Surface Water Acidification Research Articles

Single-cell view of deep-sea microbial activity and intracommunity heterogeneity.

Microbial activity in the deep sea is cumulatively important for global elemental cycling yet is difficult to quantify and characterize due to low cell density and slow growth. Here, we investigated microbial activity off the California coast, 50-4000 m water depth, using sensitive single-cell measurements of stable-isotope uptake and nucleic acid sequencing. We observed the highest yet reported proportion of active cells in the bathypelagic (up to 78%) and calculated that deep-sea cells (200-4000 m) are responsible for up to 34% of total microbial biomass synthesis in the water column. More cells assimilated nitrogen derived from amino acids than ammonium, and at higher rates. Nitrogen was assimilated preferentially to carbon from amino acids in surface waters, while the reverse was true at depth. We introduce and apply the Gini coefficient, an established equality metric in economics, to quantify intracommunity heterogeneity in microbial anabolic activity. We found that heterogeneity increased with water depth, suggesting a minority of cells contribute disproportionately to total activity in the deep sea. This observation was supported by higher RNA/DNA ratios for low abundance taxa at depth. Intracommunity activity heterogeneity is a fundamental and rarely measured ecosystem parameter and may have implications for community function and resilience.

Predicting the Solubility of Mercury in Hydrocarbons

SummaryElemental mercury (Hg0) is a common trace contaminant associated with corrosion of infrastructure impacting exploration, production, and processing of commercial hydrocarbons. Presently lacking is a model for the quantitative prediction of Hg concentration in reservoir fluids, sufficiently reliable for process engineering applications and design of mitigation strategies to ameliorate the potential risk of Hg presence.In this paper, we present a thermodynamic equilibrium mineral-based model for predicting the solubility of mercury in hydrocarbons, Hg0(org), at in-situ reservoir conditions. The model is based on literature experimental data on the solubility of Hg0 in a mixture of alkanes, in equilibrium with Hg0, H2S, O2, cinnabar (HgS), and water. As the model inputs are based on the chlorite-pyrite-H2S model, its application should primarily be limited to clastic hydrocarbon-bearing reservoirs. A global data set of Hg in hydrocarbons reveals a remarkably strong association with the presence of humic coal in subsurface formations.Assuming that pure stoichiometric cinnabar (HgS) is stable at the reducing conditions typical of hydrocarbon reservoirs (i.e., aHgS = 1) results in an overestimation of Hg0(org) solubility by up to three orders of magnitude relative to globally reported concentrations of mercury in natural hydrocarbons. A statistically robust match between model and observed concentrations of Hg0(org) was achieved using an aHgS of 0.003, consistent with reported concentrations of Hg0 from pyrite (FeS2) in coals and hydrocarbon reservoirs. The model has been validated in a case study of reservoir Hg reported in the Gorgon North-1 well, North West Shelf (NWS), Australia.The dominant process of cinnabar precipitation is by oxidation, particularly in the near-surface environment where reduced Hg0-bearing hydrocarbons mix with shallow oxygenated or acidic surface waters. Such processes are typical of the environments where most downhole fluid samples are collected during drilling, sampling, and cleanup of exploration and development wells. This leads to the invariable conclusion that much of the particulate mercury species, specifically HgS, collected with hydrocarbon fluid samples, are metastable with respect to the dissolved Hg0(org) in hydrocarbons at reservoir conditions and should not be included in the estimation of total Hg (i.e., THg) in hydrocarbons.This hypothesis has been confirmed by an extended well test in the Minami-Nagaoka gas condensate field, where it was observed that Hg dissolved in produced water decreased to negligible levels over time, while the Hg0(org) in the condensate liquid reached a stable value like what the new Hg0(org) solubility model would predict for in-situ reservoir conditions.

