Environmental Earth Sciences最新文献

In the main Ethiopian rift, litho-structural complexity and scant study on factors that control water well productivity pose difficulty in predicting well yield. This study examines the relationship between well yield and geological structures in the Gidabo watershed, southern main Ethiopian rift valley, through the characterization of physical hydrogeology. Litho-structural data was compiled from the existing maps and remotely sensed data. Lithologic log and well yield data were compiled from water well drilling completion reports. Fieldwork was conducted for data verification. Well yield data were plotted on the ArcGIS environment, and a cross-section was constructed to conceptualize well yield spatial variation and its relation to faults. The study reveals that well yield varies between 1.5 and 184 lit/sec with no systematic spatial distribution and statistically significant relation to surface elevation as well as well depth. The high-yield wells (> 8 lit/sec) are encountered along the long E-W trending fracture lines, and the low-yield wells (< 8 lit/sec) are either associated with the short lineament or the Wonji faults that are not connected to the long E-W trending lineaments. Further, wells drilled on the dip side of the first-encountered east-dipping Wonji fault along flow lines are marked by high yield. In contrast, wells drilled on the opposite side of the east-dipping first-encountered fault or beyond towards the west have low yield unless drilled along the long E-W trending lineaments. This finding guides groundwater development activities in the Gidabo watershed and in the hydrogeologically similar Ethiopian Rift Valley.

This article designed two differential cyclic loading (DCL) modes, each considering the combinations of five groups of different loading and unloading rates. Namely, Mode a: transition from fast-loading-slow-unloading to slow-loading-fast-unloading. Mode b: transition from slow-loading-fast-unloading to fast-loading-slow-unloading. The rock samples tested are slate with five different bedding angles (0°, 30°, 45°, 60°, 90°). The testing results indicate that the two DCL modes with opposite loading sequences can yield different characteristics of energy dissipation. The Mode a which varies fast-loading-slow-unloading to slow-loading-fast-unloading exhibits a sharper decline in normalized dissipated energy and simultaneously holds a smaller residual axial strain rate when compared with Mode b. The impact of loading/unloading rates on magnitudes of phase shift is independent of the applied DCL sequences.

It is essential to investigate the permeability variation in deep coal seam to prevent gas disasters, which threaten the safety of the mine. The primary inducement for the variation of coal permeability in deep coal seam is determined by analyzing the coal geological environment. The inducement of these changes is thought to be the coupling damage of mining-adsorption effect. The mining damage variable and adsorption damage variable are constructed. Subsequently, the coupling damage variable of mining-adsorption is proposed. Furthermore, the permeability model of deep coal under the coupling damage of mining-adsorption is developed relying on the coupling damage variable of mining-adsorption. According to the laboratory permeability tests of deep coal under mining stress and adsorption, the developed permeability model is validated. The variation of permeability and damage variable of deep coal under different mining paths and gas pressure distributions are analyzed. The results show that the mining damage variable in laboratory tests indicate three stages: slow increase, rapid increase, and approximately constant. The coal permeability under mining can be divided into three stages: slow increase, rapid increase, and slow increase. As the gas pressure increases, the adsorption damage variable increases; however, the increasing rate decreases. Under different mining paths and different distribution forms of gas pressure, both the coupling damage variable and permeability in front of the deep working face present three stages. The relationships of coupling damage variable at the peak stress and the permeability ratio at the working face are protective layer < top coal caving < no coal pillar. In different gas pressure distributions, the relationships of coupling damage variable and permeability ratio at the peak stress are distribution form 1 < distribution form 3 < distribution form 2, while the relationships of coupling damage variable and permeability at the working face are distribution form 2 < distribution form 1 < distribution form 3.

The escalating global population and the surging demand for oil have necessitated the advancement of enhanced oil recovery (EOR) methods to augment production. However, conventional EOR techniques, while effective, contribute substantially to environmental degradation by releasing pollutants and greenhouse gases (GHGs), highlighting the pressing need for more sustainable alternatives. In response, green-enhanced oil recovery (GEOR) has emerged as a transformative solution, incorporating eco-friendly technologies to optimize oil extraction while mitigating environmental impact. This study offers a critical evaluation of various GEOR approaches, including the injection of organic materials, microbial processes, solar energy integration, and the application of nanotechnology. The originality of this research lies in its comparative analysis of cutting-edge GEOR techniques such as Water Alternating Gas (WAG), foam injection, nanofluid injection, smart water flooding, and microbial EOR. Each method is assessed based on performance indicators, environmental repercussions, and operational efficiency. The findings demonstrate that GEOR methods not only enhance oil recovery efficiency but also significantly curtail environmental footprints compared to traditional EOR strategies. By providing an in-depth assessment of these sustainable technologies, this study identifies the most efficient methods while underscoring their unique advantages and limitations. GEOR methods offer eco-friendly solutions with varied advantages, such as WAG's mobility control, foam injection's enhanced sweep efficiency, and nano-fluid's reduced environmental impact. While techniques like smart water and microbial methods minimize chemical use, challenges such as scalability, high costs, and reservoir-specific limitations remain. The results strongly advocate for the broader adoption of GEOR technologies, emphasizing their crucial role in promoting sustainable development and environmental stewardship. This research contributes valuable insights for both academic researchers and industry professionals, encouraging the implementation of GEOR practices to achieve environmentally responsible oil recovery. The comprehensive analysis presented herein serves as an indispensable resource for advancing the domain of sustainable oil recovery practices.

