Dominant Ion Research Articles

Decadal patterns of anthropogenic salinisation in typical mountain streams in northeastern China: Increased rates and sources

Salt pollution and anthropogenic-accelerated weathering is globally shifting the ionic composition and increasing salinisation of fresh water. We analyzed a 40-year data set (1970s-2010s) to characterize the drastic change of dissolved ionic composition, conductivity and pH levels. We also identified causative factors in these highly polluted mountain streams in northeastern China. Dissolved salt ions (Ca2+, Mg2+ and SO42-) increased by 3.02-5.21 fold and conductivity (a proxy for salinisation) increased by 3.09 fold. The average pH values increased from 7.08 to 8.49. The dominant ions, Ca2+, Mg2+, SO42- and HCO3-+CO32-, accounted for ∼90% of ionic composition based on mass concentration. Between the 1970s and 2010s, the dominant anion shifted from HCO3-+CO32- to a mixture of SO42- and HCO3-+CO32-. Increasing mining and land development appear to be the primary driving factors for the change of Ca2+, Mg2+, SO42- and HCO3-+CO32- concentrations; whereas, agricultural land was the main driving factor for the variation in K+, Na+ and Cl- concentrations. The source of ions has shifted from a more natural weathering of carbonate rocks to one of mineral dissolution that is affected by anthropogenic activities. Our study shows that freshwater mountain streams are at risk of long lasting anthropogenic salinisation and should be considered in future management and conservation plans.

MALDI-HRMS imaging and HPLC-HRESI-MSn characterisation of kaurane diterpenes in the fruits of Xylopia aethiopica (Dunal) A. Rich (Annonaceae).

Kaurane diterpenes, notably xylopic acid, have demonstrated important biological activities including analgesia, anti-oxidant, antimicrobial and cytotoxicity. The fruits of Xylopia aethiopica have been reported to be a rich source of kaurane diterpenes. An analytical approach for detailed imaging and characterisation of selected kaurane diterpenes was developed using matrix-assisted laser desorption/ionisation high-resolution mass spectrometry (MALDI-HRMS) imaging techniques and high-performance liquid chromatography-high resolution electrospray ionisation-tandem mass spectrometry (HPLC-HRESI-MSn ) studies, respectively. The images of the compounds were constructed based on selected ions from their HRESI-MS spectra. The matrix employed comprised a solution of α-cyano-4-hydroxycinnamic acid (HCCA) in acetonitrile-water with trifluoroacetic acid (TFA). HPLC-HRESI-MSn measurements were conducted on an LTQ-Orbitrap spectrometer equipped with a heated electrospray ionisation (HESI)-II source. The analytical strategy adopted showed the spatial distribution of the compounds in the fruits of X. aethiopica based on the dominant ions at m/z 301.2163 [M + H - HOCOCH3 ]+ and m/z 399.1932 [M + K]+ for xylopic acid, m/z 317.2111 [M + H]+ and m/z 355.1670 [M + K]+ for 15-oxo-ent-kaur-16-en-19-oic acid and m/z 303.2319 [M + H]+ for ent-kaur-16-en-19-oic acid. The fragmentation patterns of the compounds were proposed based on the HRESI-MSn measurements. The study revealed the spatial variability, differential behaviours and specificity of the selected kaurane diterpenes in the fruit, seed and pericarp. The compounds under study were predominantly restricted to the pericarp of the fruit with trace amounts in the seed.

Hydrogeological and hydrochemical investigation in the Burdur Saline Lake Basin, southwest Turkey

