Analyzing the ecological and behavioral effects of changes in irrigation practices in oases provides valuable insights for water resource management and the sustainable development of oasis agriculture in arid regions. Taking the Yanqi Basin as a case study, this research draws on long-term empirical data and remote sensing information to evaluate the ecological and irrigation behavior effects resulting from shifts in irrigation methods. And explores the deep societal causes behind these behavioral changes. The findings demonstrate: (1). Between 2000 and 2010, the rapid adoption of groundwater extraction and mulched drip irrigation (MDI) technology temporarily alleviated the water supply-demand contradiction. However, from 2010 to 2020, as the adoption of water-saving practices significantly expanded and agricultural irrigation areas grew substantially, the irrigation paradox emerged, where increased efficiency paradoxically led to greater water consumption. (2). From 2000 to 2020, the groundwater table depth in the irrigation district dropped by 8-16 m, total soluble salt content decreased by 2-5 g/L, and soil salinity decreased by 4-12 g/kg. The proportion of severely salinized and saline soil areas fell from 21.74% in 1999 to 9.75% in 2020. The longstanding salinization issues that had plagued the irrigation district were effectively mitigated with the widespread adoption of MDI. (3). The irrigation district's vegetation ecological quality index (VEQI) showed a slow but steady upward trend in cultivated areas over the years. In contrast, natural vegetation areas such as forests and grasslands exhibited an initial increase followed by a decline. The trends in VEQI responded well to changes in irrigation practices. (4). The economic benefits driven by water-saving technologies and the expansion of cultivated land are deep societal factors behind the changes in irrigation behavior. These benefits also fostered improvements in users' understanding and awareness of irrigation practices. The shift in irrigation methods in the Yanqi Basin has led to a decline in groundwater levels, an irrigation paradox, and moderate damage to natural vegetation. However, it has had a significant positive impact on improving regional groundwater quality and mitigating soil salinization. Furthermore, it facilitates the further exploration of regional water conservation potential, enhancing the research on the regional water and soil resource management system.

Land reclamation from the sea is increasingly common in coastal areas in China as its urban population continues to grow and the construction of subways in these areas becomes an effective way to alleviate transportation problems. Earth pressure balance shield (EPBS) tunneling in reclaimed lands often faces the problem of seawater erosion which can significantly affect the effectiveness of soil conditioning. To investigate the impacts, in this work, the stratum adaptability of EPBS foaming agents in seawater environments was evaluated based on a series of laboratory tests. The Atterberg limits and vane shear tests were carried out to understand the evolution characteristics of mechanical properties of clay-rich soils soaked in seawater and then conditioned with foams. The results revealed that, for the same foaming agents, the liquid limit and plastic limit of soils soaked in seawater were lower than those in deionized water due to the thinning of bound water films adsorbed on the surface of soil particles. Similarly, soils soaked in seawater had lower shear strength. In addition, the results indicated that the foam volume (FV) produced by foaming agents using seawater as the solvent was slightly higher than that when using the deionized water due to the higher hydration capacity of inorganic salt cations in seawater compared with organic substances. It was also shown that seawater had negative effects on the half-life time (T1/2) and the dynamic viscosity (eta) of foaming agents due to the neutralization reaction between anions in the foaming agents and Na+ present in seawater. The test results also confirmed that 0.5 % of the tackifier (CMC) can alleviate the issue of thin foam films caused by seawater intrusion and improve the dynamic viscosity of foaming agents more effectively, leading to superior resistance to seawater intrusion in EPBS tunnel constructions.

Microbially induced carbonate precipitation (MICP) is an eco-friendly technique for weak soil reinforcement. In this study, Sporosacina pasteurii was used to strengthen silty sand after multigradient domestication in an artificial seawater environment. The efficiency of MICP was investigated by carrying out a series of macroscopic and microscopic tests on biocemented silty sand specimens. It was found that the salt ions in seawater impacted bacterial activity. The best activity of the bacterial solution in the seawater environment was achieved after five-gradient domestication, which was approximately 8% lower than that in the deionized water environment. The significant effects of domesticated bacteria on silty sand reinforcement were demonstrated by the content of precipitated carbonate and the unconfined compressive strength (UCS) of the treated specimens. The seawater positively impacted the MICP procedure due to the roles of calcium and magnesium ions, indicated by the X-ray diffraction spectra. The scanning electron microscopy (SEM) results showed that carbonate precipitations distributed primarily on the surfaces and near the contact points of the soil particles, contributing to the soil strength. The cementation solution concentration and injection rate significantly influenced the content and distribution of carbonate precipitations and UCS of the biocemented silty sand, and the values corresponding to good reinforcement efficiency were 1.0 mol/L and 1.0 mL/min, respectively. The results of consolidated undrained triaxial tests showed that the mechanical properties of treated specimens were influenced by biocementation cycles. It was found that the stress-strain behavior of biocemented samples changed from strain hardening to strain softening when the number of reinforcement cycles increased. The peak strength of silty sand was increased by 1.9-3 times after 5 times MICP treatment. The effect of biocementation cycles on the shear strength parameters could be represented by relating the effective friction angle and effective cohesion of biocemented silty sand to the carbonate content.

