Sulfate Enrichment Research Articles

Interplay between denitrifying and sulfate-reducing bacterial communities under acid mine drainage stress

Acid mine drainage (AMD) pollution leads to the enrichment of sulfate in paddy soil. The interplay between denitrifying and sulfate-reducing bacteria across varying soil depths, and their response to AMD pollution is not yet fully understood. The responses of denitrifying and sulfate-reducing bacteria(SRB) to AMD pollution were analyzed by collecting soil samples at four depths (0–10 cm, 10–20 cm, 20–40 cm, 40–60 cm) under two treatments (AMD-polluted and control soil). AMD pollution resulted in a significant decrease in pH value, elevated SO42- and metal concentrations. Compared to the control soil, denitrifying and sulfate-reducing bacteria in AMD-polluted soils were more sensitive to environmental fluctuations. Co-occurrence analysis revealed that there were more microbiological linkages and nodes in control soil than in polluted soil. Denitrifying and sulfate-reducing bacteria can maintain part of N and S cycle under long-term AMD pollution by increasing the negative correlation in ecological network. Desulfobacca exhibited a positive correlation with nitrate and held a significant position in the symbiotic network, suggesting its potential important role in inhibiting nitrogen loss. This study revealed the intricate ecological network of functional communities, which could have important implications for environmental management and the development of sustainable agricultural practices in areas affected by AMD pollution.

Melt Inclusions in an Aplite Vein in Granodiorite of the Lusatian Massif: Extreme Alkali Sulfate Enrichment

Melt Inclusions in an Aplite Vein in Granodiorite of the Lusatian Massif: Extreme Alkali Sulfate Enrichment

Sulfate enrichment in estuaries of the northwestern Gulf of Mexico: The potential effect of sulfide oxidation on carbonate chemistry under a changing climate

AbstractWater quality parameters from 2000 to 2020 were used to identify the spatial and temporal sulfate variations in estuaries of the northwestern Gulf of Mexico. Sulfate enrichment relative to conservative mixing was found to be associated with a low river discharge period from 2012 to 2014 in all estuaries. Based on reaction stoichiometry, sedimentary sulfide oxidation holds significant potential for reducing the alkalinity in estuarine waters. However, during this extreme drought, alkalinity enrichment was also occasionally observed in some of the southern estuaries along with sulfate enrichment, and when alkalinity depletion occurred, the magnitude of depletion was usually much less than what would be expected based on sulfide oxidation alone. This discrepancy can be partially explained by carbonate dissolution and other proton removal pathways (e.g., Fe‐oxide dissolution), and by the uncertainties in the model used to estimate alkalinity enrichment/depletion. Under a changing climate, the close coupling between river discharge variation and estuarine sulfate dynamics will significantly impact estuarine carbonate chemistry.

Enrichment of Sulfate, Acidity and Mercury in Native outcropcoal, Southwest China.

The coal found in the Longtan Formation of the Late Permian is widely distributed in Southwest China, including the northwestern Guizhou, southeastern Sichuan, and northern Yunnan regions. This coal typically has a high sulfur content. Eighty-two coal samples were collected from the coal strata in 11 counties spanning this area, including underground mine coal, native outcrop coal and man-made outcrop coal. The mercury, total fluorine, total sulfur, and sulfate contents and pH values were determined. The results showed that the average mercury content in native outcrop coal was 2233ng/g, whereas that in underground mine coal was 306ng/g, and the relative enrichment factor could reach 6.6. There was no significant difference in the total fluorine content among the three types of coals; furthermore, the total sulfur content in native outcrop coal and man-made outcrop coal was higher than that in underground mine coal because of the local policy, which strictly prohibits the mining of high-sulfur coal. Native outcrop coal is acidic, with a total average pH of 3.54 and an average sulfate content as high as 13,390μg/g. In contrast, underground coal is almost neutral (average pH 7.33), with a low sulfate content (average 3221μg/g). These characterizations indicate that native outcrop coal has been subjected to long-term weathering and the mercury enrichment is likely due to migration, oxidation, and precipitation of Hg from the underground coal seam and enriched in loose and pulverized coal particles. Further investigation is needed to determine whether other outcrop areas are affected by this phenomenon.

