Effects of Extreme Events on Arsenic Cycling in Salt Marshes.

Extreme events such as storm surges, intense precipitation and supermoons cause anomalous and large fluctuations in water level, which impacts the sediment biogeochemistry that dictates arsenic cycling in tidal salt marshes. In addition to water level changes, which impact soil redox potential, these extreme events may also change salinity due to freshwater inputs from precipitation or saltwater inputs due to surge. It is currently unknown how arsenic mobility will be impacted by extreme events in tidal salt marshes, as fluctuations in salinity and redox potential may act synergistically to mobilize the arsenic in the interstitial pore water. At the St. Jones Reserve in Dover, DE, we monitored pore water and soil samples before, during, and after two extreme events: A supermoon, followed by Hurricane Joaquin-induced storm surge and precipitation. During baseflow conditions, pore water arsenic in the zone of maximum arsenic release was inversely proportional to the redox potential and directly proportional to the electrical conductivity. These relationships were altered during the extreme events, when a distinct pulse of arsenic was observed in the pore water. These results have implications for arsenic mobility in the face of extreme weather variability.