Expanding our Knowledge on the Impact of Organic Chemicals on Freshwater Lakes

Lakes provide essential ecosystem services to humankind, with the provision of freshwater likely being their most important contribution to human well-being. Therefore, it is mandatory to prevent freshwater lakes from harm in order to protect our livelihood. Pollution is known to put the health of our planet at risk, including our aquatic ecosystems. For European lowland surface waters, certain key organisms, including algae, crustacea, and fish, have been shown to be impacted by chemical pollution. However, currently little is known about the influence on other key organisms (e.g. macrophyte communities) and the spatial extent of these impacts. To close these gaps in knowledge and generally develop a better understanding of the impact of chemical pollution on our aquatic environment, is key for its efficient protection and the preservation of its ecosystem services. This dissertation aims to close these knowledge gaps and thereby increase our understanding of the impact of organic chemicals on our aquatic environment. During the course of this dissertation, two field studies and one literature review were conducted. The first field study was performed in eight lowland lakes of Schleswig-Holstein. Goal was to demonstrate that contaminated sediments prevent macrophyte communities from reaching a good ecological state. It was possible to show that sediment toxicity, driven by antifouling biocides and polycyclic aromatic hydrocarbons, is one of the factors that limit the ecological quality macrophyte communities can reach. The second field study was performed in eight lakes of the French Pyrenees. In this case, the aim was to explore the exposure and risk for waterbodies as remote as mountain lakes by organic chemicals. It was found that also mountain lakes are exposed to a wide variety of organic chemicals, including substances introduced via the atmosphere and local sources. All lakes under investigation were experiencing a chronic toxic risk for crustacea and three of eight lakes were even exposed to an acute toxic risk for crustacea. As this risk was also reflected in lowered abundancies of crustacea, this demonstrated that also waterbodies as remote as mountain lakes are impacted by chemical pollution. Following up on these findings, a literature review was performed. While generally little investigated, the data that could be found support the idea that toxic effects on mountain lakes might be widespread. The results of this thesis add to the growing knowledge, indicating that chemical pollution is jeopardizing the ecological quality of our planet and thereby, causing it to become unhealthy and dysfunctional. To protect our aquatic ecosystems, and planetary heath in general, it will be necessary to reduce our emissions of organic chemicals and use of particularly toxic substances