Near-surface Environment Research Articles

Assessment of impacts of diphenyl phosphate on groundwater and near-surface environments: Sorption and toxicity

Wastewater recovered from hydraulic fracturing is referred to as flowback and produced water (FPW), and is often saline, contains numerous organic and inorganic constituents, and may pose threats to groundwater resources. Hundreds of spills of FPW have been reported to the Alberta Energy Regulator each year. Recently, samples of FPW derived from hydraulic fracturing of the Duvernay Formation, AB, were found to contain a previously unidentified class of aryl phosphates, including diphenyl phosphate (DPP), triphenyl phosphate (TPP), and others. Aryl phosphates are also used in a variety of other industries and their constituents can be found in flame retardants, plasticizers, lubricants, hydraulic fluids, and oxidizers. Many of these aryl phosphates break down into DPP. Therefore, it is important to determine the environmental fate and potential impact of DPP if spilled in the near-surface, as DPP is an emerging contaminant in soil and groundwater systems. This study was aimed at determining 1) the sorption behavior of DPP onto various surficial sediments collected within the Fox Creek, AB region, and 2) the toxicity of DPP toward aquatic ecosystems. We report that the sorption of DPP onto both clay-rich soils and sandy sediment was low compared to that of other aryl phosphates, with an average log KOC value of 2.30 ± 0.42 (1σ). Therefore, the transport of DPP in groundwater would be rapid due to its low degree of sorption on surficial materials. We also determined the acute 96 h-LC50 of DPP on zebrafish embryos to be 50.0 ± 7.1 mg/L. Su et al. (2014) studied the toxic effects of DPP and TPP on chicken embryonic hepatocytes and found that DPP had less cytotoxic effects than TPP but altered more gene transcripts. From the results our study, we infer that DPP may pose an environmental risk to aquatic ecosystems if released into the environment.

Predicting dynamic geotechnical parameters in near-surface coastal environment

Conduction of geotechnical survey prior construction is a non-negotiable requirement before the erection of any engineering structure so as to avoid building collapse which has been rampant in our ...

Effects of metal oxide surface doping with phosphonic acid monolayers on alcohol dehydration activity and selectivity

Controlling the near-surface environment of heterogeneous catalysts is of fundamental importance for high selectivity and activity. Self-assembled monolayers (SAMs) are effective tools to control reaction selectivity and activity for both supported noble metal and metal oxide catalysts. We previously demonstrated tunable dehydration activity of alcohols on phosphonic acid-modified, anatase-phase TiO2. In this work, we investigated the generality of this approach by studying the modification of other metal oxides including Al2O3, CeO2, CuO, Fe2O3, MgO, rutile-TiO2, SnO2, V2O5, WO3, ZrO2, and ZnO. Modification of these materials with phosphonic acids results in the formation of SAMs on the surface, as determined by infrared spectroscopy; studies of the thermal stability on selected catalysts indicated that the SAMs remained intact up to approximately 400 °C in inert environments. Decomposition of alcohols on these native materials resulted in dehydration, dehydrogenation, and condensation. Upon functionalization with phosphonic acid modifiers, the activity of all pathways decreased significantly, except for dehydration on CeO2, anatase-TiO2, and SnO2. We explored the properties of these oxides that may be responsible for this increase in dehydration activity using correlations to bulk properties. This analysis supported the hypothesis that phosphonic acid monolayers act as surface-level dopants for metal oxides of specific metal-oxygen bond strength and oxidation state.

Photoecology of the Antarctic cyanobacterium Leptolyngbya sp. BC1307 brought to light through community analysis, comparative genomics and in vitro photophysiology.

Cyanobacteria are important photoautotrophs in extreme environments such as the McMurdo Dry Valleys, Antarctica. Terrestrial Antarctic cyanobacteria experience constant darkness during the winter and constant light during the summer which influences the ability of these organisms to fix carbon over the course of an annual cycle. Here, we present a unique approach combining community structure, genomic and photophysiological analyses to understand adaptation to Antarctic light regimes in the cyanobacterium Leptolyngbya sp. BC1307. We show that Leptolyngbya sp. BC1307 belongs to a clade of cyanobacteria that inhabits near-surface environments in the McMurdo Dry Valleys. Genomic analyses reveal that, unlike close relatives, Leptolyngbya sp. BC1307 lacks the genes necessary for production of the pigment phycoerythrin and is incapable of complimentary chromatic acclimation, while containing several genes responsible for known photoprotective pigments. Photophysiology experiments confirmed Leptolyngbya sp. BC1307 to be tolerant of short-term exposure to high levels of photosynthetically active radiation, while sustained exposure reduced its capacity for photoprotection. As such, Leptolyngbya sp. BC1307 likely exploits low-light microenvironments within cyanobacterial mats in the McMurdo Dry Valleys.

