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Reclaimed water (RW) has been widely used as an alternative water resource to recharge rivers in mega-city Beijing. At the same time, the RW also recharges the ambient aquifers through riverbank filtration, and modifies the subsurface hydrodynamic system and hydrochemical characteristics. To assess the impact of RW recharge on the unconfined groundwater system, we conducted a 3D groundwater flow and solute transport model based on 10 years of sequenced groundwater monitoring data to analyze the changes of the groundwater table, Cl- loads, and NO3-N loads in the shallow aquifer after RW recharge to the river channel. The results show that the groundwater table around the river channel elevated by about 3~4 m quickly after RW recharge from Dec. 2007 to Dec. 2009, and then remained stable due to the continuous RW infiltration. However, the unconfined groundwater storage still declined overall from 2007 to 2014 due to groundwater exploitation. The storage began to recover after groundwater extraction reduction, rising from 3.76×108 m3 at the end of 2014 to 3.85×108 m3 at the end of 2017. Cl- concentrations varied from 5~75 mg/L before RW recharge to 50~130 mg/L in two years (2007–2009), and then remained stable. The zones of the unconfined groundwater quality-affected by RW infiltration increased from 11.7 km2 in 2008 to 26.7 km2 in 2017. Cl- loads of the unconfined groundwater increased from 1.66×104 t in 2008 to 3.8×103 t in 2017, while NO3-N loads decreased from 29.8 t in 2008 to 11.9 t in 2017 annually in the zones. We determined the maximum area of the unconfined groundwater quality affected by RW, and groundwater outside this area not affected by RW recharge keeps its original state. The RW recharge to the river channel in the study area is beneficial to increase the groundwater table and unconfined groundwater storage with lesser environmental impacts.

The release and transport of metals in active mines pose a threat to water quality when mine sites become abandoned. Karst aquifer systems are especially vulnerable due to their ability to quick transport polluted water over large distances through surface and subsurface routes. Surface and groundwater samples collected from the Guilin-Yangshuo Basin in southwestern China were analyzed for δ18O and δ2H of water, major and trace elements, including Sr, pH, temperature, and electrical conductivity to gain an understanding of how an abandoned Pb-Zn mine and its tailing deposits influence the groundwater quality of a downgradient karst carbonate aquifer. The δ18O and δ2H values of the water samples indicate that the karst aquifer is dominantly recharged by local precipitation during the wet season and additionally by water from upstream mountainous areas during the dry period. Severe heavy metal contamination (9154, 1081, 37 and 55 μg/L of Zn, Mn, Ni and Cd, respectively) was detected in the mine drainage water. Ninety-one percent of the downstream surface samples and 67% of the groundwater samples collected during the dry season exceeded the limit value for As (10 μg/L) according to the China Standards for Drinking Water Quality. Factor analysis was applied, and showed the river and groundwater were affected by the Pb-Zn mine and its tailing deposits and by carbonate dissolution. The Sidi River plays an important role in trace element transport, which supported by a strong correlation between sulfate and strontium (with r2 = 0.85 in the dry season; r2 = 0.94 in the wet season). The strong acid generated during sulfide oxidation of the mine tailings is neutralized by carbonate rock dissolution, resulting in neutral to alkaline water which hinders the mobility of trace elements. However, the increasing sulfate contents and the elevated total trace element concentrations (from undetectable to 1503 μg/L except for the mine drainage with 10,350 μg/L) confirm the release of toxic metals into the water system. In addition, adsorbed arsenate anions may exchange with dissolved carbonate anions and be released into the groundwater.

The rise and fall of the groundwater level can drive air flow in the vadose zone. In turn, the air flow can interact with the water flow. When the unconfined aquifer is covered by a low-permeability media, the coupling of the water flow and the air flow is more obvious. In this study, a conceptual model is established for coupling of air flow and water flow in the vadose zone in response to rapid fluctuations of the water table. Water injection and drainage experiments are conducted in a double-layered sand column with a thick layer (80.5 cm) of coarse sand and a thin layer of fine sand as a low-permeability cap. Different cap thickness (2 cm, 5 cm, 7.5 cm) and different thickness of the vadose zone (30 cm, 40 cm) are set for the experiments. Negative pressure (NP)/positive pressure (PP) of the air in the vadose zone is observed in the drainage/injection experiments, with higher pressure in experiments of thicker cap layer. In each experiment, NP or PP increases rapidly to reach a maximum in the early stage, and gradually becomes zero in the late stage. Analytical solutions on three subdivided stages indicate the permeability and thickness of the cap layer, as well as permeability and porosity of the media in the vadose zone are the key controlling factors on the process of coupling of air flow and water flow. The solutions also reveal the formation mechanism of air pressure in the vadose zone with a low-permeability cap. This study has both theoretical significance and engineering applications.

Water quality is of great concern under the threats of an abandoned Pb–Zn mine within a vulnerable karst area. This study focuses on tracing the sources, migration and relevant geochemical controls of heavy metals along with surface- and groundwater flow, and assessing their hazards posed to the environment by indexes of heavy metal pollution (HPI) and ecological risks (ERI). We analyzed the concentrations of lead (Pb), zinc (Zn), cadmium (Cd) and copper (Cu) in filtered and digested surface water (SW) and groundwater (GW) samples. Whilst sulfate concentrations, δ34SSO4 isotope, and other physical-chemical parameters were measured in filtered SW and GW. Clearly elevated concentrations of Zn and Cd have been observed in the upstream of the Sidi River (max. 1540.3/1676.7, and 19.9/19.4 μg/L, for filtered/digested contents, respectively), and that of digested Pb and Cu (max. 17.8 and 114.6 μg/L, respectively) in the downstream karst groundwater. Zn and Cd are likely introduced by the Sidi River which is found mostly in the dissolved phase. While Pb and Cu are sourced from the remobilization of upper lying polluted soil which mostly existed in the particulate phase. Zn and Cd concentrations in the karst groundwater peak at the losing section while Pb and Cu in the river peaks at the gaining section as a result of metals transport with SW-GW exchange. Dilution significantly decreases total metals concentration in the non-karst area. Due to the buffer effect caused by carbonates dissolution and bacterial sulfate reduction, a steady neutral pH can reduce the concentrations of the dissolved metals in the karst area. The ERI and HPI assessments show an acceptable level for surface- and groundwater. A long-term observation on the contents of undissolved metals needs to be conducted in karst areas which are threatened by metal(s) mines.

Long-term wastewater and reclaimed water irrigation systems constitute the major processes in local water circulation, which concomitantly introduce plenty of undesirable substances that can threaten water quality, ecosystem functions and human health. At the Southeast Reclaimed Water Irrigation Region (SRWIR) of Beijing, wastewater irrigation was adopted from 1969 to 2002, and second-treated effluents (reclaimed water) has been used thereafter. Polycyclic aromatic hydrocarbons (PAHs) were the most ubiquitously detected contaminant in wastewater and reclaimed water and are reported to be carcinogenic. Hence, we measured the concentrations of dissolved sixteen United States Environmental Protection Agency (USEPA) priority PAHs in surface water and groundwater at the SRWIR to characterize their spatial and temporal variations, and to clarify the role of reclaimed water to natural water. The concentration of 16 individual PAHs in reclaimed water, rivers and groundwater varied from 339.4 to 636.2 ng/L, 359.1 to 3435.0 ng/L and 216.5 to 488,205.2 ng/L, respectively. The lower aromatic rings of PAHs prevailed in aquatic environments rather than the higher ones. Thereinto, naphthalene was the predominant isomer within the highest concentration reached to 486,600 &mu, g/L. The groundwater samples had higher PAHs concentrations at Tongzhou district which attributed to the higher vulnerability of aquifer. Additionally, strong correlations between PAHs and total nitrogen, nitrate, dissolved oxygen and electrical conductivity suggested those potential factors affecting the photo degradation and/or biodegradation of PAHs. The relationship identified between PAHs concentrations and physical and chemical indices would help us to enhance the understanding migration and transformation of PAHs spatially and temporally, enable us to assess the potential risks of the environmental pollutants to aquatic organisms and human water supplies.

Sanmenxia Dam, one of the most controversial water conservancy projects in China, has seriously impacted the lower Weihe River of the Yellow River Watershed since its operation. At the Huaxian Station, the dam operation controls the surface water level and leads to the variation of the surface water&ndash, groundwater interaction relationship. The river channel switched from a losing reach during the early stage (1959) to a gaining reach in 2010 eventually. The comparison of tracer (Cl&minus, &delta, 18O and &delta, 2H) characteristics of surface water in successive reaches with that of ambient groundwater shows that the general interaction condition is obviously affected by the dam operation and the impact area can be tracked back to Weinan City, around 65 km upstream of the estuary of the Weihe River. The anthropogenic inputs (i.e., agricultural fertilizer application, wastewater discharge, and rural industrial sewage) could be responsible for the deterioration of hydro-environment during the investigation periods of 2015 and 2016, as the population and fertilizer consumption escalated in the last 60 years. The use of contaminated river water for irrigation, along with the dissolved fertilizer inputs, can affect the groundwater quality, in particular resulting in the NO3&minus, concentrations ranging from 139.4 to 374.1 mg/L. The unregulated industrial inputs in some rural areas may increase the Cl&minus, contents in groundwater ranging from 298.4 to 472.9 mg/L. The findings are helpful for the improved comprehensive understanding of impacts of the Sanmenxia Dam on the interaction between surface water and groundwater, and for improving local water resources management.

