Transport of Colloidal and Solute Tracers in Three Different Types of Alpine Karst Aquifers — Examples from Southern Germany and Slovenia

In many alpine karst regions, bacteriological pollution resulting from agriculture is the most important problem in groundwater protection. Colloidal tracers like fluorescent polystyrene microspheres are used to evaluate the hygienic risk for groundwater resources. Different sizes of colloids may be used to simulate the fate and transport of different types of micro-organisms. For the field tracer tests, three different types of karst systems within the alpine fold belt have been selected: karst aquifers in carbonate conglomerates and limestones in southern Germany, and unsaturated fissured carbonates in Slovenia. Large parts of Tertiary gravel fans in the foreland of European alpine orogens are made of coarse-grained conglomerates, which mainly consist of carbonate components in a carbonatic matrix. These rocks are predisposed to karstification and show a large variety of karst phenomena like dolines, karren, karst springs and estavelles. Tracer tests with fluorescent dyes and particles show high flow velocities and travel distances of up to 8 km. The flow orientation reflects the geological structure. This demonstrates the need for special groundwater protection schemes that take into consideration the heterogeneity and anisotropy of this aquifer type. The Helvetic nappes form parts of he Northern Alps and mainly consist of Jurassic and Cretaceous carbonate rocks. During low-flow conditions, a comparative tracer test with fluorescent-dyes and microspheres was carried out in the Hölloch, Germany's longest cave (9,343 m). The Association of Tracer Hydrologists (ATH) conducted a comparative tracer test in the Slovenian Dinarids in order to evaluate the behaviour of different tracers in the unsaturated zone of the fissured karst aquifer in Sinji Vrh. The behaviour of the tracers shows important differences, especially for solute and particle tracers. Therefore, the authors strongly recommend using particle tracers for the evaluation of hygienic risks to groundwater.