Soil colloids can significantly enhance spreading of polybromodiphenyl ethers in groundwater by serving as an effective carrier.

Polybromodiphenyl ethers (PBDEs), the widely used flame retardants, are common contaminants in surface soils at e-waste recycling sites. The association of PBDEs with soil colloids has been observed, indicating the potential risk to groundwater due to colloid-facilitated transport. However, the extent to which soil colloids may enhance the spreading of PBDEs in groundwater is largely unknown. Herein, we report the co-transport of decabromodiphenyl ester (BDE-209) and soil colloids in saturated porous media. The colloids released from a soil sample collected at an e-waste recycling site in Tianjin, China, contain high concentration of PBDEs, with BDE-209 being the most abundant conger (320 ± 30 mg/kg). The colloids exhibit relatively high mobility in saturated sand columns, under conditions commonly observed in groundwater environments. Notably, under all the tested conditions (i.e., varying flow velocity, pH, ionic species and ionic strength), the mass of eluted BDE-209 correlates linearly with that of eluted soil colloids, even though the mobility of the colloids varies markedly depending on the specific hydrodynamic and solution chemistry conditions involved. Additionally, the mass of BDE-209 retained in the columns also correlates strongly with the mass of retained colloids. Apparently, the PBDEs remain bound to soil colloids during transport in porous media. Findings in this study indicate that soil colloids may significantly promote the transport of PBDEs in groundwater by serving as an effective carrier. This might be the reason why the highly insoluble and adsorptive PBDEs are found in groundwater at some PBDE-contaminated sites.

Effect of Fe2+-activated persulfate combined with biodegradation in removing gasoline BTX from karst groundwater: A box-column experimental study.

In-situ chemical oxidation with persulfate (PS-ISCO) is a preferred approach for the remediation of fuel-contaminated groundwater. Persulfate (PS) can be activated by various methods to produce stronger sulfate radicals for more efficient ISCO. Despite karst aquifers being widespread, there are few reports on PS-ISCO combined with Fe2+-activated PS. To better understand the effects of Fe2+-activated PS for the remediation of gasoline-contaminated aquifers in karst areas, a box-column experiment was conducted under flow conditions, using karst groundwater and limestone particles to simulate an aquifer. Gasoline was used as the source of hydrocarbon contaminants. Dissolved oxygen and nitrate were added to enhance bioremediation (EBR) and ferrous sulfate was used to activate PS. The effect of Fe2+-activated PS combined with biodegradation was compared during the periods of EBR + ISCO and ISCO alone, using the mass flow method for data analysis. The results showed that the initial dissolution of benzene, toluene, and xylene (BTX) from gasoline injection was rapid and variable, with a decaying trend at an average pseudo-first-order degradation rate constant of 0.032 d-1. Enhanced aerobic biodegradation and denitrification played a significant role in limestone-filled environments, with dissolved oxygen and nitrate utilization ratios of 59 ~ 72% and 12-70%, respectively. The efficiency of EBR + ISCO was the best method for BTX removal, compared with EBR or ISCO alone. The pseudo-first-order degradation rate constants of BTX reached 0.022-0.039, 0.034-0.070, and 0.027-0.036 d-1, during the periods of EBR alone, EBR + ISCO, and ISCO alone, respectively. The EBR + ISCO had a higher BTX removal ratio range of 71.0 ~ 84.3% than the ISCO alone with 30.1 ~ 45.1%. The presence of Fe2+-activated PS could increase the degradation rate of BTX with a range of 0.060 ~ 0.070 d-1, otherwise, with a range of 0.034-0.052 d-1. However, Fe2+-activated PS also consumed about 3 times the mass of PS, caused a further decrease in pH with a range of 6.8-7.6, increased 3-4 times the Ca2+ and 1.6-1.8 times the HCO3- levels, and decreased the BTX removal ratio of ISCO + EBR, compared to the case without Fe2+ activation. In addition, the accumulation of ferric hydroxides within a short distance indicated that the range of PS activated by Fe2+ may be limited. Based on this study, it is suggested that the effect of Fe2+-activated PS should be evaluated in the remediation of non-carbonate rock aquifers.

Dissolved organic carbon (DOC) and labile organic compounds' spatial and temporal variations in coastal Indian groundwater: their bioavailability and transfer to neighboring coastal waters of India.

