Salinization of shallow groundwater in the Jiaokou Irrigation District and associated secondary environmental challenges

Biogeochemical mechanisms and biomarkers of groundwater salinization in Jinghuiqu Irrigation District, China

Groundwater salinization poses significant challenges to water resource management, agriculture, and ecosystem sustainability. However, the biogeochemical mechanisms and microbial responses underlying this process in irrigation districts are still poorly understood. This study integrated hydrochemical ratios (Cl--Cl-/Br-, Cl--NO3-/Cl-), stable isotopes (δ2H, δ18O, δ15N-NO3-, δ18O-NO3-), and the MixSIAR model to investigate the dominant factors contributing to salinization in the Jinghuiqu Irrigation District. The results showed that TDS concentrations in groundwater samples ranged from 688 to 5420 mg/L, with 82 % of the samples exceeding WHO drinking water standards. Groundwater salinization was predominantly driven by mineral dissolution and evaporation, compounded by agricultural and domestic inputs. 16S rRNA microbial sequencing identified Candidatus Omnitrophus from the phylum Verrucomicrobiota as a potential biomarker for saline groundwater. PICRUSt2 predictions revealed that the functional traits of microorganisms in saline groundwater tend to enhance adaptability, whereas those in fresh groundwater are more oriented toward growth and metabolism. Spearman correlation analysis showed strong correlations between carbon fixation and nitrification (r = 0.69) and thiosulfate oxidation (r = 0.60). Additionally, as groundwater salinization progressed, the abundance of nitrate- and sulfate-reducing bacteria increased, further impacting nitrogen, sulfur, and carbon cycles. This study deepens knowledge of the biogeochemical processes driving groundwater salinization in irrigation districts and provides new insights for research and management of groundwater salinization in these regions.

Hydrochemical insights into spatiotemporal characteristics of groundwater salinization and health risk assessment of fluoride in the south bank of Yellow River irrigation area, Northwest China

The groundwater salinization problem in the south bank of the Yellow River irrigation area is severe, restricting the sustainability of groundwater resources. However, the groundwater salinization formation mechanism is unclear. Accordingly, this study analyzed the chemical characteristics and salinization mechanism of groundwater based on hydrochemical analyses (self-organizing maps, SOM), isotope analyses (δ18O and δD), and quantitative models (Rayleigh distillation model), as well as evaluating the potential health risks of fluoride. The results indicated that surface water and groundwater in the study area had high salinity and weak alkalinity, with the fluoride and total nitrogen (TN) content exceeding Grade III water standards. Additionally, only 42% of the water samples were suitable for drinking, with nitrogen sources being the main cause of water quality deterioration. Around half of the samples were unsuitable for irrigation. The spatial and temporal distribution of total dissolved solids (TDS) in the irrigation area was influenced by autumn irrigation. Overall, groundwater salinization was primarily attributed to evaporite dissolution, cation exchange, silicate weathering, and human inputs. Evaporation was not the main influencing factor. In addition, the non-carcinogenic risk of fluoride in the water body decreased as follows: infants > children > adult females > adult males. The results of this study deepen understanding of the relationship between changes in groundwater quality and the ecological environment in semi-arid inland areas, thereby promoting the rational utilization and scientific management of groundwater resources in the irrigation area.

Multi-isotope tracer for identifying nitrate sources in shallow groundwater in a large irrigation area, China

Nitrate pollution of groundwater associated with anthropogenic activities and social development is a global issue, especially in agricultural regions. This study investigated the source and fate of nitrate in groundwater of the Jiaokou Irrigation Area using chemical and isotopic fingerprints (isotope tracing, graphical analysis, and d-excess) in combination with end-member mixing analysis (EMMA). The hydrochemical analysis revealed that the NO3- concentration exceeds 20 mg/L (calculated as N) in approximately 66.67% of groundwater samples. The highest NO3- concentration was observed in Cl·SO4 type water, followed by the HCO3 and SO4 types. Areas with serious nitrate pollution are mainly distributed in cultivated land. Groundwater mineralization is driven by silicate weathering and evaporite dissolution. Ion exchange and mixing processes are also major factors affecting the chemical composition of groundwater in the study area. The largest contributors to NO3-N in groundwater were found to be manure and sewage input, followed by soil N (SON) and NH4-N fertilizer (NF) application. The high nitrogen content in groundwater is mainly affected by mixing and nitrification processes. Interestingly, although evaporation is the main factor affecting groundwater mineralization in the study area, it has little effect on the high nitrate concentration in groundwater. Based on the results, a conceptual model was constructed to describe the nitrogen cycle in the irrigation area. The findings help clarify the mechanism of nitrate pollution and deepen our understanding of the role of nitrogen cycling in the soil-water-gas system.

