Biological description of the interactions between surface and groundwater: Application to the assessment of aquifer vulnerability to rivers pollution

Field investigations have shown that several rare and/or stygophilous taxa are found in surface coarse sediments of rivers upstream and/or downstream dams or gravel operations. These observations relate to species such as Propappus volki, Pristina spp.,Chaetogaster parvus, Rhyacodrilus carsticus, R. falciformis, Phallodrilus spp. .were made from hydraulic studies but the lack of biological data at the species level did not enable to get a clear understanding of the whole phenomenon. All these problems gave the opportunity to fold the missing link between hydraulics and biology. So far, elementary results of studies on the same sites have shown such correlations between the distribution of oligochaetes and soil filtration properties (gravel pits of La Wantzenau, France). One aim of common studies is to define the vulnerability of phreatic waters to surface waters pollution. The amplification of water exchanges between surface and underground waters is considered indeed as a risk of contamination of aquifers. Several studies are going on along an industrially polluted tract of the river Rhône. Preliminary results show that the absolute and relative abundances of superficial coarse substrata and to the current velocity in underground porous media. A new study is planned including the biology of suterranean water.