Submarine groundwater drainage (SGD) changes the elemental composition of the neighboring coastal ocean and impacts the biogeochemical cycles. To examine the seasonal and spatial variability in dissolved organic carbon (DOC) and labile organic compound biochemical compounds like dissolved carbohydrates (TDCHO), dissolved proteins (TDPRO), and dissolved free amino acid (TDFAA) concentrations during the dry and wet periods, groundwater samples were taken at 90 locations (180 samples) along the Indian coast. The mean DOC contents in Indian coastal groundwaters were more significant than the global mean values. DOC, TDCHO, TDPRO, and TDFAA concentrations are higher during wet than dry periods. The DOC and labile organic compound showed a substantial positive association with soil organic carbon, and respective labile compounds in soil, population, and land usage and poor relation with woodland territories, implying that soil organic compounds leaching is a source of DOC and other labile organic compounds into the groundwater. DOC and other labile compounds concentrations were linearly associated with population density, land usage, and sewage production, demonstrating that anthropogenic activities tightly regulate the formation of DOC in groundwater. During the wet and dry periods, total labile organic compounds (TDCHO, TDFAA, and TDPRO) constituted 21% and 10.5% of DOC, respectively. Compared to the wet time, more aromatic compounds accumulated during the dry season but were less bioavailable. SGD DOC flux contributed 2-7% of riverine DOC flux to the coastal ocean. The SGD flux from the Indian subcontinent to the nearby northern Indian Ocean accounts for approximately 2% of the worldwide SGD flux. The effect of DOC flux via SGD on coastal bacterial activity, the plankton food web, and the oxygen minimum zone must be studied.

Quantification of natural uranium and its risk evaluation in groundwater of Chikkaballapur district in Karnataka, India.

The present study focused on the distribution of uranium in groundwater samples collected from various sources in the Chikkaballapur district and its associated risk in humans. Seventy-five groundwater samples were collected during pre-monsoon and post-monsoon seasons and were analysed for uranium concentration along with different water quality parameters. The uranium concentration ranged from 0.23 to 285.23 µg/L in the pre-monsoon season and from 0.02 to 107.87 µg/L in the post-monsoon season. More than 90% of samples, except a few, were under the safe limits of 60 µg/L as directed by the Department of Atomic Energy (DAE) of India's Atomic Energy Regulatory Board (AERB). The study analysed physicochemical parameters like pH, total dissolved solids (TDS), nitrate, total hardness, phosphate, sulphate and fluoride in collected water samples. Out of all samples, few samples noted higher values of TDS, nitrate and fluoride. Their correlation along with uranium is detailed in the study. Owing to its slightly elevated content, an evaluation of the radiological and chemical hazards associated with uranium consumption was analysed. When the risk resulting from chemical toxicity was evaluated, relatively few samples had a hazard quotient (HQ) score higher than 1, which suggested that the people were vulnerable to chemical danger. This study also evaluates the dangers of elevated uranium levels in groundwater samples to the general public's health. It also acknowledges the importance of routinely evaluating and treating the drinking water sources in the region.

Groundwater quality evaluation of the weathering mantle in crystalline basement aquifer system, southern Brazil.

Groundwater is the main source of water for more than 2 billion people worldwide. In southern Brazil, the Crystalline Basement Aquifer System is composed of strategic groundwater reservoirs. Groundwater is mostly taken from shallow wells, and it is often used without any treatment, which poses a risk to public health. The present study aims to evaluate shallow groundwater quality and the geochemistry of shallow and deep groundwater located in the municipality of Canguçu, southern Brazil. The physicochemical and microbiological parameters of groundwater samples collected from shallow wells were monitored and analyzed using ANOVA variance analysis and water quality index (CCME WQI) approaches. Also, the results were compared with secondary data from deep wells. The monitored shallow wells had thermotolerant coliforms, Escherichia coli, pH, potassium, manganese, iron, and nitrate in disagreement with the guidelines of the World Health Organization. Moreover, variance analysis showed that the parameters temperature, dissolved oxygen, pH, chloride, and magnesium were the most influenced by seasonal variations. According to the CCME WQI, most samples had good quality (60%), 28% had fair quality, and 12% had poor quality. In addition, the field campaigns with higher precipitation rates also presented fair quality. Therefore, most of the shallow groundwater quality is affected by surface pollutants from the urban area, aggravated in rainy periods. Whereas deep groundwater is influenced by geochemistry mechanisms. The results revealed the risk of water consumption for public health and the urgent need for better maintenance of these wells and water treatment implementation.

