165 research outputs found
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Water-Rock Interaction-11: Saratoga Springs, NY 11th International Symposium on Water Rock Interaction
Boron isotope fractionation in soils at Shale Hills CZO
Isotope fractionation of many elements can fingerprint the biogeochemical, weathering and erosion processes that govern the evolution of the Critical Zone (CZ). This study investigates boron isotope fractionation in two soil profiles developed on the same shale bedrock at Shale Hills Critical Zone Observatory. The first soil profile, located at the valley floor, is isotopically similar to the bedrock and appears to have lost boron mostly through the loss of fine particles matter (clays) with no isotopic fractionation. The second soil profile, located at the ridge top appears to be more depleted in boron concentration and isotopically fractionated toward lower values, as expected from mineral dissolution followed by adsorption/co-precipitation processes
Boron isotope fractionation in soils at Shale Hills CZO
Isotope fractionation of many elements can fingerprint the biogeochemical, weathering and erosion processes that govern the evolution of the Critical Zone (CZ). This study investigates boron isotope fractionation in two soil profiles developed on the same shale bedrock at Shale Hills Critical Zone Observatory. The first soil profile, located at the valley floor, is isotopically similar to the bedrock and appears to have lost boron mostly through the loss of fine particles matter (clays) with no isotopic fractionation. The second soil profile, located at the ridge top appears to be more depleted in boron concentration and isotopically fractionated toward lower values, as expected from mineral dissolution followed by adsorption/co-precipitation processes
Biochemical Mechanisms and Energy Strategies of Geobacter Sulfurreducens
To provide the scientific understanding required to allow DOE sites to incorporate relevant biological, chemical, and physical processes into decisions concerning environmental remediation, a fundamental understanding of the controls on micro-organism growth in the subsurface is necessary. Specifically, mobility of metals in the environment, including chromium, technetium and uranium, is greatly affected by the process of dissimilatory metal reduction (DMR), which has been shown to be an important biological activity controlling contaminant mobility in the subsurface at many DOE sites. Long-term maintenance of DMR at constant rates must rely upon steady fluxes of electron donors to provide the maintenance energy needed by organisms such as Geobacter sulfurreducens to maintain steady state populations in the subsurface
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Critical Chemical-Mechanical Couplings that Define Permeability Modifications in Pressure-Sensitive Rock Fractures
This work examined and quantified processes controlling changes in the transport characteristics of natural fractures, subjected to coupled thermal-mechanical-chemical (TMC) effects. Specifically, it examined the effects of mineral dissolution and precipitation mediated by mechanical effects, using laboratory through-flow experiments concurrently imaged by X-ray CT. These were conducted on natural and artificial fractures in cores using water as the permeant. Fluid and mineral mass balances are recorded and are correlated with in-sample saturation, porosity and fracture aperture maps, acquired in real-time by X-ray CT-imaging at a maximum spatial resolution of 15-50 microns per pixel. Post-test, the samples were resin-impregnated, thin-sectioned, and examined by microscopy to define the characteristics of dissolution and precipitation. The test-concurrent X-ray imaging, mass balances, and measurements of permeability, together with the post-test microscopy, were used to define dissolution/precipitation processes, and to constrain process-based models. These models define and quantify key processes of pressure solution, free-face dissolution, and shear-dilation, and the influence of temperature, stress level, and chemistry on the rate of dissolution, its distribution in space and time, and its influence on the mechanical and transport properties of the fracture
Natural and anthropogenic processes contributing to metal enrichment in surface soils of central Pennsylvania
Metals in soils may positively or negatively affect plants as well as soil micro-organisms and mesofauna, depending on their abundance and bioavailability. Atmospheric deposition and biological uplift commonly result in metal enrichment in surface soils, but the relative importance of these processes is not always resolved. Here, we used an integrated approach to study the cycling of phosphorus and a suite of metals from the soil to the canopy (and back) in a temperate watershed. The behavior of elements in these surface soils fell into three categories. First, Al, Fe, V, Co, and Cr showed little to no enrichment in the top soil layers, and their concentrations were determined primarily by soil production fluxes with little influence of either atmospheric inputs or biological activity. Second, P, Cu, Zn and Cd were moderately enriched in surface soils due to a combination of atmospheric deposition and biological uplift. Among the metals we studied, Cu, Zn and Cd concentrations in surface soils were the most sensitive to changes in atmospheric deposition fluxes. Finally, Mo and Mn showed strong enrichment in the top soil layer that could not be explained strictly by either current atmospheric deposition or biological recycling processes, but may reflect both their unique chemistry and remnants of past anthropogenic fluxes. Mn has a long residence time in the soil partly due to intense biological uplift that retains Mn in the top soil layer. Mo, in spite of the high solubility of molybdate, remains in the soil because of strong binding to natural organic matter. This study demonstrates the need to consider simultaneously the vegetation and the soils to understand elemental distribution within soil profiles as well as cycling within watersheds
Shale weathering rates across a continental-scale climosequence
A transect of sites has been established in North America and England as part of the Critical Zone Exploration Network (CZEN) to investigate the rates of soil formation across a climate gradient. Sites reported here are all underlain by an organic-poor, iron-rich Silurian-age shale, providing a constant parent material lithology from which soil is forming. This climosequence includes relatively cold and wet sites in Wales, New York and Pennsylvania, with temperature increasing to the south in Virginia, Tennessee and Alabama. Puerto Rico provides a warm/wet end member for the transect, although this site does not lie on the same shale formation as the Appalachian Mountain sites. Geochemical, mineralogical, and cosmogenic isotope analyses are being completed similarly at all sites to allow direct comparisons and eventual modelling of the weathering processes. Preliminary results from Wales, Pennsylvania and Virginia show soils become more sodium-depleted and the depth to bedrock is significantly deeper at the wet/warm site in Virginia. The fraction of Na lost relative to parent material composition at each site varies linearly as a function of mean annual temperature. Overall, results from the transect will promote a better understanding of how climate changes and human activities impact soil formation rates
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