长江口和浙江近岸海域表层沉积物中颗粒磷的形态分布和影响因素

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

研究长江口和浙江近岸海域的水团流向、缺氧程度、潮汐作用以及养殖活动对表层沉积物中颗粒磷赋存形式的影响,对东海生态环境的可持续发展有着重要的意义。长江口以北和浙江近岸泥质区各存在一个缺氧中心,杭州湾属于强潮区,而象山港遍布养殖场。2018年8—9月在上述4个海域分别采集表层沉积物,采用SEDEX方法进行了颗粒磷的形态划分和含量测定。研究结果表明:在长江口外北部缺氧区和浙江近岸泥质区的南部缺氧区,由于沉积物-水界面的还原环境可以活化铁结合态磷,使之转变为生物可以直接利用的弱吸附态无机磷,因此表现出沉积物中铁结合态磷的低值和弱吸附态无机磷的高值;前者的缺氧程度高于后者,因此其铁结合态磷的含量相应更低。杭州湾和象山港海域均受潮汐作用影响,两者沉积物中磷的分布比较均匀。象山港表层沉积物中铁结合态磷含量均较低,这可能是因为养殖活动造成的水体缺氧通过潮汐活动扩散到整个港底。象山港废弃养殖场沉积物中的碎屑磷和残余有机磷含量显著低于非养殖区,可能是由于养殖活动累积的生物沉积稀释了陆源输入的碎屑颗粒。

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.