Lateral exchange of mangrove porewater carbon to coastal waters

This project aimed to study porewater carbon in Panamanian mangrove forests in order to understand production and lateral exchange in a mangrove system adjacent to a coral reef (Isla Colon, Bocas del Toro, Panama). We sampled mangrove sediment porewater as well as surface water from ebb and flood tides. To sample porewater we dug holes in mangrove sediments at low tide and let them fill with water before sampling them. Temperature, salinity, and pH were measured using a YSI probe. Dissolved oxygen was measured and recorded with a YSI ODO probe. pCO2 was measured using an EGM-4 Infrared Gas Analyzer and total alkalinity was measured using titration analysis. We hypothesized that the mangrove forests would have high productivity and high metabolic activity. As a result, we expected the mangroves to be important exporters of alkalinity and DIC to coastal waters through tidal exchange. DO and salinity were expected to follow high and low tidal trends. Salinity was generally lower in porewaters and outgoing tide, suggesting tidal pumping of porewaters. pH was similar and was very low in pore waters (6.2 to 6.6) and generally lower in outgoing tides compared to incoming tides. Alkalinity and pCO2 was much higher in porewaters (2.7-3.1 mmol/L) than surface waters (1.9-2.1 mmol/L), as was pCO2 (17,000 to 36,000 uatm vs. 1,000-9,000). We compared our data to other data collected throughout these reefs and into the open ocean. The data suggest that mangroves are important alkalinity exporters to the ocean and help to buffer natural ocean acidification from mangrove sediment respiration. The alkalinity from the porewater of these mangroves is sent into the nearby reefs through lateral export and then ultimately sent into the open ocean, where it helps to draw down CO2 and buffer ocean acidification.