PFOA-contaminated soil remediation: a comprehensive review.

Soil and groundwater contamination has been raised as a concern due to the capability of posing a risk to human health and ecology, especially in facing highly toxic and emerging pollutants. Because of the prevalent usage of perfluorooctanoic acid (PFOA), in industrial and production processes, and subsequently the extent of sites contaminated with these pollutants, cleaning up PFOA polluted sites is paramount. This research provides a review of remediation approaches that have been used, and nine remediation techniques were reviewed under physical, chemical, and biological approaches categorization. As the pollutant specifications, environmental implications, and adverse ecological effects of remediation procedures should be considered in the analysis and evaluation of remediation approaches, unlike previous research that considered a couple of PFAS pollutants and generally dealt with technical issues, in this study, the benefits, drawbacks, and possible environmental and ecological adverse effects of PFOA-contaminated site remediation also were discussed. In the end, in addition to providing sufficient and applicable understanding by comprehensively considering all aspects and field-scale challenges and obstacles, knowledge gaps have been found and discussed.

Understanding Environmental Fate: Soil Variability and Rainfall Influence on Triafamone and Ethoxysulfuron Leaching.

Considering the environmental impact of triafamone and ethoxysulfuron, it is crucial to investigate their leaching behaviour under different geographical conditions. The present study evaluates the effects of application rate, soil properties and rainfall conditions on leaching of these herbicides and their metabolites. Ethoxysulfuron leached up to 50-60 cm with 82.95 to 89.23% detected in leachates while triafamone leached only to 10-20 cm and was < 0.01 µg mL-1 in leachates. Highest leachability was observed in loamy sand followed by sandy loam and clay loam soil. M1 metabolite (N-(2-((4,6-dimethoxy-1,3,5-triazin-2-yl) (hydroxy) methyl) -6-fluorophenyl) -1,1-difluoro-N-methyl methane sulfonamide) was majorly present in 0 to 10 cm soil depth. With increase in rainfall, downward mobility of both parent and M1 increased. Amendment of loamy sand soil with farmyard manure reduced the leachability indicating it could mitigate groundwater pollution. However, the effect of different exogenous OM amendments on leaching behaviour of herbicides needs to be evaluated.

Ra isotope perspective on the hydrology and continuity of permafrost in the high Arctic.

The continuous permafrost in the valleys of Svalbard is dotted by pingos, which are small hills formed by the near surface freezing of ascending groundwater. In this study, we used 3H and Ra isotopes to inquire into the sub-surface residence time of groundwater discharging at these pingos. While its low 3H suggests that the pingo-associated groundwater is basically not modern (i.e. older than 60 years), Ra isotopes imply that most water has an underground residence time of several hundred years. This is deduced from the lower than equilibrium ratios (activity ratios<21.7) of the long-lived to short-lived 226Ra/223Ra. Since the freezing age of the main body of permafrost in this area is >4000 years, the presence of younger water at depth suggests that the aquifer has been recharged after permafrost formation, which could take place via faults or through the non-frozen base of wet glaciers. This active hydrology suggests that permafrost in the valleys of Svalbard was at least locally discontinuous during the Late Holocene, with likely further implications to the release of greenhouse gases during the pre-industrial period.

The use of sedimentary metals to assess anthropogenic change, ecological risk, model past and future impacts and identify contaminant sources in the eleven estuaries of Greater Sydney (Australia): A review and critical assessment.

The Greater Sydney (Australia) region is dissected by eleven major estuaries comprising a wide range of sizes, sediment and contaminant types, while the catchments also vary in size, land use type, populations size and geology/soils. The magnitude and breadth of the current study are rare and offered an unusual opportunity to provide new information on interactions between source, fate and effect relationships of a highly diverse estuarine-catchment environment using sedimentary metals (Co, Cr, Cu, Ni, Pb and Zn). Advanced methodologies used in this study revealed that although metal concentrations were generally high, ecological risk was surprisingly reduced due to the presence of metal-poor coarse sediment. Stormwater was identified as the dominant source of metals to estuaries of Greater Sydney and relates to development of high-density road networks. Industrial sources, frequently identified as a major contributor to estuarine contamination, was significantly reduced due to the decline of industry through decentralisation and gentrification and because waste is discharged to the sewer system, which is released offshore, or tertiary-treated to the Hawkesbury. Groundwater leachate associated with shoreline reclamation and wetland infilling and metals related to boating activities were important sources of metals impacting local bays and coastal lagoons. Temporal monitoring and unique modelling approaches indicated that the concentration of sedimentary metals is generally declining in these estuaries, (especially for Pb), except for areas with rapidly increasing urban populations. Multivariate statistical modelling was able to differentiate the 11 estuaries on a chemical basis by aligning Cu, Pb, Zn vectors with metal-rich estuaries and also identified catchment attributes (percent area, total yield, anthropogenic yield and population density) normalised to catchment areas as having a major influence on estuarine condition. The new knowledge derived from this study should be used to assess the environmental status of estuaries and to prioritise management actions in future investigations.

