Evaluation of sedimentary organic matter pollution in semi-enclosed coastal bays: Source identification through GDGTs biomarkers

The distribution of lipid biomarkers of glycerol dialkyl glycerol tetraethers (GDGTs) in surface sediments was investigated to trace organic matter (OM) sources in semi-enclosed coastal bay ports in South Korea. A total of 56 surface sediment samples were collected from three ports. Low BIT values (<0.3) and isoGDGTs concentration indicate the predominance of marine-OM at industrialized-urban ports (Masan and Gohyeon), and terrestrial-OM dominated at the port of Ganggu (>0.60). GDGT-0/Cren (0.48 ± 0.04, 0.42 ± 0.02) and Cren/Cren′ (135 ± 21, 117 ± 25) values suggest that urban-industrial wastewater contributed over 70 % of isoGDGTs in the total GDGTs at the Masan Gohyeon sites. Additionally, many brGDGTs and isoGDGTs compounds were significantly correlated (p < 0.05, p < 0.01) based on Pearson-correlation-analysis, along with a linear-relationship between CBT and brGDGTs (p < 0.01, R² = 0.53), suggests that in-situ brGDGT production is enriched through pH-driven bacterial cyclization. The values of CBT (0.31–0.58, 0.53–0.40), DC (0.21–0.33, 0.23–0.35), IIIa/IIa (0.24–0.60, 0.33–0.66), and #rings_tetra (0.34–0.57, 0.37–1.28) in the Masan and Gohyeon samples correspond to the observed in-situ production of brGDGTs in global-marine-sediments. One-way-ANOVA result shows that GDGTs variations among ports are significantly influenced by human-activity and land-use. Findings indicate that Masan and Gohyeon ports, influenced by high wastewater input and prolonged-seawater-residence, show elevated-OM, nutrients, and altered-pH, as a result of crenarchaeol levels comparable to the Yangtze Estuary, and in-situ brGDGTs production led to lower Ia abundance than global-surface-soils (43.5 %) and peat-sediments (55.9 %). Overall, the results of this study provide valuable insights for managing semi-enclosed coastal bays affected by various land-use patterns that contribute to sedimentary OM pollution.