Biological implications of sulfide in intermittent estuaries

Céline Pallud, Berkeley University | 8 mars 2018

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Intermittent estuaries are coastal environments characterized by the partial closure of the estuary’s mouth with a sandbar barrier, which separates the estuary from the ocean for extended periods. In recent decades, fish mortalities have been observed in intermittent estuaries around the world, usually associated with the transition from closed to open state. This transition often leads to extensive physical and chemical changes in the estuarine conditions, as water mixing and sediment resuspension are increased, which could result in the oxidation of sediment acid-volatile sulfides (AVS). The oxidative effects of sediment AVS, specifically oxygen depletion, acidification, and metal release, are believed to aggravate water conditions for fish but remain poorly understood. I will present a combination of laboratory experiments and field-scale observations to investigate spatial and temporal variation in sulfur geochemical cycling in the Pescadero Estuary (CA), where fish kills have been observed almost annually for the past two decades. We showed that sulfide was involved in worsening water quality for fish, both directly, as aqueous hydrogen sulfide concentrations were significantly higher than the recommended thresholds for aquatic life, and indirectly, through the oxidation of sediment AVS, which chemically deplete, contaminate, and acidify the water column.