Formation processes of groundwater in a non-ferrous metal mining city of China: Insights from hydrochemical and strontium isotope analyses

Tongling is a significant non-ferrous metal mining city in China, which produces waste that negatively impacts the area's water environment. It is essential to comprehend the hydrochemical properties and formation processes of groundwater to safeguard and utilize it efficiently. We explored major ions, strontium, and its isotopes in water and river-bottom samples from the northern (i.e., A-A' section) and southern (i.e., B-B' section) areas. The hydrochemical facies show the mining activities have a greater impact on surface water than on groundwater. Groundwater hydrochemical formation results from several factors, with water-rock interaction and ion exchange being primary. Additionally, the dissolution of calcite, dolomite, and feldspar, oxidation of pyrite, and hydrolysis of carbonate minerals also impact the formation of groundwater chemistry. Our analysis of strontium and its isotopes indicates that carbonate dissolution primarily occurred in the recharge area; the runoff from the recharge to the discharge area results in the dissolution of certain silicate rocks; calcite dissolution sources account for > 70% contribution in both surface water and groundwater water-rock interactions, whereas silicate rock dissolution sources and dolomite dissolution sources account for < 30%. Due to changed order of dissolved carbonate and silicate minerals during groundwater flow, the distribution of strontium and its isotopes in the A-A' section is opposite to that in the B-B' section. The findings provide a basis for developing, utilizing, managing, and protecting groundwater resources, especially in similar mining areas.

Hydrogeochemical and isotopic evolution of groundwater in shallow and deep aquifers of the Kabul Plain, Afghanistan

Groundwater from shallow and deep aquifers are widely used for drinking, agricultural and industrial use in Kabul, the capital of Afghanistan. However, unplanned urbanization and rapid population growth has led to the installation of numerous unlicensed wells to meet the public demand. This has caused to extraction of huge amounts of groundwater from the subsurface and further deterioration of groundwater quality. Therefore, understanding the hydrogeochemical characteristics of groundwater in shallow aquifers and deep aquifers is imperative for sustainable management of the groundwater resource in Kabul Plain. Thus, in this study, we used a multi-parameter approach, involving hydrochemical and environmental isotopes to understand the geochemical evolution of entire groundwater system of the Kabul Plain including river and dam water. The results of this study show that shallow and deep aquifers are dominantly of Mg-(Ca)-HCO3 and Na-Cl water type, respectively. We observed that (1) water-rock interaction is the major contributing factor to the chemical compositions of groundwater in the Kabul Plain; (2) groundwater in deep aquifer is mainly influenced by silicate weathering, and dissolution of evaporitic and carbonate minerals and reverse cation exchange; (3) dissolution of carbonates and silicate weathering plays a pivotal role in the groundwater chemistry of shallow aquifer; (4) the stable isotopes of groundwater display that the shallow aquifer is principally recharged by river water and local precipitation; (5) the tritium analysis exhibited that groundwater of shallow aquifer was primarily recharged recently, whereas groundwater of deep aquifer is the mixture of pre 1953 with post 1953 groundwater. This study revealed that there are hydraulic interactions between the two aquifers and the deep aquifer is recharged through shallow aquifer. The findings of this study would be useful for Afghanistan's water authorities to develop an effective strategy for sustainable water resources management in the Kabul Basin.

Shift of major driver for chemical weathering from the natural control to human dominance since 1980s in the Taihu watershed, China

Anthropogenic acidification has become a concerned problem in the Taihu region; however, how it affected the regional weathering rate, especially at the different sub-watershed levels has hardly been studied. To reveal the impact of human activities on watershed weathering and water chemistry in Taihu sub-watersheds, historical water chemistry data (1950s-1970s) and recent water samples (2018-2021) of the local river systems, as well as sediment samples of Taihu lake were collected and analyzed, and a linear addition mass balance method was used to determine the weathering rate at the sub-watershed level. The results indicated that, compared with 60 years ago, the current weathering rate of carbonates and silicates in the Taoge water system (TG) was the highest, reaching 67.2 and 11.4 t·km^-2·a^-1, increasing by 4.1 and 2.7-folds, respectively; and meanwhile the carbonate and silicate weathering rates increased by 3.1 and 4.9-folds in the Nanhe water system (NH), and 5.2 and 3.4-folds in the Tiaoxi water system (TX), respectively. The increasing rate was significantly correlated to the atmospheric SO₂ concentration in different sub-watersheds and was affected by the sub-watershed lithology, e.g., TX had a higher increase rate of silicate weathering due to the wider distribution of silicates in this sub-watershed than the other two. The sediment evidence of Na/K and Ca/Al on the profile in different lake parts, which was influenced by different influx river systems, confirmed that the overall intensity of watershed weathering was higher in TG than in the TX sub-watershed and was higher in the recent decade than 50-60 years ago. The accelerated weathering rate was found to present a definite consistency with the social and economic development in the watershed. Combined analyses of the accelerated weathering rate in the watershed and sedimentation evidence indicated that the major driving force for the watershed weathering has shifted from carbonic acid under the natural condition to human-induced sulfuric acid since 1980s.

Chemical Weathering and CO2 Consumption Inferred from Riverine Water Chemistry in the Xi River Drainage, South China

Hydrochemistry and strontium isotope data were analysed in water samples from the Xi River Drainage system to reveal the spatial and seasonal variations in chemical weathering, associated CO2 consumption fluxes, and their control factors. The main ions were Ca2+, Mg2+, and HCO3-, which are characteristic of a drainage system on carbonate-dominated bedrock. The dissolved loads were derived from four major end-member reservoirs: silicate, limestone, dolomite, and atmosphere. The silicate weathering rates (SWRs) increased downstream from 0.03 t/km2/year to 2.37 t/km2/year. The carbonate weathering rates (CWRs) increased from 2.14 t/km2/year in the upper reaches, to 32.65 t/km2/year in the middle reaches, and then decreased to 23.20 t/km2/year in the lower reaches. The SWR values were 281.38 and 113.65 kg/km2/month during the high- and low-water periods, respectively. The CWR values were 2456.72 and 1409.32 kg/km2/month, respectively. The limestone weathering rates were 2042.74 and 1222.38 kg/km2/month, respectively. The dolomite weathering rates were 413.98 and 186.94 kg/km2/month, respectively. Spatial and seasonal variations in chemical weathering were controlled mainly by lithology, vegetation, and climate (temperature, water discharge, and precipitation). The CO2 consumption flux by chemical weathering was estimated at 189.79 × 109 mol/year, with 156.37 × 109 and 33.42 × 109 mol/year for carbonate and silicate weathering, respectively. The CO2 fluxes by chemical weathering are substantially influenced by sulfuric acid in the system. The CO2 flux produced by sulfuric acid weathering was estimated at 30.00 × 109 mol/year in the basin. Therefore, the Xi River Basin is a CO2 sink with a net consumption of CO2 flux of 3.42 × 109 mol/year.

High-resolution mapping of the global silicate weathering carbon sink and its long-term changes

Climatic and non-climatic factors affect the chemical weathering of silicate rocks, which in turn affects the CO₂ concentration in the atmosphere on a long-term scale. However, the coupling effects of these factors prevent us from clearly understanding of the global weathering carbon sink of silicate rocks. Here, using the improved first-order model with correlated factors and non-parametric methods, we produced spatiotemporal data sets (0.25° × 0.25°) of the global silicate weathering carbon-sink flux (SCSF_α ) under different scenarios (SSPs) in present (1950-2014) and future (2015-2100) periods based on the Global River Chemistry Database and CMIP6 data sets. Then, we analyzed and identified the key regions in space where climatic and non-climatic factors affect the SCSF_α . We found that the total SCSF_α was 155.80 ± 90 Tg C yr^-1 in present period, which was expected to increase by 18.90 ± 11 Tg C yr^-1 (12.13%) by the end of this century. Although the SCSF_α in more than half of the world was showing an upward trend, about 43% of the regions were still showing a clear downward trend, especially under the SSP2-4.5 scenario. Among the main factors related to this, the relative contribution rate of runoff to the global SCSF_α was close to 1/3 (32.11%), and the main control regions of runoff and precipitation factors in space accounted for about 49% of the area. There was a significant negative partial correlation between leaf area index and silicate weathering carbon sink flux due to the difference between the vegetation types. We have emphasized quantitative analysis the sensitivity of SCSF_α to critical factors on a spatial grid scale, which is valuable for understanding the role of silicate chemical weathering in the global carbon cycle.

