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Under natural conditions, the dissolved inorganic carbon (DIC) in river water is dominantly derived from carbonate or silicate dissolution by carbonic acid. However, sulfuric and nitric acids produced by human activities provide additional acidity for chemical weathering, which would affect the DIC flux and change its isotopic composition. To identify the natural and anthropogenic impacts on DIC, the major ion concentrations and stable carbon isotopes of the DIC (δ13C-DIC) of river waters were measured in the Pearl River Delta (PRD) region, which is one of the most developed and populated areas in China. The mass balance calculations for DIC-apportionment showed that carbonate dissolution by carbonic acid was the dominant origin of DIC in the Beijiang (BJ) River (67%) and Xijiang (XJ) River (78%) and silicate dissolution by carbonic acid was the dominant origin of DIC in the Guangzhou (GZ) Channel (37%) and Dongjiang (DJ) River (50%), which was related to the lithology of the catchment. The contribution of carbonate dissolution by sulfuric and nitric acids, which represented the contribution of human activities to the total DIC concentrations in river water, showed high proportions in the GZ Channel and DJ River, with averages of 42% and 34%, respectively, which were associated with a high degree of urbanization. Evidence of hydrochemical parameters and δ13C-DIC signatures indicated that human activities had impacts on the DIC pool. Carbonate dissolution by sulfuric and nitric acids caused by human activities changed DIC apportionments rather than the DIC flux, and this part of DIC would ultimately become a source of CO2 to the atmosphere on the geological timescale and affects the CO2 budget. An increase in nutrient concentration due to increased sewage discharge in the urbanized area could promote phytoplankton photosynthesis, which could change the DIC pool and increase the δ13C-DIC value. This study quantitatively highlights the influence of human activities on DIC apportionment in river water, suggesting that anthropogenic impacts should be seriously considered when evaluating the evolution of DIC.

Benggang, a fragmented landform induced by the overall collapse of soils on slopes, is one of the most serious land erosion problems in Southern China. The reasons for the concentrated development of Benggang and the major influencing factors are still unclear. The key driving factors for Benggang development in Fujian and Jiangxi Provinces were investigated by ArcGIS spatial analysis of the effects of rainfall, lithology, elevation, and geomorphology. It was found that Benggang density increases first and then decreases with annual average rainfall, elevation, and hypsometric integral value (HI) and that the regions with a density of greater than 0.2 Benggang km⁻² are characterized with an average annual rainfall of 1,395–1,645 mm,an elevation of 200–400 m,and an HI of 0.14–0.30. Lithology and weathering crust exhibit an important influence on the development of Benggang, with the formation of 41.94% of Benggangs in 25.88% of the granite area. HI shows a significant positive correlation with elevation in the 1,680 watershed areas (r = .83, p

The coastal zone is not only a terrestrial-marine buffer system but also the main site of the organic matter decomposition process, which complicates the identification of the sources of bioactive elements (C, N and S) and the factors that control C-N-S cycling. Here, a multi-isotope approach is developed to distinguish C, N and S sources and the associated geochemical processes in a coastal aquifer system of the Pearl River Delta (PRD), China. The PRD is characterized as a typical multilayer groundwater system with a reducing environment in the confined aquifers and an oxidizing environment in the unconfined aquifer. For the groundwater samples from the unconfined aquifer, the δ15N values showed that the ammonium and nitrate originated from manure and sewage, the δ13C-DIC indicated that dissolved inorganic carbon (DIC) was mainly derived from soil CO2 and weathering of carbonate rocks, and the δ34S and δ18O signals of sulfate suggested that SO42− originated from the dissolution of continental evaporate. The oxidizing environment and the positive relationship between δ15N-NO3− and δ18O-NO3− suggested that nitrification and denitrification were the key factors influencing the transformation of nitrogen in the unconfined aquifer. No obvious correlation between C, N and S content and isotopic composition suggested C-N-S was loosely coupled in this aquifer. For the groundwater samples in the confined aquifers, the δD-H2O and δ18O-H2O signals suggested that partially confined groundwater samples were affected by seawater intrusion. In the non-seawater intrusion region (NSI zone), the C, N and S content combined with C, N and S isotopic composition indicated that ammonium was derived from the mineralization of organic matter, sulfate mainly originated from rock weathering, and DIC mainly originated from carbonate mineral dissolution and the CO2 produced by organic matter mineralization. Extremely high CH4 concentrations suggested the existence of methanogenesis, while the molar ratio of CH4/(CH4 + (1 + α) × CO2) indicated that both acetate fermentation and CO2 reduction were ubiquitous. CO2 reduction had a stronger isotopic fractionation effect on the δ13C-DIC values, thus, the relatively high δ13C-DIC values were observed. The electron acceptor was the key factor for organic matter mineralization, and CO2 acted as the main electron acceptor in the NSI Zone. Accordingly, acetate fermentation and CO2 reduction became the key factors driving ammonium release in the NSI zone. In the seawater intrusion region (SI zone), ammonium was derived from the mineralization of organic matter, sulfate was derived from the mixing of fresh water and seawater, and DIC was derived from carbonate mineral dissolution, seawater and the CO2 produced by organic matter mineralization. The δ34S-SO42− showed a positive correlation with δ18O-SO42− and a negative correlation with SO42−, suggesting the existence of bacterial sulfate reduction (BSR). High CH4 concentrations also suggested the existence of methanogenesis. The CH4/(CH4 + (1 + α) × CO2) ratios indicated that CO2 reduction existed in more than half of the confined groundwater samples in the SI zone. C-N-S was highly coupled in this region because both BSR and methanogenesis can increase the DIC content, while BSR enriches lighter carbon isotopes and methanogenesis enriches heavier carbon isotopes; thus, a wide range of δ13C-DIC values was found in SI zone. Sulfate or both sulfate and CO2 were the electron acceptors. Accordingly, acetate fermentation, sulfur reduction and CO2 reduction worked together to promote ammonium release for the groundwater samples in the SI Zone. However, the exhaustion of sulfate will make CO2 reduction the key factor for organic matter mineralization in the future.

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

Intensive groundwater development in the urban area of the Nagaoka Plain, Japan, has induced changes in the pH and saturation index of calcite in groundwater. To account for these chemical changes, it is important to determine seasonal variations of recharge and the groundwater flow system in the aquifer. This study identified the sources and flow system of groundwater in this urban area by a comprehensive method using stable isotope data and a numerical groundwater model of the Nagaoka Plain. Stable isotope evidence shows that the groundwater is recharged by meteoric water originating from low-elevation areas rather than the mountains surrounding the plain. The water table in the study area is drawn down during the winter and recovers in the other seasons. Numerical modeling shows that discharge occurs primarily along the Shinano River during the recovery period, whereas discharge is centered in urbanized areas during the drawdown period, when a conical depression of the water table stimulates recharge from the immediate area. These results are indications of a local groundwater flow system, with its recharge area between the Shinano River and the urban areas, which is governed by intensive seasonal groundwater extraction.

