5:15 PM - 7:15 PM
[BCG05-P02] Response of soil methane uptake rates to increasing atmospheric methane concentrations
Keywords:Automated chamber system, Long-term observation, Soil GHG flux, Upland
Upland forest soils can act as effective sinks for atmospheric methane (CH4). It is important to investigate the interannual variation of soil CH4 uptake rates under changing environment. In particular, there have been few direct verifications how soil CH4 uptake rates respond to currently increasing atmospheric CH4 concentrations based on long-term observation of soil CH4 fluxes. We conducted continuous measurement of soil CH4 fluxes for 11 years in a temperate forest with an automated chamber system to investigate how interannual variations of soil CH4 uptake rates vary with environmental changes, including atmospheric CH4 concentrations.
The observations were made in a temperate coniferous forest in the Kiryu Experimental Watershed (34°58’N, 136°00’E), located in Shiga prefecture, central Japan. The entire watershed was underlain by weathered granite, with abundant amounts of albite. The soil type was typical brown forest soil. The forest consisted of Japanese cypress (Chamaecyparis obtuse Sieb. Et Zucc.), which was planted in 1959. Soil chambers were installed at three points on the water-unsaturated forest floor around the meteorological tower. The chambers were connected to a laser-based CH4 analyzer (FMA-100, Los Gatos Research) and a CO2/H2O analyzer (LI-840, LI-COR) by tubes, and soil CH4 flux measurements were repeated every 30 min by switching program-controlled valves. In addition, CH4 concentrations at five heights from near the forest floor to above the canopy were measured at the tower every 30 min by the same automated system and gas analyzers. Air temperature, soil temperature at a depth of 2 cm, precipitation, soil moisture content at a depth of 0-30 cm near each chamber were also measured. Missing values for soil CH4 fluxes were filled using the random forest regression with temperature, soil moisture, and atmospheric CH4 concentration. The data analysis period was 11 years, from January 1, 2009 to December 31, 2019.
The mean annual temperature showed an increasing trend, while total annual precipitation did not show any significant increasing or decreasing trend over the 11-year period. Atmospheric CH4 concentrations observed above the canopy showed an increasing trend from 2009 to 2017, and the increasing trend stagnated since 2018. The mean annual soil CH4 uptake showed an increasing trend from 2013 to 2017, while stagnated since 2018. Principal component analysis with the mean annual soil CH4 uptake and environmental data showed that soil CH4 uptake was small in years with high precipitation, and was large when precipitation was moderate or lower and atmospheric CH4 concentrations were high. In conclusion, soil CH4 uptake in the temperate forest has increased in response to increasing atmospheric CH4 concentration from 2009 to 2019, while being influenced by precipitation.
The observations were made in a temperate coniferous forest in the Kiryu Experimental Watershed (34°58’N, 136°00’E), located in Shiga prefecture, central Japan. The entire watershed was underlain by weathered granite, with abundant amounts of albite. The soil type was typical brown forest soil. The forest consisted of Japanese cypress (Chamaecyparis obtuse Sieb. Et Zucc.), which was planted in 1959. Soil chambers were installed at three points on the water-unsaturated forest floor around the meteorological tower. The chambers were connected to a laser-based CH4 analyzer (FMA-100, Los Gatos Research) and a CO2/H2O analyzer (LI-840, LI-COR) by tubes, and soil CH4 flux measurements were repeated every 30 min by switching program-controlled valves. In addition, CH4 concentrations at five heights from near the forest floor to above the canopy were measured at the tower every 30 min by the same automated system and gas analyzers. Air temperature, soil temperature at a depth of 2 cm, precipitation, soil moisture content at a depth of 0-30 cm near each chamber were also measured. Missing values for soil CH4 fluxes were filled using the random forest regression with temperature, soil moisture, and atmospheric CH4 concentration. The data analysis period was 11 years, from January 1, 2009 to December 31, 2019.
The mean annual temperature showed an increasing trend, while total annual precipitation did not show any significant increasing or decreasing trend over the 11-year period. Atmospheric CH4 concentrations observed above the canopy showed an increasing trend from 2009 to 2017, and the increasing trend stagnated since 2018. The mean annual soil CH4 uptake showed an increasing trend from 2013 to 2017, while stagnated since 2018. Principal component analysis with the mean annual soil CH4 uptake and environmental data showed that soil CH4 uptake was small in years with high precipitation, and was large when precipitation was moderate or lower and atmospheric CH4 concentrations were high. In conclusion, soil CH4 uptake in the temperate forest has increased in response to increasing atmospheric CH4 concentration from 2009 to 2019, while being influenced by precipitation.