Estuarine and riverine sediments are naturally resuspended and mobilized by wind, waves, and water currents. In typically shallow estuaries and coastal waters, sediment-water interactions can significantly impact a variety of important biogeochemical processes such as trace metal mobilization, nutrient and organic matter cycling, and release of anthropogenic contaminants. While earlier studies have demonstrated the importance of dark release from resuspended estuarine sediments, they have not addressed the potentially more significant role that photochemical transformations play in the mobilization of organic matter and metals from these sediments.
Scientists from the University of North Carolina, Wilmington plan to carry out a series of field and laboratory experiments to examine the mechanisms of phototransformations and the impacts they have on the mobilization of organic nitrogen, organic carbon, copper (Cu), and lead (Pb) from resuspended sediments in two organic-rich coastal plain estuaries, one of which is impacted by anthropogenic activities. Specifically, the study plans to address the following questions: (1) How much dissolved organic nitrogen (DON), dissolved organic carbon (DOC), Cu, and Pb are produced upon photolysis of resuspended estuarine sediments and how do the photochemical fluxes vary seasonally and by location?; (2) What is the bioavailability of the DON and DOC produced and how does that vary by season and location?; (3) How is the photoreactivity of resuspended sediments impacted by the inorganic and organic composition of the source material and irradiation wavelength?; and (4) How do fluxes of DON, DOC, Cu, and Pb change as the dominant organic matter remineralization processes (sulfate reduction vs. methanogenesis) in the resuspended material change?. Results from this research addresses fundamentally important and globally significant questions because it considers how fluxes of organics and metals respond during changes in salinity, such as those that could occur in rising sea levels. In addition, the work would provide information regarding the role of light-induced reactions on the distributions and speciation of organic nitrogen, organic carbon, and trace metals in estuarine systems.
Educational impacts associated with this project include support and training for a postdoc, as well as graduate, undergraduate, and high school students. In addition, it is anticipated that a high school teacher would participate in the study during the summer months.