Extracellular Biomineralization of Gold by Delftia tsuruhatensis GX-3 Isolated from a Heavy Metal Contaminated Paddy Soil

The use of microorganisms in geochemical gold recycling was considered recently. To explore the feasibility of gold biomineralization in this study, bacteria GX-3 were isolated from a heavy metal contaminated paddy soil in Guangxi province, China. This sulfur-reducing bacteria, Delftia tsuruhatensis, can survive in toxic Au3+ solution. Alkaline conditions (pH 8.0) and 35 °C were optimal for GX-3 cultivation. Nanoparticle formation was promoted by the coexistence of Fe3+. Field-emission scanning electron microscopy and transmission electron microscopy (TEM) images of GX-3 showed the presence of spherical particles, ranging from 50 to 100 and 200 to 500 nm in diameter, respectively, that stuck together and distributed around the surface of the bacteria as well as outside the cell. These nanoparticles were identified as gold according to the TEM–energy dispersive X-ray spectroscopy analysis. Here, bacterial extracellular solute-binding protein and/or porin should account for the gold nanoparticle formation and the detoxification in aqueous system as it transports electrons to Au3+ for nanoparticle precipitation. The ubiquitous nature of bacteria in near-surface environments and the rapid precipitation of gold by the sulfur-reducing bacterium suggest that these bacteria could be responsible for the wide bioaccumulation of gold in natural systems.

O2 solubility in Martian near-surface environments and implications for aerobic life

Due to the scarcity of O_2 in the modern Martian atmosphere, Mars has been assumed to be incapable of producing environments with sufficiently large concentrations of O_2 to support aerobic respiration. Here, we present a thermodynamic framework for the solubility of O2 in brines under Martian near-surface conditions. We find that modern Mars can support liquid environments with dissolved O_2 values ranging from ~2.5 × 10^(−6) mol m^(−3) to 2 mol m^(−3) across the planet, with particularly high concentrations in polar regions because of lower temperatures at higher latitudes promoting O_2 entry into brines. General circulation model simulations show that O_2 concentrations in near-surface environments vary both spatially and with time—the latter associated with secular changes in obliquity, or axial tilt. Even at the limits of the uncertainties, our findings suggest that there can be near-surface environments on Mars with sufficient O_2 available for aerobic microbes to breathe. Our findings may help to explain the formation of highly oxidized phases in Martian rocks observed with Mars rovers, and imply that opportunities for aerobic life may exist on modern Mars and on other planetary bodies with sources of O_2 independent of photosynthesis.

Ge and Si isotope signatures in rivers: A quantitative multi-proxy approach

Solutes derived from the dissolution of silicate minerals play a key role in Earth's climate via the carbon and other biogeochemical cycles. Silicon (Si) is a unique constituent of silicate minerals and a biologically important nutrient, so tracing its behavior in near-surface environments may provide important insights into weathering processes. However, Si released by weathering is variably incorporated into secondary mineral phases and biota, obscuring signals derived from primary weathering processes. Due to chemical similarities, Germanium (Ge) may help better understand the Si cycle and its relationship to chemical weathering. With this aim, we report new measurements of the concentration and isotopic composition of Ge for both the dissolved and particulate phases of a variety of global rivers. These measurements are combined with analyses of concentration and isotopic ratio of Si on the exact same sample set in order to make direct comparisons of the behavior of these two elements in natural river systems. With this dataset, we develop a new modeling framework describing the full elemental and isotopic systems of these solutes in rivers (i.e., Ge/Si, δ74Ge, and δ30Si). This multi-proxy approach allows us to ascertain the relative importance of biological versus mineral uptake in modulating the fluxes of these elements delivered to the modern ocean.Dissolved δ74Ge composition of rivers studied thus far range from 0.9 to 5.5‰ with a discharge-weighted global average of 2.6 ± 0.5‰. The Ge isotope composition of riverine suspended and bedload sediments is indistinguishable from silicate source rocks, which is consistent with mass balance expectations. The multi-proxy modeling suggests that, among the watersheds studied here, the isotopic fractionation of Si during secondary mineral phase precipitation (Δ30Sisec) ranges from −2.7 to −0.2‰, which removes between 19–79% of the initial dissolved Si, while between 12–54% is incorporated by biota. For Ge, modeling indicates that 79–98% of the dissolved load is incorporated into secondary mineral phases with a Δ74Gesec ranging from −4.9 to −0.3‰. The fractionation induced by biological uptake is calculated to range from −2.6 to −1.3‰ for Δ30Sibio and −0.7 ± 0.7‰ for Δ74Gebio. In addition to improving our understanding of the coupled Ge and Si cycles, our study provides a framework for using multiple isotopic tracers to elucidate the chemical behavior of solutes in natural waters.

