Resolving Carbon Contributions in a Mangrove Estuary

Abstract

The global carbon cycle describes the flux of carbon between the atmosphere, terrestrial biosphere, and hydrosphere. Of this, the movement and storage of carbon dioxide is of great interest with the rapid changing of the climate. Mangrove forests act as a sink by removing CO2 at a rate higher than other forests. Carbon becomes trapped in sediments, where it can be exported into aquatic estuarine environments. The aim of this study was to determine whether or not tidal pumping was a significant driver of carbon movement in an attempt to help a larger study quantify the flux of carbon flow along a mangrove lined estuary in Florida Everglades National Park. This site is located in the largest protected mangrove forest in the northern hemisphere. To accomplish this, we used the naturally occurring geochemical tracers radon and radium, and discrete measurements of dissolved inorganic carbon (DIC). Isotopic equilibrium values of Rn and Ra produced by the sediments were initially established to compare in situ measurements with. Multiple measurements of these isotopes in pore water were taken at four sites, varying in distance from tidal effects, in a mangrove lined estuary. This was done for both rising and falling tides, and during the dry and wet seasons. Our data suggest that water infiltrates and resides in sediments for about 1-4 tidal cycles. DIC was present in greater amounts during falling tides in the wet season but no well-defined link between the amounts of time water resides in pore spaces and DIC content could be established in both seasons. This could be because DIC enrichment of pore water due to in situ remineralization happens on time scales much shorter than what our method was able to capture.