Abstract
Abstract. One of the best-known and largest karst areas in Germany, the Blautopf Catchment, offers unique access to waters of the unsaturated zone through a large cave system. It was investigated with stable isotopes (18O/16O and D/H ratios expressed in permille = ‰) in precipitation, seepage- and groundwater as tracers for water flow, mixing, and storage. The precipitation showed a distinct seasonality with δ18O values between −2.9 and −24.6‰ during summer and winter, respectively. However, the isotope signals in seepage water in the caves as well as the discharge were almost completely buffered and ranged around an average δ18O value of −10‰. This value was also close to the long-term average value of local precipitation, −9.3‰. The homogeneous isotopic composition of the Blautopf Spring was unexpected, as its highly variable discharge (0.3 to 32 m3 s−1) is typical for a fast responsive karst system. These isotopic similarities could be explained by nearly complete mixing of the water already in the vadose zone. The data set therefore presents a case study to narrow down zones of mixing in karst catchments. It also confirms the minor role of the fast conduit system in the water balance of the Blautopf Catchment.
Highlights
Understanding of water pathways and movements in the vadose zone is a prerequisite for evaluation of the risk for groundwater pollution
To soils and the vadose zone for mixing, the influence of the epikarst was recently investigated in more detail as it is assumed to play a major role in mixing of waters due to is finer fracture systems and associated longer residence times of water (Aquilina et al, 2006; Clemens et al, 1999; Perrin et al, 2003; Sauter, 1995)
By investigating the karst aquifer of the Blautopf Catchment with water stable isotopes the following conclusions could be drawn: (i) The variations of the stable isotope signal of the precipitation were not found in the Blautopf discharge, which was homogeneous throughout the year
Summary
Understanding of water pathways and movements in the vadose zone is a prerequisite for evaluation of the risk for groundwater pollution. In order to describe the variable flow character of karst systems, it is necessary to consider the conduits that are embedded in the fissured-porous matrix (Kiraly, 1998; Liedl and Sauter, 1998; , 2000). Even though the latter are assumed to play a minor role in water fluxes through karst systems, they may play an important role for storage of pollutants. In contrast to focused tracer tests with dyes or salts, such more widely distributed tracers may help to characterize diffuse
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