A novel wavelet-based approach to characterize dynamic environmental factors controlling short-term soil surface CO2 flux: Application to a controlled CO2 release test site (EIT) in South Korea

Soil surface CO2 flux (FCO2) fluctuates complicatedly in time and space according to hydro-meteorological and atmospheric conditions as well as physicochemical and biological conditions of soil. In this study, we developed a novel approach to identify and quantitatively evaluate the driving forces (DFs) that control FCO2 fluctuations in the near-surface environment with the combined use of dynamic factor analysis (DFA) and wavelet-based multiresolution analysis (WMRA). We focused on short-term (<16 days) periodic DFs using 6-hourly data blocks observed for 107 days. The procedures were as follows: first, potential DFs (PDFs) were examined using DFA for 11 types of data (i.e., solar radiation, air temperature, relative humidity, atmospheric pressure, wind speed, soil water content, soil temperature, soil EC, water vapor, and the concentration and flux of CO2). Then, major DFs (MDFs) were identified using multiresolution correlation analysis (MODCA) and wavelet transform coherence (WTC). MODCA, with the support of WTC, quantitatively estimated the multiscale similarities and lagged phase responses between MDFs and observations including precipitation by using a scale-localized maximum correlation coefficient (rmax). Finally, the contributions of MDFs to FCO2 were evaluated by calculating the effective dynamic efficiency (Def) based on dynamic factor loadings (α) of MDFs to FCO2 and cumulative wavelet energy ratios at main time-frequency scales. As a result, four MDFs and their maximum contributions to baseline FCO2 were characterized as follows: MDF1 represented irregular precipitation (scales of 1/2 to 2 days; α = 0.38; rmax = |−0.36|; Def ≤ 7.58%) and the effect of evapotranspiration (scales of 1/2 to 2 days; α = 0.38; rmax = 0.58; Def ≤ 21.57%); MDF2 addressed seasonal precipitation (scales of 8 to 16 days; α = 0.53; rmax = 0.91; Def ≤38.33%) and the soil moisture effect (scales of 8 to 16 days; α = 0.53; rmax = 0.79; Def ≤52.86%); MDF3 and MDF4 were the surface atmospheric stability effect (scales of 8 to 16 days; α = 0.09, rmax = |−0.85|; Def ≤ 8.25%) and the soil temperature effect (scales of 8 to 16 days; α = 0.44; rmax = 0.29; Def ≤41.79%), respectively. A comparison with conventional multiple regression showed that the combined application of DFA and WMRA supplements the conventional method by considering the dynamic properties of DFs and their contributions and by analyzing correlations at multiresolution time-frequency scales. The present method is expected to better characterize MDFs for other complex physicochemical and biological interactions in the environmental system.

Lessons learned and best practices derived from environmental monitoring at a large-scale CO2 injection project

Near-surface soil gas and groundwater measurements can be helpful tools in assuaging concerns of potential out-of-zone migration of CO2 from a geologic storage unit into the overlying near-surface environment. These data, therefore, help to build confidence with local stakeholders and regulators that stored CO2 is not impacting surface/near-surface environments. Routine monitoring of soil gas concentrations in the vadose zone can be used to show a lack of change or effect. However, both air temperature modeling and the Romanak et al. (2012) process-based approach should be applied when soil gas data are evaluated, as increased CO2 concentrations can occur naturally from changes in the soil environment. Laboratory testing of groundwater and formation rock (drill cuttings) samples, exposed to varying concentrations of CO2 under in situ temperature and pressure conditions, yield valuable information with respect to water chemistry changes that could occur from a potential out-of-zone migration. Key field-measured groundwater monitoring parameters that change significantly in response to low levels of CO2 are pH (rapid decrease), alkalinity (increase), and conductivity (increase). Empirical models that predict soil gas concentrations using routinely measured climatic data such as air temperature, as well as models that predict the magnitude and duration of potential CO2 exposure in groundwater, should be employed as components of a broad surface and subsurface monitoring program.

