A KARST SPRING’S RESPONSE TO A SNOW MELT EVENT: USING ACESULFAME, ATRAZINE, ISOPROTURON AND CHLORIDE AS INDICATORS FOR SPECIFIC FLOW COMPONENTS

Karst spring hydrographs and chemographs usually show high dynamics reflecting the complex interactions of different aquifer compartments and hence different flow components. While concentration variations of major ions have been used in various studies for chemograph analysis, organic micropollutants can reveal new information on processes in karst aquifers. Studying the input of micropollutants in terms of temporal and spatial variations as well as the compounds’ properties (e.g. persistence, sorption) allows using them as indicators for certain flow components in spring water.

The Gallusquelle karst spring in SW-Germany has a rural catchment area, that measures about 45 km². Average spring discharge is 0.5 m³/s (0.2-2 m³/s). During a snow melt event in December 2012 discharge and specific conductance were monitored and spring water was analysed for major ions and several micropollutants (sampling frequency = 6 h). Micropollutants were analysed using HPLC-MS/MS after solid phase extraction.

During the event the herbicides Atrazine (ATZ) and Isoproturon (ISO) and the artificial sweetener Acesulfame (ACE) were detected. Studies about the input revealed that ATZ and ISO stem most likely from farming areas while ACE originates from wastewater. Besides, ATZ was banned from agricultural use in Germany in 1991, while ACE was licensed at the same time (1990).

In the beginning of the event the relatively persistent compounds ATZ and ACE were detected at concentrations of 3.5 ng/L (ATZ) and 20 ng/L (ACE). About 30 h after the first rise of discharge (t₀) specific conductance begins to decrease showing the arrival of newly recharged event water. At the same time ATZ and ACE concentrations decrease as well. At t₀ + 50 h a chloride peak indicates the arrival of a rapid recharge component with deicing salt. At the same time ISO begins to exceed the method’s lower limit of detection (LOD = 3.0 ng/L). At t₀ + 68 h ISO reaches its maximum concentration (9 ng/L) and disappears at t₀ + 130 h. Except for the period of the chloride peak, ACE shows the same dynamics as the specific conductance, i.e. carbonate concentration.

Thus ACE and especially ATZ represent slow flow components. ISO and chloride represent fast recharge plus fast transport components. The sharp chloride peak reflects rather a point source, the broad ISO peak an extensive source.