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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.

AimsTo investigate whether ‘low sugar’ and related claims influence consumers’ perceptions of the healthiness or other attributes of alcoholic drinks, promote greater consumption or impact diet and activity behaviour intentions.MethodN = 501 Australian women aged 18–35 viewed and rated six images of alcoholic drinks in a randomized online experiment with a 2 (claim: low sugar claim, no claim control) × 2 (drink type: cider, ready-to-drink spirits) between-subjects design.ResultsParticipants who viewed drinks with low sugar claims rated them as healthier, less harmful to health, lower in sugar and kilojoules, and more suitable for weight management and a healthy diet than participants who viewed identical drinks with no claim (P ConclusionsLow sugar and related claims on alcoholic drinks can generate a health halo: consumers generalise from a specific favourable attribute (low sugar) to misperceive other favourable health- and nutrition-related attributes, including lower alcohol content. Findings support calls to reconsider the permissibility of low sugar claims on alcoholic drinks as they may mislead consumers.

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.

Baiyangdian lake, the largest fresh lake on the Haihe Basin in North China, has attracted wide attention on account of the distinguished ecological water bodies in Xiong’an New Area. Although remarkable achievements have been made in pollution control in Baiyangdian lake, the problem facing the overall water environment remains serious. The complex pollutant sources, drastic pollutant flux changes, and the unclear impact of the role of pollutants pose great challenges to the water quality, water environment management, and long-term restoration of the ecological environment. Here, the potential pollution sources, their contribution ratio, and the influence of the pollution load of different sources on the water quality in the priority source areas of Baiyangdian lake are discussed in detail based on collected and existing monitoring data. It is proven that the primary pollution sources of for nitrogen, phosphorus, and organic pollutants are from agricultural and rural non-point source pollution; the load contribution rates exceed 50%, of which the contribution rate to the total phosphorus load reaches 73.37%. The total load contribution of runoff to the three pollutants was small, although the contribution of soil erosion to total nitrogen was 22.95%. The contribution of point source pollution to COD was high, with a rate of 22.33%. In order to ensure the environmental quality of Baiyangdian lake, it is obligatory to strengthen the control of agricultural and rural pollution discharge and to standardize the pollution discharge of livestock and poultry breeding. This study provides a helpful support for protecting the water ecology of the national Xiong’an New Area.

Nitrification in soils is an essential process that involves archaeal and bacterial ammonia-oxidizers. Despite its importance, the relative contributions of soil factors to the abundance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and their nitrification performances are seldom discussed. The aim of this study was to determine the effects of AOA and AOB abundance and different environmental conditions (pH, TC, TN, moisture, and temperature) on nitrification performance. The soils of the long-term fertilized tea orchards and forests were sampled in the field, and nitrification experiments were conducted in the laboratory. The acid soils were collected from the field and used in laboratory incubation experiments to calculate the nitrification rate, including the net nitrification rate (NN rate), nitrification potential (NP), and nitrification kinetics. The basic parameters, different forms of nitrogen content, and AOA and AOB amoA gene copies were also analyzed. Compared with the forest soil, the tea orchard soil had a lower pH and higher nitrogen content (p

Multi-isotope tracers were applied to quantitatively reveal the sources and transformation mechanisms of inorganic nitrogen both spatially and seasonally in a complex land use area in China. Based on land use and the level of socioeconomic development, the study area was divided into four zones: the rural area, developed urban area, developing urban area and industrial urban area. The redox condition and isotope analysis results indicated that the nitrification process dominated in the Han and Rong River, which were characterized by ammonium nitrogen (NH4+-N) and oxidizing conditions, while neither nitrification nor denitrification occurred in the Lian River. The inorganic nitrogen sources of the four areas were revealed from the results of a stable isotope analysis in R (SIAR) and a two-component mixing model after determining the transformation mechanisms. In the rural area, nitrate nitrogen (NO3−-N) was mainly sourced from the increased fertilization of nitrogen fertilizer (42–56%) to farmland during the wet season, and from soil nitrogen (33–62%) related to increased nitrification during the dry season. In the urban area, the contributions of soil nitrogen, manure and sewage and industrial wastewater to the total inorganic nitrogen exhibited large seasonal and spatial differences, which were distinguished by the environmental management supported by gross domestic production (GDP). In the developed and developing urban areas, soil nitrogen contributed 41% and 47% of the NO3−-N, respectively, during the wet season, and 47% and 54%, respectively, during the dry season. The second highest contribution was from manure and sewage (30–41%) with no seasonal differences. In the industrial urban area, the dominant contribution to the NH4+-N was from manure and sewage (81%) during the wet season, but industrial wastewater (84%) in the dry season. Our findings elucidate the multiplex sources and transformation mechanisms of inorganic nitrogen, and promote the management of nitrogen tracing to control nitrogen pollution in complex land use areas.

