A multi-methodological approach to create improved indicators for the adequate karst water source protection

Abstract Karst water sources already meet about a quarter of the world's drinking water needs, and their importance is growing. Due to the complexity of water flow in carbonate aquifers, karst water sources require particularly appropriate protection. The scientific literature lacks analytical evidence of the effects of the current legislative frameworks and improved methodological approaches for ecological indications to design alternative strategies. This gap is addressed in the present study, which draws on a combination of investigation methods considering specifics of water flow in karst and on a comprehensive database of general knowledge to gain relevant understanding of the hydrological system functioning. An advanced, multi-methodological approach, which was developed in this study and includes geological and hydrogeological mapping, spring monitoring, tracer tests, water balance and groundwater vulnerability assessment, enabled achievement of optimized indicators for the adequate karst water source protection measures. It demonstrates, that protection zoning based solely on fundamental hydrogeological knowledge, general prediction of groundwater residence times or distance criteria may lead to a high degree of imprecision. Currently valid protection measures may therefore generally be associated with great uncertainties and the high vulnerability of karst areas may be underestimated. In addition to the existing legal requirements for karst water source protection zoning, environmental indicators such as natural and artificial tracers should be considered, which most reliably confirm the directions and characteristics of groundwater flow in karst. Similarly, mapping of groundwater vulnerability to contamination can be of particular importance for the implementation of freshwater protection and spatial planning at least in karst-rich countries. The approach enables scientists to gain relevant insights into the functioning of the hydrological system and environmental managers to protect karst water sources.