The study provided the major ion chemistry, chemical weathering rates and temporary and net CO2 sinks in the Bei Jiang, which was characterized as a hyperactive region with high chemical weathering rates, carbonate and silicate mixing lithology, and abundant sulfuric acid chemical weathering agent of acid deposition and acid mining drainage (AMD) origins. The total chemical weathering rate of 85.46 t km −2 a −1 was comparable to that of other rivers in the hyperactive zones between the latitudes 0 and 30 ∘ . A carbonate weathering rate of 61.15 t km −2 a −1 contributed to about 70 % of the total. The lithology, runoff, and geomorphology had a significant influence on the chemical weathering rate. The proportion of carbonate outcrops had a significant positive correlation with the chemical weathering rate. Due to the interaction between dilution and compensation effect, a significant positive linear relationship was detected between runoff and total carbonate and silicate weathering rates. The geomorphology factors such as catchment area, average slope, and hypsometric integral value (HI) had nonlinear correlation with chemical weathering rate and showed significant scale effect, which revealed the complexity in chemical weathering processes. Dissolved inorganic carbon (DIC) apportionment showed that CCW (carbonate weathering by CO2 ) was the dominant origin of DIC (35 %–87 %). SCW (carbonate weathering by H2SO4 ) (3 %–15 %) and CSW (silicate weathering by CO2 ) (7 %–59 %) were non-negligible processes. The temporary CO2 sink was 823.41×103 mol km −2 a −1 . Compared with the temporary sink, the net sink of CO2 for the Bei Jiang was approximately 23.18×103 mol km −2 a −1 of CO2 and was about 2.82 % of the “temporary” CO2 sink. Human activities (sulfur acid deposition and AMD) dramatically decreased the CO2 net sink, even making chemical weathering a CO2 source to the atmosphere.

Organochlorine pesticides legacies, such as hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT), remained in sediments or soils due to their difficulty in decomposition, especially in the agricultural areas where pesticides were widely used historically. Different from the little disturbed depositional environment of lake, it was difficult for rivers to explore the timing of DDT and HCH inputs through dating sediment cores as records. Based on groundwater dating, this study ascertained the historic pollution of DDT and HCH in Taizi River basin. HCH and DDT residues in groundwater were consistent with the historical production and usage, which increased from the 1950s to the 1980s and declined from the 1980s to the 1990s. Moreover, the partitioning behaviours of HCHs and DDTs in surface water and suspended particulate matter were discussed. It was revealed that β-HCH and o,p’-DDT were more likely to attach to suspended particulate matter than other isomers. Furthermore, species sensitivity distribution curves were generated using 54 toxicity data records to assess the risk of HCHs and DDTs in water and suspended particulate matter. These results indicated that p,p’-DDT in surface water posed a high risk to 95% of the aquatic life in the long run.

Timescale problems of nitrate behavior (i.e. seasonal variation and long-term trend) in headwater are closely related to its hydrological process. In a typical agricultural headwater catchment in the Chiba prefecture, Japan, the groundwater nitrate concentration showed an increasing trend, while for spring water, a substantial decreasing trend was observed during our monitoring period. Two key issues, (1) identification of multiple flow pathways and (2) evaluation of the residence time for different pathways, were emphasized to reveal the factors controlling the different patterns of nitrate trend. Three major flow pathways including vertical soil water flow (VF), lateral groundwater flow (LG) and deep groundwater flow (DG) along the upland-slope-valley were differentiated. Different timescales of three flow pathways were identified. The residence time of VF was calculated as 9–10 years based on the soil water budget equation and the apparent age of LG was estimated as 41 years by chlorofluorocarbon (CFC) traces. The increasing trend of NO3− in groundwater agreed well with the historical nitrate loading, and the decreasing trend of NO3− in spring was mainly influenced by nitrate behavior of LF, which substantially decreased due to reduction of nitrogen fertilizer loadings since 2000.

Urban rivers are important sources of greenhouse gases (GHGs) to the atmosphere; however, these high dissolved GHGs are not well studied. We report the first detailed investigation on an urban river influenced by wastewater treatment plant (WWTP), dam and aeration device, with a focus on the concentration of GHGs and their underlying microbial processes basing on isotope approaches. The result revealed that these infrastructures influenced carbon and/or nitrogen input and redox condition of the river system, leading to impaction of GHGs concentrations and spatiotemporal pattern. The WWTP effluent was the point-source of N2O loading to rivers, and also contained high NO3– and dissolved organic carbon, creating favorable conditions for denitrification by microbes. We measured isotopic compositions (δ15N-N2O and δ18O-N2O) and site preference (SP) of dissolved N2O to differentiate the relative contribution of N2O production processes and calculate the degree of N2O reduction (Fr). The relative contribution of denitrification increased at downstream and Fr suggested that N2O was produced and consumed by heterotrophic denitrification, resulting in a sink of N2O downstream. The closure of dam increased water residence time, trapped the sediment, accelerated oxygen consumption, and development of anoxic conditions that stimulating the production of CO2 and CH4, as well as consumption of N2O. Aeration devices maintained oxic condition, that slowing the development of the anoxic stage and eliminating the methanic stage at downstream. As a result, CO2 concentrations increased along the river due to production of CO2 via anaerobic and aerobic respiration of aqueous organic matter. CH4 concentrations increased at downstream from organic matter biodegradation under anoxic conditions. The measured dissolved GHGs, especially the upper ranges, correspond to a large oversaturation of surface water with respect to atmospheric equilibrium, leading high fluxes to the atmosphere. Our values are on the high end of estimates reported in the literature among different climate regions, indicating that urban river influenced by various of infrastructures are comparable to those in wetlands and intensively agricultural rivers in terms of GHGs emissions. Urban river should be urgently included in the determination of global carbon and nitrogen budgets from rivers.

Nitrate accumulation due to anthropogenic input in highly urbanized rivers is a general recognition. The excess anthropogenic nitrogen (N) can alter N transformations and would further accelerate nitrate accumulation. However, there is lack of direct evidence to reveal the mechanisms of nitrate accumulation in the urbanized river. In this study, multi isotopes of nitrate (δ15N-NO3−, δ18O-NO3−), ammonium (δ15N-NH4+) and suspended particulate nitrogen (δ15N-PN) were obtained to investigate mechanisms of nitrate accumulation in typical highly urbanization rivers in the Pearl River Delta (PRD). Firstly, source apportionment revealed sewage was the dominant source of nitrate and ammonium, evidenced by higher δ15N values (>+5‰). Secondly, in the dry season, a significant correlation between the δ15N-NO3− and δ15N-NH4+ values, an increasing trend of δ15N-NO3− with NO3−-N concentration, and lower δ18O-NO3− values provided isotopic evidence of nitrate accumulation that NO3− was increased by enhanced nitrification of sewage effluent NH4+. Thirdly, in the wet season, the relationships between the δ15N-NO3− and δ18O-NO3−, and lower isotope enrichment factor of denitrification indicated that denitrification in soils or riparian zones was weakened due to urbanization, which increased NO3− fluxes to the river water. Fourthly, the δ15N-PN was significantly correlated with δ15N-NH4+ rather than δ15N-NO3−, revealing the preference of NH4+ uptake by phytoplankton. The NH4+ preferred assimilation repressed NO3− removal and consequently result in nitrate accumulation. This study provided direct lines of evidence by multi isotopes to understand the mechanisms of nitrate accumulation in the urbanized rivers, which deepens our understanding of roles of isotopes in the study of N biogeochemical processes and has important implication for regional and global N cycling.