Single-crystal hematite (U–Th)/He dates and fluid inclusions document widespread Cryogenian sand injection in crystalline basement

The Tavakaiv Quartzite (informal) in Colorado, USA, is one of the world's largest basement-hosted clastic injectite systems and provides a glimpse into the tectonic and near-surface environment of ancient North America. The age, origin, and significance of Tavakaiv injectites has been debated for over a century, owing to inherent difficulties with assigning absolute age constraints to unfossiliferous sandstone intrusions. Here, we apply an innovative combination of single-crystal hematite (U–Th)/He thermochronometry and fluid inclusion microthermometry to hematite mineralization associated with the injectites to document the age and ambient fluid conditions of Tavakaiv injectite formation. Our approach confirms individual hematite crystals comprising commonly analyzed polycrystalline aggregates are the He diffusion domains and that hematite (U–Th)/He closure temperature increases with crystal size. We apply apatite and zircon fission-track thermochronometry to the Tavakaiv Quartzite and host rock to account for the consequences of Phanerozoic orogenic episodes on the hematite (U–Th)/He dates and explain the observed trends between hematite He date and crystal size. Our results indicate that hematite formed 676 ± 26 million years ago (arithmetic mean date ±1σ), constraining the timing of the Tavakaiv injection event. Fluid inclusion studies reveal that this mineralizing fluid was at least 200 °C and saline (>20 wt% CaCl2 equiv.). Comparison of new and previously published detrital zircon U–Pb age populations from quartzite samples yield a sediment source common to Tavakaiv bodies across a broader region and illuminate the greater areal extent of the Cryogenian injection event. We interpret that formation of basement-penetrating fracture arrays was associated with crustal extension within Rodinia at this time. This was accompanied by sand remobilization that promoted widespread sand injection within horsts bounding Neoproterozoic rift basins. The resulting sand injectites served as permeable pathways for contemporaneous circulation of saline groundwater, driven by fluid gradients in extensional and/or transtensional basins.

Weathering of Bi-bearing tennantite

The tennantite-tetrahedrite solid-solution series [called fahlore; (Cu,Ag)6Cu4(Fe,Zn,Cu,Hg,Cd)2(Sb,As,Bi,Te)4(S,Se)13] is widespread in many geological environments. Since it incorporates heavy metals and toxic elements, a better understanding of its weathering behaviour and details of its weathering process is important to evaluate environmental risks (emerging mainly from the mobilization of As-Sb-Bi) and local and global metal fluxes in stream waters and oceans. In this study, weathering of Bi-rich members of this mineral group was investigated using microscopy, EMPA, SEM, TEM, LA-ICP-MS, Raman, μXRD, and MLA.Observations reveal a succession of four distinct stages of weathering: During stage 1, irregular tubes within fahlore show an assemblage of nm- to μm-sized roméite group minerals, tripuhyite, crystalline Cu-oxides and Cu-sulfides. Stage 1 textures and secondary sulfides indicate a low redox-potential and a low fluid/rock ratio, typical of cementation zones. Mass balance calculations show that during this stage all Zn and the majority of As and S are released to the weathering fluids. Bismuth is immobile in this stage and Sb and Fe are immobile, if Bi is sufficiently available from fahlore, but both are partly released, if the fahlore did not contain sufficient Bi. During stage 2, amorphous and nano-crystalline arsenates replace fahlore as weathering fronts. Such assemblages indicate a higher redox-potential than in stage 1, typical for oxidation zones. Mass balance calculations reveal that Zn, Sb, S and partially Cu are lost. Arsenic and Bi are immobile. Stage 3 occurs only locally, dissolving former weathering stages and/or precipitating amorphous Cu-arsenates/silicates reflecting processes in micro-compartments, not characteristic for the general weathering process. Stage 4 is characterized by the formation of crystalline Bi-, Cu-, Ba-, Ca- or Al-bearing arsenates and Cu-carbonates, spatially independent of the precursor fahlore. Copper and As originate from older weathering assemblages, whereas many other elements are derived externally (Ca, Ba, Al). This stage reflects the increasing importance of the local host rock and gangue mineralogy, as it is typical in near-surface environments of oxidation zones or on mine dumps, where elements are highly mobile and a high fluid/rock ratio prevails (gossan mineralization).The temporal evolution of fahlore weathering textures reflects the transition from fresh ore to cementation zone, oxidation zone and gossan assemblages in one hand specimen. Thus, one fahlore grain can record the uplift and erosion and the increasing fluid/rock interaction of a weathered ore deposit with time. Tube-like textures similar to the ones observed in stage 1 have been reported from other weathering environments and from a variety of element, oxide, arsenide, and sulfide phases. They also were produced during experimental work in ilmenite. This is clear evidence, that the diffusive process during the first contact with alteration fluids is a basic physical process and that it is not only valid for fahlore.The importance of Bi to stabilize Sb-bearing supergene phases (and thereby for the immobilization of toxic Sb) shown in the present work, may stimulate further investigations on the environmental immobilization of toxic elements by “companion metals” during weathering processes.