The Burdur Saline Lake Basin is semi-closed and it is situated in the southwest of Turkey. This saline and highly alkaline lake has a tectonic origin. Alluvium represents the most important aquifer and other aquifer is granular and karstic in nature. In the present study, we collected 35 groundwater samples and analyzed them to characterize the groundwater chemistry and investigate hydrogeochemical processes. Na+, Ca2+, Mg2+, HCO32− and SO42− are the dominant ions and the samples are grouped into different hydrochemical facies such as Ca–HCO3, Ca–Mg–HCO3, Mg-Ca-HCO3, Na-Mg-SO4 and Na-SO4-HCO3. Limestone, silicate and gypsum controlled the groundwater chemistry through reverse ion exchange, dissolution of carbonates and silicate weathering. Presence of more iron, arsenic and boron in the groundwater is geogenic. The statistical analysis, i.e. R-mode factor, determined interrelationships within the chemical data through five factors accounting 85.32 % of the total variance of the dataset. Factor 1 is represented by strong loadings of EC, TDS, Mg2+, Na+, SO42−, As and B, and moderate loadings of K+ and Cl-. Factor 2 has strong positive loadings for Ca and CO3-, and moderate negative loading for pH. Factor 3 has strong positive loadings for Zn and has moderate positive loading for Cl-. Factor 4 has strong negative loadings for T (°C), and has moderate positive loadings for pH and K+. Factor 5 has strong positive loadings for HCO3- and has moderate positive loading for Fe. Geochemical variables of Factors 1, 2, 4 and 5 represented the natural hydrogeochemical processes like water-rock interaction. The variables present in factor 3 reflected the anthropogenic effects in the Burdur Lake Basin.

Hydro-geochemical characteristics of glacial meltwater from Naradu Glacier catchment, Western Himalaya

The pattern of changing hydro-geochemical characteristics of water in Himalayan rivers is primarily controlled by sediment load from natural sources in higher altitudes and anthropogenic sources such as the burning of fossil fuels for domestic use, vehicular emissions, and wind transported industrial pollutants in the downstream region. The assessment of water quality is critical for the comparison of natural and anthropogenic sources in the downstream areas due to the dependence of the population on the glacial meltwater for freshwater supply. In the present study, we investigate the physical and ionic characteristics of glacial meltwater from Naradu Glacier catchment concerning the dominant weathering process. The freshwater samples were collected during the ablation period of 2016 and 2017 from specified locations. The physical parameters (pH, electrical conductivity, and temperature) were measured in the field while the analyses for concentrations of major cations (Ca2+, Mg2+, K+, Na+) and major anions (Cl−, SO42−, HCO3−, NO3−) were done in the laboratory. The anions (HCO3− > SO42− > Cl− > NO3−) and cations (Ca2+ > Mg2+ > Na+ > K+) concentrations were observed to have similar trends for both of the ablation period. The statistical analysis shows the predominance of geological weathering processes in the catchment as the controlling factor for the variation in concentration of different ionic species. The catchment was found to be rich in rocks with carbonate mineral making the Ca2+ and HCO3− the most dominant ions in the glacial meltwater.

Hydrogeochemical characterization and water quality assessment of springs in the Emirdağ (Afyonkarahisar) basin, Turkey

The investigation area includes the Emirdag (Afyonkarahisar) basin and its vicinity located in the Upper Sakarya section of Central Anatolia Region. Mesozoic aged recrystallized limestone and dolomites forming the basis of the investigation area, Cretaceous ophiolites, Neogene aged pyroclastic rocks, and unconstructed terrestrial clastics are the dominant rocks. There are many natural water springs in this region. Springs are the primary source for drinking and household needs. Besides, these springs are used for agricultural irrigation, trout plant, etc. In this study, a total of 10 spring samples collected from the Emirdag basin and waters were evaluated for hydrochemical processes, drinking water chemistry, and irrigation water quality. Generally, the yield of water springs which are discharged from volcanic rocks and limestones varies between 0.02 and 2.00 l/s. The pH, temperatures, electrical conductivity, total dissolved solids, and redox potential are changed between 6.53 and 7.86, 11.50 and 17.80 °C, 251 and 790 μS/cm, 132 and 490 mg/l, and 204.10 and 262.30 mV, respectively. The major ion sequence of waters is generally Ca2+ > Mg2+ > Na+ > K+ and HCO3− > SO42− > Cl− > F− > PO43−. Ca2+, Mg2+, and HCO3− are the dominant ions in the groundwater of the study area. The hydrochemical facies of the majority of the study area spring samples are “CaMgHCO3” and “CaMgSO4” types. The distribution of sample points in the Gibbs diagram suggests a rock dominance area. The Schoeller drinkability diagram shows very good and good quality waters. The springs’ suitability for irrigation classification suggests that more than 90% of the water sampling locations are suitable for irrigation. However, the water quality of Pinarbasi spring is different from the other springs due to the high electrical conductivity value (790 μS/cm). Also, the Wilcox and US Salinity Laboratory diagrams show that groundwater samples are good for irrigation. As a result of the analysis of nitrogen compounds, nitrate concentration in the Agzioren (64.09 mg/l) and Ufukpinar (62.01 mg/l) springs only exceeds drinking water standards. It is thought that the increase of nitrate in these springs is due to agricultural pollution. The values in the isotopic composition are above the local and global meteoric water lines, probably indicating similarity in the mechanism of recharge, and the tritium level shows recent groundwater contribution. The springs generally are represented as shallow and have fast circulation.