Overexploitation of groundwater has resulted in seawater intrusion in many semiarid and arid coastal areas. This study illustrates the origin of groundwater salinity and assesses seawater intrusion/extrusion process in the Yang-Dai River plain aquifer, by analyzing hydrochemical and stable isotopic compositions of surface water, groundwater, geothermal water, and seawater. A cone of depression in groundwater is caused by intensive groundwater pumping formed in the late 1980s in the alluvial Yang-Dai River plain. In the northern part, groundwater exploitation has caused seawater intrusion identified by Ca-Cl type water. However, the widely distributed silty clay prevented the seawater intrusion in the southern part, evidenced by Ca-HCO3 type water with depleted δ2H (−60 to −46‰) and δ18O (−8.9 to −4.7‰). Anthropogenic pollution also plays a significant role in groundwater salinization. The positive correlation between Cl and NO3- for most groundwater and the extremely high nitrate concentrations (up to 652.7 mg/L) indicate that fertilizer from agricultural activities has greatly influenced groundwater quality. Irrigation return flow evaporation during agricultural activities also accounts for groundwater salinity. Besides the intensive fertilizer usage, seawater intrusion and the established anti-tide dams reduced the surface water and groundwater discharge to the sea and then resulted in the extremely high nitrate concentration. This study may improve the understanding of the groundwater salinization processes in a complex coastal aquifer, which is greatly influenced by anthropogenic activities.

The collapse of a tailings dam of a Pb-Zn mine, caused by a storm in 1978, resulted in severe heavy metals contamination in the valley downstream the mine, located in the Guangxi Province, southwest of China. The metals still pose a risk to the adjacent fragile karst environment. Especially, the potential for leaching of the heavy metals to the adjacent environment is of concern due to the high average annual precipitation of >1500 mm in the subtropical climate. Previous studies have classified areas of the valley as slightly (SP), moderately (MP) or heavily polluted (HP) based on heavy metals content (Pb, Cd, As, Cu, Zn) of the upper 20 cm of the soils. We analysed soil and sediment profiles up to 2 m deep, obtained in areas of the three pollutions levels, for basic chemical and physical parameters including pH, total organic carbon (TOC), soil moisture, particle size, total metals concentrations (Pb, Zn, Cd, and Cu), and δ18O and δ2H of soil moisture. Further, we measured the δ34S of soil extractable sulphate, and the content of chromium-reducible sulphur (CRS) and soluble sulphates (SS), to investigate the link between sulphur cycling and heavy metals mobilization. Today, four decades after the dam collapse, heavy metal concentrations are still highly elevated in the valley. In the HP profile concentrations of Pb, Cd, Cu and Zn range between 800–8120, 8–132, 156–616, and 2647–12250 mg/kg, respectively, between surface and 2 m depth. Concentrations of CRS in the HP profile of 287–5530 mg/kg were observed, while no CRS could be extracted from the SP and MP soil profiles. The δ34S-SO42- of the HP profile (0.4‰–16.0‰) matches values previously measured in the original tailing. The matching δ34S-SO42- and elevated CRS values of the HP profile indicate that the valley contains thick deposits (up to at least a 2 meters) of resettled tailings sediments of the original upstream tailings dam. However, these sediments are clayey, with >50%wt being

Mountainous areas are characterized by steep slopes and rocky landforms, with hydrological conditions varying rapidly from upstream to downstream, creating variable interactions between groundwater and surface water. In this study, mechanisms of groundwatersurface water interactions within a headwater catchment of the North China Plain were assessed along the stream length and during different seasons, using hydrochemical and stable isotope data, and groundwater residence times estimated using chlorofluorocarbons. These tracers indicate that the river is gaining, due to groundwater discharge in the headwater catchment both in the dry and rainy seasons. Residence time estimation of groundwater using chlorofluorocarbons data reveals that groundwater flow in the shallow sedimentary aquifer is dominated by the binary mixing of water approximating a piston flow model along 2 flow paths: old water, carried by a regional flow system along the direction of river flow, along with young water, which enters the river through local flow systems from hilly areas adjacent to the river valley (particularly during the rainy season). The larger mixing ratio of young water from lateral groundwater recharge and return flow of irrigation during the rainy season result in higher ion concentrations in groundwater than in the dry season. The binary mixing model showed that the ratio of young water versus total groundwater ranged from 0.88 to 0.22 and 1.0 to 0.74 in the upper and lower reaches, respectively. In the middle reach, meandering stream morphology allows some loss of river water back into the aquifer, leading to increasing estimates of the ratio of young water (from 0.22 to 1). This is also explained by declining groundwater levels near the river, due to groundwater extraction for agricultural irrigation. The switch from a greater predominance of regional flow in the dry season, to more localized groundwater flow paths in the wet season is an important groundwatersurface water

Long-standing wastewater and reclaimed water irrigation systems degrade groundwater quality and thus pose great risks to local soils and even to human health. In this study, seasonal variations in hydrochemical characteristics of groundwater were assessed to determine possible processes that induce groundwater degradation. Beijing was used as the focus area. A total of 82 wells at the southeast irrigation region of Beijing were investigated in 2014. Descriptive statistics, correlation analysis, Piper diagram, and saturation indices were used to distinguish seasonal variations in hydrochemistry in shallow and deep groundwater and possible reclaimed water irrigation effects. The main natural controlling processes include mineral precipitation and dissolution, cation exchange reactions, and dilution effects in shallow and deep groundwater. However, cation exchange reactions are considered to be intense in deeper aquifer. Additionally, shallow groundwater sites subjected to salinization and nitrate contamination were associated with intensive agricultural input and reclaimed water leaching. Sites continuously contaminated by nitrate were mainly distributed on highly permeable sediments. Irrigation with deep groundwater may reduce soil drainage conditions due to a high percentage of sodium. Overall, seasonal replenishment for subterranean quaternary aquifers from rainfall or irrigation plays a vital role in seasonal variation in shallow groundwater hydrochemistry.

Seawater intrusion (SWI) is becoming one of the major environmental issues in more and more coastal areas around the world. Understanding the current SWI situation and forming research consensus are of great significance for further studies and coastal water resources management. In this study, we analyzed the SWI-associated literature available from the Science of Citation Index Expanded (SCIE) bibliographic database by using CiteSpace to further excavate existing research achievement. We explored a new method for identifying global geographic distributions of 501 coastal cities where SWI has been reported. It can be found that SWI is more likely to occur in well-recharged major basins (recharge rate 100–300 mm/a) or local shallow aquifers with high population density. According to current reports, about 32% of the coastal metropolitan cities (population > 1 million within 150 km from coastline) have been threatened. There was a 20-fold increase rate in the number of papers related to SWI compared to that in general science and technology. The United States of America, China, Australia were the top 3 contributors in SWI scope, contributed 46.4% of the total number of articles. More than 600 researches were supported by Chinese funds, which made China become the second contributor. But the number of citations per Chinese article was the lowest among the top 10 contributors. By co-citation analysis, we identified top 5% articles, and elaborated the background knowledge by taking Top 10 co-cited articles as example. A series of keywords with high co-occurrence were identified. Their meanings and relations were stated and graphically illustrated. As a keyword, SWI frequently appears in the following five research directions: analysis of the location or morphology of fresh and salt water interface, the prediction of groundwater quality, the geothermal circulation and tectonic activities, the coastal mangrove wetlands protection, and the management of water resources in coastal zones. We critically evaluated the bibliometric results and reviewed future opportunities and challenges for this field. With the development of new technology and the accumulation, the improvement of coastal environment will certainly benefit from the study of SWI.

