Environmental Earth Sciences最新文献

The chemical corrosion environment significantly affects the mechanical properties and fissure evolution of fissured rocks, which is vital for understanding rock mass instability and ensuring the safety of underground engineering projects. Uniaxial compression tests on double-fissured rocks with varying fissure thicknesses under chemical corrosion were conducted to analyze mechanical behavior in different chemical environments. Particle flow simulation software (PFC2D) and acoustic emission technology were used to study fissure evolution, acoustic emission, and damage characteristics. The results show that, for a given fissure thickness, higher acid concentrations reduce peak stress and compressive strength. At constant pH values, smaller fissure thicknesses lead to higher peak stress and compressive strength. The elastic modulus follows a “V”-shaped trend with changes in chemical environment and fissure thickness. Tensile failure is the primary failure mode, with shear failure occurring secondarily. As fissure thickness increases, failure shifts from tensile wing cracks to reverse tensile wing cracks. In acidic environments, the damage variable (D) increases with factors such as acid concentration, exposure time, and mineral composition. Larger fissure thicknesses intensify stress concentration, accelerating crack propagation and reducing strength and modulus. This study provides insights for mitigating safety risks in underground rock mass engineering.

The proposed China-Nepal railway passes through rivers on the southern slope of the Himalayas, characterized by sharp incision and a dense distribution of various types of knickpoints. To enhance the understanding and practical relevance of knickpoint landforms, this paper takes the Gyirong corridor section of the China-Nepal railway as the research area. Firstly, combined with the morphological characteristics and causes of the knickpoints, different types of knickpoint characteristics and geomorphic evolution effects are proposed. Then, according to the requirements of railway route selection at the geomorphic scale, an integrated knickpoint identification method is proposed, combining the gradient threshold method, steepness index, and field investigation. Finally, based on the analysis of Gyirong-Tsangpo river knickpoints, the railway geological route selection principles based on knickpoint effects on landform evolution are proposed. The results show that this method can significantly reduce field workload and determine the influence range of the knickpoint with high accuracy and efficiency. Thus, a new method for identifying river knickpoints that matches the accuracy requirements of the principal route selection stage is established using only publicly available data. This research provides a new method for determining the area and extent of river stability and provides a scientific basis for the alignment of the China-Nepal railway.

In aquatic ecosystems, phytoplankton and macrophytes are main primary producers, and their interaction is profoundly influenced by global warming. Existing studies have primarily focused on exposure experiments involving metabolites or extracts. However, there is limited understanding of the actual and direct interactions between macrophytes and cyanobacteria under elevated temperatures. In the present study, a common submerged macrophyte, Ceratophyllum demersum, and a widespread cyanobacteria species, Microcystis aeruginosa, were cultivated alone or together under three different temperature gradients (25℃, 30℃, and 35℃) for 7 days. Results showed that the negative effect of M. aeruginosa on C. demersum was only observed at 30℃ and 35℃ with decreased fresh weight increment of 31.5% and 31.7%, respectively. The presence of M. aeruginosa induced oxidative stress in C. demersum, as indicated by the increased catalase (CAT) activity, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content. Our results first found that the presence of C. demersum significantly increased the cell density of M. aeruginosa at high temperatures (30℃, 35℃). Moreover, microcystins (MCs) synthesis was stimulated by C. demersum with elevated mcyB gene (encodes microcystin synthetase subunit B) expression in M. aeruginosa. In addition, extracellular polymeric substances (EPS) contents in co-cultivation treatments were 32.4% (30℃) and 50.1% (35℃) higher than those of the corresponding controls on day 7. Our findings contribute to understanding the temperature-dependent interactions between macrophytes and cyanobacteria, providing a mechanistic basis for exploring their dynamics in warming aquatic ecosystems.

Assessment of hydrogeochemical characteristics of groundwater in space and time is crucial in arid areas where limited groundwater resources have been overexploited for socioeconomic development. This study investigates governing hydrogeochemical processes and spatiotemporal evolution of groundwater hydrochemistry utilizing long-term (1986–2019) hydrochemical data of groundwater of Umm Gudair groundwater field following geostatistical and isotope techniques. Ion exchange, dissolution of evaporites, weathering of silicates and dissolution of carbonates were governing hydrogeochemical processes. Temporal trend analyses for a period of 34 years of hydrochemical parameter data revealed the presence of six trends:1) stable, 2) no trend, 3) probably decreasing, 4) decreasing, 5) probably increasing and 6) increasing with the dominance of trends 1 to 4, indicating an overall improvement in groundwater quality due to the influx of high-quality groundwater from the recharge area. The groundwater exploitation has resulted in variation of groundwater flow manifested by drop in water level and thus extraction promotes the flow of high-quality water from the recharge area. Spatial interpolation of hydrochemical parameters revealed an increase in magnesium, potassium, sulfate, and boron concentrations while decreasing pH, electrical conductivity, total dissolved solids, sodium, chloride, bicarbonate, nitrate, silica, and fluoride. Magnesium, sulfate and boron concentrations were found to be sensitive to groundwater production volume and drawdown. Their concentrations increased with increase in groundwater production volume and drawdown, implying that groundwater quality can be regulated through adjustment in groundwater production and drawdown.

