Biological Reduction of Nitrate and Perchlorate in Soil Microcosms: An Electron Donor Comparison of Glycerol,Emulsified Oil,and Mulch Extract

Diverse technologies have been developed and tested for their efficacy in remediating perchlorate-contaminated surface water, groundwater, and soil. Biological reduction, particularly when coupled with electron donor augmentation, has been shown to be one of the most cost-effective alternatives. Numerous electron donors have been evaluated in the literature, but few studies have compared standard vs. slow-release electron donors for sequential nitrate and perchlorate reduction. This study evaluated the efficacy and kinetics of biological reduction in soil microcosms augmented with emulsified oil (EO), glycerol, and mulch extract. Results indicated that EO and glycerol spiked at approximately 100 times stoichiometric excess (i.e., 100x) achieved similar overall reductions and degradation rates for nitrate and perchlorate, although nitrate appeared to exhibit zero order kinetics while perchlorate exhibited first order kinetics. The zero order rate constants for nitrate reduction were 3.32 mg/L d and 2.57 mg/L d for EO and glycerol, respectively. The first order rate constant for perchlorate reduction was 0.36 day⁻¹ for both EO and glycerol. Stable chemical oxygen demand (COD) concentrations also highlighted the slow-release properties of EO, which would reduce electron donor consumption in comparison to soluble substrates in soil remediation applications. The microcosms augmented with mulch extract failed to demonstrate any nitrate or perchlorate reduction due to the extract's lower COD concentration. Augmentation with compost or additional processing (i.e., concentration) would be necessary to make the extract a viable alternative.     

River-dominated and tide-influenced shelf-edge delta systems: Coarse-grained deltas straddling the Early–Middle Jurassic shelf–slope break and transforming downslope,Lajas–Los Molles formations,Neuquén Basin,Argentina

The three-dimensional facies and architecture variability of shelf-edge deltaic units cropping out at the transition between the Lower–Middle Jurassic Lajas and Los Molles formations of southern Neuquén Basin, Argentina, is presented here, as well as their stratigraphic relationship to uppermost deep-water slope channel systems. Deep-water, slope mudstones with thin turbidite beds merge upward with prodelta mudstones and thin sandstones, which are truncated by delta-front to mouth-bar sandstones. The latter sandstones are then downcut by large-scale, trough cross-stratified coarse-grained sandstones and conglomerates of distributary channel systems and along-strike, amalgamated with cross-bedded sandy units showing evidence of tidal reworking. Proximal–distal facies and architecture variability within a shelf-edge deltaic succession demonstrates that distributary channel-complexes become wider and deeper basinward, forming channelized river-dominated distributary fairways separated by tidally reworked inter-distributary sand belts at the shelf edge. Evidence from depositional-dip oriented outcrops shows a lack of collapsed and slumped strata at the shelf edge, and that the coarse shelf-edge distributary channel fills continue far down the deepwater slope, and conglomerates transform to become high-density turbidites to mainly thick-bedded, sand-matrix-supported debrites. The interplay between flood tides and river currents is interpreted to have primarily modulated the focusing of river drainages, and consequently coarse-grained sediment transport, along preferential routes on the outer-shelf to shelf-edge and down onto the slope. This contribution documents a unique example of coarse-grained (mostly conglomeratic) shelf-edge delta systems, tying bed-scale facies and architecture data to a seismic-scale shelf-margin morphology, thus providing outcrop analogue data for the characterization of shelf-edge delta systems in the subsurface.     

HT-fabrics in a garnet-bearing quartzite from Western Portugal: geodynamic implications for the Iberian Variscan Belt

ABSTRACT The study of a garnet-bearing quartzite from a major suture zone in Iberia reports an unusual high-T fabric. Quartz c -axis patterns were plotted using shaped garnet as reference axis for the finite stretch ( X -axis). The pole figures are characterized by a dominant single maximum around X together with other point maxima along the XY plane (mylonitic foliation). These patterns suggest that dominant < c > prism slip and subordinated < a > prism slip operated during quartz plastic deformation in agreement with P–T conditions for syntectonic garnet growth (4–5 kbar and 700 ± 50 °C) and, pre-dating the well-known (late) Variscan D1 event (<6 kb and 600 ± 30 °C). The geotectonic framework suggests that the fabrics were formed along the western shear margin of the Ossa-Morena Zone during the early stages of the Variscan orogeny.     

Timing and duration of supergene mineralization at the Xinrong manganese deposit,western Guangdong Province,South China: cryptomelane <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating

Supergene Mn-oxide deposits are widely distributed in Guangxi, Guangdong, Yunnan, and Hunan Provinces, South China, accounting for 18% of the total Mn reserves in the country. Direct dating of supergene Mn enrichment, however, is lacking. In this paper, we present high-resolution ⁴⁰Ar/³⁹Ar ages of Mn oxides from the Xinrong Mn deposit, western Guangdong, to place numerical constraints on the timing and duration of supergene Mn enrichment. A total of ten cryptomelane samples, spanning a vertical extent of 67 m, were dated using the ⁴⁰Ar/³⁹Ar laser incremental heating technique, with seven samples yielding well-defined plateau or pseudo-plateau ages ranging from 23.48 ± 0.91 to 2.06 ± 0.05 Ma (2σ). One sample yields a staircase spectrum that does not reach a plateau; the spectrum, however, indicates the presence of two or more generations of Mn oxides in the sample, whose ages are best estimated at 22.34 ± 0.31 and 10.2 ± 0.86 Ma, respectively. The remaining two samples gave meaningless or uninterpretable results due to significant ³⁹Ar recoil and contamination by old phases. The ⁴⁰Ar/³⁹Ar data thus reveal a protracted history of weathering and supergene Mn enrichment that started at least in the end of the Oligocene or beginning of Miocene and extending into the latest Pliocene. Staircase-apparent age spectra, resulting from banded or botryoidal samples, yield an average growth rate of Mn oxides at 0.6–0.7 × 10⁻³ mm kyr⁻¹. The values indicate that a 1-mm grain of Mn oxides may host minerals precipitated during a time span of ca. 1.5 m.y., and accumulation of Mn oxides to form economic deposits under weathering environments may take millions of years. The distribution of weathering ages shows that the oldest Mn oxides occur on the top of the profile, whereas the youngest minerals are found at the bottom, suggesting downward propagation of weathering fronts. However, two samples located at the intermediate depths of the profile yield ages comparable with those occurring at the highest elevations. Such a complexity of age distribution is interpreted in terms of preferential penetration of Mn-rich weathering solutions along more permeable fault zones, or as a result of multi stages of dissolution and re-precipitation of Mn oxides. A synthesis of geochronological and geological data suggests that formation of the Xinrong deposit was a consequence of a combination of favorable lithological, climatic, and structural conditions. Because the climatic and structural conditions are similar among the provinces of South China during the Cenozoic, the geochronological results obtained at Xinrong may also have implications for the timing of supergene Mn enrichment throughout South China.     

Eutrophication processes and trophic interactions in a shallow estuary: Preliminary results based on stable isotope analysis (δ13C and δ15N)

Stable isotopes ratios (δ¹³C and δ¹⁵N) were measured in primary producers and consumers of two bays with contrasting eutrophic conditions in the Patos Lagoon estuary, southern Brazil: the Justino bay, a more pristine ecosystem, and the Mangueira bay, a heavily polluted region that receives the Rio Grande city sewage and effluencts of several industries. δ¹³C values of organisms collected in both subsystems were not different, but δ¹⁵N values had significant statistical differences, ca. 3.5‰ higher in the Mangueira bay. It is likely that primary producers and consumers in this subsystem are greatly influenced by higher nitrogen input due to domestic and industrial sewages. The stable isotope analysis also corroborated several trophic interactions previously established by gut content analysis, and due to its higher sensitivity, it was possible to better determine the contributions of different primary producers and detrital fractions to the consumers' diets. It was confirmed that plant detritus represents the main food source for most organisms. The stable isotope analysis also demonstrated that detritivorous benthic organisms in the same habitat have distinct diet compositions, with differential consumption of C3 and C4 plants. This technique showed that some consumers that eat detritus do not have in their stable isotopic signature any relationship with that of plants. It is likely that these consumers assimilate their carbon and nitrogen from other sources like microalgae or microorganisms that colonize decaying plants.     

The link between partial melting,granitization and granulite development in central Ribeira Fold Belt,SE Brazil: New evidence from elemental and Sr–Nd isotopic geochemistry

Elemental and Sr–Nd isotopic data on metatexites, diatexites, orthogneisses and charnockites from the central Ribeira Fold Belt indicate that they are LILE-enriched weakly peraluminous granodiorites. Harker and Th–Hf–La correlation trends suggest that these rocks represent a co-genetic sequence, whereas variations on CaO, MnO, Y and HREE for charnockites can be explained by garnet consumption during granulitic metamorphism.Similar REE patterns and isotopic results of ?_Nd⁵⁶⁵ = ?5.4 to ?7.3 and ⁸⁷Sr/⁸⁶Sr₅₆₅ = 0.706–0.711 for metatexites, diatexites, orthogneisses and charnockites, as well as similar T_DM ages between 2.0 and 1.5 Ga are consistent with evolution from a relatively homogeneous and enriched common crustal (metasedimentary) protolith.Results suggest a genetic link between metatexites, diatexites, orthogneisses and charnockites and a two-step process for charnockite development: (a) generation of the hydrated igneous protoliths by anatexis of metasedimentary rocks; (b) continuous high-grade metamorphism that transformed the “S-type granitoids” (leucosomes and diatexites) into orthogneisses and, as metamorphism and dehydration progressed, into charnockites.     

Modeling rock permeability from NMR relaxation data by PLS regression

This study explores the application of the partial least squares regression (PLSR) technique to rock permeability prediction from nuclear magnetic resonance (NMR) relaxation data. A total of 68 Brazilian sandstone cores selected from reservoirs and outcrop analogs were fully saturated and analyzed by NMR. The permeability of the cores ranged from 0.007 to 9,800 mD. From their ¹H transverse relaxation times (T₂) measured at 2 MHz, two PLSR models were developed for the relaxation spectra and the raw relaxation curves. Both models led to more uniform and accurate predictions (RMSE = 0.47 and 0.50 log mD, respectively) compared with the classical Kenyon model (RMSE = 0.78 log mD).