Release of per- and polyfluoroalkyl substances (PFAS) from a waste management facility fire to an urban creek

This study examined the release of per- and poly fluoroalkyl substances (PFAS) into an urban freshwater stream and sediments due to a large-scale industrial fire in Melbourne, Australia. The fire occurred at an industrial warehouse which was illegally storing excessive amounts of unknown chemicals and industrial waste. The runoff of the waste and used firefighting foam was contained in the adjacent freshwater creeks. The concentration of 50 PFAS in freshwater samples and 16 PFAS in sediment samples were determined by HPLC-MS/MS. Of the fifty targeted PFAS in the freshwater samples, fluorotelomer sulfonates including (6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB or 6:2 FTSA-PrB; CAS NO:34455-29-3), Perfluorocarboxylates (PFCAs: C4-C12), Perfluoroalkane sulfonates (PFSAs: C4-C8) and perfluoroalkanesulfonyl fluorides including perfluorobutane sulfonamide (FBSA) were the most elevated PFAS. There were clear differences in ∑50PFAS mean concentrations detected on the day of the fire (3843 ng/L) relative to one month post fire (352 ng/L), indicating the effect of the fire on freshwater system. The concentration of ∑50PFAS at the point source was 3400 ± 324 ng/L on the day of the ignition and decreased significantly to 93 ±14 ng/L in the second campaign. This is the first study to document 6:2 FTAB and perfluorohexane sulfonamide (FHxSA; CAS NO 41997-13-1), perfluoro-4-methoxybutanoic acid (PFMBA; CAS NO 863090-89-5), perfluoro-3-methoxypropanoic acid (PFMPA; CAS NO 377-73-1), Hexafluoropropylene oxide dimer acid (HFPO-DA; CAS NO 13252-13-6), Nonafluoro-3,6-dioxaheptanoic acid (NFDHA; CAS NO 151772-58-6) and Perfluoro(2-ethoxyethane) sulfonic acid (PFEESA CAS NO 113507-82-7) in Australian surface waters. Only three PFAS were detected in the sediment samples which collected from five sites in the second campaign which could be negligible based on the detection. In the meanwhile, the concentration of PFAS were also compared to the available guideline values in Australia for freshwater, recreational water, and sediments. The analysed water samples indicated that PFOS contamination level might have a short-term risk to the aquatic organisms. Further monitoring is in need to evaluate the contamination and the long-term risk in freshwater and sediments in the region.

Control of the Remediation of Anoxic AMD Groundwater by Sulphate Reduction in a Subsoil Reactor

Groundwater containing high amounts of products of pyrite weathering as a consequence of lignite mining flows into receiving waters for a number of years. Iron hydroxides causing turbidity and silting will strongly affect the river Spree for many decades. In addition to liming acidic surface waters and the conventional treating of mine waters, microbial sulphate reduction of the inflowing anoxic AMD groundwater is tested for long-term remediation. During a pilot project at Lusatia / Germany, glycerin as a carbon source and nutrient solutions of N and P are infiltrated into an anoxic AMD groundwater stream by lances. Planning and operations were carried out based on the model as proposed below. Doi: 10.28991/HEF-2022-03-03-02 Full Text: PDF

Using Periphyton Assemblage and Water Quality Variables to Assess the Ecological Recovery of an Ecologically Engineered Wetland Affected by Acid Mine Drainage after a Dry Spell

The Grootspruit valley bottom wetland in South Africa, due to the impact of acid mine drainage (AMD) from an abandoned coal mine, was severely degraded before ecologically engineered interventions, as a passive treatment process, in 2014. The surface water flow of the wetland was redirected using concrete structures to enlarge the surface area of the wetland by 9.4 ha and to optimize passive treatment. Although the ecologically engineered interventions showed an improvement in water quality after the rewetting of the enlarged wetland areas, the 2016 drought had a devastating effect on the wetland’s water quality. Limited natural removal of metals and sulfate concentrations by the wetland occurred during the 2016 drought, when compared with the 2015 pre-drought conditions. This period showed higher concentrations of metals, sulfate (SO42−), and electrical conductivity (EC) associated with the acidic surface water. Of particular interest was an observation of a substantial shift in pollutant-tolerant algae species in the ecologically engineered wetland outflow between the years 2015 and 2016. During the dry spell period of 2016, the diatoms Gyrosigma rautenbachiae (Cholnoky), Craticula buderi (Brebisson), and Klebsormidium acidophilum (Noris) were observed at the outflow. The latter species were not observed during the wetland surveys of 2015, before the dry spell. From late 2017 onwards, after the drought, environmental conditions started improving. In 2018, periphyton indicator species and the surface water quality were comparable to the wetland’s recorded status pre-2016. The study revealed not only a regime shift, but also an ecological function loss during the drought period of 2016, followed by recovery after the dry spell. A distinct reduction in SO42−, sodium (Na), magnesium (Mg), EC, manganese (Mn), iron (Fe), silicon (Si), aluminum (Al), and pH, following the 2016 drought, highlights the utilization of water quality variables to not only assess the passive treatment responses of an ecologically engineered wetland, but also the progress relating to ecological recovery.

