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Updated: Mar 2, 2026

Laboratory-determined Phosphorus Flux from Lake Sediments as a Measure of Internal Phosphorus Loading
Published on: March 6, 2014
Intensified water column hypoxia drives disproportionate benthic P release and N:P imbalance via enhanced sedimentary
Sangbeom Baek1, Jin-Sook Mok1, Haneul Kim1
1Department of Marine Science and Convergence Technology, Hanyang University, 55 Hanyangdaehak-ro, Ansan, Gyeonggi-do, 15588, South Korea.
Abstract:
Ocean deoxygenation, driven by human activities and climate change, increasingly threatens the sustainability of marine ecosystems. This study investigates how water column hypoxia (WCH; dissolved oxygen (DO) < 63 μM) intensity regulates sedimentary sulfate reduction (SR), sulfur-iron-manganese-phosphorus (S-Fe-Mn-P) dynamics, benthic nutrient fluxes (BNF) and nitrogen (N):P ratio in Jinhae Bay, Korea, characterized by seasonally recurring WCH. As bottom-water DO declined from 206 to 17 μM, SR rates in surface sediments increased 6-fold, from 46.0 to 281 nmol cm-3 d-1, accompanied by elevated pore-water sulfide (H₂S) and depletion of Fe(III)/Mn oxides. These redox changes markedly enhanced ammonium (NH4+) and phosphate (PO43-) release into the overlying water, with NH4+ and PO43- fluxes 6.5- and 17-fold, respectively, higher under severe hypoxia (NH4+: 7.70; PO43-: 0.52 mmol m-2 d-1) than under normoxia (NH4+: 1.18; PO43-: 0.03 mmol m-2 d-1). Intensified SR and dissolution of Fe(III)/Mn oxides further enhanced the disproportionate release of P relative to N, leading to a threefold decrease in the N:P ratio of benthic nutrient fluxes (N:P = 14.8 under severe WCH vs. 45.2 under normoxia). Long-term monitoring (1997-2024) revealed persistent bottom-water P enrichment, despite reduced external (terrestrial) inputs following environmental regulations, underscoring the dominance of internal (benthic) sources. Our findings demonstrate that intensified WCH enhances SR-driven internal BNF, reinforcing eutrophication and challenging the effectiveness of external nutrient reduction strategies in hypoxia-prone coastal systems.
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