Geochemical characteristics of strontium isotopes in a coastal watershed: implications for anthropogenic influenced chemical weathering and export flux

Coastal watershed are essential in transporting dissolved loads from terrestrial biogeochemical process of surface environment to the adjacent oceans. The solute chemistry of coastal river water contains significant information about environmental processes under the impact of both natural lithology and anthropogenic pressure. In this study, strontium (Sr) isotopes and water chemistry data of the Jiulongjiang (JLJ) river water were analyzed in detail to trace the contribution of bedrock weathering, and quantify Sr flux to the East China Sea (ECS). The dissolved Sr contents ranged 0.07-0.90 μmol L^-1 and greatly fluctuated where tributaries encountered, and ⁸⁷Sr/⁸⁶Sr values relatively fluctuated between 0.7140 and 0.7514. Silicate weathering was identified to be the predominant contribution of riverine dissolved loads. Strontium flux to the ocean in dry season was estimated to be 689.2 tons per year, implying an essential influence on oceanic strontium evolution. In accordance with forward model, the silicate weathering rate and CO₂ consumption rate were 55.7 tons km^-2 per year and 16.9 × 10⁵ mol km^-2 per year, respectively, slightly higher than world average. Considering anthropogenic impacts alongside the river, the integrated effect of lower runoff and longer retention time of river water in dry season may aggravate weathering processes. Although CO₂ sink by silicate weathering in JLJ seems less than the sink in world's central reservoirs, it should still be taken into consideration for coastal carbon budget. These findings highlight the use of geochemical characteristics of strontium and its isotopes in identifying weathering process and output flux to the ocean, which provides basic data for sustainable coastal water resource management.

Preparation and related properties of geopolymer solidified uranium tailings bodies with various fibers and fiber content

Uranium tailing ponds are a potential major source of radioactive pollution. Solidification treatment can control the diffusion and migration of radioactive elements in uranium tailings to safeguard the surrounding ecological environment. A literature review and field investigation were conducted in this study prior to fabricating 11 solidified uranium tailing samples with different proportions of PVA fiber, basalt fiber, metakaolin, and fly ash, and the weight percentage of uranium tailings in the solidified body is 61.11%. The pore structure, volume resistivity, compressive strength, radon exhalation rate variations, and U(VI) leaching performance of the samples were analyzed. The pore size of the solidified samples is mainly between 1 and 50 nm, the pore volume is between 2.461 and 5.852 × 10^-2 cm³/g, the volume resistivity is between 1020.00 and 1937.33 Ω·m, and the compressive strength is between 20.61 and 36.91 MPa. The radon exhalation rate is between 0.0397 and 0.0853 Bq·m^-2·s^-1. The cumulative leaching fraction of U(VI) is between 2.095 and 2.869 × 10^-2 cm, and the uranium immobilization rate is between 83.46 and 85.97%. Based on a comprehensive analysis of the physical and mechanical properties, radon exhalation rates, and U(VI) leaching performance of the solidified samples, the basalt fiber is found to outperform PVA fiber overall. The solidification effect is optimal when 0.6% basalt fiber is added.

Legume-microbiome interactions unlock mineral nutrients in regrowing tropical forests

Legume trees form an abundant and functionally important component of tropical forests worldwide with N2-fixing symbioses linked to enhanced growth and recruitment in early secondary succession. However, it remains unclear how N2-fixers meet the high demands for inorganic nutrients imposed by rapid biomass accumulation on nutrient-poor tropical soils. Here, we show that N2-fixing trees in secondary Neotropical forests triggered twofold higher in situ weathering of fresh primary silicates compared to non-N2-fixing trees and induced locally enhanced nutrient cycling by the soil microbiome community. Shotgun metagenomic data from weathered minerals support the role of enhanced nitrogen and carbon cycling in increasing acidity and weathering. Metagenomic and marker gene analyses further revealed increased microbial potential beneath N2-fixers for anaerobic iron reduction, a process regulating the pool of phosphorus bound to iron-bearing soil minerals. We find that the Fe(III)-reducing gene pool in soil is dominated by acidophilic Acidobacteria, including a highly abundant genus of previously undescribed bacteria, Candidatus Acidoferrum, genus novus. The resulting dependence of the Fe-cycling gene pool to pH determines the high iron-reducing potential encoded in the metagenome of the more acidic soils of N2-fixers and their nonfixing neighbors. We infer that by promoting the activities of a specialized local microbiome through changes in soil pH and C:N ratios, N2-fixing trees can influence the wider biogeochemical functioning of tropical forest ecosystems in a manner that enhances their ability to assimilate and store atmospheric carbon.

Dating the megalithic culture of laos: Radiocarbon, optically stimulated luminescence and U/Pb zircon results

The megalithic jar sites of Laos (often referred to as the Plain of Jars) remain one of Southeast Asia's most mysterious and least understood archaeological cultures. The sites, recently inscribed as UNESCO World Heritage, host hollowed stone jars, up to three metres in height, which appear scattered across the landscape, alone or clustered in groups of up to more than 400. Until now, it has not been possible to estimate when the jars were first placed on the landscape or from where the stone was sourced. Geochronological analysis using the age of detrital zircons demonstrates a likely quarry source for one of the largest megalithic jar sites. Optically Stimulated Luminescence (OSL) dating suggests the jars were positioned at the sites potentially as early as the late second millennium BC. Radiocarbon dating of skeletal remains and charcoal samples places mortuary activity around the jars from the 9-13th century AD, suggesting the sites have maintained ritual significance from the period of their initial placement until historic times.

Chemical weathering and atmospheric carbon dioxide (CO2) consumption in Shanmuganadhi, South India: evidences from groundwater geochemistry

Chemical weathering in a groundwater basin is a key to understanding global climate change for a long-term scale due to its association with carbon sequestration. The present study aims to characterize and to quantify silicate weathering rate (SWR), carbon dioxide consumption rate and carbonate weathering rate (CWR) in hard rock terrain aided by major ion chemistry. The proposed study area Shanmuganadhi is marked with superior rainfall, oscillating temperature and runoff with litho-units encompassing charnockite and hornblende-biotite gneiss. Groundwater samples (n = 60) were collected from diverse locations and analysed for major chemical constituents. Groundwater geochemistry seems to be influenced by geochemical reactions combining dissolution and precipitation of solids, cation exchange and adsorption along with minor contribution from anthropogenic activities. The SWR calculated for charnockite and hornblende-biotite gneiss was 3.07 tons km^-2 year^-1 and 5.12 tons km^-2 year^-1, respectively. The calculated CWR of charnockite and hornblende-biotite gneiss was 0.079 tons km^-2 year^-1 and 0.74 tons km^-2 year^-1, respectively. The calculated CO₂ consumption rates via silicate weathering were 1.4 × 10³ mol km^-2 year^-1 for charnockite and 5.8 × 10³ mol km^-2 year^-1 for hornblende-biotite gneiss. Lithology, climate and relief were the key factors isolated to control weathering and CO₂ consumption rates.

0.25 Ga Salt Deposits Preserve Signatures of Habitable Conditions and Ancient Lipids

Polygonal features in a ∼250 million-year-old Permian evaporitic deposit were investigated for their geological and organic content to test the hypothesis that they could preserve the signature of ancient habitable conditions and biological activity. Investigations on evaporitic rock were carried out as part of the MIne Analog Research (MINAR) project at Boulby Mine, the United Kingdom. The edges of the polygons have a higher clay content and contain higher abundances of minerals such as quartz and microcline, and clays such as illite and chlorite, compared with the interior of polygons, suggesting that the edges were preferred locations for the accumulation of weathering products during their formation. The mineral content and its strontium isotope ratio suggest that the material is from continental weathering at the borders of the Permian Zechstein Sea. The edges of the polygons contain material with mean δ¹³C and δ¹⁵N values of -20.8 and 5.3, respectively. Lipids, including alkanes and hopanes, were extracted from the interior and edges of the polygons, which are inferred to represent organic material entrained in the evaporites when they were formed. The presence of long-chain alkanes (C₂₀-C₃₅) that lack a carbon preference, low abundances of C₂₃-C₂₉ hopanes, and lack of marine, evaporitic, or thermal maturity indicators show that lipid biomarkers were, at least in part, potentially derived from a continental source and have not undergone significant thermal maturation since deposition. Lipid extractions using weak acids revealed significantly more lipids than those without acid, potentially indicating that encapsulation was not the only type of preservation mechanism occurring in Boulby salts. These data demonstrate the potential for ancient evaporites and their polygons to preserve information on local geological conditions, ancient habitability, and evidence of life. The data show that analogous martian evaporitic deposits are good targets for future life detection missions and the investigation of ancient martian habitability.

