ABSTRACT

The evaluation of tracer experiments and the analyses of environmental tracers in ground waters of the Karst of the Franconian Alb demonstrates the importance of facies of limestones on tracer dilution. In bedded facies tracers propagate quickly and are detected with high recovery rates; contrary, in the reef facies tracers propagate slowly and are diluted to their detection limits (20 to 2 ng/1) within 1.5 to 2 km of distance. These differences in tracer dilution are attributed to a considerable matrix porosity in which pollutants enter by diffusion processes. Ground water out of this matrix has mean residence times of tenth of years as compared to flow velocities of hundreds of meters a day in fissures. - The existence of a matrix porosity in limestones may lead to a storage of contaminants for long times and would produce serious long-term ground water contamination problems as far as microbiological activity is absent. Recent isolation of microorganisms from karst ground waters and denitrification experiments demonstrate a considerable quick nitrate decomposition towards N2O and N2. With respect to pesticides there seems to exist a comparable decomposition. - From the research in the Franconian Alb a new concept of ground water protection in reef carbonates comprising two protection zones has been developed.