The structural and dynamical role of water in natural organic matter: A 2H NMR and XRD study

Natural organic matter (NOM) is an important component in many near-surface geochemical environments, and its properties are greatly affected by the incorporation of water. Because of its importance, the macroscopic behavior and effects of water in NOM and soil organic matter (SOM) have been extensively studied using a wide range of experimental and computational methods. The molecular scale structural and dynamical behavior of water in these materials, however, is less well understood. This paper presents a variable temperature 2H NMR and XRD study of water in Suwannee River NOM and its fulvic acid (FA) and humic acid (HA) fractions that provides new insight into the dynamical behavior of structurally different types of water and exchangeable hydrogen environments in NOM. The results provide a basis for future studies of more complex natural organic materials and the interaction of organic materials with mineral surfaces. Room temperature 2H NMR spectra of samples hydrated in 2H2O and then dehydrated, distinguish 2H2O molecules that are in rapid reorientational motion (correlation times, νc, > 105 Hz), 2H exchanged onto carboxylic sites of the NOM that do not undergo rapid reorientation at frequencies >∼103 Hz, and 2H exchanged onto phenolic and possibly other alcohol sites of the NOM that undergoes rapid, but anisotropic, dynamical reorientation. For samples exposed to water and not dried, the XRD results collected at temperatures from 173 to 298 K show the formation of ice-1h in samples exposed to 100% relative humidity (R.H.) but not in samples exposed to 43% R.H. 2H NMR of those samples collected at temperatures from 313 K to 173 K show the presence of multiple sites. Near room temperature, the spectra contain a narrow resonance for mobile water undergoing rapid isotropic motion, and a broader symmetrical resonance probably due to a combination of more dynamically restricted water molecules and 2H exchanged onto phenolic and alcohol functional groups undergoing rapid anisotropic motion. The 43% R.H. samples also yield a broader, quadrupole-dominated, resonance for 2H exchanged onto functional groups of the NOM. With decreasing temperature the resonances for dynamically restricted water molecules and 2H exchanged onto phenolic and alcohol functional groups become broader, reflecting a decreasing rate of exchange between the water molecules and functional groups and a decreasing rate of reorientation of the 2H2O molecules. The formation of ice-1h is directly reflected in the 2H spectra of the 100% R.H. samples as a resonance with a quadrupole coupling constant (QCC) of ∼180 kHz. For the 43% R.H. samples, there is also a broad, poorly resolved resonance with typical QCCs of ∼180 kHz for which the relative signal intensity increases with decreasing temperature. This signal represents 2H2O molecules that are not crystallized in ice-1h but have greatly reduced reorientation frequencies at low temperature and a hydrogen bonding network with hydrogen bond strengths similar to, but somewhat weaker than, ice-1h. Such molecules are also likely to be present in the 100% R.H. samples. At both R.H.s, some of the 2H2O molecules do not freeze and retain their isotropic motion down to 173 K, the lowest temperature investigated.

The origin of clay-coated sand grains and sediment heterogeneity in tidal flats

The presence and distribution of clay minerals attached to grain surfaces as coats (also known as rims) are of great interest because they affect petroleum reservoir quality via the inhibition of the porosity-occluding quartz cement during prolonged burial and heating. Being able to predict the distribution of clay-coated sand grains in petroleum reservoirs is thus important to help find and exploit anomalously high porosity sandstones deep in sedimentary basins. The few studies focused on the distribution of clay coats in marginal marine sediments derive from surface sediment-based data sets, with limited emphasis placed on the preservation of the surface trends in sediment undergoing eodiagenesis in the near-surface environments. The post-depositional processes of bioturbation (sediment homogenization) and infiltration of clay into sand-grade sediment have been widely invoked as potential mechanisms that produce clay coats in modern sands and ancient sandstones. However, the potential for such processes to alter surface trends and govern clay-coat distribution in the subsurface remains unconstrained. In this study, we report the development of a novel, quantitative model of clay-coat coverage in order to identify the controlling mechanisms that govern clay-coat distributions. This study has focused on surface and near-surface sediments in the Saltcoats tidal flat deposits of the Ravenglass Estuary, UK. This unique bio-sedimentary study involved geomorphic mapping, core logging, a range of scanning electron microscopy techniques, and quantification of grain-size, clay fraction content, biofilm abundance (total carbohydrate and biomarker analysis), clay-coat coverage, and clay-coat mineralogy. In this study, against established convention, we demonstrate that infiltration and bioturbation do not significantly affect clay-coat grain coverage in near-surface sediments. Instead, we show that the extent, distribution, and mineralogy of clay coats in near-surface sediment are governed by the surface-based hydrological segregation of the clay mineral assemblage and biological clay-coat formation.

