长江口海域沉积物中痕量稳定同位素环境指示意义的解析

Stable isotopes of trace elements are key tracers that the GEOTRACES programme focuses on. They serve important roles in tracing the biogeochemical cycling of trace element contaminants and reconstructing the past changes of marine environment. However, the study on tracing implications and sediment records of those non-traditional stable isotopes (Zn, Cu, Cd and Pb isotopes) is at its preliminary stage. This project chooses the Changjiang Estuary and adjacent waters which has been significantly disturbed by human activities as the research subject, and focuses on the stable isotopes of Zn, Cu, Cd and Pb in sediments which are considered as contaminant elements in this area. The geochemical characteristics and tracing implications of stable isotopes in the suspended particulate matter (SPM) and sediment will be systematically studied. The project is expected to clarify the sources, fate and other transport processes of trace element contaminants, and further establish the budgets of particulate trace elements in the Changjiang Estuary and adjacent waters. Furthermore, the implications of the sediment records of stable isotopes are expected to be revealed and further be used to reconstruct the past environment changes including anthropogenic input of heavy metals in the Changjiang Estuary for the past century. Efficient stable isotope-tracer system in sediment will be developed. In conclusion, this project will bring deep insight into biogeochemical cycling of trace elements and isotopes in near-shore waters, and provide important theoretical basis for paleoenvironment research and marine environment protection.

痕量元素稳定同位素是GEOTRACES计划重点关注的一类示踪指标，对于追踪海洋痕量元素污染物的生物地球化学循环、重建海洋环境演变过程具有重要作用。但目前对于海洋中Zn、Cu、Cd、Pb等非传统稳定同位素的示踪作用尤其沉积记录的研究仍处于起步阶段。本课题选取长江口及邻近海域这一受人类活动影响显著的热点区域为研究对象，聚焦该海域沉积物中Zn、Cu、Cd、Pb四种污染元素的稳定同位素，系统研究水体悬浮颗粒物和沉积物中稳定同位素的地球化学特征及示踪作用；应用其辨析痕量元素污染物的来源、归宿等迁移转化特征，建立长江口海域颗粒态痕量元素的通量过程；深入解析稳定同位素的柱状沉积记录，应用其重建长江口海域百年来发生的重金属污染输入等环境演变过程；建立可靠的沉积物稳定同位素指标体系。本课题的实施，将深化对近海海域痕量元素及同位素的生物地球化学循环的认识，为近海的古环境研究和环境保护提供重要的理论基础。

痕量元素及其稳定同位素在追踪海洋痕量元素污染物的生物地球化学循环、重建海洋环境演变过程中具有良好的应用前景，但目前对于海洋中Zn、Cu、Pb等非传统稳定同位素的示踪作用及沉积记录的研究仍较为空缺。本课题选取长江口海域这一受人类活动影响显著的热点区域为研究对象，系统研究了长江口海域Zn、Cu、Pb、Cd、Hg等痕量元素的时空分布、影响因素等生物地球化学特征，解析了沉积物中痕量元素总量及形态的环境指示意义，并应用其沉积记录重建了长江口海域百年来自然的（长江径流输入变化等）和人为的（污染输入、水体富营养化等）环境演变过程；研究了长江口海域水体悬浮颗粒物（SPM）中Zn、Cu、Pb、Cd等痕量元素的时空分布、影响因素等生物地球化学特征及其环境指示意义，发现SPM中痕量元素除了受到长江输入及其沉积物运移的影响外，Zn、Cd受生物活动及污染输入的影响，而表层水体SPM中Pb受到大气污染输入的影响。获取了长江口海域沉积物和悬浮颗粒物中Pb稳定同位素（207Pb/206Pb、208Pb/206Pb）的特征值、时空分布及示踪意义，并应用其沉积记录重建了世界含铅汽油的使用及中国1980s后经济发展所带来的Pb污染输入不断增加的环境变化过程；探索确立了海洋沉积物的消解及其中Zn、Fe、Cu元素的色谱分离纯化过程，为后续海洋沉积物中Zn、Fe、Cu稳定同位素的分析测试奠定了基础；分析测定了长江口海域表层和柱状沉积物中Zn稳定同位素（66Zn/64Zn、68Zn/64Zn）的特征值，获得了长江口海域沉积物中Zn稳定同位素的分布特征及示踪意义，δ66Zn/64Zn在沉积柱上层的升高可能反映了长江口海域近四十年来Zn污染输入的不断增加。本项目的实施，加深了对于近海海域痕量元素及Zn、Pb、Cu等稳定同位素的生物地球化学循环的认识，证实了Zn、Pb、Cu等痕量元素及其稳定同位素在指示水体物质来源、反映近海环境变化等方面的重要作用，也为海洋沉积物痕量元素指标体系的建立与应用提供了重要的基础。