The stable isotopic compositions (δD and δ18O) of precipitation were firstly investigated from May 2012 to November 2013 in the Jinshui River basin of the South Qinling Mts., China. The local meteoric water lines (LMWLs) based on all daily and monthly precipitation-weighted data were defined as δD = 8.32 δ18O + 12.57 (r 2 = 0.957, n = 47, p

Stable isotopes in precipitation are useful tracers to strengthen understanding of climate change and hydrological processes. In this study, the moisture sources of 190 precipitation events in Beijing were analysed using the Hybrid Single-particle Lagrangian Integrated Trajectory model, based on which we studied the relation between variations in precipitation O-18 and dynamics in moisture sources and atmospheric circulation in seasonal and interannual timescales. Categorization of 7 groups of moisture sources was performed, among which oceanic moisture sources presented lower O-18 in precipitation than continental moisture sources. The results show that seasonal variations of precipitation O-18 were caused by changes of moisture sources. In summer, moisture from proximal oceans dominated vapour transport to Beijing due to increasing monsoon strength and resulted in a relatively small variation of precipitation O-18. At the interannual timescale, the variations of O-18 in summer precipitation were related to dynamics in oceanic moistures, showing depleted values when the contribution of oceanic moistures, especially the proportion of long-distance oceanic moisture, was high. Further analysis indicated that changes of oceanic moisture sources were controlled by the strength of summer monsoons. These findings address the complexity of moisture sources in midlatitude monsoon areas and suggest that isotopic signals in precipitation have the potential to deduce changes in moisture sources and atmospheric circulation and can therefore serve for palaeoclimate reconstruction.

Oxygen (δ18O) and hydrogen (δD) stable isotopes in the surface waters of the Huai River basin were analyzed in this study. Results indicated the northern waters had higher δ18O and δD than the southern waters, the water δ18O and δD increased along the water flow directions. These variations mostly resulted from the spatial differences of precipitation and evaporation. Comparing with published different continents' river water δ18O data, this study suggests that evaporation effect is a more plausible interpretation than altitude effect as the cause of δ18O increasing from upriver to downriver waters. This region's local surface water line (LSWL, δD = 5.36δ18O − 18.39; r2 = 0.84) represents one of the first presented LSWLs in eastern China. The correlation between d-excess and δ18O demonstrates this region is dominated by the Pacific oceanic moisture masses in summer. Comparing the various LSWLs from eastern China and eastern United States river waters, this study proposes a hypothesis that the water LSWLs slopes of lower latitude regions may be less than those of higher latitude regions within similar topographic areas. This hypothesis may be tested in other geographically comparable coupled areas in the world if corresponding large-scale data can be found.

Groundwater is increasingly exploited for energy production in arid areas globally, which will inevitably disrupt the natural equilibrium of groundwater and the ecological environment. A groundwater flow model for Subei Lake basin, Ordos energy base, was developed and calibrated to predict groundwater levels' variation and the impact of heavy groundwater pumping on the ecological environment for the period 2010–2039 under two different pumping scenarios. Results showed that rainfall infiltration and groundwater evapotranspiration were the major source/sink terms for the groundwater system. The obvious groundwater depression cone will be formed in the production field at the end of 30 years and the maximum drawdown will be 11.70 m if the waterworks maintains the present situation. However, recovery of groundwater level will be obvious and the groundwater depression cone will disappear as a result of the implementation of the water diversion project. The increased volume of groundwater pumping between the two scenarios was derived from storage depletion, the activated lateral inflow, the captured groundwater evapotranspiration, lateral outflow and discharge into Subei Lake. Groundwater pumping from Haolebaoji waterworks has caused the decline of the Subei Lake and the noticeable degradation of phreatophyte.

Some of the rivers in northern China are dried, and reclaimed water (RW) is used to restore these degraded river ecosystems, during which the RW could recharge the aquifer by river bank infiltration. From 2007 to 2018, 2.78 × 108 m3 of RW has been replenished to the dried Chaobai River (Shunyi reach), Beijing, China, which is located on the edge of one depression cone in groundwater caused by groundwater over-pumping. The groundwater hydrodynamic variations and the flow path of the RW were identified by eight-year hydrological, hydrochemical, and stable isotopic data, together with multivariate statistical analysis. The RW infiltration drastically impacts the groundwater dynamics with a spatiotemporal variation. The 30-m depth groundwater levels at Perennial intake reach increased quickly around 3 m after 2007, which indicated that they were dominated by RW infiltration. Other 30-m depth groundwater levels were controlled by precipitation recharge from 2007 to 2011, showing significant seasonal variations. In 2012, with more RW transferred to the river, the hydrodynamic impact of the RW on 30-m depth aquifer expanded downstream. However, the 50-m and 80-m depth groundwater levels showed decreasing trend with seasonal variations, due to groundwater pumping. The 30-m depth aquifer was mainly recharged by RW, being evidenced by the enriched δ2H and δ18O. The depleted δ2H and δ18O of the 50-m and 80-m depth groundwater indicated that they were dominated by regional groundwater with meteoric origin. The heterogenous properties of the multi-layer alluvial aquifer offer the preferential flow path for RW transport in the aquifers. The proportion of the RW in the aquifers decreases with depth that was calculated by the chloride conservative mixing model. The increased lateral hydraulic gradient (0.43%) contributes to the RW transport in the 30-m depth aquifer. RW usage changed 30-m depth groundwater type from Ca·Mg-HCO3 to Na·Ca·Mg-HCO3·Cl. RW preferentially recharged the 50-m and 80-m depth aquifers by vertical leakage.

Root water uptake plays an important role in water cycle in Groundwater-Soil-Plant-Atmosphere-Continuum. Stable isotopes (δ2H and δ18O) are effective tools to quantify the use of different water sources by plant roots. However, the widespread δ2H offsets of stem water from its potential sources due to δ2H fractionation during root water uptake result in conflicting interpretations of water utilization using stable isotopes. In this study, a potential water source line (PWL), i.e., a linear regression line between δ18O and δ2H data of both soil water at different depths and groundwater, was proposed to correct δ2H offsets of stem water. The PWL-corrected δ2H was determined by subtracting the deviation between δ2H in stem water and PWL from the original value. The MixSIAR model coupled with seven types of input data (i.e. various combinations of single or dual isotopes with uncorrected or corrected δ2H data by PWL or soil water line (SWL)) were used to determine seasonal variations in water uptake patterns of riparian tree of Salix babylonica (L.) along the Jian and Chaobai River in Beijing, China. These methods were evaluated via three criteria including Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC) and root mean square error (RMSE). Results showed that different types of input data led to considerable differences in the contributions of soil water at upper 30 cm (9.9–57.6%) and below 80 cm depths (29.0–76.4%). Seasonal water uptake patterns were significantly different especially when δ2H offset was pronounced (p

Due to the serious nitrate pollution in Northeast China, the in-stream nitrate and its isotopic composition (δ15N-NO3 and δ18O-NO3) were analyzed to explore the seasonal nitrate sources and its transformation processes combining with chemical indicators in the Haicheng River during the spring, early summer, late summer, and autumn seasons throughout the year of 2010. The nitrate nitrogen (NO3-N) concentrations in riverine water co-varied with the discharge data of the river, showing significant seasonal variations (p

Reclaimed water is efficient for replenishing the dry rivers in northern China, but regional groundwater may be at risk from pollution. Therefore, samples of reclaimed water, river water, and groundwater were collected at the Huai River in the Chaobai River basin in 2010. The water chemistry and isotopic compositions of the samples were analyzed in the laboratory. The reclaimed water had stable compositions of water chemistry and isotopes, and the Na·Ca-HCO3·Cl water type. The water chemistry of the river water was consistent with that of the reclaimed water. A June peak of total nitrogen was the prominent characteristic in the shallow groundwater, which also had the Na·Ca-HCO3·Cl water type. However, the water chemistry and isotopes in most of the deep groundwater remained stable, and the water type was Ca·Mg-HCO3. The amount of reclaimed water recharging the groundwater was about 2.5 × 107 m3/yr. All of the shallow groundwater was impacted by the reclaimed water, with the mixing proportion of reclaimed water ranging from 42% to 80 % in the dry season and from 20% to 86% in the wet season. Only one deep well, with proportions of 67% (dry season) and 28% (wet season), was impacted. TDS, EC, and major ions (Na, K, Cl, NH4-N, NO2-N, and NO3-N) were increased in the impacted wells.

The hydrogeochemical processes controlling groundwater evolution in the Daweijia area of Dalian, northeast China, were characterised using hydrochemistry and isotopes of carbon and sulfur (δ13CDIC and δ34SSO4). The aim was to distinguish anthropogenic impacts as distinct from natural processes, with a particular focus on sulfate, which is found at elevated levels (range: 54.4 to 368.8 mg L−1; mean: 174.4 mg L−1) in fresh and brackish groundwater. The current investigation reveals minor seawater intrusion impact (not exceeding 5 % of the overall solute load), in contrast with extensive impacts observed in 1982 during the height of intensive abstraction. This indicates that measures to restrict groundwater abstraction have been effective. However, hydrochemical facies analysis shows that the groundwater remains in a state of ongoing hydrochemical evolution (towards Ca–Cl type water) and quality degradation (increasing nitrate and sulfate concentrations). The wide range of NO3 concentrations (74.7–579 mg L−1) in the Quaternary aquifer indicates considerable input of fertilisers and/or leakage from septic systems. Both δ13C (−14.5 to −5.9 ‰) and δ34SSO4 (+5.4 to +13.1 ‰) values in groundwater show increasing trends along groundwater flow paths. While carbonate minerals may contribute to increasing δ13CDIC and δ34SSO4 values in deep karstic groundwater, high loads of agricultural fertilisers reaching the aquifer via irrigation return flow are likely the main source of the dissolved sulfate in Quaternary groundwater, as shown by distinctive isotopic ratios and a lack of evidence for other sources in the major ion chemistry. According to isotope mass balance calculations, the fertiliser contribution to overall sulfate has reached an average of 62.1 % in the Quaternary aquifer, which has a strong hydraulic connection to the underlying carbonate aquifer. The results point to an alarming level of impact from the local intensive agriculture on the groundwater system, a widespread problem throughout China.