Synchronous observations of the isotopic composition of water vapor and precipitation for 24 rain events were performed. Rain events driven by low-level jets exhibited similar isotopic changes in precipitation and water vapor. The vertical activity of water vapor in convection causes the isotopic variation in precipitation to be opposite to that of water vapor. Isotopic changes of precipitation in low-pressure systems were partially synchronized with that of water vapor at high but not low water vapor concentrations. Changes in microphysical meteorological properties in stratiform precipitation give rise to different patterns of isotopic changes in water. The re-evaporation of raindrops can be determined by the enrichment ratio of heavy isotopes in the water under the cloud base, which is closely related to the raindrop radius. Stratiform precipitation, with small raindrop sizes, was prone to kinetic fractionation under the cloud base. The raindrop radius of low-level jets was small, favoring exchange with surrounding air and re-evaporation. The moist air mass in convection facilitates isotopic exchange of raindrops with surrounding water vapor, leading to low enrichment ratios. The lowest enrichment ratios in low-pressure systems were due to environments characterized by large-scale water vapor convergence.

A novel Microcystis bloom caused by Microcystis densa has occurred in a typical subtropical reservoir every spring and summer since 2012, and it has caused several ecological and economic losses. To determine the environmental factors that influence the growth and physiological characteristics of M. densa, we investigated the variations in physicochemical factors and M. densa cell density from 2007 to 2017. The results showed that the urea-N concentration increased significantly (from 0.02 ± 0.00–0.20 ± 0.01 mg N l−1), whereas other factors did not vary significantly. NO3−-N and urea-N concentrations were higher than the NH4+-N concentration during the M. densa bloom. The nitrogen composition changed, and urea-N and NO3−-N became a major nitrogen sources in the reservoir. Water temperature and increased urea-N concentrations were the primary factors that influenced variations in M. densa cell density (45.5%, p

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

The UV/chlorine advanced oxidation process (AOP), which forms HO˙ and reactive chlorine species (RCS such as Cl˙, ClO˙ and Cl2˙−), is being considered as an alternative to the UV/H2O2 AOP for the degradation of emerging organic contaminants. This study compared the kinetics and pathways of the degradation of a recalcitrant pharmaceutically active compound, naproxen (NPX), by the UV/chlorine and UV/H2O2 AOPs. The degradation of NPX by both AOPs followed pseudo first-order kinetics, and, at pH 7, the first-order rate constant (k′) in UV/chlorine was 4.9 times higher than that in UV/H2O2. At pH 7, in the UV/chlorine process, the HO˙ and RCS contributed to 15.9% and 76.3%, respectively, of the NPX degradation. Radical scavenging tests indicated that ClO˙ and CO3˙− were important to the NPX degradation by UV/chlorine. A higher efficiency was observed in UV/chlorine than in UV/H2O2 at the pH range of 6–9, but as the pH rose from 6 to 9, k′ decreased from 6.10 × 10−3 s−1 to 2.98 × 10−3 s−1 in UV/chlorine. However, in UV/H2O2, k′ was only slightly affected by pH. In both AOPs, k′ increased linearly with increasing dosages of oxidants (chlorine or H2O2) from 20 μM to 200 μM. The UV/H2O2 process was less affected by the water matrix than the UV/chlorine process. Compared to pure water, k′ in tap water was reduced by 9% and 23.2% by UV/H2O2 and UV/chlorine, respectively. The degradation by both AOPs was associated with hydroxylation and demethylation. Decarboxylation was particularly observed in UV/H2O2, and chlorine substitution was observed in UV/chlorine. During the UV/chlorine process, the acute toxicity to Vibrio fischeri increased and then decreased in the system.

