Soil salinization is an important factor affecting agricultural production in arid regions. Soil salinity has strong spatial variability. Xinjiang, located in the northwest of China, lies in an arid to semi-arid region where mulched drip irrigation technology is widely adopted to save irrigation water. However, soil salinization in Xinjiang remains severe, and soil salinity exhibits strong spatial variability. Therefore, investigating the spatial variability characteristics of soil salinity under mulched drip irrigation is of great scientific significance for efficient water conservation and salinity control in the arid regions.

To study the spatial variability of soil salinity in cotton fields under mulched drip irrigation, cotton fields at the experimental fields are located at paotai soil improvement experimental station of the 8th division, xinjiang production and construction corps (abbreviated as "paotai experimental station") and irrigation experimental station of water conservancy research institute, bayingolin administration bureau of tarim river basin, xinjiang (abbreviated as "bazhou experimental station") were selected for study. Soil salinity profiles were monitored in detail, and a combination of traditional statistical and geostatistical methods was used to analyze the spatial variability and distribution characteristics of soil salinity profiles in the study area based on the soil water flow system in cotton fields under mulched drip irrigation.

The results indicated that the coefficient of variation of soil electrical conductivity in the three profiles ranged from 0.54 to 0.67. The variability of topsoil electrical conductivity was largest, and the degree of spatial variability at depths of 10 to 45 cm decreased with increasing depth. Soil electrical conductivity had a strong spatial correlation in the three profiles. Spatial variability was mainly attributable to structural factors, and random factors accounted for 3.53%, 5.03%, and 6.61%, respectively. Soil electrical conductivity characteristics across the profiles exhibited low conductivity in shallow layers, locally high conductivity in intermediate zones, and high conductivity in deep layers. Horizontally, conductivity was lower near drip lines, while values between plastic mulch strips and in wide rows were higher, which correlated with factors such as soil water flow systems and particle composition. Overall, the soil salinity of the cotton field at the Paotai experimental station was higher than that at the Bazhou experimental station. The soil electrical conductivity was higher than 7.7 mS/cm, which had a negative effect on cotton growth.

The findings can provide a scientific basis for implementing efficient water conservation and salinity control measures and precision agriculture in arid regions.

Tight-sandstone fault-fracture reservoirs controlled by intra-plate strike-slip faults represent important exploration targets in the southern Ordos Basin. Nevertheless, these reservoirs exhibit highly complex internal architectures. Restricted by sparse well datasets and limited seismic resolution, conventional modeling approaches cannot adequately characterize the fine-scale internal structures of small-scale strike-slip fault-fracture bodies, resulting in insufficient geological constraints for high-precision three-dimensional reservoir modeling. These limitations severely constrain sweet-spot identification and reasonable deployment of development wells for tight oil exploitation.

Taking the Triassic Yanchang Formation of Jinghe Oilfield in the southern Ordos Basin as the research case, this study constructed a geological-knowledge database for fault-fracture reservoirs based on high-resolution outcrop datasets obtained via unmanned-aerial-vehicle (UAV)-based oblique photogrammetry. A three-level hierarchical modeling workflow was proposed, comprising fault-fracture reservoir outline delineation, internal structural-zone division, and internal reservoir-attribute characterization. The external boundary of fault-fracture reservoirs was jointly constrained by outcrop-derived statistical dimensions and seismic negative-curvature attributes. A fluctuating decreasing function describing fracture-density variation was introduced to characterize fracture attenuation away from faults. Combined with fracture-density thresholds of different structural units, this function enabled quantitative division of internal zones. Constrained by fracture-orientation, height and aperture statistics from outcrop observations and borehole-imaging logs, the discrete fracture network (DFN) technique was adopted to build a 3D fracture model. During the simulation of matrix-reservoir properties, the porosity-enhancement effect induced by fracture development was fully considered.

(1) Field statistics indicated that the width of fault-fracture reservoirs in the study area mainly ranged from 80 m to 160 m, and reservoir width presented a logarithmic correlation with vertical throw of strike-slip faults. (2) Fault-fracture reservoirs were internally divided into three units: crushed zone (5–20 m in width), fracture zone (15–50 m in width), and matrix zone (40–60 m in width). Fracture density showed a fluctuating decline with increasing distance from faults, which differed from conventional monotonic exponential-decay models reported in previous studies. (3) Fracture geometrical parameters of each internal structural unit were consistent with statistical results from outcrop analogues and borehole-imaging logs. The matrix-porosity enhancement coefficient exhibited positive correlation with fracture density. Validation against actual drilling data showed that the established 3D geological model achieved a consistency of up to 75% with well-log interpretation results.

