Abstract
Abstract. Artificial tracers are powerful tools for investigating karst systems. Tracers are commonly injected into sinking streams or dolines, while springs serve as monitoring sites. The obtained flow and transport parameters represent mixed information from the vadose, epiphreatic and phreatic zones (that is, the aquifer remains a black box). Accessible active caves constitute valuable but underexploited natural laboratories to gain detailed insights into the hydrologic functioning of the aquifer. Two multi-tracer tests in the catchment of a major karst spring (Blautopf, Germany) with injections and monitoring in two associated water caves aimed at obtaining spatially and temporally resolved information on groundwater flow in different compartments of the system. Two tracers were injected into the caves to characterize the hydraulic connections between them and with the spring. Two injections at the land surface, far from the spring, aimed at resolving the aquifer's internal drainage structure. Tracer breakthrough curves were monitored by field fluorimeters in caves and at the spring. Results demonstrate the dendritic drainage structure of the aquifer. It was possible to obtain relevant flow and transport parameters for different sections of this system. The highest mean flow velocities (275 m h−1) were observed in the near-spring epiphreatic section (open-channel flow), while velocities in the phreatic zone (pressurized flow) were one order of magnitude lower. Determined conduit water volumes confirm results of water balances and hydrograph analyses. In conclusion, experiments and monitoring in caves can deliver spatially resolved information on karst aquifer heterogeneity and dynamics that cannot be obtained by traditional investigative methods.
Highlights
Karst aquifers are characterized by strong heterogeneity and anisotropy related to the diverse distribution of solutionally enlarged conduits in the carbonate rock (Worthington and Ford, 2009)
Relevant conservative and reactive transport parameters, such as dispersion and retardation can be obtained by quantitative analysis and modeling of tracer breakthrough curves (BTCs) (e.g., Geyer et al, 2007; Massei et al, 2006; Morales et al, 2007; Goldscheider et al, 2008)
This paper presents the first tracer tests that were done inside the active conduit network of this karst system, accompanied by detailed geological investigations and water balances (Lauber et al, 2013)
Summary
Karst aquifers are characterized by strong heterogeneity and anisotropy related to the diverse distribution of solutionally enlarged conduits in the carbonate rock (Worthington and Ford, 2009). Groundwater flow and contaminant transport in karst aquifers are difficult to predict because of the unknown configuration and geometry of the conduit network. The sustainable use and protection of karst groundwater resources requires detailed knowledge of the underground flow paths and spring catchment areas. Geological mapping and speleological investigations can deliver direct information about karst development and the presence of larger conduits (Goldscheider and Drew, 2007). Artificial tracer tests are often used to investigate the drainage pattern of karst aquifers. In contrast to other methods, tracer tests deliver clear information on hydraulic connections, spring catchment areas, transit time distributions and linear flow velocities.
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