纳木错高寒湿地自然水位梯度上的CH4和CO2通量研究

Wetlands are the largest individual CH4 sources across the world, as well as vital sinks/sources for CO2. For the reason of huge water storage, complex topographic relief and vast permofrost distribution, there are widespread wetlands on the Tibetan Plateau, which account for 1/3 of China's natural wetlands.However, large uncertainties for estimation of CH4 and CO2 exchanges, especially potential over-estimation of CH4 emissions,are still remained due to scarce observations there. Furthermore, the alpine wetlands are affected by water level changes and thus enlarged uncertainties, caused by both enhanced evaporation and glacier melting under the fast warming climate in recent decades. Therefore,measurements of CH4 and CO2 fluxes are proposed to carry out in a typical alpine wetland on the hiterland of the Tibetan Plateau, dominated by Kobresia littledalei and Carex moocroftii. It's sheduled to investigate the variations of CH4 and CO2 fluxes across a gradient of water levels in situ, to predict future influences of water level shifts on CH4 and CO2 exchanges.Preliminary researches on CH4 production, transportation and oxidation are also about to conducted along the gradient, to understand the mechanisms of CH4 fluxes changes. In summary, this proposal is dedicated to quatify the CH4 and CO2 exchanges in a typical alpine wetland, to provide foundation for the climate-related negotiations, as well as forcast and explore the feedbacks of the biogeochemical cycles to climatic changes on the Tibetan Plateau.

湿地是全球最大的CH4排放源，也是重要的CO2源汇功能区。我国青藏高原水源丰富、地形起伏大、冻土发育水分不易下渗，其高寒湿地面积约占我国天然湿地的1/3。但目前对高寒湿地CH4和CO2通量估算不确定性较大，尤其是对CH4排放存在潜在高估。同时，在气候变暖引起的蒸发增强和冰川融化的背景下，由此导致的水位变化可能影响着高寒湿地的CH4和CO2通量，这进一步加剧了通量的不确定性。本项目拟选取位于青藏高原腹地纳木错湖滨的藏北嵩草-苔草高寒湿地，进行自然水位梯度上的全年观测，定量CH4和CO2通量，减小二者通量估算中的不确定性尤其是CH4高估问题；并进一步指示长期水位变化对CH4和CO2通量的影响趋势和程度；探索性开展机理实验，初步理解水位变化对CH4影响的机理机制。本项目旨在摸清典型高寒湿地主要温室气体源汇的"家底"，并明确和理解高寒湿地生物地球化学循环对气候变化的反馈过程。

湿地是全球最大的CH4排放源，也是重要的CO2源汇功能区。我国青藏高原水源丰富、地形起伏大、冻土发育水分不易下渗，其高寒湿地面积约占我国天然湿地的1/3强。但目前对高寒湿地CH4和CO2通量估算不确定性较大，尤其是对CH4排放存在潜在高估。本项目通过选取位于青藏高原腹地纳木错湖滨的藏北嵩草-苔草高寒湿地，开展了自然水位梯度上的通量观测，并结合数据汇总和机理模型模拟，研究了高寒湿地水位变化对CH4释放和碳平衡的影响。通过连续的观测结果发现，沼泽化草甸CH4释放显著低于典型沼泽，这一现象在青藏高原普遍存在，说明基于典型沼泽的估算可能高估了青藏高原高寒湿地CH4释放量。高寒湿地CO2吸收并不能抵消其CH4释放带来的增温效应；水位升高（水分增加）能够促进高寒湿地CH4释放，并提高高寒湿地植物群落对大气CO2的吸收能力，但生态系统净吸收的增加并不能抵消CH4释放的促进作用。依托本次观测获取的数据，结合其他已有观测数据，本项目还使用机理模型模拟了青藏高原区域尺度上的高寒湿地CH4通量，发现青藏高原仅是一个弱的CH4源，低于之前对这一地区的预期；然而，在气候变暖和湿地面积扩张的双重影响下，CH4释放将对气候变化形成正反馈。本研究的观测结果初步认识了高寒湿地CH4释放强度的现状，初步摸清了这一地区高寒湿地CH4释放的“家底”。