Potential methanogenic evidence related to the transportation of anthropogenic elements in semi-closed estuarine system (Masan-Jinhae Bay, South Korea)

We investigated water chemical properties (chlrolophyll a, nutrients), particulate/dissolved organic carbon (POC, DOC) and methane in water columns of the semi-closed estuarine system (Masan-Jinhae Bay, South Korea). Together with the overall OM increase in upper boundaries (chlrolophyll a; 13.3±2.3 μg/L, POC and DOC; 0.2-2.1 mg/L) of Masan-Jinhae Bay, methane profiles within water columns showed the distinct predominance (101.2±7.6 nM) near surface layers. Considering OC isotopic compositions (δ¹³C_POC; -19.4±0.6 ‰, δ¹³C_DOC; -22.5±0.4 ‰) may reflect the decomposition of autochthonous OC sources, the methane production near surface seems to be potentially related to chemical reactions (e.g., demethylation and OM aggregates) of biological sources. Specifically, methane concentrations at adjacent terrestrial realm (inner Masan Bay) showed the most increased patterns (401.5±47.3 nM), indicating significant correlations with dissolved nitrogen and DOC. Together with the substantial transport of anthropogenic derived-nitrogen (δ¹⁵N_NO3,δ¹⁸O_NO3; 4.3±0.3 ‰, 6.0±1.0 ‰), our results infer that methanogenic process may be potentially influenced from the predominant OC production/decomposition under increased discharge of domestic wastewater. In near future, the additional analysis of methane isotopes may provide important clues for effectively understanding methane dynamics such as production and removal.