BASELINE PHYSICOCHEMICAL INVESTIGATIONS ON WATERS FROM THREE BLUE HOLES, SAN SALVADOR ISLAND, BAHAMAS

Measuring the physical and geochemical parameters in the water column of blue holes has the potential to help our understanding of various hydrological issues and geochemical processes occurring between the water-rock interfaces. Physicochemical parameters have been studied in the water column of Inkwell, Church, and Watling’s Blue Holes (San Salvador Island, Bahamas). Water samples were collected from multiple depths at the three blue holes to identify physical and chemical parameters. The values were compared to the average ocean concentrations in order to assess how the freshwater versus saline groundwater responses to evaporation, tidal influences, freshwater input, and bacterial activity.

The salinity concentrations vary at the surface of each blue hole until ~ 4 m where the concentrations reach similar values (19.6 ± 1.6 ‰). The mixing zones of Inkwell and Watling’s can be identified by changes in the parameter values. The degree of variation is a result of the different water-rock interactions that are occurring at each location. Inkwell is influenced by tidal pumping, identified by the large range in values, notably salinity (1.01 to 21.8‰) and total hardness (9 to 293 mg/L). This location is the only site that has a true halocline. Watlings’s geochemical parameters vary the least (i.e. salinity 30.19 – 34.30 ‰), but the irregular and continual changing of values identifies this site as having direct conduit connection to the ocean. Church Blue Hole has a slight decrease in salinity from the surface (21.47 ‰) to ~ 1 m (17.78 ‰) likely a result of seasonality and evaporation. Lack of significant geochemical changes within the water column suggests narrow conduits or matrix flow. The high sulfate values ranging between 2634 – 4009 mg/L are characteristic of seawater values (> 2,700 mg/L). Therefore, seawater seepage is the probable cause for the elevated sulfate levels. The sulfate-rich seawater also supplies nutrients beneficial to bacteria that decrease the physiochemical gradient influencing the shape and visibility within the blue hole. While, salinity is the first parameter evaluated, identification of the water-rock interactions are accomplished by evaluating patterns and values of other geochemical parameters.