THE PORE WATER CHEMISTRY, MICROBIAL PROCESSES, AND TRACE METAL MOBILITY OF BIOLUMINESCENT BAYS

This research considers three bioluminescent bays on the island of Vieques, Puerto Rico, where spectacular nighttime displays are produced by the dinoflagellate Pyrodinium bahamense var. bahamense. Concentrations of these dinoflagellates and thus the extent of bioluminescence vary greatly among the three bays. Puerto Mosquito exhibits particularly strong bioluminescence, while the other two bays, Bahia Tapon and Puerto Ferro, exhibit the phenomenon to lesser degrees. The population of dinoflagellates may be controlled by environmental parameters including nutrient and metal cycling, both of which are in turn controlled by microbial processes in the sediment column. This study examines the sediment composition and pore water chemistry in the three bays to better understand the microbial processes, nutrient cycling and possible metal release in these ecosystems.

Puerto Mosquito has lower δ13C(CaCO3) and higher %N and total organic carbon content in fine fraction (<63μm) sediments than the other two bays, suggesting higher concentrations of organic matter consistent with higher dinoflagellate concentrations. Pore water profiles from deep bay cores indicate decreasing sulfate and increasing dissolved inorganic carbon (DIC, an approximation of acid neutralizing capacity) with depth, as predicted by progressive sulfate reduction. Shallower cores, however, show low sulfate and high DIC concentrations near the sediment-water interface with flat profiles of sulfate comparable to seawater concentrations and slightly elevated DIC concentrations at depth. This can be explained by particularly active sulfate reduction near the sediment-water interface and possible sulfate oxidation at depth that would not show changing concentrations despite ongoing sulfate reduction. Preliminary measurements of protein concentrations, a rough proxy for microbial populations, indicate the highest levels of microbial activity near the sediment-water interface, consistent with microbial catalysis of high sulfate reduction in these intervals. Ongoing analysis of pore water trace metal concentrations will investigate other microbially-controlled redox systems, including iron and manganese reduction, to aid in determining nutrient availability and uptake.