Transformation of uranium species in soil during redox oscillations

Redox oscillation is commonly found in near-surface environment, where soils are often polluted with many redox active contaminants, including uranium (U). In order to investigate the transformation of U species in near-surface soil under redox oscillations conditions, redox oscillations and reduction experiments were performed, biogeochemical parameters and native microbial community composition were monitored, main elements on the surface of solid-phase were analyzed by XPS, and labile U(IV) species and stable U(IV) species in solid-phase were provisionally defined using an anoxic 1 M sodium bicarbonate extraction. It was found that redox oscillations slightly increased the water-soluble U but significantly increased the stable U(IV) species (P < 0.05) in soil. In reduction experiment, there was upper limit value for percentage of stable U(IV) species, and the labile U(IV) species could not transform to stable U(IV) species in a short period of time under reduction conditions. The redox transition of Fe enriched on the surface of soil and the conversion of microbial community composition played a major role in speciation transformation of U under redox oscillations conditions. In addition, sequential extraction revealed that the increase of stable U(IV) species content reflected the U speciation transition from acetate extract to more recalcitrant hydroxylamine extract. The finding provides a potential method for improving the stability of U when bio-reduction is used to remediate the U-contaminated soils.

Exceptionally high whole-rock δ18O values in intra-caldera rhyolites from Northeast Iceland

ABSTRACTThe Icelandic crust is characterized by low δ18O values that originate from pervasive high-temperature hydrothermal alteration by18O-depleted meteoric waters. Igneous rocks in Iceland with δ18O values significantly higher than unaltered oceanic crust (~5.7‰) are therefore rare. Here we report on rhyolitic intra-caldera samples from a cluster of Neogene central volcanoes in Borgarfjörður Eystri, Northeast Iceland, that show whole-rock δ18O values between +2.9 and +17.6‰ (n= 6), placing them among the highest δ18O values thus far recorded for Iceland. Extra-caldera rhyolite samples from the region, in turn, show δ18O whole-rock values between +3.7 and +7.8‰ (n= 6), consistent with the range of previously reported Icelandic rhyolites. Feldspar in the intra-caldera samples (n= 4) show δ18O values between +4.9 and +18.7‰, whereas pyroxene (n= 4) shows overall low δ18O values of +4.0 to +4.2‰, consistent with regional rhyolite values. In combination with the evidence from mineralogy and rock H2O contents, the high whole-rock δ18O values of the intra-caldera rhyolites appear to be the result of pervasive isotopic exchange during subsolidus hydrothermal alteration with18O-enriched water. This alteration conceivably occurred in a near-surface hot spring environment at the distal end of an intra-caldera hydrothermal system, and was probably fed by waters that had already undergone significant isotope exchange with the country rock. Alternatively,18O-enriched alteration fluids may have been produced during evaporation and boiling of standing water in former caldera lakes, which then interacted with the intra-caldera rock suites. Irrespective of the exact exchange processes involved, a previously unrecognized and highly localized δ18O-enriched rock composition exists on Iceland and thus probably within the Icelandic crust too.

Novel Method of Quantifying Radioactive Cesium-Rich Microparticles (CsMPs) in the Environment from the Fukushima Daiichi Nuclear Power Plant.