Investigations were undertaken in the riparian zone near Shangba village, an AMD area, in southern China to determine the effects that river–groundwater interactions and groundwater residence time have had on environmental quality and geochemical evolution of groundwater. Based on the Darcy’s law and ionic mass balances as well as the method of isotopic tracer, the results showed that there were active interactions between AMD-contaminated river water and groundwater in the riparian zone in the study area. River water was found to be the main source of groundwater recharge in the northwestern part of the study area, whereas groundwater was found to be discharging into the river in the southeastern part of the study area throughout the year. End-member mixing analysis quantified that the contributions of river water to groundwater decreased gradually from 35.9% to negligible levels along the flow path. The calculated mixing concentrations of major ions indicated that water–rock reactions were the most important influence on groundwater quality. The wide range of Ca2+ + Mg2+ and HCO3− ratios and the change of groundwater type from Ca2+–SO42− type to a chemical composition dominated by Ca2+–HCO3− type indicated a change of the major water–rock reaction process from the influence of H2SO4 (AMD) to that of CO2 (soil respiration) along a groundwater flow path. Furthermore, the kinetics interpretation of SO42− and HCO3− concentrations suggested that the overlapping time of their kinetics triggered the hydrochemical evolution and the change of major weathering agent. This process might take approximately 8 years and this kinetic time will be continued when a steady source of contamination enter the aquifer.

An aquifer where receives steady lateral recharge from an AMD-polluted river, was chosen to understand the profound influence of the "solid-liquid phase" evolution on the mobility of trace metals. The results showed that the accumulation of trace metals in groundwater was observed near the riparian zone. Zn and Cd almost remained in the "truly dissolved" phase (3 kDa), whereas Cu and Pb were mainly in the coarse colloid (0.22 μm-30 kDa) and shifted from the coarse colloid to the "truly dissolved" phase along the flow path. The evolution of relatively high dispersive colloids to low dispersive colloids indicated that the Al-rich mineral colloids as the dominance migrated with the groundwater flow path, and flocculated gradually so that the porous matrix was coated by gibbsite. The coating of gibbsite dissociates OH

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.

An analysis of the stable isotopes and the major ions in the surface water and groundwater in the Leizhou Peninsula was performed to identify the sources and recharge mechanisms of the groundwater. In this study, 70 water samples were collected from rivers, a lake, and pumping wells. The surface water was considered to have a lower salinity than the groundwater in the region of study. The regression equations forδD andδ18O for the surface water and the groundwater are similar to those for precipitation, indicating meteoric origins. TheδD andδ18O levels in the groundwater ranged from −60‰; to −25‰; and −8.6‰; to −2.5‰, respectively, and were lower than the stable isotope levels from the winter and spring precipitation. The groundwater in the southern area was classified as the Ca2+-Mg2+-HCO3--type, whereas the groundwater in the northern area included three types (Na+-Cl−-type, Ca2+-Mg2+-HCO3--type, and Ca2+-Mg2+-Cl−-type), indicating rapid and frequent water-rock exchange in the region. A reasonable conclusion is that the groundwater chemistry is dominated by rock weathering and rainwater of local origin, which are influenced by seawater carried by the Asian monsoon.

The distribution, migration and potential risk of heavy metals in water and soil environments, related to city water supply, were investigated. Heavy metal concentrations in waters from the Shima River water ranged from not detected (n.d.) to 749 μg L(-1) for Mn, n.d. to 151 μg L(-1) for Ni, 7.00 to 494 μg L(-1) for Zn, n.d. to 93.0 μg L(-1) for Cu and n.d. to 9860 μg L(-1) for Fe. The highest concentration of heavy metals was found at an upstream site in February as a result of industrial effluent discharge. Groundwater (GW1-GW5) and soil (S1-S8) samples along the riverbank showed similar levels of contamination due to a close hydraulic relationship and frequent exchange of water, probably resulting in migration of heavy metals from river water to the aquifer and accumulation at the interface. The mean concentrations of heavy metals in soil profiles were in the ranges of 2.50-19.0 mg kg(-1) for As, 2.80-11.2 mg kg(-1) for Cd, 20.3-165 mg kg(-1) for Cr, 14.5-298 mg kg(-1) for Cu, 11.4-102 mg kg(-1) for Ni, 7.00-95.0 mg kg(-1) for Pb, 40.4-465 mg kg(-1) for Zn, 8.80 × 10(3)-21.8 × 10(3) mg kg(-1) for Fe, and 62.2-430 mg kg(-1) for Mn, showing severe soil pollution by Cd. LUMISTox testing and the potential ecological risk index (RI) were used to assess the potential for adverse ecological effects caused by heavy metals in water and soil media. River water samples posed slight acute toxicity to Vibrio fischeri with luminescence inhibition rates (LIRs) ranging from 24.6% to 38.4% in February. Elevated Zn and Cu concentrations significantly contributed to the toxicity. However, groundwater did not exhibit any toxicity to Vibrio fischeri. The severity of the potential ecological risk for individual metals (Er(i)) decreased in the order of Cd > Cu > Ni > As > Pb > Zn > Cr. RI values indicated that all soil samples in the study area posed a high level of ecological risk. Cd contributed significantly (95.5-98.9%) to potential ecological risk in soils.

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.

Karst water resources, which are critical for the support of human societies and ecological systems in many regions worldwide, are extremely sensitive to mining activities. Identification and quantification of stable isotope (δ(2)HH2O andδ(18)OH2O) composition for all sources is essential if we are to fully understand the dynamics of these unique systems and propose successful remediation strategies. For these purposes, a stable isotope study was undertaken in two similar watersheds, one impacted by acid mine drainage, and the other not. It was found that the majority of δ(2)HH2O and δ(18)OH2O values of acid mine drainage (AMD), AMD-impacted and Main channel mix waters plotted above the local meteoric water line (LMWL), while the non-AMD-impacted water was below the LMWL. The AMD and AMD-impacted water had a similar composition ofδ(18)OH2O and heavierδ(2)HH2O than that of the other waters as a result of pyrite oxidation and Fe hydrolysis. The non-AMD-impacted and spring waters were the background waters in the study area. The composition ofδ(2)HH2O and δ(18)OH2O for the former was influenced by the re-evaporation and water-rock interaction, and that for the latter was controlled by re-condensation. Along the water flow, the Main channel mix water is recharged by AMD-impacted, non-AMD-impacted and spring waters. The composition ofδ(2)HH2O andδ(18)OH2O for the Main channel mix water was coincident with the characteristics of water mixing, supported by three-component mixing modeling of upstream spring, non-AMD-impacted and AMD-impacted waters. The composition of δ(2)HH2O and δ(18)OH2O for the Main channel mix water was mainly affected by the AMD-impacted water. These results help elucidate the impact of AMD on δ(2)HH2O and δ(18)OH2O compositions for karst waters and demonstrate the utility for impact assessments and remediation planning in these unique systems.