Hydrogeochemical assessment and suitability of groundwater in a typical Mediterranean coastal area: A case study of the Marathon basin, NE Attica, Greece

This study aims to determine the major factors controlling the qualitative characteristics of groundwater and examine the drinking and irrigation suitability in the Marathon basin, NE Attica, Greece. In this frame, a total of 25 groundwater samples were collected from irrigation wells during October 2014. The dominant ions are Cl− for anions and Ca2+ for cations in the study area. Elevated concentrations of Cl− and Na+ were observed near the coastline indicating a zone of seawater intrusion (SWI). The groundwater quality in the coastal alluvial aquifer system of the Marathon basin is affected by several factors such as water-rock/soil interaction, SWI, reverse ion exchange, and intense agricultural activities. Saturation index (SI) of carbonate (calcite, aragonite, dolomite), sulfate (gypsum, anhydrite), and halide (halite, sylvite) mineral phases were calculated using PHREEQC geochemical software. Carbonate minerals are present in the unsaturated zone (UZ), possibly increasing Ca2+, Mg2+ and HCO3– concentrations when they are dissolved, whereas sulfate and halide minerals are minor or absent in the host rock. The water suitability assessment showed that the groundwater resources are chemical or qualitatively unsuitable for drinking purposes due to the SWI regime and the NO3− pollution, whereas they are suitable for agricultural uses according to various indices (SAR, %Na, RSC, and PI).

Chemistry of size-segregated particles: study of sources and processes in N-NW India

PM0.95,PM0.95-1.5,PM1.5-3.0,PM3.0-7.2 and PM7.2-10 particles were collected simultaneously during summer season from Bikaner (BKR), Jhunjhunu (JHJ) and New Delhi (DEL) located in windward direction of south-westerly winds in north-northwestern, India and studied for mass concentrations and water-soluble inorganic ions (WSIIs). Organic carbon (OC) and elemental carbon (EC) were analyzed only for PM0.95. Particle mass concentrations, size distribution of WSIIs/elements suggested that winds selectively picked PM0.95 and PM3.0-7.2 from BKR and transported them downwind (DEL). Variations in WSIIs and elements were specific to ion/element, particle size and location(s). Secondary inorganic ions (SIN; NO3−, SO42−, NH4+) and Ca2+ were dominant ions compared to other ions and PM0.95 carried high WSIIs compared to other particles at all locations, due to more SIN formation in PM0.95. OC and EC increased significantly from BKR to DEL due to increasing combustion sources. Char-EC was more than soot-EC at all locations. Re-suspension of roadside/surface dust, and biomass burning were potentials sources of OC. Volatile organic compounds at DEL have resulted in formation of high secondary organic carbon. Major elements (MEs; Al, Ca, Fe, Mn, Ti) and trace elements (TEs; Ba, Sr, Zn, Cu, Cr, Pb, Co, Cd) were enriched in PM0.95 compared to other particles. Silica dilution effect resulted in lower enrichment ratios (ERs) of MEs with respect to Upper Continental Crust (UCC) whereas anthropogenic contributions for TEs, more in PM0.95, resulted in higher ERs. Homogenization effects on particle loading and composition were observed at BKR whereas lowering of wind speed and anthropogenic sources introduced heterogeneity at DEL.

