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Concentrated rainfall and water transfer projects result in slight and dramatic increases in flow volume over short periods of time, causing nitrogen recontamination in the water-receiving areas of nitrogen-rich rivers. This study coupled hydrodynamic and biochemical reaction models to construct a model for quantifying diffusive transport and transformation fluxes of nitrogen across the water-sediment interface and analysed possible changes in the relative abundance of microbial functional genes using high-throughput sequencing techniques. In this study, the processes of ammonium (NH

Under the influence of water diversion, the microbial community composition of estuarine waters and sediments might have complex spatiotemporal variations. Microbial interactions with N are significant for lake water quality. Therefore, the largest lake receiving seasonal water diversion in the North China Plain was selected as the study area. Based on 16S rRNA high-throughput sequencing and metagenomic sequencing techniques, this study analysed temporal (June-December) and spatial (estuary-pelagic zone) changes in the microbial community and functional gene composition of water and sediment. The results showed that the water microbial community composition had temporality, while sediment microbes had spatiality. The main causes of temporality in the aquatic microbial community were temperature and nitrate-N concentration, while those of sediment were flow velocity and N content. Additionally, there were complex interactions between microbial communities and N. In water, temporal variation in the relative abundance of N-related functional genes might have indirectly contributed to inorganic N composition in June (nitrite-Nammonia-Nnitrate-N) and August (nitrite-Nnitrate-Nammonia-N). High nitrate-N concentrations in December influenced the microbial community composition. In sediment, the estuary had higher N functional genes than the pelagic estuary, creating a relatively active N cycle and reducing total N levels in the estuary. This study revealed a potentially overlooked N sink and a flow velocity threshold that has great impacts on microbial community composition. This research contributes to a deeper understanding of the estuarine N cycle under the influence of water diversions, with implications for the calculation of global N balances and the management of lake water environments.

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 partitioning of evapotranspiration (ET) into soil evaporation (E) and crop transpiration (T) is fundamental for accurately monitoring agro-hydrological processes, assessing crop productivity, and optimizing water management practices. In this study, the isotope tracing technique was used to partition ET of winter wheat under different irrigation (100, 160 and 240 mm) and fertilization (105, 210 and 315 kg N ha−1) treatments during the 2014 and 2015 growing seasons in Beijing, China. The correlations between seasonal ET partitioning and the leaf area index (LAI), grain yield, and water use efficiency (WUE, ratio of crop yield and ET) were investigated and agricultural management practices were optimized. The fraction of T in ET (FT) between the greening and harvest seasons was 0.82 on average and did not vary significantly among the treatments (p > 0.05). However, the values of FT during the individual growth periods ranged from 0.51 to 0.98, and they were remarkably distinct for all treatments. The seasonal variability in FT could be effectively explained via a power-law function of the LAI (FT = 0.61 LAI0.21, R2 = 0.66, p 0.05). The total T during the jointing-heading and heading-filling periods (Tjf) had significantly quadratic relationships with the crop yield and WUE (p

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.

Studying soil water dynamics and water balance on coral islands is important to utilize and manage the limited freshwater resources of these islands. In this study, we investigated the soil water dynamics of Zhaoshu Island, Xisha Archipelago, using observed data and the Richards equation and analyzed the water balance of this island from October 2018 to September 2019. We found a dry soil layer at depths between 40 cm and 160 cm of the soil profile from November 2018 to April 2019 (dry season) which prevented the exchange of water between upper soil layers and groundwater. Therefore, the vegetation developed deep roots to take up water from the groundwater. Precipitation is the only source of the freshwater, while approximately 38% of the precipitation infiltrated into the groundwater, 22% of the precipitation was taken up by vegetation, and 39% of the precipitation evaporated from the land surface during the entire observed year. In the dry season, evapotranspiration (ETa) was only 44 mm/month, which was 94% greater than the amount of precipitation, and approximately 14 mm/month of water was taken up from the groundwater by plants. However, in wet season, infiltration dominated the processes of soil water movement. Approximately 56% of the precipitation infiltrated into the groundwater and 37% of the precipitation was consumed by ETa. This study can help us to better understand the process of water movement on coral islands and provide references for further management to protect coral island ecology.

