Controlling factors and health risks of groundwater chemistry in a typical alpine watershed based on machine learning methods.

Groundwater is a key water resource in alpine watersheds, but its quality is deteriorating due to human activities. The Golmud River watershed is a representative alpine watershed in Northwest China, and it was chosen to explore groundwater chemistry, associated controlling factors, source contributions, and potential health risks. The analysis includes the use of a self-organizing map (SOM), positive matrix factorization (PMF), ionic ratios, and a Monte Carlo simulation. The content of total dissolved solids in phreatic water was higher in the dry season and increased from the mountainous zone to the fine-soil plain-overflowing zone. Additionally, the water type varied from HCO3- to Cl- types whereas confined groundwater was chemically stable and of a HCO3- type. The SOM results showed a visual correlation between the ions in groundwater. The combination of SOM, PMF, and ionic ratios identified water-rock action as a dominant factor of groundwater chemistry. It was also found that Clusters I and III were mainly influenced by silicate weathering (a total contribution of 38.4 %), whereas evaporation was dominant in Cluster VI (a contribution of 32.5 %). Anthropogenic pollution was mainly associated with clusters V and IV and was related to industrial and agricultural activities during the snowmelt and wet seasons, and fluorine deposition formed by residential coal heating during the dry season (contributions of 1.4 % and 23.8 % in Clusters V and IV, respectively). The sudden increases in B3+ and Li+ in Cluster II were due to inputs from small tributaries (a contribution of 3.9 %). The probabilistic health risk assessment showed that fluoride posed a greater non-carcinogenic risk to human health than Sr2+, B3+, and NO3-, and its potential threat to children was more significant during the dry season than in other seasons. It is necessary for local governments to establish urgent fluoride emission control policies within the Golmud River watershed.

Base flow in the Yarlungzangbo River, Tibet, maintained by the isotopically-depleted precipitation and groundwater discharge.

The extension-induced rift systems on the Tibetan Plateau (TP) may convey large amount of groundwater to rivers, but sources and flow paths of such groundwater are unknown. The Yarlungzangbo River (YR) is the only large river that traverses the southern Tibetan plateau from west to east, following one major suture zone that is cut by extensional normal faults. The faults could influence the flow paths of groundwater discharging to the river. In this study, O and H isotopes, major ions and 222Rn concentrations are analyzed along the YR, and interpreted in relation to structural geology and tectonics. The YR exhibits an abrupt change of isotopic and chemical compositions along with a large increase in flow where the middle reach intersects NE-SW-trending rifts. Low values of δD and δ18O and high concentrations of major ions and 222Rn in the middle reach show that waters are modified isotopically and chemically by a variety of possible water origins, such as recharge of high-altitude glacier melt and discharge from groundwater. Groundwater contributes 27 to 40% of the river flow in the middle reach. Isotopically-light meltwater from high-altitude glacier melt cannot account for the isotope composition of the present outflow of groundwater. The O and H isotope data in the YR and discharging groundwater can be well explained by the groundwater originated as paleo-precipitation during a cooler time, such as the late Pleistocene to early Holocene. The paleo-groundwater discharge can account for about 36 × 108 m3 water budget unbalance in the middle reach. The study provides the first clear isotope evidence for the source of groundwater discharge into a large river through favorable conduits in large-scale active tensile fault zones and confirms the regional scale of groundwater flow on the Tibetan Plateau. Understanding the characteristics and changes of streamflow and surface-groundwater circulation on the Tibetan Plateau will help to manage water resources under a changing environment.

Evolution of groundwater chemistry in coastal aquifers of the Jiangsu, east China: Insights from a multi-isotope (δ2H, δ18O, 87Sr/86Sr, and δ11B) approach.

