大兴安岭多年冻土退化对沼泽湿地溶解有机碳动态的影响研究

The Greater Xing'an Mountain where the permafrost exists is an important distributed region of mire-wetlands in China. The presence of permafrost is closely linked to the mire evolution and the processes of carbon balance in mire soil. But in the last fifty years, large area of permafrost degradation has occourred due to global climate warming. By now, there are still no answers to the questions that how the alteration in surface hydrology and temperature could change the export dynamics of organic dissolved carbon (DOC) from the mires, and what is the tendency and strength of DOC dynamics and what is the driving machanism. There has no enough systematic research, especially field comparing obvservation, to be conducted to reply these questions. My project will research the influences of permafrost degradation on the dynamic processes of DOC production, accumulation and exportation with the methods of field comparing observation in parallel to regional surveys and simulated experiments. The research aims to reveal the response rule, as well as the sensibility, of DOC dynamics to altered hydrlogical and thermal conditions in the mires if the permafrost degradation sustained. Besides, the driving mechanism of the effect of permaforst degradation on DOC exportation from mires in the scale of small catchment will be paid special attention to. Meanwhile, the futher DOC export potential from mires under the condition of sustained permafrost degradation will be forcasted in the study area of the North Greater Xing'an Mountain. This project will promote the research of carbon balance in the boreal area in Northeast China, and provide basic data and theoretical foundation to the regional carbon and hydrology management in the future.

大兴安岭多年冻土区是我国沼泽湿地的重要分布区，多年冻土的存在与沼泽湿地碳循环过程密切相关。过去50年里，气候变暖已导致该地区多年冻土大面积退化，地表水热条件的改变对沼泽湿地溶解性有机碳（DOC）输出过程会产生怎样的影响？DOC生成和输出动态变化趋势和强度如何？驱动机理如何？目前尚缺少系统研究，特别是野外对比观测研究尚属空白。本项目拟选取不同类型冻土区（连续多年冻土和岛状多年冻土）沼泽湿地，采用野外对比观测的方法，结合样带调查和模拟控制试验，系统研究多年冻土退化对沼泽湿地DOC生成、累积和输出过程的动态影响，阐明湿地DOC输出动态对水热条件变化的响应规律及敏感性特征，在小流域尺度上揭示多年冻土退化对湿地DOC输出通量变化影响的驱动机理，预测区域多年冻土退化背景下沼泽湿地DOC输出通量的未来变化趋势，为精确评价气候变暖情势下东北寒区沼泽碳平衡趋势和实施区域水资源科学管理提供基础数据和理论支持。

大兴安岭多年冻土的存在与沼泽湿地碳循环过程密切相关。气候变暖已导致该地区多年冻土大面积退化，地表水热条件的改变对沼泽湿地溶解性有机碳（DOC）输出过程会产生怎样的影响？DOC生成和输出动态变化趋势和强度如何？亟待开展相关研究。本项目选取大兴安岭多年冻土沼泽湿地，采用对比观测的方法，研究多年冻土退化对沼泽湿地DOC输出过程的动态影响，阐明湿地DOC输出动态对径流过程的响应规律，预测多年冻土退化背景下沼泽湿地DOC通量的变化趋势，为评价气候变暖情势下东北寒区沼泽碳平衡趋势和实施区域水资源科学管理提供基础数据和理论支持。. 通过4年的野外监测，获取大兴安岭多年冻土区流域DOC通量的重要数据。研究区大片和岛状连续冻土沼泽流域生长季TDC多年平均输出系数分别为41.93 和39.85 kg C/ha，流域DOC输出通量平均2.60 g/m2，与其它冻土区研究结果相比（0.36 to 3.0 g/m2），输出水平较高。冻土区沼泽湿地的DOC输出量为7.62 gC/m2，此通量为大兴安岭地区沼泽湿地净生态系统交换量的31%（不考虑DOC输出情况下，只考虑CO2和CH4净交换量，NEE=30.59 ± 1.98 g C/m2/a，2011-2012）。因此，DOC通量是多年冻土区沼泽湿地碳交换量的重要组成部分，对评价全球变化背景下多年冻土区碳汇功能具有重要意义。. 大兴安岭冻土区沼泽湿地DOC输出浓度和通量受到径流过程的显著影响。洪峰期径流输出的DOC占生长季DOC输出通量的主要部分，DOC通量主要受降雨量的限制，而非湿地碳循环过程的限制，原因在于多年冻土区沼泽湿地具有较高的DOC生成潜力。因此，径流量是预测冻土区流域DOC输出通量的最佳指标。. 温度升高将引起多年冻土区湿地土壤DOC浓度升高，并改变DOC化学组成，同时导致径流输出路径的变化，整体上推测，增温将导致DOC输出通量将增加。但通过对大兴安岭北部至南部地区的大区域样带调查发现，区域气候变暖降低冻土区河流基流期的DOC浓度。因此，温度升高对多年冻土区DOC通量的提升可能存在短期效应，长期的温度增加会大量消耗流域碳储量，从而导致径流输出的DOC通量减少。