Four decades of regional wet deposition, local bulk deposition, and stream-water chemistry show the influence of nearby land use on forested streams in Central Appalachia

Hydrologic monitoring began on two headwater streams (<1 km2) on the University of Kentucky's Robinson Forest in 1971. We evaluated stream-water (1974–2013) and bulk-deposition (wet + dust) (1984–2013) chemistry in the context of regional wet-deposition patterns that showed decreases in both sulfate and nitrate concentrations as well as proximal surface-mine expansion. Decadal time steps (1974–83, 1984–93, 1994–2003, 2004–2013) were used to quantify change. Comparison of the first two decades showed similarly decreased sulfate (minimum flow-adjusted annual-mean concentration of ≈13.5 mg/L in 1982 to 8.8 mg/L in 1992) and increased pH (6.6–6.8) in both streams, reflecting contemporaneous changes in both bulk and wet deposition. In contrast, concentrations of nitrate (0.14 to >0.25 mg/L) and base cations increased between these two decades, coinciding with expansion of surface mining between 1985 and 1995. In 2004, stream-water pH (6.7 in 2004), sulfate (9.2 mg/L), and nitrate (>0.11 mg/L) were similar to 1982, despite wet-deposition concentrations being lower. Base-cation concentrations were higher in the stream adjacent to ongoing surface mining relative to the stream situated near the middle of the experimental forest. However, pH decreased to approximately 5.7 by 2013 for both streams, which, combined with a shift in dominant cations from calcium to magnesium and potassium, indicates that the soil-buffering capacity of this landscape has been exceeded. Ratios of bulk deposition and stream-water concentrations indicate enrichment of sulfate (1.7–25.2) and cations (0.5–64.8), but not nitrogen (0.1–5.6), indicating that the Forest is not nitrogen saturated and that ongoing changes in water-quality are sulfate driven. When concentrations were adjusted to account for changes in streamflow (climate) over the 4 decades, external influences (land management/regulation) explained most change. The amount and direction of change differed among constituents, both between consecutive decades and between the first and last decades, reflecting the influence of localized surface mining even as regional wet deposition continued to improve due to the Clean Air Act. The implication is that localized stressors have the potential to out-pace the benefits of national environmental policies for communities that depend on local water-resources in similar environments.

Tracing Sulfate Source and Transformation in the Groundwater of the Linhuan Coal Mining Area, Huaibei Coalfield, China.

Mining activities cause surface sulfate enrichment, which has negative impacts on human health and ecosystems. These high concentrations of sulfate may enter groundwater through the unsaturated zone (UZ), threatening groundwater quality. Therefore, we combined hydrochemical and dual isotopic analyses of sulfate in surface water, soil water and groundwater with evaluations of the UZ to identify the groundwater sulfate source and transformation in the coal mining area. Soil profile samples were collected near gangue heaps (UZ-1, UZ-2) and the mean sulfate concentrations of the UZ-1 profile and UZ-2 profile were 35.4 mg/L and 69.63 mg/L, respectively. The shallow groundwater sulfate was mainly from dissolution of evaporite, sulfide oxidation and sewage. Different sulfate contaminated areas showed different characteristics of sulfate sources. The sulfate source to groundwater near the coal gangue heaps was sulfide oxidation. The groundwater sulfate near the gangue heaps and industrial park compound contamination area was mainly derived from industrial and domestic sewage and sulfide oxidation. In addition, the role of bacterial sulfate reduction (BSR) in the groundwater was not obvious. This research result is of great significance for promoting the safe mining of coal resources and sustainable utilization of groundwater in the Huaibei coal mining area and other coal mining areas in China.

Hydrogeochemistry mechanism contrasts between low and high sulfate in limestone aquifers at the massive coalfield in Anhui province, China

Abstract High sulfate mine groundwater at the Huaibei coalfield has exceeded the permissible limit (250 mg/l) of World Health Organization, posing serious threat to nearby water resource. A total of 28 samples were collected from Taiyuan formation aquifer (TA) and Ordovician aquifer (QA). In view of the mean concentration in two aquifers, the TA and OA were identified as high sulfate group and low sulfate group. The contrast on hydrochemical characterization and water-rock interactions were analyzed to reveal the mechanism of sulfate enrichment in mine groundwater. Compared with low sulfate groundwater, the high sulfate groundwater possess a higher content of TDS, Na+ and Cl−, which elevated by 3.83, 4.0 and 3.29 times, respectively. The low sulfate groundwater is controlled by Ca-Na-HCO3 type (82%), whereas the high sulfate groundwater is dominated by Na-SO4-HCO3 type (88%). The geochemical process of low sulfate groundwater is influenced by dissolution of carbonate minerals and weak ion exchange. The mechanism of sulfate enrichment in mine groundwater are predominately controlled by both silicate and carbonate minerals weathering, strong ion exchange interaction and competitive effect. The outcomes enhance understanding of the mechanism of high sulfate mine water and provide theoretical support for mine wastewater treatment. HIGHLIGHTS Hydrogeochemistry mechanism contrasts between low and high sulfate in limestone aquifers were studied. Water environment for high sulfate mine groundwater was revealed from comparative analysis with low sulfate mine groundwater. Corresponding minerals dissolution dominated the hydro-chemistry process together with ion exchange and competitive effect.

