若尔盖高原湿地甲烷排放的时空异质性

集中于北美落基山高山湿地甲烷排放的零星报道远不能解析全球高山湿地甲烷源强. 因此,世界范围内其他区域高山湿地甲烷排放的研究对于合理估计全球高山湿地甲烷源强,意义重大.采用静态箱-气相色谱法,基于3种典型湿地类型的甲烷排放数据,认为若尔盖高原湿地生长季甲烷的平均排放量为4.69 mg CH4 m-2 h-1.同时根据2a数据,初步分析了甲烷通量及其对环境因素和生物因素的响应特征,结果表明:(1)甲烷排放昼夜变化具有双峰模式 (主峰出现在15:00,次峰出现在06:00),可由土壤温度以及植物气孔开启来解释.(2)若尔盖湿地甲烷排放季节动态较为典型,即在7月份或8月份出现排放高峰,冬季甲烷排放较少.生长季,对3类群落类型,表面温度与甲烷排放显著相关 (r2=0.55,P<0.05,n=30),地表水位和植物群落高度与甲烷排放相关性更为显著 (r2=0.32,0.61,P<0.01,n=30).分析认为该季节节律是由温度以及植物生长状况直接影响的,而水位则是使该节律发生波动的原因(高原气候).(3)群落尺度下,物候学上相当重要的两个时期,甲烷排放通量均有较高的空间变异 (植物生长高峰变异系数为38%,积雪融化高峰为61%).通过逐步回归线性分析,发现植物生长高峰期,地表水位和群落高度是影响甲烷排放空间差异的主要因素 (r2= 0.43,0.59,P<0.01,n=30).(4)景观尺度下,生长季,景观尺度下甲烷排放有较大的空间变异,湖滨湿地甲烷平排放量最高为11.95 mg CH4 m-2h-1,其次为宽谷湿地,其排放量为2 12 mg CH4 m-2h-1,河岸湿地表现为甲烷吸收,其吸收量为0.007 mg CH4 m-2h-1.地表水位、植物地上生物量以及植物高度能够很好地解释甲烷排放的景观差异.

patiotemporal variation of methane emissions from alpine wetlands in Zoige Plateau

Zoige Plateau (av. 3400 m a.s.l.), located in the eastern edge of Qinghai-Tibetan Plateau (av. 4000 m a.s.l.), is a complete and orbicular plateau surrounded by a series of alpine mountains (av. 4000 m a.s.l.), covering an area of 2.8×104 km2. Due to the unique alpine climate of the plateau, characterized by cold-long winters alternating with cool-short summers with relatively high precipitation, these alpine wetlands undergo a continuous methane emission through the frozen soil, and then an impulse of methane emission during and immediately following the soil thawing. It was found that methane emission was well coupled with the growing rhythm of plants. However, the magnitude, temporal, and spatial patterns of methane fluxes in alpine wetlands on Zoige Plateau are still highly uncertain. To refine the actual global methane budget of alpine wetlands, methane fluxes were measured among three wetland landscapes at the Zoige National Wetland Reserve. Based on such measurements, it was roughly estimated that mean methane flux from Zoige Plateau was 4.69 mg CH4 m-2 h-1 in the growing season. A special diurnal variation pattern of methane emission was observed that there was two emission peaks: one minor peak occurred at 06:00 and the major one at 15:00. In this study, soil temperature of 5cm depth was considered as the key factor to explain the higher peak at 15:00. After clipping, the methane flux from the Eleocharis valleculosa and Carex muliensis sites were dropped substantially by 47.1% and 63.2%, respectively. The stomata whose opening and closure were under the control of light (PAR) should be major vents for methane efflux. Therefore, one hour after sunrise, the stomata opened substantially and methane efflux reached a small climax at 06:00 because a lot of methane accumulated at night.There were clearly seasonal patterns of methane flux in different environmental types during the growing and non-growing seasons. In the growing season, the main maximum values of methane flux were found in July and August, except for a peak value in September in CM sites. In the non-growing season, the similar seasonal variation pattern was shared among all of three sites, in which the methane emissions increased from February to April. It was found that the determining factors in the growing season were ground surface temperatures, standing water depths and plant community heights; while in the non-growing season, ice thickness was found most related to flux. Different environmental types within the wetland also influenced the seasonal pattern of methane flux. There were high spatial variations among environmental types and for all spots in the two phenological seasons. In the peak growing season, coefficients of variation were on the average 38% among environmental types and 57% within environmental types; in the quickly thawing season, coefficients of variation were on the average 61% among environmental types and 77% within environmental types. The key influencing factors were standing water depths and plant community height in the peak growing season, while in the quickly thawing season, the redox potentials were best related with the methane emissions due to the complex of the water phases (r2=0.72, P<0.05).Landscape types had significant impacts on methane fluxes. Standing water depth was the major factor to explain the landscape variation of methane flux, while vegetation characteristics were also valuable to predict methane flux from Zoige Plateau.