MICROPOLLUTANTS AS INDICATORS IN A KARST CATCHMENT

High flow dynamics and variations in water quality are typical for karst springs and reflect the complex interaction of different flow and storage components. Event-based monitoring of mobile micropollutants in spring water combined with input functions was used (1) to quantify the impact of certain contamination scenarios on spring water quality and (2) to gain additional information on the intrinsic characteristics of a karst system.

We employ the artificial sweeteners acesulfame and cyclamate as source specific indicators for sewage along with the herbicides atrazine and isoproturon for agriculture. Moreover, the combined evaluation of the persistent compound acesulfame with the rather degradable cyclamate allows for the distinction of long and short transit times and thus slow and fast flow components. The same applies for atrazine (persistent) and isoproturon (degradable). In Germany, acesulfame was licensed in 1990, atrazine was banned shortly after, in 1991.

The study site is the 45 km² rural catchment of the perennial karst spring Gallusquelle in SW-Germany (mean discharge: 0.5 m³ s^-1). Overflow events of a storm water detention basin (combined sewer system) are known to cause water quality deteriorations. Most of the sewer system is situated in the SW of the catchment, while most agricultural land is found in the NE. No atrazine and infrequently traces of isoproturon were detected in wastewater. Concentrations and mass fluxes of acesulfame and cyclamate in wastewater were determined.

During low flow conditions only atrazine and acesulfame were detected in spring water. After a recharge event without overflow of the storm water detention basin concentrations decreased and a breakthrough of isoproturon indicated the arrival of water from croplands. After a recharge event that was accompanied by a wastewater overflow cyclamate was detected. Simultaneously, acesulfame exhibited a breakthrough superposed on its diluted background concentration. 1-D-transport-modelling of the cyclamate breakthrough curve revealed results that are in good agreement with previous findings.

Analyses of micropollutants may become very sensitive tools in karst hydrogeology where natural background concentrations and signal dampening are limiting factors for conventional investigation methods.