This multi-source-fusion modeling method constrained by outcrop geological knowledge effectively solves the technical bottleneck of high-precision 3D modeling for tight-sandstone fault-fracture reservoirs under sparse-well and low-seismic-resolution conditions. It can provide solid technical support for exploration-development practices in the study area and offers valuable references for research on analogous fault-fracture reservoirs in other cratonic basins.

The source and concentration of phosphorus are key factors determining the occurrence of eutrophication in surface water. However, seasonal quantitative source apportionment of multi-source phosphorus remains a major technical bottleneck for urban compound-polluted lakes. Accurately identifying the seasonal contribution of different phosphorus pollution sources serves as an important basis for realizing differentiated phosphorus pollution control.

This study focused on Tangxun Lake (a typical urban lake) as the study area. It comprehensively adopted methods including field observation and phosphate oxygen isotope composition analysis, combined with the Bayesian MixSIAR isotope-mixing model for simulation, to quantitatively analyze phosphorus pollution sources in different seasons and their contribution to dissolved inorganic phosphorus (DIP) in lake water.

The MixSIAR model calculation showed that during the wet season, urban stormwater sewage contributed the most to DIP in lake water, accounting for 35.8%, followed by domestic sewage (18.9%) and fish pond water (15.9%). During the dry season, the contribution of urban stormwater sewage to DIP in lake water was 30.7%, while that of domestic sewage was 21.4% and fishpond water was 18.7%. Overall, urban stormwater sewage had the highest contribution to DIP in lake water, but there were significant seasonal differences. These differences were mainly caused by the combined effects of higher summer precipitation and stronger microbial degradation. Several unknown phosphorus sources jointly formed a stable contribution system, ultimately resulting in no significant seasonal variation in the contribution of unknown sources to DIP in lake water.

This study clarifies the seasonal contribution characteristics of phosphorus sources in a typical urban lake with complex pollution, and points out that the identification of unknown phosphorus sources such as internal-source phosphorus and hidden point-source pollution still needs further improvement. It provides a scientific basis and technical reference for the accurate source apportionment and targeted control of phosphorus pollution in similar lakes.

Accurate characterization of micro/nanoscale pores and fractures in tight sandstone is fundamental for revealing the mechanisms of multiphase interactions within rocks, and it provides support for hydrocarbon exploitation, geothermal development, and geohazard assessment. Nevertheless, conventional image segmentation techniques suffer from obvious accuracy limitations when handling intricate pore-fracture structures. Moreover, few studies have systematically evaluated how segmentation algorithms affect subsequent three-dimensional pore reconstruction and seepage simulation results.

In this study, micro-focus X-ray computed tomography (μCT) was adopted to build a self-established CT dataset containing micro/nanoscale pores and fractures of tight sandstone. Two conventional segmentation approaches—grayscale thresholding and the watershed algorithm—were employed as baseline comparisons. Four convolutional-neural-network-based deep learning models including U-Net, SegNet, DeepLabv3-ResNet50, and DeepLabv3-ResNet101 were implemented for pore-fracture segmentation. A publicly available micrometer-scale sandstone dataset was further utilized to conduct cross-scale transfer validation. Model performance was comprehensively compared and evaluated in terms of two-dimensional segmentation accuracy, three-dimensional pore network model (PNM) reconstruction, and single-phase seepage simulation.

The experimental results showed that deep learning models outperformed traditional segmentation methods in general. Among all tested models, the U-Net achieved optimal comprehensive performance. Compared with the best results obtained using conventional segmentation methods, U-Net increased the intersection over union (IoU) and F1-score by 18.70% and 16.47%, respectively, with an overall accuracy of 99.03%. The corresponding standard deviations of these three indicators were 0.012, 0.010, and 0.004, demonstrating high stability and robustness. U-Net could effectively preserve the boundary integrity and fine-scale continuity of nanoscale pores and fractures. Its three-dimensional reconstructed porosity reached 2.408%, which was close to the original porosity of 2.785%, and the pore-throat parameters of the reconstructed pore network model (PNM) exhibited good consistency with the actual sample. It was noteworthy that data augmentation operations could destroy the inherent topological features of natural fractures and reduce model segmentation accuracy. The DeepLabv3 series models suffered from obvious over-segmentation artifacts, while traditional algorithms tended to produce missed detection of tiny pores or spurious pore connectivity. These defects further induced non-negligible deviations in permeability calculation and pressure-field distribution during seepage simulation.

