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General Session 2: Marine & estuarine biogeochemistry |
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The status and characteristics of eutrophication in the Bohai Sea
GS2-64-S
Liwen Zheng* , Institute of marine science and technology, Shandong University
Weidong Zhai, Institute of marine science and technology, Shandong University
Lifang Wang, state key laboratory of marine environmental science, xiamen university
Tao Huang, state key laboratory of marine environmental science, xiamen university
Presenter Email: zhengliwen516@163.com
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| The Bohai Sea is a shallow semi-enclosed marginal sea of the northwest Pacific, characterized by undoubted eutrophication. To better understand eutrophication characteristics in this important coastal sea of ecological and economic significance, we investigated three surveying datasets of nutrients, covering summer (June 2011), fall (November 2011) and winter (January 2016). Nutrient concentrations and distributions in the Bohai Sea were subject to seasonal variations. Influenced by the Yellow River floods, dissolved inorganic nitrogen (DIN) slightly declined from 59.98-0.46 mM in summer to 41.13-1.93 mM in fall. During each survey, surface water DIN decreased along with the salinity increase. In winter, the dry season of the Bohai Sea, DIN concentrations ranged between 7.82 and 22.83 mM, increased from the south to the north. Correspondingly, the seasonal concentrations of dissolved inorganic phosphorus (DIP) increased from the lowest level of 0-0.16 mM in summer to a relatively high level of 0.24-0.66 mM in fall, and to the highest level of 0.34-0.72 mM in winter. The central Bohai Sea DIN/DIP ratios were 16.94 in fall and 15.99 in winter, similar to the traditional Redfield ratio. Moreover, both DIN and DIP were exhausted in summer in this region, suggesting that biological consumptions of DIN and DIP follow the Redfield ratio. This finding is much different from those earlier reports in Chinese literatures, in which the Bohai Sea DIN and DIP distributions are quite imbalanced in compared with the Redfield ratio. Our results also showed that, the seasonal concentrations of dissolved silicate (DSi) varied from 0.48-21.41 mM in summer, to 1.38-17.58 mM in fall, and to 10.73-15.53 mM in winter. Considering historical data, DSi has declined for 3 decades in several regions in the Bohai Sea, except for the central basin, where DSi increased during the past 30 years. Such nutrient changes may contribute to recent emergency of summertime hypoxia in several bottom waters in the Bohai Sea. |
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