Multiple tracers were used to assess the spatial distribution of hydrogeochemistry and its kinetic process in a typical karst basin in Guizhou Province, China. The groundwater apparent age in study area is from 26 to 37.5 years based on CFC-113 (trichlorotrifluoroethane, C2F3Cl3). Based on the characteristics of major ions and the SI values of minerals in groundwater, the rise in the Ca2+ and SO4 2− with the increasing groundwater age is mainly controlled by natural water–rock interaction; however, the Mg2+ and HCO3 − of groundwater should be supplied more by contamination processes than the interaction between water and rocks. The change of major ions in the main stream compared with the groundwater was attributed to the change of the partial pressure of CO2 and varied ratio of groundwater discharge to the total stream flow, which was estimated to range from 35 to 80 %. Land use can be considered as the dominant factor that affects the temporal changes of NO3 −, Cl−, Na+ and K+ in groundwater which have increased since the 1970s. From the viewpoint of residence time, the concentration of these ions in springs and groundwater will continue for decades even if the fertilizer application is under control in a reasonable level from now on.

Groundwater pumping induces changes in the hydrodynamics of aquifer systems. Rapid urbanization and pumping-induced changes in local groundwater flow can change the natural heat and chemical balances of an aquifer. In the Nagaoka Plain, Japan, groundwater is being extracted at 145 × 10(6) m3 /year from a highly permeable aquifer consisting of coarse-grained sediments of Late Pleistocene to Holocene age. We used land-cover and groundwater analyses to investigate the processes that change subsurface temperature and water quality induced by urbanization and intensive groundwater extraction. Comparison of temperature and water quality measurements in 2009 with measurements made between 1977 and 2000 revealed an increase in subsurface temperature (at 18 m depth) of 0.050 °C/year in the main urban area of the Nagaoka Plain, which is equivalent to the rate of increase of mean air temperature during that period. The effects of surface warming are apparent as a warm zone under the urban area. An area with low saturation index of calcite (-3.0 to -2.0) was centered around urban areas in 2009, whereas in 2000 the index there was higher (-1.5 to -0.5). The decrease in this index in the center of Nagaoka City over the last decade is consistent with continuous dissolution of carbonates induced there by changes in recharge water sources due to groundwater pumping. These findings suggest that urbanization, intensive groundwater extraction, and recharge with chemically modified surface water are responsible for changes in thermal and chemical properties under the urban area of the Nagaoka Plain.

The nitrogen aspects of hydrological processes must be determined to identify nitrogen sources and relevant mechanisms. Landfills are the dominant disposal approach to deal with solid waste in urban areas in China. Landfills require adequate land and pose a potential threat to aquifer contamination, particularly in the humid zone, such as Guangzhou. The unlined Likeng landfill in Guangzhou was investigated in three campaigns during the period 2001-2007: water was sampled and analyzed for major ions, heavy metals, and stable isotopes of (18)O and (2)H in water, and (18)O and (15)N in nitrate. Contamination sources, water components, and groundwater flow were examined, revealing a mixture of various sources from landfill effluent, septic tank leakage, fertilizer, and manure following complex processes of recharge, mixing, and denitrification. The effluent from the landfill was rich in Na(+), Ca(2+), K(+), HCO3(-), and Cl(-) ions. A similar process of high NH4(+) in effluent resulting in episodic increases in NO3(-) because of NH4(+) oxidation was found in Likeng landfill when compared with landfills in Denmark and the USA. Twenty-five percent of the precipitation was lost to evaporation before recharging the aquifer, indicating a possible maximum recharge rate of 75% and the potential for a large amount of water penetration to the landfill if not well constructed. Apparent groundwater flow velocity of 3.7 × 10(-7) m s(-1) (11.67 m/a) was found for the front of the effluent under the landfill by considering the vertical and horizontal flow. These findings provide background to delineate the plume from Likeng landfill and to conceptualize the natural attenuation processes of other toxic compounds, which are imperative for any remediation strategy.

To delineate the groundwater flow system in a basin, the groundwater age was estimated by analyzing chlorofluorocarbons (CFC-11, CFC-12 and CFC-113) in a typical headwater wetland in Ichikawa, Japan. Feasibility of groundwater dating by CFCs was assessed comprehensively based on the concentrations of NO3−, SO42−, Fe2+ and dissolved CH4 in the groundwater, because the CFCs would be degraded under the reduction condition available in a wetland. It was found that the CFC-11 apparent age was much older than that estimated by other CFC species. It showed that CFC-12 and CFC-113 were suitable tracers for groundwater dating because of their stability in the wetland environment. Furthermore, the mixture of groundwater with different age was discussed by CFC-12 and CFC-113 based on the binary mixing model and piston-flow model. As a result, the apparent age of groundwater in the study area is in the range of 38–48 years.

Interactions between river water and groundwater have been used to help understand the movement of water and to evaluate water quality in the semi-arid area of the North China Plain (NCP). Stable isotopes, chlorofluorocarbons (CFCs) and hydrochemistry were used to study the influence of surface water from the Xiao River on regional groundwater. Using a mass balance approach based on chloride concentrations, hydrogen and oxygen isotope ratios, the average fraction of surface water recharging to groundwater was 50–60 %. CFC results indicated that the groundwater recharge age varied from 22.5 to 39.5 years. The vertical flow velocity of groundwater was estimated at about 1.8–3.5 m year−1. Nitrate concentrations in groundwater varied from 9.42 to 156.62 mg L−1, and exceeded 50 mg L−1 in most aquifers shallower than 80 m bordering the Xiao River. The δ 15N-NO3 data indicate that the major sources of nitrogen in groundwater are human sewage and animal excreta. Because groundwater is the main source of drinking water, there should be concern about public health related to the elevated nitrate concentrations in the NCP.