Compared with traditional segmentation approaches, the pore-network topology derived from U-Net segmentation matches well with real pore-fracture structures. The U-Net model substantially improves the quantitative analysis accuracy of porosity, pore-throat geometry, and permeability properties. This study provides a feasible reference for automatic identification and digital modeling of micro/nanoscale pore-fracture systems within tight sandstone.

The Miocene north–south rift systems within the Qinghai-Xizang Plateau represent a key expression of intracontinental east–west extension following the India–Eurasia collision, and investigating their initiation mechanism and along-strike propagation patterns is critical for deciphering deep lithospheric geodynamic processes. Two competing end-member hypotheses have been proposed for these rifts. One advocates north-to-south rift propagation, whereas the other supports south-to-north unidirectional expansion, and this controversy remains unresolved. This study focuses on the Lunggar Rift and the Dangre Yongcuo–Xuru Co Rift in the western Lhasa terrane. It aims to constrain the timing of tectonic activity along the southern segments of these two major rifts, compare the new results with published thermochronological datasets from their northern segments, discriminate the along-strike propagation behaviour, and further unravel the deep geodynamic driving forces.

Zircon and apatite fission-track low-temperature thermochronology was applied to Gangdese granite and Miocene clastic sandstone samples collected from the southern segments of the two rifts. Monte Carlo thermal-history inversion was implemented via the HeFTy software package to reconstruct the cooling-exhumation evolutionary paths of rocks and provide chronological constraints on the activation timing of normal faults.

Zircon fission-track dating on granite samples yielded an early-Miocene cooling age of (25.9 ± 2.7) Ma. Apatite fission-track ages were predominantly clustered within 12-10 Ma. Thermal-history modeling identified a prominent rapid-cooling episode during 10-8 Ma, with an estimated cooling rate of ～50 ℃/Ma and a corresponding vertical uplift rate of ～2 km/Ma. When integrated with previously published thermochronological results from northern rift segments, data from this study demonstrated roughly synchronous rift-related exhumation along strike. Detrital apatite fission-track analyses resolved two distinct exhumation age peaks at (13.7 ± 2.0) Ma and (8.0 ± 2.9) Ma, documenting multiphase tectonic exhumation of source terranes. No northward-only or southward-only unidirectional rift propagation was observed.

The initiation of north–south rifts in the Qinghai-Xizang Plateau is predominantly driven by asthenospheric upwelling induced by Indian lithospheric slab tearing, together with vertical buoyancy stresses generated by middle-lower crustal flow. There is no one-to-one spatial correspondence between the surface distribution of rifts and deep slab-tear windows. The development of these rifts marks a critical tectonic transition from mechanical coupling to decoupling between the upper crust and the underthrust Indian lithosphere. Therefore, classical unidirectional rift-propagation models should be reconsidered. This study provides new thermochronological constraints for understanding continental extensional deformation within collisional orogens of the Xizang-Himalayan system.

Polycyclic aromatic hydrocarbons (PAHs) may be produced during the processes of shale gas exploitation, which may threaten both the environment and human health. The largest shale gas exploitation area in China is located in the Fuling karst region of Chongqing, and the produced PAHs may affect the karst groundwater system.

To explore the transport processes of PAHs in karst groundwater systems within shale gas exploitation areas, a typical exploitation site from the shale gas exploitation area in Fuling was selected as the study area. The concentrations, spatial distribution, and compositional characteristics of PAHs in soils, spring water, surface water, and corresponding sediments were analyzed. Additionally, their potential sources were identified.

