COMPARISON OF THE OCCURRENCE OF HERBICIDES WITH TURBIDITY AND PARTICLE SIZE DISTRIBUTIONS IN A KARST SPRING IN SW-GERMANY

Particle mediated transport in the aquatic environment has widely been discussed, as it can facilitate the transport of contaminants. This also applies to karst aquifers as their conduits serve exceptionally well as pathways for particulate matter. During a snowmelt event concentrations of suspended particles were measured in the size range of 0.5 to 150 µm in karst spring water on-site and in real-time. Sampling for several organic micropollutants like the herbicide isoproturon was performed. Also, turbidity, specific conductance and major ions were measured. The study site is a rural karst catchment of 45 km²in SW-Germany that has its main drainage at the Gallusquelle.

The combination of chemograph analysis for major ions and turbidigraph separation allows for the distinction of remobilized (autochthonous) and freshly infiltrated (allochthonous) suspended matter. The occurrence of the herbicide isoproturon follows the trend of turbidity regardless of the origin of the suspended matter (allochthonous or autochthonous). Both breakthrough curves are nearly congruent. The similarity of the curves implicates a similar input and transport of both, isoproturon and particles. However, there is a small temporal misfit between the peak concentrations of isoproturon and the turbidity peaks. Furthermore the tailing of isoproturon is stronger. Assuming the same input function of suspended matter and isoproturon, different travel velocities may explain this effect. The different velocities may result from: (1) transport as a solute vs. particulate transport (2) transport attached to a specific size fraction of particles.

First results of measurements during a flood event in summer 2013 indicate that the herbicide metazachlore and turbidity behave in similar ways compared to isoproturon. Still, further studies are necessary to examine the possibility of particle related transport.