Alkalinity production as an indicator of failure in steel slag leach beds treating acid mine drainage

Acid mine drainage is a serious environmental problem throughout mining regions of the US and around the world. In Appalachia, reuse of steel slag from steel production as a source of alkalinity for treatment of acid mine drainage has become a common practice. In these systems, dubbed steel slag leach beds, relatively clean surface water is percolated through a bed of steel slag to add large amounts of alkalinity to the water before mixing it with acidic, metalliferous mine water. These beds do not operate consistently and their failure mechanisms are poorly understood. Using the experience of Raccoon Creek watershed in southern Ohio, the alkalinity distribution of the discharge of six steel slag leach beds is compared. Two of these beds are still functional, one has been abandoned and three are operating poorly. The difference in alkalinity distribution between these beds suggests that a carbonate-dominated alkalinity system is an indicator of a poorly performing steel slag leach bed, while a more even distribution between hydroxide, carbonate and bicarbonate may point to more ideal operating conditions. In eight laboratory column experiments, this evidence was then expanded upon by testing different mixed media substrates (differing mixes of steel slag, wood chips and river gravel) to see which provided the most ideal alkalinity distributions. The columns that had steel slag mixed either with wood chips or wood chips and river gravel outperformed the column with slag only in terms of alkalinity distribution, perhaps due to microbial processes or increased hydraulic conductivity without significant added calcium or carbon that could drive calcium carbonate precipitation within the beds and causing them to fail.     

Co‐development of alluvial fan surfaces and arid botanical communities,Stonewall Flat,Nevada, USA

Arid alluvial fan and fluvial dry wash surfaces in Stonewall Flat, Nevada, USA, are characterized using surface geomorphic surveys, soil pits, botanical line surveys, and varnish microlamination dating techniques. Active and abandoned washes, and active fan surfaces are dominated by primary geomorphic processes of high‐energy sedimentation from flash floods. These surfaces are characterized by bar and swale topography, a lack of stone pavements, soil horizons, and rock varnish. Younger terraces and slightly older intermediate fan surfaces are in transition from primary sedimentation processes to lower energy secondary surface‐modifying processes of sheet wash and eolian transport and deposition. These surfaces are characterized by faint to no bar and swale topography, incipient to moderately well‐developed pavements and soil horizons, and abundant coppices. Old and stable fan surfaces are dominated by lower energy secondary processes and manifest well‐developed pavements, soils, and sparse coppices around widely distributed shrubs. Varnish microlamination dating yields ages of 13·15 ka for intermediate fan surfaces and 25·55 to 86·75 ka for stable fan surfaces. Plant communities co‐developing with these surfaces affect and are affected by both primary and secondary geomorphic fan processes. Relatively active surfaces contain few woody species. Co‐dominance of shrubs and annuals with abundant annuals between the shrubs is characteristic of surfaces transitional from primary processes to secondary processes. Stable surfaces dominated by secondary processes are characterized by woody perennials, with long‐lived woody species inhabiting the oldest surfaces. Feedback mechanisms between early botanical communities and eolian deposition affect coppice and pavement development. In turn, these surface features control both the composition and distribution of botanical communities on older, more stable surfaces. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.     

Magnesian anorthositic granulites in lunar meteorites Allan Hills A81005 and Dhofar 309: Geochemistry and global significance

Abstract– Fragments of magnesian anorthositic granulite are found in the lunar highlands meteorites Allan Hills (ALH) A81005 and Dhofar (Dho) 309. Five analyzed clasts of meteoritic magnesian anorthositic granulite have Mg′ [molar Mg/(Mg + Fe)] = 81–87; FeO ≈ 5% wt; Al₂O₃ ≈ 22% wt; rare earth elements abundances ≈ 0.5–2 × CI (except Eu ≈ 10 × CI); and low Ni and Co in a non‐chondritic ratio. The clasts have nearly identical chemical compositions, even though their host meteorites formed at different places on the Moon. These magnesian anorthositic granulites are distinct from other highlands materials in their unique combination of mineral proportions, Mg′, REE abundances and patterns, Ti/Sm ratio, and Sc/Sm ratio. Their Mg′ is too high for a close relationship to ferroan anorthosites, or to have formed as flotation cumulates from the lunar magma ocean. Compositions of these magnesian anorthositic granulites cannot be modeled as mixtures of, or fractionates from, known lunar rocks. However, compositions of lunar highlands meteorites can be represented as mixtures of magnesian anorthositic granulite, ferroan anorthosite, mare basalt, and KREEP. Meteoritic magnesian anorthositic granulite is a good candidate for the magnesian highlands component inferred from Apollo highland impactites: magnesian, feldspathic, and REE‐poor. Bulk compositions of meteorite magnesian anorthositic granulites are comparable to those inferred for parts of the lunar farside (the Feldspathic Highlands Terrane): ～4.5 wt% FeO; ～28 wt% Al₂O₃; and Th <1 ppm. Thus, magnesian anorthositic granulite may be a widespread and abundant component of the lunar highlands.     