Water quality impacts of in-stream mine tailings on a headwater tributary of the Rio Pilcomayo, Potosí, Bolivia

Rio Tarapaya, a major tributary of the upper Rio Pilcomayo and a crucial water resource in the arid Southeastern Bolivian highlands, has been impacted by in-stream mine tailings and acid rock drainage over the past five centuries, from historic and ongoing mining at Cerro Rico de Potosí. Identification of the effects of in-stream mine tailings on the waters of Rio Tarapaya is essential to better understand the dynamics of these complex systems and propose successful management strategies. A study was performed on river waters and sediments at six sites in a reach of Rio Tarapaya, beginning at the city limits of Potosí and ending just after the confluence with Rio Cayara, a relatively unimpaired river 7.3 km downstream. Concentrations of dissolved metals (such as Fe, Al, Mn, and As) in the Ca–Mg–HCO3–SO4 dominated stream were generally orders of magnitude greater than Bolivian receiving water body criteria and United Nations Food and Agriculture Organization irrigation and livestock drinking water guidelines. Variability of Ca and Mg in water and sediment was controlled by dissolution of gypsum, dolomite and calcite, which was supported by Spearman correlation coefficients. The primary ionic products of in-stream sulfide mineral weathering (SO42−, Fe, Al, Mn, Zn and As), are the dominant ions of stream water and sediment leachate. Results are consistent with PHREEQC modeling of minerals such as gibbsite, melanterite, goethite, calcite and dolomite. In general, the reactivity of bed material increased and stream water quality decreased with increasing distance from Potosí. Metals and metalloids are spiraling downstream via seasonally driven particle transport, sulfide weathering, and salt dissolution coupled with biotic interactions. The reactivity of the millions of tonnes of in-stream tailings in Rio Tarapaya and persistence of contemporary illicit tailings discharges indicates that the upper Rio Pilcomayo will remain severely degraded for the foreseeable future unless substantial remediation is undertaken.

Seasonal Variations of Streams Hydrochemistry and Relationships with Morphometric/Landcover Parameters in the Bhagirathi Watersheds, Garhwal Himalaya, India

ABSTRACT The Bhagirathi streams are a major source of fresh water in the form of glaciers meltwater streams and monsoonal phenomena. The watersheds of the Bhagirathi basin is trending towards water chemistry as well as changing morphological and land cover features due to the climatic and anthropogenic activity. To understand seasonal hydrochemistry and the impact of watershed morphology a total of 32 stream water samples collected during post and pre-monsoon seasons. The bicarbonate is the most dominant ion in the streams water followed by Na+, Ca+2, SO4-2, Cl-, SiO2, K+, and Mg+2. The results were found that HCO3- is in very good correlation with the base cations Ca+2, Mg+2 and Na+ in both pre and post-monsoon seasons. The higher concentration of HCO3- in Bhagirathi stream water and its positive correlation with Ca+2 and Mg+2 indicates that their main source comes from the dissolution of carbonates. Most of the hydro-chemical parameters (EC, pH) and ions (Ca+2, Mg+2, Na+, K+, HCOf-, SO4-2, Cl-, and F-) indicated a relationship with morphometric and land cover and these parameters vary with the season. It is observed that elevation, relief, basin length, area, and perimeter impact on stream water chemistry. Due to the processes of chemical weathering, mixing of the groundwater, snow/glacier meltwater, and surface water components responsible for the seasonal variation in the hydrochemistry of streams. Impact of agriculture land is more dominant than any land cover followed by barren land and glacier cover that influence the hydrochemistry of streams.