Groundwater salinization is currently a very serious and challenging issue in many parts of the world. With an increasing demographic pressure and remarkable changes of water and land uses over the last decades, the multilayer coastal aquifer system of Jiangsu province, east China, was affected by increasing salinization. In this study, we investigate the groundwater salinization process and the salinity sources of the aquifer system in Nantong area (southern part of the Jiangsu coastal plain) using a multi-isotope (δ2H, δ18O, 87Sr/86Sr, and δ11B) approach. The results show that the TDS (total dissolved solids) values in most deep groundwater samples are generally lower than those of the shallow groundwater samples. The TDS of both shallow and deep groundwater increase from western Nantong (inland) to the eastern coastal region of the Yellow Sea. The chemical types transform from Ca-Mg-HCO3 or Mg-Ca-HCO3 to NaCl. The stable hydrogen and oxygen isotopes signatures of the groundwater samples indicate that local precipitation likely acts as the main recharge source of both the shallow and deep confined groundwater systems. The deep groundwater shows more depleted isotopes, suggesting recharging by the precipitation under a cold climate before the Holocene period. The shallow groundwater features heavier water isotopes, indicating recharging source from recent precipitation under a warm climate. The variations in δ11B and 87Sr/86Sr of groundwater samples can be explained by the changes of solute sources. In the inland region (western Nantong), shallow groundwater with higher TDS is mainly caused by evaporation-induced concentration, whereas in coastal areas, seawater intrusion exerts a major influence on the chemical composition of the shallow groundwater. Our results show that that seawater intrusion mainly occurs in eastern and southeastern Nantong area. We also find that hydraulic connection between shallow and deep groundwater is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points. The mixing between upper saline water and deep freshwater, together with water-rock interactions, likely explain the observed low salinity in deep groundwater in coastal areas. Overall, with growing observations of salty seawater intrusion in the estuary region of the Yangtze River, future efforts are needed to prevent further seawater intrusion as sea level rises and groundwater table declines. In this context, our findings provide key information for groundwater management in other coastal aquifers, east China.

Major ion chemistry of a representative river in South-central China: Runoff effects and controlling mechanisms.

The Gan River is a large tributary of the Yangtze River in Jiangxi Province, South-central China. Hydrochemical data for this river were analyzed for the period 1958-2016. Ca2+, Na+ + K+, HCO3-, and SO42- were dominant in river water, and pH and total dissolved solids (TDS) varied from 6.0 to 8.8 and 15.7 to 141 mg/L, respectively. The chemical composition of river water was different between the two periods 1958-1979 and 1980-2016. Monthly yields of all ions were positively correlated with river runoff. Monthly yields of SO42-, NO3-, and Cl- were more positively correlated with river runoff before 1980, indicating non-point sources, while multiple sources were indicated after 1980. Sea salt-sourced Cl- comprised less than 19% of the total Cl- in river water. Weathering of basin rocks with sulfuric acid reflected strengthening of anthropogenic activities after 1980. This was reflected by increases in Cl-/(Na+ + Cl-) and SO42-/(Na+ + Cl-) with gross domestic production, population, coal consumption, fertilizer use, and wastewater discharge. Although water quality in the Gan River makes the water acceptable for drinking according to the World Health Organization standards, increases in Cl- and NO3- concentrations after 1980 are of some concern.

The origin of rare alkali metals in geothermal fluids of southern Tibet, China: A silicon isotope perspective.

Geothermal waters from the Semi, Dagejia and Kawu hot springs in the Shiquanhe-Yarlung Zangbo geothermal field of southern Tibet (China) are highly enriched in rare alkali metals (RAM). However, the enrichment mechanism is still hotly debated. Here, we report the first silicon isotope data of these geothermal waters to unravel the origin of the extreme RAM enrichments. Sinter precipitation in the spring vents and water-rock interaction in the deep reservoir controlled both the silicon budget and silicon isotope fractionation. The rates of water-rock interaction and sinter precipitation in three spring sites decrease in the sequences Semi > Kawu > Dagejia, and Dagejia > Kawu > Semi respectively. Silicon isotope fractionation during sinter precipitation (i.e. Δ30Siprecipitate-solution < -0.1‰) is less than that due to water-rock interaction (i.e. Δ30Sisolution-rocks at least as high as -0.47‰), which makes it possible to use the δ30Si signatures of springs to evaluate the intensity of water-rock interaction. Based on the available evidence, a conceptual model of RAM enrichment is proposed: (i) persistent magmatic activity in southern Tibet provided the initial enrichment of the RAM in host rocks and a heat sources for the deep reservoirs of geothermal systems; (ii) the high Cl- content and long residence time (thousands of years) promote the leaching of RAM from the silicate host rocks.