Seasonal change on Saturn from Cassini/CIRS observations, 2004-2009

Five years of thermal infrared spectra from the Cassini Composite Infrared Spectrometer (CIRS) are analyzed to determine the response of Saturn’s atmosphere to seasonal changes in insolation. Hemispheric mapping sequences at 15.0 cm⁻¹ spectral resolution are used to retrieve the variation in the zonal mean temperatures in the stratosphere (0.5-5.0 mbar) and upper troposphere (75-800 mbar) between October 2004 (shortly after the summer solstice in the southern hemisphere) and July 2009 (shortly before the autumnal equinox).Saturn’s northern mid-latitudes show signs of dramatic warming in the stratosphere (by 6-10 K) as they emerge from ring-shadow into springtime conditions, whereas southern mid-latitudes show evidence for cooling (4-6 K). The 40-K asymmetry in stratospheric temperatures between northern and southern hemispheres (at 1 mbar) slowly decreased during the timespan of the observations. Tropospheric temperatures also show temporal variations but with a smaller range, consistent with the increasing radiative time constant of the atmospheric response with increasing pressure. The tropospheric response to the insolation changes shows the largest magnitude at the locations of the broad retrograde jets. Saturn’s warm south-polar stratospheric hood has cooled over the course of the mission, but remains present.Stratospheric temperatures are compared to a radiative climate model which accounts for the spatial distribution of the stratospheric coolants. The model successfully predicts the magnitude and morphology of the observed changes at most latitudes. However, the model fails at locations where strong dynamical perturbations dominate the temporal changes in the thermal field, such as the hot polar vortices and the equatorial semi-annual oscillation (Orton, G., and 27 colleagues [2008]. Nature 453, 196-198). Furthermore, observed temperatures in Saturn’s ring-shadowed regions are larger than predicted by all radiative-climate models to date due to the incomplete characterization of the dynamical response to the shadow. Finally, far-infrared CIRS spectra are used to demonstrate variability of the para-hydrogen distribution over the 5-year span of the dataset, which may be related to observed changes in Saturn’s tropospheric haze in the spring hemisphere.     

Hydrological functions of a peatland in a Boreal Plains catchment

Streamflow response in Boreal Plains catchments depends on hydrological connectivity between forested uplands, lakes, and peatlands, and their hydrogeomorphic setting. Expected future drying of the Boreal Plains ecozone is expected to reduce hydrological connectivity of landscape units. To better understand run‐off generation during dry periods, we determined whether peatland and groundwater connectivity can dampen expected future water deficits in forests and lakes. We studied Pine Fen Creek catchment in the Boreal Plains ecozone of central Saskatchewan, Canada, which has a large, valley‐bottom, terminally positioned peatland, two lakes, and forested uplands. A shorter intensive study permitted a more detailed partitioning of water inputs and outputs within the catchment during the low flow period, and an assessment of a 10‐year data set provided insight into the function of the peatland over a range of climate conditions. Using a water balance approach, we learned that two key processes regulate flow of Pine Fen Creek. The cumulative impact of landscape unit hydrological connectivity and the peatland's hydrological functional state were needed to understand catchment response. There was evidence of a run‐off threshold which, when crossed, changed the peatland's hydrological function from transmission to run‐off generation. Results also suggest the peatland should behave more often as a transmitter of groundwater than as a generator of run‐off under a drier climate future, owing to a reduced water supply.     

