Proposal Defense: Bryce Van Dam

Estuaries are important biogeochemical transition zones between terrestrial and marine systems. Nutrients supplied externally or recycled internally help to drive these systems to become highly productive, removing CO2 from the atmos-phere. At the same time, estuaries may also receive large allochthonous organic matter loads, driving high rates of remineralization, causing the system to func-tion as a net CO2 source to the atmosphere. This balance between nutrient-driven production and decomposition largely determines the direction of CO2 exchange into or out of estuaries. To improve our understanding of the role of estuaries in the context of the global C cycle, it is imperative to first constrain the environmental controls (both internal and external) that regulate C transport and processing within estuaries. This is the primary goal of the proposed re-search. Recently developed techniques are used to assess CO2 fluxes, and their environmental drivers in two neighboring, NC estuaries, the New and Neuse Riv-er Estuaries. Preliminary data show these estuaries to be small CO2 sources to the atmosphere, well below the global average. The passing of a large storm sys-tem during the Fall of 2015 was documented, and was found to drive strong CO2 degassing, increasing annual fluxes by 45-210%. Despite annualized CO2 fluxes always being positive, the New River Estuary was found to be net autotrophic, indicating thatCO2 released from the estuary may have been generated upstream. This finding served as the motivation for a project investigating net ecosystem metabolism in the tidal-fresh portion of the New river. A third project investigating the potential for C limitation in the hypereutrophic Lake Taihu, China is also proposed. Collectively, the proposed studies seek to advance our understanding of how coastal systems act as both conduits and reactors for C as it travels along the freshwater-marine continuum.