张掖湿地甲烷通量动态特征及其影响因子

于2012年7月—2014年6月对地处干旱区的张掖湿地甲烷(CH_4)通量进行观测,分析其CH_4通量的变化特征及其影响因子。结果表明:CH_4通量的日变化趋势总体表现为白天大于夜间;不同季节CH_4通量排放特征差异明显,夏季最大,春秋次之,冬季最小;CH_4通量日总量与空气温度、土壤温度之间指数相关关系显著,其中4 cm处土壤温度与之相关性最强;1—6月摩擦风速(U*)与CH_4通量显著正相关;结合CO_2通量观测数据,研究时段张掖湿地净碳吸收量为495.92 g C m~(-2)a~(-1),为明显碳汇。

CH4 flux variations and main factors from a reed wetland oasis-desert area in Zhangye, China

Analyzing the characteristics and variations of CH₄ flux in wetland would be very helpful in order to understand the importance of the carbon cycle in the terrestrial ecosystem. In the arid area, the Zhangye wetland features complex meteorological conditions, which have introduced obvious uncertainties into the carbon fluxes. However, there are few research studies on the carbon flux of wetland in the arid areas. It is helpful to strengthen the study of wetland ecological system in the arid areas. In order to study the dynamics of carbon flux in a wetland ecosystem, CO₂ flux and CH₄ flux were measured using an eddy covariance technique over a phragmites-dominated wetland in Zhangye, Gansu Province (from June in 2012 to August in 2014). In the present study, the CH₄ flux variations and its main driving factors were analyzed based on the eddy covariance observations. The raw 10 Hz data were processed into 30 min mean values based on data quality control (spike detection, coordinate rotation, frequency response correction, etc.) and gap-filling (linear interpolation and Look-up Table method). The result showed the CH₄ flux reaching its maximum in summer (0.34 g CH₄ m^-2 d^-1), then spring and autumn, while getting the minimum values in winter (0.02 g CH₄ m^-2 d^-1). Diurnal variation of CH₄ flux indicated that the daytime values were higher than that of nighttime. There was an exponential relationship between CH₄ flux and air temperature and soil temperature, and it was mostly correlated with the soil temperature in 4-cm depth, where the relationship was y=0.07614e^0.03402x and R² is 0.3560. CH₄ fluxes also exhibited a strong relationship with friction velocity (R²=0.91 and 0.94, respectively, from January to March and from April to June). The enhanced turbulence could increase the ventilation and exchange of CH₄ flux. CH₄ flux significantly influenced the total carbon budget. By considering the absorption and emission of CO₂ and CH₄ fluxes, the net carbon uptake was 495.92 g C m^-2 a^-1. The carbon sink in Zhangye wetland was apparent during the study period.