Fault activation is a primary cause of rockburst in working faces of coalmines. To reveal the full-cycle impact gestation process, a numerical model consisting of a normal fault is established using FLAC^3D. The spatio-temporal evolution laws of the displacement field, stress field, strain field, and energy field of coal seam during the advance from hanging wall to footwall are obtained. Additionally, the energy level frequency division characteristics and the spatio-temporal distribution of the energy levels of microseismic signals during the working face crossing the fault are analyzed. The relationship between the risk level of fault-slip burst and microseismic information, stress field, strain field, and energy field around the fault region are established. This lays a foundation for implementing fault-slip burst risk classification control in deep working faces mining through faults. The results show that the distance between the working face and the fault significantly influences the energy concentration of the coal pillar, the rocks in footwall exhibiting a higher energy concentration than that in hanging wall. The spatial position relationship between the working face and the fault affects the failure mode of the coal and rock mass. The stress field, strain field, and displacement field of the coal seam and its roof or floor in the fault region show significant differences in sensitivity to the distance between the working face and the fault. Microseismic events indicate that fault activation can be divided into three stages: stress development, energy storage, and structural activation. During stress development and structural activation, there are more microseismic events and higher energy values. The microseismic energy of the working face is primarily concentrated within 10–20 m from hanging wall and throughout footwall of the fault. In addition, the pre-evaluation results of the impact risk of the working face prove that the evaluation model can effectively distinguish the leading role of different working face distances from fault. This provides reference and guidance for risk assessment of fault-slip bursts in deep working face mining through faults.

Uncertainties of sliding surfaces and structures of soil-rock mixture are two critical factors that affect slope stability. In this study, an uncertainty slope stability analysis method of a landslide with several potential sliding surfaces is proposed. Two geostatistical simulation methods, i.e., single normal equation simulation and sequential indicator simulation, are chosen to quantify the geological uncertainty of slopes by generating a large number of simulation maps with different positions of potential sliding surfaces and different structures of soil-rock mixtures. These maps are imported into the discrete element method program MatDEM, and uncertainty analysis is carried out through Monte Carlo simulations. A case study named Dahua landslide is carried out using the proposed method, where limited monitoring data is available. Based on the results of uncertainty analysis, it is found that displacements of most areas in the Dahua landslide are very small, and the frontal part of this slope is the most dangerous. Through field survey found that there are many large cracks in the frontal part of the Dahua landslide.

The paper presents a geochemical approach to estimating the local background values of major ionic solutes and trace elements in headwater streams. Understanding the natural geochemical properties of each surface water body is essential for tracking environmental changes, identifying anthropogenic influences, and establishing baseline conditions for water quality management. This research aims to evaluate the elemental concentrations, water quality, and background values (BGVs) of stream water through systematic sampling, laboratory analysis, and hydrogeochemical and statistical interpretations. Water samples were analyzed for hydrochemical solutes such as major cations and anions using standard procedures, whereas concentrations of 44 trace elements, including heavy metals and metalloids, were determined using inductively coupled plasma mass spectrometry (ICP-MS). Water samples were collected in places that were unaffected by industrial or mining activity, as well as in generally clean areas. Statistical techniques were employed to distinguish between natural variability and potential human impacts. Hence, the mean + 2SD was then used to determine the BGV. In addition, spatial distribution maps of hydrochemical parameters were used to identify potential sources of contamination. The obtained concentrations were then compared to global water quality standards. The calculated BGVs revealed critical concentration levels of Al and Fe that surpassed the maximum limitations set by the legislation. These significantly elevated levels may constitute a health risk to people, particularly in rural locations where they rely solely on stream water and the aquatic environment. Heavy metals and metalloids including As, Cr, Cd, Pb, Ni, Hg, Zn, Cu, and Mn are found in trace amounts or below detection limits and pose no threat to the environment or human health. The levels of dissolved REEs in water samples are relatively low, indicating a geologic source. The proposed BGVs will serve as a reference to determine the impact of human activities (such as industrial discharges, agricultural runoff, and urban expansion) on water quality at the local level. The geochemical study of water also provides a robust framework for assessing the health of public and aquatic ecosystems and designing effective environmental management plans.