Summary A paired catchment study was used to assess hydrochemical characteristics of streams in AMD (acid mine drainage)-impacted and non-AMD-impacted catchments in a karstic region, SW China. The catchments shared similar geology, slope, aspect, area and climate, but different land use since one encompassed mining activities. As a result, hydrogeochemical characteristics of the AMD-impacted water were dominantly controlled by oxidation of pyrite, while that of non-AMD-impacted were influenced by water–rock reactions. It is also coincident with the source of δ 34 S SO4 in both waters. Upstream, unit ion fluxes of the AMD-impacted catchment for Ca, Mg, H, Fe and SO 4 were 17 g/(m 2 yr), 2 g/(m 2 yr), 0.0002 g/(m 2 yr), 17 g/(m 2 yr) and 136 g/(m 2 yr), respectively, while unit ion fluxes of the non-AMD-impacted catchment were much lower than that of the AMD-impacted catchment. Along the flow, fluxes of H, Ca, Mg, Fe and SO 4 decreased in the AMD-impacted water, but increased in the non-AMD-impacted water. The observation was coincident with variations of ion concentrations in both waters along the flow, supported by PHREEQC modeling of minerals such as goethite, jarosite(ss), melanterite, scorodite, calcite, and dolomite. It suggests that the transport of constituents of interest (except for Ca and Mg) is dramatically different in these catchments. Results provide important information on karst system response to AMD, together with the baseline data to understand the degree and type of impairment.

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.

Discriminating the hydrochemical origins in the polluted rivers is a challenge work due to multiple sources contributing to the river’s chemical composition. The Taizi River, as an important tributary of the Liao River, in Northeast China, is flowing through an urban-, industry-, and agriculture-intensive area, and its hydrochemistry has been disturbed by human activities especially in the lower basin. In this study, an extensive analysis has been conducted to evaluate the natural and anthropogenic origins of the hydrochemistry in the Taizi River Basin. Three hydrochemical zones are determined based on hydrological connectivity, land use types and lithology, and the hydrochemistry pattern has changed from Ca-HCO3 type to Ca-HCO3-SO4 type from the upper basin to the lower basin due to increasing areas of agriculture and residence land. Six end members including the rain inputs, sewage discharge, mine drainage, carbonate, silicate and evaporate weathering are discriminated in the study area by applying a two stage stoichiometric method. The first stage is used to separate the anthropogenic inputs (sewage discharge and mine drainage) by an inversion technique, and the second stage is evaluating the rock weathering contributions from carbonates, silicates and evaporates by a forward method. Chemical budget calculation shows that carbonate weathering and anthropogenic inputs are two important factors controlling the hydrochemistry with contributions of about 52 and 27 % of the TDS, respectively. In addition, the contribution of anthropogenic inputs increases from 20 % in the upper basin to 30 % in the lower basin.

Epikarst water, which is one of the most important water resources in karst mountain areas, is extremely sensitive to mining activities. Acid mine drainage (AMD) with high levels of heavy metals can degrade the water quality. A typical coalfield basin was chosen to research the migration process of heavy metals. It was found that the chemical compositions of the stream water in the research field were controlled by the dissolution of carbonate rocks or/and the weathering and oxidation of pyrite in the mining area. Excluding a few sites in the mining area, As(V) was dominant species of arsenic in the form of H2AsO4 − or HAsO4 2− in the research field. Based on the mass balance concept, it was found that fluxes of As, Zn, Cu and Cd in water from the mining area (site 17) affected by AMD were 18, 871, 281 and 12 kg year−1, respectively. Also, concentrations of Cd, Zn, As and Cu in the stream water decreased along the flow, because these ions deposited from the water to the stream bed as the redistribution processes in environment.

Wetland is important as a source of nitrous oxide (N2O), which depends on groundwater and anaerobic conditions involved for denitrification in the aquifer. In order to study the behavior of N2O in wetland, a typical headwater wetland has been chosen in Ichikawa, Chiba prefecture, Japan. It was found that N2O fluxes were high at the sides of valley where groundwater flowed in with high concentration of nitrate, and less than 0.045 mg N m–2 h–1 in the wetland where groundwater was almost free of nitrite. Also, the concentration of dissolved N2O in groundwater ranged from 0.78 to 80.5 μg N L–1 in the study area. Based on the spatial distributions of nitrate, dissolved N2O, hydraulic head, temperature, dissolved oxygen, and oxidation–reduction potential, etc., it is reasonable to consider that denitrification mainly occurred in the wetland aquifer through which groundwater flowed. Because the concentration of dissolved N2O was much higher than ambient air, its emission from the water table became the main source of N2O flux in the study area. The temporal and spatial changes of N2O flux were strongly affected by the concentration of dissolved N2O, precipitation and temperature. Finally, the budget of nitrogen in the groundwater was estimated based on the variations of nitrate, the dissolved N2O and the calculated nitrogen gas along the flow path of groundwater where denitrification was available.

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.

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.

Groundwater is a very significant water source used for irrigation and drinking purposes in the karst region, and therefore understanding the hydrogeochemistry of karst water is extremely important. Surface water and groundwater were collected, and major chemical compositions and environmental isotopes in the water were measured in order to reveal the geochemical processes affecting water quality in the Gaoping karst basin, southwest China. Dominated by Ca 2+ , Mg 2+ , HCO 3 ― and SO 4 2― , the groundwater is typically characterized by Ca―Mg―HCO 3 type in a shallow aquifer, and Ca―Mg―SO 4 type in a deeper aquifer. Dissolution of dolomite aquifer with gypsiferous rocks and dedolomitization in karst aquifers are important processes for chemical compositions of water in the study basin, and produce water with increased Mg 2+ , Ca 2+ and SO 4 2― concentrations, and also increased TDS in surface water and groundwater. Mg 2 +/Ca 2+ molar ratios in groundwater decrease slightly due to dedolomitization, while the mixing of discharge of groundwater with high Mg 2+ /Ca 2+ ratios may be responsible for Mg 2+ /Ca 2+ ratios obviously increasing in surface water, and Mg 2+ /Ca 2+ ratios in both surface water and groundwater finally tending to a constant. In combination with environmental isotopic analyses, the major mechanism responsible for the water chemistry and its geochemical evolution in the study basin can be revealed as being mainly from the water―rock interaction in karst aquifers, the agricultural irrigation and its infiltration, the mixing of surface water and groundwater and the water movement along faults and joints in the karst basin.

The groundwater flow system and the flow velocity in the alluvial fan plain of the Hutuo River, China, have been studied, with an emphasis on relating geochemical characteristics and isotopes factors. Seven stretches of one river, six springs and 31 wells, with depths ranging from 0 m (river waters) to 150 m, were surveyed. The groundwater has a vertical two-layer structure with a boundary at about 80–100 m depth, yielding an upper and a lower groundwater layer. The δ18O and δD values range from −10.56 to −7.05‰ and −81.83 to −59‰, respectively. The groundwater has been recharged by precipitation, and has not been subjected to significant evaporation during infiltration into the aquifer in the upper layer. Using a tritium model, the groundwater flow in the alluvial fan plain showed horizontal flow velocity to be greater than vertical velocity. Groundwater in the upper layer is characterized by Ca–HCO3 type. From the spatial distribution characteristics of the stable isotope and chemical composition of the groundwater, agricultural irrigation was considered to have an influence on the aquifer by causing excessive groundwater abstraction and irrigation return.

