Links between pore system evolution, lake genesis and limnological characteristics: Evidence from basin morphology, specific conductivity and lake level variability on San Salvador Island, Bahamas

Lake-aquifer connectivity in coastal carbonate platforms is governed by diagenetic and depositional processes which influence basin morphology. Because coastal aquifers are known to have tidally controlled water levels, tidal fluctuations in lakes may be used to expand areal measurements of permeability and establish a link between regional-scale connectivity and lake genesis. To evaluate the link between basin connectivity and genesis, we compared time series of water level fluctuations collected at high temporal resolution in the ocean and 24 lakes and ponds on San Salvador Island, Bahamas. By treating each lake as a well with a very large footprint, we calculated apparent hydraulic diffusivity and aquifer permeability of the rocks surrounding each lake to relative and regional-scale connectivity of lakes to the ocean. We paired apparent permeabilities (10^−14.4 to 10^−9.8 m²) with observations of basin morphologies derived from light detection and ranging (LIDAR) to identify five distinct lake types that reflect varying degrees of diagenesis of rocks separating lakes from the ocean: (1) Back beach flood basins formed due of sedimentation and sea-level rise. Back beach flood basins that formed during the Holocene have the lowest apparent permeabilities (10^−14.4 m²). (2) Cutoff lagoons, which sediments connect offshore cays, and plug tidal inlets resulting in isolated lakes. Cutoff lagoons which formed during the Holocene also have low apparent permeabilities (10^−13.9 to 10^−12.8 m²). (3) Dune swale lakes formed when rising sea-levels flooded topography created by previous sea-level highstands and have apparent permeabilities of 10^−12.5 m². Dune swale lakes have (4) karst lakes, which form when caves or touching vugs link lakebeds to the ocean have the highest apparent permeabilities of 10^−9.8 m². (5) Overflow ponds, which receive water when high tides, cause neighbouring karst lakes to spill over a topographic divide. For lakes which do not exhibit any aquifer/ocean connectivity, we suggest low permeability exposure surfaces lining the lakebed drive hydraulic isolation.