Metabolic adaptations underpin high productivity rates in relict subsurface water.

Groundwater aquifers are ecological hotspots with diverse microbes essential for biogeochemical cycles. Their ecophysiology has seldom been studied on a basin scale. In particular, our knowledge of chemosynthesis in the deep aquifers where temperatures reach 60 °C, is limited. Here, we investigated the diversity, activity, and metabolic potential of microbial communities from nine wells reaching ancient groundwater beneath Israel's Negev Desert, spanning two significant, deep (up to 1.5 km) aquifers, the Judea Group carbonate and Kurnub Group Nubian sandstone that contain fresh to brackish, hypoxic to anoxic water. We estimated chemosynthetic productivity rates ranging from 0.55 ± 0.06 to 0.82 ± 0.07 µg C L-1 d-1 (mean ± SD), suggesting that aquifer productivity may be underestimated. We showed that 60% of MAGs harbored genes for autotrophic pathways, mainly the Calvin-Benson-Bassham cycle and the Wood-Ljungdahl pathway, indicating a substantial chemosynthetic capacity within these microbial communities. We emphasize the potential metabolic versatility in the deep subsurface, enabling efficient carbon and energy use. This study set a precedent for global aquifer exploration, like the Nubian Sandstone Aquifer System in the Arabian and Western Deserts, and reconsiders their role as carbon sinks.

Arsenic release during groundwater recharge and effects of coexisting ions in a typical inland basin with high arsenic concentration: Modeling and batch experiment.

Groundwater recharge is a viable solution to groundwater overexploitation. However, the injection of recharge water may break the dissolution balance and induce the release of trace elements especially arsenic (As), which has been identified in river deltas. Only a few studies have been conducted in inland basins with high As concentration, high pH, and low Eh. Aiming to analyze As release with groundwater recharge in inland high-As regions and determine the effects of coexisting ions in recharge water, this study established PHase Equilibria Calculation (PHREEQC) models using rainwater and groundwater data from three inland sedimentary basins with slow groundwater flow in semi-arid regions. The simulations fitted with the batch experiments, achieving an R-squared (R2) of 0.98. The coexisting ions in the recharge water significantly affected As release during recharge. Ca2+ inhibited the release of total arsenic (Total-As) by increasing the surface charge of iron oxides. NO3- inhibited Total-As release by promoting the conversion of trivalent As into pentavalent As. Conversely, HCO3- facilitated As release by competing with arsenate for adsorption sites. On the basis of the modeling and batch experiment results, Total-As release with groundwater recharge was predicted. The results indicated that the high Ca2+ concentration in the recharge water inhibited the As release by 83.5 %, which can be used as a strategy to control As release during groundwater recharge in high-As inland basins.

Strontium isotopes in the atmosphere, geosphere and hydrosphere: Developing a systematic "fingerprinting" framework of rocks and water in sedimentary basins in eastern Australia.