The concentrations of dissolved strontium (Sr) and isotope ratios ((87)Sr/(86)Sr) in rainwater, river water, and water from forest soil are measured to investigate the contributions of these sources to a river during base flow conditions in the relatively pristine South Qinling Mountains, China. Dissolved Sr concentrations and (87)Sr/(86)Sr ratios vary significantly between different water types (p < 0.01) suggesting that it is suitable for differentiating sources. Dissolved Sr is also positively correlated with most ions and a range of physicochemical parameters (p < 0.01 and p < 0.05 respectively) in water samples including Ca(2+), Mg(2+), EC, and TDS (p < 0.001) indicating their similarities in the drivers of biogeochemical processes and common origins. The correlations between Sr isotopes and Ca/Na, Ca/K, and 1000/Sr ratios suggest that three end-members of atmospheric inputs, carbonate and silicate weathering control the Sr water chemistry in the river water. Using the three-source mixing model, atmospheric inputs, carbonate, and silicate weathering contribute 74%, 20%, and 6% respectively to the dissolved Sr in the river water. This research has provided new insights into the contribution of sources of Sr to a river system in a mountainous catchment.

Nitrate contamination is a common problem in groundwater of the North China Plain (NCP) owing to overuse of fertilizers and discharge of wastewater. Accordingly, it is important to investigate nitrate contamination in recharge areas to understand the fate of nitrate in the plains area. In this study, the spatial and temporal distribution characteristics of nitrate and factors contributing to its sources and transformation in shallow groundwater of the Beiyishui River watershed, NCP, were analysed by a combination of multiple regression and multi-tracer methods. The nitrate concentration of 79% of the samples exceeded the natural environmental standard of 13.3mgl(-1), while that of 23% of the samples exceeded the World Health Organization (WHO) drinking water standard of 50mgl(-1). Groundwater age estimation of the hill regions based on chlorofluorocarbons (CFCs) revealed a mix of young water from 1982 to 1990 and old, low CFC water. The analysis based on the variations in land use in past years revealed that part of the grassland was converted into woodland between 1980 and 1995; therefore, the land use at the recharge time was used to determine which surface conditions influence groundwater nitrate concentrations. Multiple regression analysis showed that point source pollution contributed to the high concentration of nitrate in the hill region. Fertilizer application associated with land use change from grassland to woodland was also related to the present nitrate concentration. In the plains area, the contribution of fresh water from fault fractures and denitrification led to 31 to 72% and 6 to 51% reductions in nitrate concentrations, respectively. Our results suggested that controlling point source contamination and fertilizer input to hilly regions of the study will prevent groundwater of the plains area from deterioration in future years by mixing fresh water into the aquifers and decreasing denitrification, and therefore nitrate concentrations. Copyright (c) 2015 John Wiley & Sons, Ltd.

Groundwater is increasingly exploited for energy production in arid regions, which necessitates a deeper insight into the impact of the enhanced human pressure on the groundwater. This study applied an integrated method (statistical analysis, water table fluctuation method, hydrograph analysis and remote sensing) to identify the impact of Energy Base Water Project on the groundwater in the Subei Lake basin. Groundwater levels in eight observation wells at 30 min intervals during the 2013–2014 period were monitored using automatic groundwater monitoring data loggers. Results showed that precipitation infiltration, irrigation return flow, groundwater pumping and evapotranspiration controlled the hydrodynamics of unconfined groundwater. The average evapotranspiration rates in the Quaternary phreatic aquifer and the Cretaceous phreatic aquifer were 6.15 and 12.48 mm/d. The unusual hourly hydrographs fall into three patterns (mutational, irregular and gradual hydrographs). Different recovery times after being influenced by pumping may be related to the presence of the mudstone lenses. The extent of the groundwater depression cone was qualitatively identified by gradual hydrographs, which may spread from the center area to the western boundary. Only some individual wells from Haolebaoji waterworks had conducted the intermittent pumping activities at random times and caused the decline of the lakes.

As an important part of the water cycle, the hydrologic process and chemical compositions of groundwater have changed significantly due to the joint influence of climate change and human activities. Groundwater salinization becomes a serious threat to water security in coastal areas. In order to assess the relationships between surface water, groundwater and seawater in the coastal plain, we performed a synthesis study based on hydrochemical-isotopic data, hydro-dynamical records and environmental tracers. Deuterium and oxygen isotopes and water chemical indicators were used to identify pollution status, salt sources and migration processes. Radioactive isotopes and gaseous tracers were used to obtain reasonable groundwater age. With the help of multi-tracer approach, the surface-groundwater interaction, salinization of groundwater and nitrate pollution were identified in the Yang-Dai River plain, northern China. The estimated groundwater ages determined from chlorofluorocarbons (CFCs) and tritium (3H) ranges from 18 to 41 years in this area, suggesting a modern groundwater circulation. The spatial distribution of the groundwater age varies significantly due to horizontal hydrogeological heterogeneity. The total dissolved solids (TDS) content of the groundwater near the Well Field (average: 970 mg/L) was higher than the TDS values in samples derived from places located at an equivalent distance to the coastal line (average is 708 mg/L), which resulted from the vertical seawater intrusion through river channels and pollutant inputs from agriculture activities. The nitrate concentrations in groundwater were elevated up to 271 mg/L and increased with increasing groundwater age, which was another water environment problem that should be solved urgently but lacks sufficient attention for years. This study provides a conceptual model with a number of comparable hydrochemical information, which is significant for regional pollution control and water resources management.

Understanding the hydrologic and hydrochemistry processes in the riparian area is of great importance for managing and protecting riparian water resources. This paper took a highly disturbed and polluted Shaying River Basin (SRB) of China as the study area. In this research, environmental tracers (hydrochemical and isotopic data of222Rn, &delta, 18O, and &delta, D) and corresponding models (two-component mixing model and 222Rn mass balance model) were employed to investigate the hydrologic and associated hydro-chemical process of riparian groundwater. The results indicated that rivers received groundwater discharge located at Xihua (J8), Zhoukou (Y1), Luohe (S2), and Shenqiu (SY2), and the mixing extent with groundwater was greater in wet seasons than in dry seasons. The 222Rn mass balance model showed that the flux of river water leakage was 3.27 &times, 10&minus, 4 m3/(s&middot, m) at the front of Zhoukou sluice while groundwater discharge was 3.50 &times, 3 m3/(s&middot, m) at the front of Shenqiu sluice during the sampling period. The cation exchange and the dissolution/precipitation of aquifer minerals (including calcite, dolomite, gypsum, and halite) were dominated by geochemical processes. The untreated sewage discharge and fertilizer usage were the main anthropogenic activities affecting the hydrochemistry process in surface water and riparian groundwater. Additionally, our results found that nitrate pollutants derived by riparian groundwater were potential threats to river quality at the lower reaches of Jialu River and Shenqiu county of Shaying River, where the nitrate inputs could be larger during the wet seasons because of higher groundwater discharge.

How the water transfer imposes impacts on the groundwater in the water-receiving area is still unknown. Here, we employed hydrometric observations, hydrogeochemical analyses and data analysis methods to address this issue, taking one of the Yellow River water transfer project of China for example. We found that the interaction between river and groundwater is totally changed by the water transfer and the impact of the water transfer on groundwater is confined by the high stream gradient. With the water transfer, the natural annual pattern of rainy-season high river flow is inversed with low flow in rainy seasons and high flow during the water transfer. Moreover, the river stage is always higher than the groundwater level throughout the year. The usual bidirectional river–groundwater hydraulic gradient is altered to be a gradient always away from the river. The groundwater directly connects with the river water. The regime of groundwater level follows the change of the river stage, even in the valley side. A long-term standing groundwater mound is formed within the riparian zone due to the continuous recharge from the water-receiving river. The transferred Yellow River water is hydrochemically featured by high EC value and concentrations of Na+ and Cl−. The hydrochemical features of the water-receiving river are obviously changed by the transferred Yellow River water. The hydrochemical impact of the river on the groundwater is mainly confined to the riparian zone and some low-reach transections, despite of the dominated control of the river on the valley groundwater table. The high stream gradient trends to produce the downstream groundwater flow and hinder the lateral groundwater flow from river to valley sides in the upper reaches, responsible for the confined impact on groundwater. Our study highlights that the stream gradient could obviously influence the river water and groundwater interaction promoting or confining the impact of river water on groundwater.

