The Rhine rift valley ground water—river interactions: Evolution of their susceptibility to pollution

Abstract

AbstractThe exchange processes between the Rhine river and the alluvial aquifer were analysed in the upper part of the rift valley (upstream of Strasbourg). Hydraulic works, and the consequent suppression of flooding, along the Alsace Rhine floodplain greatly modified these processes. The transfer of persistent toxic micropollutants (organochlorine compounds, mercury), and non‐persistent pollutants (organophosphorous compounds: Sandoz spill) from the Rhine to the groundwater‐fed streams was exhibited by pollutant bioaccumulation in fish (particularly in the eel) and eutrophication of these streams near the canalized river.Comparison of the hydrological functioning of the two main river floodplains (the Rhine and its tributary, the Ill in the Alsace Rhine plain) shows two completely different exchange processes: in the case of the canalized Rhine, the groundwater is affected by direct transfer of pollutants through the channel bed. In the other case, that of the river Ill, where the floodplain is still widely flooded each year, the self‐purification of the floodwaters transferred to the groundwater is very effective: the soil‐root system of alluvial forest and meadow apparently having a high purification capacity.