Testing Flight-like Pyrolysis Gas Chromatography-Mass Spectrometry as Performed by the Mars Organic Molecule Analyzer Onboard the ExoMars 2020 Rover on Oxia Planum Analog Samples

The Mars Organic Molecule Analyzer (MOMA) onboard the ExoMars 2020 rover (to be landed in March 2021) utilizes pyrolysis gas chromatography-mass spectrometry (GC-MS) with the aim to detect organic molecules in martian (sub-) surface materials. Pyrolysis, however, may thermally destroy and transform organic matter depending on the temperature and nature of the molecules, thus altering the original molecular signatures. In this study, we tested MOMA flight-like pyrolysis GC-MS without the addition of perchlorates on well-characterized natural mineralogical analog samples for Oxia Planum, the designated ExoMars 2020 landing site. Experiments were performed on an iron-rich shale (that is rich in Fe-Mg-smectites) and an opaline chert, with known organic matter compositions, to test pyrolytic effects related to heating in the MOMA oven. Two hydrocarbon standards (n-octadecane and phytane) were also analyzed. The experiments show that during stepwise pyrolysis (300°C, 500°C, and 700°C), (1) low-molecular-weight hydrocarbon biomarkers (such as acyclic isoprenoids and aryl isoprenoids) can be analyzed intact, (2) discrimination between free and complex molecules (macromolecules) is principally possible, (3) secondary pyrolysis products and carryover may affect the 500°C and 700°C runs, and (4) the type of the organic matter (functionalized vs. defunctionalized) governs the pyrolysis outcome rather than the difference in mineralogy. Although pyrosynthesis reactions and carryover clearly have to be considered in data interpretation, our results demonstrate that pyrolysis GC-MS onboard MOMA operated under favorable conditions (e.g., no perchlorates) will be capable of providing important structural information on organic matter found on Mars, particularly when used in conjunction with other techniques on MOMA, including derivatization and thermochemolysis GC-MS and laser desorption/ionization-MS.

Lacustrine micro-ecosystem responses to the inflow discharge gradient of water diversion from Yangtze River to Lake Taihu

Water diversion project is always taken as the emergency and effective engineering measure to deal with the cyanobacterial blooms in eutrophic lakes. The inflow discharge and duration are the critical parameters influencing the effects and costs of the water diversion activities. Due to the impacts of meteorological and hydrological factors such as precipitation and wind-wave currents, the environmental influence of water diversion on shallow eutrophic lakes is always unclear. To explore the quantitative relationships among inflow discharges, duration and ecological parameters in water-receiving lakes, the typical water diversion engineering-Water Diversion Project from Yangtze River to Lake Taihu was taken as an example and the mesocosm experiment modeling the micro-ecosystem of the water-receiving Meiliang Bay in Lake Taihu was conducted with five groups of inflow discharges according to the practical discharges of the main river channel-Wangyu River. Each micro-ecosystem had a volume of 15 L and was studied for a period of 30 days (25 days for the water diversion period and 5 days for the stop period). The results showed that the inflow discharges had different extents of impact on the physicochemical and biological characteristics of the micro-ecosystems. The concentrations of total dissolved solids, total nitrogen, nitrate, active silicate and bacterial abundance in the experimental groups (inflow discharges > 100 m³/s) were all decreased compared with the control group, with the lowest values in the period of 10-15 days. During the stop period, the concentrations of sensitive biotic and abiotic parameters were all recovered with different extents and different from the initial state of this experiment, which revealed that the effects of the short-term water diversion on lake ecosystems were resilient and durable. There were quantitative relationships among the inflow discharge, content interpolation and variation in water nutrients, with different relationships in different periods of the water diversion. The influence of water diversion on lake ecosystems was not only related to the direct impacts of allochthonous inputs, but also with the indirect effects of internal habitat variation in lakes.

Boron Isotopes in the Puga Geothermal System, India, and Their Implications for the Habitat of Early Life

Boron is associated with several Archean stromatolite deposits, including the tourmaline-rich Barberton stromatolites in South Africa and tourmaline-bearing pyritic laminae associated with stromatolites of the 3.48 Ga Dresser Formation in the Pilbara Craton, Australia. Boron is also a critical element in prebiotic organic chemistry, including in the formation of ribose, a crucial component in RNA. As geological evidence and advances in prebiotic chemistry are now suggesting that hot spring activity may be associated with the origins of life, an understanding of boron and its mobility and isotopic fractionation in geothermal settings may provide important insights into the setting for the origin of life. Here, we report on the boron isotopic compositions and elemental concentrations in a range of fluid, sediment, and mineral samples from the active, boron-rich Puga geothermal system in the Himalayas, India. This includes one of the lowest boron isotope values ever recorded in modern settings: diatom-rich sediments (δ¹¹B = -41.0‰) in a multiphase fractionation system where evaporation is not the dominant form of isotope fractionation. Instead, the extreme boron isotopic fractionation is ascribed to the incorporation of tetrahedral ¹⁰B borate anions in precipitating amorphous silica. These findings expand the known limits and drivers of boron isotope fractionation, as well as provide insight into the concentration and fractionation of boron in Archean hot spring environments.

The benthic fluxes of nutrients and the potential influences of sediment on the eutrophication in Daya Bay, South China

Nutrient concentrations in porewater and their benthic fluxes were investigated in Daya Bay, South China, to study the accumulation and transfer of nutrients at sediment-water interface, as well as the impact of human activities on nutrients. The contributions of sediment to nutrients in water column and the potential influences on eutrophication were also discussed. Nutrients in porewater and overlying water changed in different seasons and areas, which was mainly attributed to human activities, hydrodynamic force and biogeochemical conditions. Mean concentrations of DIN (dissolved inorganic nitrogen), PO₄ and SiO₃ were 70 ± 61, 3.1 ± 4.3, 103 ± 105 μmol/L, and 234 ± 166, 15.6 ± 4.0, 353 ± 48 μmol/L in overlying water and porewater, respectively. Annual mean DIN, PO₄ and SiO₃ fluxes were 330 ± 249, -1.3 ± 16 and 549 ± 301 μmol/(m²d), respectively, indicating that sediment was generally the source of DIN and SiO₃, but was the sink of PO₄. The mean exchange capacities were (7.8 ± 5.5) × 10⁷, (-1.2 ± 34.0) × 10⁵ and (1.2 ± 0.6) × 10⁸ mol/a for DIN, PO₄ and SiO₃, respectively, in Daya Bay.

Sorption of phosphate and silicate alters dissolution kinetics of poorly crystalline iron (oxyhydr)oxide

Iron (oxyhydr)oxides (FeOx) control retention of dissolved nutrients and contaminants in aquatic systems. However, FeOx structure and reactivity is dependent on adsorption and incorporation of such dissolved species, particularly oxyanions such as phosphate and silicate. These interactions affect the fate of nutrients and metal(loids), especially in perturbed aquatic environments such as eutrophic coastal systems and environments impacted by acid mine drainage. Altered FeOx reactivity impacts sedimentary nutrient retention capacity and, eventually, ecosystem trophic state. Here, we explore the influence of phosphate (P) and silicate (Si) on FeOx structure and reactivity. Synthetic, poorly crystalline FeOx with adsorbed and coprecipitated phosphate or silicate at low but environmentally relevant P/Fe or Si/Fe ratios (0.02-0.1 mol mol^-1) was prepared by base titration of Fe(III) solutions. Structural characteristics of FeOx were investigated by X-ray diffraction, synchrotron-based X-ray absorption spectroscopy and high-energy X-ray scattering. Reactivity of FeOx was assessed by kinetic dissolution experiments under acidic (dilute HCl, pH 2) and circum-neutral reducing (bicarbonate-buffered ascorbic acid, pH 7.8, E_h ∼ -300 mV) conditions. At these loadings, phosphate and silicate coprecipitation had only slight impact on local and intermediate-ranged FeOx structure, but significantly enhanced the dissolution rate of FeOx. Conversely, phosphate and silicate adsorption at similar loadings resulted in particle surface passivation and decreased FeOx dissolution rates. These findings indicate that varying nutrient loadings and different interaction mechanisms between anions and FeOx (adsorption versus coprecipitation) can influence the broader biogeochemical functioning of aquatic ecosystems by impacting the structure and reactivity of FeOx.

Spatial patterns, geochemical evolution and quality of groundwater in Delta State, Niger Delta, Nigeria: implication for groundwater management

Delta State of the Niger Delta, Nigeria, is an oil exploration and production region that is characterized by huge revenue generation but with its attendant waste generation and oil spillage that impact the environment. The variability in the hydrochemical characteristics, hydrochemical controlling processes and quality in space has been investigated. The pH of the groundwater samples ranged from slightly acidic to slightly alkaline nature. Biological oxygen demand and chemical oxygen demand of the coastal area are higher than those of the inland area indicating more domestic and industrial contamination. Total dissolved solid values across the region indicated fresh and brackish water for the coastal area and fresh water only for the inland area. The orders of abundance of the cations and anions for the coastal and inland areas are Ca>Mg>Na>K/Cl>HCO₃>SO₄>NO₃ and Na>Ca>K>Mg/HCO₃>Cl>NO₃>SO₄ respectively. A Piper diagram identified four hydrochemical facies, namely CaHCO₃, NaHCO₃, NaCl and CaMgClSO₄. Ionic cross plots and correlation matrix revealed that the groundwater chemistry of the inland area is predominantly influenced by silicate weathering and ion exchange processes while those of the coastal area are influenced by silicate weathering, ion exchange processes and seawater tidal flushing. The groundwater from the coastal area is more polluted by heavy metals than those from the inland area. The observed variability may be attributed to effects of industrial wastes and exploration activities. In terms of water quality for domestic and irrigation, the groundwater of the coastal and the inland areas are not generally potable and suitable as drinking and irrigation water sources.