PM2.5 in Carlsbad Caverns National Park: Composition, sources, and visibility impacts

ABSTRACT Carlsbad Caverns National Park in southeastern New Mexico is adjacent to the Permian Basin, one of the most productive oil and gas regions in the country. The 2019 Carlsbad Caverns Air Quality Study (CarCavAQS) was designed to examine the influence of regional sources, including urban emissions, oil and gas development, wildfires, and soil dust on air quality in the park. Field measurements of aerosols, trace gases, and deposition were conducted from 25 July through 5 September 2019. Here, we focus on observations of fine particles and key trace gas precursors to understand the important contributing species and their sources and associated impacts on haze. Key gases measured included aerosol precursors, nitric acid and ammonia, and oil and gas tracer, methane. High-time resolution (6-min) PM2.5 mass ranged up to 31.8 µg m−3, with an average of 7.67 µg m−3. The main inorganic ion contributors were sulfate (avg 1.3 µg m−3), ammonium (0.30 µg m−3), calcium (Ca2+) (0.22 µg m−3), nitrate (0.16 µg m−3), and sodium (0.057 µg m−3). The WSOC concentration averaged 1.2 µg C m−3. Sharp spikes were observed in Ca2+, consistent with local dust generation and transport. Ion balance analysis and abundant nitric acid suggest PM2.5 nitrate often reflected reaction between nitric acid and sea salt, forming sodium nitrate, and between nitric acid and soil dust containing calcium carbonate, forming calcium nitrate. Sulfate and soil dust are the major contributors to modeled light extinction in the 24-hr average daily IMPROVE observations. Higher time resolution data revealed a maximum 1-hr extinction value of 90 Mm−1 (excluding coarse aerosol) and included periods of significant light extinction from BC as well as sulfate and soil dust. Residence time analysis indicated enrichment of sulfate, BC, and methane during periods of transport from the southeast, the direction of greatest abundance of oil and gas development. Implications: Rapid development of U.S. oil and gas resources raises concerns about potential impacts on air quality in National Parks. Measurements in Carlsbad Caverns National Park provide new insight into impacts of unconventional oil and gas development and other sources on visual air quality in the park. Major contributors to visibility impairment include sulfate, soil dust (often reacted with nitric acid), and black carbon. The worst periods of visibility and highest concentrations of many aerosol components were observed during transport from the southeast, a region of dense Permian Basin oil and gas development.

The transformation and enrichment of rare earth sulfate in Bayan Obo ore water leaching solution by dibenzyl phosphate based extraction-precipitation method

Chemical precipitation and solvent extraction have been widely used to transform rare earth (RE) sulfate into RE chloride in the field of hydrometallurgical process for monazite and bastnaesite, but there are some industrial challenges such as consuming a large amount of chemical reagents and producing wastewater. As for the transformation field of RE sulfate liquor, the development of sustainable and efficient transformation technology is an important industrial challenge. In this study, one step transformation and enrichment of RE sulfate into RE chloride using dibenzyl phosphate (DBP), diphenyl phosphate (DPP), triphenyl phosphate (TPP), diphenylphosphinic acid (DPPO) and 1,1′-binaphthyl-2,2′-diylhydrogenphosphate (DHGP) was studied. Unlike common solvent extraction, volatile organic solvents are not required in the extraction-precipitation processes. Different from the common chemical precipitation, the extraction-precipitants can be recycled. The investigation shows that DBP has a higher precipitation efficiency of RE than those of DPP, DPPO, TPP and DHGP. RE can be selectively separated from Mg and Ca by DBP. After stripping with concentrated hydrochloric acid, a high-concentration rare earth chloride solution of 187 g/L is obtained. This new method is easy to be implemented and has shown the potential of saving resources and protecting the environment.