Removal of Disinfection By-Products Precursor (Humic Acid) by Graphene-Silica Composites

Graphene-silica (RGO-SiO2) was successfully synthesized by a simple hydrothermal method. The composites were used to study the adsorption properties of humic acid and disinfection by-product precursors in natural surface water. Compared with reduced graphene oxide (RGO), the specific surface area of the composites doped with silica (SiO2) increased by 31.2% to 259.43 m2/g. RGO-SiO2 could achieve 66.91% adsorption of humic acid (HA), while the maximum adsorption of HA on RGO-SiO2 reached 925.91 mg/g. The adsorption and removal rates of HA by RGO-SiO2 were significantly higher than those of RGO. The whole adsorption process was in accordance with the quasi-secondary kinetic model, the Langmuir isothermal adsorption model. RGO-SiO2 has good adsorption performance for organic matter of different water qualities. RGO-SiO2 has a better removal ability for hydrophobic organics than hydrophilic and nitrogenous organics. The adsorbent was reusable, and the organic removal efficiency of RGO-SiO2 decreased insignificantly after four cycles.

Soil acidification and loss of base cations in a subtropical agricultural watershed

Soil acidification along with base cations loss degrades soil quality and is a major environmental problem, especially in agroecosystems with extensive nitrogen (N) fertilization. So far, the rates of proton (H+) production and real soil acidification (loss of base cations) remain unclear in subtropical agricultural watersheds. To assess the current status and future risk of soil acidification in subtropical red soil region of China, a two-year monitoring was conducted in a typical agricultural watershed with upland, paddy fields, and orchards where high N fertilizers are applied (320 kg N ha−1 yr−1). H+ production, neutralization and base cations losses were quantified based on the inputs (rainwater, inflow of water, and fertilizer) and outputs (outflow of water, groundwater drainage, and plant uptake) of major elements (K+, Ca2+, Na+, Mg2+, Al3+, NH4+, NO3−, SO42−, Cl−, and H+). The result showed that total H+ production in the watershed was 5152 molc ha−1 yr−1. N transformation was the most important H+ source (68%), followed by excess plant uptake of cations (25%) and H+ deposition (7%). Base cations exchange and weathering of minerals (3842 molc ha−1 yr−1) dominated H+ neutralization, followed by SO42− adsorption (1081 molc ha−1 yr−1), while H+ and Al3+ leaching amounted to 431 molc ha−1 yr−1, only. These results state clearly that despite significant soil acidification, the acidification of surface waters is minor, implying that soils have buffered substantially the net H+ addition. As a result of soil buffering, there was abundant loss of base cations, whose rate is significantly higher than the previously reported weathering rate of minerals in red soils (3842 vs 230–1080 molc ha−1 yr−1). This suggests that the pool of exchangeable base cations is being depleted in the watershed, increasing the vulnerability of the watershed, and posing a serious threat to future recovery of soils from acidification.

Perfluoroalkyl acids (PFAAs) in urban surface water of Shijiazhuang, China: Occurrence, distribution, sources and ecological risks

It is extremely important to analyze the contaminative behaviors of Perfluoroalkyl acids (PFAAs) due to their serious threats to urban environments which are closely related to humans. Current study aimed to explore the distribution, source apportionment and ecological risk assessment of PFAAs in surface water from Shijiazhuang, China. The concentrations of ∑PFAAs ranged from 19.5 to 125.9 ng/L in the investigation area. Perfluorobutanesulfonic acid (PFBS) and perfluoropentanoic acid (PFPeA) were the predominant contaminants (mean value: 14.3 ng/L and 16.6 ng/L, respectively). The distribution of PFAAs according to geospatial analysis and hierarchical clustering analysis (HCA) showed that higher levels of ∑PFAAs were detected in the southern surface water of Shijiazhuang and there was a stepwise decrease from the wet season to the dry season. Furthermore, based on source apportionment, the dominant potential sources were found to be wastewater treatment plant (WWTP) effluents and industrial discharge. The risk quotients (RQs) revealed low ecological risks of all PFAAs for aquatic organisms in Shijiazhuang surface water. Collectively, this study provided basic data for regulatory strategies for controlling PFAA pollutions in urban surface water.