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 (

The increase in atmosphere carbon dioxide (CO

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

This paper describes a technique of making carbonate by rapid CO2 capture from groundwater for direct measurement of the 14C content by accelerator mass spectrometry (AMS). The DIC in groundwater was extracted from acidified water in the form of carbon dioxide (CO2), and transferred into saturated barium hydroxide solution to form barium carbonate (BaCO3). After the BaCO3 precipitate was freeze-dried, it was mixed with a metal powder and pressed into an AMS target for measurement. The behaviors of Si, Al, Fe and Ta powder as the binder with carbonate were evaluated. The C3+ currents from carbonate targets mixed with Fe or Ta were found generally larger than those with Si or Al by a factor of two. The baked Ta was shown to produce fewer contaminating 14C counts than all the others, with or without baking. The CaCO3/Ta and BaCO3/Ta mass mixing ratios in the range from 1:2 to 1:4 and in 1:1.5, respectively, produced optimized currents. The precision and accuracy of the measurement by direct CaCO3 or BaCO3 sputtering using Ta as the binder, were evaluated in comparison to a selected reference material. The agreement was reasonably good between the direct carbonate measurement and the high precision measurement through combustion and graphitization. These findings support the further development of a rapid assessment method directly from field work to measurement.

Mountain block recharge is the least well quantified owing to the lack of a thorough understanding of mountain block hydrological processes. Observations of spatio-temporal variations of groundwater were employed to clarify hydrologic processes in a semi-arid mountainous watershed of northern China. Results showed that the annual feeding rate of precipitation changed between 21% and 40%. However, infiltration of precipitation was mainly drained as interflow on slopes and recharged into the mountain valley as focused recharge. As a result, the mean correlation coefficient between precipitation and groundwater level was only 0.20 and seasonal variations were reduced. Mountain slope is essentially impermeable with no bedrock percolation under arid circumstances. Only a bedrock percolation event occurred after multiple closely-spaced heavy rains during the four-year observation, which induced a local rapid ascending of the water table and an enhanced lateral recharge from upgradient watersheds. The influence of the enhanced lateral recharge lasted three years, suggesting a huge groundwater catchment overcoming local watershed divides in mountain blocks. The average of the gradual recession of the water table was 5.1 mm/d with a maximum of 11.4 mm/d in the beginning stage. Both interflow and bedrock percolation are important. Our results highlight the changeability of hydrologic processes in mountain watersheds.

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.

Warming affects tremendously agricultural water cycle though crop evapotranspiration, soil evaporation, crop water uptake pattern etc. Crop water uptake pattern plays an important role on water cycle of the groundwater-soil-plant-atmosphere continuum (GSPAC). A comprehensive assessment of climatic factors, water sources supply dynamics and crop seasonal water uptake pattern under warming is lacking. Here, climatic factors, water sources supply dynamics during the whole growing stages for summer maize under warming 2 ℃ were monitored by a Water Transformation Dynamical Processes Experimental Device (WTDPED). Isotopic labeling experiments by deuterium oxide (2H2O) were conducted to determine seasonal variations in crop water uptake patterns. The contributions of soil water at different depths to water uptake were quantified by the MixSIAR Bayesian mixing model and dual stable isotopes (δD and δ18O). Results showed that warming enriched the δD values in topsoil (10–20 cm) and depleted the δD values in deep soil (80–270 cm). Warming increased the proportional contributions of soil water at 0–40 cm layer to maize crop uptake by 3.5%, 19.9%, 5.3%, 14.4% and 29.8% during transplanting to maturation stage compared with ambient temperature. It means that deficit irrigation is better applied to reduce root biomass accumulation in the superficial soil layer (0–40 cm) especially at sixth leaf to 12th leaf stage and milk to physiological maturity stage for maize. To some extent, the reduced water infiltration in soil profile offset the increased soil evaporation at 0–80 cm layer under warming. Simultaneously, the maize water uptake for shallow soil layers was greatly induced due to the decrease acclimation of vapor pressure deficit (VPD) especially during tasseling-silking to maturation stage. Smaller water supply and more irrigation times were required for adapting warming condition for summer maize, particularly in water-limited regions. The study gives new perspectives of the effect mechanisms for crop water utilization and agricultural water cycles under future climate change.

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.

Harmful algal bloom is prevalent in the reclaimed-water-source (RWS) river caused by the excessive nutrient's inputs. Rainfall water may be the sole nutrient-diluted water source for the RWS river. However, the effects of storm events on the algal bloom in the RWS river are poorly understood. This study presents chlorophyll-a (Chl-a) variations before, during, and after the initial storm events (Pre-storm, In-storm, and Post-storm) at four representative sites with distinct hydraulic conditions in a dam-regulated RWS river system, Beijing. The response of Chl-a to the initial storm events mostly depends on the ecosystem status that caused by the river hydraulic properties. The upstream is more river-like and downstream is more lake-like. In the river-like system, elevated water temperature (WT, increased by 2 %) could support the dominating algae (diatom) growth (Chl-a increased by 130 %) from Pre-storm to In-storm period. In the lake-like system, the dominant algae (blue algae) declined (Chl-a sharply decreased by 96%–99 %) due to the lower WT (decreased by 3%–7%) and increased flow velocities from Pre-storm to In-storm period. During the Post-storm period, the dominant algae break out (Chl-a surged by 20%–319 %) in the lake-like system caused by the recovered WT (increased by 3%–6%) and flow velocity. The occurrence of algal bloom can be predicted by the Random Forest (RF) model based on water quality parameters such as total nitrogen (TN). The thresholds of algal bloom for the Pre-storm, In-storm, and Post-storm periods were identified as 30 μg/L, 10 μg/L, and 10 μg/L, respectively. The two driven factors were WT and nitrate (NO3-N) for the Pre-storm period and were WT and TN for the In- & Post-storm periods. A higher risk of algal bloom is highlighted during the initial storm events in the RWS river. We propose recommendations for improving water quality in the RWS river systems under the climatic change.