A series of changes in groundwater systems caused by groundwater exploitation in energy base have been of great concern to hydrogeologists. The research aims to identify the origin and geochemical evolution of groundwater in the Subei Lake basin under the influence of human activities. Water samples were collected, and major ions and stable isotopes (δ18O, δD) were analyzed. In terms of hydrogeological conditions and the analytical results of hydrochemical data, groundwater can be classified into three types: the Quaternary groundwater, the shallow Cretaceous groundwater and the deep Cretaceous groundwater. Piper diagram and correlation analysis were used to reveal the hydrochemical characteristics of water resources. The dominant water type of the lake water was Cl-Na type, which was in accordance with hydrochemical characteristics of inland salt lakes; the predominant hydrochemical types for groundwater were HCO3–Ca, HCO3–Na and mixed HCO3–Ca–Na–Mg types. The groundwater chemistry is mainly controlled by dissolution/precipitation of anhydrite, gypsum, halite and calcite. The dedolomitization and cation exchange are also important factors. Rock weathering is confirmed to play a leading role in the mechanisms responsible for the chemical composition of groundwater. The stable isotopic values of oxygen and hydrogen in groundwater are close to the local meteoric water line, indicating that groundwater is of modern local meteoric origin. Unlike significant differences in isotopic values between shallow groundwater and deep groundwater in the Habor Lake basin, shallow Cretaceous groundwater and deep Cretaceous groundwater have similar isotopic characteristics in the Subei Lake basin. Due to the evaporation effect and dry climatic conditions, heavy isotopes are more enriched in lake water than in groundwater. The low slope of the regression line of δ18O and δD in lake water could be ascribed to a combination of mixing and evaporation under conditions of low humidity. Comparison of the regression line for δ18O and δD showed that lake water in the Subei Lake basin contains more heavily isotopic composition than that in the Habor Lake basin, indicating that lake water in the discharge area has undergone stronger evaporation than lake water in the recharge area. Hydrochemical and isotopic information of utmost importance has been provided to decision makers by the present study so that a sustainable groundwater management strategy can be designed for the Ordos energy base.

Using multivariate statistical analysis, the study evaluated anthropogenic sources of river water contamination and their relationships with river water quality in the Haicheng River basin near to the Liaodong Bay in Northeast China. The results showed that nitrogen (N) and phosphorous (P) were identified as the main pollutants in the river water by factor analysis. Human population and elevational gradient were all significantly correlated with N, P, and other water quality variables in correlation analysis and explained chemical oxygen demand (COD), N, and P variables from 23.9% (TN) to 53.1% (NH3+-N) of the total variances in regression analysis, indicating that population and its distribution were all responsible for river contaminations, especially for COD, N, and P contaminations. The excessive applications of fertilizers and pesticides were all positively correlated with nitrogen variables and nitrogen pollution factor in correlation analysis, suggesting that agricultural activities were contributed to the river nitrogen pollution. Due to inadequate or lack wastewater treatment facilities, huge amounts of domestic sewage and industrial effluents were released into the river, becoming the predominant anthropogenic sources for the river water deterioration of COD, N, and P. Multivariate statistical analysis provided useful tools to correlate sources of contamination with water quality data. This approach will provide a better management for river pollution control in a human-driven river ecosystem.

Groundwater within the coastal aquifer systems of the Daweijia area in northeastern China is characterized by a large of variations (33-521mg/L) in NO3(-) concentrations. Elevated nitrate concentrations, in addition to seawater intrusion in the Daweijia well field, both attributable to anthropogenic activities, may impact future water-management practices. Chemical and stable isotopic (δ(18)O, δ(2)H) analysis, (3)H and CFCs methods were applied to provide a better understanding of the relationship between the distribution of groundwater mean residence time (MRT) and nitrate transport, and to identify sources of nitrate concentrations in the complex coastal aquifer systems. There is a relatively narrow range of isotopic composition (ranging from -8.5 to -7.0‰) in most groundwater. Generally higher tritium contents observed in the wet season relative to the dry season may result from rapid groundwater circulation in response to the rainfall through the preferential flow paths. In the well field, the relatively increased nitrate concentrations of groundwater, accompanied by the higher tritium contents in the wet season, indicate the nitrate pollution can be attributed to domestic wastes. The binary exponential and piston-flow mixing model (BEP) yielded feasible age distributions based on the conceptual model. The good inverse relationship between groundwater MRTs (92-467years) and the NO3(-) concentrations in the shallow Quaternary aquifers indicates that elevated nitrate concentrations are attributable to more recent recharge for shallow groundwater. However, there is no significant relationship between the MRTs (8-411years) and the NO3(-) concentrations existing in the carbonate aquifer system, due to the complex hydrogeological conditions, groundwater age distributions and the range of contaminant source areas. Nitrate in the groundwater system without denitrification effects could accumulate and be transported for tens of years, through the complex carbonate aquifer matrix and the successive inputs of nitrogen from various sources.

Groundwater resources are increasingly exploited for industrial and agricultural purposes in many arid regions globally, it is urgent to gain the impact of the enhanced anthropogenic pressure on the groundwater chemistry. The aim of this study was to acquire a comprehensive understanding of the evolution of groundwater chemistry and to identify the impact of natural and anthropogenic factors on the groundwater chemistry in the Subei Lake basin, Northwestern China. A total of 153 groundwater samples were collected and major ions were measured during the three campaigns (August and December 2013, May 2014). At present, the major hydrochemical fades in unconfined groundwater are Ca-Mg-HCO3, Ca-Na-HCO3, Na-Ca-HCO3, Na-HCO3, Ca-Mg-SO4 and Na-SO4-CI types, while the main hydrochemical fades in confined groundwater are Ca-Mg-HCO3, Ca-Na-HCO3, Na-Ca-HCO3, Ca-HCO3 and Na-HCO3 types. Relatively greater seasonal variation can be observed in the chemical constituents of confined groundwater than that of unconfined groundwater. Rock weathering predominates the evolution of groundwater chemistry in conjunction with the cation exchange, and the dissolution/precipitation of gypsum, halite, feldspar, calcite and dolomite are responsible for the chemical constituents of groundwater. Anthropogenic activities can be classified as: (1) groundwater overexploitation; (2) excessive application of fertilizers in agricultural areas. Due to intensive groundwater pumping, the accelerated groundwater mineralization resulted in the local changes in hydrochemical fades of unconfined groundwater, while the strong mixture, especially a large influx of downward leakage from the unconfined aquifer into the confined aquifer, played a vital role in thefundamental variation of hydrochemical facies in confined aquifer. The nitrate contamination is mainly controlled by the local hydrogeological settings coupled with the traditional flood irrigation. The deeper insight into geochemical evolution of groundwater obtained from this study can be beneficial to improving groundwater management for sustainable development in the rapidly industrialized areas. (C) 2015 Elsevier B.V. All rights reserved.

Summary Seawater intrusion (SWI) has led to salinization of fresh groundwater reserves in coastal areas worldwide and has forced the closure of water supply wells. There is a paucity of well-documented studies that report on the reversal of SWI after the closure of a well field. This study presents data from the coastal carbonate aquifer in northeast China, where large-scale extraction has ceased since 2001 after salinization of the main well field. The physical flow and concomitant hydrogeochemical processes were investigated by analyzing water level and geochemical data, including major ion chemistry and stable water isotope data. Seasonal water table and salinity fluctuations, as well as changes of δ 2 H–δ 18 O values of groundwater between the wet and dry season, suggest local meteoric recharge with a pronounced seasonal regime. Historical monitoring testifies of the reversibility of SWI in the carbonate aquifer, as evidenced by a decrease of the Cl − concentrations in groundwater following restrictions on groundwater abstraction. This is attributed to the rapid flushing in this system where flow occurs preferentially along karst conduits, fractures and fault zones. The partially positive correlation between δ 18 O values and TDS concentrations of groundwater, as well as high NO 3 − concentrations (>39 mg/L), suggest that irrigation return flow is a significant recharge component. Therefore, the present-day elevated salinities are more likely due to agricultural activities rather than SWI. Nevertheless, seawater mixing with fresh groundwater cannot be ruled out in particular where formerly intruded seawater may still reside in immobile zones of the carbonate aquifer. The massive expansion of fish farming in seawater ponds in the coastal zone poses a new risk of salinization. Cation exchange, carbonate dissolution, and fertilizer application are the dominant processes further modifying the groundwater composition, which is investigated quantitatively using hydrogeochemical models.

