Journal of Marine Sciences ›› 2022, Vol. 40 ›› Issue (4): 73-81.DOI: 10.3969j.issn.1001-909X.2022.04.007

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Influencing factors and distribution of particulate phosphorus in the surface sediments of the Changjiang Estuary and coastal waters of Zhejiang

YAO Huabo1, ZHANG Zhaohui*1, JIN Haiyan2, CHEN Jianfang2   

  1. 1. Institute of Marine Chemistry and Environment, Ocean College, Zhejiang University, Zhoushan 316021, China;
    2. Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, MNR, Hangzhou 310012, China
  • Received:2020-04-09 Online:2022-12-15 Published:2023-02-09

Abstract: A knowledge of the effects of major currents, extent of hypoxia, tidal effects, and aquaculture activities on speciation and distribution of particulate phosphorus in surface sediments in the Changjiang Estuary (CJE) and coastal waters of Zhejiang is critical to develop a sustainable strategy for the East China Sea (ECS). Two hypoxic zones are located in this region, one off the CJE in the north and the other in the muddy deposits along the Zhejiang coast of the ECS. Hangzhou Bay is a tide-dominated bay, and Xiangshan Bay is an aquaculture area influenced by tidal mixing. Surface sediments were collected from above four regions during August to September, 2018, and sedimentary phosphorus speciation were quantified using SEDEX method. Under reducing conditions at the mud-water interface in the two hypoxic zones of the ECS, iron bound phosphorus (Fe-P) in the sediments were transformed into exchangeable inorganic phosphorus (Ex-iP) which were immediately bioavailable, as evidenced by low Fe-P and high Ex-iP in the sediments. As the hypoxic zone off the CJE was more oxygen deficit, the contents of Fe-P in the sediments were also lower. Tidal mixing in Hangzhou Bay and Xiangshan Bay led to homogeneous distribution of particulate phosphorus in the surface sediments. All surface sediments in Xiangshan Bay were characterized by very low Fe-P, because tidal mixing caused the hypoxic areal extent, resulted from dense aquacultures, to be further increased to cover the whole bay area. The contents of detrital and refractory phosphorus in the surface sediments in a deserted aquaculture farm were substantially lower than those in non-aquaculture area, most likely due to dilution by biomass accumulated during culturing.

Key words: Changjiang Estuary, coastal waters of Zhejiang, speciation of particulate phosphorus, surface sediments, tidal mixing, hypoxic zones, aquaculture zones

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