Origin and formation mechanism of salty water in Zuli River catchment of the Yellow River.

The Zuli River is one of the branches of the upper Yellow River, as an inland catchment with semiarid climate in northwestern China, and the formation, evolution, and development of brackish water at such a large scale have remained unclear. This study aims to find clues about the origin and formation mechanism of salty water through multiple methods of hydrochemistry and isotope hydrology. The results show that groundwater is dominantly recharged by precipitation, and the river water was mainly recharged by groundwater discharge. The relatively high tritium content of groundwater (>5.0 TU) clearly suggests the occurrence of a modern recharge and rapid circulation. The dissolution of evaporate minerals, followed by incongruent dissolution of carbonate minerals (dolomite), constituted the main processes controlling groundwater salinization. In addition, the intense evaporation and unreasonable use of fertilizers further increase the TDS of the river, which should be the primary external mechanism of water salinization. PRACTITIONER POINTS: The authors aimed to find clues about the formation mechanism of salty water in an inland catchment of the Yellow River. The results of this research shows that the dissolution of dissolved minerals constituted the main processes controlling groundwater salinization. In addition, the intense evaporation and unreasonable use of fertilizers, which should be the primary external mechanism of water salinization. This work would provide a theoretical basis for government to develop rational utilization of brackish water resources in the study area, which is also significant for understanding the mechanism of water salinization in an inland mountain watershed and even in similar inland watersheds around the world.

Isotope fractionation of sandy-soil water during evaporation - an experimental study.

Soil samples containing water with known stable isotopic compositions were prepared. The soil water was recovered by using vacuum/heat distillation. The experiments were held under different conditions to control rates of water evaporation and water recovery. Recoveries, δ18O and δ2H values of the soil water were determined. Analyses of the data using a Rayleigh distillation model indicate that under the experimental conditions only loosely bound water is extractable in cases where the recovery is smaller than 100 %. Due to isotopic exchange between vapour and remaining water in the micro channels or capillaries of the soil matrix, isotopic fractionation may take place under near-equilibrium conditions. This causes the observed relationship between δ2H and δ18O of the extracted water samples to have a slope close to 8. The results of this study may indicate that, in arid zones when soil that initially contains water dries out, the slope of the relationship between δ2H and δ18O values should be close to 8. Thus, a smaller slope, as observed by some groundwater and soil water samples in arid zones, may be caused by evaporation of water before the water has entered the unsaturated zone.

Geochemical and isotopic data for restricting seawater intrusion and groundwater circulation in a series of typical volcanic islands in the South China Sea.

The decline of groundwater table and deterioration of water quality related to seawater have long been regarded as a crucial problem in coastal regions. In this work, a hydrogeologic investigation using combined hydrochemical and isotopic approaches was conducted in the coastal region of the South China Sea near the Leizhou peninsular to provide primary insight into seawater intrusion and groundwater circulation. Hydrochemical and isotopic data show that local groundwater is subjected to anthropogenic activities and geochemical processes, such as evaporation, water-rock interaction, and ion exchange. However, seawater intrusion driven by the over-exploitation of groundwater and insufficient recharge is the predominant factor controlling groundwater salinization. Systematic and homologic isotopic characteristics of most samples suggest that groundwater in volcanic area is locally recharged and likely caused by modern precipitation. However, very depleted stable isotopes and extremely low tritium of groundwater in some isolated aquifers imply a dominant role of palaeowater.

PPAR gamma protects cardiomyocytes against oxidative stress and apoptosis via Bcl-2 upregulation.

