长江口－东海内陆架泥质区典型污染物的季节性源汇作用与机制

The Yangtze River estuarine-inner shelf mud area of the East China Sea is the major sink for the sediments and associated hydrophobic pollutants mainly discharged from the Yangtze River. The Yangtze River-dominated sediment supply, coastal currents and sedimentary dynamic environment show a seasonal variation in this area significantly, therefore, it should be a good laboratory in the world to study the source and sink of the fluvial materials from the large river into the sea. The hydrophobic pollutants including heavy metals (Pb, Zn, Cu, Cd, As and Cr) as well as persistent organic pollutants (polychlorinated biphenyls and polycyclic aromatic hydrocarbons) are selected as the research targets. Based on the analyses of the speciation of heavy metals, Pb stable isotopic composition and the molecular compositions of organic pollutants, this proposal is to reveal the seasonal source to sink interchange, the sedimentary dynamic-geochemical depletion and the release from the sediments to the water columns of target pollutants during the sediment resuspension, transport and deposition from the Yangtze River Estuary to the Min-Zhe coastal mud area; to explore the effect of the benthic boundary layer on the source to sink of these pollutants in the area; and to preliminarily establish the budgets of these pollutants in the Yangtze River estuarine-inner shelf mud area of the East China Sea. This study will provide scientific perspectives for the understanding of the source and fate of the typical pollutants and their biogeochemical cycles in the East China Sea, and the approach in this work should be meaningful for the study of the dispersal, and transformation of the hydrophobic pollutants in other large river dominated margins around the world.

长江口－东海内陆架泥质区是长江入海沉积物和疏水性污染物的主要汇，这里长江沉积物输入、河口－近海环流和沉积动力环境存在显著的季节性变化，是研究大河入海物质从源到汇的"天然实验室"。本申请以典型疏水性重金属（Pb、Zn、Cu、Cd、As和Cr）、和持久性有机污染物（多氯联苯和多环芳烃）为对象，基于重金属形态、Pb稳定同位素组成和有机污染物分子化合物的分析，揭示长江入海沉积物从长江口到闽浙近岸泥质区复杂的搬运-沉积过程中，目标污染物的季节性源-汇效应、沉积动力-地球化学分异过程及从沉积物向水体的释放；阐明长江口－东海内陆架泥质区底边界层对目标污染物源-汇的影响；初步建立研究区目标污染物的收支。成果对认识东海典型污染物的源－汇及生物地球化学循环具有重要的科学意义，对理解世界其他大河河口－近海污染物的迁移、转化也有重要的参考价值。

长江口－东海内陆架泥质区是研究大河入海物质从源到汇的“天然实验室”。本课题对长江口－东海内陆架泥质区沉积物中的典型持久性有机污染物（POPs）和重金属的源-汇过程与机制进行了系统探讨，取得了如下主要成果：1）发现大河输入是东海沉积汞的重要来源，沉积动力环境对汞的地球化学行为有显著影响。汞稳定同位素组成表明近海工业源汞相对贡献大，大气沉降源汞对远海的贡献显著高于近海；土壤源汞的贡献近海明显高于远海，长江口泥质区相对高于南部内陆架泥质区。长江口－东海内陆架泥质区沉积汞的总埋藏通量为51 t/yr，是全球重要的“汞汇”。2）PCBs在研究区的源-汇主要受控于长江输入、陆源地表径流输入以及点源污染（如浙江沿岸电子垃圾处理排放）；研究区是全球重要的“PCBs汇”，沉积通量为2.63吨/年。3）沉积柱孔隙水PAHs浓度远高于长江口-东海内陆架表层水，存在低环PAHs从底泥向上覆水体的扩散，是上覆水体的重要“PAH源”。沉积物-孔隙水中多环芳烃的分布、分配对PAHs的源－汇转换有重要制约作用。4）建立了中国东部陆架泥质区PBDEs和PCBs沉积通量的高分辨沉积记录，发现PBDEs沉积通量自20世纪70年代开始均出现持续增加的趋势，这响应于近年来中国PBDEs污染（如家电和电子产品）日益加剧，以及存在PBDEs污染企业从发达国家向中国的迁移。PCBs沉积通量在20世纪50-70年代中期和20世纪90年代-至今出现两个峰值，分别对应于中国PCBs的十年生产期（1965-1974年）和高速经济发展期导致的无目的性PCBs加速排放，表明伴随中国工业经济发展和大规模土地覆被变化，PCBs污染呈增加趋势。5）发现海气交换是长江口PAHs海气界面交换的主导过程，每年有9.6吨的PAHs由海水挥发到大气中；长江口区域DDTs呈现净挥发的趋势，HCHs在水－气界面则呈微弱的净沉降趋势。研究成果对认识研究区典型污染物的生物地球化学循环有着重要意义，对世界其他大河控制性影响下的陆架区类似研究也有其重要价值。