Interactive dynamics of particulate and dissolved organic matter under sustained hypoxia in a semi-enclosed bay (Jinhae Bay) = 진해만 내 지속적인 저산소 환경에 따른 입자성 및 용존 유기물의 상호적 거동

다국어 초록 (Multilingual Abstract)

Hypoxia is increasingly common in semi-enclosed coastal systems, yet its influence on organic matter (OM) cycling remains poorly constrained. We investigated seasonal variations in stable isotopes of particulate and dissolved OM (δ¹³CPOC, δ¹⁵NPN, δ¹³CDOC) in Jinhae Bay, South Korea, where recurrent hypoxia develops under strong stratification. Together with physical properties (temperature; 25.8±3.0 ℃, salinity; 30.5±1.9 psu, dissolved oxygen; 7.0±2.0 mg/L) within surface water during the hypoxia occurrence (August-October, 2024), concentrations of particulate/dissolved organic elements showed the significant increase (POC; 0.5±0.2 mg/L, PN; <0.1 mg/L, DOC; 1.3±0.3 mg/L, DTN; 0.3±0.1 mg/L) within water columns. In such settings, isotopic signatures of particulate and dissolved OM showed discriminative ranges (δ13CPOC; -20.7±1.8 ‰, δ15NPN; 4.8±1.7 ‰, δ13CDOC; -22.1±0.9 ‰), indicating in situ remineralization of autochthonous sources (e.g., phytoplankton). By integrating apparent oxygen utilization with Bayesian end-member mixing (C₃ terrestrial plants, marine phytoplankton, tidal-derived coastal water), we identified seasonal transition in OM processing from new production in spring to degradation and regenerated production under progressive oxygen depletion. Particularly, isotopic variations estimated during autumn (Δδ13CPOC; 2.4±1.8 ‰, Δδ15NPN; -2.4±2.4 ‰, Δδ13CDOC; 1.0±1.4 ‰) infer that the preferential utilization of regenerated dissolved nitrogen (i.e., DIN and DON) released via microbial degradation, supporting the proliferation of harmful dinoflagellates during persistent hypoxia. Our findings highlight the role of hypoxia-driven microbial recycling in sustaining nutrient availability and emphasize stable isotopes as a tool for diagnosing OM dynamics in eutrophic coastal systems.

목차 (Table of Contents)

• 1. Introduction 1
• 2. Materials and Methods 5
• 2.1. Site information 5
• 2.2. Sample collection 7
• 2.3. Physico-chemical parameters 9
• 2.4. Isotopic analysis 11
• 2.5. Statistical analysis 13
• 2.6. Isotopic mixing model 13
• 3. Results 15
• 3.1. Physico-chemical parameters at Jinhae Bay 15
• 3.2. Bulk elemental properties (concentrations and isotopic compositions) at Jinhae Bay 16
• 3.3. Principal component analysis 30
• 4. Discussion 31
• 4.1. Spatio-temporal variation of physico-chemical properties 31
• 4.2. Origin and reactivity of particulate and dissolved organic matter 42
• 4.3. Discriminative pathway of OM cycling under sustained anoxic conditions 48
• 5. Conclusions 56
• References 57
• Appendixes 72
• Acknowledgments 82