Unraveling methanogenesis processes and pathways for Quaternary shallow biogenic gas in aquifer systems through geochemical, genomic and transcriptomic analyses.

Shallow biogenic gas is crucial in global warming and carbon cycling. Considering the knowledge gap in the understanding of methanogenesis and metabolic mechanisms within shallow groundwater systems, we investigated Quaternary shallow biogenic gas resources from the Hetao Basin in North China, which were previously underexplored. We systematically analyzed the genesis of gas and formation water, microbial communities, methanogenic processes, and pathways using geochemistry, genomics, and transcriptomics. Our findings indicated that active freshwater environments are conducive to microbial activity and the generation of primary microbial gases. A diverse range of microbes with functions, such as hydrolysis (e.g., Caulobacter), acidogenesis, and hydrogen production (e.g., Sediminibacterium), synergistically contributed to the methanogenic process. Methanogens predominantly comprised hydrogenotrophic methanogens (e.g., Methanobacteriales), although H2-dependent methylotrophic methanogens (e.g., Methanofastidiosa) were also prevalent. The metabolic processes of the different methanogenic pathways were revealed based on functional gene analysis and mapping results. Furthermore, the composition of the community structure, functional predictions, metagenomics, and metatranscriptomics underscored the contribution of the hydrogenotrophic pathway, which ranged from 52.22 % to 79.23 %. The aceticlastic pathway exhibited high gene abundance and was primarily associated with methylotrophs and other potential pathways. The H2-dependent methylotrophic methanogenesis pathway was constrained by low metabolic activity. By revealing the methane production mechanism of biogenic gas in shallow aquifer systems, this study provides a new perspective and profound comprehension of its ecological and environmental implications worldwide.

Mineral Characteristics of Low-Rank Coal and the Effects on the Micro- and Nanoscale Pore-Fractures: A Case Study from the Zhundong Coalfield, Northwest China.

The mineral characteristics (occurrence, type, and content) of low-rank coal and their influence on coalbed methane (CBM) reservoirs are investigated at the micro- and nanoscales. Six coal samples of three representative coalmines were used to demonstrate the uniform tectonization from the Zhundong coalfield, NW China. Based on optical microscopy and scanning electron microscopyenergy dispersive spectrum (SEM-EDS) analysis, the mineral composition and occurrence characteristics were discussed. The micro- and nanoscale reservoir characteristics in low-rank coal (pore size distribution and adsorption capability) were studied by diverse methods, including lowtemperature N2 adsorption/desorption, mercury intrusion porosimetry and CH4 isotherm adsorption analysis. The coal reservoir nuclear magnetic T2 spectra of porosity and movable fluid were obtained by combining low-field nuclear magnetic resonance (NMR) analysis, which has an advantage of determining pore fluid technology. The mineral content is highly variable (4˜16 vol.%) in the Xi Heishan prospecting area of the Qitai region. Kaolinite, goyazite, ankerite and anorthosite were microscopically observed to be filling in coal pores and microfractures, and the minerals are given priority to silicate minerals. There is a greater content of mesopores (100-1000 nm) and transition pores (10-100 nm), and they are well connected. The micropores (0-10 nm) are dominated by parallel plate, closed or wedge-shaped pores. Furthermore, the microfractures are mainly observed for types B (width ≥ 5 µm and length≤ 10 mm) and D (width<5 µm and length<300 µm). The results show that microfractures B and C (width< 5 µm and length ≥ 300 µm) are better connected, but the orientation and connectivity of type D are worse. The Langmuir volume and mesopore content decreased with increasing mineral content, which shows that the low-rank coal minerals filled some adsorption space; the reduced CBM adsorption capacity and cellular pore and intergranular pore filled with minerals affect the mesopore content. Therefore, mineral characterization significantly influences methane adsorption capacity and pore structure.

A Refinement of Nitrogen Isotope Analysis of Coal Using Elemental Analyzer/Isotope Ratio Mass Spectrometry and the Carbon and Nitrogen Isotope Compositions of Coals Imported in China.

The ability to accurately analyze nitrogen (N) isotopes of coal is important for evaluating its contribution to NO X emissions to the atmosphere via coal combustion. Although an elemental analyzer/isotope ratio mass spectrometer is highly efficient for analyzing the N isotopes of coal, it requires large amounts of organic matter (>3 mg) to produce enough N2 to enable N isotope measurements due to the high organic carbon contents of coal with relatively low N contents. Therefore, to completely oxidize the organic matter, more oxidant matter is required to enhance coal combustion in a reactor tube in an elemental analyzer through injecting O2 during the combustion process. One reference material (RM) (GBW11104) was used to determine the effect of amounts of O2 on the accuracy of nitrogen isotope values obtained. Our results show that small amounts of O2 injected into the EA resulted in incomplete coal combustion, which yielded a lower N content and more positive N isotope ratio for RM (GBW11104) than those obtained by complete combustion. Thus, to ensure the complete combustion of coal, large O2 injection amounts are required. The refined method was applied to provide the N isotope values of coals imported from Southeast Asia, Russia, and Australia. Combined with the carbon isotope values, the imported coals from three coal-producing regions (Southeast Asia, Russia, and Australia) display distinct characteristics.