A comprehensive insight on the impact of individual ions on Engineered Waterflood: With already strongly water-wet sandstone

Engineered Waterflood (EWF) has drawn increasing attention as an emerging economic-friendly technique. However, the underlying mechanisms still remain ambiguous. Wettability alteration has been claimed as the main reason to the additional oil recovery by EWF. In contrast, limited work was devoted to investigate the contribution of fluid-fluid interaction. To fill this gap, in the study, strongly water-wet rock samples (artificial clay-free sandstones) were used to minimize wettability alteration, thereby highlighting the fluid-fluid interaction. A high-salinity single-component NaCl solution (100 kppm) was used as a base line; three low salinity (1 kppm) brines (i.e., NaCl, CaCl2 and Na2SO4) were adopted in our experiments to explore the effect of brine salinity and ion types. Moreover, an offshore heavy oil was chosen in our study to emphasize fluid-fluid interfacial response. First, secondary EWFs were conducted to demonstrate the brine chemistry effect on core scale. Subsequently, oil/brine interfacial properties including IFT and IVE were analyzed at the interfacial film scale. Thereafter, visible micromodel experiments were performed to manifest the fluid-fluid interaction on pore-scale displacement events. On the other hand, zeta potential measurements along with the disjoining pressure isotherm calculation by the extended-DLVO theory were used to study the rock-fluid interaction. Our results show that both low salinity and the sulfate enrichment increase the interfacial visco-elasticity, which hinders the microscopic displacement events of both snap-off and coalescence. In addition, as engineered water is injected at secondary mode, the overall oil continuity is primarily improved by suppressing snap-off. Additionally, disjoining pressure calculation reveal that a lower brine salinity and an enrichment of sulfate can decrease the attraction force between oil and rock, imparting a lubricating effect on the flow of crude oil. Therefore, this work has shed light on EWF mechanisms by considering both fluid-fluid and fluid-rock interactions from multi-scales. It also clarifies the effect of sulfate on EWF in sandstone, unlike previous studies that mainly evaluated the performance of sulfate in carbonate.

Groundwater Hydrogeochemical Mechanisms and the Connectivity of Multilayer Aquifers in a Coal Mining Region

Multiple runoff connections for groundwater supply and water quality evolution mechanisms were disclosed using hydrochemistry, multivariate statistics, stable hydrogen and oxygen isotopes, and inverse hydrogeochemical modeling in a multi-layer groundwater system in a north China coal-mining district. Groundwater quality was mainly influenced by dissolution and weathering of carbonate, silicate, gypsum, halite, and fluorite, as well as cation exchange. Sulfate enrichment in the Carboniferous limestone aquifer may be due to pyrite oxidation, while gypsum dissolution and sewage contribute sulfate to the Quaternary alluvium. The Ordovician limestone groundwater is hydraulically connected to the other two aquifers. Incongruent dissolution of dolomite occurs when the Ordovician limestone water contacts the Carboniferous aquifer, while evaporation occurs when the Ordovician limestone water migrates upward through fractures to the Quaternary aquifer.

Performance damage characteristics of asphalt mixture suffered from the sulphate–water–temperature–load coupling action

ABSTRACT In order to evaluate the macro-mechanical performance of asphalt mixture suffered from the sulphate–water–temperature–load coupling action, the self-designed asphalt mixture dynamic water–salt attack apparatus was adopted for the accelerated simulation of real service conditions in sulphate enrichment environment. Splitting test at room temperature and low temperature was conducted for assessing the performance of asphalt mixture suffered from still water immersion and multi-factor coupling action. Then the performance damage characteristics of asphalt mixture under different conditions were explored. The multi-linear regression analysis and t-test were applied to determine the significance of factors on the performance of asphalt mixture. The performance deterioration mechanism of asphalt mixture exposed to dynamic water and sulphate attack was preliminarily analysed. The results show that the sulphate–water–temperature–load coupling action plays an important role in the macro-mechanical performance deterioration of asphalt mixture and dynamic water further accelerates the deterioration process of sulphate attack to asphalt mixture. The dynamic water scouring times, temperature and sulphate solution concentration have a significant impact on the performance of asphalt mixture. The decreasing adhesion between asphalt and aggregate, along with exterior/interior sulphate crystallisation erosion contributes the important inducement for the performance deterioration of asphalt mixture.