Elucidating the hydrochemistry and REE evolution of surface water and groundwater affected by acid mine drainage

The impact of pyrite mining on water quality is a global concern. This study investigates the impact of acid mine drainage (AMD) from an abandoned pyrite mine in the Qinling Mountains on surface and groundwater hydrochemistry and rare earth elements (REEs) evolution. A total of 54 water samples were collected in 2021, of which the Muzi River downstream of the mining area was repeated three times in three sampling periods. Hydrogeochemical methods and stable isotope techniques were used to analyze the impacts of AMD. Results showed that tailing water in comparison to groundwater and surface waters exhibits low pH with high concentrations of SO42-, potentially toxic elements (PTEs), and REEs, and is characterized by normalized middle REE (MREE) enrichment. Groundwater is less influenced by AMD and shows HCO3-Ca and HCO3-Ca·Na types. AMD contaminates surface water to different degrees. Surface water received SO42- input from AMD, exhibited SO4-Ca, SO4·HCO3-Ca, and HCO3·SO4-Ca types within the mining area, and evolved from HCO3·SO4-Ca to HCO3-Ca downstream as AMD influence diminishes. High concentrations of PTEs and REEs are presented in AMD and seepage near the slag heap, and decreased rapidly along the flow path, while SO42- migrated over longer distances. The water in the study area primarily originates from atmospheric precipitation, with close relation among surface water, groundwater, and tailing water. Water-rock interactions and pyrite oxidation governed the hydrochemical composition, with sulfide oxidation facilitated the carbonatite-water reaction, which alleviated sulfide oxidation-induced acidification. The concentrations of PTEs are regulated by adsorption and precipitation, carbonate buffering, and dilution along the flow path. REEs are mainly controlled by pH, inorganic complexation, and secondary mineral adsorption. As the pH changes from acidic to neutral or weakly alkaline, REEs shift from sulfate-complex dominated to carbonate-complex dominated. These insights contribute to a better understanding of AMD impacts on surface and groundwater, providing a basis for the rational management of AMD.

Effect of soil-groundwater system on migration and transformation of organochlorine pesticides: A review

Soil is the place where human beings, plants, and animals depend on for their survival and the link between the various ecological layers. Groundwater is an important component of water resources and is one of the most important sources of water for irrigated agriculture, industry, mining and cities because of its stable quantity and quality. Soil and groundwater are important strategic resources highly valued by countries around the world. However, in recent years, the deterioration of the ecological environment of soil-groundwater caused by industrial, domestic, and agricultural pollution sources has continued to threaten human health and ecological security. Among them, organochlorine pesticides (OCPs), as typical organic pollutants, cause very serious pollution of soil and groundwater environment. However, most studies on the pollution of OCPs have focused on the aboveground or surface water environment, and little consideration has been given to the pollution and hazards of OCPs to the deep soil and groundwater environment, especially the effects of different environmental factors on the transport and transformation of OCPs in soil-groundwater. Moreover, in addition to the influence of a single factor on it, the interactions that arise between different factors cannot be ignored. This paper focuses on two major sources of OCPs in soil and groundwater environments, compiles and summarizes the effects of environmental factors such as pH, microbial communities and enzyme activities on the transport and transformation of OCPs in soil and groundwater systems, discusses the synergistic effects of individual environmental factors and others, and comprehensively analyses the effects of synergistic effects of various environmental factors on the transport and transformation of OCPs. In the context of ecological civilization construction, it provides the scientific basis and theoretical foundation for the prevention and treatment of OCPs-contaminated soil and groundwater, and puts forward new ideas and suggestions for the research and development of green, eco-friendly remediation and treatment technologies for OCPs-contaminated sites.

