Dynamics of dissolved O2, CO2, CH4, and N2O in a tropical coastal swamp in southern Thailand

We studied the distribution of dissolved O-2, CO2, CH4, and N2O in a coastal swamp system in Thailand with the goal to characterize the dynamics of these gases within the system. The gas concentrations varied spatially and seasonally in both surface and ground waters. The entire system was a strong source for CO2 and CH4, and a possible sink for atmospheric N2O. Seasonal variation in precipitation primarily regulated the redox conditions in the system. However, distributions of CO2, CH4, and N2O in the river that received swamp waters were not always in agreement with redox conditions indicated by dissolved O-2 concentrations. Sulfate production through pyrite oxidation occurred in the swamp with thin peat layer under aerobic conditions and was reflected by elevated SO42-/Cl- in the river water. When SO42-/Cl- was high, CO2 and CH4 concentrations decreased, whereas the N2O concentration increased. The excess SO42- in the river water was thus identified as a potential indicator for gas dynamics in this coastal swamp system.