Superior energy-saving catalyst of Mn@ZIF67 for reclaiming byproduct in wet magnesia desulfurization

Catalyst for sulfite oxidation can substantially reduce the energy penalty on reclaiming the byproduct in wet magnesia desulfurization. Here we reported a novel self-assembled bimetallic catalyst, being accomplished by the in situ incorporation of Mn metal into the metal organic framework (MOF) structure to constitute Mn@ZIF-67. The ultrahigh performance of Mn@ZIF-67 was attributed to its unique hollow structure and exposed active Co sites in the organic skeleton, allowing sufficient contact and diffusion of the reactants. Meanwhile, doping Mn in the MOF skeleton favored to enhance the interaction between Co and sulfite, thus promoting sulfite oxidation by 8.6-folder compared with un-catalysis. The critical mass concentration of magnesium sulfate was increased from 10% to 25%, thus reducing the heat consumption by approximately 75% for sulfate enrichment prior to crystallization. This study serves to cap the oxidation rate of sulfite in wet desulfurization, thus enabling the feasibility to reduce the energy penalty.

In situ S-isotope compositions of sulfate and sulfide from the 3.2 Ga Moodies Group, South Africa: A record of oxidative sulfur cycling.

Sulfate minerals are rare in the Archean rock record and largely restricted to the occurrence of barite (BaSO4 ). The origin of this barite remains controversially debated. The mass-independent fractionation of sulfur isotopes in these and other Archean sedimentary rocks suggests that photolysis of volcanic aerosols in an oxygen-poor atmosphere played an important role in their formation. Here, we report on the multiple sulfur isotopic composition of sedimentary anhydrite in the ca. 3.22Ga Moodies Group of the Barberton Greenstone Belt, southern Africa. Anhydrite occurs, together with barite and pyrite, in regionally traceable beds that formed in fluvial settings. Variable abundances of barite versus anhydrite reflect changes in sulfate enrichment by evaporitic concentration across orders of magnitude in an arid, nearshore terrestrial environment, periodically replenished by influxes of seawater. The multiple S-isotope compositions of anhydrite and pyrite are consistent with microbial sulfate reduction. S-isotope signatures in barite suggest an additional oxidative sulfate source probably derived from continental weathering of sulfide possibly enhanced by microbial sulfur oxidation. Although depositional environments of Moodies sulfate minerals differ strongly from marine barite deposits, their sulfur isotopic composition is similar and most likely reflects a primary isotopic signature. The data indicate that a constant input of small portions of oxidized sulfur from the continents into the ocean may have contributed to the observed long-term increase in Δ33 Ssulfate values through the Paleoarchean.

Modeling wettability change in sandstones and carbonates using a surface-complexation-based method

After testing proposed models in the literature on sandstones and carbonates, we propose a mechanistic surface-complexation-based model that quantitatively describes observations for ionically treated waterfloods. We model wettability change by directly linking wettability to brine chemistry using detailed colloidal science. Brine has charged ions that interact with polar acidic/basic components at the oil-water interface and rock surface and therefore oil/brine and rock/brine interfaces are charged and exert both Van der Waals and electrostatic forces on each other. If the net result of the forces is repulsive, the thin water film between the two interfaces is stable (i.e., the rock is water-wet) otherwise, the thin water film is unstable and the rock becomes oil-wet. We describe a ratio of electrostatic force to Van der Waals force with a dimensionless group, called “wetting film stability number,” where rock wettability is water-wet for values greater than one and oil-wet for values less than one. For sandstones, the zeta potentials of oil/brine and rock/brine interfaces become more negative/less positive by diluting or softening the brine and/or increasing pH. Similarly, for carbonates, dilution and/or sulfate enrichment of brine makes surface potentials more negative. Such brine modification can therefore be used to improve oil recovery. We implemented the improved wettability change model in a comprehensive coupled reservoir simulator, UTCOMP-IPhreeqc, in which oil/brine and rock/brine zeta potentials are modelled using the IPhreeqc surface complexation module. Surface potentials obtained from the geochemical model are used to calculate the dimensionless group controlling wettability change, which is dynamically modelled in the transport simulator. The model is validated in sandstones and carbonates by simulating an inter-well test, and several corefloods and imbibition tests reported in the literature. For sandstones, we model Kozaki (2012) and BP's Endicott trial. For simple dilution in carbonates we model experiments by Shehata et al. (2014) and Yousef et al. (2010). For enrichment with sulfate we model Zhang and Austad (2006) and for increasing total ionic strength via sodium chloride enrichment, Fathi et al. (2010a).