A fully coupled mathematical model of land subsidence caused by groundwater pumping was established based on the mechanics of porous seepage and the theory of fluid–solid interaction. The mathematical model employing the Galerkin finite element method was proposed to simulate the deformation dependencies of hydraulic properties due to the water pressure decrease in aquifers. This model has been verified by comparing with the known analytical solutions in the confined aquifer. Results show that the simulated drawdown and displacements match well with those of analytical solutions. To evaluate the nonlinear effects of hydraulic properties in the seepage and consolidation coupling phenomena, the numerical model is applied to an ideal three layers numerical experiment. The results show that the subsidence rate is faster than conventional groundwater theory when the nonlinear hydraulic properties (NHP) are considered in the coupled model. The reason is that the water level decline due to groundwater withdrawal induces the soil compression and the porosity and permeability decrease. Decrease of permeability in regions adjacent to the pumping well produces hydraulic gradient and seepage forces that may result in accelerated subsidence. Therefore, the effect of the NHP is an interaction process of pore water pressure and soil consolidation deformation and should not be ignored. Further studies of various hydrogeology problems are recommended to consider the heterogeneity concerning different stratigraphic condition in the field.

A detailed analysis of the major ion chemistry, chemical weathering and CO2 consumption was conducted in the Songhua River basin, which is the largest basin with a draining area of 557 thousand km2 in Northeast China. The dataset used in this study included major ion concentrations came from 56 hydrological stations from the year of 1962 to 1984. The median of the total dissolved solid concentration of the Songhua River was 104.8 mg/L, about two times higher than the global average (65.0 mg/L), but lower than that of other Chinese Rivers. Prevalent ions were Na+, Ca2+ and HCO3 −, and the average Ca2+/Na+ and Mg2+/Na+ molar ratios were 0.70 and 0.42, which were close to silicate weathering end-member. Long-term trend analysis by seasonal MK test showed that from 1962 to 1984, Ca2+, Na+ + K+ and HCO3 − were significantly increasing, and the increasing rates calculated by linear fit slopes for Ca2+, Na+ + K+ and HCO3 − ions were 0.22, 0.63 and 2.35 mg/year, respectively. An inverse model showed that the dissolved loads primarily came from rock weathering (91.5 %), including silicate weathering (66.4 %) and a small portion from carbonates (16.1 %) and evaporites (9.0 %). Other origins consisted of anthropogenic inputs (5.3 %) and atmospheric inputs (3.2 %). Average silicate and carbonate weathering rates were estimated as 4.03 and 1.76 t km−2 year−1, and CO2 consumption rates of silicates and carbonates were 17.1 × 104 and 1.85 × 104 mol km–2 year−1, respectively. These results are consistent with the lithologies of the study area, which mainly consisted of silicate rocks.

The utilization of reclaimed water could be an efficient tool to alleviate water scarcity, especially for dry river augmentation. However, it is crucial to monitor water quality to ensure safety to human health and to avoid negative effects on the environment. Reclaimed water samples were collected bimonthly from May to November in 2010 in Chaobai River, and the physiochemical parameters were determined. The main results are as follows: The parameters exceeding the threshold value of the water guidelines are mainly nutrition related to nitrogen and phosphorus, which are known to increase the risk of eutrophication in surface waters. Additionally, nitrite and nitrate can be detrimental to human health. The majority of the parameters have a peaking concentration in May, whereas others either show significant temporal variation over the entire period or remain relatively constant in all four months. Correlation analysis shows that some parameters (pH, T and B) have no significant correlation with others, whe...

Understanding the interference of natural processes and anthropogenic activities in geochemical evolution of groundwater is vital for groundwater sustainable management in water-stressed regions. This study is devoted to the identification of the main factors controlling the evolution of groundwater chemistry by the combined use of hydrogeochemical indicators along with isotope tracers in the Heilongdong Spring Basin, North China. Thirty-nine groundwater samples and twelve surface water samples were collected, and major ions and stable isotopes were measured during the two campaigns (December 2017 and August 2018). The isotope approach indicates that the groundwater is recharged by precipitation infiltration after evaporation, and interacts with surface water along preferential flow paths in fault zones and karst conduits. Currently, the main chemical facies of groundwater evolve from Ca-HCO3 and Ca-Mg-HCO3 types with low TDS, through Ca-Mg-HCO3-SO4 and Ca-HCO3-SO4 types with moderate TDS, to Ca-SO4, Ca-SO4-Cl and Ca Cl types with high TDS. Apart from natural processes (involving dissolution/precipitation of minerals, cation exchange, and evaporation) regulating the groundwater quality, the stagnant zones also play a crucial role in the formation of severe localized nitrate contamination. The deterioration in groundwater quality can be attributed to anthropogenic factors (including the change in groundwater exploitation, the leaching of solid waste, and the overuse of agricultural fertilizers). The high loads of agricultural fertilizers in irrigation return flows are likely to be the main contributor of the dissolved nitrate in groundwater. The findings of this work not only have important implications for groundwater sustainable utilization, but also could serve as a template for other rapidly industrialized and water-stressed regions.

A hydrochemical-isotopic investigation of the Laizhou Bay Quaternary aquifer in north China provides new insights into the hydrodynamic and geochemical relationships between freshwater, seawater and brine at different depths in coastal sediments. Saltwater intrusion mainly occurs due to two cones of depression caused by concentrated exploitation of fresh groundwater in the south, and brine water for salt production in the north. Groundwater is characterized by hydrochemical zonation of water types (ranging from Ca-HCO3 to Na-Cl) from south to north, controlled by migration and mixing of saline water bodies with the regional groundwater. The strong adherence of the majority of ion/Cl ratios to mixing lines between freshwater and saline water end-members (brine or seawater) indicates the importance of mixing under natural and/or anthropogenic influences. Examination of the groundwater stable isotope delta O-18 and delta H-2 values (between -9.5 parts per thousand and -3.0 parts per thousand and -75 parts per thousand and -40 parts per thousand, respectively) and chloride contents (similar to 2 to 1000 meq/L) of the groundwater indicate that the saline end-member is brine rather than seawater, and most groundwater samples plot on mixing trajectories between fresh groundwater (delta O-18 of between -6.0 parts per thousand and -9.0 parts per thousand; Cl 1000 meq/L). Locally elevated Na/Cl ratios likely result from ion exchange in areas of long-term freshening. The brines, with radiocarbon activities of similar to 30 to 60 pMC likely formed during the Holocene as a result of the sequence of transgression-regression and evaporation: while deep, fresh groundwater with depleted stable isotopic values (delta O-18 = -9.7 parts per thousand and delta H-2 = -71 parts per thousand) and low radiocarbon activity (

summary Whether a recharge was induced by groundwater depression cones is a crucial issue for water resource management. In the North China Plain, shallow groundwater had been over-pumped since 1970s and many groundwater depression cones formed. The groundwater depression cone, Daceying–Machang, occurred even in the piedmont plain. In the area, water levels of deep and shallow groundwater were observed since 2005 and field survey was conducted in the dry season 2010. The upward recharge induced by the depression cone is verified based on water level records, major ions, 2 H, 18 O and kinds of statistical analyses. Since August 2006, the water level of the deep groundwater ascended by 1.9 mm/d. High correlations (r = 0.86, s = 0.67) between the water level series of shallow and deep groundwater were found by two distinct correlation analyses only in the center of depression cone. Further, the reversion of hydraulic gradient of the depression cone occurred in dry seasons since September 2008. Hydro-geochemical features of the shallow groundwater are consistent with deep groundwater in the center of depression cone, which was demonstrated by the fuzzy C-means clustering based on principal components and paired t test, respectively. It is concluded that the deep groundwater recharged the shallow groundwater from the center of the depression cone. As a result, the groundwater mixture occurred that improves the quality of the shallow groundwater. Seasonally changed flow of shallow groundwater enhanced the mixture. The persistent overpumping of shallow groundwater and the large elevation difference (around 1200 m) between the recharge zone and the discharge point of deep groundwater facilitate the upward recharge.

The Kuye River is the primary tributary located in the sediment concentrated regions in the Middle Yellow River in China. Significant decrease in streamflow has been observed in the Kuye River. The non-parametric Mann–Kendall test was applied to detect the change in annual streamflow for the period of 1960 to 2006. Mean annual streamflow in the Kuye River was 84.9 mm from 1960 to 1979 (period I), while it decreased to 58.2 mm from 1980 to 1998 (period II) and 20.5 mm from 1999 to 2006 (period III), respectively. The climate elasticity method and the hydrological modeling method were individually employed to assess the impact of climate variability and human activities on the decrease in streamflow. The results showed that climate variability was responsible for 29.6 and 27.1 % of the streamflow decrease from the climate elasticity method and the hydrological modeling method, respectively; while human activities accounted for 70.4 and 72.9 % of the streamflow decrease in period II. In period III, climate variability contributed 40.9 and 39.3 % of the streamflow decrease from the climate elasticity method and the hydrological modeling method, respectively; while human activities accounted for 59.1 and 60.7 % of the streamflow decrease. Therefore, human activities were the main reason of the streamflow decrease. Soil conservation measures (planting trees, improving pastures, building terraces and sediment-trapping dams) and coal mining led to the streamflow reduction in the Kuye River.

