SPATIAL HETEROGENEITY OF ORGANIC AND INORGANIC CARBON FROM SURFACE WATERS ON EOGENETIC CARBONATE ISLANDS—SAN SALVADOR ISLAND, BAHAMAS

Water rock interactions and the transport of dissolved organic carbon are fundamental to the development of karst features common to the eogenetic karst landscapes of the Bahamas. This study presents the results from surface water samples collected from 10 sites on San Salvador Island, Bahamas (Church, Inkwell, and Watlings Bluehole; Reckley, Flamingo, Southside, and unnamed ponds; Crescent, Little, and Clear Lakes). The surface water ranged from nearly fresh to hypersaline. The site location on the island is not an indicator of the water composition; adjacent lakes have well known differences based upon connection to the ocean. The addition of this data builds on the current information available for surface water chemistry on San Salvador.

Samples were collected over a three-day period in January 2016. In this abstract, we consider measurements of non-purgeable organic carbon (NPOC), dissolved inorganic carbon (DIC), specific ultraviolet absorbance (SUVA), and the stable isotopes of carbon (d¹³C). DIC concentrations ranged from 3.4–5.1 mM/L. Values of d¹³C were largely depleted in the heavier isotopes (min = -10.3‰), except for Little Lake with a positive d¹³C of +1.3‰. Respiration of organic matter likely influences the water chemistry at all sites. For example, excluding Inkwell and the unnamed ponds, d¹³C is inversely proportional to DIC; organic respiration leads to additional DIC. Additionally, NPOC ranged from 1.8–5.0 mM/L and is directly correlated to DIC; waters with greater concentrations of organic carbon undergo enhanced respiration. This is supported by an inverse relationship between NPOC and d¹³C. SUVA values ranged from 0.1–1.3 and is directly proportional to NPOC; surface waters with more concentrated organic carbon are less degraded and thus closer to their source. Finally, an inverse relationship between d¹³C and SUVA suggests that waters with more concentrated and ‘fresher’ organic matter are experiencing the greatest rates of respiration.