MAVEN and MEX Multi‐instrument Study of the Dayside of the Martian Induced Magnetospheric Structure Revealed by Pressure Analyses

AbstractA combination of statistical studies and 18 case studies have been used to investigate the structure of the induced Martian magnetosphere. The different plasma and magnetic pressure forces on the dayside of the induced magnetosphere of Mars have been studied using 3.5 years of Mars Atmosphere and Volatile Evolution (MAVEN) and Mars Express (MEX) observations. We present estimates of typical values for the dominant pressure terms, that is, the thermal pressures of the ionosphere and the magnetosheath, the magnetic pressure of the magnetic pile‐up region, and the solar wind dynamic pressure. For 18 typical orbits the altitudes and relative distances of the pressure balance boundaries, the photoelectron boundary, the ion composition boundary, and the induced magnetosphere boundary are estimated. The magnetic pile‐up boundary is discussed but not further studied since earlier characterizations of the magnetic pile‐up boundary do not agree with our results. This study focuses on the transition region between the ionosphere and the magnetosheath on the dayside of Mars. We show that earlier definitions of the photoelectron boundary, ion composition boundary, and induced magnetosphere boundary do not characterize the transition region well, mainly because each boundary is based on measurements from only one or two instruments. In order to characterize the transition region correctly, changes in magnetic field strength and fluctuations, dominant ion species, electron and ion densities and energy distributions need to be considered. This article confirms a complex interaction between Mars and the solar wind and can explain why previous studies have had difficulties to describe the force balance.

Impact of Coal Replacing Project on atmospheric fine aerosol nitrate loading and formation pathways in urban Tianjin: Insights from chemical composition and 15N and 18O isotope ratios

The ‘Coal Replacing Project’ (CRP), replacing coal with cleaner energy like natural gas and electricity, was implemented in North China to curb PM2.5 pollution; therefore, it is important to explore the sources and transformation mechanisms of PM2.5 nitrate under this strategy for examining its effectiveness. In this study, daytime and nighttime PM2.5 samples of one summer (Jul-2016, C1) and two winters (Jan-2017, C2 and Jan-2018, C3, before and during the CRP, respectively) were collected in urban Tianjin. Concentrations of PM2.5 and water-soluble inorganic ions were analyzed, and δ15N and δ18O were used to calculate the contributions of different NOX sources to nitrate based on a Bayesian mixing model. The results showed that the average concentrations of PM2.5 and its dominant inorganic ions (SO42−, NO3−, NH4+) in C3 during the CRP, compared to C2, decreased by 62.13%, 79.69%, 55.14% and 38.84%, respectively, attesting the improvement of air quality during the CRP. According to the correlation between [NO3−/SO42−] and [NH4+/SO42−] as well as δ18O variations, the homogeneous formation pathway might be dominant in C1, while the heterogeneous pathway would be primary in C2 and C3 during the formation of nitrate. Moreover, the heterogeneous pathway contributed more in C3 than in C2. The dominant sources in C1 were biogenic soil emission (37.0% ± 9.9%) and mobile emission (25.7% ± 19.1%), while coal combustion (42.4% ± 13.8% in C2 and 34.9% ± 14.4% in C3) and biomass burning (31.0% ± 21.2% and 34.7% ± 22.7%) were the main sources in C2 and C3. In the winter, the contribution of coal combustion dropped by about 8% during the CRP (C3) in comparison with that in C2, suggesting the implementation of CRP played an important role in reducing NOX from coal combustion.

Chemical Characteristics and Ionic Sources of Precipitation in the Source Region of the Yangtze River

Using 64 precipitation samples collected from June to September 2013 in the Dongkemadi Basin in the source region of the Yangtze River, the pH, conductivity, and main ionic concentration characteristics of precipitation were analyzed. The main ionic sources of precipitation and their relationships with atmospheric circulation were examined using factor analysis, correlation analysis, enrichment factor analysis, and backward trajectory analysis. The results showed that the range of precipitation pH values varied from 5.26 to 9.25 with a weighted average of 6.70, and conductivity ranged from 0.23 to 28.70 μS·cm-1 with a weighted average of 3.45 μS·cm-1. The conductivity of precipitation was lower than for the Mt. Waliguan basin (China Global Atmosphere Watch baseline observatory). The total ionic concentrations in the precipitation ranged from 7.0 to 376.9 μeq·L-1 with a weighted average of 40.8 μeq·L-1. The ranked order of ionic concentrations was HCO3- > NH4+ > Ca2+ > NO3- > SO42- > Na+ > Cl- > K+ > Mg2+. HCO3-, NH4+,Ca2+, and NO3- were the dominant ions, which accounted for 74.75% of the total ionic concentration. Fractional acidity (FA) analysis showed that 97.8% of the precipitation acidity was neutralized by alkaline constituents. Neutral factor (NF) analysis indicated that NH4+ and Ca2+ were the dominant neutralization constituents in the precipitation. The precipitation ions in this study area were mainly derived from terrestrial material, while input from marine sources was relatively low. Backward trajectory analysis revealed that the total ionic concentrations varied significantly between the different sources, which followed the order of local sources>westerly sources>monsoon sources. This indicates that different atmospheric circulation conditions and air mass sources have a significant influence on the chemical composition of precipitation in this area. To some extent, the chemical characteristics of precipitation could reflect the air quality and background values for remote areas due to the limited effect of human activities. The results of this study provide a scientific basis for the protection of water quality and the assessment of the impact of human activities on the atmospheric environment in the source region of the Yangtze River.