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.

The accurate measurement of precipitation is crucial for hydrological studies. This is especially true for the Hindu Kush–Karakoram–Himalaya (HKKH) mountain region, which is characterized by high s...

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.

By using the standard climate in Beijing during 2000–2010 as baseline, a current and warming contrast experiment was conducted with the Water Transformation Dynamical Processes Experimental Device (WATDPED) to quantify the responses of a maize system to warming in terms of growth and water consumption. Under 2 °C warming, the maize growth period was shortened by 8 days. Chlorophyll content and N content of leaves were enhanced but C content and C/N ratio were decreased. Similarly, there were slight decreases in plant height and stem diameter. The stalk biomass component decreased in leaf and stem ratio, whenever increase in ear ratio over the total biomass. The 100-seed weight and yield were enhanced slightly as a result of the increase of net photosynthesis rate and the decrease of leaf area index. Although the daily evapotranspiration was increased, the total water consumption over the entire growth period was decreased mainly due to the shortened growth period. The values of water use efficiency leaf scale, ecosystem scale (irrigation water use efficiency), and ecosystem scale (evapotranspiration efficiency) were boosted to 28.88%, 6.78% and 5.38%, respectively. It was concluded from the experiments that under 2 °C warming at the p = 0.05 significant level, maize’s yield did not change but the size of maize became smaller in terms of stalk diameter and biomass was higher on the ear. It showed a stronger physiological vigor (higher N content and chlorophyll content) plus a lower total water consumption. Maize’s responses to warming were shown diversified and ensemble assessment by using multiple indicators including yield, biomass component, nutrient and water consumption among others is recommended.

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.

Groundwater recharge variations in time and space are crucial for effective water management, especially in low-precipitation regions. To determine comprehensive groundwater recharge processes in a catchment with large seasonal hydrological variations, intensive field surveys were conducted in the Wangkuai Reservoir watershed located in the Taihang Mountains, North China, during three different times of the year: beginning of the rainy season (June 2011), mid-rainy season (August 2012), and dry season (November 2012). Oxygen and hydrogen isotope and chemical analyses were conducted on the groundwater, spring water, stream water, and reservoir water of the Wangkuai Reservoir watershed. The results were processed using endmember mixing analysis to determine the amount of contribution of the groundwater recharging processes. Similar isotopic and chemical signatures between the surface water and groundwater in the target area indicate that the surface water in the mountain–plain transitional area and the Wangkuai Reservoir are the principal groundwater recharge sources, which result from the highly permeable geological structure of the target area and perennial large-scale surface water, respectively. Additionally, the widespread and significant effect of the diffuse groundwater recharge on the Wangkuai Reservoir was confirmed with the deuterium (d) excess indicator and the high contribution throughout the year, calculated using endmember mixing analysis. Conversely, the contribution of the stream water to the groundwater recharge in the mountain–plain transitional area clearly decreases from the beginning of the rainy season to the mid-rainy season, whereas that of the precipitation increases. This suggests that the main groundwater recharge source shifts from stream water to episodic/continuous heavy precipitation in the mid-rainy season. In other words, the surface water and precipitation commonly affect the groundwater recharge in the rainy season, whereas the reservoir and stream water play important roles in the groundwater recharge in the low-precipitation period. The results should contribute not only to the understanding of the mountain hydrology but also to groundwater resource management in the North China Plain.

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

Groundwater is a key component for water resources in Sanjiang and Songnen Plain, an important agriculture basement in China. The quality and the renewability of irrigation groundwater are essential for the stock raising and agricultural production. Shallow groundwater was sampled and analyzed for various variables. The salinity sodium concentration and bicarbonate hazard, were examined with regard to the United States Department of Agriculture (USDA) irrigation water standards. The concentration of chlorofluorocarbons (CFCs) was determined to analyze the age of groundwater. Most groundwater samples labeled as excellent to good for irrigation with low salinity hazard or medium salinity hazard. Four groundwater samples were good and suspected for irrigation with high salinity hazard. Generally groundwater in Sanjiang Plain was younger than the groundwater in Songnen Plain. Meanwhile, groundwater nearby river is younger than the groundwater further away inside the watershed. The mean age of groundwater in Sanjiang Plain is in average of 44.1, 47.9 and 32.8 years by CFC-11 (CCl3F), CFC-12 (CCl2F2) and CFC-113 (C2Cl3F3), respectively. The mean ages of groundwater in Songnen Plain is in average of 46.1, 53.4, and 40.7 years by CFC-11, CFC-12 and CFC-113, respectively. Thus, groundwater nearby rivers could be directly exploited as irrigation water. Partial groundwater has to be processed to lower the salt concentration rather than directly utilized as irrigation water in Songnen Plain. Both water quality and renewability should be put in mind for sustainable agricultural development and water resources management.

