Diffuse Schadstoffe als reaktive Tracer zur Identifikation und Quantifizierung der im Einzugsgebietsmaßstab relevanten Transportprozesse am Beispiel von Karstquellen
Zusammenfassung der Projektergebnisse
The aim of this work was to identify the relevant processes for the fate and transport of persistent organic pollutants (POPs) at the field scale. Polycyclic aromatic hydocarbons (PAHs) were chosen as anthropogenic tracers, because they are ubiquitously distributed and have a high input rate into soils via atmospheric deposition. They can undergo different processes such as ad/-desorption, biodegradation, particle associated transport and preferential flow. Thus, PAHs are reactive and space integrating tracers, which allow identification and quantification of primary transport processes. A suitable karst system (Blautopf Catchment) was chosen, for which a reliable in/-output mass balance could be established. Additionally, the vulnerability of the karst system with respect to diffuse groundwater pollution with PAHs was successfully assessed. A fairly stable deposition rate was recorded over the entire catchment area covering a time period of approximately two years. Seasonal variations were observed with higher deposition rates during winter. Soils have a large storage capacity with respect to hydrophobic organic contaminants. Thus, determination of PAH concentrations in the soils is a key factor for understanding the fate of PAHs at the catchment scale under a long-term perspective. Matching distribution pattern of PAHs from soils and atmospheric deposition, respectively, suggest the latter as the primary input pathway into the catchment. Seepage water was sampled in caves of the karst system, and consistently extremely low concentrations of PAHs occurred during ordinary flow conditions. However, during distinct events such as snow melts, the PAH concentrations in seepage water peaked and even exceeded the legal limit for benzo(a)pyrene in drinking water. Similar results were obtained from groundwater monitoring. In the Blautopf Spring, rising PAH concentrations correlated with increasing discharge and turbidity, respectively. This correlation suggests particle facilitated transport of PAHs. However, at some events high particle fluxes were not accompanied by increased pollutant fluxes, suggesting different origins of the particles (i.e., the particles could come from the surface and flushed through the system, or sediments have been re-suspended in the cave system). Based on time integrated PAH measurements of atmospheric deposition and water samples, a mass balance of PAHs were calculated. This input/output mass balance shows that approximately 90 % of the PAHs from atmospheric deposition remain in the system (mostly in the soils). Furthermore, more than 50 % of the output flux was associated with distinct high flow events. As a consequence, PAHs accumulate in the top soils of the investigated system.