To investigate the potential application of geopolymer materials in pile foundation post-grouting engineering, this study utilized industrial solid wastes such as fly ash (FA), slag (SL), and steel slag (SS) to prepare geopolymer grouting materials (GGMs) with various mix proportions. The fluidity, setting time, bleeding rate, and mechanical properties of these materials were evaluated to determine the optimal mix proportions for pile foundation grouting. Furthermore, the influence mechanisms of different maintenance conditions on material performance were investigated, including unconfined compressive strength, flexural strength, and microstructural changes. The results indicated that when the SL-to-FA ratio was 1:1, the GGMs satisfied the requirements for pile foundation grouting, and their mechanical properties significantly improved with extended curing time. Under Yellow River water maintenance conditions, the materials formed a dense three-dimensional network of hydrated products, notably enhancing their mechanical characteristics. Additionally, field tests confirmed that GGMs effectively improved the shear strength of the pile-soil interface. The grout distribution pattern on the pile side exhibited a compaction-splitting mechanism. These research findings provide theoretical support for applying geopolymer materials in pile foundation grouting engineering.

During the landfilling and resource utilization of solidified soil, it is inevitable that the material will be influenced by the surrounding water environment. Processes such as soaking and infiltration of both clean water and contaminated liquids can have an impact. This paper investigates the strength and structural stability of soil contaminated with a high concentration of lead or copper that has been solidified with red mud-carbide slag-phosphogypsum (RCP-Pb or RCP-Cu, respectively) in strongly acidic water, weakly acidic water, and pure water, as well as in two different modes of soaking and infiltration. The unconfined compressive strength, apparent and microscopic morphology, mineral composition, and functional groups of solidified soil before and after the action of different water solutions were compared, and the water and acid resistance of solidified soil was comprehensively analyzed. The results indicate that under the influence of a strongly acidic water environment, the strength of RCP-Pb and RCP-Cu can decrease by up to 26.4% and 18.5%, respectively, compared to the standard solidified specimens. Conversely, in a weakly acidic environment, the strength of the specimens can increase by a maximum of 21.1% and 32.8%, respectively. Under the two different water environment modes of action, RCP-Pb exhibits a greater increase in strength (39.8%) under soaking conditions, while RCP-Cu shows a greater increase (44.4%) under water infiltration. Based on the microscopic images, the pore counts in specimens in weakly acidic and pure water environments are greater than those in standard solidified specimens, while the porosity is less than that in standard solidified specimens. The surface of the particles exhibited increased roughness. A noticeable finding is that, under the infiltration of a strongly acidic water environment, the porosity of RCP-Pb increases to 20.22%, and the pore counts of RCP-Cu rise to 534. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses revealed that as the acidity of the water environment increased, the CaCO3 content significantly decreased. However, hydration products such as calcium silicate hydrate (C-S-H), calcium aluminate hydrate (C-A-H), calcium aluminosilicate hydrate (C-A-S-H), and ettringite (AFt) did not show significant differences. Consequently, the specimens maintained a stable strength and structure even under such a water environment.

Heavy metal-organic pollutants compound pollution at industrial legacy sites and have caused damage to the ecological environment and human health during recent decades. In view of the difficulty and high cost of post-contamination remediation, it is worth studying, and practically applying, cutoff walls to reduce the spread of pollution in advance. In this study, field-scale studies were carried out at e-waste dismantling legacy sites in Taizhou, Zhejiang Province of China, through the process of site investigation, numerical simulation, and cutoff wall practical application. Firstly, the concentrations and spatial distributions of Pb, Cd and polychlorinated biphenyls (PCBs) and poly brominated diphenyl ethers (PBDEs) were identified in both soil and groundwater. Then, potential dispersal routes of key combined contaminants (Pb and PCBs) at the soil-groundwater interface were systematically studied through numerical simulation applying Visual MODFLOW-MT3DMS. One site was chosen to predict the barrier effect of differently sized cutoff walls based on the migration path of compound pollutants. A protocol for a cutoff wall (50 m length x 2 m width x 3 m height) was finally verified and applied at the real contaminated site for the blocking of compound pollutant diffusion. Further, the groundwater quality of the contaminated site was monitored consecutively for six months to ensure the durability and stability of barrier measures. All pollutant indicators, including for Pb and PCB complex pollutants, were reduced to below the national Grade IV groundwater standard value, achieving environmental standards at these polluted sites and providing possibilities for land reuse. In summary, this field-scale test provided new ideas for designing cutoff walls to block the diffusion of complex pollutants; it also laid a basis for the practical application of cutoff walls in pollution prevention and control of complex contaminated sites and for soil-groundwater environmental protection at industrial heritage sites.

