Beyond the Blue: C:N:P relationships across tidal and seasonal time-scales within a salt-marsh estuary

Marsh-estuarine systems serve as an essential biogeochemical link between freshwater/terrestrial ecosystems and the marine biosphere. Within an estuary system, the relative inventories of carbon (C), nitrogen (N), and phosphorus (P) are significantly influenced through a variety of biotic and chemical transformations. While open ocean patterns of C, N, and P are relatively well studied, fewer efforts have been directed towards the dynamic estuary environment, despite the use of elemental stoichiometry in monitoring water quality and ecosystem function. Samples were collected over complete tidal cycles (24-hr diurnal period every 2 hrs) over the course of a seasonal cycle (effort conducted twice per environmental season) for inorganic and organic C, N, and P concentrations in particulate and dissolved material. This study was conducted within North Inlet, SC (NI), a well-studied site within the National Estuarine Research Reserve System (NERRS). NI is considered to be in relatively pristine ecosystem condition, providing assessment without complicating anthropogenic influences. NI also experiences significant turnover over a tidal cycle (55% volume; 3,300 hectares), which allowed for sampling at a single monitoring station to observe the transition of distinct signals from the salt marsh and the coastal ocean. To investigate potential mechanisms which shape observed C:N:P variability, bulk signatures of particulate 13C and isolated (via electrodialysis/reverse osmosis) dissolved organic material 13C and 15N are compared.