Fig. 7. General procedure to estimate baseflow concentration (C_bf) from the discharge-weighted age distribution of ground water seepage. (a–c) The basin-wide mean annual concentration in ground water recharge (total NO₃^–) from regression line in Fig. 5a. (a) Selection of using the discharge-weighted age-date distribution (vertical point diagram) of the 27 June 2000 dataset (Fig. 6). (b) Weighting of values by the discharge-weighted relative frequency. (c) Summation of weighted concentrations to obtain C_bf.