Cool, alkaline serpentinite formation fluid regime with scarce microbial habitability and possible abiotic synthesis beneath the South Chamorro Seamount

South Chamorro Seamount (SCS) is a blueschist-bearing serpentinite mud volcano in the Mariana forearc. Previous scientific drilling conducted at SCS revealed highly alkaline, sulfate-rich formation fluids resulting from slab-derived fluid upwelling combined with serpentinization both beneath and within the seamount. In the present study, a time-series of ROV dives spanning 1000 days was conducted to collect discharging alkaline fluids from the cased Ocean Drilling Program (ODP) Hole 1200C (hereafter the CORK fluid). The CORK fluids were analyzed for chemical compositions (including dissolved gas) and microbial community composition/function. Compared to the ODP porewater, the CORK fluids were generally identical in concentration of major ions, with the exception of significant sulfate depletion and enrichment in sulfide, alkalinity, and methane. Microbiological analyses of the CORK fluids revealed little biomass and functional activity, despite habitable temperature conditions. The post-drilling sulfate depletion is likely attributable to sulfate reduction coupled with oxidation of methane (and hydrogen), probably triggered by the drilling and casing operations. Multiple lines of evidence suggest that abiotic organic synthesis associated with serpentinization is the most plausible source of the abundant methane in the CORK fluid. The SCS formation fluid regime presented here may represent the first example on Earth where abiotic syntheses are conspicuous with little biotic processes, despite a condition with sufficient bioavailable energy potentials and temperatures within the habitable range.

Hydrogeochemical exploration for volcanic-hosted massive sulfide deposits in semi-arid Australia

ABSTRACTResearch on hydrogeochemistry for mineral exploration for inland Australia includes development of weathering models and extensive mine-scale and regional groundwater data. Mineral saturation indices for groundwater, activity–activity plots and reaction modelling simulate weathering of volcanic-hosted massive sulfide (VHMS) deposits in deeply weathered environments. At 10 m or more below surface, dissolved O2 is very low and other solutes such as sulfate, carbonate and nitrate are more likely oxidants. Modelling indicates that these processes differ from oxic weathering of highly eroded terrains, and provide the framework to develop robust hydrogeochemical exploration procedures in covered terrains. Sulfide weathering potentially occurs in two or more phases that effect surrounding groundwaters in differing manners. Deeper oxidative alteration of sulfides (e.g. bornite to chalcopyrite), occurring tens to hundreds of metres below surface, uses sulfate and carbonate as oxidants, causing neutral to alkaline conditions. In this zone, only pyritic massive sulfides potentially generate acidic conditions. Thus, deep sulfide-rich rocks are indicated by sulfate-depleted groundwater. Closer to the surface, sulfides are oxidised to soluble sulfates by dissolved nitrate, with much less acid production than if dissolved oxygen was the main oxidant. Thus, in shallow groundwater, sulfides are indicated by sulfate enrichment and nitrate depletion. Elements are released from sulfides and wall rocks by acid or alkaline conditions. The derived FeS (pH–Eh + Fe + Mn) and AcidS (Li + Mo + Ba + Al) indices distinguish sulfide systems through tens of metres of cover. VHMS systems are distinguished from other non-economic sulfide deposits where there is little transported cover, using various dissolved elements, including Zn, Pb and Cu. Elsewhere, ‘patchiness’ and limited aerial extent of metal signals are due to adsorption effects, that intensify with depth. Other elements such as Mn and Co have lesser diminution effects, but are less selective indicators for VHMS. There is exploration potential for elements such as Pt or Ag. These varying sulfide indicators have moderate utility, even for large-scale (∼5 km spacing) sampling. Results indicate that hydrogeochemistry can add value to greenfields exploration for VHMS ore deposits in deeply weathered terrains. It is also moderately successful at indicating the presence of sulfide-rich systems (whether magmatic or hydrothermal) under >100 m cover, thus providing a rapid and cost-effective regional prospectivity tool for deeply buried terrains. Such mineral exploration tools will encourage exploration investment for more difficult regions of Australia and in other deeply weathered regions of the world.

