Preliminary results on the dynamics of particles and their size distribution at a karst spring during a snowmelt event

Recharge events in karst catchments are often accompanied by rapid changes of electrical conductivity, temperature or turbidity in associated karst springs. Turbidity is usually used as a proxy for suspended matter. However, it is not capable to characterize suspended matter in detail as it lumps signals of particles of a wide range of sizes. Changes in particle size distribution (PSD) of suspended matter have rarely been measured although they may contain information on particles' origin, transport, or mobilization. In few cases PSD could even be used to predict bacterial contamination of karst springs. This study is one among few, measuring concentrations of suspended particles in the size range of 0.5-150 mu m on-site and in real-time. The study was performed during a single snow-melt event at one individual karst spring (Gallusquelle, Germany), the findings are therefore of preliminary character. Generally, the PSDs follow a power law (Pareto distribution). In some cases, however, a two parted Pareto distribution provides a better fit. The combination of chemograph analysis and turbidigraph separation demonstrates remobilized (autochthonous) and freshly infiltrated suspended (allochthonous) matter. Visually, there is no relation between PSD and the origin of the suspended matter. This may be caused by the superposition of signals from both origins. Therefore, utilizing the PSD as an indicator for the origin of suspended matter may be restricted to local applications. Furthermore, PSD does not seem to be a clear indicator for a bacterial contamination at the investigated spring, at least for this particular event. The study indicates, that the karst system itself and the type of discharge event may play a crucial role in the successful application of PSD as an adequate source indicator for suspended matter. (C) 2015 Elsevier B.V. All rights reserved.