长江源区有机碳的迁移转化及冰冻圈过程的影响机制研究

The source region of Yangtze River is an idea catchment to study the degradation of the Cryosphere and its influences on ecology and environment. The shrinkage of the glaciers and permafrost results in an increasing meltwater discharge, strengthened interaction of water-soil/rock and biological activity, and release of organic carbon (OC) from glaciers and permafrost, which will eventually affects the ecological systems and carbon cycles in oceans. However, how do the shrinkage of glaciers and permafrost affect the release, and the migration and transformation processes of OC, and what is the amplitude and strength and the ecological and environmental effects on earth? There remains unclear at present. Based on the observations of the water-heats of snow/soils, the meltwater hydrology of glaciers and permafrost, and their meltwater chemistry in the source region of Yangtze River, together with the investigation of plant coverage and the model of runoff hydrograph, this program is going to collect samples (e.g. river water, precipitation, groundwater, meltwater) and then analyze these samples in laboratory in one whole year. Firstly, this program will study the variation process and evolution rule of discharge and sediments, the spatial and temporal variations and influencing factor of all kinds of OC, the sources of river water and its OC, and then reveals the transportation and migration processes of OC and the variation rules of its fluxes. Secondly, this program will study the associations of the water-heat of snow/soil, the hydrology of glacier/permafrost and their meltwater chemistry with river discharge and the chemical process of its OC, establish the conceptual model among the Cryosphere process, hydrological process and water chemistry process, and then reveal the influencing mechanism of the Cryosphere process on the migration and transformation processes of OC in the source of Yangtze River.

长江源区是冰冻圈退化及生态环境效应研究的理想地区。冰川/冻土退化导致融水径流增加、水-土/岩作用及微生物活动增强，冰川/冻土源有机碳（OC）的释放，最终将影响海洋生态系统和碳循环！然而，OC的释放及迁移转化如何响应冰川/冻土退化且其生态环境效应究竟如何？目前还不清楚！本项目依托源区的水文/气象监测站，结合植被调查和物质平衡模型，通过一个完整年内端元样品的连续采集及测试分析，辨析历史径流/泥沙的变化规律及影响因素、识别径流/泥沙的演化趋势；研究各形态OC（DOC和POC）的变化过程及影响因素，解析OC及河水的来源、揭示OC的迁移转化及通量变化规律；分析积雪/土壤水热、冰川/冻土水文水化学过程与径流及OC迁移转化的相关关系，交叉对比分析（由小流域向源区拓展），建立冰冻圈过程-水文过程-水化学过程的概念性模型，揭示冰冻圈过程对长江源区OC迁移转化的影响机制。

长江源区是冰冻圈退化及生态环境效应研究的理想地区。冰川/冻土退化导致融水径流增加、水-土/岩作用及微生物活动增强，冰川/冻土源有机碳（OC）的释放，最终将影响海洋生态系统和碳循环。（1）项目研究了冰川径流/泥沙过程的演变规律及影响因素，揭示了长江源区OC的迁移转化/通量变化规律及其冰川圈过程的影响机制。冰川径流的DOC浓度在消融初期和末期较小、日变化明显，在洪峰期浓度较低、日变化不明显，这与排水系统的演变（（从冰面向冰内再向冰下演变））和径流量密切相关。径流和泥沙向下游迁移时DOC浓度呈现出逐渐增加的趋势，说明河道内的清除过程比较复杂，清除速率因流域不同而有差异。DOC通量与径流量、累积DOC通量与径流量随时间的变化趋势一致，说明DOC的输出或释放主要受冰川径流量控制。全球冰川每年释放的DOC为786 Gg C，预计在全球变暖背景下冰川源有机碳在全球碳循环中的重要性会越来越显著。（2）项目研究了生物活性铁浓度/通量和迁移转化规律。冰川径流中dFe的浓度与径流量存在明显的负相关关系，表明dFe输出量/释放率主要受冰川径流量控制。在向下游迁移过程中，dFe浓度逐渐增加，说明河道内dFe的清除过程比较复杂，清除速率因流域不同而有所差异。全球冰川释放的dFe为185±172 Gg，先前的研究可能没有充分认识到冰川作为生物活性Fe来源的重要性，预计在全球变暖背景下冰川在全球Fe循环中的重要性可能会越来越显著。（3）研究了典型海洋型冰川流域的化学风化过程。冰川河流中的主要离子浓度和悬浮泥沙浓度分别与流量呈负相关和正相关关系，说明对融水径流化学和悬浮泥沙的输移有较强的水文控制作用。流域径流水化学主要由碳酸盐矿物风化和硫化物氧化控制，而离子数据证明了该假设：即使基岩主要由硅酸盐岩石组成，痕量碳酸盐岩依然会优先风化。