Sea Level Rise Impacts on the Biogeochemistry of the Coastal Critical Zone: Characterization of Dissolved Organic Matter

Sea level rise (SLR) is altering coastal areas, initiating negative impacts on coastal ecosystems. Damage from saltwater intrusion results in lower crop yields, and coastal forests are being converted to "ghost forests." These alterations change the processing and export of dissolved organic matter (DOM) from terrestrial to coastal environments. Resulting variations to coastal hydrology occur through fast (e.g., intense storms) and slow (e.g., SLR) processes, and aquatic DOM composition may be transformed in a way that influences other important biogeochemical processes (e.g., nutrient cycling, redox speciation). These changes in DOM composition can alter how it is utilized by microorganisms, which may in turn affect the cycling of carbon. For this study, we analyzed DOM collected from paired agricultural and forested sites on the Chesapeake Bay, Delaware Bay, and Atlantic Ocean at the bulk and molecular level during storm events and a perigean spring tide in summer 2022. Preliminary data shows that forested sites generally have higher concentrations of chromophoric carbon than agricultural sites as quantified by specific UV absorbance at 254 nm (SUVA254). Additionally, DOM concentration tracks inversely with tidal cycles suggesting inputs of low DOM coastal waters. In future work, we will continue to analyze DOM to determine how the amount and its composition respond to fast and slow hydrologic processes.