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Karst aquifers are a major source of drinking water with intrinsic features that increase the pollution risk from anthropogenic and natural impacts. In Yucatan, Mexico, groundwater is the sole source of drinking water, also acting as receptor of untreated wastewater due to the low regional coverage of sewer systems. To protect karst groundwater, vulnerability methodologies are widely used. Worldwide, multiple karst vulnerability schemes have been developed and tested; however, none of these consider pollutant residence time or pollutant concentration as core parameters to estimate vulnerability. This work aims to define important considerations regarding the behavior of nitrates (NO3) in a real scenario, to be included in a new integrated vulnerability method. This work has two main objectives: to set up a groundwater model to depict as close as possible the groundwater behavior of the Yucatan karst system, and to introduce a transport model to estimate the behavior of a pollution plume. Model outcomes suggest that pollutants have a short residence time, reaching the coast in the north after 3 years. Well fields are also affected by pollution at variable NO3 concentrations. Results can be further discretized to establish a base and to include these parameters as part of a new integrated groundwater vulnerability approach.

Dolines are important features strongly influencing the outcomes of groundwater vulnerability maps, subsidence risk and land use studies. Their relationship with subsurface features like epikarst, stresses the importance of doline mapping for environmental and hydrological management strategies. Current methodologies to map dolines from elevation models apply morphometric attributes on depressions, including a depth threshold, to filter depressed areas and to define dolines. However, the use of a single threshold tends to overlook dolines located in already depressed areas. In this work a new geographic information systems (GIS)-based methodology is proposed to identify karst depressions within digital elevation models, applying a multidepth threshold approach. The method statistically classifies depression intervals to identify dolines at variable depths. The method was tested in the Yucatan karst, displaying a final accuracy of 63% after testing different parameters. The results are affected by false positives due to the impossibility of verifying by imagery 190 possible dolines in areas of dense vegetation. Nevertheless, out of 655 estimated dolines, 464 match those located by imagery giving sensitivity and precision values of 85% and 71%, respectively. Comparing this methodology against single threshold outcomes, improvement is evident in doline mapping. Notwithstanding, its application and performance with lower and higher resolution elevation models must be investigated.

Karst groundwater vulnerability maps are important tools for the development of groundwater management and protection strategies. However, current methodologies do not always match regional characteristics and parameter adaptations are necessary. In addition, other important processes such as dilution and aquifer residence time are not included in vulnerability analysis for the complications of evaluating two or more criteria simultaneously. The integrated karst aquifer vulnerability approach (IKAV) project aims to develop an integrated approach to include these parameters and estimate global change implications in current and future scenarios. As a first step, intrinsic vulnerability methodologies are studied in order to highlight important parameters and the congruence with regional characteristics of the Yucatan karst. Results demonstrate agreement between methods for the evaluation of high and very high vulnerabilities and their relation with fissures and dolines. Moderate vulnerabilities are assigned to more than 50% of the area. However, moderate vulnerabilities, assigned to the coastal area and the Southern hill, are highly questionable. Intrinsic features affecting moderate classes vary according to the method. Parameter sensitivity analysis and overlap analysis demonstrate the influence of depth to the unsaturated zone, soils, precipitation, and slope on moderate values. Therefore, such parameters must be re-evaluated and discretized according to the characteristics of the study area to match Yucatan regional characteristics.

Abstract. Groundwater vulnerability maps are important decision support tools for water resource protection against pollution and helpful in minimizing environmental damage. However, these tools carry a high subjectivity along the multiple steps taken for the development of such maps. Additionally, the theoretical model on which they are based does not consider other important parameters, such as pollutant concentration or pollutant residence time in a given section of the aquifer, solely focusing on the theoretical travel time of a pollutant particle from a release point towards a target. In this work, an integrated methodology for the evaluation of potential (intrinsic) and actual vulnerability is presented. This integrated method, named Integrated Karst Aquifer Vulnerability (IKAV), was developed after the analysis of several study cases around the world and the application of multiple intrinsic groundwater vulnerability methods in a selected study area. Also, a solute transport model served as the basis to define additional parameters for vulnerability analysis for areas severely affected by anthropogenic practices. However, the focus of the transport model must not be mistaken to be hazards and risk mapping. A defined workflow and several criteria for parameters and attributes selection, rating and weighting, and vulnerability classification are presented here. The first application of the IKAV method was carried out in the Yucatán karst, demonstrating to be a reliable method for vulnerability estimation. Results demonstrated the scope of the IKAV method in highlighting important regional conditions, minimizing the subjectivity, and expanding the analysis of vulnerability.