Abstract:

We selected the Dajiuhu Peatland, located in Shennongjia, Hubei Province, China, as the study site. Based on the monitoring data from 2016 to 2019 using the eddy covariance technique, the variation pattern and influencing factors of methane flux were analyzed. The results demonstrated that the Dajiuhu peatland served as a net source of CH₄, and the annual CH₄ emissions displayed an increasing tendency. On an annual scale, the CH₄ emission showed an upward trend followed by a decline, and the largest emission emerged in summer. On the diurnal scale, the highest CH₄ flux occurred in the daytime, which was higher than the nocturnal CH₄ flux. From 2016 to 2019, the annual diurnal fluxes accounted for 57.76%, 59.09%, 61.34%, and 50.84% of the total emissions, respectively, which were the primary components of CH₄ fluxes in the Dajiuhu Peatland. Between 2016 and 2019, the maximum ratio of diurnal fluxes were 74.59%, 81.85%, 67.22%, and 70.12%, respectively, which mostly occurred in spring. The maximum ratio of nocturnal fluxes were 48.82%, 50.54%, 44.59%, and 54.31%, which mainly occurred in summer. This phenomenon might be related to the distinct diurnal temperature difference in spring and the small difference in summer. Correlation analysis suggested that the variation of CH₄ emission was positively correlated with air temperature (t_s) and soil temperature (t_a) (r=0.61, P=0.000; r=0.59, P=0.000), whereas negatively correlated with surface soil moisture content (SWC) (r= ?0.24, P=0.000). Path analysis and multiple linear regression analysis illustrated that t_s, t_a, and photosynthetically active radiation (PAR) were the major factors affecting the diurnal CH₄ flux, and t_s was the most important factor (standardized coefficient=0.418, P=0.000). Furthermore, t_s, t_a and SWC had more regulating effects on nocturnal CH₄ flux changes, and t_a played the most significant role in the process (standardized coefficient=0.246, P=0.000). From 2016 to 2019, the interannual variation ranges of SWC were 29.99%?81.70%, 61.88%?80.76%, 61.38%?81.35%, 54.95%?80.17%, and the annual mean values of SWC were 70.35%, 78.23%, 77.82%, 68.10%, respectively. SWC presented frequent and prominent fluctuations in 2016 and 2019, while relatively stable in 2017 and 2018. In addition, supplemented with linear regression, we found that t_s was a stronger indicator of CH₄ flux when SWC fluctuated frequently, while t_a was more indicative when SWC was steady.

Key words: peatland, eddy covariance, methane emission, correlation analysis

摘要：

研究选取神农架大九湖泥炭湿地作为研究对象，基于2016－2019年涡度相关设备观测数据，分析大九湖泥炭湿地CH₄通量变异特征及其影响因素。结果表明，大九湖泥炭湿地是“CH₄源”，CH₄年排放量呈逐年上升趋势。大九湖泥炭湿地CH₄排放呈现以下规律：年尺度来看，CH₄排放量呈先上升后下降的趋势，高排放量集中在夏季；日尺度来看，CH₄高排放量集中在白天，CH₄昼通量高于夜通量。2016－2019，年昼通量百分比分别达到57.76%、59.09%、61.34%、50.84%，为大九湖泥炭湿地CH₄通量主要组成部分。昼通量占比最大值分别为74.59%、81.85%、67.22%及70.12%，主要发生在春季；夜通量占比最大值分别为48.82%、50.54%、44.59%及54.31%，主要出现在夏季，该现象可能与春季昼夜温差较大而夏季昼夜温差较小有关。CH₄通量与气象因子相关性分析结果表明，整体上来看，大九湖泥炭湿地CH₄通量与气温（t_a）和土壤温度（t_s）呈正相关（r=0.61，P=0.000；r=0.59，P=0.000），与表层土壤含水率（SWC）呈负相关性（r= ?0.24，P=0.000）。路径分析和多元线性回归分析结果表明，t_s、t_a和光合有效辐射（PAR）是影响昼通量的主要因子，其中t_s的影响最重要（标准化系数=0.418，P=0.000）；t_s、t_a和SWC对夜通量更具调节作用，其中t_a的影响最显著（标准化系数=0.246，P=0.000）。2016－2019年，研究区内SWC年际变化范围分别为29.99%－81.70%、61.88%－80.76%、61.38%－81.35%、54.95%－80.17%，年均值为70.35%、78.23%、77.82%、68.10%，2016年和2019年波动频繁，幅度较大，2017年和2018年较为平稳。结合一元线性回归结果得出，SWC波动频繁时，t_s对CH₄通量呈现更强的指示作用，SWC相对稳定时，t_a更具有指示意义。

关键词: 泥炭湿地, 涡度相关, 甲烷通量, 相关性分析