Nitrate: Nitrate concentrations in the samples collected from the main river and the tributaries ranged between 0.2 and 5.3 mg N/l in SC1 and between 0.6 and 5.3 mg N/l in SC2. Seasonal and spatial changes were noted (although the mean value of 1.5 mg N/l over all the stations, remained the same between the two seasons). The concentrations of nitrate were lower than 1.5 mg N/l in the samples from the upper Thur SC and the headwaters of the tributaries (M1, N1, N2, S1, T1 and T2) in both seasons (Figs. 1 and 3, Table S1). However, from SC1 to SC2 there was an increase in the concentration of nitrate (0.5 mg/l increase) in the headwaters of the Thur River (samples from T1, T2) and the Murg River (sample from M2).