Hydrochemical properties and groundwater quality evaluation in Suzhou City, lower Yangtze Delta, China

Detailed study of the chemical analysis results of 49 groundwater samples collected from the region’s second confined aquifer were carried out in an attempt to identify the samples’ hydrochemical properties and to assess the quality and usability of groundwater in Suzhou city, China. The results revealed that sodium, calcium and bicarbonate were the dominant ions in the groundwater samples. Na-HCO3, mixed Na-Ca-HCO3, Ca-HCO3, and Na-Cl type were the four major hydrochemical facies identified by a Piper Trilinear diagram. It was observed that the concentration of ammonia and nitrite in most of the samples in study area exceeded the permissible limit values prescribed by the national (China) and international (WHO) drinking water guidelines. Anthropogenic activities have been shown to be largely responsible for groundwater contamination. Scatter diagrams and factor analysis suggest that natural weathering processes, along with anthropogenic activities, control the hydrogeochemistry of groundwater. On the basis of the analytical results of the 49 groundwater samples as compared to water quality standards, it was found that majority of groundwater samples were not suitable for drinking or for industrial uses directly. Toxic metals and high levels of ions must be removed to render the groundwater suitable for drinking and industrial purposes. However, salinity, sodium adsorption ratio (SAR), residual sodium carbonate (RSC) and sodium percentage (Na%) values indicate that most of groundwater samples were suitable for irrigation purposes.

Impact of Cosmic-Ray Feedback on Accretion and Chemistry in Circumstellar Disks

Abstract We use the gas-grain chemistry code uclchem to explore the impact of cosmic-ray feedback on the chemistry of circumstellar disks. We model the attenuation and energy losses of the cosmic rays as they propagate outward from the star and also consider ionization due to stellar radiation and radionuclides. For accretion rates typical of young stars of M ⊙ yr−1, we show that cosmic rays accelerated by the stellar accretion shock produce an ionization rate at the disk surface ζ ≳ 10−15 s−1, at least an order of magnitude higher than the ionization rate associated with the Galactic cosmic-ray background. The incident cosmic-ray flux enhances the disk ionization at intermediate to high surface densities (Σ > 10 g cm−2), particularly within 10 au of the star. We find that the dominant ions are C+, S+, and Mg+ in the disk surface layers, while the ion dominates at surface densities above 1.0 g cm−2. We predict the radii and column densities at which the magnetorotational instability (MRI) is active in T Tauri disks and show that ionization by cosmic-ray feedback extends the MRI-active region toward the disk midplane. However, the MRI is only active at the midplane of a minimum-mass solar nebula disk if cosmic rays propagate diffusively (ζ ∝ r −1) away from the star. The relationship between accretion, which accelerates cosmic rays, the dense accretion columns, which attenuate cosmic rays, and the MRI, which facilitates accretion, creates a cosmic-ray feedback loop that mediates accretion and may produce variable luminosity.