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.

A comprehensive understanding of the impacts of natural and human activities on groundwater evolution is critical for sustainable groundwater resource management, as groundwater quality degradation from urbanization has raised widespread concerns. However, conclusions based only on basic hydrochemical data would be fragmentary because complex processes occur with high concentrations of pollutants in rapidly urbanized areas. Thus, the hydrogeochemical and multi-isotope approaches were combined to elucidate the groundwater hydrogeochemical evolution in such an area. The results demonstrated that the major hydrochemical types of groundwater were Cl Na and HCO3-Ca in 2018 and that the hydrochemical patterns had changed since 1980. The predominant controlling factors for groundwater hydrochemistry were rock weathering due to carbonic, sulfuric and nitric acids, while the cation exchange and evaporation processes acted as natural factors; redox reactions, including denitrification, sulfate reduction, and methanogenesis, also affected groundwater hydrochemistry. The impacts of anthropogenic activities on groundwater hydrochemistry consisted of direct impacts that referred to the infiltration of manure and septic waste responsible for the occurrence of high NO3− content and part of the SO42− content in groundwater and indirect impacts that included the following issues: (1) acid rain accelerated water-rock interactions and resulted in the accumulation of SO42−; (2) sulfate reduction and methanogenesis increased the HCO3– content and expanded the distribution of HCO3-type water; (3) organic matter associated with manure and septic waste accelerated the development of a reducing environment in groundwater; and (4) the occurrence of a strong reducing environment promoted the release of Mn, aggravated heavy metal pollution and imposed adverse effects on the ecological system.

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.

Although indispensable, significant uncertainty still exists in the underlying processes of the formation, dynamics, and emission of greenhouse gases (GHGs), the critical elements needed for the accurate estimation of greenhouse gas fluxes in inland lakes and reservoirs. Seasonal changes in water thermal stratification and turbulence strongly influence the concentration and emission of dissolved GHGs in water columns. Here, we studied the stratification and overturn processes of water column in the subtropical Lianhe Reservoir during different seasons and determined the dynamics of dissolved CO2, CH4, and N2O in the reservoir. Observation of temperature and analysis of chlorofluorocarbons (CFCs) clearly suggested that stratification of water column occurred in summer, but not in winter. The results showed that while dissolved oxygen (DO) was high in the top 5-m layer (the upper epilimnion layer), it dropped considerably especially below 10 m, resulting in an increase in concentration of CO2 and CH4. The high concentrations of dissolved N2O and CH4 were related to the decomposition of organic matter in the hypolimnion layer under anaerobic conditions after stratification. In winter overturn period, vertical circulants of water not only homogenized the concentration of DO in the water column, but also potentially moved CO2, CH4, and N2O from the bottom to the surface of the reservoir. The estimated GHG flux from the reservoir was − 7.13 mmol m−2 day−1 in summer and 2.14 mmol m−2 day−1 in winter. There was the potential that CO2 fluxes from subtropical lakes and reservoirs are overestimated by traditional geochemical models.

