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.

Risk of groundwater contamination widely underestimated because of fast flow into aquifers.

Groundwater pollution threatens human and ecosystem health in many regions around the globe. Fast flow to the groundwater through focused recharge is known to transmit short-lived pollutants into carbonate aquifers, endangering the quality of groundwaters where one quarter of the world's population lives. However, the large-scale impact of such focused recharge on groundwater quality remains poorly understood. Here, we apply a continental-scale model to quantify the risk of groundwater contamination by degradable pollutants through focused recharge in the carbonate rock regions of Europe, North Africa, and the Middle East. We show that focused recharge is the primary reason for widespread rapid transport of contaminants to the groundwater. Where it occurs, the concentration of pollutants in groundwater recharge that have not yet degraded increases from <1% to around 20 to 50% of their concentrations during infiltration. Assuming realistic application rates, our simulations show that degradable pollutants like glyphosate can exceed their permissible concentrations by 3 to 19 times when reaching the groundwater. Our results are supported by independent estimates of young water fractions at 78 carbonate rock springs over Europe and a dataset of observed glyphosate concentrations in the groundwater. They imply that in times of continuing and increasing industrial and agricultural productivity, focused recharge may result in an underestimated and widespread risk to usable groundwater volumes.

Author Correction: Global karst springs hydrograph dataset for research and management of the world's fastest-flowing groundwater.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Modelling the effects of climate change and population growth in four intensively exploited Mediterranean aquifers. The Mijas range, southern Spain.

Groundwater is key to economic growth in the Mediterranean region. This is particularly true of areas such as southern Spain, where aquifers underpin social development by supplying water to a booming tourist industry. Intensive groundwater use raises sustainability concerns, as pumping often exceeds the long-term recharge rate. Climate change and population growth are likely to exacerbate the water supply challenge in the coming years, due to the expected decrease in rainfall and to increasing competition among users. This paper examines some of the main aquifers in the Costa del Sol region, one of Spain's leading tourist destinations, where intensive groundwater extraction has led to water table drawdowns and the desiccation of all major springs. A numerical model was developed and calibrated for the purpose of evaluating the likely evolution of the system in the future. Downscaled scenarios from global circulation models were coupled with population growth forecasts to establish a range of plausible water management scenarios. Given the relatively small size of the aquifers and the limited recharge rate, the current pumping patterns appear unsustainable. Results suggest that drawdowns in excess of 150 m could take place within the next decade, thus compromising domestic supplies.

Global karst springs hydrograph dataset for research and management of the world's fastest-flowing groundwater.

Karst aquifers provide drinking water for 10% of the world's population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset's coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a wide range of applications: comparative studies, trend analysis and model evaluation. This database will largely contribute to research advancement in karst hydrology, supports karst groundwater management, and promotes international and interdisciplinary collaborations.

Proposed methodology to delineate bodies of groundwater according to the European water framework directive. Application in a pilot Mediterranean river basin (Málaga, Spain).

The term "body of groundwater" represents a new administrative tool established by the water framework directive (WFD) in order to manage European groundwaters. Its practical application raises some difficulties due to unclear definitions and the large heterogeneity of European aquifers. In this work, a methodology is proposed to carry out the delineation of bodies of groundwater according to the requirements of the WFD. This methodology faces up to some of the major difficulties that can arise during the delineation, such as the identification of bodies of groundwater in multilayered aquifers, boundaries between superposed groundwater bodies, and delimitation in low permeability materials or in dismembered aquifers. In order to show its practical application, the proposed methodology is applied in a pilot Mediterranean river basin located in southern Spain. Results show that previous knowledge of the hydrogeological conditions is necessary to enable a correct delineation of groundwater bodies. Finally, alternative procedures are proposed for low permeability and small aquifers in order to reduce the number of groundwater bodies identified and simplify their overall management.

Karst groundwater protection: First application of a Pan-European Approach to vulnerability, hazard and risk mapping in the Sierra de Líbar (Southern Spain).

The European COST action 620 proposed a comprehensive approach to karst groundwater protection, comprising methods of intrinsic and specific vulnerability mapping, validation of vulnerability maps, hazard and risk mapping. This paper presents the first application of all components of this Pan-European Approach to the Sierra de Líbar, a karst hydrogeology system in Andalusia, Spain. The intrinsic vulnerability maps take into account the hydrogeological characteristics of the area but are independent from specific contaminant properties. Two specific vulnerability maps were prepared for faecal coliforms and BTEX. These maps take into account the specific properties of these two groups of contaminants and their interaction with the karst hydrogeological system. The vulnerability assessment was validated by means of tracing tests, hydrological, hydrochemical and isotope methods. The hazard map shows the localization of potential contamination sources resulting from human activities, and evaluates those according to their dangerousness. The risk of groundwater contamination depends on the hazards and the vulnerability of the aquifer system. The risk map for the Sierra de Líbar was thus created by overlaying the hazard and vulnerability maps.