Seasonal cycling of sulfur and iron in porewaters of a Delaware salt marsh

Abstract

An extensive porewater data set has been gathered in the Great Marsh, Delaware over various seasons, salinities and tides. The data all point to a complimentary redox cycle for sulfur and iron which operates seasonally and tidally. Surface oxidizing conditions prevail in summer; more reducing conditions prevail at depth during the winter. During the spring tides which flood the marsh, pyrite oxidation occurs, releasing excess dissolved iron(II) and sulfate to the porewaters, and precipitating authigenic solid iron phases. The redox conditions in the porewaters of the upper zone during the summer are poised between mildly oxidizing and mildly reducing conditions as shown by p E calculations. This redox environment and the intermediate iron-sulfur redox species may be important for the stimulation of plant growth (photosynthesis) and for the sustenance of a viable microbial community (heterotrophy and chemoautrophy).