Comment on “Estimating groundwater mixing ratios and their uncertainties using a statistical multi parameter approach” by Rueedi, J., Purtschert, R., Beyerle, U., Alberich, C., Kipfer, R. J. Hydrol., 2005, 305: 1–14

The paper of Rueedi et al. (2005) proposes a statistical approach for a multi-layered system in order to determine intrinsic characteristics of each aquifer and the mixing ratios in places where leakage exists and applies it in central Niger. Despite of its potential interest, the paper misses its objective because (i) it relies on a poor knowledge of the regional literature, (ii) it suffers from internal inconsistency and (iii) it lacks validation. Many previous publications dedicated to semiarid areas (e.g. Wood and Sanford, 1995 and Scanlon et al., 1999) showed that considering various temporal and spatial scales and crossing different methods is often the only key to reliable results. The authors unintentionally demonstrate the limits of a too rapid monothematic study in a region where exchanges between aquifers are often complex. Concrete drawbacks of such a self-limitation are illustrated in this comment.