Mineralogy, Structure, and Habitability of Carbon-Enriched Rocky Exoplanets: A Laboratory Approach

Carbon-enriched rocky exoplanets have been proposed to occur around dwarf stars as well as binary stars, white dwarfs, and pulsars. However, the mineralogical make up of such planets is poorly constrained. We performed high-pressure high-temperature laboratory experiments (P = 1-2 GPa, T = 1523-1823 K) on chemical mixtures representative of C-enriched rocky exoplanets based on calculations of protoplanetary disk compositions. These P-T conditions correspond to the deep interiors of Pluto- to Mars-sized planets and the upper mantles of larger planets. Our results show that these exoplanets, when fully differentiated, comprise a metallic core, a silicate mantle, and a graphite layer on top of the silicate mantle. Graphite is the dominant carbon-bearing phase at the conditions of our experiments with no traces of silicon carbide or carbonates. The silicate mineralogy comprises olivine, orthopyroxene, clinopyroxene, and spinel, which is similar to the mineralogy of the mantles of carbon-poor planets such as the Earth and largely unaffected by the amount of carbon. Metals are either two immiscible iron-rich alloys (S-rich and S-poor) or a single iron-rich alloy in the Fe-C-S system with immiscibility depending on the S/Fe ratio and core pressure. We show that, for our C-enriched compositions, the minimum carbon abundance needed for C-saturation is 0.05-0.7 wt% (molar C/O ∼0.002-0.03). Fully differentiated rocky exoplanets with C/O ratios more than that needed for C-saturation would contain graphite as an additional layer on top of the silicate mantle. For a thick enough graphite layer, diamonds would form at the bottom of this layer due to high pressures. We model the interior structure of Kepler-37b and show that a mere 10 wt% graphite layer would decrease its derived mass by 7%, which suggests that future space missions that determine both radius and mass of rocky exoplanets with insignificant gaseous envelopes could provide quantitative limits on their carbon content. Future observations of rocky exoplanets with graphite-rich surfaces would show low albedos due to the low reflectance of graphite. The absence of life-bearing elements other than carbon on the surface likely makes them uninhabitable.

Temporal and spatial variations and impact factors of nutrients in Bohai Bay, China

The temporal and spatial distributions of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicate (DSi), and their long-term changes were investigated in Bohai Bay (BHB) in spring, summer, and autumn (2013-2014). The high DIN values were consistently distributed in the western inshore waters, mainly determined by terrestrial factors, e.g., riverine input, while DIP and DSi were mostly distributed in the southern coastal waters, the central BHB, or near the sea port Caofeidian in northern BHB, largely related to non-terrestrial factors, e.g., sediment release. Based on the nutrient distribution, BHB could be partitioned into western and eastern parts, with -15 m depth as the separation. The long-term variations of nutrients since 2000 showed an increase in DIN and decreases in DIP and DSi. Relatively slow changes in DIN and DIP and a rapid decrease in DSi were exhibited in summer, which was associated with precipitation and sediment release.

Hydro-Geochemistry of the River Water in the Jiulongjiang River Basin, Southeast China: Implications of Anthropogenic Inputs and Chemical Weathering

This study focuses on the chemical weathering process under the influence of human activities in the Jiulongjiang River basin, which is the most developed and heavily polluted area in southeast China. The average total dissolved solid (TDS) of the river water is 116.6 mg/L and total cation concentration (TZ+) is 1.5 meq/L. Calcium and HCO3− followed by Na+ and SO42− constitute the main species in river waters. A mass balance based on cations calculation indicated that the silicate weathering (43.3%), carbonate weathering (30.7%), atmospheric (15.6%) and anthropogenic inputs (10.4%) are four reservoirs contributing to the dissolved load. Silicates (SCW) and carbonates (CCW) chemical weathering rates are calculated to be approximately 53.2 ton/km²/a and 15.0 ton/km²/a, respectively. When sulfuric and nitric acid from rainfall affected by human activities are involved in the weathering process, the actual atmospheric CO2 consumption rates are estimated at 3.7 × 10⁵ mol/km²/a for silicate weathering and 2.2 × 10⁵ mol/km²/a for carbonate weathering. An overestimated carbon sink (17.4 Gg C/a) is about 27.0% of the CO2 consumption flux via silicate weathering in the Jiulongjiang River basin, this result shows the strong effects of anthropogenic factors on atmospheric CO2 level and current and future climate change of earth.

Spatially-resolved mineral identification and depth profiling on chondrules from the primitive chondrite Elephant Moraine 14017 with confocal Raman spectroscopy

Confocal Raman spectroscopy is effective in unveiling structures of minerals without destruction from surface to certain depth. In this study, we introduce an application of confocal Raman spectroscopy on minerals in a primitive chondritic meteorite. The experimental lateral resolution on silicate minerals in this study is ~1.0 μm. Raman spectrum of mesostasis in a named "Tear Drop" chondrule, a spherule object from a primitive chondrite, of Elephant Moraine 14017 (EET 14017) shows a broad feature indicating amorphous phase, which is a common characteristic of primitive chondrule mesostasis. Weak intensities of 825 and 858 cm^-1 peaks were observed in the glassy mesostasis, probably originated from olivine below the surface. A plagioclase-rich chondrule (PRC-1) of EET 14017 was investigated with Raman spectroscopy, which contains two different occurrences of plagioclase: lath-shaped and interstitial grains. The strong intensity of 488 and 505 cm^-1 (plagioclase) and weak intensity of 461 cm^-1 band were observed on the lath-shaped plagioclase. The weak 461 cm^-1 peak from the plagioclase is probably from the subsurface quartz. Raman spectrum of interstital plagioclase in PRC-1 shows 488 and 505 cm^-1 bands and weak pyroxene bands. Depth profiling conducted on the interstitial plagioclase clearly shows that pyroxene exists below the surface. High-lateral resolution and well-resolved depth profiling with the confocal Raman spectroscopy allows us to identify tiny grains and investigate hidden phases underneath the surface without destruction of extraterrestrial materials.

Ecological health assessment of a coastal ecosystem: Case study of the largest brackish water lagoon of Asia

This study focuses on the ecological health assessment of Chilika, a shallow lagoon present in east coast of India, through nutrient stoichiometry and trophic state index (TSI). Multivariate statistical analysis such as ANOVA, Pearson's correlation, Principal Component Analysis (PCA), and Discriminant Analysis (DA) were employed for data interpretation. Nutrient stoichiometry revealed that the Chilika Lagoon experiences phosphorus limitation with regard to nitrogen and silicate (N:P:Si = 16:1:16) throughout the study period. As per the computed TSI values, the southern sector (SS), central sector (CS), and outer channel (OC) were assigned with a mesotrophic status, whereas the northern sector (NS) was assigned with the eutrophic status. From PCA, total nitrogen was found to be negatively correlated with salinity and positively correlated with silicate, thus indicating that the major source of nitrogen in the lagoon was freshwater ingress by rivers with high silicate content. DA indicated that it was successful in discriminating the groups as predicted.

Characterization of drilling waste from shale gas exploration in Central and Eastern Poland

The purpose of this research was to determine and evaluate the chemical properties of drilling waste from five well sites in Central and Eastern Poland. It was found that spent drilling fluids can contain high values of nickel and mercury (270 and 8.77 mg kg^-1_, respectively) and can exceed the maximum permissible limits recommended by the EC regulations for safety of soils (75 mg kg^-1 for nickel and 1.5 mg kg^-1 for mercury). The heavy metal concentrations in the studied drill cuttings did not exceed the maximum permissible limits recommended by the EC regulation. Drilling wastes contain macroelements (e.g., calcium, magnesium, and potassium) as well as trace elements (e.g., copper, iron, zinc, and manganese) that are essential for the plant growth. It was stated that water extracts of drilling fluids and drill cuttings, according to anions presence, had not any specific constituents of concern based on FAO irrigation guidelines, the USEPA WQC, and toxicity values. X-ray diffraction analysis was used to understand the structure and texture of waste drilling fluid solids and drill cuttings. Analysis of the mineralogical character of drilling fluid solids revealed that they contained calcite, quartz, muscovite, sylvite, barite, dolomite, and orthoclase. Drill cuttings contained calcite quartz, muscovite, barite, dolomite, and barium chloride.

