晚更新世以来淮河上游河流地貌对气候变化的响应过程研究

The response of fluvial landscape to climate change is a classic subject of geomorphology, and so far it has not been able to establish a generally accepted theory. The study of river landscape and its climate-driven mechanism in climate-sensitive areas is key to strengthening relevant scientific theories. The Huaihe River Basin is located in the North-South Transition Zone of China. This project intends to conduct a detailed field survey of the Tongbai section in the upper Huaihe River. Based on the sedimentary analysis of the typical modern river sections, the sedimentary stratigraphic characteristics of different river types in the study area are obtained. Through the investigation and measurement of the river terraces and their sedimentary profiles, combined with the indoor numerical geomorphic mapping, the spatial distributions of the river terraces are obtained. Then the sedimentary stratigraphy method is used to extract the sedimentary environment changes of the ancient river in the terrace profiles. Under the precise age control of the optical stimulated luminescence and 14C methods, reconstructing the evolution of river aggradation/incision and river style in the Tongbai section of the upper Huaihe River since the late Pleistocene. Combining the climate records of existing loess, stalagmite and sporopollen in the study and surrounding areas, exploring the fluvial responses to short time-scale (1-10 ky) climate change, and the laws and trends of river evolution. This study can help to enrich the relevant theories of fluvial geomorphology, and also to provide an effective scientific basis for river basin governance and ecological environment construction.

河流地貌对气候变化的响应研究是地貌学界关注的经典课题，迄今未能建立完善的理论。加强气候敏感区域河流地貌及其气候驱动机理的研究，是强化相关科学理论的关键。淮河流域位于我国东部南北过渡带，本项目拟通过对淮河上游桐柏段的详细野外调查，基于对现代典型河型段的沉积地层分析，获得该区现代不同河型的沉积地层学特征；通过对河流阶地及其沉积剖面的调查和测量，结合室内数值地貌制图，获得河流阶地的空间展布特征；进而采用沉积地层学方法，提取阶地沉积地层中的古河流沉积环境变化信息，在光释光和14C方法的精确年代控制下，重建晚更新世以来淮河上游桐柏段的堆积/下切和河型演变过程；结合研究区及周边已有的黄土、石笋和钻孔孢粉等气候记录，发掘河流系统对短尺度（1-10 ky）气候变化的响应过程，探求河流演变所遵循的规律和趋势；不仅有助于丰富相关的河流地貌理论体系，还可以为流域的河道治理和生态环境建设决策提供有效的科学依据。

不同气候地貌单元之间的河流地貌过程常存在着差异，河流系统对气候变化的响应也表现出一定的复杂性。尤其在晚更新世以来的千年尺度上，河流对气候变化响应的“非线性”特征更加显著。因此，加强不同典型区域下河流地貌过程及其气候驱动机理的研究，是深化相关科学理论的关键。淮河位于中国东部南北过渡带，其河流地貌过程具有显著的独特性。本项目通过对淮河上游桐柏段河流地貌的野外考察，发现桐柏段至少发育并保存了4级河流阶地。通过对桐柏段河流阶地、现代河漫滩的沉积地层学和年代学研究，重建了研究区末次冰盛期（Last Glacial Maximum, LGM）以来的河流地貌过程。LGM以来淮河桐柏段发生了2次显著的下切，分别发生于中-晚全新世转型期（5.8-3 ka）和小冰期（0.5-0.2 ka）。末次冰消期以来，淮河桐柏段河道形态以曲流河为主，未发生显著的变化。气候记录表明，LGM以来研究区的气候并未发生显著的干旱化。淮河桐柏段的河流下切是在相对湿润的气候背景下，气候波动引起季节性洪水增多的结果；而河道形态的演变主要受湿润气候下以森林为主的植被组合的影响。从更广泛的区域对比上发现，不同区域之间河流行为的差异可能是由区域水文气候组合所控制的。此外，本项目基于ArcGIS平台对淮河中上游段水系的形态学特征进行了分析，发现淮河中上游段支流的走向与地形呈现出较好的一致性，为典型的顺向河。淮河北侧、南侧支流与干流的平均走向交汇角分别为42°和59°；淮河北侧、南侧支流走向与水平方向的夹角分别为30°和28°，呈现出南北对称分布，表明淮河水系的平面展布特征受区域地形和河流系统自我调节所控制。