Understanding the connection between aquifers, aquitards, and groundwater-dependant ecosystems remains a key challenge when developing a conceptual hydrogeological model. The aim of this study was to develop a systematic strontium isotope (87Sr/86Sr) fingerprinting framework of rocks and water within the sedimentary Surat and Clarence-Moreton basins (SCM basins) in eastern Australia - an area of extensive coal seam gas development and high potential for aquifer and groundwater-surface water connectivity. To do this, new groundwater samples (n = 298) were collected, analyzed and integrated with published data (n = 154) from the basins' major sedimentary, volcanic and alluvial aquifers, including the major coal seam gas target, the Walloon Coal Measures. Samples were also analyzed from rainfall (n = 2) and surface water (n = 40). In addition, rock core samples (n = 39) from exploration and stratigraphic wells were analyzed to determine the range of Sr isotope composition from host rocks. The analyses of cores demonstrate a distinct and systematic contrast in 87Sr/86Sr between different hydrogeological units. The analyses confirm that all major hydrogeological units have a narrow range with unique 87Sr/86Sr population characteristics that are useful for guiding conceptual model development. Comparison with selected hydrochemical and groundwater age tracers (14C and 36Cl) suggests only limited changes of 87Sr/86Sr from recharge beds to the deeper parts of the basins or with a decrease in natural 14C and 36Cl tracer content along flow paths. Stream sampling during baseflow conditions confirms that 87Sr/86Sr in surface waters are similar to those of the underlying bedrock formations. We demonstrated that 87Sr/86Sr analyses of rocks and water provide a powerful hydrostratigraphic and chemostratigraphic fingerprinting framework in the SCM basins, enabling reliable assessments of plausible aquifer and groundwater-surface water interconnectivity pathways. Applied in other complex multi-aquifer sedimentary basins in Australia, and globally, a similar approach can help to constrain conceptual hydrogeological models and facilitate improved water resource management.

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.

Statistical and geospatial assessment of trace and toxic elements distribution in ground and surface water of northern parts of the Indo-Gangetic plains: Source identification and health risk assessment.

This study focusses on ground and surface water resources in the northern parts of the Indo-Gangetic Plains. The study aims to identify potential contaminants, analyse their distribution, trace their origins, and evaluate associated health risk. Samples from 80 locations; groundwater (n = 69) and surface water (n = 11) were analysed for nineteen trace and toxic elements using ICP-MS. Eight elements in groundwater (Mn, Fe, Ni, Zn, As, Tl, U and Se) and six in surface water (Al, Mn, Fe, Ni, Zn, and Tl) exceeded WHO (2011) and BIS (2012) limits in certain areas. The geospatial analysis reveals hotspots of trace and toxic element concentration, with higher levels detected in the southeast and western regions of the study area. Correlation matrices revealed a robust correlation (∼>0.75-0.99, p < 0.01) among all trace and toxic elements (excluding Li, Be, As, Ag, and U) in surface water samples when compared to groundwater samples. Cluster analysis and principal component analysis (PCA) (explains 70.09 cumulative percent for total 6 of factors) of groundwater chemistry indicates that Zn, Ni and Tl contamination may originate from industrial activities (metallurgical processes and manufacturing). The potential sources of Mn may be both geological and human-induced, while Fe, Se, As and U can originate from specific geological formations or human-related activities like over-extraction and leaching of excess fertilizers into aquifers. For surface water, PCA (explains 92.92 cumulative percent for total 5 of factors) identifies industrial activities as the main source of Mn, Fe, Tl, Ni, and Zn, while Al originates from both geological and anthropogenic sources. The water quality index indicated poor to very poor water quality in the western and central regions, whereas the northern and eastern regions exhibited excellent water quality. Health risk assessment reveals HI values for groundwater water: 3.85 (adults), 7.70 (children); surface water: 1.52 (adults), 3.05 (children), emphasizing the urgent need for remediation measures.

Leachate reduction and pollution control strategies for landfills in hilly areas based on site condition analysis and numerical simulation.

Landfill is an important means of municipal solid waste treatment. Previous studies have shown that the combination of "cut-off wall and pumping well" technology is an effective measure to deal with the leachate emission reduction and pollution control of landfill, and has been widely used in plain areas. However, for landfills in hilly areas with complex terrain and geological conditions, there is still a lack of clear and referable ideas and operational strategies for leachate emission reduction and pollution control. In this study, we proposed strategies for determining the position and depth of cut-off walls and pumping wells and reasonable combinations of the cut-off wall depth and pumping quantity for leachate reduction and pollution prevention of landfills in hilly areas. The determination of leachate reduction and pollution control strategy need to be achieved in two stages, qualitative and quantitative: (1) In the qualitative stage, the natural conditions (Weathering degree, groundwater flow characteristics, topography condition, hydrometeor condition, and aquifer thickness) and engineering conditions (Operation status, landfill location, and excavation status) of the study area are analysed in detail, and then the depth range and location of the cut-off wall and pumping well are determined. (2) In the quantitative stage, we need to quantify the combination of the cut-off wall depth and pumping quantity by using profile particle tracing and pollutant transport modelling. A reasonable cut-off wall depth needs to control the leakage of pollutants inside the wall, and a reasonable pumping quantity needs to ensure that the depth of the pollutant distribution is equivalent to the depth of the separation line, which separates the water flow towards the pumping well and the water flow downstream. (3) The effectiveness of the leachate reduction and prevention strategies proposed in this study was verified through an example of a landfill in Northeast China. This study provides a reference and operation method for leachate emission reduction and pollution control of landfills in hilly areas.