Comparison of static and mineralogical ARD prediction methods in the Nordic environment

Acid rock drainage (ARD) is a major problem related to the management of mining wastes, especially concerning deposits containing sulphide minerals. Commonly used tests for ARD prediction include acid-base accounting (ABA) tests and the net acid generation (NAG) test. Since drainage quality largely depends on the ratio and quality of acid-producing and neutralising minerals, mineralogical calculations could also be used for ARD prediction. In this study, several Finnish waste rock sites were investigated and the performance of different static ARD test methods was evaluated and compared. At the target mine sites, pyrrhotite was the main mineral contributing to acid production (AP). Silicate minerals were the main contributors to the neutralisation potential (NP) at 60% of the investigated mine sites. Since silicate minerals appear to have a significant role in ARD generation at Finnish mine waste sites, the behaviour of these minerals should be more thoroughly investigated, especially in relation to the acid produced by pyrrhotite oxidation. In general, the NP of silicate minerals appears to be underestimated by laboratory measurements. For example, in the NAG test, the slower-reacting NP-contributing minerals might require a longer time to react than is specified in the currently used method. The results suggest that ARD prediction based on SEM mineralogical calculations is at least as accurate as the commonly used static laboratory methods.

Model of Mercury Flux Associated with Volcanic Activity

Volcanic activity is one of the primary sources of mercury in the earth's ecosystem. In this work, volcanic rocks from four geotectonically distinct localities (the Czech Republic - intraplate, rift-related alkaline basaltic rocks; Iceland - hotspot/rift-related tholeiitic basaltic rocks; Japan - island arc calc-alkaline andesites; and Alaska - continental arc calc-alkaline dacites) were studied. Ultra-trace Hg contents in all samples ranged from 0.3 up to 6 µg/kg. The highest Hg content was determined for volcanic ash from Mount Redoubt (Alaska, USA). In the case of basaltic volcanic rocks, the obtained results are about two orders of magnitude smaller than values formerly assumed for primary mercury contents in basaltic lavas. They are close to predicted Hg contents in the mantle source, i.e. below 0.5 µg/kg. Hg degassing is probably a key process for the resulting Hg contents in material ejected during volcanic eruption, which is previously enriched by Hg in the shallow-crust.

Long-term variations and influence factors of nutrients in the western North Yellow Sea, China

This study investigated the long-term variations and compositions of nutrients and the associated controlling factors in the western North Yellow Sea on the basis of historical data. The NO₃-N and DIN concentrations and N/P showed continuous increases over the past two decades, which were dominantly affected by riverine inputs, such as inputs from the Yellow River, Yalujiang River and Jia River and atmospheric deposition. However, due to human activities, such as dam construction in rivers and climate change, the SiO₃-Si concentrations and Si/P ratios decreased before the early 1990s and then gradually increased. The vertical distributions of nutrients displayed higher concentrations at the bottom than those at the surface in summer, which was attributed to the combined influence of the thermocline, the Yellow Sea Cold Water Mass, the Yellow Sea Warm Current and biological activities.

Relationship between phytoplankton community succession and environmental parameters in Qinhuangdao coastal areas, China: A region with recurrent brown tide outbreaks

The picoplanktonic pelagophyte Aureococcus anophagefferens could trigger harmful algal blooms (HABs) to discolor water in brown, known as brown tide. Since 2009, large-scale brown tides, caused by A. anophagefferens, had been occurred in early summer for three consecutive years in the coastal waters of Qinhuangdao, China and resulted considerable deleterious effects on the scallop mariculture industry. The causes for the occurrence of brown tides were not fully understood. Therefore, we conducted a one-year survey from June 2013 to May 2014 to study the seasonal succession of the phytoplankton community, including A. anophagefferens and its relationship with environmental variables in the area. The results revealed that the population dynamics of the phytoplankton community were significant variation with seasonal succession, in which A. anophagefferens played an important role during the entire year. The trend of the whole diversity index indicated that the community structure became more stable in winter. The results of principle component analysis (PCA) applied to the environmental factors indicated four major seasonal groups in the environmental variables. The water temperature, silicate and total nitrogen were contributed to the environment in summer, autumn and spring, respectively. In addition, a few another environmental factors commonly contributed to the winter waterbody, indicated that the aquatic environment is more complex in the cold season. The result revealed that the phytoplankton community structure and its variation were mainly affected by the hydrological factors, by using the redundancy analysis (RDA) for the relationship between dominant species and the environment. Furthermore, we inferred Chaetoceros decipiens as a potential species for the breakout of harmful algae blooms (HABs) by RDA ordination. We concluded that the key factor for the seasonal variations in the dynamics of phytoplankton community could be the hydrological parameters in Qinghuangdao coastal area. This research may provide more insight into the occurrence mechanism of brown tide.

Performance and adsorption mechanism of a magnetic calcium silicate hydrate composite for phosphate removal and recovery

A novel magnetic calcium silicate hydrate composite (Fe₃O₄@CSH) was proposed for phosphorus (P) removal and recovery from a synthetic phosphate solution, facilitated by a magnetic separation technique. The Fe₃O₄@CSH material was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), zeta-potential and magnetic curves. The chemical composition and structure of Fe₃O₄@CSH and the successful surface loading of hydroxyl functional groups were confirmed. Phosphate adsorption kinetics, isotherm, and thermodynamic experiments showed that adsorption reaches equilibrium at 24 h, with a maximum adsorption capacity of 55.84 mg P/g under optimized experimental conditions. Adsorption kinetics fitted well to the pseudo second-order model, and equilibrium data fit the Freundlich isotherm model. Thermodynamic analysis provided a positive value for ΔH° (129.84 KJ/mol) and confirmed that phosphate adsorption on these materials is endothermic. The P-laden Fe₃O₄@CSH materials could be rapidly separated from aqueous solution by a magnetic separation technique within 1 min. A removal rate of more than 60% was still obtained after eight adsorption/desorption cycles, demonstrating the excellent reusability of the particles. The results demonstrated that the Fe₃O₄@CSH materials had high P-adsorption efficiency and were reusable.

Derivation of intermediate to silicic magma from the basalt analyzed at the Vega 2 landing site, Venus

Geochemical modeling using the basalt composition analyzed at the Vega 2 landing site indicates that intermediate to silicic liquids can be generated by fractional crystallization and equilibrium partial melting. Fractional crystallization modeling using variable pressures (0.01 GPa to 0.5 GPa) and relative oxidation states (FMQ 0 and FMQ -1) of either a wet (H₂O = 0.5 wt%) or dry (H₂O = 0 wt%) parental magma can yield silicic (SiO₂ > 60 wt%) compositions that are similar to terrestrial ferroan rhyolite. Hydrous (H₂O = 0.5 wt%) partial melting can yield intermediate (trachyandesite to andesite) to silicic (trachydacite) compositions at all pressures but requires relatively high temperatures (≥ 950°C) to generate the initial melt at intermediate to low pressure whereas at high pressure (0.5 GPa) the first melts will be generated at much lower temperatures (< 800°C). Anhydrous partial melt modeling yielded mafic (basaltic andesite) and alkaline compositions (trachybasalt) but the temperature required to produce the first liquid is very high (≥ 1130°C). Consequently, anhydrous partial melting is an unlikely process to generate derivative liquids. The modeling results indicate that, under certain conditions, the Vega 2 composition can generate silicic liquids that produce granitic and rhyolitic rocks. The implication is that silicic igneous rocks may form a small but important component of the northeast Aphrodite Terra.

Commercial silicate phosphate sequestration and desorption leads to a gradual decline of aquatic systems

Laboratory desorption behaviour, function and elemental composition of commercially marketed silicate minerals used to sequester phosphorus pollution as well as Zeolite, Smectite, and Kaolinite were determined to see whether their use by environmental scientists and water managers in eutrophic waterways has the potential to contribute to longer-term environmental impacts. As expected, lower phosphorus concentrations were observed, following treatment. However, data relating to desorption, environmental fate and bioavailability of phospho-silicate complexes (especially those containing rare earth elements) appear to be underrepresented in product testing and trial publications. Analysis of desorption of phosphate (P) was > 5 μg[P]/L for all three non-commercial samples and 0 > μg[P]/L > 5 for all commercial silicates for a range of concentrations from 0 to 300 μg[P]/L. Based on a review of bioaccumulation data specific to the endangered Cherax tenuimanus (Hairy Marron) and other endemic species, this is significant considering anything > 20 μg[La]/L is potentially lethal to the hairy marron, other crustaceans and even other phyla. Where prokaryotic and eukaryotic effects are underreported, this represents a significant challenge. Especially where product protocols recommend continual reapplication, this is significant because both the forward and reverse reactions are equally important. The users of silicate minerals in water columns should accept the dynamic nature of the process and pay equal attention to both adsorption and desorption because desorption behaviour is an inherent trait. Even if broader desorption experimentation is difficult, expensive and time-consuming, it is a critical consideration nonetheless.