Evaluation of LPM permafrost distribution in NE Asia reconstructed and downscaled from GCM simulations

A high‐resolution map of potential frozen ground distribution in NE Asia (90–150°E, 25–60°N) at the period of the Last Permafrost Maximum (LPM, c. 21 000 years ago) was dually reconstructed by means of a statistical classification using air freezing and thawing indices and a topographical downscaling using a digital relief model (ETOPO1). Background LPM climate data were derived from global climate model simulations of the Paleoclimate Model Intercomparison Project, Phase II (PMIP2). The reconstructed LPM map shows the southward shift of the southern limit of climate‐driven permafrost by 400–1500 km, with the greatest advance in the western sector (90–110°E), encompassing an area from central Siberia to most of the Altai area. The advance of environmentally conditional permafrost and seasonally frozen ground was greatest in the eastern sector (110–150°E), with an average shift of about 450 km. The descent of the lower limit of LPM alpine permafrost was in the range of 400–800 m. A comparison of the reconstructed map with published literature shows that this method, simplistically constructed yet effectively recognizing seasonality, continentality and topography, captures local features better than more elaborate methods. The sensitivity examination of a constant atmospheric lapse rate shows that altitudes of 2000–5000 m a.s.l. were most sensitive, though with only a limited effect on overall LPM distribution.     

Marine debris impacts to a tidal fringing-marsh in North Carolina

We evaluated injuries to Spartina alterniflora by debris items common to North Carolina coastal waters as a function of debris type (wire blue crab pots, vehicle tires, and anthropogenic wood) and deployment duration, and monitored S. alterniflora recovery following debris removal. Injuries sustained by S. alterniflora and subsequent recovery, varied considerably between debris types. Differences were likely due to dissimilarities in the structure and composition of debris. Tires caused an immediate (within 3 weeks) and long-term impact to S. alterniflora; tire footprints remained devoid of vegetation 14 months post-removal. Conversely, crab pot impacts were not as abrupt and recovery was short-term (<10 months). We suggest that removal programs specifically target habitats that are susceptible to negative impacts (e.g., salt marsh) and prone to debris accumulation. Management would benefit from the inclusion of habitat information in removal databases.     

Evaluation of on-line pyrolysis two-dimensional gas chromatography time-of-flight mass spectrometry (Py-GC × GC-ToFMS) on whole sediments from a Mediterranean sapropel sequence

Analysis of the molecular composition of the organic matter (OM) from whole sediment samples can avoid analytical bias that might result from isolation of components from the sediment matrix, but has its own analytical challenges. We evaluated the use of GC × GC-ToFMS to analyze the pyrolysis products of six whole sediment samples obtained from above, within and below a 1 million year old OM-rich Mediterranean sapropel layer. We found differences in pyrolysis products <n-C₂₂ between the OM-rich sapropel samples and the OM-poor background marls. The presence of alkyl pyrroles, probably derived from chlorophyll, in pyrolysates of the sapropels but not in those of the marls suggests that higher marine productivity and greater OM preservation accompanied deposition of the sapropels. Detection of tetramethyl benzenes considered to be pyrolysis products of isorenieratene in the sapropel samples is evidence that nitrogen-fixing green sulfur bacteria contributed to the high productivity. Greater abundances of shorter chain aliphatic hydrocarbons, pyrroles, furans and alkyl aromatics in the pyrolysates of sapropel samples relative to the marls confirm better preservation of marine OM in the sapropels. In addition, the presence of greater amounts of thiophenes in the sapropels than in the marls is consistent with the existence of euxinic conditions during sapropel deposition. The combination of whole sediment pyrolysis and GC × GC-ToFMS is promising, but the procedure requires careful selection of its multiple analytical variables, particularly the pyrolysis temperature and the operational features of the GC columns.     

Hydrocarbon biomarkers of Neoproterozoic to Lower Cambrian oils from eastern Siberia

The Neoproterozoic Era is of widespread geobiological interest because it marks the critical transition from a world of microbes to one where animals become an established feature of the landscape. Much research into this time period has focused on the ventilation of the oceans, as this is widely considered a primary factor driving the diversification of complex, multicellular life. In this study, Proterozoic to Cambrian aged oils from eastern Siberia were analyzed for their hydrocarbon biomarker contents and compound specific carbon isotopes in order to further our understanding of the prevailing environment and its microbial and metazoan communities. Geochemically, these oils are broadly comparable to those of the Ediacaran-Cambrian sedimentary rocks and oils of the South Oman Salt Basin. Organic matter in the source sedimentary rocks included significant contributions from green algae, demosponges and bacteria including cyanobacteria and methanotrophic proteobacteria. Although the ages of the Siberian oils and putative parent source rock intervals are poorly constrained, the geochemical similarities between the Ediacaran Oman Huqf and Nepa-Botuoba-Katanga family of Siberian oil samples are impressive, leading to the inference that their source rocks are coeval. On the other hand, oils from the Baykit High are distinctive, likely older and possibly of Cryogenian age.