The results showed that the total concentrations of 16 priority PAHs (Σ₁₆PAHs) in the water, soils, and sediments ranged from 17.3 to 57.4 ng/L, from 16.1 to 162 ng/g, and from 35.3 to 962 ng/g, respectively. The concentration ranges of Σ₁₆PAHs in spring water from the southern tributary and western tributary of the Baishui River were 20.3-57.4 ng/L and 18.4-34.4 ng/L, respectively. The operation of the shale gas site may have increased the concentrations of PAHs in the spring water of the southern tributary, but the affected range was limited and the site did not have an obvious influence on the water further downstream in the Baishui River. Compositional analysis showed that low-molecular-weight PAHs (LMW-PAHs) accounted for 59%-82% of PAHs in water and 15%-42% of PAHs in sediments and soils. The source analysis results showed that the largest contributors to PAHs in the study area were petrogenic and petroleum combustion sources (37.3%), followed by coal and biomass combustion (31.9%), and traffic emission (30.8%). Multiple linear regression (MLR) analysis revealed that spring water from the southern tributary (p < 0.01) and western tributary (p < 0.01) contributed 41.9% and 29.0%, respectively, of PAHs in the river water of the Baishui River. Soils (p < 0.01) contributed 38.9% of the PAHs in the sediments. These results indicated that PAHs could be transported further to downstream water under the influence of the groundwater system and could also be transported from recharge zone soils to spring sediments through surface or subsurface transport processes.

This study provides a system-scale characterization of PAH occurrence, source signatures, and multi-media transport processes in a karst aquifer system affected by shale gas exploitation. The findings advance understanding of contaminant migration in structurally complex karst aquifers and highlight the critical role of groundwater–surface water interactions in regulating downstream water quality. The results deliver a scientific basis for groundwater pollution prevention, risk management, and sustainable resource protection in shale gas-producing karst regions.

This study aims to enhance flocculation-sedimentation performance by optimizing parameters such as slurry mass concentration, specific flocculant consumption, and agitation rate, thereby solving problems such as slow sedimentation speed and low dewatering efficiency during the filling of geotextile tubes with ultra-fine tailings. The ultimate goal is to improve the mechanical strength and storage stability of dewatered tailings.

Cylinder sedimentation tests were conducted, with "flocculation efficiency" introduced as the core evaluation indicator. Single-factor analysis was employed to investigate the effects of slurry mass concentration, specific flocculant consumption, and agitation rate on flocculation performance. A three-factor, three-level Box-Behnken design (BBD) was utilized for response surface methodology (RSM) experiments. Design-Expert software was applied to establish a quantitative model between flocculation efficiency and various factors to analyze multi-factor interactions and their underlying mechanisms.

Single-factor tests indicated that higher flocculation efficiency was achieved within the following ranges: slurry mass concentration of 4%-8%, specific flocculant consumption of 0.5-1.5 mL, and agitation rate of 300-500 r/min. Analysis of variance of the response surface optimization model showed that the significance of factors affecting flocculation efficiency followed the order: square of agitation rate > square of slurry mass concentration > specific flocculant consumption > interaction between slurry mass concentration and specific flocculant consumption > slurry mass concentration > square of specific flocculant consumption > agitation rate > interaction between specific flocculant consumption and agitation rate > interaction between slurry mass concentration and agitation rate. The optimal parameter combination was identified as slurry mass concentration of 5.45%, specific flocculant consumption of 0.5 mL, and agitation rate of 415 r/min, yielding a predicted flocculation efficiency of 8.086 %/(mg·kg⁻¹). The error between measured and predicted values was less than 5%.

The established flocculation efficiency model can effectively predict the flocculation-sedimentation performance of ultra-fine tailings. The response surface methodology can reveal the mechanisms of multi-factor interactions, and the optimized parameter combination significantly enhances flocculation efficiency. This study provides a theoretical foundation and technical support for the dewatering process of geotextile tubes.

The Qaidam Basin is the largest Cenozoic continental intermountain basin on the northeastern Qinghai-Xizang Plateau. The continuous and complete lacustrine sedimentary sequence recorded in the Miocene provides a good carrier for the accurate reconstruction of the paleoenvironment and the ecological evolution process of the lake basin. This study aims to reveal the controlling mechanism of the climate–tectonic coupling process on the evolution of the lake basin ecosystem in the Qaidam Basin during the Miocene, and to clarify the synergistic evolution relationship between climate change and the evolution of the lake basin and watershed ecological environment.

In this study, the Well JS-2 in the Yiliping Sag of the Qaidam Basin was taken as the research object. By comprehensively applying technical methods including elemental logging, rock pyrolysis, and saturated hydrocarbon chromatography analysis, the evolutionary characteristics of the lake basin ecological environment during the Miocene sedimentary period were systematically analyzed from the perspectives of organic matter types, paleoclimate, and sedimentary environment.

