Fokus på Mälaren 2019: sammanfattande resultat från miljöövervakning och forskningsprojekt knutna till samarbetet mellan SLU och Mälarens vattenvårdsförbund

The collaboration between Mälaren's water conservation association (MVVF) and the Swedish University of Agricultural Sciences continues with good cooperation between research and social interests in and around Lake Mälaren. In 2019, we increased the visibility of this collaborative work through the website Focus on Lake Mälaren. Including information in English was one of MVVF’s priorities as MVVF’s own website was only in Swedish. Seminars and webinars are another area of fruitful partnership with many participants during 2019.Results from 2019’s environmental monitoring in Lake Mälaren generally showed better status for variables such as total phosphorus and phytoplankton than 2018. The higher number of stations with oxygen measurements in 2019 revealed however low oxygen concentration in the bottom waters of large parts of the lake; a finding that will likely contribute to higher internal phosphorus loading from the sediments.The research project Crosslink published in a scientific article that species in streams benefit if there is a forest strip closest to the water’s edge, a finding that should be of interest and used in community planning. Crosslink is an EU funded project that includes many study streams in the Lake Mälaren basin. Another project showed that concentrations of organic micropollutants in Lake Mälaren are higher closer to emission points from cities' (e.g. sewage treatment plants) and that levels are highest in spring and in the bottom water.Three students wrote theses focusing on Lake Mälaren. A study of Mälaren's common zebra mussel found fewer organic environmental pollutants in mussels than in the surrounding water and that the organisms mainly absorbed medicines and not any other groups of pollutants. Another student modeled future water temperatures in Ekoln. Using different climate scenarios the models predict ice free winter conditions and that the duration of the summer stratification will increase by 9 days. A third study tested if cyanobacteria pigments, and not only chlorophyll pigments, can be used in satellite monitoring of cyanobacteria blooms. This work showed that there were too few simultaneous sampling events of phytoplankton in the water and satellite imagery to adequately assess the method.