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Impacts of riparian wetlands on the seasonal variations of watershed‐scale methane budget in a temperate monsoonal forest
Author(s) -
Sakabe Ayaka,
Kosugi Yoshiko,
Okumi Chika,
Itoh Masayuki,
Takahashi Kenshi
Publication year - 2016
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2015jg003292
Subject(s) - environmental science , riparian zone , forest floor , sink (geography) , hydrology (agriculture) , temperate climate , wetland , watershed , soil water , riparian forest , spatial variability , monsoon , temperate forest , atmospheric methane , temperate rainforest , seasonality , atmospheric sciences , methane , ecology , ecosystem , soil science , climatology , geology , geography , habitat , mathematics , computer science , biology , machine learning , statistics , cartography , geotechnical engineering
Forest soils are considered a methane (CH 4 ) sink because dry soils can oxidize CH 4 ; however, previous studies on CH 4 fluxes in humid temperate forests indicated a high spatial and temporal variability in CH 4 fluxes, especially in CH 4 emissions from wet soils close to riparian zones, which can turn the soil of a whole forest from a CH 4 sink to a CH 4 source. In this study, the spatial and temporal variability of soil CH 4 fluxes was investigated in a Japanese coniferous forest, including a riparian wetland and a hillslope water‐unsaturated forest floor, based on multipoint flux measurements using laser‐based CH 4 analyzers over a period of 2 years. We identified CH 4 emission hot spots (60.2 ± 169.1 nmol m −2 s −1 from 117 sampling points) in the wetland in late summer, while the CH 4 absorption rate in the forest floor was comparatively lower (−1.2 ± 1.4 nmol m −2 s −1 from 119 sampling points). The temporal variability of watershed‐scale CH 4 flux was amplified by a clear seasonal cycle of soil temperature and rainfall pattern under the Asian monsoon climate. The watershed‐scale CH 4 budget showed that the forest turned into a CH 4 source during the summer owing to the high and variable CH 4 emissions from the riparian wetland and the lower part of the hillslope. Overall, our results indicated that CH 4 emissions from small riparian areas are important in controlling forest CH 4 dynamics at a watershed scale.