Sleepless Carbonights: How tidal pumping in a tropical mangrove creek affects carbon export over a diel cycle

Mangroves are known to pump large amounts of carbon to the coastal zone. This project studies the carbon export over a tidal cycle in a tropical mangrove creek (Ground Creek, in the Bocas del Toro Island of Panama). It has been hypothesized that changing oxygen concentrations and temperatures over the tidal cycle have a direct correlation to changing photosynthesis and respiration rates. It was found that this affected the levels of alkalinity, H+, and dissolved inorganic carbon (DIC) in the water of the creek. The importance of the exchange of carbon between tidal mangroves and the coastal ocean in the overall oceanic carbon budget is becoming more important, due to increasing ocean acidification. The natural acidification of mangrove sediments may also have an effect on the adjacent corals. However, if the saturation state of the coastal ocean remains high enough with tidal pumping bringing alkalinity from the mangrove creek, these corals may be able to remain healthy. This study focused on the flux of carbon between the coastal ocean and the mangroves over a 24-hour period using total alkalinity, dissolved inorganic carbon, and pCO2 measurements in order to determine the impact of tidal pumping of DIC in the creek. Alkalinity nearly doubled during the outgoing tide (from 2.3 to 4.3 mmol/L), which helped buffer the large rise in CO2 over this same time period (1000 to >6000 ppm). Our results suggest that a combination of CO2 outgassing and alkalinity production in the mangrove ecosystem buffers the nearby reefs from ocean acidification.