Regional Hydrogeochemical Evolution of Groundwater in the Ring of Cenotes, Yucatán (Mexico): An Inverse Modelling Approach

Evaluating spatiotemporal groundwater quality changes in the Rhodope coastal aquifer system (NE Greece) employing a GIS-assisted hybrid approach of multivariate statistics and inverse geochemical modeling

This research employs a GIS-assisted approach of multivariate statistics and inverse geochemical modeling to unravel the processes driving groundwater salinization in a complex aquifer system. Multivariate statistical methods define the end-member water groups, identifying dominant processes explaining hydrogeochemical variance in wet and dry season water chemistry datasets. Mineral saturation indices (SIs) and inverse geochemical modeling (IGM) investigate potential geochemical reactions and mixing processes responsible for the observed groundwater compositions and their spatiotemporal evolution along reversed flow paths caused by overexploitation in the Rhodope aquifer system. Results reveal that a concise set of reactant and product phases, including CO2(g), H2O, calcite, gypsum, halite, celestite, plagioclase, K-feldspar, illite, and Ca-montmorillonite, along with ion exchange processes (CaX2, MgX2, and NaX), explains the hydrogeochemical evolution of groundwater along reversed flow paths between genetically and compositionally different surface and groundwater bodies. Systematic changes in water chemistry along the flow paths are attributed to mixing of surface waters and/or different groundwater end-members, dilution by a freshwater component, water-rock interaction (WRI) processes, and ion exchange involving Ca/Mg- and/or Na-clays. The chemical evolution represented by IGMs initiates with the mixing of Aegean seawater and Aspropotamos River, incorporating WRI and ion exchange processes (Mg- and Na-clays) to produce the water chemistry of Vistonida Lake, the only surface water body with hydraulic interaction with the groundwater system in the study area. Statistically-defined end-member water groups effectively explain the groundwater flow system and evolutionary processes between hydraulically connected surface and groundwater bodies. Overall, the fusion of multivariate statistical analysis (MVSA), inverse geochemical modeling (IGM), and GIS techniques proves potent and comprehensive, enhancing understanding of groundwater dynamics, improving prediction accuracy, aiding proficient management, and facilitating data-driven decision-making within the realm of groundwater assessment and management.

Diversity and Bioprospection of Gram-positive Bacteria Derived from a Mayan Sinkhole

Water-filled sinkholes known locally as cenotes, found on the Yucatán Peninsula, have remarkable biodiversity. The primary objective of this study was to explore the biotechnological potential of Gram-positive cultivable bacteria obtained from sediment samples collected at the coastal cenote Pol-Ac in Yucatán, Mexico. Specifically, the investigation aimed to assess production of hydrolytic enzymes and antimicrobial compounds. 16 S rRNA gene sequencing led to the identification of 49 Gram-positive bacterial isolates belonging to the phyla Bacillota (n = 29) and Actinomycetota (n = 20) divided into the common genera Bacillus and Streptomyces, as well as the genera Virgibacillus, Halobacillus, Metabacillus, Solibacillus, Neobacillus, Rossellomorea, Nocardiopsis and Corynebacterium. With growth at 55ºC, 21 of the 49 strains were classified as moderately thermotolerant. All strains were classified as halotolerant and 24 were dependent on marine water for growth. Screening for six extracellular hydrolytic enzymes revealed gelatinase, amylase, lipase, cellulase, protease and chitinase activities in 93.9%, 67.3%, 63.3%, 59.2%, 59.2% and 38.8%, of isolated strains, respectively. The genes for polyketide synthases type I, were detected in 24 of the strains. Of 18 strains that achieved > 25% inhibition of growth in the bacterial pathogen Staphylococcus aureus ATCC 6538, 4 also inhibited growth in Escherichia coli ATCC 35,218. Isolates Streptomyces sp. NCA_378 and Bacillus sp. NCA_374 demonstrated 50-75% growth inhibition against at least one of the two pathogens tested, along with significant enzymatic activity across all six extracellular enzymes. This is the first comprehensive report on the biotechnological potential of Gram-positive bacteria isolated from sediments in the cenotes of the Yucatán Peninsula.

Identification of Natural and Anthropogenic Geochemical Processes Determining the Groundwater Quality in Port del Comte High Mountain Karst Aquifer (SE, Pyrenees)

The Port del Comte Massif (SE, Pyrenees) contains one of the most important vulnerable and strategic karst aquifers for supplying freshwater to the city of Barcelona (Spain). It is a fragile system, whose possible environmental impact is highly conditioned by land use. To improve the hydrogeological knowledge of the system, between September 2013 and October 2015, a detailed fieldwork was carried out for the revision of the geological model, the inventory of water points, and the in situ physico-chemical characterization on major elements and isotopes of up to a total of 43 springs, as well as precipitation water. This paper focuses on the characterization of the geochemical processes that allow explanation of the observed chemical variability of groundwater drained by the pristine aquifer system to determine the origin of salinity. The results show that the main process is the dissolution of calcite and dolomite, followed by gypsum and halite, and a minor cation exchange-like process. Sulfur and oxygen isotopes from dissolved sulfate in the studied springs point out a geogenic origin related to the dissolution of gypsum from Triassic and Tertiary materials, and that the contribution from anthropogenic sources, like fertilizers, is lower. Nitrate in groundwater is not an important issue, with a few localized cases related with agricultural activities. The multidisciplinary approach has allowed the development of a consistent hydrogeological conceptual model of the functioning of the aquifer system, which can be replicated in other places to understand the geogenic character of the hydrogeochemistry.