A multi-perspective exploration of the salinization mechanisms of groundwater in the Guanzhong Basin, China

A comprehensive understanding of the salinization of groundwater in the Guanzhong Basin, China, is crucial for ensuring sustainable groundwater development. However, the mechanism driving salinization in different regions of the basin remains unclear. Therefore, this study employed multivariate statistical methods, hydrochemical analysis, isotope studies, and hydrochemical modeling to uncover the factors and processes influencing groundwater salinization. The results indicate significant regional variations in total dissolved solids (TDS), with concentrations exceeding 1000 mg/L predominantly occurring to the north of the Weihe River and the east of the Jinghe River. The correlations of groundwater chloride (Cl-) with Cl/Br molar ratio and stable isotopes show that groundwater salinity in the Guanzhong Basin is mainly controlled by mineral dissolution, and evaporation. In addition, human activities, such as vertical irrigation recharge and excessive fertilizer use, exacerbate local salinity levels. Irrigation activities worsen the shallow groundwater salt enrichment in the runoff zone of the central basin, revealed by the high salinity (TDS>3000 mg/L), high Cl/Br ratios (>2000), moderate δ2H (-57.5 to -67.5 ‰) and moderate δ18O (-8.1 to -8.9 ‰). High salinity (TDS>1000 mg/L), high nitrate concentration (>100 mg/L), and moderate Cl- (100 to 500 mg/L) indicate the impact of excessive fertilizer use. It is worth noting that intensive groundwater withdrawal disrupts the dynamic balance within the aquifer, causing shallow high-saline groundwater to percolate downward, thereby increasing the risk of deep groundwater pollution. The research enhances the understanding of groundwater salinity transport and provides insights into the effects of groundwater salinization in the irrigation area.

Hydraulic recharge and element dynamics during salinization in an overexploited coastal aquifer of the world's driest zone: Atacama Desert

The management of water resources in hyper-arid coastal regions is a challenging task because proper information regarding groundwater recharge and water budget is needed for maintaining the hydraulic balance in optimal conditions, avoiding salinization and seawater intrusion. Thus, this article deals with the estimation of the hydraulic recharge and the study of the effects of salinization on the dynamics of major and trace elements in an alluvial aquifer located in the world's driest zone, the northern Atacama Desert. The result of stable water isotopes (δD and δ18O) and tritium (3H) indicated that groundwater in the area is not recent, whereas 14C results estimated a groundwater residence time ranging between 11,628 and 16,067 yBP. The estimation of the artificial recharge coming from the urban water-supply-system leaks and wastewater/river-water/groundwater infiltration during irrigation was about 19.84 hm3/year, which represents an annual negative water balance of 177 hm3/year for the aquifer. The groundwater salinization triggered by seawater intrusion (up to 32.6 %) has caused the enrichment of Li, Rb, Ca, Ba, and Sr in groundwater by cationic exchange, where the excess of aqueous Na is exchanged by these elements in the aquifer sediments. Other elements such as B, Se, Si, and Sb are enriched in groundwater by ionic strength and/or anionic exchange during salinization. The heightened B concentrations derived from the B-rich alluvial sediments were higher than the limit suggested by international guidelines, representing a risk to consumers. Vanadium seems to be unaffected by salinization, whereas Pb, Mo, As, U, and Zr did not show a clear behavior during saline intrusion. Finally, this article highlights the consequences of conducting improper water management in coastal hyper-arid regions with exacerbated agriculture.

Chloride accumulation in inland rivers of China and its toxic impact on cotton

The escalation of major ion concentrations in freshwater and soil poses diverse effects on ecosystems and the environment. Excessive ions can exhibit toxicity to aquatic organisms and terrestrial plants. Currently, research on ion toxicity primarily focuses on cation toxicity. Notably, there is a noticeable research gap in understanding the impact of chloride ion (Cl-) on plant growth and development, as well as on the defense mechanisms against Cl- toxicity. In the present study, sampling was conducted on major rivers in China to measure Cl- concentrations. The results revealed that certain rivers exhibited excessive levels of Cl-, emphasizing the critical need to address Cl- toxicity issues. Subsequently, when salt-tolerant cotton seedlings were subjected to various chloride treatments, it was observed that excessive Cl- severely hindered plant growth and development. A combined analysis of transcriptomic and metabolomic data shed light on significantly enriched pathways related to galactose metabolism, arginine and proline metabolism, carotenoid metabolism, and alpha-linolenic acid metabolism under chloride stress. In summary, this research provides a scientific foundation and references for environmental management and water resource protection and offers novel insights for mitigating the adverse impacts of Cl-, thereby contributing to the preservation of ecosystem health.