Dissolved trace element concentrations (Ba, Fe, Mn, Si, Sr, and Zn) were investigated in the Haicheng River near to the Liaodong Bay in Northeast China during 2010. Dissolved Ba, Fe, Mn, and Sr showed significant spatial variation, whereas dissolved Fe, Mn, and Zn displayed seasonal variations. Conditions such as water temperature, pH, and dissolved oxygen were found to have an important impact on redox reactions involving dissolved Ba, Fe, and Zn. Dissolved Fe and Mn concentrations were regulated by adsorption or desorption of Fe/Mn oxyhydroxides and the effects of organic carbon complexation on dissolved Ba and Sr were found to be significant. The sources of dissolved trace elements were found to be mainly from domestic sewage, industrial waste, agricultural surface runoff, and natural origin, with estimated seasonal and annual river fluxes established as important inputs of dissolved trace elements from the Haicheng River into the Liaodong Bay or Bohai Sea.

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.

A better understanding of the multi-temporal variation in evapotranspiration (ET) at different crop growth stages is the key for determining a reasonable irrigation schedule. In this study, a new device known as ‘Water Transformation Dynamical Processes Experimental Device’ (WTDPED) was used to monitor ET for maize under controlled environmental and groundwater conditions, and the multi-temporal variations of ET considering the combined impact of environmental factors (air temperature (AT), relative humidity (RH)) and groundwater in homogeneous and layered soils were focused on. During the whole growing period, the ET peaked at 14:00–15:00 on a daily basis. The variation in daily ET followed a bell curve during the entire growing period. The 5-day ET reached its maximum during the 12th leaf and maturity stage. The correlation coefficient between ET and AT reached its maximum value of 0.70 during planting and the third leaf stage. The negative correlation coefficient between RH and ET reached its maximum during the 12th leaf and tasseling-silking stage. Groundwater recharge was positively correlated to ET and the daily contribution was up to 10.07%. The silt sandy loam–loam layered soil was favorable for water and nutrient uptake during the entire growing period of maize.

Groundwater chemistry is diverse and complicated and is regulated by both natural hydrogeochemical and anthropogenic processes. Determining the governing processes and their influence on groundwater chemistry is very important to understand groundwater quality evolution and establish reasonable water management strategies. Main cations (Ca 2+ , Mg 2+ , Na + , K + , and Sr 2+ ), anions (Cl − , SO 2− 4 , HCO − 3 , NO − 3 , and F − ), and SiO 2 and UV254 of 50 shallow groundwater samples were treated and analyzed. Factor analysis combined with ionic ratio and correlation analysis was used to identify the major hydrogeochemical processes responsible for the variation of hydrochemical components. Approximately 76% of the total variance of the data set can be explained by the four factors identified. Composing of Sr 2+ , Mg 2+ , Ca 2+ , and electrical conductivity (EC), Factor 1 accounted for 25.67% of the total variances, and represented groundwater formation background and fundamental water-soil/rock interaction. Factor 2 with high loadings on NO − 3 , U(Cl − , SO 2− 4 , HCO − 3 , NO − 3 , and F − ), and F − )254, and F − , was related to anthropogenic activities, especially the release of domestic sewage and industrial effluents. Factor 3 composed of Na + , HCO − 3 and EC was interpreted as cation exchange process. Factor 4 explained 15.75% of the total variance, and was attributed to the influence of agricultural activities, especially chemical fertilizer application.

The relationship between surface water and groundwater not only influences the water quantity, but also affects the water quality. The stable isotopes (δD, δ 18O) and hydrochemical compositions in water samples were analysed in the Second Songhua River basin. The deep groundwater is mainly recharged from shallow groundwater in the middle and upper reaches. The shallow groundwater is discharged to rivers in the downstream. The runoff from upper reaches mainly contributed the river flow in the downstream. The CCME WQI indicated that the quality of surface water and groundwater was ‘Fair’. The mixing process between surface water and groundwater was simulated by the PHREEQC code with the results from the stable isotopes. The interaction between surface water and groundwater influences the composition of ions in the mixing water, and further affects the water quality with other factors.

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.