EVAPORITE DEPOSITIONAL SYSTEMS ECOLOGY: MICROBIOLOGICAL, MINERALOGICAL AND GEOCHEMISTRY CONSTRAINTS

Classical definitions state that evaporite depositional environments contain water-soluble mineral sediments that result from evaporation of surface waters. The definition implies that there is no variation between depositional sites, that the surrounding geology, groundwater chemistry and relation of microorganisms and the minerals has no impact on hypersaline deposits. In our studies of modern evaporites each basin has a unique geochemical and microbial signature and that there can be variation within the larger basins. For example, hypersaline waters containing elevated levels of Ca with an acidic pH do not precipitate significant calcium carbonate deposits, but can have microscopically detectable quantities associated with microbial activities including biofilm formation. Gypsum can be found in a wide variety of hypersaline waters and the mineral is an S resource for some halophilic and sulfate reducing species. Some microorganisms, based on observations with environmental scanning electron microscopy, appear to use the mineral as an attachment site and can “excavate” cavities in a manner similar to some invertebrates. These and other adaptions to the microenvironment are key to understanding microbial and geochemical interactions. The variations within larger basins, such as the Dead Sea, can yield additional information. For example, water is currently diverted to the southern basin for commercial mineral extraction. The process alters the overall water chemistry as the three most common elements identified in the main body are Mg, Ca, Na while in the southern basin the elements are K, Mg, Na. The resulting mineral gradient influences the microbial activity associated with the sediments and water. A better understanding of these dynamic interactive systems could lead to better management practices of such heavily impacted natural resources. We will discuss our research findings, including information on the microbial ecology of two evaporite environments, Storrs Lake, San Salvador Island, Bahamas and the Dead Sea, Israel.