Real-time karst groundwater monitoring and bacterial analysis as early warning strategies for drinking water supply contamination

Karst aquifers have been globally exploited as a reliable source of drinking water but their intrinsic characteristics (concentrated recharge, high groundwater flow velocities, etc.) and the increase of anthropogenic pressures makes them highly vulnerable to pollution. Continuous monitoring of karst springs constitutes an effective approach for identifying episodic groundwater contamination and assuring safety conditions in drinking water supply systems. This study aims to improve groundwater protection insights through an integrated methodological approach based on real-time measurements of continuous water parameters coupled to bacterial analysis for the characterization of contamination events in a carbonate karst aquifer of a mountainous and rural area in S Spain. For this purpose, environmental, hydrodynamic and physico-chemical data in addition to bacterial activity (Escherichia coli) analysis were gathered from the analysis of eight flooding events at the two main outlets. In these karst springs, partially captured for drinking water supply, the recurrent turbid groundwater episodes suppose an important limitation for groundwater exploitation during several days, but also a concerning human health risk. The results revealed the different flow and sediment dynamics and mixing processes which determine the impact of faecal contamination derived from human activities on the karst groundwater drained by each spring. The described processes control the variable influence of allogenic recharge, which provokes notable differences regarding response times and maximum values of turbidity and associated bacterial activity in the investigated outlets. The outcomes of this work highlight the usefulness of the applied methodological framework to set the bases for an efficient implementation of early-warning strategies to prevent public health issues worldwide.

Funding for open access charge: Universidad de Malaga/CBUA. This research is a contribution to the PRIMA funded European project KARMA (Karst Aquifer Resources availability and quality in the Mediterranean Area – ANR-18-PRIM-0005); the Spanish project (ref. PCI2019-103675) funded by the International Joint Programme of the Ministry of Science, Innovation and Universities; the project PID2019-111759RB-I00; and to the Research Group RNM-308 of the Junta de Andalucía, funded by the Autonomous Government of Andalusia (Spain). The authors thank the local government of Ubrique town and the local water company “Empresa Mixta de Aguas de Ubrique” and the authorities of the Sierra de Grazalema Natural Park for its collaborative behaviour.