Levels and distributions of organochlorine pesticides (OCPs) and phenolic endocrine-disrupting chemicals (EDCs) in surficial sediments of the Shaying River, the largest tributary of the Huaihe River in eastern China, were investigated to understand their relationship with the hydrodynamics. Concentrations of total hexachlorocyclohexane isomers (ΣHCHs) and dichlorodiphenyltrichloroethanes (ΣDDT) were in the range of 26.7–119 and 9.64–214 ng g−1 with mean values of 104 and 80.7 ng g−1, respectively. Residues of HCHs in sediments can be considered as originating from the application of both technical mixtures and lindane in the past. According to the spatial distribution of (DDD + DDE)/ΣDDT ratios, the influence of recent DDT inputs was dominant upstream, whereas DDD prevailed downstream, due to anaerobic degradation. Concentrations of total phenolic EDCs (ΣEDCs) including nonylphenol (NP), octylphenol (OP) and bisphenol A (BPA) ranged widely from 425 to 3,953 ng g−1 with the highest level occurring in the middle reach. This accumulation could be attributed to the retransfer of surficial sediment from upstream, where the main sources are located. Spatial distribution of contaminants indicated that riverine hydrodynamics can significantly affect their behavior and fate in sediment. This evidence was further verified by multivariate statistical techniques such as Cluster Analysis (CA), Principle Component Analysis (PCA) and Discriminant Analysis (DA). The CA identified three distinct clusters reflecting the large complexity of river system like geography setting, hydrodynamic condition, etc. This finding was also confirmed by the DA. Furthermore, a PCA demonstrated that about 80.8 % of total spatial variance can be explained by the first three factors, which also indicated that contaminant spatial distributions are driven by local inputs, biodegradation and riverine hydrodynamics.

Nitrate contamination in both surface water and groundwater has received considerable attentions in irrigated agricultural areas. Nitrate concentrations, and its nitrogen and oxygen isotopic compositions, as well as oxygen and deuterium isotopic compositions and chloride concentrations of surface water and groundwater from a typical area in the lower reaches of the Yellow River irrigation district were analyzed to ascertain spatial variations of nitrate and its possible sources and transformations. The results of this study showed nitrate in the Yellow River mainly derived from mineralization of organic matter in sediments and nitrification of atmospheric deposition, and nitrate in other important tributaries were greatly affected by agricultural activities, especially synthetic fertilizer. Nitrate in irrigation canals which go through concentrated residential zone mainly originated from domestic effluent and experienced nitrification. Nitrate in groundwater is not only affected by surface nitrate sources, but also closely related to hydraulic conditions which make nitrate source discrimination more complex. In areas belonging to the Yellow River basin with shallow water tables, nitrate is mainly derived from synthetic fertilizer, and denitrification processes controlled nitrate isotopic compositions in extremely shallow groundwater with low hydraulic gradients. While in places belonging to the Haihe River basin with deep water table, groundwater nitrate is largely affected by mixing process of irrigation water. The main sources of nitrate in groundwater are manure and sewage and soil organic matter, while chemical fertilizer and atmospheric deposition in large amount of rainfall are its minor contributors.

Increasing population is generally responsible for the degraded river ecosystem. Using regression models and mathematical functions, the research quantitatively estimated the population and elevational gradient effects on river water quality during nine surveys from 2006 to 2008 in the Jinshui River basin of the South Qinling Mts., China. The total factor scores at 11 different sampling sites were calculated in factor analysis and first used as pollution index to represent the water quality levels. Population and elevational gradient both significantly linked with most water quality variables and pollution index in correlation analysis and explained 36.5–77.8 % of the total variances in regression analysis, indicating that human activities were gradually frequent with population growth and affected the input and output of pollutants in river water. On the basis of regression models and quadratic functions among population, elevational gradient, and pollution index, the population capacity of the river basin was estimated as 1815 people, and the threshold value of elevation was calculated as 1174 m. The results of multivariate linear models further confirmed that population and population distribution had direct influences on river water quality. This study will facilitate the ecosystem management for mountainous streams and provide quantitative models for understanding and mitigating human impacts on river system.

The Jialu River, a secondary tributary of the Huaihe River, has been severely contaminated from major contaminant sources, such as a number of untreated or lightly treated sewage waste in some cities. Groundwater along the river is not an isolated component of the hydrologic system, but is instead connected with the surface water. This study aims to investigate temporal and spatial variations in water chemistry affected by humans and to characterize the relationships between surface water (e.g. reservoirs, lakes and rivers) and groundwater near the river in the shallow Quaternary aquifer. Concentration of Cl− in north Zhengzhou City increased prominently due to the discharge of a large amount of domestic water. Nitrate and potassium show maximum concentrations in groundwater in Fugou County. These high levels can be attributed to the use of a large quantity of fertilizer over this region. Most surface water appeared to be continuously recharged from the surrounding groundwater (regional wells) based on comparison surface water with groundwater levels, stable-isotopes and major ion signatures. However, the groundwater of a transitional well (location SY3) seemed to be recharged by river water via bank infiltration in September 2010. Fractional contributions of river water to the groundwater were calculated based on isotopic and chemical data using a mass-balance approach. Results show that the groundwater was approximately composed of 60–70% river water. These findings should be useful for a better understanding of hydrogeological processes at the river-aquifer interface and ultimately benefit water management in the future.

Water quality is the critical factor that influence on human health and quantity and quality of grain production in semi-humid and semi-arid area. Songnen plain is one of the grain bases in China, as well as one of the three major distribution regions of soda saline-alkali soil in the world. To assess the water quality, surface water and groundwater were sampled and analyzed by fuzzy membership analysis and multivariate statistics. The surface water were gather into class I, IV and V, while groundwater were grouped as class I, II, III and V by fuzzy membership analysis. The water samples were grouped into four categories according to irrigation water quality assessment diagrams of USDA. Most water samples distributed in category C1-S1, C2-S2 and C3-S3. Three groups were generated from hierarchical cluster analysis. Four principal components were extracted from principal component analysis. The indicators to water quality assessment were Na, HCO3, NO3, Fe, Mn and EC from principal component analysis. We conclude that surface water and shallow groundwater are suitable for irrigation, the reservoir and deep groundwater in upstream are the resources for drinking. The water for drinking should remove of the naturally occurring ions of Fe and Mn. The control of sodium and salinity hazard is required for irrigation. The integrated management of surface water and groundwater for drinking and irrigation is to solve the water issues. (C) 2012 Elsevier Ltd. All rights reserved.

This study characterizes the major ion chemis- try for river water in the upper reaches of Bengbu Sluice in the Huai River Basin in wet and dry seasons, and assessed the suitability of water quality for irrigation and human consumption. It is found that sodium and calcium are the dominant cations and bicarbonate is the dominant anion in most river water samples. River water in Zhoukou of the Ying River and Bozhou of the Guo River is characterized as a Na-Cl water type, whereas river water from the upper reaches and the lower reaches of the two cities is charac- terized as a Na-HCO3 water type, which may be attributed by anthropogenic influences in these cities. The river water types vary from the upstream to the downstream of the Fuyang sluice, which indicates that the sluices play a crit- ical role in determining the water type. The water chemistry of these rivers clearly shows that the second group of rivers is affected more severely by waste effluent than is the first group. Calculated values of sodium adsorption ratio, %Na, and residual sodium carbonate indicate that, in general, most of the river water is of acceptable irrigation quality. The river water in Zhoukou section of the Ying River and the Bozhou section of the Guo River cannot be used as drinking water; pollution control should be further improved and enhanced across the river.