Cardiovascular disease (CVD) is a leading cause of death and disabilities worldwide. Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists possess potent anti-inflammatory actions and have recently emerged as potential therapeutic agents for CVD. Here we show that H2O2 induced apoptosis in cardiomyocytes with a marked down-regulation of Bcl-2 protein. The PPARgamma agonist rosiglitazone protected cardiomyocytes from oxidative stress and apoptosis. Cardiomyocytes constitutively overexpressing PPARgamma were resistant to oxidative stress-induced apoptosis and protected against impairment of mitochondrial function. On the contrary, cells expressing a dominant negative mutant of PPARgamma were highly sensitive to oxidative stress. Cells overexpressing PPARgamma exhibited an almost 3 fold increase in Bcl-2 protein content; whereas, in PPARgamma dominant negative expressing cells, Bcl-2 was barely detected. Bcl-2 knockdown by siRNA in cells overexpressing PPARgamma results in increased sensitivity to oxidative stress, suggesting that Bcl-2 up-regulation mediated the protective effects of PPARgamma. These data suggest that, in oxidative stress-induced cardiomyocyte apoptosis, PPARgamma protects cells from oxidative stress through upregulating Bcl-2 expression. These findings provide further support for the use of PPARgamma agonists in ischemic cardiac disease.

Advanced glycation end products depress function of endothelial progenitor cells via p38 and ERK 1/2 mitogen-activated protein kinase pathways.

OBJECTIVE: Advanced glycation end products (AGEs) and endothelial progenitor cells (EPCs) play divergent roles in the process of atherosclerosis. We investigated the effects of AGE-human serum albumin (AGE-HSA) on receptor expression for AGEs (RAGE) and EPCs apoptosis. METHODS: The human mononuclear cells were obtained by Ficoll density gradient centrifugation and cultured in M199 medium containing rh-VEGF (30 ng/ml), rh-b-FGF(6 ng/ml) and 20% NBCS for 8 days. The adhesive EPCs were sequentially harvested after 24 h synchronization and challenged with AGE-HSA (concentration range from 0 to 300 microg/ml) for 24 h and 200 microg/ml AGE-HSA (time range from 0 to 36 h). EPCs apoptosis and migration were determined, expressions of RAGE, phosphorylated ERK1/2, JNK and p38 mitogen-activated protein kinase (MAPK) of EPCs were quantified by fluorescent quantitation RT-PCR and Western-blot, effect of AGE-HSA on NF-kappaB activtiy was determined by EMSA (electrophoretic mobility shift assay) in the presence and absence of special MAPK pathways pathway inhibitors. RESULTS: AGE-HSA upregulated the expression of RAGE, this effect could be significantly inhibited by p38 MAPK and ERK MAPK inhibitor, but not by JNK MAPK inhibitor. AGE-HSA also promoted EPCs apoptosis and inhibited EPCs migration and increased NF-kappaB activity, these effects could be significantly attenuated by the anti-RAGE neutralizing antibody as well as by p38 and ERK MAPK inhibitors. CONCLUSION: AGE-HSA could promote atherosclerosis by upregulating EPCs RAGE expressions and promoting EPCs apoptosis via p38, ERK MAPK pathways, activation of NF-kappaB might also play a role in this process.

[High-concentration palmitic acid inhibits the proliferation of peripheral blood-derived human endothelial progenitor cells in vitro].

OBJECTIVE: To study the effects of palmitic acid (PA) on the proliferation of peripheral blood-derived endothelial progenitor cells (EPCs) in vitro. METHODS: The mononuclear cells (MNCs) were isolated from the peripheral blood by Ficoll density-gradient centrifugation. The isolated EPCs were characterized by Di-LDI uptake and FITC-lectin binding assay using laser confocal microscope, and further identified by detection of CD34, CD133 and VEGFR2 expression using flow cytometry. The cultured EPCs were incubated in the presence of PA at the concentrations of 0, 50, 100, 200, 400 and 800 micromol/L for different durations (0, 12, 24, 36, 48 and 60 h). The cell morphology was observed and cell proliferation determined with CCK-8 assay. RESULTS: Incubation with 400 and 800 micromol/L of PA significantly inhibited the proliferative ability of EPCs as compared with the control group (P < 0.05). PA at 400 micromol/L had the strongest effect on the cell proliferation, and this effect was intensified with the passage of time, reaching the peak at 48 h with the growth inhibition rate of 58.59% (P < 0.05). CONCLUSION: High-concentration PA can significantly inhibit the proliferation of EPCs in vitro.