Located at southern coast of China, the Pearl River Delta (PRD) is facing serious water problems in both quantity and quality after its rapid urbanization in the last decade. Most remarkably, the local groundwater, that was used to be the source of drinking water before the urbanization was polluted due to poor management of the septic tanks. In order to study the effects of suburban development on local groundwater flow and water quality in the PRD region, Fengcun of Guangzhou has been chosen as the study area. In Fengcun, drinking water was groundwater before the 1990s, but now piped reservoir water is used by each family because the groundwater has been polluted. This study clarifies the source and process of the groundwater pollution from septic tanks using isotopic and geochemical characteristics, especially nitrate (NO3−) concentrations. Water samples were collected from the wells and ponds in Fengcun in March and July 2005 and in July 2006. Based on the pe–pH diagram, NO3− and ammonium of groundwater are from the effect of human activities, rather than from nitrification and ammonification of N2. NO3− pollution of groundwater is from point sources, and NO3− concentrations decrease from northeast to southwest. Groundwater is polluted rapidly by the leakage of septic tanks. NO3− concentrations of pollution sources were lower than 20 mg l−1 in March 2005, but had increased to about 120 mg l−1 in July 2006. This implies that groundwater protection should be strengthened in rural areas of the PRD. Copyright © 2007 John Wiley & Sons, Ltd.

Hanjiang River, the largest tributary of Yangtze, faces environmental pressures from South-to-North Water Transfer project and anthropogenic influences. In order to reveal the chemical characteristics of river and contribution of groundwater to the river along mid-lower reaches of Hanjiang River, field works have been conducted in wet and dry seasons. The major ion compositions are characterized by the dominance of Ca2+, and HCO3 − in surface water and groundwater. As a result, calcite weathering is a dominant process for surface water and groundwater. Additionally, dolomite weathering also contributes to hydrochemical evolution in the groundwater of the basin. Stable isotopes (δ18O, δD) show that both surface and groundwater most probably originate from present-day precipitation. Isotopic of both surface water and groundwater can provide greater confidence in identifying the weathering and extent of interaction processes. It was found that river water was mainly recharged by tributaries in wet season while recharged by groundwater in dry season. Dissolved solute flux from tributaries and groundwater to the river was estimated by water balance budget model and environmental tracer mass balance approach. Tributaries and groundwater contribute to mid-lower reach of Hanjiang River in wet season and dry season, respectively. From section H1 to H9, there were 455.4 kg/s of total dissolved solute (TDS) transferred from tributaries to the main channel and 99.8 kg/s of TDS fluxed from groundwater to river water in dry season.

Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population, quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater was recharged by precipitation and was characterized by Ca–HCO3 type water with depleted δ18O and δD (mean value of −8.8‰ δ18O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex (Ca–Na–Mg–HCO3–Cl–SO4 type), and heavier δ18O and δD were observed (around −8‰ δ18O). Before the surface water with mean δ18O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ18O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal end of the fan. The groundwater underwent chemical evolution from Ca–HCO3, Na–HCO3, to Na–SO4. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical evolution, and groundwater flow paths in the complex alluvial fan aquifer system.

To identify the groundwater flow system in the North China Plain, the chemical and stable isotopes of the groundwater and surface water were analysed along the Chaobai River and Yongding River basin. According to the field survey, the study area in the North China Plain was classified hydrogeologically into three parts: mountain, Piedmont alluvial fan and lowland areas. The change of electrical conductance and pH values coincided with groundwater flow from mountain to lowland areas. The following groundwater types are recognized: Ca-HCO(3) and Ca-Mg-HCO(3) in mountain areas, Ca-Mg-HCO(3) and Na-K-HCO(3) in Piedmont alluvial fan areas, and HCO(3)-Na in lowland areas. The stable isotope distribution of groundwater in the study area also has a good corresponding relation with other chemical characteristics. Stable isotope signatures reveal a major recharge from precipitation and surface water in the mountain areas. Chemical and stable isotope analysis data suggest that mountain and Piedmont alluvial fan areas were the major recharge zones and the lowland areas belong to the main discharge zone. Precipitation and surface water were the major sources for groundwater in the North China Plain. Stable isotopic enrichment of groundwater near the dam area in front of the Piedmont alluvial fan areas shows that the dam water infiltrated to the ground after evaporation. As a result, from the stable isotope analysis, isotope value of groundwater tends to deplete from sea level (horizontal ground surface) to both top of the mountain and the bottom of the lowland areas in symmetrically. This suggests that groundwater in the study area is controlled by the altitude effect. Shallow groundwater in the study area belongs to the local flow system and deep groundwater part of the regional flow system. Copyright (C) 2007 John Wiley & Sons, Ltd.

This paper presents an integrated study of urbanization trends in Shijiazhuang City, Hebei Province of China, by using Geographical Information Systems (GIS) and remote sensing. The study explores the temporal and spatial characteristics of urban expansion from 1934 to 2001, and land use/cover change from 1987 to 2001. Temporally, urban expansion shows fast and slow growth stages, with the high-speed growth districts shifting to the east or west side of the city. The spatial patterns of urban growth can be categorized into three types: special objectives oriented type, social-political intervention type, and normal urban growth type. The remotely detected land use/cover change from 1987 to 2001 shows that the land use/cover was largely changed. The land use/cover conversion relationship implies that these changes are governed by urban expansion, which produces a force to drive the land use changes in search of a higher return. Lastly, the major factors influencing urban expansion and land use/cover change are also discussed. In general, the population, traffic conditions, industrialization, and policy are the major factors that influenced the urban expansion. © 2005 Elsevier B.V. All rights reserved.

In arid and semi-arid regions there is usually a shortage of irrigation water; thus, wastewater water, as well as other low-quality water resources, may become an important source of water and nutrients. However, (pre)treated wastewater may contain elements and compounds that can damage the environment. It also has the potential to affect water quality adversely in an aquifer that may be the source of drinking water in the area. In order to assess the impacts of wastewater on the environment, groundwater samples were taken and analysed in typical croplands in the North China Plain, where urban wastewater or groundwater have been used for irrigation for several decades. Concentrations of nitrate (NO3−) in groundwater in the study area varied from 50 to 130 mg l−1 in the croplands irrigated by wastewater, but in the croplands irrigated by pumping wells, away from the Dongming Canal, NO3− concentrations are less than 35 mg l−1. It was found that values of δ15N ranged from +5 to +13‰, and dominantly from +7 to +11‰, and the NO3− concentration in most wells with depths of less than 40 m was higher than the drinking water standard set by the WHO. Cluster analysis was used to classify the spatial distribution of nitrates resulting from the wastewater. Identification of chemical patterns is found to be effective for the comprehensive assessment of the spatial distribution of groundwater quality. It is also emphasized that the wastewater in this area controls the NO3− distribution in the groundwater, and should be used carefully to protect both soil and groundwater from NO3− pollution. Copyright © 2004 John Wiley & Sons, Ltd.

