Fokus på Mälaren 2020: sammanfattande resultat från miljöövervakning och forskningsprojekt knutna till samarbetet mellan SLU och Mälarens vattenvårdsförbund

The collaboration between the Mälaren’s Water Conservation Association (MVVF) and the Swedish University of Agricultural Sciences (SLU) continues. In 2020, the pandemic affected the opportunities to meet physically during MVVF's Annual General Meeting and the yearly Lake Mälaren Seminar in November. We trans-formed the Lake Mälaren Seminar to a digital meeting which were well attended. All environmental monitoring of the lake could be carried out as planned. Characteristic of 2020 was the mild winter with rain in the beginning of the year. This increased the turbidity of the western and northeastern parts of the lake during spring and early summer. It is difficult to say whether it clearly affected other measurement values. The total phosphorus concentration were in general slightly higher than the year before, which could be an effect, but the oxygen levels near the bottom were instead better than the year before. It does not appear that sedi-mentation processes of the turbid water generally affected the oxygen levels nega-tively. The ecological status assessment of Lake Mälaren shows that stations with moder-ate status dominate. This year, four of the 33 sampled stations had good ecological status, which is slightly better than the year before when only two stations had good status. This year, as usual, results from the Crosslink project are shown, which have shown biodiversity in streams benefit if there is a forest strip closest to the water’s edge. Two articles and a film are news for the year from this project that has just been finalized. Several doctoral students have had dissertations during the spring and we present highlights from their studies of organic micropollutants in Lake Mälaren and methods of how to get rid of them when preparing drinking water. New for 2020 is that we show results from our research groups studying phospho-rus. Several projects study the processes how phosphorus leakage to water occurs and how to stop nutrient leakage with measures in the form of wetlands and by growing mussels in the lake. The year 2020-student projects are partly linked to the research and have dealt with purification techniques for drinking water to remove organic substances of several types, analysis of environmental pollutants in rivers entering Lake Mälaren, and modelling of how organic material is transported with lake water.