During coal mining, the application of overburden separation grout filling (OSGF), i.e., grout injection into the separation layer within the overburden through surface boreholes, serves to control the deformation and fracturing of key strata in the overburden and significantly reduce surface subsidence. However, its resultant disturbance to the stress field will change the compaction characteristics of the goaf and thus affect the spontaneous combustion hazard zones there. In view of this fact, with a Y-shaped ventilation working face of Tunlan Coal Mine as the research prototype, the evolutions of the flow field and spontaneous combustion hazard zones in the goaf under OSGF disturbance were comprehensively investigated through coal seam excavation experiments, flow field similarity experiments, on-site coal mine measurements, and CFD simulation of goaf. The following research findings were obtained. First, OSGF avoids the air leakage from the working face to the deep part of the goaf to a certain extent, thereby weakening the oxidation capacity of the compacted area and its rear area. Secondly, as the working face advances, the relative distance between the working face and the adjacent grouting boreholes changes periodically, leading to dynamic changes in the spontaneous combustion risk zone in the goaf, with the oxidation zone fluctuating within a range of 38.4 m. Among OSGF-related borehole parameters, the borehole spacing affects the spontaneous combustion zones the most, followed by the number of borehole rows and the borehole influence radius in sequence. This study reveals the impact and mechanism of OSGF on the flow field and spontaneous combustion hazard zones in the goaf, which provides a theoretical basis for the safe application of OSGF and the prevention and control of spontaneous combustion disasters in goafs.

Exploring the impacts of anthropogenic processes on the organic matter (OM) input and phosphorus (P) burial characteristics is essential for describing the carbon (C) cycle and its environmental effects on aquatic ecosystems from multiple perspectives. In this study, the centennial sedimentary P, C, and nitrogen (N) characteristics and terrestrial OM input changes in the upper Yangtze River were reconstructed by ²¹⁰Pb-dated and positive matrix factorization (PMF) methods, and the key factors were identified. The P accumulation and stock averaged at 2.23 ± 1.08 g P m⁻² yr⁻¹ and 0.01–0.07 Mg P ha⁻¹ from 1855 to 2019. Changes in corresponding loads of total organic C (TOC) and N (TN) separately ranged between 0.58 and 1.81 Mg C ha⁻¹ and 0.07–0.29 Mg N ha⁻¹ over the past century. The total sequestration was 4.20 × 10⁵ t of C, 5.51 × 10⁴ t of N, and 1.22 × 10⁴ t of P, respectively, accounting for 33%, 54%, and 14% of Dianchi Lake. The strength and contribution of terrestrial OM driven by anthropogenic activities were constantly increased, and the proportion increased sharply from 34 to 52%. About 67–86% of biogenic OM was the main source of P sedimentation. In the context of recent warming, the combined effects of C and N loading, redox environment, climate change, and anthropogenic activities enhanced the P accumulation and retention by 1.29 g P m⁻² yr⁻¹ per 1 ℃ increase in temperature. These findings suggest that the sediment in this area generally acts as a sink pool of nutrients, which is critical for predicting P fate and nutrient cycle.

The present study investigates the complex relationship between soil properties and adsorption-desorption dynamics of lead (Pb) within soils, examining two distinct temperature environments and its impact on plant accessibility. Through laboratory and pot experiments encompassing twenty-five soils with diverse physico-chemical properties, important findings emerged, which highlighted the essential role of free-sesquioxide (Fe₂O₃ and Al₂O₃) as the primary soil component dictating Pb adsorption, followed by electrical conductivity (EC), and cation exchange capacity (CEC). Notably, the adsorption capacity of Pb across soils exhibited enhancement with increasing initial metal concentrations and temperatures, delineating the temperature-dependent nature of the adsorption process. Thermodynamic analysis revealed that adsorption was endothermic, supported by positive enthalpy (∆H°) values. Additionally, negative ∆G° values at both temperatures confirmed the spontaneous nature of the adsorption process. The average values of desorption Index was close to be 1 for some soils suggesting reversible adsorption-desorption. As high as 76 and 67% variability in Pb content in plant could be explained by adsorption parameters. These findings provide valuable insights into Pb adsorption-desorption in soil ecosystems, guiding the development of effective strategies for Pb remediation in contaminated soils.