Quantifying depression trapping effect on rainwater chemical composition during the rainy season in karst agricultural area, southwestern China

Atmospheric wet deposition is a vital part of biogeochemical cycles in earth surface environment systems, which is not only controlled by local sources and long-range transported continental substances from natural and anthropogenic sources, but also potentially influenced by the topographical features (e.g. peak clusters and depressions in karst areas). To investigate the depression trapping effect of vertical distribution of rainwater chemical composition and evaluate the effect of trapping by depression on wet deposition flux, rainwater samples from two sites (HR, a hilltop shrubbery area, and LR, inside a depression paddy field area) of a karst agricultural depression in Southwest China, were collected during the rainy season. From these, the major ionic concentrations were measured. The results indicated a variance in pH from 4.8 to 6.4 with a volume-weighted mean (VWM) value of 5.7 at the HR, and, a range of 5.4–6.9 with a VWM of 6.0 at the LR. The VWM concentrations of ions were decreased in the order of SO42- > NH4+ > Ca2+ > NO3- > Mg2+ > K+ > Na+ > Cl− > F− at both sites, and were dominated by SO42-, NH4+, Ca2+, and NO3-, accounting for >87% of the total ions at the two sites. The result of fractional acidity (FA) and neutralization factors (NF) revealed that the relatively high pH values were the result of neutralization of the alkaline substances (NH4+ and Ca2+) rather than the scarcity of acidic materials. Source analysis of major ions showed that anions were predominantly controlled by anthropogenic emission, while cations originated from both terrestrial sources and anthropogenic activity. The vertical distribution of dominant ions (NH4+, NO3-, Ca2+, Mg2+, and SO42-) were ascribed to the relatively weak air convection movement within the depression area (specific atmospheric circulations) and the differences in human interference at two sites (LR, cultivated land; HR, luxuriant vegetation). This is further supported by the more negative rainwater δ15N–NO3- values (−8.5 to −6.0‰), in LR than that in HR (−6.2 to −3.4‰). The depression trapping effect could significantly affect the estimation of wet deposition fluxes (up to 80.6% for Ca2+ and 68.7% for NH4+), which requires consideration in future studies, e.g. N wet deposition.

Mass-Transport Resistances of Acid and Alkaline Ionomer Layers: A Microelectrode Study Part 1 - Microelectrode Development

One of the most critical issues limiting widespread commercialization of polymer-electrolyte fuel cells is catalyst cost, which is directly related to dominant unexplained local gas and ion transport resistances at low catalyst loading (1). These resistances are believed to be highly correlated to the ionomer thin films in the catalyst layer. Unfortunately, current understanding of transport resistances in the catalyst layer is largely inferred from limiting current experiments employing heterogeneous, complex and multi-interfaced membrane electrode assemblies. An alternative study providing a more localized probe and promising fundamental insight is the microelectrode method (2). Ionomer thin film-coated microelectrodes can simulate an idealized thin film operating condition similar to that found at the platinum/ionomer interface in the catalyst layer of a typical fuel cell. In this work, an in-house, custom-made microelectrode setup with good humidity, temperature and potential control is used to determine the transport coefficient of hydrogen and oxygen gas across the ionomer thin film layer. The set-up is also capable of examining gas transport and evaluating the impact of ion activity on electrochemical kinetics in both acid and alkaline conditions, making it ideal for expanded understanding of gas and ion transport in both polymer electrolyte membrane and alkaline anion exchange fuel cells, respectively. A. Z. Weber and A. Kusoglu, J. Mater. Chem. A., 2, 17207 (2014).D. Novitski and S. Holdcroft, ACS Appl. Mater. Interfaces, 7, 27314 (2015). Acknowledgements: This study was partially funded under the Fuel Cell Performance and Durability Consortium (FC-PAD) funded by the Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U.S. Department of Energy under contract number DE-AC02-05CH11231.