Optimized groundwater quality evaluation using unsupervised machine learning, game theory and Monte-Carlo simulation

Assessing groundwater quality is essential for achieving sustainable development goals worldwide. However, it is challenging to conduct hydrochemical analysis and water quality evaluation by traditional methods. To fill this gap, this study analyzed the hydrochemical processes, drinking and irrigation water quality, and associated health risks of 93 groundwater samples from the Sichuan Basin in SW China using advanced unsupervised machine learning, the Combined-Weights Water Quality index, and Monte-Carlo simulations. Groundwater samples were categorized into three types using the self-organizing map with the K-means method: Cluster-1 was Ca-HCO3 type, Cluster-2 was dominated by Ca-HCO3, Na-HCO3, and mixed Na-Ca-HCO3 types, Cluster-3 was Ca-Cl and Ca-Mg-Cl types. Ion ratio diagrams revealed that carbonate dissolution and silicate weathering primarily influenced the hydrochemical characteristics. Cluster-1 samples exhibited high NO3- contents from intensive agricultural activities. Cluster-2 samples with high Na+ contents were characterized by positive cation exchange, while Cluster-3 samples with elevated Ca2+ and Mg2+ contents were influenced by reverse cation exchange. Combined-Weights Water Quality Index indicated that 62.37% of total samples were suitable for drinking, predominantly located in the central part of the study area. Irrigation Water Quality Index revealed that 33.34% of total samples were suitable for irrigation, mainly in the northeastern region. NO3- concentration and electrical conductivity (EC) value were the main indicators with the highest sensitivity for drinking and irrigation suitability, respectively. Probabilistic health risk assessments suggested that a significant portion of the groundwater samples posed a health risk greater than 1 to children (63%) and adults (52%) by Monte-Carlo simulation. The high-risk areas (hazard index >4), primarily in the eastern region, are closely associated with nitrate distribution. Sensitivity analysis demonstrated that NO3- concentration is the primary indicator accounting for health risks. Reducing the application of nitrogen-based fertilizers on cultivated land is the most effective approach to improve drinking quality and mitigate the associated health risks to the population. This study's findings aim to produce a novel groundwater quality evaluation for promoting the sustainable management and utilization of groundwater resources.

Genome-wide identification and characterization of the LRX gene family in grapevine (Vitis vinifera L.) and functional characterization of VvLRX7 in plant salt response

BACKGROUND

Leucine-rich repeat (LRR) extensins (LRXs), which are cell wall-localized chimeric extensin proteins, are essential for the development of plants and their resistance to stress. Despite the significance of these genes, an extensive genome-wide analysis of the LRX gene family in grapevine (Vitis vinifera L.) is lacking.

RESULTS

We here detected 14 grapevine LRX genes and classified them into four groups through phylogenetic analysis. Then, their physiological and biochemical properties and gene/protein structures were analyzed. According to synteny analysis, tandem and segmental duplications have appreciably affected the expansion of the grapevine LRX gene family. On investigating tissue-specific expression profiles and cis-regulatory elements, we observed that VvLRXs likely serve as regulators of both the growth of grapevines and their responses to various environmental stresses. Salt stress treatments induced the expression of several VvLRXs, and VvLRX7 expression was the most significantly upregulated. Furthermore, VvLRX7 expression was positively correlated with the salt tolerance of grape rootstocks. VvLRX7 overexpression in Arabidopsis markedly enhanced its salt tolerance.

CONCLUSION

This study provides a general understanding of the characteristics and evolution of the LRX gene family in grapevine. VvLRX7 may function as a positive regulator of plant's response to salt stress. These findings offer a basis for future studies on the function of grapevine LRXs and their role in improving salt stress tolerance in grapevine.

