication and brownification

Eutrophication and brownification are ongoing environmental problems affecting aquatic ecosystems. Due to anthropogenic changes, increasing amounts of organic and inorganic compounds are entering aquatic systems from surrounding catchment areas, increasing both nutrients, total organic carbon (TOC), and water color with societal, as well as ecological consequences. Several studies have focused on the ability of wetlands to reduce nutrients, whereas data on their potential to reduce TOC and water color is scarce. Here we evaluate wetlands as a potential multi-functional tool for mitigating both eutrophication and brownification. Therefore, we performed a study over 18 months in nine wetlands allowing us to estimate the reduction in concentrations of total nitrogen (TN), total phosphorus (TP), TOC, and water color. We show that wetland reduction efficiency with respect to these variables was generally higher during summer, but many of the wetlands were also efficient during winter. We also show that some, but not all, wetlands have the potential to reduce TOC, water color, and nutrients simultaneously. However, the generalist wetlands that reduced all four parameters were less efficient in reducing each of them than the specialist wetlands that only reduced one or two parameters. In a broader context, generalist wetlands have the potential to function as multi-functional tools to mitigate both eutrophication and brownification of aquatic systems. However, further research is needed to assess the design of the generalist wetlands and to investigate the potential of using several specialist wetlands in the same catchment.

Methods
The data was collected once a month over 18 months (April 2020 - September 2021) from 9 wetlands. Water samples were collected from the inlet and outlet of the wetlands each month and analysed for total phosphorus, total nitrogen, total organic carbon, and water color. Simultaneously, flow (m/s) and water area of the inlet and outlet were measured. Furthermore, analysis of the catchment and land use was performed. For detailed method description, see connected article.