Seasonal controls of meltwater runoff chemistry and chemical weathering at Urumqi Glacier No.1 in central Asia

AbstractTemporal variation of runoff chemistry and its seasonal controls relating to chemical weathering processes and drainage system evolution were examined at Urumqi Glacier No.1 in Xinjiang, China, over a full melt season. The dominant ions in meltwater runoff are HCO3−, Ca2+, and SO42−; and Fe, Sr, and Al are dominant elements. Concentrations of major ions and some elements show periodic variations with seasons and negatively correlate with discharge, whereas other elements (e.g., Al, Ni, Cu, Zn, Cd, and Pb) show a random change, providing insights into the hydrological and physicochemical controls. HCO3− and Ca2+ are primarily derived from calcite, SO42− and Fe mainly come from pyrite, and Sr and Al principally originate from silicate. Hydrochemical fluxes of solutes exhibit strong seasonality but are positively related to discharge, suggesting an increasing release of solutes during higher flow conditions. Solute yields, cation denudation rate, and chemical weathering intensity observed at Urumqi Glacier No.1 are higher than those at most basins worldwide. This suggests that chemical weathering in central Asia may be stronger than at other glacial basins with similar specific discharge. Concentrations of some elements (e.g., Fe, Al, As, Pb, and Zn) are close to or exceed the guidelines for drinking water standards in meltwater‐fed rivers. These rivers may face future challenges of water quality degradation, and relationships between changing flow and water quality conditions should be established soon, given that development of channelized flow is expected to be earlier over a melt season in a warming climate.

THE ASSESSMENT OF IRRIGATIONAL QUALITY OF SURFACE WATERS IN EL TARF AREA, ALGERIA

Wadi Bounamoussa, located in El Tarf (the extreme Northeast Algerian) which has an agricultural vacation. During two seasons (winter and summer), the sampling of surface waters of nine stations along wadi Bounamoussa is analyzed.In order to evaluate preliminarily the pollution of surface water, the study methodology carried out in order to check the current state of water chemistry, its evolution over time and in space depending on the variation of the physicochemical parameters of the water. The results of the physicochemical analyses of the waters samples of our study area shows that are very poor in soluble and moderately mineralized and accentuated with a neutral appearance require certain precautions such as leaching, which can reduce the yield of sensitive plants and cause slow salinization of the soil hence the need for this research. We got the same order of abundance decreasing for both seasons as follows : Na+> Ca+2 > Mg+2> K+and Cl-> SO4-2> NO3-> NO2-with absence of carbonates and bicarbonates. The use of graphical water diagrams made it possible to define the dominant ions responsible for the chemical facies of waters and the geological formations at the origin of these facies.The results of the statistical analysis confirm those obtained in the laboratory and reveal, firstly a variability between intra-period stations (inter-site), and secondly, a potential variability between the two periods (inter-period variability). The physicochemical characteristics of this surface water show that it is appropriate to irrigation and agriculture.

ULF Waves Modulating and Acting as Mass Spectrometer for Dayside Ionospheric Outflow Ions

AbstractIonospheric outflow has been shown to be a dominant ion source of Earth's magnetosphere. However, most studies in the literature are about ionospheric outflow injected into the nightside magnetosphere. We still know little about ionospheric outflow injected into the dayside magnetosphere and its further energization after it enters the magnetosphere. Here, with data from Magnetospheric Multiscale mission, we report direct observations of the modulation of dayside ionospheric outflow ions by ultralow frequency (ULF) waves. The observations indicate that the modulation is mass dependent, which demonstrates the possibility of using ULF waves as a mass spectrometer to identify ion species. Moreover, the measurement suggests that polarization drift may play a role in O+ modulation, which may lead to a true acceleration and even nonadiabatic behavior of O+. This interaction scenario can work throughout the whole magnetosphere and impact upon the plasma environment and dynamics.

Fast Ion Transport in the Three-Dimensional Reversed-Field Pinch.

We report on the first comprehensive experimental and numerical study of fast ion transport in the helical reversed-field pinch (RFP). Classical orbit effects dominate the macroscopic confinement properties. The strongest effect arises from growth in the dominant fast ion guiding-center island, but substantial influence from remnant subdominant tearing modes also plays a critical role. At the formation of the helical RFP, neutron flux measurements indicate a drastic loss of fast ions at sufficient subdominant mode amplitudes. Simulations corroborate these measurements and suggest that subdominant tearing modes strongly limit fast ion behavior. Previous work details a sharp thermal transport barrier and suggests the helical RFP as an Ohmically heated fusion reactor candidate; the enhanced transport of fast ions reported here identifies a key challenge for this scheme, but a workable scenario is conceivable with low subdominant tearing mode amplitudes.