人类活动影响下的长江水下三角洲地貌动力系统状态转换

Quantification of anthropogenic activities is one of the important and difficult problems faced by earth science researchers. In the latest decades, anthropogenic activities in Changjiang drainage basin (such as dam construction) and Changjiang Delta (such as urbanization and groundwater pumping), along with global warming,have led to a significant decrease in sediment flux into the estuary as well as accelerating relative sea-level rise. As a consequence, these activities and changes brought about regime shift in the Changjiang subaqueous delta.morphodynamic system from progradation to retreat. Moreover, the cumulative effects of human activities in Changjiang Subaqueous Delta become much more active and comparable to natural dynamic process in terms of magnitude. Therefore, sedimentary and geomorphological effects caused by anthropogenic activities could be identified unprecedentedly. This project focus on human activities and their environmental impacts, including sedimdent partition caused by dredging along deep-water channel, sediment trap caused by sea dyke construction and reclamation over tidal flat, and mophological pattern changes caused by estuarine regulation projects. In-situ observations, physical process-based numerical modelling and state-behavior-based conceptual modelling will be adopted in this research, and the stability and mobility of sediment and sediment retention index, the overall pattern of source-sink, the balance and budget of sediment, as well as the future geomorphological state of Changjiang subaqueous delta, will be evaluated and predicted. With large river deltas being the important base of human civilization in Anthropocene, this study attempts to quantify the strength of anthropogenic effects, to enrich research content of geomorphodynamics and sediment dynamics, and further to support scientific decision-making concerning a sustainable development of the Changjiang Delta.

人新世地球科学研究的重点和难点之一是人类活动的定量化。过去几十年里，由于相对海面上升和长江入海沉积物减少，长江水下三角洲正在发生由淤涨向蚀退的系统状态转化，人类活动成为影响长江水下三角洲地貌动力系统状态的活跃且重要的因素。现代长江口的人类活动形式多样、规模可观，但是其作用强度和沉积与地貌效应等问题尚不明确。本项目运用现场观测、数值模拟和情景预测等方法，对河口整治工程、深水航道疏浚和潮滩围垦所反映的边界条件与地貌格局调整、沉积物再分配与捕获效应进行参数化，在此基础上分析沉积物活动时间与活动层物质总量、滞留系数与滞留时间，从沉积物供应量、沉积量与逸出量的角度全面了解长江水下三角洲的源汇格局，了解长江水下三角洲地貌动力系统的状态并预测其演化。开展此项研究，对于回答人类营力的作用强度和效应等科学问题，丰富地貌动力学和沉积动力学的研究内容，辅助长江三角洲可持续发展战略的决策，具有理论和实践价值。

人新世地球科学研究的重点和难点之一是人类活动的定量化。过去几十年里，由于相对海面上升和长江入海沉积物减少，长江水下三角洲正在发生由淤涨向蚀退的系统状态转化，人类活动成为影响长江水下三角洲地貌动力系统状态的活跃且重要的因素。现代长江口的人类活动形式多样、规模可观，但是其作用强度和沉积与地貌效应等问题尚不明确。本项目运用沉积动力学观测分析与数值模拟，沉积学采样与实验室测试等技术手段，并结合历史资料进行综合研究，在Ⅰ沉积物特征与物源识别，Ⅱ沉积动力过程与地貌效应，Ⅲ沉积记录与全球变化，Ⅳ人类活动影响及其沉积信息提取等四方面做出有创新性的贡献。发现：（1）提出了两种新方法（角闪石单矿物地化元素指标、岩心扫描之钙—锆—钛三角图）来区分长江与黄河的沉积物；（2）发现人类活动改变了大河流域沉积物产出的特征，此类变化有望成为未来地学标志物（geo-marker）；（3）对研究区的沉积物干容重及临界起动切应力进行了系统的测试分析，对于长江水下三角洲的沉积物平衡分析及可侵蚀性分析提供了重要的数据集；（4）研究了海运航道的沉积记录特征与生态环境效应，从沉积物供应与地貌动力平衡角度提出了潮滩围垦的适宜性评价方法；（5）对台风影响下三角洲的地貌动力响应，层化效应与长江三角洲最大浑浊带的关系，冬季波浪有助于高悬沙事件等沉积动力学过程进行了观测与模拟，深化了有关沉积动力学机制的认识；（6）提出台风沉积的多指标识别方法，利用陆架沉积反演了百年尺度与千年尺度的台风事件记录。研究成果积累了一批基础数据，丰富了地貌动力学和沉积动力学的研究内容，有助于回答人类营力的作用强度和效应等科学问题，对于河口海岸可持续发展战略与人类社会适应等重大需求与决策具有参考价值。