Impact of nutrient enrichment on productivity of coastal water along the SE Mediterranean shore of Israel - A bioassay approach

The coastal waters of the southeastern Mediterranean-Sea (SEMS) are routinely enriched with naturally-occurring and anthropogenic land-based nutrient loads. These external inputs may affect autotrophic and heterotrophic microbial biomass and activity. Here, we conducted 13 microcosm bioassays with different additions of inorganic NO₃-(N), PO₄-(P) and Si(OH)₄-(Si) in different seasons along the Mediterranean coast of Israel. Our results indicate that cyanobacteria are mainly N-limited, whereas N or Si (or both) limit pico-eukaryotes. Furthermore, the degree to which N affects phytoplankton depends on the ambient seawater's inorganic N and N:P characteristics. Heterotrophic bacteria displayed no response in all treatments, except when all nutrients were added simultaneously, suggesting a possible co-limitation by nutrients. These results contrast the N+P co-limitation of phytoplankton and the P-limitation of bacteria in the open waters of the SEMS. These observations enable the application for a better science-based environmental monitoring and policy implementation along the SEMS coast of Israel.

Water quality assessment of the ecologically stressed Hooghly River Estuary, India: A multivariate approach

Spatio-temporal and seasonal variation of the water quality characteristics of the Hooghly River Estuary, India were studied considering eight stations of diverse eco-hydrological characteristics. Wide variations in turbidity, total dissolved solids and fecal coliform exceeded the permissible BIS drinking water level limit. The estuary is observed to be relatively low-oxygenated, mesotropic and phosphate limiting. Spatial heterogeneity and impact of the southwest monsoon were remarkably pronounced in the distribution of the inorganic nutrients revealing the following values (expressed in μgatml^-1): nitrate+nitrite (2.42-37.19), phosphate (0.41-1.52) and silicate (38.5-187.75). Water Quality Index (WQI) values confirmed the prevailing 'bad' condition, detrimental for sustenance of aquatic biota. Results of Principal Component Analysis identified the major factors liable for water quality deterioration while cluster analysis categorized the stations on the basis of similar water quality status. The authors recommend adopting preventive measures for water quality improvement linked to biodiversity conservation.

The utilization of waste by-products for removing silicate from mineral processing wastewater via chemical precipitation

This study investigates an environmentally friendly technology that utilizes waste by-products (waste acid and waste alkali liquids) to treat mineral processing wastewater. Chemical precipitation is used to remove silicate from scheelite (CaWO₄) cleaning flotation wastewater and the waste by-products are used as a substitute for calcium chloride (CaCl₂). A series of laboratory experiments is conducted to explain the removal of silicate and the characterization and formation mechanism of calcium silicate. The results show that silicate removal reaches 90% when the Ca:Si molar ratio exceeds 1.0. The X-ray diffraction (XRD) results confirm the characterization and formation of calcium silicate. The pH is the key factor for silicate removal, and the formation of polysilicic acid with a reduction of pH can effectively improve the silicate removal and reduce the usage of calcium. The economic analysis shows that the treatment costs with waste acid (0.63 $/m³) and waste alkali (1.54 $/m³) are lower than that of calcium chloride (2.38 $/m³). The efficient removal of silicate is confirmed by industrial testing at a plant. The results show that silicate removal reaches 85% in the recycled water from tailings dam.

The Lost City Hydrothermal Field: A Spectroscopic and Astrobiological Analogue for Nili Fossae, Mars

Low-temperature serpentinization is a critical process with respect to Earth's habitability and the Solar System. Exothermic serpentinization reactions commonly produce hydrogen as a direct by-product and typically produce short-chained organic compounds indirectly. Here, we present the spectral and mineralogical variability in rocks from the serpentine-driven Lost City Hydrothermal Field on Earth and the olivine-rich region of Nili Fossae on Mars. Near- and thermal-infrared spectral measurements were made from a suite of Lost City rocks at wavelengths similar to those for instruments collecting measurements of the martian surface. Results from Lost City show a spectrally distinguishable suite of Mg-rich serpentine, Ca carbonates, talc, and amphibole minerals. Aggregated detections of low-grade metamorphic minerals in rocks from Nili Fossae were mapped and yielded a previously undetected serpentine exposure in the region. Direct comparison of the two spectral suites indicates similar mineralogy at both Lost City and in the Noachian (4-3.7 Ga) bedrock of Nili Fossae, Mars. Based on mapping of these spectral phases, the implied mineralogical suite appears to be extensive across the region. These results suggest that serpentinization was once an active process, indicating that water and energy sources were available, as well as a means for prebiotic chemistry during a time period when life was first emerging on Earth. Although the mineralogical assemblages identified on Mars are unlikely to be directly analogous to rocks that underlie the Lost City Hydrothermal Field, related geochemical processes (and associated sources of biologically accessible energy) were once present in the subsurface, making Nili Fossae a compelling candidate for a once-habitable environment on Mars. Key Words: Mars-Habitability-Serpentinization-Analogue. Astrobiology 17, 1138-1160.

Assessment of the potential respiratory hazard of volcanic ash from future Icelandic eruptions: a study of archived basaltic to rhyolitic ash samples

BACKGROUND

The eruptions of Eyjafjallajökull (2010) and Grímsvötn (2011), Iceland, triggered immediate, international consideration of the respiratory health hazard of inhaling volcanic ash, and prompted the need to estimate the potential hazard posed by future eruptions of Iceland's volcanoes to Icelandic and Northern European populations.

METHODS

A physicochemical characterization and toxicological assessment was conducted on a suite of archived ash samples spanning the spectrum of past eruptions (basaltic to rhyolitic magmatic composition) of Icelandic volcanoes following a protocol specifically designed by the International Volcanic Health Hazard Network.

RESULTS

Icelandic ash can be of a respirable size (up to 11.3 vol.% < 4 μm), but the samples did not display physicochemical characteristics of pathogenic particulate in terms of composition or morphology. Ash particles were generally angular, being composed of fragmented glass and crystals. Few fiber-like particles were observed, but those present comprised glass or sodium oxides, and are not related to pathogenic natural fibers, like asbestos or fibrous zeolites, thereby limiting concern of associated respiratory diseases. None of the samples contained cristobalite or tridymite, and only one sample contained quartz, minerals of interest due to the potential to cause silicosis. Sample surface areas are low, ranging from 0.4 to 1.6 m² g^-1, which aligns with analyses on ash from other eruptions worldwide. All samples generated a low level of hydroxyl radicals (HO^•), a measure of surface reactivity, through the iron-catalyzed Fenton reaction compared to concurrently analyzed comparative samples. However, radical generation increased after 'refreshing' sample surfaces, indicating that newly erupted samples may display higher reactivity. A composition-dependent range of available surface iron was measured after a 7-day incubation, from 22.5 to 315.7 μmol m^-2, with mafic samples releasing more iron than silicic samples. All samples were non-reactive in a test of red blood cell-membrane damage.

CONCLUSIONS

The primary particle-specific concern is the potential for future eruptions of Iceland's volcanoes to generate fine, respirable material and, thus, to increase ambient PM concentrations. This particularly applies to highly explosive silicic eruptions, but can also hold true for explosive basaltic eruptions or discrete events associated with basaltic fissure eruptions.

Impacts of human activities on nutrient transport in the Yellow River: The role of the Water-Sediment Regulation Scheme

Anthropogenic activities alter the natural states of large rivers and their surrounding environment. The Yellow River is a well-studied case of a large river with heavy human control. An artificial managed water and sediment release system, known as the Water-Sediment Regulation Scheme (WSRS), has been carried out annually in the Yellow River since 2002. Nutrient concentrations and composition display significant time and space variations during the WSRS period. To figure out the anthropogenic impact of nutrient changes and transport in the Yellow River, biogeochemical observations were carried out in both middle reaches and lower reaches of the Yellow River during 2014 WSRS period. WSRS has a direct impact on water oxidation-reduction environment in the middle reaches; concentrations of nitrite (NO₂^-) and ammonium (NH₄⁺) increased, while nitrate (NO₃^-) concentration decreased by enhanced denitrification. WSRS changed transport of water and sediment; dissolved silicate (DSi) in the middle reaches was directly controlled by sediments release during the WSRS while in the lower reaches, DSi changed with both sediments and water released from middle reaches. During the WSRS, the differences of nutrient fluxes and concentrations between lower reaches and middle reaches were significant; dissolved inorganic phosphorous (DIP) and dissolved inorganic nitrogen (DIN) were higher in low reaches because of anthropogenic inputs. Human intervention, especially WSRS, can apparently change the natural states of both the mainstream and estuarine environments of the Yellow River within a short time.