Sulfur accumulation in soil in a forested watershed historically exposed to air pollution in central Japan

Forest soils that have accumulated anthropogenic sulfur (S) as a result of historical air pollution may gradually or suddenly release inorganic sulfate either by desorption of inorganic sulfate or by mineralization of organic S, even after mitigation of previous air pollution. The release of inorganic sulfate from soil to surface water leads directly to watershed acidification. Thus, whether the organic S compounds that have accumulated in soils are resistant to microbial activity, due to formation of organo-mineral complexes, is essential information for management of forest soil ecosystem services. A nationwide air pollution monitoring survey by the Japanese Ministry of the Environment identified acidification of both surface water and soil in the Lake Ijira watershed of central Japan, presumably sourced from the Chukyo Industrial Area which lies upwind of the watershed. We compared the amount of S accumulated in the Ijira soils (Dystrudepts) with that in comparable soils in other watersheds in central Japan that were less affected by industrial air pollution. To determine how much mineral-associated organic S had accumulated in the Ijira soils, we measured pyrophosphate- extractable S. We used high-resolution x-ray fluorescence (HRXRF) spectroscopy with a double-crystal type high energy resolution spectrometer to estimate the oxidation states of both mineral-associated and free organic S. We also measured S isotope compositions to explore S dynamics in the soils. We found that more S had accumulated in the Ijira soils than in the comparable soils from other watersheds in central Japan. Concentrations of total S in the Ijira soils varied among soil horizons, reaching more than 1000 mg S kg−1 in some horizons. Mineral-associated organic S accounted for more than half of the total accumulated S. High-resolution x-ray fluorescence spectrum analyses showed that mineral-associated organic S was retained at both high and low oxidation states. The δ34S values of total S in the deeper horizons tended to be higher than those of the uppermost horizons of the Ijira soils and correlated positively with concentrations of extractable Al and Fe oxides (which characterize pedogenic minerals). Our results suggest that about half of total accumulated S in Ijira soils is stabilized in pedogenic minerals and the remainder comprises free organic S and adsorbed inorganic sulfates. There might have been repetitive mobilization and immobilization of S and the degraded organic S might have greater affinity with pedogenic minerals. Further, the ratio of total C to mineral-associated organic S correlated negatively with concentrations of extractable Al and Fe oxides, suggesting that organic S is more resistant to mineralization than organic C because S is preferentially associated with the pedogenic minerals. Monitoring of the chemical states of S compounds in soils historically exposed to air pollution is recommended to assist in prediction of the fate of the S compounds that have accumulated in them.

Vertical environmental gradient drives prokaryotic microbial community assembly and species coexistence in a stratified acid mine drainage lake

Acid mine drainage (AMD) lakes are typical hydrologic features caused by open pit mining and represent extreme ecosystems and environmental challenges. Little is known about microbial distribution and community assembly in AMD lakes, especially in deep layers. Here, we investigated prokaryotic microbial diversity and community assembly along a depth profile in a stratified AMD lake using 16S rRNA gene sequencing combined with multivariate ecological and statistical methods. The water column in the AMD lake exhibited tight geochemical gradients, with more acidic surface water. Coupled with vertical hydrochemical variations, prokaryotic microbial community structure changed significantly, and was accompanied by increased diversity with depth. In the surface water, heterogeneous selection was the most important assembly process, whereas stochastic processes gained importance with depth. Meanwhile, microbial co-occurrences, especially positive interactions, were more frequent in the stressful surface water with reduced network modularity and keystone taxa. The pH was identified as the key driver of microbial diversity and community assembly along the vertical profile based on random forest analysis. Taken together, environmental effects dominated by acid stress drove the community assembly and species coexistence that underpinned the spatial scaling patterns of AMD microbiota in the lake. These findings demonstrate the distinct heterogeneity of local prokaryotic microbial community in AMD lake, and provide new insights into the mechanism to maintain microbial diversity in extreme acidic environments.

