Vertical profiles of methane concentration above and within the canopy of a temperate Japanese cypress forest
Vertical profiles of methane concentration above and within the canopy of a temperate Japanese cypress forest
复制标题
DOI：
10.1016/j.aeaoa.2021.100143
复制
发表时间：
2021-11
影响因子：
--
通讯作者：
Kenshi Takahashi;Ayaka Sakabe;Akito Kanazawa;Y. Kosugi
中科院分区：
文献类型：
--
作者：
Kenshi Takahashi;Ayaka Sakabe;Akito Kanazawa;Y. Kosugi
甲烷（CH 4）是主要的温室气体之一，因此其来源的识别和量化是非常重要的。目前，高地森林土壤水分不饱和通常被认为是CH 4的汇，但近年来越来越多的证据表明，某些环境下的树干也可以成为CH 4的源，森林生态系统CH 4动态的研究进入了一个新的阶段。在这项研究中，我们测量了CH 4浓度的垂直分布内和上方的森林冠层，以研究它们是如何影响当地的生态过程和天气到当地尺度的大气过程。剖面测量进行了使用气象塔在温带日本柏树林与30分钟的时间分辨率。在我们的网站冠层以上的CH 4浓度的时间序列数据显示偶尔尖峰相对于背景水平，这些尖峰对应于CO2浓度的时间变化。后向轨迹分析表明，大部分的空气质量与峰值的CH 4和CO2浓度有大陆的起源。CH 4浓度的季节平均日变化特征弱于CO2浓度。据认为，夜间积累的CH 4在一个稳定的地面层和对流扩散到混合层占CH 4的昼夜特性，而生态过程中发挥了重要作用，在观测到的CO2水平的昼夜特性。林冠内CH 4浓度的垂直分布从林冠到林下呈单调递减的趋势，随季节变化较大。剖面同意土壤-大气CH 4通量在我们的网站上使用密闭室的方法测量，表明在高地地区的表层土壤起着决定冠层内CH 4的分布的主要作用。此外，据推测，至少在我们的网站，从茎和叶的CH 4排放，这已成为近年来的一个热门话题，是不显着的柏树在高地地区足以影响冠层内CH 4的分布在研究期间。
Methane (CH4) is one of the major greenhouse gases, and therefore its source identification and quantification are quite important. So far water-unsaturated soils of upland forests are usually recognized as sinks, but recent increasing evidence supports tree stems in certain environments can be a source of CH4, and thereby research on the dynamics of CH4in forest ecosystems has entered a new phase. In this study, we measured vertical distributions of CH4concentrations within and above a forest canopy to examine how they are influenced by local ecological processes and synoptic-to local-scale atmospheric processes. Profile measurements were conducted using a meteorological tower in a temperate Japanese cypress forest with a 30-min time resolution. Time series data of CH4concentrations above the canopy at our site showed occasional spikes relative to background levels, and these spikes corresponded with temporal variations in CO2concentrations. Backward trajectory analyses showed that most of the air masses associated with the spikes in CH4and CO2concentrations had continental origins. Seasonal-mean diurnal properties in CH4concentrations above and within the canopy were weaker than those for CO2concentrations. It was considered likely that nighttime accumulation of CH4in a stable surface layer and its convective diffusion into a mixed layer accounted for the diurnal properties in CH4, while ecological processes played a major role in the diurnal properties observed in CO2levels. Vertical distributions in CH4concentration within the canopy showed a monotonic decrease from the canopy to the forest floor, with variations depending on the season. The profiles agreed with soil-atmosphere CH4fluxes measured using a closed-chamber method at our site, indicating that the surface soil in upland areas plays a major role for determining the within-canopy distributions of CH4. Also, it was inferred that at least at our site, CH4emissions from stems and leaves, which has become a hot topic over the recent years, was not significant for cypress trees in upland area enough to influence the within-canopy distributions of CH4during the study period.