BIOGEOCHEMICAL CYCLING IN A SALT MARSH ESTUARINE ECOSYSTEM IN COASTAL NORTH CAROLINA

Both climate change and local anthropogenic pressures have impacted biogeochemical cycling in coastal systems. Here we study a coastal ecosystem in North Carolina in order to determine spatial relations, seasonal changes, and overall fluxes of carbon, as well as the influences of these factors on the biogeochemistry of the system as a whole. Partial pressure of carbon dioxide (pCO₂), percent dissolved oxygen (DO%), total dissolved inorganic carbon (DIC), total alkalinity (TA), carbon isotopes of dissolved inorganic carbon, and pH values—amongst additional data—were collected from numerous study locations in the Cape Lookout region of North Carolina in April 2017, October 2017, April 2018, and June 2018. Three creeks flowing into Jarrett Bay depict distinct seasonal trends of varying levels of pCO₂and DO% related to phytoplankton cycles. Most notably, the salt marsh ecosystem surrounding Smyrna Creek causes particularly high pCO₂levels in this creek, peaking at 14606 ppm in the head of the creek in June 2018. However, creeks were occasionally undersaturated in pCO₂, likely from phytoplankton blooms occurring during spring and summer. Carbon flux from these three creeks into Jarrett Bay is evident, as is further flux of pCO₂through the sound and out into the ocean where the pCO₂-saturated estuarine waters combine with the less pCO₂-rich marine waters to produce ocean values of ~625 ppm. TA shows an increasing spatial trend moving through the system with the lowest values (1.109-2.002 mmol/kg) in the creeks and Jarrett Bay, and the highest values (2.320-2.342 mmol/kg) in the ocean. DIC also increases from Jarrett Bay (1739-1774 µmol/kg) to the ocean (1927-1966 µmol/kg); however, the head of Smyrna Creek exhibits notably high DIC values of ~2074 µmol/kg. Similarly, TA increases moving from Smyrna Creek out through the system into the ocean because CO₂does not contribute to TA while HCO₃^-does. The system as a whole is a source of CO₂to the atmosphere with an average air-sea flux of ~35.5 mmol/m²/day.