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

We studied the distribution of dissolved O₂, 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 O₂ concentrations. Sulfate production through pyrite oxidation occurred in the swamp with thin peat layer under aerobic conditions and was reflected by elevated SO₄/^2-/Cl^- in the river water. When SO₄/^2-/Cl^- was high, CO₂ and CH₄ concentrations decreased, whereas the N₂O concentration increased. The excess SO₄/^2- in the river water was thus identified as a potential indicator for gas dynamics in this coastal swamp system.