Variation of nitrate sources affected by precipitation with different intensities in groundwater in the piedmont plain area of alluvial-pluvial fan.

A substantial reservoir of nitrogen (N) in soil poses a threat to the quality and safety of shallow groundwater, especially under extreme precipitation that hastens nitrogen leaching into groundwater. However, the specific impact of varying precipitation intensities on the concentration and sources of nitrate (NO3-) in groundwater across diverse hydrogeological zones and land uses remains unclear. This study aims to elucidate the fluctuations in NO3- concentration, sources, and controlling factors in shallow groundwater under different intensities of precipitation (extreme heavy precipitation and continuous heavy precipitation) in a typical alluvial-pluvial fan of the North China Plain by using stable isotopes (δ2H-H2O, δ18O-H2O, δ15N-NO3-, δ18O-NO3-), hydrochemical analyses and the SIAR model. Affected by extreme heavy precipitation the depleted isotopes of δ2H-H2O and δ18O-H2O in groundwater of the entire area suggested the rapid recharge of fast flow by precipitation. The enriched isotopes of δ2H-H2O and δ18O-H2O of north part in alluvial fan after continuous heavy precipitation showed the recharge of translatory flow of soil water. NO3-concentrations increased to 78.9 mg/L after extreme heavy precipitation and increased to 105.3 mg/L after continuous heavy precipitation when compared to those in normal year (56.8 mg/L) of north part of the alluvial fan. However, NO3- concentrations had slight variation after continuous heavy precipitation of south part of the fan due to the deep vadose zone. The contribution ratio of sources of NO3- in groundwater by using SIAR analysis revealed manure & sewage (MS) as the primary NO3- source (accounting for 59.7-78.1%) before extreme heavy precipitation, chemical fertilizer (CF) making a minor contribution (6.9-17.3%). Different precipitation events and land use types lead to changes in NO3- sources. Affected by extreme heavy precipitation, the contribution of MS decreased while CF increased, particularly in vegetables (26.2-28.1%) and farmland (29.2-34.7%). After continuous heavy precipitation, MS increased again, particularly in vegetables (50.0%) and farmlands (20.4-66.4%), with CF either increasing or remaining steady. This indicated that continuous heavy precipitation accelerated the leaching of nitrogen (organic manure application) stored in deep soil to groundwater and it has a larger influence on the increasing of NO3- concentrations of groundwater than extreme heavy precipitation which carried nitrogen (chemical fertilizer application) in shallow soil to groundwater by fast flow. These findings underscore the importance of considering soil chemical N stores and their implications for groundwater contamination mitigation under future extreme climate scenarios, particularly in agricultural management practices.

Analysis of the evolution and causes of groundwater chemistry after ecological water replenishment of the Jialu River, China.

Ecological water replenishment is an important measure for conserving water sources and improving the water environment. To explore the evolution and causes of groundwater chemistry after ecological water replenishment in the Jialu River, this study utilized groundwater monitoring data from 2015 to 2019 following ecological water replenishment. Various methods, including Piper's trilinear diagram, Gibbs diagram, principal component analysis, and ion ratio analysis, were employed for research purposes. The results indicate that (1) since the implementation of ecological water replenishment in the Jialu River, there has been a general downwards trend in total dissolved solids (TDS) in groundwater. The dominant cation in groundwater is Ca2+, whereas HCO3- is the dominant anion. The concentration of cations in groundwater has generally decreased, with noticeable reductions in SO42- and Cl- concentrations in the upper reaches of the recharge river contributing to improved groundwater quality. (2) A comparison with 2015 reveals a gradual transition at sampling points from chemical types such as HCO3-Ca·Mg and HCO3·Cl-Ca·Mg to an ecological water replenishment chemical type (HCO3-Ca).

Multiscale spatiotemporal characteristics and influencing factors of ecosystem service value of groundwater in China.

