Benthic Primary Production in a Saltmarsh Pond: Insights from Fluxes of Dissolved Inorganic Carbon and Oxygen

Abstract:

Salt marshes are important carbon sinks that exist at continental margins and act as mediators in the exchange of nutrients and carbon between terrestrial and marine environments. Within salt marshes, 10-20% of total surface area is covered by marshtop ponds. The fractional area of marshtop ponds is predicted to increase as sea level rises. Despite their potential importance, the balance between autotrophic and heterotrophic processes within such ponds remain poorly understood. To quantify the balance of metabolic fluxes within salt marsh ponds, chemical fluxes of dissolved inorganic carbon (DIC) and dissolved oxygen (DO) were measured in July, 2014 in benthic flux chambers inserted into a salt marsh pond in the Plum Island Estuary Long-Term Ecosystem Research (PIE-LTER) site. Light and dark chambers were used to enable separation of rates of photosynthesis and respiration. Separate chambers were used to enclose sediment covered by primarily benthic microalgae and primarily benthic macroalgae. Net ecosystem metabolism in the microalgae was ~10 and in the macroalgae ~15 mmol C/m²/hour. Respiration rates were ~10 mmol C/m²/ hour for both microalgae and macroalgae. The resulting fluxes of net ecosystem production in the ponds will be compared with overall marsh net ecosystem flux as measured by an eddy flux tower that was located 100 meters from the pond. Additionally, concurrent measurements of DIC and DO allow quantification of the C:O ratio during respiration (i.e. respiratory quotient) in this system.