Pescadero Estuary is an extensive marshland and intermittent estuary located south of San Francisco, California. It is characterized by the annual formation of a sandbar at the estuary's mouth, separating it from the Pacific Ocean for 3-10 months per year. The watershed has experienced fish kill events since 1995, occurring with the annual breaching of the sandbar closure and these events have been more regular in Pescadero than in other nearby California estuaries. As these mortality events are likely an environmental issue relating to poor water quality, the specific reasons for the fish kills are not known. Kills could result from a high concentration of toxic hydrogen sulfide (H2S), low dissolved oxygen, low pH, salinity and temperature stratifications, or a combination of these factors in conjunction with Pescadero's unique physical dynamics. Understanding and quantifying the biogeochemical mechanisms and kinetics of sulfur cycling, specifically sulfate (SO42-) reduction and hydrogen sulfide oxidation, is crucial to determine causal reasons for fish kills at Pescadero.We will combine (i) laboratory-based quantification of biogeochemical reaction rates in sediments; (ii) in situ and laboratory physical and biogeochemical characterization of the sediments, porewater, and overlying water; and (iii) biogeochemical characterization of sediment accumulating in fish gills and mouth. The kinetics and potential reaction rates of sulfate reduction and sulfide oxidation will be measured on undisturbed sediment cores using flow-through reactors, thus obtaining kinetic parameters whose values are representative of initial in situ conditions. We are searching for simplified descriptions of estuarine conditions at Pescadero that can be used predictively in the management of this system, and more generally, other small California coastal estuaries. Furthermore, in using fundamental and innovative techniques, this research will enhance and influence our scientific, technological, and ecological understanding of complex soil and aquatic environments.

Sulfur redox processes in littoral sediments of the intermittent Pescadero Estuary

248th National Meeting (2014)

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