The impacts of conifer afforestation and climate on water quality and freshwater ecology in a sensitive peaty catchment: A 25 year study in the upper River Halladale in North Scotland

Our study was driven by objections to afforesting the sensitive peaty headwaters of the River Halladale in Northern Scotland on the grounds that this would damage water quality and the local salmon fishery. Approval was given in 1995 for the planting to proceed on condition that monitoring was carried out to assess the effects of forest establishment and growth on water quality and ecology. The long-term data also allowed us to study the effects of climate on water quality.Stream turbidity, colour and DOC levels were unaffected by ploughing and drainage that preceded tree planting in 1996, indicating that good forestry practice measures were effective in limiting soil disturbance and transport of mobilised sediment to the watercourses. Nitrate and ammonium concentrations remained low following afforestation but Total P increased in response to a series of fertiliser applications over the proceeding 20 years. These increases were temporary and have had no impact on river ecological status; calculated phosphorus fluxes were low.Concerns over the potential for afforestation to increase surface water acidification were not borne out, even in the most acid-sensitive tributary. None of the acidity parameters increased over the course of the study and conditions in all watercourses remained suitable for supporting salmonid fish. Decreasing SO4 concentrations indicate an improvement in water quality due to reduced sulphur deposition, with no evidence of any afforestation or forest scavenging effect.Significant changes in streamwater acidity were seen after two hurricanes in winter 2011/12. Two sites showed a marked reduction in stream pH and aluminium, and a marked rise in Acid Neutralising Capacity (ANC), that lasted for a period of at least four years. These changes accorded with notable rises in base cation concentrations and turbidity, suggesting a temporary increase in mineral weathering, most likely caused by a localised land slip or bank collapse. Sea-salt inputs and soil ion-exchange reactions are also thought to have affected the response in streamwater chemistry.The water quality results correspond well with data from the fish and benthic invertebrate surveys, which showed that forestry operations and forest growth to age 24 years have had no adverse impact on population diversity or abundance with no evidence of deterioration in freshwater ecology over the time series. These findings will help inform future woodland expansion for multiple benefits, including within sensitive water catchments.

Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) in Surface Water of China: National Exposure Distributions and Probabilistic Risk Assessment.

This study presents a comprehensive application of the probabilistic risk assessment methodology for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), which are two types of perfluoroalkyl acids frequently studied in recent years. The exposure characteristics of PFOA and PFOS in Chinese surface water on a nationwide scale were summarized. Individual predicted no-effect concentration (PNEC) and the sensitivities for taxonomic groups of primary producers, invertebrates, and vertebrates were derived by the species sensitivity distributions method. Both hazard quotients (HQs) and joint probability curves were calculated to assess the risks to aquatic organisms. Among seven Chinese river basins, the mean concentrations of PFOA and PFOS in the Yangtze River Basin were the highest (58ng/L and 22ng/L, respectively), while the lowest concentrations (< 1ng/L) were in the Songhua River Basin. The acute PNEC value was 2.43mg/L for PFOA and 0.96mg/L for PFOS, and the chronic PNEC value was 0.0067mg/L for PFOA and 0.0012mg/L for PFOS, respectively. The sensitivities of different taxonomic groups revealed higher sensitivity of primary producers for PFOA and higher sensitivity of invertebrates for PFOS. The acute HQs of PFOA and PFOS were less than 1. The probabilities of exposure concentrations exceeding 5th percentile toxicity value of the chronic data for all aquatic organisms were 1.65% for PFOA and 1.23% for PFOS, respectively, suggesting a low probability of effects to aquatic organisms. Compared with the risk scenarios worldwide, the ecological risks for chronic effects decreased in the order of PFOS (worldwide) > PFOA (China) > PFOS (China) > PFOA (worldwide).