Response of Thalassia Testudinum Morphometry and Distribution to Environmental Drivers in a Pristine Tropical Lagoon

This study was undertaken to determine the relationships between the biomass, morphometry, and density of short shoots (SS) of the tropical seagrass Thalassia testudinum and the physical-environmental forcing in the region. Seasonal sampling surveys were undertaken four times in Bahia de la Ascension, a shallow estuary in the western Mexican Caribbean, to measure plant morphology and environmental variables. The estuary has a fresh water-influenced inner bay, a large central basin and a marine zone featuring a barrier reef at the seaward margin. Leaf size was positively correlated with increasing salinity, but total biomass was not, being similar across most of the sites. Aboveground biomass exhibited seasonal differences in dry and rainy seasons along the bay, most markedly in the brackish inner bay where an abrupt decline in biomass coincided with the rainy season. The relationship between nutrients and biomass indicates that the aboveground/belowground biomass ratio increases as nutrient availability increases. Areal cover was inversely correlated with SS density during both dry and rainy seasons. Maximum SS recruitment coincided with the rainy season. Peaks in SS density were recorded in the freshwater-influenced inner bay during an ENSO cold phase in 2007 (“La Niña”) which is associated with a wetter dry season and following a strong storm (Hurricane Dean). The onset of the rainy season influences both shoot density and T. testudinum biomass by controlling the freshwater input to the bay and thus, the system’s salinity gradient and external nutrients supply from the coastal wetland.

Cationic polyelectrolyte induced separation of some inorganic contaminants and their mixture (zirconium silicate, kaolin, K-feldspar, zinc oxide) as well as of the paraffin oil from water

The flocculation efficiency of a cationic polyelectrolyte with quaternary ammonium salt groups in the backbone, namely PCA5 was evaluated on zirconium silicate (kreutzonit), kaolin, K- feldspar and zinc oxide (ZnO) suspensions prepared either with each pollutant or with their mixture. The effect of several parameters such as settling time, polymer dose and the pollutant type on the separation efficacy was evaluated and followed by optical density and zeta potential measurements. Except for ZnO, the interactions between PCA5 and suspended particles led to low residual turbidity values (around 4% for kreutzonit, 5% for kaolin and 8% for K-feldspar) as well as to the reduction of flocs settling time (from 1200 min to 30 min and 120 min in case of kaolinit and K-feldspar, respectively), that meant a high efficiency in their separation. The negative value of the zeta potential and flocs size measurements, at the optimum polymer dose, point to contribution from charge patch mechanism for the particles flocculation. A good efficiency of PCA5 in separation of paraffin oil (a minimum residual turbidity of 9.8%) has been also found.

Comparison of surface water chemistry and weathering effects of two lake basins in the Changtang Nature Reserve, China

The geochemistry of natural waters in the Changtang Nature Reserve, northern Tibet, can help us understand the geology of catchments, and provide additional insight in surface processes that influence water chemistry such as rock weathering on the Qinghai-Tibet Plateau. However, severe natural conditions are responsible for a lack of scientific data for this area. This study represents the first investigation of the chemical composition of surface waters and weathering effects in two lake basins in the reserve (Lake Dogaicoring Qiangco and Lake Longwei Co). The results indicate that total dissolved solids (TDS) in the two lakes are significantly higher than in other gauged lakes on the Qinghai-Tibet Plateau, reaching 20-40g/L, and that TDS of the tectonic lake (Lake Dogaicoring Qiangco) is significantly higher than that of the barrier lake (Lake Longwei Co). Na(+) and Cl(-) are the dominant ions in the lake waters as well as in the glacier-fed lake inflows, with chemical compositions mainly affected by halite weathering. In contrast, ion contents of inflowing rivers fed by nearby runoff are lower and concentrations of dominant ions are not significant. Evaporite, silicate, and carbonate weathering has relatively equal effects on these rivers. Due to their limited scope, small streams near the lakes are less affected by carbonate than by silicate weathering.

Assessment of waste oyster shells and coal mine drainage sludge for the stabilization of As-, Pb-, and Cu-contaminated soil

A novel treatment mix was designed for the simultaneous immobilization of As, Cu, and Pb in contaminated soils using natural (waste oyster shells (WOS)) and industrial (coal mine drainage sludge (CMDS)) waste materials. The treatments were conducted using the standard U.S. sieve size no. 20 (0.85 mm) calcined oyster shells (COS) and CMDS materials with a curing time of 1 and 28 days. The As immobilization treatments were evaluated using the 1-N HCl extraction fluid, whereas the Pb and Cu immobilization treatments were evaluated using the 0.1-N HCl extraction fluid based on the Korean leaching standards. The treatment results showed that the immobilization of As, Cu, and Pb was best achieved using a combination mix of 10 wt% COS and 10 wt% CMDS. This treatment mix was highly effective leading to superior leachability reductions for all three target contaminants (>93 % for As and >99 % for Cu and Pb) for a curing period of 28 days. The X-ray absorption near-edge structure (XANES) results showed that As was present in the form of As(V) in the control sample and that no changes in As speciation were observed following the COS-CMDS treatments. The scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) sample treated with 10 wt% COS and 10 wt% CMDS indicated that As immobilization may be associated with the formation of Ca-As and Fe-As precipitates while Pb and Cu immobilization was most probably linked to calcium silicate hydrates (CSHs) and calcium aluminum hydrates (CAHs).

Nano-mineralogy of suspended sediment during the beginning of coal rejects spill

Ultrafine and nanometric sediment inputs into river systems can be a major source of nutrients and hazardous elements and have a strong impact on water quality and ecosystem functions of rivers and lakes regions. However, little is known to date about the spatial distribution of sediment sources in most large scale river basins in South America. The objective of this work was to study the coal cleaning rejects (CCRs) spill that occurred from a CCRs impoundment pond into the Tubarão River, South Brazil, provided a unique occasion to study the importance and role of incidental nanoparticles associated with pollutant dispersal from a large-scale, acute aquatic pollution event. Multifaceted geochemical research by X-ray diffraction (XRD), High Resolution-Transmission Electron microscopy (HR-TEM)/(Energy Dispersive Spectroscopy) EDS/(selected-area diffraction pattern) SAED, Field Emission-Scanning Electron Microscopy (FE-SEM)/EDS, and Raman spectroscopy, provided an in-depth understanding of importance of a nano-mineralogy approach of Aqueous Pollution Scenarios. The electron beam studies showed the presence of a number of potentially hazardous elements (PHEs) in nanoparticles (amorphous and minerals). Some of the neoformed ultrafine/nanoparticles found in the contaminated sediments are the same as those commonly associated with oxidation/transformation of oxides, silicates, sulfides, and sulfates. These data of the secondary ultra/nanoparticles, puts in evidence their ability to control the mobility of PHEs, suggesting possible presentations in environmental technology, including recuperation of sensitive coal mine. The developed methodology facilitated the sediment transport of the catchment providing consistent results and suggesting its usefulness as a tool for temporary rivers management.

Diffusion of Na(I), Cs(I), Sr(II) and Eu(III) in smectite rich natural clay

Diffusion of Na(I), Cs(I), Sr(II) and Eu(III) in smectite rich natural clay, proposed as a backfill material in the Indian geological repository, was studied using the out-diffusion method. Radiotracers (22)Na, (137)Cs, (85)Sr and (154)Eu were used; the first three are carrier-free enabling experimental work at sub-micromolar metal ion concentration, and Eu(III) tracer (154)Eu was used at sub millimolar concentration. An out-diffusion methodology, wherein a thin planar source of radioactivity placed between two clay columns diffuses out, was used to obtain the apparent diffusion coefficient (Da) values. This methodology enabled determination of diffusion coefficient even for strongly sorbing (154)Eu. Da values for (22)Na, (137)Cs, (85)Sr and (154)Eu were 2.35 (±0.14) × 10(-11), 2.65 (±0.09) × 10(-12), 3.32 (±0.15) × 10(-11) and 1.23 (±0.15) × 10(-13) m(2) s(-1), respectively. Da values were found to be in fair agreement with literature data reported for similar mineralogical sediments. Sorption of radionuclides on the clay was also determined in the present study and differences in Da values were rationalized on the basis of sorption data. Distribution ratios (Kd) for Cs(I) and Eu(III) were higher than that for Sr(II), which in turn was higher than that for Na(I).

Effects of Volcanic Pumice Inputs on Microbial Community Composition and Dissolved C/P Ratios in Lake Waters: an Experimental Approach

Volcanic eruptions discharge massive amounts of ash and pumice that decrease light penetration in lakes and lead to concomitant increases in phosphorus (P) concentrations and shifts in soluble C/P ratios. The consequences of these sudden changes for bacteria community composition, metabolism, and enzymatic activity remain unclear, especially for the dynamic period immediately after pumice deposition. Thus, the main aim of our study was to determine how ambient bacterial communities respond to pumice inputs in lakes that differ in dissolved organic carbon (DOC) and P concentrations and to what extent these responses are moderated by substrate C/P stoichiometry. We performed an outdoor experiment with natural lake water from two lakes that differed in dissolved organic carbon (DOC) concentration. We measured nutrient concentrations, alkaline phosphatase activity (APA), and DOC consumption rates and assessed different components of bacterial community structure using next-generation sequencing of the 16S rRNA gene. Pumice inputs caused a decrease in the C/P ratio of dissolved resources, a decrease in APA, and an increase in DOC consumption, indicating reduced P limitation. These changes in bacteria metabolism were coupled with modifications in the assemblage composition and an increase in diversity, with increases in bacterial taxa associated with biofilm and sediments, in predatory bacteria, and in bacteria with gliding motility. Our results confirm that volcanic eruptions have the potential to alter nutrient partitioning and light penetration in receiving waterways which can have dramatic impacts on microbial community dynamics.