Nitrogen source identification is critical to effectively govern nitrogen contamination, as excessive nitrogen content in groundwater has become a crucial global environmental problem. The traditional stable isotope approach (δ15N-NO3–, δ18O-NO3–, δ15N-NH4+) has been widely used to identify nitrogen sources by comparing the isotopic signals between groundwater samples and the possible nitrogen source. However, nitrogen source apportionment based only on that method would be inaccurate because isotopic signals overlap between the nitrogen sources and nitrogen that has undergone biochemical reactions. To solve the shortcomings of the traditional stable isotope approach, the isotope ratios of N2O, the SP-δ18O model and the traditional stable isotope approach were combined to depict the nitrogen transformation processes and reconstruct the “initial” isotopic compositions of nitrogen sources. A total of 58 groundwater samples were collected in the Dongguan Basin and were analysed during June-July 2018. NO3–-N was the dominant species of dissolved inorganic nitrogen in most of the groundwater samples. In the groundwater flow direction, NO3– contents decreased, while the δ15N-NO3– and δ18O-NO3– values increased. The positive relationship between δ15N-NO3– and δ18O-NO3– and the calculation results of the SP-δ18O model indicated that both denitrification and nitrification processes occurred in the groundwater, and denitrification acted as the dominant nitrogen transformation process. The initial isotope ratio of nitrogen obtained from the combined use of the calculation results of the SP-δ18O model and δ15N-NO3– (or δ15N-NH4+) value suggested that manure and septic wastes were the primary sources of NO3– and NH4+ in the groundwater. The redox-sensitive components and the calculation results of the SP-δ18O model depicted the reductive level of NO3– in the groundwater flow direction: NO3– reduction did not occur in the upstream area, NO3– reduction was strong in the intermediate transition zone, and NO3– contents were completely consumed and CH4 occurred in the downstream region. This study demonstrated that the combination of the traditional stable isotope approach and the isotope ratios of N2O are useful tools for revealing the source and transformation of nitrogen in groundwater. The method used in this study provides new insight for nitrogen source identification.

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.

Metal pollution in sediments from the Shima River, a typical transboundary watercourse in the Pearl River Delta area, was investigated. Sediment cores were collected at eight sites from the upper to the lower reaches crossing Shenzhen, Dongguan and Huizhou cities. Sediment physicochemical properties and the total concentrations of trace metals (V, Cr, Co, Ni, Cu, Zn, As, Cd and Pb) were determined. The results showed that riverine sediment was significantly polluted by Cr (content range: 13.8-469mgkg-1), Ni (14.1-257mgkg-1), Cu (10.8-630mgkg-1), Zn (50.2-1700mgkg-1) and Cd (0.172-2.26mgkg-1). The geoaccumulation indices (Igeo) of trace metals decreased in the order Cd>Zn>Ni>Cu>Co>Cr>Pb>As>V. The pollution load indices and potential ecological risk indices (RI) at the sampling sites were similar, with more severe pollution and greater risk presenting in the upper and middle reaches (S1-S6) compared with the lower reaches (S7 and S8). Cd contributed significantly (77.2-87.6%) to the RI. Source identification based on multivariate statistical techniques, including principal component analysis (PCA), correlation analysis (CA) and hierarchical cluster analysis (HACA), was performed to differentiate the origins of trace metals. PCA and CA yielded similar results, indicating that As and V originated from natural sources (e.g., parent materials) and that the other metals were related to anthropogenic activities. HACA based on the Igeo showed that Cd was associated mainly with fertilizers, and the origins of Cr, Ni, Cu and Zn were probably industrial effluents, whereas Co and Pb were related to traffic activities. HACA of sediment cores suggested that Dongguan and Shenzhen cities contribute large quantities of metals to the riverine sediment, whereas few metals were discharged from Huizhou City.

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.

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.

The deltaic and coastal region is an important area for transportation, production and transformation of organic matter (OM). However, the high degree of urbanization and seasonal variability of runoff in this region significantly impact source apportionments and biogeochemical processes of the OM. In this study, stable isotopes of carbon (C) and nitrogen (N) in both suspended particulate matter (SPM) and sedimentary organic matter (SOM) were measured in the highly urbanized Pearl River Delta (PRD), China. The results revealed that source apportionments exhibited spatial variations due to different degrees of urbanization and seasonal variations due to seasonal changes in runoff. High urbanization could increase the contribution of sewage-derived OM in the SPM and decrease the proportion of soil OM in the SOM. Increased precipitation and runoff during wet season could result in a greater contribution of sewage-derived OM (55%), and decreased runoff during the dry season resulted in an increased proportion of phytoplankton (51%) in the SPM. Urbanization and runoff also affected C and N transformation processes of OM. An increased volume of sewage discharge due to urbanization provided nutrients for phytoplankton growth, promoting photosynthesis and assimilation processes. Increased light intensity due to decreased precipitation and runoff during the dry season could facilitate photosynthesis by phytoplankton. This study suggested that OM could record the impacts of urbanization and hydrology on C and N transformation processes in the rivers, further improving knowledge on the C and N cycling processes in highly urbanized river ecosystems.

