Groundwater chemistry and Sr isotope ratios shed light on connectivity and water-rock interactions in the coastal aquifer of the Caribbean coast, Mexico.

Radiogenic strontium isotopic ratios (87Sr/86Sr) and solute concentrations in groundwater samples from the coastal area of the eastern Yucatán Peninsula, Quintana Roo, Mexico were measured to assess connectivity and water-rock interactions within different groundwater systems in the region. The average 87Sr/86Sr ratios vary from south to north with values in Xcalak around 0.70889, Sian Ka'an around 0.70847 and at Cancun and Puerto Morelos around 0.70880. The values show 3 clusters suggesting 3 distinct groundwater systems, Cancun-Puerto Morelos in the north, Tulum-Sian Ka'an in the center and Xcalak in the South. Water-rock interactions, while unique within each aquifer system, encompass processes observed throughout the Yucatan karst system including dissolution of evaporites, precipitation of carbonate, sulfate reduction and mixing with seawater. This study highlights the use of groundwater chemistry of understanding groundwater connectivity and the importance of potential distal anthropogenic impacts on groundwater quality and related effect on coastal population and ecosystems. • Interactions with aquifer rocks and mixing with present day seawater impact groundwater 87Sr/86Sr ratios in Quintana Roo. • Four processes co-occur: evaporites dissolution, carbonate precipitation, sulfate reduction and mixing. • Three distinct groundwater systems identified based on 87Sr/86Sr signatures, Cancun-Puerto Morelos, Sian Ka'an and Xcalak. • Chemical data shed light on the degree of groundwater connectivity on coastal ecosystems of Mexican Caribbean. [ABSTRACT FROM AUTHOR]