Effekten av brunifiering på primärproduktion och sekundärproduktion i tre olika sjöar

The browning of surface waters, often referred to as brownification, is an environmental problem that is becoming increasingly common in the boreal region. Changes in water color are believed to be due to an increased occurrence of dissolved organic carbon and increasing concentrations of iron in bodies of water. These changes are mainly due to changes in land use, climate change and reduced acidification. Darker water color is expected to contribute to a decrease in the concentration of phytoplankton and an increase in the production of bacteria. Since phytoplankton are primary producers, this change is expected to affect the food web in all aquatic ecosystems. In this study, three different types of lakes were investigated, with the aim of finding out where the effects of brownification are the greatest. We measured primary production as the concentration of chlorophyll and secondary production as bacterial production with radioactive isotopes. Bolmen was able to incorporate the added nutrients most efficiently, as the lake had an increase in both primary and secondary production. Mälaren had a decrease in primary production and an increase in secondary production, while Siljan had a decrease in both primary and secondary production over time. The results suggest that the processes for dealing with an increase in DOC differ between lakes with different water colors.