A numerical model study on the spatial and temporal variabilities of dissolved oxygen in Qinzhou Bay of the northern Beibu Gulf
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Abstract: Oxygen facilitates the breakdown of the organic material to provide energy for life. The concentration of dissolved oxygen (DO) in the water must exceed a certain threshold to support the normal metabolism of marine organisms. Located in the northern Beibu Gulf, Qinzhou Bay receives abundant freshwater and nutrients from several rivers which significantly influence the level ofthe dissolved oxygen. However, the spatial-temporal variations of DO as well as the associated driving mechanisms have been rarely studiedstudied through field observations. In this study, a three-dimensional coupled physical-biogeochemical model is used to investigate the spatial and seasonal variations of the DO and the associated driving mechanisms in Qinzhou Bay. The validation against observations indicates that the model can capture the seasonal and inter-annual variability of the DO concentration with the range of 5−10 mg·L−1. Sensitivity experiments show that the river discharges, winds and tides play crucial roles in the seasonal variability of the DO by changing the vertical mixing and stratification of the water column and the circulation pattern. In winter, the tide and wind forces have strong effects on the DO distribution by enhancing the vertical mixing, especially near the bay mouth. In summer, the river discharges play a dominant role in the DO distribution by inhibiting the vertical water exchange and delivering more nutrients to the Bay, which increases the DO depletion and results in lower DO on the bottom of the estuary salt wedge. These findings can contribute to the preservation and management of the coastal environment in the northern Beibu Gulf.
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Key words:
- river plume /
- dissolved oxygen /
- stratification /
- physical-biological model
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Table 1. The multiplying factors of monthly discharge for different rivers during 2012−2017
Year Maoling Qin Dafeng Nanliu 2012 1.17 0.67 0.36 0.71 2013 2.92 1.65 1.67 1.75 2014 0.86 0.72 0.86 0.97 2015 2.16 0.56 1.30 1.12 2016 0.97 1.10 1.20 1.17 2017 0.94 1.02 1.52 1.72 Table 2. List of experiments.
Experiment Nutrient River discharge Tide Wind CTRL 100% 100% Yes Yes 0.6RD 100% 60% Yes Yes 1.5RD 100% 150% Yes Yes Notide 100% 100% No Yes Nowind 100% 100% Yes No -
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