A survey of the quality of groundwater across a broad area of the North China Plain, undertaken in 1998 to 2000, indicates that nitrate pollution is a serious problem affecting the drinking water for a vast population. The use of nitrogen (N)-fertilizer in agriculture has greatly increased over the past 20 years to meet the food needs of the rapidly expanding population. During the study, 295 water samples were collected from wells and springs to determine the water chemistry and the extent of nitrate pollution. High concentrations of nitrate, especially in a recharge area along the western side, but also in the vicinity of Beijing and locally in other parts of the plain, pose a serious problem for the drinking water supply. In places, the nitrate concentration exceeds the maximum for safe drinking water of 45 mg/L. The intense use of N-fertilizer and the widespread use of untreated groundwater for crop irrigation contribute greatly to the problem, but no doubt the disposal of industrial and municipal waste into streams and infiltrating the aquifer also contribute to the problem; however, the lack of data prevents evaluation of those sources. In the recharge area, nitrate is found at depths of as much as 50 m. Near Beijing, relatively high concentrations of nitrate occur at depths of as much as 80 m. In the discharge area, in the vicinity of the Yellow River, high concentrations of nitrate occur at depths of

The North China Plain (NCP) is an important agricultural area in China and has a high population density. Serious water shortages have occurred in this region over the last 20 years. Water transfer from the Yangtze River (the east route) was initiated in the year 2002 to provide water for the major cities of the NCP. This study was carried out before the implementation of the water transfer project, focusing on the spatial integration of the groundwater flow system and geochemical characteristics, which are mainly controlled by tectonics, geomorphology, and lithology. The field survey and the geochemical analyses of the groundwater samples indicated that the groundwater in the NCP has a two-layer structure, with a boundary at a depth of about 100-150 in. The two layers differ in pH, concentrations of SiO2, and major ions, and isotopes (O-18, deuterium and tritium (T)). Chemical components in the upper layer showed a wider range and higher variability than those in the lower layer, indicating the impact of human activity. The flow direction of the groundwater in the upper layer was examined in detail in two profiles, showing that the upper layer flows east towards the Canozhou-Daming fault, while the groundwater in the lower layer flows northeast towards Tianjin. Three hydrogeological zones are identified: recharge (Zone 1), intermediate (Zone II), and discharge (Zone 111). The recharge zone was found to be low in chloride (Cl-) but high in T. The discharge zone was found to be high in Cl- and low in T. This may be due to the difference in groundwater age. The discharge zone was subdivided into two sub-zones, Zone II1 and Zone III2 by considering the effects of human activities. Zone III2 was strongly affected by water diversions from the Yellow River. As groundwater flows from the recharge zone to the intermediate and discharge zones, chemical patterns evolve in the order: Ca-HCO3 > Mg-HCO3 > Na-Cl + SO4. Copyright (C) 2004 John Wiley Sons, Ltd.

A wetland is an important part of the headwater in the discharge area of a basin. It controls not only groundwater discharge such as seepage or springs, but also the migration of chemical matter from the basin. In order to make clear how and where natural attenuation processes happen in wetlands, a typical headwater in Chiba, Japan, was chosen for an investigation of the behaviour of nitrate in groundwater. From the viewpoint of hydro-geomorphology, the wetland in the study site can be divided into three zones: the shallow water-table zone, the seepage zone, and the spring zone along the downstream direction. There were six piezometer groups; each group contained four piezometers, individually set at depths of 1, 2, 3 and 4 m. Major ions and δ15N of groundwater from piezometers, wells and springs were analysed. It was found that nitrate in groundwater mainly came from the fertilizers used in the upstream recharge area of the study site. When the groundwater moved up across the wetland, nitrate concentration in the groundwater decreased rapidly in the shallow water-table zone due to denitrification. Nitrate-free water can be found at the seepage zone. However, the behaviour of nitrate in the spring water was different from that in the seepage zone, since both dilution and denitrification processes were involved in the decrease of nitrate concentration in groundwater. In particular, the dilution process mainly controlled the decline of nitrate at the location where the nitrate-free groundwater flowing horizontally from the seepage zone mixed with the high-nitrate groundwater flowing upward before emerging as a spring. It was also found that denitrification only occurs suddenly in a narrow zone or a thin layer of the order of a few metres. Copyright © 2004 John Wiley & Sons, Ltd.

In arid environments groundwater may represent the most important source of water for sustaining life. The timing and nature of precipitation may induce infiltration and recharge on a small scale. The Al Ain region, UAE was chosen and from 1996 to 1997 studies were conducted to illustrate spatial distribution of recharge for groundwater by using chemical and isotopic methods. According to the field survey, UAE can be hydrogeologically classified into five parts: mountain area, wadis, sand dunes, inland sabkhas and coastal sabkhas, respectively. In this report, we studied a typical wadi, Wadi Mieshiq area. Upstream of the wadi, it was found that the groundwaters were characterized by low salinity. Stable isotopes of groundwaters in the wadi were lighter than those of the stream waters in the mountain area, since stream water was affected by evaporation before it infiltrated into the ground. The isotopes of recharged water into the wadi must have isotopically light values. From the results above, groundwater along the wadi was mainly derived from not only water from the mountain area but also infiltrated water during the flood period. Wadis are an important recharge region for groundwater. Copyright © 2001 John Wiley & Sons, Ltd.

From the aspect of ecohydrology, a wetland is the discharge area for the groundwater system and supports habitats of high biodiversity. A typical headwater wetland in Chiba, Japan, was chosen to investigate nitrate behavior in the wetland through which the groundwater flowed.

Understanding the spatial and temporal pattern of dissolved nitrous oxide (N 2 O) in groundwater is essential to estimate the N 2 O emissions from groundwater to the unsaturated zone and to the atmosphere. In order to study the spatial distribution and seasonal change of dissolved N 2 O in wetland, a headwater wetland in Ichikawa, Chiba Prefecture, Japan, was chosen. Variations of nitrate (NO 3 - ), dissolved N 2 O and ? 15 N-NO 3 - indicated that the dissolved N 2 O in the groundwater of study wetland consists of two parts, one from denitrification within the wetland, and another from nitrification at upland. Principal component analysis (PCA) was used to assess the shallow groundwater parameters in the wetland. And t-test was conducted to find statistically significant differences of the variables between the ASW and NS, warm season and cool season. The concentrations of dissolved N 2 O increased from the upland to the zone of adjacent area between slope and wetland (ASW) and then decreased at the zone near the stream (NS). In sight of dissolved N 2 O associated nitrogen migration, groundwater in the study area can be divided into three stages: upland as the stage 1, ASW as the stage 2, and NS as the stage 3. Higher temperature results in higher denitrification rate, lower dissolved oxygen (DO) and oxidation-redox potential (ORP), yielding higher concentration of N 2 O in the warm season. Therefore, the seasonal change of dissolved N 2 O in study wetland can be mainly interpreted by the variation of temperatures of groundwater.