Ecosystem services are fundamental to human survival on Earth, but studies on ecosystem service value of groundwater (ESV-G) are rare. The multiscale characteristics and influencing factors of ESV-G in China from 2000 to 2020 were analyzed in this study. The results showed that ESV-G decreased first and then increased, the average ESV-G was 130.30 thousand yuan/km2, and ESV-G tended to shift towards middle level (second to fourth class). The Hu Line was the dividing line between the first class (more than half area) and the others. The AI and FRAC values indicated that the patches of ESV-G were more concentrated, with simpler shapes that were more amenable to governance at the province scale. Hot spots and cold spots were mainly located in the eastern and western parts of Hu Line, respectively. The ESV-G of the cold spots per unit area at the province scale was higher than that at the city scale, which indicated that the province scale had the potential for higher ESV-G per unit area and cost advantage. Precipitation and temperature were the main factors affecting ESV-G; the influence of human activities on ESV-G increased on a larger scale as time went by. Combination of precipitation and Digital Elevation Model (DEM) had the greatest influence on ESV-G among the combinational influencing factors. The province scale was the optimal scale to manage ESV-G. Climate change had led to the expansion of hot and cold spots of ESV-G, northern and southern areas should combine existing policies to carry out differentiated governance. This study extended the scope of ecosystem service value studies from land surface to underground, providing a scientific basis for the management of groundwater ecosystem.

Multi-objective double layer water optimal allocation and scheduling framework combing the integrated surface water - groundwater model.

Balancing the water consumption of agricultural and ecological is the key point of sustainable social and economic development in an inland river basin. The growth of desert riparian forests in inland river basins mainly depends on a certain phreatic water table depth (PWTD). The main object of this study was to allocate and schedule water resources to regulate the PWTD and satisfy agricultural water demand. Therefore, a multi-objective double layer optimal allocation and scheduling framework based on the computationally efficient integrated surface water-groundwater model (ISGWM), which can simulate the surface water processes, groundwater recharge and discharge processes, and PWTD changes, was constructed and applied to the mainstream of Tarim River Basin (TRB). The top layer model of the framework is an optimal ecological water allocation model, and its optimal allocation results are used as the initial solution of the bottom layer model. The results show that under 5 different inflow frequencies, the agricultural water shortage rate is 0, 17.38 %, 17.41 %, 14.06 %, and 19.94 %, respectively. The PWTD regulation has a great performance. After the optimal scheduling, the proportions of good growth of the control area behind the gate under different inflow frequencies were 98.18 %, 98.18 %, 98.18 %, 90.91 %, and 94.55 %. Agricultural water shortage is mainly due to the non-uniformity distribution of intra-annual inflow and the lack of controlling hydraulic engineering. The regulation of PWTD can guarantee the growth of desert riparian forests on both sides of the mainstream of TRB. Besides, we explored the feasibility of exploiting groundwater to supplement agricultural water consumption. The groundwater exploitation should be controlled within the scope of not causing excessive increase of PWTD (difference between PWTD and target depth <1 m), due to the groundwater exploitation to supplement agricultural water will lead to the increase of PWTD. Overall, this framework, which regulates the PWTD with the change of ecological water supply based on the ISGWM, provides a new idea for the allocation and scheduling of agricultural and ecological water resources in arid inland river basins. It also provides a new method for the coupled cooperative operation of surface water and groundwater.

Modelling approach integrating climate projections for coastal groundwater management.

Climate change and excessive groundwater extraction are major contributors to rising groundwater salinization due to seawater intrusion in coastal aquifers. This study aims to define a wide-applicable approach in which hydrological balance, boundary conditions, and irrigation water demand, defined over time considering climate change predictions, can integrated into a numerical model of the groundwater system. The approach was tested in a selected coastal aquifer. The approach spans from the past, used to define steady or almost natural conditions for calibration purposes (1950-2000 in the test), to the future (2100), divided in decade steps. The water balance analysis is based on an inverse hydrogeological water balance approach. The future climate change predictions are used to assess variations in boundary conditions of the groundwater model concerning salinity and sea level, recharge, and inflow from upstream aquifers. The approach considers changes in agricultural activities, groundwater demand, and river stage. The regional model is generated using the MODFLOW code for the groundwater flow model and the SEAWAT code for the salt transport model. The test concerns the Metaponto coastal plain, in which a porous aquifer is at salinization risk due to seawater intrusion. In this way, different influences of climate change and human activities are combined to define a 3d view of groundwater depletion and salinization effects. Quantifying these potential effects or risks, adaptation scenarios with numerical assessments are outlined in this study.