Hydrochemical assessment of groundwater utilizing statistical analysis, integrated geochemical methods, and EWQI: a case study of Laiwu region, North China

The investigation of groundwater quality and hydrochemical assessment holds immense significance in safeguarding and ensuring the rational utilization of groundwater resources. This study utilizes groundwater sampling and testing data from the Laiwu region (LWR), encompassing both dry and wet seasons, to delve into the hydrochemical characteristics, ion sources, and overall groundwater quality. The research findings indicate that the groundwater in LWR exhibits weak alkalinity, with the dominant ions being Ca2+ followed by Mg2+, Na+, and K+, and HCO3-, SO42-, NO3-, Cl-, and F-. The average total dissolved solids (TDS) concentrations during the dry and wet seasons are recorded as 683 mg/L and 679 mg/L, respectively, classifying LWR's groundwater primarily as hard-fresh water. The spatial pattern of TDS concentration in LWR displays consistency throughout both the dry and wet seasons, with relatively low TDS levels observed in the northern and southeastern regions and higher concentrations in the lower reaches of the Dawen River and nearby Gangcheng. Predominantly, Ca2+, Mg2+, and HCO3- ions in groundwater originate from the dissolution of calcite and dolomite, with the hydrogeochemical process of carbonate rock weathering involving the presence of sulfuric acid. It is noteworthy that human activities significantly impact the chemical composition of groundwater in LWR. Notably, during the dry and wet seasons, the average concentration of NO3- in groundwater is 102.81 and 106.61 mg/L respectively, and the analysis shows that agricultural practice is the main source. Furthermore, the calculated average values of the entropy water quality index (EWQI) during those seasons are 58.44 and 57.24, respectively. The EWQI shows good to moderate water quality in most areas, except for a few poor-quality spots in the west. It is worth mentioning that LWR's groundwater is deemed suitable for agricultural irrigation. These research findings provide valuable insights and serve as a significant reference for the rational development and sustainable utilization of groundwater resources in the LWR region.

Driving mechanism of groundwater quality and probabilistic health risk quantification in the central Yinchuan Plain

The environmental changes from climatic, terrestrial and anthropogenic drivers can significantly influence the groundwater quality that may pose a threat to human health. However, the driving mechanism of groundwater quality and potential health risk still remains to be studied. In this paper, 165 groundwater samples were analyzed to evaluate the groundwater quality, driving mechanism, and probabilistic health risk in the central Yinchuan Plain by applying fuzzy comprehensive evaluation method (FCEM), redundance analysis (RDA) and Monte Carlo simulation. The results showed that hydrochemical evolution of groundwater were strongly influenced by water-rock interaction, evaporation and human activities. While 55.2% of groundwater samples reached the drinking water quality standard (Class I, II and III), 44.8% of samples exceeded the standard limits of Class III water quality (Class IV and V), indicating a high pollution level of groundwater. Mn, TDS, NH4+, NO3-, Fe, F-, NO2-, As were among major indicators that influence the groundwater quality due to the natural and anthropogenic processes. The RDA analysis revealed that climatic factors (PE: 10.9%, PRE: 1.1%), GE chemical properties (ORP: 20.7%, DO: 2.4%), hydrogeological factors (BD: 16.5%, K: 4.1%), and terrestrial factors (elevation: 1.2%; distanced: 5.6%, distancerl: 1.5%, NDVI: 1.2%) were identified as major driving factors influencing the groundwater quality in the study area. The HHRA suggested that TCR values of arsenic in infants, children and teens greatly exceeded the acceptable risk threshold of 1E-4, indicating a high cancer risk with a basic trend: infants > children > teens, while TCR values of adults were within the acceptable risk level. THI values of four age groups in the RME scenario were nearly ten times higher than those in the CTE scenario, displaying a great health effect on all age groups (HQ > 1). The present study provides novel insights into the driving mechanism of groundwater quality and potential health hazard in arid and semi-arid regions.

Identifying the spatio-seasonal pattern of hydrochemical evolution and surface water-groundwater interaction in a large urban river basin, Northwest China

