Total phosphorus: The mean TP concentrations over all stations were similar for both seasons (SC1 and SC2). However, there was a decrease of the concentration of TP in the headwaters of the Sitter, it increased in the headwaters of the Murg, Necker and the Thur from SC1 to SC2 (Fig. 3, Table S1). The maximum change in TP concentration was observed at M3 (with 100 lg P/l increase from SC1 to SC2). Station M3, located in the lower part of the Murg (before it joins the Thur), is critical because of the presence of WWTPs mentioned in Section 2. At M3, the increase in TP in spring (SC2) was accompanied by high concentrations of Na+ and Cl as shown in Table S1 and