大型河口连续体中重金属的复杂转化限制了我们对其污染历史的理解。这项研究调查了重金属的沉积组成,主要元素,总有机碳,晶粒尺寸,和放射性核素研究长江口(YRE)四个沉积物岩心(E1-E4)中重金属积累模式的时空变化及其控制机制。结果表明,由于在稳定的沉积环境中连续沉积,只有YRE远端前表面的E3很好地反映了重金属污染历史,E1和E2明显记录了河流和河口项目和过程的影响。YRE近端前缘的E1通过沉积物疏浚和倾倒活动记录了强烈的人为干扰,产生了一层异常低的210Pbex和少量重金属浓度的厚层。YRE中间前缘的E2显示,随着重金属浓度的降低,其上游粗化趋势对沉积物排放减少的影响最近增加。洪水和风暴事件在E2和E3的核心沉积物中留下了不同的印记,它们的粗地层单位具有较少的重金属浓度。来源分析表明,河口沉积物中的重金属主要来自自然过程,但受人类活动的影响很大。通过对潮汐河到河口的核心数据的比较研究,发现了近几十年来重金属积累历史与社会经济发展的直接联系,尽管有显著的时空差异,这是由晶粒尺寸共同决定的,离岸距离,水动力条件,沉积状态,除河口过程外,还有沉积速率。这警告我们要从大型河口系统中单个或稀疏的核心数据中仔细解释重金属历史,该系统具有类似于YRE的强烈自然力和人为干扰。
Complex transformations of heavy metals in the mega-river-estuary continuum limit our understanding of their pollution history. This study investigated sedimentary compositions of heavy metals, major elements, total organic carbon, grain size, and radionuclides to study spatiotemporal variations in heavy metal accumulation patterns and their controlling mechanisms in four sediment cores (E1-E4) from the Yangtze River Estuary (YRE). Results show that only E3 in the distal YRE front mirrors well the heavy metal pollution history due to its continuous deposition in a stable sedimentary environment, while E1 and E2 record the influence of riverine and estuarine projects and processes apparently. E1 in the proximal YRE front registers intense human disturbance through sediment dredging and dumping activities to produce a thick layer of abnormal low 210Pbex and minor heavy metal concentrations. E2 in the intermediate YRE front demonstrates the recently increasing influence of reduced sediment discharge by its upcore coarsening trend with decreased heavy metal concentrations. Flood and storm events left different imprints in core sediments of E2 and E3 by their coarse stratal units with fewer heavy metal concentrations. The source analysis indicates that heavy metals in estuarine sediments mainly come from natural processes but are significantly affected by human activities. A direct linkage of the heavy metal accumulation history with the socioeconomic development in recent decades is found by a comparison study of core data from the tidal river to the estuary, albeit with a remarkable spatiotemporal difference, which is jointly determined by grain size, offshore distance, hydrodynamic condition, depositional status, and sedimentation rate besides estuarine processes. This warns us to carefully interpret the heavy metal history from single or sparse core data in a mega estuary system with intense natural forces and human disturbances analogous to the YRE.