The Case for a Gaian Bottleneck: The Biology of Habitability

The prerequisites and ingredients for life seem to be abundantly available in the Universe. However, the Universe does not seem to be teeming with life. The most common explanation for this is a low probability for the emergence of life (an emergence bottleneck), notionally due to the intricacies of the molecular recipe. Here, we present an alternative Gaian bottleneck explanation: If life emerges on a planet, it only rarely evolves quickly enough to regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability. Such a Gaian bottleneck suggests that (i) extinction is the cosmic default for most life that has ever emerged on the surfaces of wet rocky planets in the Universe and (ii) rocky planets need to be inhabited to remain habitable. In the Gaian bottleneck model, the maintenance of planetary habitability is a property more associated with an unusually rapid evolution of biological regulation of surface volatiles than with the luminosity and distance to the host star.

Chemical characterization, nano-particle mineralogy and particle size distribution of basalt dust wastes

Understanding the geochemistry of basalt alteration is central to the study of agriculture systems. Various nano-minerals play an important role in the mobilization of contaminants and their subsequent uptake by plants. We present a new analytical experimental approach in combination with an integrated analytical protocol designed to study basalt alteration processes. Recently, throughout the world, ultra-fine and nano-particles derived from basalt dust wastes (BDW) during "stonemeal" soil fertilizer application have been of great concern for their possible adverse effects on human health and environmental pollution. Samples of BDW utilized were obtained from companies in the Nova Prata mining district in southern Brazil for chemical characterization and nano-mineralogy investigation, using an integrated application of advanced characterization techniques such as X-ray diffraction (XRD), High Resolution-Transmission Electron microscopy (HR-TEM)/Energy Dispersive Spectroscopy (EDS)/(selected-area diffraction pattern) SAED, Field Emission-Scanning Electron Microscopy (FE-SEM/EDS), and granulometric distribution analysis. The investigation has revealed that BDW materials are dominated by SiO2, Al2O3, and Fe2O3, with a complex micromineralogy including alkali feldspar, augite, barite, labradorite, hematite, heulandrite, gypsum, kaolinite, quartz, and smectite. In addition, we have identified a number of trace metals such as Cd, Cu, Cr, and Zn, that are preferentially concentrated into the finer, inhalable, dust fraction and, thus, could present a health hazard in the urban areas around the basalt mining zone. The implication of this observation is that use of these nanometric-sized particulates as soil fertilizer may present different health challenges to those of conventional fertilizers, inviting future work regarding the relative toxicities of these materials. Our investigation on the particle size distribution, nano-particle mineralogy and chemical composition in typical BDW samples highlights the need to develop cleaning procedures to minimize exposure to these natural fertilizing basalt dust wastes and is, thus, of direct relevance to both the industrial sector of basalt mining and to agriculture in the region.

Copepod carcasses in a tropical estuary during different hydrographical settings

Dead copepods (carcasses) are widespread in aquatic systems, but their scientific quantification is rare due to the difficulty in discriminating them from live ones. In this paper, we hypothesized that due to large spatial and temporal changes in hydrography in the Cochin backwaters, the percentage of copepod carcasses in the system could also change significantly on a spatial and temporal scale. In order to understand this aspect, we quantified the live and dead copepods in the Cochin backwaters under different hydrographical settings based on live and mortal staining technique. The most prominent temporal hydrographical feature during the study period was the large decline in salinity across the system, which was more pronounced downstream (15-20 units) and was caused by the large freshwater influx associated with the southwest monsoon. During the entire sampling period, copepod carcasses were pervasive all over the study area with large spatial and temporal variations in their percentage contribution (2.5-35.8 %) to the total community abundance. During all sampling, carcasses concentrated more in the downstream region, with maximum turbidity (16.5-35.8 %), than in the upstream region (2.5-14.5 %). The percentage of carcasses was the highest during the onset of the southwest monsoon (av. 23.64 ± 8.09 %), followed by the pre-southwest monsoon (av. 13.59 ± 6.72 %) and southwest monsoon (av. 8.75 ± 4.14 %). During the onset of the southwest monsoon, copepod carcasses in the downstream were contributed by ∼80 % high saline and ∼15 % low saline species, indicating a salinity shock-induced mortality. On the other hand, the cumulative effect of the long residence time of the Cochin backwaters and high partial predation rate of carnivores contributed to the high abundance of carcasses during the pre-monsoon.

Soil and plant response to used potassium silicate drilling fluid application

Use of drilling waste generated from the oil and gas industry for land reclamation has potential to be a practical and economical means to improve soil fertility and to decrease landfills. A four month greenhouse experiment with common barley (Hordeum vulgare L.) on three different textured soils was conducted to determine soil and plant response to incorporated or sprayed potassium silicate drilling fluid (PSDF). Two PSDF types (used once, used twice) were applied at six rates (10, 20, 30, 40, 60, 120m(3)ha(-1)) as twelve PSDF amendments plus a control (non PSDF). Effects of PSDF amendment on plant properties were significant, and varied through physiological growth stages. Barley emergence and below ground biomass were greater with used once than used twice PSDF at the same application rate in clay loam soil. Used twice PSDF at highest rates significantly increased barley above ground biomass relative to the control in loam and sand soil. All PSDF treatments significantly increased available potassium relative to the control in all three soils. Soil electrical conductivity and sodium adsorption ratio increased with PSDF addition, but not to levels detrimental to barley. Soil quality rated fair to poor with PSDF amendments in clay loam, and reduced plant performance at the highest rate, suggesting a threshold beyond which conditions are compromised with PSDF utilization. PSDF application method did not significantly affect plant and soil responses. This initial greenhouse research demonstrates that PSDF has potential as a soil amendment for reclamation, with consideration of soil properties and plant species tolerances to determine PSDF types and rates to be used.

Seasonal Variation and Sources of Dissolved Nutrients in the Yellow River, China

The rapid growth of the economy in China has caused dramatic growth in the industrial and agricultural development in the Yellow River (YR) watershed. The hydrology of the YR has changed dramatically due to the climate changes and water management practices, which have resulted in a great variation in the fluxes of riverine nutrients carried by the YR. To study these changes dissolved nutrients in the YR were measured monthly at Lijin station in the downstream region of the YR from 2002 to 2004. This study provides detailed information on the nutrient status for the relevant studies in the lower YR and the Bohai Sea. The YR was enriched in nitrate (average 314 μmol·L(-1)) with a lower concentration of dissolved silicate (average 131 μmol·L(-1)) and relatively low dissolved phosphate (average 0.35 μmol·L(-1)). Nutrient concentrations exhibited substantial seasonal and yearly variations. The annual fluxes of dissolved inorganic nitrogen, phosphate, and silicate in 2004 were 5.3, 2.5, and 4.2 times those in 2002, respectively, primarily due to the increase in river discharge. The relative contributions of nutrient inputs to nitrogen in the YR were: wastewater > fertilizer > atmospheric deposition > soil; while to phosphorus were: wastewater > fertilizer > soil > atmospheric deposition. The ratios of N, P and Si suggest that the YR at Lijin is strongly P-limited with respect to potential phytoplankton growth.

Possible Biosphere-Lithosphere Interactions Preserved in Igneous Zircon and Implications for Hadean Earth

Granitoids are silicic rocks that make up the majority of the continental crust, but different models arise for the origins of these rocks. One classification scheme defines different granitoid types on the basis of materials involved in the melting/crystallization process. In this end-member case, granitoids may be derived from melting of a preexisting igneous rock, while other granitoids, by contrast, are formed or influenced by melting of buried sedimentary material. In the latter case, assimilated sedimentary material altered by chemical processes occurring at the near surface of Earth-including biological activity-could influence magma chemical properties. Here, we apply a redox-sensitive calibration based on the incorporation of Ce into zircon crystals found in these two rock types, termed sedimentary-type (S-type) and igneous-type (I-type) granitoids. The ∼400 Ma Lachlan Fold Belt rocks of southeastern Australia were chosen for investigation here; these rocks have been a key target used to describe and explore granitoid genesis for close to 50 years. We observe that zircons found in S-type granitoids formed under more reducing conditions than those formed from I-type granitoids from the same terrain. This observation, while reflecting 9 granitoids and 289 analyses of zircons from a region where over 400 different plutons have been identified, is consistent with the incorporation of (reduced) organic matter in the former and highlights one possible manner in which life may modify the composition of igneous minerals. The chemical properties of rocks or igneous minerals may extend the search for ancient biological activity to the earliest period of known igneous activity, which dates back to ∼4.4 billion years ago. If organic matter was incorporated into Hadean sediments that were buried and melted, then these biological remnants could imprint a chemical signature within the subsequent melt and the resulting crystal assemblage, including zircon.