Nano-SiO2, a highly acclaimed nanomaterial for enhancing cemented soil, has shown remarkable improvements in the physical properties and microstructure of cemented soil. The organic matter content in soil plays a crucial role in determining the engineering quality of cemented soil, regardless of whether it is in a freshwater or seawater environment. Therefore, when employing Nano-SiO2 as an amendment for cemented soil, it is crucial to consider the influence of different soil types and environmental conditions on the effectiveness of the enhancement. This study presents a scientific approach for enhancing the consolidation of cemented soil by incorporating Nano-SiO2 as an additive in both freshwater and seawater environments. To ensure consistency with practical construction practices, the experiments were divided into freshwater preparation and curing groups, as well as seawater preparation and curing groups. In soils with distinct characteristics, we utilized five different gradient levels of Nano-SiO(2 )additives and subjected the cemented soil specimens to a 60-day immersion curing process. Subsequently, unconfined compressive strength (UCS) tests were performed on samples that had reached the specified curing age to investigate the alterations in the mechanical properties of cemented soil caused by Nano-SiO2. The internal microstructure and chemical composition of the cemented soil were analyzed utilizing scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The UCS and deformation modulus of cement soil composed of silty clay A and silty clay D with low organic matter content in fresh water environment increased by 109%, 24.7% and 117%, 43% respectively after adding 3.2% Nano-SiO2; In freshwater environments, the cemented soil composed of high-organic-matter content mucky silty clay B, muddy soil C, and dredged silt E experienced respective increases of 16% and - 27%, 2% and 42%, 6% and - 6% in UCS and deformation modulus after adding 3.2% Nano-SiO2; The UCS and deformation modulus of cemented soil with high organic matter content in seawater and freshwater environment increased by 3% and 6% ( Soil B), 12% and 67% ( Soil C), 23% and 27% ( Soil E), respectively, after adding 3.2% Nano-SiO2; The increase of UCS and deformation modulus of cement soil by adding Nano-SiO(2 )is negatively correlated with the content of organic matter. in the case of cemented soil with high organic matter content in a seawater environment, the specific type of soil not only impacts UCS and deformation modulus of the soil but also influences the effectiveness of enhancement. Due to the organic matter, the rate of hydration reaction in cemented soil is reduced, resulting in a decrease in the formation of pozzolanic reaction products with SiO2. As a result, the improvement in Nano-SiO(2 )effectiveness is diminished.

Microplastics have been noticed as widespread in an aquatic environment at the microscale. They have nonstop increased due to the increase in the production of synthetic plastics, population and poor waste management. They are ubiquitous in nature and slowly degrade in water and soil. They are emerging pollutants that have received interest from public audiences and research communities. They have great stability and can adsorb various other pollutants like pesticides, heavy metals, etc. After entering the freshwater environment, microplastics can be stored in the tissue of organisms and stay for a long time. They can generate a serious threat to freshwater ecosystems and can cause physical damage to organisms. Visual identification, Raman spectroscopy, pyrolysis-gas chromatography-mass spectrometry (Pyro-GC-MS), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and combined methods are the commonly known methods for the quantification and identification of microplastics. The detected concentration of microplastics depends on the sampling method, locations and identification techniques. The authors assessed the sources, transport, impacts, identification and characterization, and treatment of microplastics in freshwater environments in detail. The authors are also giving some recommendations for the minimization of the MPs from the freshwater environment. This review article will provide the baseline facts for the investigators to do more research on microplastic pollution in the future.

The current water environment carrying capacity assessment method has a single assessment index and does not constrain the scope of assessment. It is not possible to adaptively assess the water environment carrying capacity layer by layer. In order to solve this problem, in this paper. we propose an adaptive assessment method of urban water environment carrying capacity based on water quality target constraints. This method constructs a new evaluation index system for water environment carrying capacity, which takes water resources and environment, water pollution control, and economic carrying capacity as the criteria, and takes water quality status, pollution discharge, technology management. economic development, and social development as the constraint target layer, and takes the total wastewater discharge, industrial water consumption, and urbanization level as the constraint index layer. Two methods of structural entropy weight and mean square error decision are introduced to realize the adaptive joint weight assignment evaluation of the reference layer and the target layer. Through experimental analysis, the assessed area has a good water environment carrying capacity and foundation, and the overall water environment carrying capacity of the study area from 2016 to 2019 was on the rise.