EVALUATING CARBON SEQUESTRATION POTENTIAL OF NATURAL AND RESTORED TIDAL MARSHES IN CHESAPEAKE BAY THROUGH QUANTIFICATION OF METHANE FLUXES AND IDENTIFICATION OF DRIVERS

The production of methane in brackish marshes may offset the carbon sequestered by these wetlands. Brackish tidal marshes are widespread in Chesapeake Bay and there exists a need for understanding the carbon balance of these ecosystems. This thesis presents the results of measurements of methane flux, through static flux chamber experiments, and analysis of marsh porewater to examine biogeochemical and plant-mediated drivers of methane flux in marshes of Chesapeake Bay. In addition, there is growing interest from the scientific and resource management community in how natural marshes cycle carbon and whether restored marshes show biogeochemical similarities. Therefore, I tested my hypotheses in the natural marshes of Monie Bay, part of the Chesapeake Bay National Estuarine Research Reserve – Maryland, and in restored tidal marshes created with dredged sediments at Poplar Island. Methane emissions offset annual carbon storage at Monie Bay and Poplar Island by 0.7 and 2.1 percent, respectively, based on average values of annual fluxes. However, there remains uncertainty in the accuracy of this estimate given the spatial and temporal variability in my observed fluxes, and the limited sampling frequency and spatial extent of my study. Within such uncertainty lays a justification for continued long-term monitoring of methane emissions in restored and natural marshes of Chesapeake Bay to resolve this important marsh management question

Stable isotopic evidence of nitrogen sources and C4 metabolism driving the world’s largest macroalgal green tides in the Yellow Sea

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 17437, doi:10.1038/s41598-018-35309-3.During recent years, rapid seasonal growth of macroalgae covered extensive areas within the Yellow Sea, developing the world’s most spatially extensive “green tide”. The remarkably fast accumulation of macroalgal biomass is the joint result of high nitrogen supplies in Yellow Sea waters, plus ability of the macroalgae to optionally use C4 photosynthetic pathways that facilitate rapid growth. Stable isotopic evidence shows that the high nitrogen supply is derived from anthropogenic sources, conveyed from watersheds via river discharges, and by direct atmospheric deposition. Wastewater and manures supply about half the nitrogen used by the macroalgae, fertiliser and atmospheric deposition each furnish about a quarter of the nitrogen in macroalgae. The massive green tides affecting the Yellow Sea are likely to increase, with significant current and future environmental and human consequences. Addressing these changing trajectories will demand concerted investment in new basic and applied research as the basis for developing management policies.This work was supported by the State Key Project of Research and Development Plan (2016YFC1402106)

Effects of urbanization of coastal watersheds on growth and condition of juvenile alewives in New England

Alosa pseudoharengus (alewife) have declined throughout New England, a factor that may be responsible for such stock reductions is urbanization of watersheds discharging into alewife nursery ponds. We found that young of the year (YOY) alewife length, weight, condition factor, and growth rate decreased in relation to increased urban land covers on watersheds of nine Massachusetts and Maine ponds. The watersheds ranged 3–60% urbanized land cover. YOY δ15N increased significantly in proportion to urbanized land cover on watersheds, suggesting a concrete link between watershed land covers and YOY alewife metrics, in agreement with previous knowledge that N discharges from more urbanized watersheds bear higher δ15N. The New England results confirmed results across a wide latitudinal gradient that suggested that size of YOY alewife decreased as urban land cover on watersheds increased. The dominant influence of urban land cover in the YOY is highlighted, however, in that YOY alewife from ponds with the highest percent urban cover reached δ15N as high as those in adult spawners migrating from the ocean, that feed at higher trophic levels.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author