Sea‐level rise should cause salt‐water intrusion into coastal aquifers and limit fresh submarine groundwater discharge. Pargos Spring offshore of Puerto Morelos, Quintana Roo, Mexico, intermittently discharges brackish water and allows intrusion of lagoon water with seawater salinity to the aquifer. Lagoon water intrusion occurred when sea level was > 0.08 m above mean observed values during the study period. Salt water intrusion will be permanent within a few decades at the current eustatic sea‐level rise rate of ∼ 3 mm/yr. A mixing model demonstrates that oxygen dissolved in the lagoon water is reduced as it intrudes the spring. Dissolved oxygen (DO) reduction is greater at the spring vent than at sensors ∼ 10 m inside the conduit, reflecting rapid reaction kinetics. DO reduction results from organic carbon remineralization, which also releases N and P to the water. Increased frequency of intrusion events or continuous intrusion may alter microbially mediated biogeochemical reactions, thereby increasing aquifer vulnerability to sea‐level rise.

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The Cedar Key Marina is inundated by rapid sediment accumulation due to its orientation in relation to along shore sediment transport and other littoral processes. This results in a significant cost to the city to perform dredging operations to maintain marina navigability. This report reviews potential dredge methods and several options for spoils placement. It also proposes solutions to increase the marinas dredge life, or the time between dredges, through technology and marina redesign. A combination of these options are shown to create a more sustainable sedimentation cycle, which in the long term may have positive impacts on the Cedar Key economy, livelihood, and lifestyle.