Formation of large carbonate concretions in black cherts in the Gufeng Formation (Guadalupian) at Enshi, South China.

The formation of carbonate concretions is a cementation process which passively infills the pore spaces within sediments. They record the original environments of deposition and diagenetic conditions of the host rocks. Little is known about the precise mechanisms responsible for the precipitation of carbonate concretions. The most common host rocks are mudstones/shales, sandstones, and limestones. This study presents an example of large carbonate concretions from an unusual host rock, the black bedded cherts of the Gufeng Formation (Guadalupian) at Enshi on the northern Yangtze Platform, South China. Petrographic observations (X-ray diffraction, optical microscopy, scanning electron microscopy) and multiple geochemical analyses (pyrite- and carbonate-associated-sulfate (CAS)-sulfur isotopes, carbon isotopes) indicate that (a) the studied carbonate concretion are mainly composed of micritic calcite with subordinate dolomite; (b) the concretions may have been mainly formed in the bacterial sulfate reduction (BSR) zone during very early diagenesis near the sediment-water surface; (c) the paleo-bottom water overlying the sediments during formation of the concretions was mainly euxinic; and (d) the growth of the studied concretions proceeded via a pervasive model, where later cementation phase initiated in the lower part of the concretions and progressed upward.

Hydrogeochemistry signatures of produced waters associated with coalbed methane production in the Southern Junggar Basin, NW China.

The Southern Junggar Basin (SJB) in China is an emerging coalbed methane (CBM) development area with abundant low-rank CBM resources. CBM development is accomplished by pumping significant volumes of water from the aquifer, and this water is commonly termed as produced water, which has great utilization values for the water-deficient areas like SJB. Geochemistry signatures are prerequisites in the management of the produced water. Meanwhile, geochemistry surveys of this produced water could also help study the basin hydrogeology and then serve the CBM development. In this study, geochemical compositions of the produced waters, including major ions, stable isotopic compositions, trace elements, and rare earth elements, were analyzed. Results show that produced waters from CBM wells in the SJB are of Na-HCO3 type and have wide total dissolved solid (TDS) ranges from 963 to 11,916 mg/L (avg. 7417 mg/L). Cl-, Na+, and HCO3- are the principal determinates of the TDS contents of the produced waters, and their concentrations all increase with greater depth of the produced waters. Overall, the net results of groundwater-aquifer mineral-bacteria interactions with groundwater flowing along the flow path are to deplete Ca2+, Mg2+, and SO42- and increase Na+, Cl-, HCO3-, and TDS. Stable isotopic values of the CBM produced waters (δDH2O and δ18OH2O) cluster along or below the local meteoric water line (LMWL), and the shift of stable isotopic values to the right side of LMWL was affected by a joint effect of evaporation and mixing with near-surface water. Trace elements that exceed the regulated concentrations for drinking water of China include As, Fe, Mn, Ba, and Ni, among which Ba and Fe need to be most concerned because over 50% of the CBM produced waters exceed the regulated values. Through principal component analysis, the trace element associations in the CBM produced waters and their potential origins were analyzed. The ∑REY concentrations of the CBM produced waters increase exponentially with the increase of pH and present a certain correlation with TDS. The relationship between ∑REY concentrations and TDS reflects different water-rock reaction degrees and hydrogeological backgrounds.

Changes in Concentration and Distribution of Biomarkers in Biodegraded Oils from Dongying Depression, China.

The alkane fraction of 11 biodegraded oils and five non-biodegraded oils from the Dongying Depression, Bohai Bay Basin, eastern China, were analyzed by gas chromatography-mass spectrometry to investigate the biomarker alteration caused by biodegradation. Results indicated that the concentration of 25-norhopanes was correlated with increased biodegradation. The oil samples showed an increase in the C31 and C32 hopane 22S/(22S + 22R), C29 sterane C2920S/(20S + 20R), and C29ßß/(ßß + αα) thermal maturity parameters in the heavily biodegraded oils. Oleanane was preferentially biodegraded compared with C3017α-hopane, which was preferentially biodegraded compared with C2917α, 21ß-norhopane, C30 moretane, and C29 25-norhopane. The selective depletion of C27-C29 steranes followed the order ααα 20R > ααα 20S + αßß 20R > αßß 20S and C27 > C29 > C28, and the diasteranes and C20-C21 steranes were much more resistant to biodegradation than regular C27-C29 steranes. The steranes were generally preferentially biodegraded compared with the hopanes in this study.

[Design of an artificial sphincter system with bio-feedback function based on MSP430].

In this paper, we advance a new treating method for rectectomy postoperative anus incontinence, which is called "artificial sphincter system with biofeedback-function". The system simulates the function of human's sphincter and has entered into a stage of simulation experiments on animals.