Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Mark J Brush
Among the most valuable natural ecosystems, estuaries and marshes are areas of high productivity, have high economic value, and provide numerous ecosystem services. However, there is still uncertainty in marsh and estuarine carbon budgets and in our overall understanding of the drivers, composition, and fluxes of organic matter in these habitats. Part of this uncertainty is due to high spatial and temporal variability within these habitats and the range of methods used in previous studies. While the number of studies is increasing, there are still large gaps in our knowledge of marsh-estuarine interface dynamics. This study examined the concentrations, fluxes, and composition of particulate and dissolved organic carbon (POC, DOC) and dissolved inorganic carbon (DIC), with a focus on the temporal patterns and drivers of carbon pools at the marsh-estuarine interface. Taskinas Creek, a Chesapeake Bay National Estuarine Research Reserve, was chosen for this study as it provides a near-pristine location to measure current baseline data and is equipped with long-term water quality and meteorological monitoring stations that provided valuable ancillary data. Water samples were collected from Taskinas Creek from 2013 to 2018 to measure POC, DOC, and DIC concentrations, stable isotopes of carbon and nitrogen, colored dissolved organic matter (CDOM), and lipid biomarker compounds. Linear mixed effects (LME) modeling identified that the total suspended sediments were the primary driver of POC concentrations and marsh sources were the primary drivers of both DOC and DIC. Measured carbon concentrations were then used calculate carbon fluxes based on parameters measured via continuous water quality monitoring at Taskinas Creek, allowing for a high-frequency, long-term carbon flux record. On an annual basis, the marsh acted as a source of carbon to the York River (53 g C m-2 y-1) but the fluxes of the different pools of carbon differed in direction and magnitude. On a net basis, the York River was a source organic matter to the marsh (58 to 77 g POC m-2 yr-1 and 3.9 to 18 g DOC m-2 yr-1) whereas DIC was exported from the marsh (114 to 193 g DIC m-2 yr-1). Stable isotopes, lipid biomarkers, and CDOM were used to determine the primary sources of organic matter at Taskinas Creek. Lipid biomarker and stable isotope analyses revealed that POC was primarily derived from algal sources, likely originating from the adjacent York River. In contrast, CDOM spectral measurements and stable isotopes of DOC and DIC indicated that dissolved carbon was primarily marsh-derived, and CDOM was primarily composed of humic-like and fulvic-like compounds. These results agree with previous studies conducted in similar habitats and within the York River estuary. The import of labile POC into the marsh and the export of DOC, DIC, and CDOM to the estuary can have important consequences for marsh and estuarine food webs, marsh surface stability, and the overall biogeochemistry of these habitats. The results found in this study can be used to improve carbon budget models by not only providing current baseline carbon concentrations, but also the primary drivers and sources of these carbon pools. As these drivers and sources may face changes in times of future anthropogenic and climate change, understanding how they affect carbon pools can enable better predictions of how these carbon pools will change in the future.
© The Author
Knobloch, Amanda, "Fluxes, drivers, and composition of carbon exchanged at the Taskinas Creek, VA coastal marsh creek-estuarine interface" (2019). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1582642587.