Identification of chemical and physical key water quality drivers in the urban Grunewald Chain of Lakes, Berlin.

Aquatic ecosystems are threatened by high nutrient loads. Particularly urban lakes that are used as storm water reservoirs are polluted by phosphorus, nitrogen and other pollutants. Improving the water quality of urban lakes is both a benefit for the ecosystem, and for the socio-ecological value of the waterbody. This study investigates the Grunewald chain of lakes in Berlin, Germany which is threatened by high nutrient loads from surrounding urban areas. To date, measures to improve the water quality failed to achieve a resilient, long-term balanced and stable aquatic ecosystem. Connected lakes pose major challenges for water management due to their interactions. To better understand the exchange of nutrients in the Grunewald chain of lakes, a monitoring campaign and data analysis were conducted, with monthly water samples over a period of 13 months at 17 sampling stations, focusing on the inlets, outlets and connections of the lakes. This study reveals the relevance of temperature, volume ratio, depth and phosphorus concentrations affecting the nutrient limitation of the lakes and how water quality of the lakes are affected by each other. The study gives insights to cascading effects on nutrient accumulation along a chain of lakes, providing guidance for further management practices.