Trace analysis of resin acids in surface waters by direct injection liquid chromatography time of flight mass spectrometry and triple quadrupole mass spectrometry

A rapid and sensitive liquid chromatography (LC) quadrupole time of flight (QTOF) method has been developed for the determination of resin acid concentrations in aqueous pulp and paper effluent related samples. Calibration R2 of ≥0.995 for twelve resin acids, namely dehydroabietic, 8(14)-abietenic, dihydroisopimaric, levopimaric, neoabietic, pimaric, sandaracopimaric, abietic, isopimaric, palustric, chlorodehydroabietic, and dichlorodehydroabietic acids, was demonstrated in the range 1 µgL−1 to 40 µgL−1. An improved lower limit of quantitation was achieved without use of complex sample extraction and clean-up procedures undertaken by other published methods. Excellent precision and accuracy results were achieved for dehydroabietic, chlorodehydroabietic, dichlorodehydroabietic, isopimaric (integrated inclusive of all C20H30O2 resin acids), dihydroisopimaric and 8(14)-abietenic resin acids, with t-99 percentile detection limits spanning the range 0.05 to 0.07 µgL−1. While measurement for the C20H30O2 resin acids by isopimaric equivalence is considered semi-quantitative and could be an under estimate for the abietic acid component, the developed method demonstrated clear advantage over time consuming, hazardous, and unstable derivatization procedures used for gas chromatography and capillary electrophoresis. The developed LC/QToF method was successfully transferred to an LC triple quadrupole mass spectrometer for routine high throughput trace level analysis. Real world samples, including sea water and estuary water, demonstrated excellent spike recoveries by this procedure, indicating that the method is well suited to the monitoring of industrially derived resin acids in environmental surface waters. While no interferences were observed during routine sample analysis using myristic-1-13C acid and palmitic-1-13C acid internal standards, these were later substituted by myristic-d27 and palmitic-d31 acid in order to improve method robustness for environmental samples where endogenous parent fatty acids could be present.

Development, validation, and application of a new method for the quantitative determination of monohydrogen-substituted perfluoroalkyl carboxylic acids (H–PFCAs) in surface water

Per- and polyfluoroalkyl substances (PFASs) are a large and diverse class of chemicals. While some have been phased out internationally due to concerns over their human and environmental health risks, novel alternative PFASs continue to be manufactured and detected in environmental samples. The occurrence and fate of these alternatives remain poorly understood. The present study investigated the occurrence of an emerging class of PFAS alternative, the monohydrogen-substituted perfluoroalkyl carboxylic acids (H–PFCAs), in conjunction with the more well-known PFCAs. A weak anion exchange solid phase extraction-liquid chromatography tandem mass spectrometry method for quantitative determination of H–PFCAs in surface water was developed, validated, and applied on samples collected from the Netherlands. To improve chromatography, especially for short-chain (H-)PFCAs, an ion-pairing agent, tetrabutylammonium hydrogen sulphate, was used. The method was validated for linearity (R2 > 0.99), instrumental detection limits (0.01–0.09 ng/mL), method detection limits (0.03–0.75 ng/mL), matrix effects (<20%), percent absolute- and relative recovery (57–121%), trueness (130-80%), repeatability (<20%), and within-lab reproducibility (<20%). Eleven out of fourteen PFASs showed acceptable results. Application of the newly validated method to surface water throughout the Netherlands revealed trace levels of H–PFCAs (including two new H–PFCAs) and high concentrations of PFCAs.

Critical loads of headwater streams in China using SSWC model modified by comprehensive F-factor

In order to evaluate the potential risk of surface water acidification in regions with historically-elevated acid deposition and to measure the recovery of such ecosystems after policy changes, critical loads and their exceedances were estimated for 349 headwater streams across China using a modified SSWC model. Such a model considered the acid-neutralizing capacity derived from high base cation deposition and the robust retention of sulfate and nitrate. Results indicated that China's streams had higher critical loads (averaged at 4.7 keq·ha−1·yr−1) and were less sensitive to acid deposition as compared to Europe and North America. The proportion of surveyed streams with acid deposition exceeded critical load decreased from 40.4% in 2005 to 29.5% in 2018, indicating a significant decrease in risk of surface water acidification, and thus a benefit from the emission abatement in recent years. Nonetheless, a relatively high risk of acidification still existed in southeast China with lower critical loads and most critical load exceedances. More efforts should be put into implementing emission control policies in the future.

