Fokus på Mälaren 2021: sammanfattande resultat från miljöövervakning och forskningsprojekt knutna till samarbetet mellan SLU och Mälarens vattenvårdsförbund

Mälaren’s Water Conservation Association (MVVF) and the Swedish University of Agricultural Sciences are continuing their collaboration with focus on Lake Mälaren. In 2021, the pandemic affected the opportunity to meet during the MVVF Annual General Meeting in Spring but the yearly Lake Mälaren Seminar in the Autumn was possible to attend both physically at SLU in Uppsala and via video link with about half, about 40, attending in Uppsala. Four well attended webinars, called Mälarinars, was also presented to the members of the MVVF. A new contact person at SLU, Faruk Djodjic, are now leading the project together with Stina Drakare. During the winter sampling, all stations had ice, which is the first time since this collaboration started in 2017. May and August had high precipitation and the summer months of July and August were warm compared to the long term mean. The status assessment shows that stations with moderate status dominate (13) and that there are several stations with poor (7) and bad status (5). Only two stations were assessed to good status and none to high status. The number of stations with good status varies between two and four between the years, which depends on which stations are included in that particular year. These status assessments are mainly related to eutrophication problems, which the sampling program is designed to follow. Three doctoral students with subjects that concern Lake Mälaren have had dissertations during the period. Two of them concern the eutrophication problem and subjects such as a tools for reducing the transport of phosphorus from land to Lake Mälaren and tools for inactivating phosphorus on lake bottoms to reduce internal load from bottom sediments. The third dissertation provided tools for improving drinking water purification when there is a problem with organic environmental pollutants. Other scientific publications of interest for Lake Mälaren presented briefly in the report are e.g. a tool for identifying potential high-risk substances in the aquatic environment linked to impacts from sewage treatment plants, and that the brownification of our waters seems to have stopped with a turning point in 2010. Another publication shows with a first study that antibiotic resistance genes are common and cover several types of antibiotics in water around Västerås, Uppsala, Eskilstuna and Stockholm. This year's bachelor projects were done in wetlands with a focus on those used as phosphorus traps and in horse paddocks to find out if nutrient leakage from these can be reduced by mocking. At the master level, projects finding out the conditions under which nitrogen-fixing cyanobacteria thrive and measuring algal blooms with sensors for higher time and depth resolution are presented.