Research on aerobic oxidation of methane bacteria and its influencing factors in Chongqing central city section of the Yangtze River, China.

Bacterial communities play an important role in the carbon cycle of freshwater ecosystems. In order to understand the influencing factors of bacterial community in the process of carbon cycle and search for measures to reduce carbon emissions, Chongqing central city section of the Yangtze River and its tributaries were selected to be the study area in this research. High-throughput sequencing was applied to study aerobic oxidation of methane bacteria (MOB) in sampling area. The results showed that there were spatial differences in the community diversity of aerobic MOB in the Yangtze River in central Chongqing. The Shannon index in the sediment (2.389-2.728) was higher than that in the water (1.820-2.458), and the community diversity in the middle reaches of the main river was higher than that in the upstream and the downstream. The aerobic MOB community was mainly dominated by Type II (Methylocystis). Most of operational taxonomic units (OTUs) in the top ten had high homology with MOB from river and lake sediments, and a few OTUs had high homology with MOB from paddy fields, forests and wetland soils. The main environmental factors affecting the community structure of aerobic MOB were NH4+-N, dissolved oxygen (DO), temperature (T, p ≤ 0.001), pH (p ≤ 0.05), methane (CH4) and carbon dioxide (CO2).

Community structure and network interaction of aerobic methane-oxidizing bacteria in Chongqing's central urban area in the Three Gorges Reservoir, China.

A reservoir is an important source of methane (CH4), which is consumed by aerobic methane-oxidizing bacteria (MOB), representing the main CH4 sink in water. The central urban area of Chongqing in the Three Gorges Reservoir (TGR) area was selected as the study area in 2021. High-throughput sequencing was used to analyze the community structure and abundance of MOBs. The results showed that Methylocystis (Type II) was the dominant MOB in water, whereas Methylococcus (Type I) and Methylocystis co-dominated the sediments. High water temperature in the study area largely accounted for the predominance of Type II MOBs in the two habitats. Moreover, the influence of environmental factors on MOB community and its interspecific relationship were significantly regulated by the operation of the TGR. In the low-water-level period, NO2--N and CO2 concentration significantly correlated with Methylocystis, whereas in the high-water-level period, the higher discharge and velocity weakened the influence of all environmental factors on Methylocystis. In addition, the scouring of sediments by increasing discharge in the high-water-level period caused a significant decrease in dissolved CH4 concentration. The decrease in substrate increased interspecific competition within the MOB community, especially between different types of MOBs, in the high-water-level period.

The characteristics and influencing factors of dissolved methane concentrations in Chongqing's central urban area in the Three Gorges Reservoir, China.

Methane (CH4) emissions from reservoirs have received widespread attention. The central urban area of Chongqing in the Three Gorges Reservoir area was selected as the study area in 2020. The temporal and spatial distribution of dissolved CH4 concentration and flux, key generation pathways, and influencing factors have been studied. The dissolved CH4 concentration in low-water-level period and impoundment period varied from 0.037~0.12 µmol·L-1 and 0.11~0.23 µmol·L-1, with the average values of (0.066 ± 0.0067) µmol·L-1 and (0.13 ± 0.034) µmol·L-1. The CH4 flux was (0.941 ± 0.217) µmol·m-2·h-1 in low-water-level period and (1.915 ± 0.204) µmol·m-2·h-1 in impoundment period. CH4 was produced by CO2 reduction and acetic acid fermentation, accounting for 17.95% and 82.05% of the total CH4 production, respectively. The dissolved CH4 concentration was significantly positively correlated with DO and NO3--N, and it is opposite with dissolved inorganic carbon. The dissolved CH4 concentration in this study area is affected by water environment (33.42%), inorganic nitrogen (29.60%), organic carbon (23.88%), and inorganic carbon (13.10%), and anthropogenic influences promoted dissolved CH4 concentration.