Elucidating the effects of agricultural utilization on soil nutrient levels and their stoichiometry is important for proposing sustainable agricultural management practices in the northeastern Qinghai-Xizang Plateau. In total, 204 and 405 soil samples were collected from different agricultural land uses at three soil depths (0–10 cm, 10–20 cm, and 20–40 cm) in two climatically distinct regions on the northeastern Qinghai-Xizang Plateau: the Qaidam Basin and the Hehuang Valley. The differences in soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) contents and their stoichiometric ratios among land types and soil depths were investigated, and the main environmental factors were identified. The results show that: SOC, TN, and TP contents under all agricultural land-use types decreased with soil depth in both regions, with a pronounced decline in the deepest layer. In the Qaidam Basin, TP contents under all agricultural land-use types were significantly higher than those in grassland across all soil layers, whereas in the Hehuang Valley, only irrigated land and facility land showed significantly higher TP contents than grassland in all three layers. The C: N, C: P and N: P ratios converged across horizons in different agricultural land soils of both regions. In the Qaidam Basin, SOC, TN, TP, and their stoichiometry in the surface layer (0–10 cm) were mainly regulated by geoclimatic factors and soil pH, while no significant drivers were detected in the deeper layer (20–40 cm). In contrast, in the Hehuang Valley, BD and soil texture significantly influenced all three depths, with their effects strengthening with depth. These findings suggest that nutrient management strategies should consider depth-specific and region-specific controlling factors to optimize nutrient use efficiency and sustain soil fertility.

The safe geological disposal of high-level radioactive waste requires consideration of the inflow of groundwater from faults or fractures encountered during excavation of deep underground tunnels, as this inflow may adversely affect the installation and performance of bentonite buffers. The water pressure diffusion equation, assuming uniform hydraulic conductivity and specific storage, predicts that the inflow rate from faults or fractures naturally decays at a rate depending on the flow dimension when the cross-sectional area of the flow areas in the fault or fracture system is proportional to the power of the distance from the inflow point. Although this prediction has been verified for decay ratios measured a few weeks after tunnel excavation, its applicability to long-term predictions several years after excavation has not yet been assessed. We investigated the natural inflow decay ratios (i.e., the inverse of the current inflow rate normalized to the initial inflow rate at excavation) at fault-related inflow points in a tunnel at 350 m depth in the Horonobe Underground Research Laboratory, Japan, 10 years after tunnel excavation, and compared them with those modelled using the diffusion equation and flow dimension. The natural inflow decay ratio measured at each inflow point was equal to or higher than the modelled ratio. Although in some cases the measured ratios may be up to four times as high as the maximum modelled ratio, this difference can be explained by the effect of hydraulic interference between adjacent inflow points. The diffusion equation and flow dimension can be used to predict the minimum long-term (several years or longer) natural decay ratio, providing useful insight to implications for repository design timelines or regulatory decisions (e.g., determining when and where to install waste and bentonite buffers in a repository).

To clarify the spatial distribution of heavy metals and assess their potential health risks under the influence of seawater intrusion, 48 groundwater samples were collected from three confined aquifers in the coastal zone of Weifang, China. The concentrations of 13 heavy metals were analyzed. Spatial distribution patterns and inter-element correlations were assessed, and Cl^- was used as a proxy to explore the impact of seawater intrusion on heavy metal enrichment. Additionally, a quantitative health risk assessment was performed following USEPA guidelines. The results show that Fe and Mn concentrations exceed the standards. The distribution of heavy metals exhibits obvious stratigraphic and regional differences, with high spatial heterogeneity. The shallow aquifer is significantly influenced by anthropogenic pollution and seawater intrusion along paleochannel. The middle aquifer is the primary layer for heavy metal accumulation. The deep aquifer is more controlled by geological background conditions. Production activities have not caused large-scale vertical water quality exchange. Strong correlations were found between Cl^- and certain heavy metals (Cd, Mn, Co, V), suggesting that seawater intrusion may enhance the mobilization of specific contaminants. Health risk assessment indicates that ingestion is the primary exposure pathway, with adults facing higher health risks than children. The non-carcinogenic risk is mainly attributed to Mn, with Aquifer II showing higher risk, primarily in coastal region. The carcinogenic risk is mainly attributed to Cd and As, with Aquifer I showing higher risk. These findings provide a scientific basis for groundwater quality protection and pollution control in coastal aquifer systems.

The Bartın Kirazlı Bridge Dam construction has started on Gökırmak stream, western Black Sea Region, for the purposes of irrigation and power generation, and is continuing at present. By the end of construction, it is anticipated that the existing Bartın-Safranbolu Highway will be submerged underwater due to the increase in the Gökırmak stream level. With the start of construction of the new highway alignment for the relocation of the submerged road named as the “Bartın Kirazlı Bridge Dam Diversion”, the paleo-landslide regions alongside the new alignment have been triggered and led to mass movement along a segment of the new highway. This study aims to define the characteristics of this landslide, determine the sliding surface geometry and location, reveal the mobilized mass amount, and specify the appropriate remediation measures for long-term stability. For this purpose, geotechnical investigations and laboratory tests were conducted. With the data obtained from the engineering geological and geotechnical investigations, the landslide geometry and the shear strength parameters of the landslide mass were determined by back analysis. In addition, slope stability analysis was performed by limit equilibrium analyses for both static and dynamic conditions. As a result of these studies, groundwater level reduction by pumping in short-term, rock buttress application after temporary toe excavation and de-watering of the area by surface and subsurface drainage remediation phases were determined to be suitable for the long-term stability of the landslide.