Highly radioactive cesium-rich microparticles (CsMPs) were released from the Fukushima Daiichi nuclear power plant (FDNPP) to the surrounding environment at an early stage of the nuclear disaster in March of 2011; however, the quantity of released CsMPs remains undetermined. Here, we report a novel method to quantify the number of CsMPs in surface soils at or around Fukushima and the fraction of radioactivity they contribute, which we call "quantification of CsMPs" (QCP) and is based on autoradiography. Here, photostimulated luminescence (PSL) is linearly correlated to the radioactivity of various microparticles, with a regression coefficient of 0.0523 becquerel/PSL/h (Bq/PSL/h). In soil collected from Nagadoro, Fukushima, Japan, CsMPs were detected in soil sieved with a 114 μm mesh. There was no overlap between the radioactivities of CsMPs and clay particles adsorbing Cs. Based on the distribution of radioactivity of CsMPs, the threshold radioactivity of CsMPs in the size fraction of <114 μm was determined to be 0.06 Bq. Based on this method, the number and radioactivity fraction of CsMPs in four surface soils collected from the vicinity of the FDNPP were determined to be 48-318 particles per gram and 8.53-31.8%, respectively. The QCP method is applicable to soils with a total radioactivity as high as ∼106 Bq/kg. This novel method is critically important and can be used to quantitatively understand the distribution and migration of the highly radioactive CsMPs in near-surface environments surrounding Fukushima.

Stable Isotope Probing for Microbial Iron Reduction in Chocolate Pots Hot Spring, Yellowstone National Park.

Chocolate Pots hot springs (CP) is a circumneutral-pH Fe-rich geothermal feature located in Yellowstone National Park. Previous Fe(III)-reducing enrichment culture studies with CP sediments identified close relatives of known dissimilatory Fe(III)-reducing bacterial (FeRB) taxa, including Geobacter and Melioribacter However, the abundances and activities of such organisms in the native microbial community are unknown. Here, we used stable isotope probing experiments combined with 16S rRNA gene amplicon and shotgun metagenomic sequencing to gain an understanding of the in situ Fe(III)-reducing microbial community at CP. Fe-Si oxide precipitates collected near the hot spring vent were incubated with unlabeled and 13C-labeled acetate to target active FeRB. We searched reconstructed genomes for homologs of genes involved in known extracellular electron transfer (EET) systems to identify the taxa involved in Fe redox transformations. Known FeRB taxa containing putative EET systems (Geobacter, Ignavibacteria) increased in abundance under acetate-amended conditions, whereas genomes related to Ignavibacterium and Thermodesulfovibrio that contained putative EET systems were recovered from incubations without electron donor. Our results suggest that FeRB play an active role in Fe redox cycling within Fe-Si oxide-rich deposits located at the hot spring vent.IMPORTANCE The identification of past near-surface hydrothermal environments on Mars emphasizes the importance of using modern Earth environments, such as CP, to gain insight into potential Fe-based microbial life on other rocky worlds, as well as ancient Fe-rich Earth ecosystems. By combining stable carbon isotope probing techniques and DNA sequencing technology, we gained insight into the pathways of microbial Fe redox cycling at CP. The results suggest that microbial Fe(III) oxide reduction is prominent in situ, with important implications for the generation of geochemical and stable Fe isotopic signatures of microbial Fe redox metabolism within Fe-rich circumneutral-pH thermal spring environments on Earth and Mars.

Paleo-environment and reservoir evolution of the Middle Ordovician Kelimoli Formation in the northern Tianhuan area, Ordos Basin, China: implications for high-quality reservoir development

ABSTRACTThe Middle Ordovician Kelimoli Formation carbonate reservoirs in the northern Tianhuan area, Ordos Basin, China are main exploration targets. Subsurface core samples, logging, drilling and production data from the area were used to characterise the carbonate reservoir and to construct a genetic model for exploration. The sedimentary facies identified include trough–continental rise, upper–lower slope, platform margin reef-shoal, open platform and evaporation-restricted platform. The slope and platform margin facies are potential zones for high-quality reservoirs. Porosity in the study area comprises intergrain, intercrystal, intragrain and intracrystal pores, fractures and vughs. The Sr/Ba (0.40–4.87) and V/(V + Ni) (0.64–0.97) ratios indicate deposition in a brackish water-dominated environment under reducing conditions, associated with sea-level fluctuations during the deposition of the Kelimoli Formation. The Sr/Ba, V/(V + Ni), 87Sr/86Sr ratios, δ18O values and crystal texture of dolomite samples suggest that meteoric water was involved in the diagenetic fluid in the near-surface depositional environment. Isotopes (δ13C and δ18O) and trace elements (Fe and Mn) allowed the identification of seepage-reflux and mixed-water dolomitisation. The crystal textures of the samples consist of micritic, bioclastic and reefal limestones, and dolomite with gypsum, which were easily dissolved during the early diagenetic stage. The epidiagenetic stage was the key period for the development of high-quality reservoirs because of large-scale bedding-parallel karstification from meteoric water. The reservoir zones, dominated by partially filled and unfilled vughs, and fractures, are favourable exploration targets in the northern Tianhuan area.

