Hydrogeochemistry of Coastal Karst Aquifers

Coastal karst aquifers form dynamic interfaces where fresh groundwater lenses overlie denser saline water within soluble carbonate rock. The hydrogeochemistry of these systems is controlled by the interplay of tidal forcing, sea-level fluctuations, episodic precipitation and anthropogenic influences. A sharp salinity gradient, or halocline, separates fresh and marine water, and its vertical and lateral migration drives mixing and reactive transport. Flow occurs both through high-velocity conduits and slow diffuse permeation of the rock matrix, creating spatially variable residence times that influence mineral dissolution, precipitation and redox reactions. Submarine groundwater discharge exports solutes and nutrients to coastal waters, shaping nearshore biogeochemistry and ecosystem health. Organic carbon turnover, methane cycling and oxygen dynamics in subterranean estuaries respond rapidly to hydrological events, including storms, which may induce episodic oxygenation and long-lasting shifts in carbon processing. Recent advances in hydroacoustic imaging, isotopic fingerprinting, geochemical modelling and in situ sensor networks have elucidated the mechanisms underpinning salinisation, contaminant transport and carbonate mineral transformations. A comprehensive understanding of these processes is essential for sustainable water management, protection of coastal ecosystems and forecasting the impacts of sea-level rise and climate variability.

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Hydrogeochemistry of Coastal Karst Aquifers publication trend

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Technical terms

Halocline: A subsurface boundary marked by a rapid change in salinity between fresher meteoric water and denser saline groundwater.

Submarine groundwater discharge: The flow of groundwater from coastal aquifers directly into the marine environment, transporting dissolved constituents and nutrients.

Karst subterranean estuary: The mixing zone in coastal karst aquifers where freshwater and seawater interact within conduits and the porous rock matrix.

Conduit flow: Rapid groundwater movement through large solutional channels or caves within karst systems.

Diffuse flow: Slow percolation of groundwater through fractures and pore spaces in the rock matrix of karst aquifers.

References

1. Hydroacoustic Observations Reveal Drivers of Mixing and Salinization of a Karst Subterranean Estuary During Intense Precipitation. Geophysical Research Letters (2024).
2. Oxygenation of a karst subterranean estuary during a tropical cyclone: mechanisms and implications for the carbon cycle. Limnology and Oceanography (2022).
3. First insights into an exceptionally deep blue hole in the Western Caribbean: The Taam ja’ Blue Hole. Frontiers in Marine Science (2023).