Date of this Version
Schoepfer, Valerie A. 2013. The influence of sea-water inundation on coupled iron and sulfur cycling in a coastal freshwater wetland. MS thesis, University of Nebraska-Lincoln.
Coastal freshwater wetland chemistry is rapidly changing due to increased frequency of saltwater inundation, a consequence of global change. Seasonal salt water inundation introduces sulfate, which biologically reduces to sulfide via microbial metabolism. Sulfide binds with reduced iron producing iron sulfide (FeS), recognizable in wetland soils by its characteristic black color. The objective of this study is to document rates of iron and sulfate reduction, as well as product formation (acid volatile and chromium reducible sulfide, AVS and CRS) in a coastal freshwater wetland undergoing seasonal salt water inundation. Understanding iron and sulfur cycling, as well as their reduction products allow for calculation of the Degree of Sulfidization (DOS), from which we can estimate how long iron in the sediment will buffer against chemical effects of sea level rise. Soil chloride predicted iron and sulfate reduction rates as it is a direct indicator of inundation extent. Correlations between soil chloride and both reduction rates were stronger at the surface (0-3 cm), indicative of surface water inundation, rather than groundwater intrusion. AVS correlated strongly to soil moisture, however CRS was strongly correlated to soil chloride. For the tidal freshwater TOWeR wetland, the current DOS is very low, which is a result of the high iron content of the Ultisol soils. However with time and continuous inundation, iron will bind to incoming sulfide, creating FeS and DOS will increase. With current conditions, it will take approximately 175 years for the wetland to become sulfidic, and begin to transition to a saltwater marsh.
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