Irrigation water quality and the threat it poses to crop production: evaluating the status of the Crocodile (West) and Marico catchments, South Africa.

Ensuring food security is becoming increasingly difficult due to limited freshwater resources. Low-quality irrigation water also poses a severe threat to crop yield and quality. The aim of this study was to evaluate the water quality associated with the Crocodile (West) and Marico catchments, which represent one of South Africa's most developed regions. Sources of irrigation water include the hypertrophic Hartbeespoort Dam, as well as the heavily impacted Crocodile (West) River. Analysis of historical irrigation water quality data (from January 2005 to December 2015) revealed that the Hartbeespoort and Crocodile (West) irrigation schemes were exposed to calcium sulfate enrichment, likely as a result of extensive mining activities in the Bushveld Igneous Complex. Also, significant differences in water quality parameters occurred between these irrigation schemes and the reference system (Marico-Bosveld Irrigation Scheme), while important salt (chloride and sodium) and nutrient (inorganic nitrogen and orthophosphate (as phosphorus)) concentrations exceeded threshold values provided by irrigation water quality guidelines. The Hartbeespoort and Crocodile (West) irrigation schemes also presented distinctive temporal (long-term and seasonal) patterns in water quality. Seasonal variation in pH levels at the Hartbeespoort Irrigation Scheme is likely caused by excessive algae growth and cyanobacteria blooms (Mycrocystis sp.), which also pose an important threat to human and animal health. Despite mitigation efforts by government and other stakeholders, some of South Africa's major irrigation schemes remain highly impacted as a result of water quality deterioration.

Electrospray surface-enhanced Raman spectroscopy (ES-SERS) for probing surface chemical compositions of atmospherically relevant particles

Abstract. We present electrospray surface-enhanced Raman spectroscopy (ES-SERS) as a new approach to measuring the surface chemical compositions of atmospherically relevant particles. The surface-sensitive SERS is realized by electrospraying Ag nanoparticle aerosols over analyte particles. Spectral features at v(SO42−), v(C–H) and v(O–H) modes were observed from the normal Raman and SERS measurements of laboratory-generated supermicron particles of ammonium sulfate (AS), AS mixed with succinic acid (AS ∕ SA) and AS mixed with sucrose (AS ∕ sucrose). SERS measurements showed strong interaction (or chemisorption) between Ag nanoparticles and surface aqueous sulfate [SO42−] with [SO42−]AS ∕ sucrose &gt; [SO42−]AS ∕ SA &gt; [SO42−]AS. Enhanced spectra of the solid AS and AS ∕ SA particles revealed the formation of surface-adsorbed water on their surfaces at 60 % relative humidity. These observations of surface aqueous sulfate and adsorbed water demonstrate a possible role of surface-adsorbed water in facilitating the dissolution of sulfate from the bulk phase into its water layer(s). Submicron ambient aerosol particles collected in Hong Kong exhibited non-enhanced features of black carbon and enhanced features of sulfate and organic matter (carbonyl group), indicating an enrichment of sulfate and organic matter on the particle surface.

Impacts of increasing salinity and inundation on rates and pathways of organic carbon mineralization in tidal wetlands: a review

To improve our understanding of the carbon cycling response to imminent sea-level rise and saltwater intrusions, we review the existing literature on the likely effects of the increasing salinity and inundation on organic carbon mineralization in tidal wetlands. Enhanced salinity and inundation will reduce the pool of the organic carbon substrate, but may expand that of microbes with strong capacities for carbon metabolism. Sulfate availability increases with the increasing salinity, while availability of other electron acceptors, e.g., oxygen, nitrate, ferric oxides, and carbon dioxide, could transiently increase but would ultimately fall with the increasing salinity and inundation. The changing electron acceptor pattern may result in microbial sulfate reduction predominating over other carbon mineralization pathways. Data derived from natural salinity and inundation gradients suggest clear negative effects of salinity and inundation on production rates or emission fluxes of carbon dioxide and methane. However, results for brackish wetlands are conflicting, probably due to their unique geographic location. Salinity and inundation exert their influence on organic carbon mineralization through sulfate enrichment, elevating ionic and osmotic stress and decreasing oxygen concentrations and redox conditions, among other biogeochemical changes. Future studies should address the combined effects of salinity and inundation on carbon biogeochemistry in low-level salinity tidal wetlands.