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.

Novel alternatives of perfluorooctane sulfonate (PFOS), chlorinated polyfluorinated ether sulfonates (Cl-PFAESs) are increasingly being detected in the aquatic and terrestrial environment. Previous studies mainly focused on aquatic biota; however, the knowledge about the ecotoxicological risk they pose to terrestrial plants was still lacking. In this study, the accumulation of two Cl-PFAES (6:2 and 8:2 Cl-PFAES) and PFOS in wheat seedlings at environmentally relevant levels (50 and 100 μg L−1) was investigated. Concentrations of Cl-PFAESs in the roots were an order of magnitude higher than those in shoots, indicating that they were primarily accumulated in the roots. The values of root and shoot bioconcentration factor was comparable between 6:2 Cl-PFAES and PFOS. However, these indexes of 8:2 Cl-PFAES were 42–91% higher and 70–76% lower than PFOS, respectively. As a result, 6:2 Cl-PFAES had a similar accumulation pattern as PFOS, whereas 8:2 Cl-PFAES was predominantly restricted to the roots, which might be attributed to their hydrophobicity and carbon chain length. In addition, at 250 mg L−1 of Cl-PFAESs, plant biomass and pigment content were 24–30% and 0.4–18%, respectively, which were lower than those of PFOS. As compared with PFOS, Cl-PFAESs induced higher levels of root membrane permeability, reactive oxygen species and malondialdehyde content, as well as reduced the activities of antioxidant enzymes and glutathione content. These suggested the occurrence of a severer oxidative damage and the breakdown of the antioxidant defence system in wheat cells. Therefore, we conclude that Cl-PFAESs might pose a higher potential threat to the environment than PFOS.

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.

Three sediment cores were collected from the Beijiang River to investigate the effects of human activities on the geochemical fractions of trace metals (Ni, Cr, Cu, Zn, Cd, Pb and Fe) and to reconstruct the ecological risks for the period 1951-2015. Cd had the highest concentration in exchangeable and carbonate fractions and was probably contributed by smelting wastewater. High Cu, Zn and Pb contents were observed in the iron oxide fraction (mean values of 32.2%, 38.2% and 43.9%, respectively), reflecting the influence of mining activities. Flood events led to coarser sediment grain sizes and higher trace metal residual fractions at upstream sites (S1 and S2). Similar to the mining history of the basin, the excess metal fluxes of Cu, Zn, Pb, and Fe in the 210Pb-dating core (S3) increased slowly from 1951 to 1987, increased rapidly from 1988 to 1998 and decreased gradually after 1999 because of government intervention. However, the excess Cd flux decreased continuously from 1951 to 1961, increased from 1961 to 2005, and declined by approximately 78.2% from 2005 to 2014. The excess Ni and Cr fluxes increased noticeably after 1996 because of the increasing sedimentation rate after the construction of the Feilai Gorge Dam. The enrichment factor (EF) and ratio of secondary and primary phases (RSP) indicated that sediments (S3) were moderately to strongly polluted by Cu, Zn and Pb from 1961 to 2007 and extremely polluted by Cd from 1951 to 2011. Human activities increased the bioavailable metal concentrations and resulted in a high risk of toxicity to benthic organisms, especially during intense mining activity (1990s) and Cd pollution incidents (2005). Cd and Pb were primarily responsible for the sediment toxicity in the Beijiang River. The integrated pollution and risk assessment methods provided a clearer understanding of the aquatic environmental quality.

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.

