[Denitrification of waters on the way from surface to underground levels in a karstic area]

The failure of the biological processes of waters' recycling in their passing through the soil occurs more and more frequently in calcareous areas. This led us to consider the problem of conditions necessary to the good development of the biological activity. This uses enzymatic reactions activated by chemical elements in very low concentrations: the oligo-elements. The experimental study, in drainage basin in a calcareous area, consisted in finding the percentage of oligo-elements in the waters, in the soils and in the parent rocks. This allowed us to draw a map of the probable lack of oligo-elements and thus to foresee the vulnerability of phreatic waters.