The southern coastal plain of Laizhou Bay, which is the area most seriously affected by salt water intrusion in north China, is a large alluvial depression, which represents one of the most important hydrogeological units in the coastal region of northern China. Chlorofluorocarbons (CFCs, including CFC-11, CFC-12 and CFC-113) and tritium were used together for dating groundwater up to 50?years old in the study area. There are two cones of depression, caused by intensive over-exploitation of fresh groundwater in the south and brine water in the north. The assigned CFC apparent ages for shallow groundwater range from 8 a to >50 a. A binary mixing model based on CFC-113 and CFC-12 concentrations in groundwater was used to estimate fractions of young and pre-modern water in shallow aquifers and to identify groundwater mixing processes during saltwater intrusion. Discordance between concentrations of different CFC compounds indicate that shallow groundwater around the Changyi cone of depression is vulnerable to contamination. Pumping activities, CFC contamination, mixing and/or a large unsaturated zone thickness (e.g. >20?m) may be reasons for some groundwater containing CFCs without tritium. Saline intrusion mainly occurs because of large head gradients between fresh groundwater in the south and saline water bodies in the north, forming a wedge of saline water below/within fresh aquifer layers. Both CFC and tritium dates indicate that the majority of the saline water is from >50 a, with little or no modern seawater component. Based on the distribution of CFC apparent ages, tritium contents plus chemical and physical data, a conceptual model of groundwater flow along the investigated Changyi-Xiaying transect has been developed to describe the hydrogeological processes. Three regimes are identified from south to north: (i) fresh groundwater zone, with a mixing fraction of 0.800.65 young water calculated with the CFC binary mixing model (groundwater ages 50a water group (iii), indicating slow velocity of groundwater circulation and possible drawing in of saline or deep groundwater that is tracer-free. Copyright (c) 2012 John Wiley & Sons, Ltd.

In mid-latitude continental and island regions, the isotope composition of air masses often varies according to both their origin and their interaction with topography along their path of travel. Comparison of stable isotopes in continental and island precipitation events can reveal climatic controls upon isotopic content and yield information about patterns of atmospheric circulation. The overall deuterium (D) and oxygen-18 ((18)O) characteristics of 64 precipitation events observed in continental Beijing, China, and 109 precipitation events observed at Seongsan (Jeju Island, Republic of Korea) were investigated. The established local meteoric water lines, delta D = 7.49 delta(18)O + 1.53 (R(2) = 0.96, n = 64) and delta D = 8.36 delta(18)O + 19.05 (R(2) = 0.86, n = 109), indicated periodic drought in Beijing and a kinetic effect in the condensation process in Seongsan. To trace moisture origins and transport paths for all precipitation events, the 96 h backward trajectories of air masses arriving at 3000 m above ground level were calculated and categorized using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results indicate that during the Asian monsoon period, the air mass categories represented at Seongsan were principally from the southeast, southwest, and continental vicinity (CV). Those observed for Beijing were more varied (northwest, west, north, marine vicinity, south, and CV). Additionally, the meteorological controlling factors of each air mass category were identified using non-linear stepwise regression. The precipitation amount was the main predictor for (18)O in precipitation in Seongsan, while the controlling factors involved in Beijing were more complicated.

BACKGROUND: To enable effective management and decision making for the sustainable use of water resources, we successfully integrated factors such as dams, land use and soil properties as well as management factors in the Hanjiang River basin, a subtropical catchment of China, into the SWAT model to simulate water cycles as well as the distribution, movement, and transformations of nutrients. RESULTS: The accuracy of the model was validated by monitoring data over the Hanjiang River. The validated model was then used to evaluate the effects of the Reforestation of Cultivated Land (RFCL) initiative. The simulation results showed that RFCL would cause an obvious decrease in surface runoff (-23.6%, P < 0.01) but an increase in groundwater (71.8%, P < 0.01) and percolation out of the soil (24.7%, P < 0.01). The total water yield does not change significantly (-4.4%), but the decrease in total sediment loading is substantial (-56.2%, P < 0.01). The simulation results also show that RFCL would greatly decrease the organic N (-42.6%, P < 0.01), NO3 yield in surface flow (-37.1%, P < 0.01), and the NO3 yield in subsurface flow (-25.5%, P < 0.01), whereas the NO3 yield in groundwater flow would increase (107%, P < 0.01). In terms of phosphorus, RFCL would cause both organic phosphorus (-38.2%, P < 0.01) and the phosphorus yield from the soil (-33.3%, P < 0.01) to decrease. CONCLUSION: The results suggest that RFCL is an effective policy for watershed environment management, which might have a relatively small effect on river discharge but that the purification effects on water quality in the river would be remarkable. (C) 2011 Society of Chemical Industry

Large salinated areas are distributed in the middle and east of the North China Plain (NCP), where the fresh water shortage is serious. In this study, two sites in Cangzhou (CZ) and Hengshui (HS) of Hebei Province were selected to study the dynamics of shallow groundwater level and salinity. Electrical conductivity (EC) of groundwater was combined with the isotope compositions of δ18O and δ2H to identify the origin of salinity. Results showed that the dynamics of groundwater level at both sites were mainly controlled by precipitation and evaporation. Soil texture and structure played a significant role in the dynamics of salinity. The summer precipitation diluted the EC of groundwater at the HS site with homogeneous soil of sand loam, suggesting the larger infiltration rate; however, it did not dilute the EC at the CZ site with heterogeneous soil of sand loam and silt loam, suggesting that the summer precipitation could not recharge the groundwater directly. In winter, the EC decreased rapidly due to the temperature gradient underground if the groundwater was above the threshold level (at least 3 m below the ground surface) after the rainy season. Isotopes of δ18O and δ2H showed that precipitation was the major recharge source for the groundwater at the two sites. The salt mainly comes from the dissolution of soil or rock at the CZ site. While, the evaporation effect was strong at the HS site leading to the increase of the salt concentration.

A thorough understanding of recharge is usually a prerequisite for effective groundwater management. The recharge regime remains unrevealed in the piedmont plain of the North China Plain, where is considered as the main recharge zone of the Quaternary aquifer. To characterize the recharge regime, a case study is presented in the piedmont plain of the Beiyishui River Watershed. The piedmont plain consists of proluvial fan and alluvial fan/plain, and groundwater quality in the two parts is distinct. Total dissolved solids and isotopic compositions are higher in the groundwater of proluvial fan than the groundwater of the alluvial fan/plain. Local precipitation only recharges the groundwater in the proluvial fan. Fracture water ascending along a buried normal fault and lateral inflow from the proluvial fan feed the unconfined aquifer in the alluvial fan/plain. The runoff of the Beiyishui River seeps in the streambed of upper reaches and then overflows seasonally in middle reach. The recharge from middle reach to the aquifer is negligible. In addition, the fracture water originates from precipitation in the mountainous area with an average elevation about 500 m and discharges to the overlaying aquifer. The contribution of fracture water to the aquifer was estimated to be 77.9% in the alluvial fan/plain area. Due to the mixture in the aquifer, major ions leached from soil of the proluvial fan are diluted and the hydrochemical pattern is changed from Ca Mg–HCO3 SO4 to Ca Mg–HCO3. It is considered that fracture water is the major recharge source of the unconfined aquifer and the variation of precipitation in mountainous area would primarily affect the recharge. This paper also shows the hydrological efficiency of buried normal fault as preferential flow.

Analysis of the water budget, along with hydrochemistry and stable isotopes in shallow groundwater were carried out in the Karamay Agricultural Development Area (KADA) in order to assess the impact of transfer of irrigation water from the IrtySh River, in particular in relation to the mechanisms of salinization and the nature of the water table regime. In terms of aquifer dynamics, the addition of the irrigation water without any groundwater abstraction has caused a sharp rise in the water table is and the development of serious soil salinity, together with an almost complete attenuation of inter-seasonal water table oscillations. The mean rise in the groundwater table from September 1997 to October 2009 was 6.9 m, representing an accumulated total water storage change of close to 150 million cubic meters. The analysis of aquifer water budget shows that infiltration of irrigation water occupied over 90% of the total recharge of the groundwater in the KADA. Sources of groundwater recharge and mechanisms of salinization in the KADA were also investigated using geochemical and isotopic techniques. The groundwater is characterized by Cl(SO 4 )–Na type, generally becoming more Na and Cl dominated with increasing salinity. The total dissolved solids (TDS) content of the groundwater ranges from 0.5 g/L to over 65 g/L, with greater TDS values in areas of low topographic relief and shallow water tables. Where the sediments are more permeable (e.g. due to the presence of palaeochannels), TDS values are generally lower and the seasonal water table fluctuations greater. The ratios of K/Cl, Ca/Cl, Na/Cl, and Mg/Cl decrease with increasing Cl − concentrations especially in the shallow groundwater from 10 to 15 m depth, indicating hydrogeochemical evolution via minor water-rock interaction (feldspar weathering) and significant evaporation. The stable isotopic compositions show a characteristic evaporation effect in the shallow groundwater and confirm that direct infiltration of precipitation is generally not a volumetrically important source of recharge to the shallow aquifer. Preferential recharge of river water after irrigation events and/or precipitation from rare heavy rain events is likely responsible for the depleted δ 2 H and δ 18 O values in some of the groundwater samples. The negative relationship between deuterium excess and δ 18 O values indicates that even in groundwater with relatively depleted δ 2 H and δ 18 O values, evaporation has occurred to a significant degree. Careful management of water quantity and quality and implementation of salinity management strategies are considered necessary in order to reduce the risk of further salt accumulation and damage to farming and local ecosystems.