长江流域两千年以来入海水沙通量变化及其对河口-陆架泥质沉积体系发育和演化的影响

Owing to the effects of changing climate and frequent human activities during the past 2000 years, the water and sediment discharge entering the sea of the Changjiang greatly changed, thereby exerting significant impact on the development and evolvement of the mud deposition system of the estuary-shelf. In order to explore the changes in water and sediment discharge into the sea of the Changjiang catchment during the past 2000 years, associate with its impact on the Changjiang subaqueous delta and inner shelf of the East China Sea, the present study aims to : (1) quantitatively reveal the variation of the water and sediment discharge entering the sea of the Changjiang induced by climatic and anthropogenic impact during the past 2000 years using watershed hydrological model; (2) through constructing geometric conceptual model, systematically explore the overall response pattern of the development and evolvement of the mud deposition system of the estuary-shelf to the sediment load variation of the Changjiang catchment, and generally understand the phase changes of mud deposition system of the estuary-shelf during the past 2000 years; combined with catchment sediment load variation, analyze sediment record variation, and discuss temporal-spatial variation of the information of catchment sediment load change within catchment-estuary-shelf, which provide scientific basis for interpretation of high resolution sedimentary record of mud deposits. This research will be beneficial to understand geomorphological response pattern of the Changjiang subaqueous delta and inner shelf of the East China Sea to human activities of the Changjiang catchment, and also helpful to putting forward resources and environment protection countermeasures for Changjiang delta under high intensity development, from the point of view of material origin and earth surface processes.

在过去的两千年里，气候变化频繁，流域人类活动的影响不断加剧，导致长江入海水沙通量发生了巨大的变化，进而对河口-陆架沉积体系产生了巨大的影响。本项目将长江流域-河口三角洲-东海内陆架泥区作为整体，选择两千年以来这个关键且有代表性的时间段，运用流域水文模型，定量揭示气候变化和人类活动共同影响下的长江流域入海水沙通量在过去两千年来的变化规律；建立几何概念模型，系统的研究长江三角洲和东海内陆架在发育规模和演化过程等方面对流域入海输沙量的总体响应格局，从宏观上了解过去两千年里长江三角洲-东海内陆架泥质沉积体系阶段性变化；结合流域输沙量变化信息，分析沉积记录变化，探讨流域输沙量变化信息在河口-陆架泥质沉积体系中的时间和空间变化规律。此项研究不但有利于了解长江三角洲-东海陆架泥区对流域人类活动的地貌响应规律，也有利于从物质来源和地表过程角度提出在高强度开发背景下三角洲区域的资源环境保护对策。

气候变化和人类活动导致长江入海水沙通量发生了巨大的变化，进而对河口-陆架沉积体系产生了重要的影响。本项目将长江流域-河口三角洲-东海内陆架泥区作为整体，模拟了气候变化和人类活动共同影响下的长江流域入海水沙通量在过去两千年来的变化规律，揭示长江三角洲和东海内陆架在发育规模和演化过程等方面对流域入海输沙量的总体响应格局，探讨了流域输沙量变化信息在河口-陆架泥质沉积体系中的时间和空间变化规律。研究结果显示，长江流域入海径流受气候变化驱动的降水主导，多年际均值整体波动较小，但短时间内气候变化驱动下的径流量变化较大，仍可对人类社会的发展产生重要影响。受制于气候变化和人类活动，长江整体的输沙量分三个阶段呈跳跃式增加，即，0-960年960-1840和1840-1985；但受水库建设影响，1985-2015年流域入海输沙量降至较低水平仅为2.62亿t/yr，与960-1840年水平相当。由于流域入海输沙量减少，目前长江中下游各主要沉积体系已经由长江沉积物的汇，变成了入海沉积物最主要的源；从长江水下三角洲到长江远端泥的北部和南部，三个沉积体系对流域变化的响应强度减弱，而响应时间增加，自北向南出现了显著的空间分异特征。流域输沙量变化信息在长江水下三角洲-东海内陆架泥区间的传递来看，细颗粒组分更能反映长江流域变化信息，且泥质区的不同位置对流域变化信息的响应强度差异显著。几何模型分析结果也表明，在未来流域入海输沙量仍保持目前低值且没有人为干预情况下，长江三角洲的三角洲平原面积和体积都将较目前规模大幅度减少。综合来看，在过去的几千年里，受流域沉积物供给影响，长江远端泥物源和沉积速率变化显现出了显著的时空演化特征。