Zones d'oxydo-réduction dans l'aquifere de la Craie des bassins de Paris et de l'Allemagne du nord = Redox zones in the chalk aquifer of the Paris and North German basins

A combined geochemical and isotopic study of chalk groundwater in the Paris Basin and northern Germany shows a distinct chemical zonation with respect to elements with different oxidation states (O, N, S, Fe, Mn, U) and to measured Eh. During the passage of a “redox-barrier” separating oxidizing and reducing groundwater O2 and N-NO3 are removed. The observed reaction sequence corresponds to the theoretical sequence proposed by Stumm & Morgan (1981) and to those described by Champ et al. (1979) and Edmunds et al. (1984). Measured Eh can be used as a semi-quantitative master variable in order to interpret the observed reactions. Apparent stabilities of redox species are very similar to those in English chalk groundwater.