Anthropogenic activities in the Pearl River Delta (PRD) have caused a deterioration of groundwater quality over the past twenty years as a result of rapid urbanization and industrial development. In this study, the hydrochemical characteristics, quality, and sources of heavy metals in the groundwater of the PRD were investigated. Twenty-five groundwater samples were collected and analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), δ18O, δ2H, major ions, and heavy metals. The groundwater was slightly acidic and presented TDS values that ranged from 35.5 to 8,779.3 mg·L−1. The concentrations of the major ions followed the order Cl−>HCO 3 − >Na+>SO 4 2− >NO 3 − >NH 4 + >Ca2+>K+>Mg2+>Fe2+/3+>Al3+. Ca-Mg-HCO3 and Na-K-HCO3 were the predominant types of facies, and the chemical composition of the groundwater was primarily controlled by chemical weathering of the basement rocks, by mixing of freshwater and seawater and by anthropogenic activities. The heavy metal pollution index (HPI) indicated that 64% of the samples were in the low category, 16% were in the medium category and 20% were in the high category, providing further evidence that this groundwater is unsuitable for drinking. Lead, arsenic, and manganese were mainly sourced from landfill leachate; cadmium from landfill leachate and agricultural wastes; mercury from the discharge of leachate associated with mining activities and agricultural wastes; and chromium primarily from industrial wastes. According to the irrigation water quality indicators, the groundwater in the PRD can be used for irrigation in most farmland without strong negative impacts. However, approximately 9 million people in the Guangdong Province are at risk due to the consumption of untreated water. Therefore, we suggest that treating the groundwater to achieve safer levels is necessary.

The concentrations of Cu, Zn, Pb, Cd, and As varied quite differently in the water, suspended particulate matter (SPM), and sediment along the middle reach of the Beijiang River in southern China. The total concentrations of trace metals and As in the water column were significantly affected by the concentration of SPM, while the metals and As in the sediment were mainly influenced by fine particle component, OM and Fe/Mn/Al. The partitioning coefficient of trace metals and As in the water column generally appeared in the following order: Pb > Cd > Cu > Zn > As. Accordingly, approximately 67.9% of Pb migrated with SPM in the river because of its higher particle reactivity, while the SPM-bound Cu, Zn, and As were approximately 43.4, 37.3, and 26.7%, respectively. The fractions of Cd in the dissolved and particulate phases were almost the same. Sediment resuspension and deposition in the Beijiang River were considered as important factors controlling the concentrations of dissolved Cu, Zn, Pb, Cd, and As in the bottom of the water column.

Differentiating contribution of natural sources and anthropogenic inputs to soil element concentrations can provide important basis for pollution and risk assessments. Fifty-five surface soil samples were collected from farmland (n = 33) and forest land (n = 22) in the Leizhou Peninsula for the measurement of trace elements (Cr, Co, Ni, Cu, Zn, As, Pb, and Cd) concentrations. It was found that soil Cr, Ni, Cu, Zn and Cd concentrations were significantly higher in farmland soils than in forest soils (p < 0.05). Industrial discharges accounted for the increase in Cr, Co, Ni, and Cu concentrations with mean contribution rates of 10.9%, 29.4%, 23.2%, and 25.3%, whereas agricultural activities contributed significantly (14.6%−92.4%) to soil Cd levels. The pollution levels of individual element based on a geo-accumulation index, and enrichment and contamination factors roughly followed a decreasing order of Cd > Co ≈ Cu ≈ Ni ≈ Cr > Zn ≈ As ≈ Pb. Severe contamination was found near industrial areas, which resulted in a moderate or considerable ecological risk. Soil Cr mainly derived from weathering process of basaltic rocks and industrial sources resulted in non-carcinogenic hazard and carcinogenic risk indices up to 2.47 and 2.79 × 10–4, respectively, near industrial areas, leading to that children suffered more from higher non-carcinogenic and carcinogenic risks than adults.

To improve water management, the relation and the hydrochemical evolution of surface water and groundwater were studied in the Songnen Plain. The surface water and groundwater samples were evaluated for stable isotopes and hydrochemistry analyses. The stable isotopic compositions (δ18O, δ D) indicate the groundwater recharges from the precipitation. However, the connectivity between surface water and groundwater is weak, because of the clay layer and the interrupted aquifer. The water evolution is from Ca–Mg–HCO3 to Na–HCO3 by the evaporation, water–rock interaction, and ion exchange processes. The water evaporation and leaching of saline–alkaline soil are the main reasons for water salinity. Further, the leaching of salts in the soil during recharging from backwater and irrigation water intensifies the salinization. The relationship between and evolution of surface water and groundwater provide important guidance for water management not only in the arid and semi-arid area, but also in the soda saline–alkali soil regions of the world.