NEW APPROACHES IN QUANTIFYING LATERAL CARBON FLUXES IN SALT MARSH ENVIRONMENTS

Coastal salt marshes are threatened globally by climate change and urban development. In addition to removing excess nutrients and providing buffer zones from flooding, these vulnerable systems have recently been shown to play a significant role in the global sequestration of carbon (C) and are potentially viable candidates for use in the offset of anthropogenic greenhouse gas (GHG) emissions. Much of the past research on C in salt marshes, however, has not captured temporal dynamics, particularly of GHG fluxes, and has not included comprehensive measurements of sequestration in the context of exchange with the atmosphere and ocean. The lateral (tidal) components of C and GHG budgets are particularly uncertain, and many existing estimates are based on low-frequency sampling. As part of a broader study to construct a C and GHG budget for a set of salt marshes on Cape Cod, Mass., high-frequency time-series chemical and velocity data (across tidal and diel cycles) were measured with optical and acoustic sensors in a salt marsh creek to resolve the lateral flux component of dissolved carbon and gases. Discrete water samples were also collected seasonally over a complete tidal cycle. Using multiple linear-regression, concentrations of dissolved organic and inorganic C were calculated from sensor data, and high-frequency fluxes of these carbon pools were estimated over extended time periods. Here, we demonstrate the value (and challenges) of collecting high-frequency chemical data, and the ability to use these measurements to gain more representative estimates of carbon fluxes from salt marshes. Lateral fluxes were found to be substantial relative to vertical fluxes and longer term sequestration. Current results will be presented to construct a rarely measured full carbon budget.