Interfacial photoreactions of Cr(VI) and oxalate on lepidocrocite surface under oxic and acidic conditions: Reaction mechanism and potential implications for contaminant degradation in surface waters

The transformation of contaminants by photocatalysts under light illumination has been extensively studied in engineered water systems. However, the interfacial photoreaction mechanism for the reduction of chromium (Cr(VI)) on natural iron (Fe) oxides in acidic and oxic surface waters associated with soil remain unclear. Herein, the photochemical behavior of Cr(VI) and oxalate on lepidocrocite surfaces was investigated to disclose the natural detoxification process of Cr(VI). Kinetic results showed that Cr(VI) was quickly reduced in the system with lepidocrocite and oxalate under light illumination, while no Cr(VI) reduction was observed in the dark. No obvious secondary Fe oxides and Cr-containing precipitates were found, but the newly generated Cr(III) was evenly distributed on the lepidocrocite surface or entered into the lepidocrocite defects. Cr(VI) and oxalate can form ternary complexes with lepidocrocite, and Cr(VI) reduction and the oxidation of oxalate to carbon dioxide occurred simultaneously on the lepidocrocite surface. Amongst the reactions involving lepidocrocite, oxalate, and Cr(VI), the oxidation of oxalate was attributed to reactive oxygen species such as H2O2, OH, and ·O2−, while Cr(VI) reduction was mainly caused by photogenerated electrons, CO2−, H2O2, Fe(II), and through the direct electron transfer in the Cr(VI)-oxalate complex. The findings of the Cr(VI) molecular-scale photoreduction mechanism on mineral surfaces would have implications for interpreting the natural attenuation of Cr(VI) toxicity in natural surface waters associated with soil.

Study of the Diagenetic Characteristics of Uraniferous Sandstone and Its Relationship with Uranium Mineralization of the Bayin Gobi Formation, Lower Cretaceous Tamusu Deposit

The Tamusu uranium deposit in the southern part of the Bayin Gobi Basin is a typical hard-sandstone uranium deposit， but with very different diagenetic characteristics from other sandstone-type uranium deposits in northern China. The characteristics of uraniferous sandstone （K1b2-2） and its relationship to uranium mineralization in the Tamusu deposit have been studied In recent years by petrology， petrography， geochemical， scanning electron microscope （SEM） and so on. The detritus is composed of quartz （average content 2.38%） and feldspars （average content 50.33%）. The cements comprise gypsum （average content 12.57%）， ankerite （average content 3.20%）， ferruginous dolomite （average content 9.33%）， dolomite （average content 9.76%） and a small amount of complex matrix material （average content 2.62%）， causing both basal cementation and porous cementation. The diagenetic process is characterized by early stage B diagenesis and later stage A diagenesis， with alkaline water （pH 7.52）. Early stage B diagenesis is characterized by chemical cementation， water-rock interaction， dissolution and metasomatism. The formation sequence of the cements is ankerite-ferruginous dolomite-dolomite-gypsum； the carbonate cements， from center to edge， are automorphic ankerite， automorphic-hypidiomorphic ferruginous dolomite， and hypidiomorphic-xenomorphic dolomite. Gypsum forms last， with metasomatism of quartz， feldspar and dolomite. In this process， plagioclase is altered to albite due to the presence of Na+ in the highly saline water replacing Ca2+， with dissolution microcavities formed on the surface of the plagioclase and microcracks along cleavage planes. During early stage B diagenesis， no auto-cementation takes place， and clay minerals are affected by alkaline groundwater. During late stage A diagenesis， acidic surface water containing S O 4 2 - dissolves the carbonate cement， forming cavities. The uraniferous sandstone does not favor interlayer oxidation due to its low porosity and permeability. It is inferred that the genesis of uranium mineralization in the Tamusu deposit occurs by sedimentary diagenesis and interlayer oxidation.

