Transport of bacteria, bacteriophages, and extracellular DNA as surrogates for pathogens and antibiotic resistance genes in a karst aquifer (Gallusquelle, South-West Germany)

Karst aquifers are vulnerable to contaminations due to their specific characteristics which allow for a rapid recharge and high velocities within the saturated zone. Contaminants such as pathogenic bacteria, viruses, and antibiotic resistance genes (ARG) can enter the groundwater and reach springs at high concentrations (Auckenthaler et al., 2002). This poses a potential threat, especially considering that drinking water treatment is less effective against microbial contaminations (Auckenthaler & Huggenberger, 2003) or missing, particularly in developing countries. Potential input of such contaminants is related for example to spills and leaks of waste water or application of manure. Many small-scale laboratory studies have been performed to understand the mobility of virus and bacteria, yet only little is known from large scale field tracer tests.

We performed tracer tests using different non-pathogenic bacteria, bacteriophages, and extracellular DNA as surrogates for pathogens and ARGs together with uranine within the catchment of the Gallusquelle karstic spring. The average flow velocities in the groundwater system were about 30 and 87 m/h during our tracer tests. Tracers were injected as instantaneous input (10 minutes input time). Periodical sampling for the biological tracers started with the first detection of uranine about 80 to 90 hours after injection. Bacterial and eDNA tracers were analysed using qPCR methods while bacteriophages were additionally analysed using a culture-based method (plaque assay) to count active phages. First data indicates that all tracer materials were successfully injected into the groundwater and detected at the Gallusquelle spring. Results of the first tracer test suggest that all used tracer materials were transported over at least 3 km within the system. Furthermore, active bacteriophages of the second tracer test were transported over 9 km from a stormwater detention basin to the spring within 90 hours. 1D-transport modelling revealed much lower mass recovery for these active phages compared to the soluble tracer uranine (about 1% as maximum compared to approximately 31% for uranine).

 

Auckenthaler, A., Raso, G. & Huggenberger, P. (2002): Particle transport in a karst aquifer: natural and artificial tracer experiments with bacteria, bacteriophages and microspheres. Water Sci. Technol., 46, 131-138

Auckenthaler, A. & Huggenberger, P. (2003): Schlussfolgerungen und Empfehlungen. In: Auckenthaler, A. & Huggenberger, P. [eds.]: Pathogene Mikroorganismen im Grund- und Trinkwasser. Birkhäuser Verlag, Basel, 184 S.