In semi-arid regions, most human activities occur in alluvial fan areas; however, NO3(-) pollution has greatly threatened the shallow groundwater quality. In this paper, δ(15)N-NO3(-) and multi-tracers were used to identify the origin and fate of NO3(-) in groundwater of the Baiyangdian lake watershed, North China Plain. The investigation was conducted in two typical regions: one is the agricultural area located in the upstream of the watershed and another is the region influenced by urban wastewater in the downstream of the watershed. Results indicate that the high NO3(-) concentrations of the upstream shallow groundwater were sourced from fertilizer and manure or sewage leakage, whilst the mixture and denitrification caused the decrease in the NO3(-) concentration along the flow path of the groundwater. In the downstream, industrial and domestic effluent has a great impact on groundwater quality. The contaminated rivers contributed from 45% to 76% of the total recharge to the groundwater within a distance of 40 m from the river. The mixture fraction of the wastewater declined with the increasing distance away from the river. However, groundwater with NO3(-) concentrations larger than 20 mg l(-1) was only distributed in areas near to the polluted river or the sewage irrigation area. It is revealed that the frontier and depression regions of an alluvial fan in a lake watershed with abundant organics, silt and clay sediments have suitable conditions for denitrification in the downstream.

The influence of arsenic coal mine on nearby paddy fields was surveyed in Guizhou province, China. The paddy fields were divided into three areas using cluster analysis based on the soil pH, Fe and As contents. The average values were 6.5, 68.70 g/kg and 47.36 mg/kg in Area I, were 5.2, 62.36 g/kg and 82.88 mg/kg in Area II, and were 4.3, 78.38 g/kg and 121.03 mg/kg in Area III, respectively. The mobile As contents in Areas II and III were higher than in Area I. The enrichment of As in paddy soil and change of soil properties increased the arsenic concentration in rice plants, where the transfer factor of As from soil to rice grain was about 0.009. The average As concentrations in Areas I, II and III were 9.58, 21.67 and 25.41 mg/kg in roots of rice, 2.50, 3.41 and 3.90 mg/kg in straw, and 0.42, 0.85 and 1.09 mg/kg in grain, respectively. It was estimated that the daily intake of total As and inorganic As for a 60 kg adult through rice consumption were above 4.2 ?g/kg body weight/day and above 0.144 mg/day, respectively. The correlation analysis showed that As concentration in rice had a significant positive correlation with soil As concentration (r root = 0.672, p < 0.05; r straw = 0.725, p < 0.01; r grain = 0.759, p < 0.01), a negative correlation with soil pH, K, Ca and Mg contents, and a positive correlation with soil organic matter and Fe content.

The behavior and fate of alkylphenols (APs) were studied in surface water from the Jialu River, Henan Province, China. Located at its upper stream, Zhengzhou city is regarded as the major discharge source to this river with its annual effluents containing 726 kg for nonylphenol (NP) and 30.2 kg for octylphenol (OP). The concentrations of NP and OP in surface water ranged from 75.2 to 1520 ngL(-1) and from 20.9 to 63.2 ngL(-1), respectively. To assess the behavior of APs along the river, a mass balance equation based on chloride was adopted, due to its relative conservation. The results showed that dilution effect was prevailing in determining the APs concentrations in surface water along the river. The effect of potential biodegradation was also estimated with an assumption of the optimized biodegradation. The contributions of dilution and biodegradation to the decline of APs concentrations were 38.8%, 23.7% for NP and 57.8%, 24.3% for OP, respectively. The other contribution to the decline of APs concentrations along the river was considered as an integrated effect of adsorption and air-water exchange with the values of 37.5% for NP and 17.9% for OP. The decay half-lives of NP and OP from surface water bodies were 1.6 and 2.4d, respectively. About 70.2% of total NP and 24.1% of total OP were finally eliminated from water phase to surrounding matrix in the downstream. The results suggested that the downstream river channel served as the net sink of APs in the study area.

The distribution and adsorption characteristics of phosphorus were investigated in a typical headwater wetland in Ichikawa City, Chiba Prefecture, Japan. Total dissolved phosphorus (TDP) was the main phosphorus fraction in the waters, ranging from limit of quantification (0.002 mg/L) to 0.059 mg/L in spring water, from limit of quantification to 0.128 mg/L in groundwater and from 0.012 to 0.048 mg/L in river water. TDP in 33% water samples were higher than the environmental quality standard for eutrophication (0.020 mg/L). Next, phosphorus adsorption experiment was conducted to study phosphorus distribution in the aquifer where the equilibrium phosphorus concentration (CEPC) is the key to access the phosphorus in the waters. In addition, the amount of TDP releasing from the wetland through river was 20.9 g/day.

The characteristics of nitrate (NO(3)(-)) in major rivers and aquifers of the Sanjiang Plain, China were investigated by hydrogeochemical conditions, nitrogen isotope technique and CFCs trace. An overall understanding on the sources and fate of NO(3)(-) in the surface water and the groundwater was obtained. The NO(3)(-) concentrations in the surface water were low and no samples exceeds the WTO standards. However, 11.4% of the groundwater samples exceeded the WTO standards, indicating local NO(3)(-) pollution in rural areas. Redox condition analysis revealed that most of the surface water had oxic condition, while for the shallow groundwater (mean well depth smaller than 30 m), the redox condition began to change into anoxic zone, and the deep groundwater (mean well depth larger than 50 m) showed strong anoxic condition. The δ(15)N-NO(3) data indicated soil N and fertilizer contributed the major sources in the surface water, and NO(3)(-) in the groundwater mainly showed a manure origin. In the Songhua-Heilong River, dilution effect was dominating, while for the Wusuli River, it showed that mix with water contained excess of NO(3)(-) resulted in the NO(3)(-) concentration increased along the river. Additionally, the NO(3)(-) transportation in the groundwater was analyzed by groundwater ages derived from environmental tracer (CFCs) data. The relation between the groundwater ages and the NO(3)(-) concentrations showed that the young groundwater with the age less than 60 years had higher NO(3)(-) concentrations than the old groundwater over the age of 60 years because anthropogenic activities began to boom from 1950s in the Sanjiang Plain.

Water samples were collected from the Yellow River and from wells for chemical and isotopic measurement in the counties of Yucheng and Qihe, to which 6–9×108 m3 of water is diverted annually from the Yellow River. A zone of high electrical conductivity (EC) in groundwater corresponds well on the regional scale with a ridge in groundwater level, which is the main flow path through the region, but has a low gradient. The zone of highest EC along this ridge occurs at a position with the lowest ground altitude in the study area. The unique characteristic of the groundwater is the linear relationship among the principal anions as the result of mixing. The mixing effect is confirmed by its isotopic signature, which was then used to calculate the contributions from three sources: rainfall, old water, and diverted water with an average mixing rate of 18, 17, and 65%, respectively. As an indicator of water movement, Cl– content varies across a wide range in the profile from 30–10 m with a maximum concentration at about 1.2 m depth. Concentrations are relatively stable at about 2 m, which is the average boundary of the saturated and unsaturated zone. The water from the Yellow River has proved to be dominant in mixing in the aquifer in terms of groundwater flow and geochemistry.