Nutrients in Water Masses in the Atlantic Sector of the Arctic Ocean: Temporal Trends, Mixing and Links With Primary Production

AbstractThere is strong evidence of an increase in primary production (PP) in the Arctic Ocean (AO) over the last two decades. Further increases will depend on the interplay between decreasing light limitation for primary producers, as the sea ice extent and thickness decrease, and the availability of nutrients, which is controlled by, but not limited to, inputs from the Atlantic and the Pacific Oceans. While these inputs are the major nutrient sources to the AO, ocean vertical mixing is required to bring the nutrients into the photic zone. We analyze data collected in the Western Eurasian Basin (WEB) between 1980 and 2016 and characterize the nutrient climatology of the various water masses. We conclude that there were no significant trends in the concentrations of the two macronutrients that typically limit PP in the AO (nitrate and silicic acid, in the case of diatoms), except a decreasing trend for silicic acid in Polar Surface Water (PSW), which is consistent with the reported increase in PP in the AO. We suggest that the Whalers Bay polynya, located in the northwestern corner of Svalbard, may act as a mixing hotspot, creating patches of nutrient replenished PSW. These patches may then be advected to higher latitudes under the ice pack, later boosting PP upon release from light limitation or else, keeping a nutrient reservoir that may be used in a subsequent growth season. It is likely that this remaining nutrient reservoir will decrease as sea ice cover retreats and light limitation alleviates.

Distribution characteristics and source analysis of sulfate in the main rivers of Heze city, China.

Throughout the last few decades, sulfate concentrations in streamwater have received considerable attention due to their dominant role in anthropogenic acidification of surface waters. In order to determine the cycle of riverine sulfate, affected by natural weathering and anthropogenic activities, the Zhuzhaoxin River Basin and Dongyu River Basin in Heze City, China are selected. The conventional hydrochemical characteristics, distribution characteristics of sulfate concentration, and distribution characteristics of sulfur and oxygen isotopes are analyzed and texted. The results are as follows: the concentration of SO42- in the surface water of the study area increased gradually from upstream to downstream. In the study area, the δ34SSO4 and δ18OSO4 value in the surface water of Zhuzhaoxin River Basin ranges from +8.0‰ to +22.3‰ and +7.3‰ to +10.5‰, respectively, while the values of Dongyu River Basin are between +9.3‰ ∼ +9.5‰ and +4.2‰ ∼ +8.1‰. The main sources of SO42- in the Zhuzhaoxin River Basin are domestic sewage, industrial and mining wastewater and the evaporation of dissolved salt rock, and their average contribution rates are more than 50% and 30%, respectively; the main sources of SO42- in the Dongyu River Basin are agricultural activities and atmospheric precipitation, and their average contribution rates are more than 60% and 20%, respectively.

Декомпозиция временного ряда величины рН поверхностных вод глубоководной части Черного моря по архивным данным второй половины XX века

Based on the archival data of the Institute of Natural and Technical Systems for the period from 1956 to 1996 the decomposition of the time series of the pH value of the surface layer of the deep-water part of the Black Sea was carried out with subsequent extrapolation until 2010. The analysis shows that the reconstructed time series is divided into two time interval trends with different sign and data quality: from 1956 to 1976 and from 1977 to 1996. The presence of these two fundamentally different time periods is largely due to the method for determining the pH value. Until about the mid-1970s the pH value in the Black Sea was determined mainly by the colorimetric method with an accuracy of tenths of pH, i.e. with a high error. In subsequent years, the potentiometric method began to be widely used, the accuracy of which is an order of magnitude higher. Therefore, further in the work, the second time period is analyzed – since 1977. In the time course of pH, a regular seasonal variation, interannual quasicyclic components of variability with periods of about 6.7 and 2.5 years, and a significant negative linear trend are identified. It is most likely that the main reason for the quasiperiodic variability of pH in the upper layer of the open part of the Black Sea on an interannual scale is related to variations in atmospheric precipitation caused by changes in cyclonic activity in the Atlantic-European sector, including the Black Sea region, in different phases of climatic modes in the ocean-atmosphere system (such as, in particular, NAO). The highlighted tendency of the pH value since 1977 indicates the acidification of the upper layer of the Black Sea waters, with an average rate of about 0.013pH units / 10 years. This corresponds to the rate of increase in acidity of surface waters in other regions of the World Ocean. Expedition data from 2010 confirm the validity of the extrapolation performed.