The results indicated that during the sedimentary period from the lower member of the Lower Youshashan Formation to the Upper Youshashan Formation, the climate of the basin exhibited obvious fluctuations between arid and humid conditions. Meanwhile, the lacustrine sedimentary environment gradually became hypoxic, with multiple synchronous fluctuations occurring in salinity and water depth, and the organic matter was dominated by aquatic plants and terrestrial higher plants. In contrast, during the sedimentary period of the Shizigou Formation, the basin climate was persistently arid, the lake basin shrank significantly, and the lake water column developed salinity stratification. The sedimentary environment was characterized by a strongly reducing state, the input of terrestrial organic matter increased remarkably, and herbaceous plants further became the dominant vegetation type.

During the Miocene, tectonic evolution and climatic fluctuations were the key drivers of changes in the lake basin ecological environment and vegetation communities in the Qaidam Basin. The aridity during the deposition of the lower member of the Lower Youshashan Formation results from global cooling and the initial uplift of the East Kunlun Mountains, which blocks moisture transport into the basin. During the deposition of the upper member of the Lower Youshashan Formation, global warming and the periodic melting of ice sheets enhance moisture transport by monsoons into the basin, resulting in a warm and humid climate during this period. From the deposition of the Upper Youshashan Formation to the Shizigou Formation, the basin climate shifts to cold and dry conditions, with pronounced aridification across the basin. This change was primarily driven by global cooling (marked by the establishment of a permanent Antarctic ice sheet) coupled with the accelerated uplift of the Qinghai-Xizang Plateau and its surrounding ranges, which effectively obstructs moisture transport into the Qaidam Basin. Based on geological fundamentals, climate fluctuations drive the transformation of the lake aquatic environment, regulate the basin's productivity and ecological space, and ultimately control the succession of vegetation communities.

The Jimsar area in the southern margin of the Junggar Basin is rich in low- to medium-rank coalbed methane (CBM) resources, showing distinct characteristics of microbial gas. To date, it remains unclear whether there is an active supply of microbial gas in the Jimsar area, which restricts the evaluation of CBM resource potential and the subsequent exploration deployment in this area.

In this study, the water samples of CBM development wells and the coal samples of adjacent CBM parameter wells in the Jimsar area were taken as the main research objects, and the actual coal reservoir medium environment was taken as the constraint condition. An anaerobic fermentation gas production simulation device under near in situ conditions was constructed. Based on the comparative analysis of gas production characteristics, changes in pore volume and pore size of coal samples, microbial community structure evolution, and microbial gene function characteristics at different stages, the gas production potential and metabolic mechanism of in situ microorganisms in the Jimsar area were investigated.

The results showed that the in situ microorganisms in the Jimsar area had the potential to produce microbial gas under the current conditions, and the cumulative gas production of CH₄ in the experiment was 9.49 × 10⁻² mL/g. Metagenomic sequencing revealed that there were many types and high abundances of hydrolytic bacteria in the in situ microorganisms of the Jimsar area. The typical acidogenic fermentation bacteria and hydrogen-producing acetogenic bacteria were relatively scarce, and the methanogenic archaea were mainly Methanosarcina. Although there were relatively few acidogenic fermentation bacteria and hydrogen-producing acetogenic bacteria, most of the hydrolytic bacteria could directly degrade the macromolecules in coal into short-chain fatty acids, acetic acid, hydrogen and carbon dioxide, which could provide sufficient substrates for methanogenic archaea.

In the early stage of anaerobic fermentation, Aliarcobacter rapidly proliferates and inhibits hydrolytic bacteria such as Pseudomonas. The abundance of gene functions such as carbohydrate metabolism decreases, and the hydrolysis process is limited, which cannot provide sufficient substrates for methanogens. The abundance of the methanogen Methanosarcina decreases, and the amount of methane produced in the stage decreases. Subsequently, the reduction in Aliarcobacter abundance is followed by the reactivation of hydrolytic bacteria and an enhancement in the functional potential for carbohydrate metabolism and xenobiotics biodegradation. This leads to the enrichment of substrates available for methanogens, which results in an increased abundance of Methanosarcina and a concurrent rise in methane production. The findings can provide a theoretical basis for the evaluation of low- to medium-rank CBM resources, the formulation of exploration plans, and the smooth implementation of coalbed gas bioengineering.