There is insufficient understanding of the spatio-temporal evolution of surface water-groundwater quality and hydraulic connection under both natural and human influences in urban river basins. To this end, this paper investigated the spatio-seasonal pattern of hydrochemical evolution and surface water-groundwater interaction in a typical urban river basin (Dahei River basin) based on isotopic and hydrochemical data of 132 water samples collected during three seasons (normal, wet and dry seasons). From the normal season to the wet season, surface water in the Dahei River basin was dominated by the impacts of evaporation and groundwater discharge processes. During this period, the precipitation and agricultural activities (canal irrigation) were frequent. Thus, groundwater was affected by irrigation infiltration of surface water and precipitation from high-altitude areas. From the wet season to the dry season, precipitation decreased and irrigation methods changed (canal irrigation → well irrigation). In this case, groundwater discharge had a stronger impact on surface water, and shallow groundwater was recharged by deep groundwater through the well irrigation. Under this hydrological pattern, the hydrochemical characteristics of surface water were mainly influenced by evaporation, human activities (agricultural irrigation and sewage treatment) and groundwater discharge. In contrast, the hydrochemical characteristics of groundwater were main influenced by water-rock interactions (dissolution of evaporites and silicates, and cation exchange) and human activities. This study contributed to a better understanding of the hydrochemical and hydrological processes in urban river basins and provided a theoretical basis for the sustainable management of water resources.

Integrated approach to understand the multiple natural and anthropogenic stresses on intensively irrigated coastal aquifer in the Mediterranean region

Understanding the major factors influencing groundwater chemistry and its evolution in irrigation areas is crucial for efficient irrigation management. Major ions and isotopes (δD-H2O together with δ18O-H2O) were used to identify the natural and anthropogenic factors contributing to groundwater salinization in the shallow aquifer of the Wadi Guenniche Plain (WGP) in the Mediterranean region of Tunisia. A comprehensive geochemical investigation of groundwater was conducted during both the low irrigation season (L-IR) and the high irrigation season (H-IR). The results show that the variation range and average concentrations of almost all the ions in both the L-IR and H-IR seasons are high. The groundwater in both seasons is characterized by high electrical conductivity and CaMgCl/SO4 and NaCl types. The dissolution of halite and gypsum, the precipitation of calcite and dolomite, and Na-Ca exchange are the main chemical reactions in the geochemical evolution of groundwater in the Wadi Guenniche Shallow Aquifer (WGSA). Stable isotopes of hydrogen and oxygen (δ18O-H2O and δD-H2O) indicate that groundwater in WGSA originated from local precipitation. In the H-IR season, the δ18O-H2O and δD-H2O values indicate that the groundwater experienced noticeable evaporation. The enriched isotopic signatures reveal that the WGSA's groundwater was influenced by irrigation return flow and seawater intrusion. The proportions of mixing with seawater were found to vary between 0.12% and 5.95%, and between 0.13% and 8.42% during the L-IR and H-IR seasons, respectively. Irrigation return flow and the associated evaporation increase the dissolved solids content in groundwater during the irrigation season. The long-term human activities (fertilization, irrigation, and septic waste infiltration) are the main drives of the high nitrate-N concentrations in groundwater. In coastal irrigation areas suffering from water scarcity, these results can help planners and policy makers understand the complexities of groundwater salinization to enable more sustainable management and development.

Groundwater salinization risk assessment using combined artificial intelligence models

Assessing the risk of groundwater contamination is of crucial importance for the management of water resources, particularly in arid regions such as Menzel Habib (south-eastern Tunisia). The aim of this research is to create and validate artificial intelligence models based on the original DRASTIC vulnerability methodology to explain groundwater salinization risk (GSR). To this end, several algorithms, such as artificial neural networks (ANN), support vector regression (SVR), and multiple linear regression (MLR), were applied to the Menzel Habib aquifer system. The results obtained indicate that the DRASTIC Vulnerability Index (VI) ranges from 91 to 141 and is classified into two categories: low and moderate vulnerability. However, the correlation between groundwater total dissolved solids (TDS) and the Vulnerability Index is relatively weak (r < 0.5). Indeed, the original DRASTIC index needs some improvements. To improve it, some adjustments are required, notably by incorporating the TDS-groundwater salinization risk (GSR) indicator. The seven parameters of the original DRASTIC model were used as inputs for the artificial intelligence models, while the GSR values were used as outputs. Performance indicators, such as the correlation coefficient (r) and the Willmott Agreement Index (d), showed that the ANN model outperformed the SVR and MLR models. Indeed, during the training phase, the ANN model obtained r values equal to 0.89 and d values of 0.4, demonstrating the superiority, robustness, and accuracy of ANN-based methodologies over the original DRASTIC model. The findings could provide valuable information to guide management of groundwater contamination risks, especially in arid regions.