Geological methane emissions and wildfire risk in the degraded permafrost area of the Xiao Xing’an Mountains, China

Abstract

With global warming, the carbon pool in the degradation zone of permafrost around the Arctic will gradually be disturbed and may enter the atmosphere in the form of released methane gas, becoming an important factor of environmental change in permafrost areas. We selected the northwestern section of the Xiao Xing'an Mountains in China as the study area, located in the degradation zone on the southern margin of the permafrost region in Eurasia, and set up multiple study monitoring areas equipped with methane concentration sensors, air temperature sensors, pore water pressure sensors and soil temperature sensors for long-term monitoring of data changes using the high-density electrical method, ground penetrating radar and on-site drilling to survey the distribution of frozen soil and geological conditions in the study area, combined with remote sensing images of Sentinel-2 L1C and unmanned aerial vehicle photographs and three-dimensional image reconstruction, analysis of fire activities and related geological environmental factors. The results show that since 2004, the permafrost thickness of the marsh wetland in the study area has gradually reduced and the degradation rate obviously accelerated; the organic matter and methane hydrate (metastable methane hydrate and stable methane hydrate) stored in the permafrost under the marsh wetland are gradually entering the atmosphere in the form of methane gas. Methane emissions show seasonal changes, and the annual methane emissions can be divided into three main stages, including a high-concentration short-term emission stage (March to May), a higher-concentration long-term stable emission stage (June to August) and a higher-concentration short-term emission stage (September to November); there is a certain correlation between the change in atmospheric methane concentration and the change in atmospheric pressure and pore water pressure. From March to May every year (high-concentration short-term emission stage), with snow melting, the air humidity reaches an annual low value, and the surface methane concentration reaches an annual high value. The high concentration of methane gas entering the surface in this stage is expected to increase the risk of wildfire in the permafrost degradation area in two ways (increasing the regional air temperature and self-combustion), which may be an important factor that leads to a seasonal wildfire frequency difference in the permafrost zone of Northeast China and Southeast Siberia, with the peak in spring and autumn and the monthly maximum in spring. The increase in the frequency of wildfires is projected to further generate positive feedback on climate change by affecting soil microorganisms and soil structure. Southeastern Siberia and northeastern China, which are on the southern boundary of the permafrost region of Eurasia, need to be targeted to establish fire warning and management mechanisms to effectively reduce the risk of wildfires.

Response: Commentary: The Impact of Climate Change on Landslides in Southeastern of High-Latitude Permafrost Regions of China

“…We found that during every spring in the study area, a large amount of methane gas is released, which mainly comes from the release of geological methane and microbial methane production in permafrost, and the release of this part of greenhouse gas will lead to an increase of air temperature, it will accelerate the degradation of permafrost, will then play a role in promoting global warming, and also lead to geomorphic changes (Shan et al, 2020a;Shan et al, 2020b;Shan et al, 2021).…”

“…The soil composition in the study area contains both fine-grained structures such as clay and coarsegrained structures such as gravelly sandstone. After observation, it was found that the frozen soil layer near the study area is gradually degrading (Shan et al, 2020a), which leads to a higher damping ratio of the soil in the study area, resulting in a faster attenuation of traffic load and a smaller spreading distance. In addition, statistics on landslides near K177 + 550 in the study area found that not only do landslides exist in the area close to the highway, but also in areas far away from the road (845.86 m).…”

“…In addition, since 2004, the surface melting index near the study area has increased significantly; the surface freezing index and the surface freezing number have shown a significant downward trend. Affected by factors such as rising air temperature, the remaining shallow permafrost in the study area may be completely thawed, as shown in Figure 1B (Guo et al, 2020;Shan et al, 2020a;Shan et al, 2020b).…”

“…In addition, China's population, economy, and urbanization are mainly concentrated in eastern and southern areas, while population growth and economic development in the Sunwu FIGURE 1 | Permafrost degradation, population, urbanization, and landslide distribution near the study area. (A) Surface temperature changes of the Sunwu area, including the data of Sunwu national weather station and MODIS data (Guo et al, 2020;Shan et al, 2020b). (B) Changes of surface freezing, thawing index, and freezing number from 1960 to 2019.…”

“…(B) Changes of surface freezing, thawing index, and freezing number from 1960 to 2019. The calculation method is shown in reference (Guo et al, 2020;Shan et al, 2020b) (located in Heihe City, Heilongjiang Province) in northern China are relatively slow, and some areas even show negative growth (Hua, 2018). Since 1971, the population growth rate of Heilongjiang Province has shown a gradual decline, and there has been a negative population growth from 2013 to 2018 (Figure 1C).…”