Cu, Pb, and Zn Sorption to Biogenic Iron (Oxyhydr)Oxides Formed in Circumneutral Environments

The transportation and immobilization of potentially toxic metals in near-surface environments may be partially controlled by sorption processes at the solid-water interface. Myriad studies have shown that iron (oxyhydr)oxides have large sorption capacities and form strong surface complexes with metal ions. Biogenic iron (oxyhydr)oxides (BIOS) form at redox gradients where dissolved ferrous iron encounters oxygenated conditions, allowing bacteria to outcompete abiotic Fe oxidation. This process produces biominerals with distinct surface and structural properties (incorporation of cell-derived organic matter, poor crystallinity, and small particle sizes) that may alter their metal-binding affinity and sorption processes. To better understand metal binding by BIOS, Cu, Pb, and Zn, sorption rate and isotherm studies were conducted with synthetic two-line ferrihydrite and BIOS. Additionally, X-ray absorption spectroscopy and total scattering were used to elucidate the BIOS mineral structure and metal ion surface structures. On a mass normalization basis, BIOS sorbed approximately 8, 4, and 2 times more Cu, Pb, and Zn, respectively, than 2LFh over similar dissolved concentrations. Spectroscopic analyses revealed poorly crystalline structures and small coherent scattering domain sizes for BIOS. Additionally, extended X-ray absorption fine-structure spectroscopy revealed Cu, Pb, and Zn sorbed to BIOS via inner-sphere complexes, similar to 2LFh. These results suggest that, in metal contaminated environments, BIOS are more efficient in metal binding than their synthetic counterparts.

Bioavailability of Mineral-Bound Iron to a Snow Algal-Bacterial Coculture and Implications for Albedo-Altering Snow Algal Blooms.

Snow algae can form large-scale blooms across the snowpack surface and near-surface environments. These pigmented blooms can decrease snow albedo and increase local melt rates, and they may impact the global heat budget and water cycle. Yet, the underlying causes for the geospatial occurrence of these blooms remain unconstrained. One possible factor contributing to snow algal blooms is the presence of mineral dust as a micronutrient source. We investigated the bioavailability of iron (Fe)-bearing minerals, including forsterite (Fo90, Mg1.8Fe0.2SiO4), goethite, smectite, and pyrite as Fe sources for a Chloromonas brevispina-bacterial coculture through laboratory-based experimentation. Fo90 was capable of stimulating snow algal growth and increased the algal growth rate in otherwise Fe-depleted cocultures. Fo90-bearing systems also exhibited a decrease in the ratio of bacteria to algae compared to those of Fe-depleted conditions, suggesting a shift in microbial community structure. The C. brevispina coculture also increased the rate of Fo90 dissolution relative to that of an abiotic control. Analysis of 16S rRNA genes in the coculture identified Gammaproteobacteria, Betaproteobacteria, and Sphingobacteria, all of which are commonly found in snow and ice environments. Archaea were not detected. Collimonas and Pseudomonas, which are known to enhance mineral weathering rates, comprised two of the top eight (>1%) operational taxonomic units (OTUs). These data provide unequivocal evidence that mineral dust can support elevated snow algal growth under otherwise Fe-depleted growth conditions and that snow algal microbial communities can enhance mineral dissolution under these conditions.IMPORTANCE Fe, a key micronutrient for photosynthetic growth, is necessary to support the formation of high-density snow algal blooms. The laboratory experiments described herein allow for a systematic investigation of the interactions of snow algae, bacteria, and minerals and their ability to mobilize and uptake mineral-bound Fe. Results provide unequivocal and comprehensive evidence that mineral-bound Fe in Fe-bearing Fo90 was bioavailable to Chloromonas brevispina snow algae within an algal-bacterial coculture. This evidence includes (i) an observed increase in snow algal density and growth rate, (ii) decreased ratios of bacteria to algae in Fo90-containing cultures relative to those of cultures grown under similarly Fe-depleted conditions with no mineral-bound Fe present, and (iii) increased Fo90 dissolution rates in the presence of algal-bacterial cocultures relative to those of abiotic mineral controls. These results have important implications for the role of mineral dust in supplying micronutrients to the snow microbiome, which may help support dense snow algal blooms capable of lowering snow albedo and increasing snow melt rates on regional, and possibly global, scales.