Characterizing snowmelt anomalies in hydrochemographs of a karst spring,Cumberland Valley,Pennsylvania (USA): evidence for multiple recharge pathways

Conductivity, water level, air temperature, and depth of snowpack were monitored during a 26-day melt period of 88-cm-deep snowpack at a karst spring to characterize internal runoff and diffuse infiltration. Chloride from road salt provided a tracer and the snowpack a recharge source during the melt period. The melt period was divided into phases based on air temperature and chemograph pattern. For the first and third phases, mean air temperatures were below freezing, but above freezing during the second and fourth phases. During the first phase when the temperature peaked above freezing, conductivity typically spiked 10–50 μS/cm, suggesting input of road salt from conduits. When the snowpack continuously melted, conductivity and water-level trends were upward with smaller daily spikes in conductivity indicating infiltration from the dilute snowpack. This pattern suggests that road salt input continued when snowmelt recharged through the epikarst, but at lower concentrations than the conduit input. Refreezing of the snowpack and shallow subsurface for a brief period interrupted the recharge, and there was no longer a sawtooth pattern of conductivity. It is apparent that frozen conditions did not cease recharge because a dual recharge process was evident. While dual recharge from internal runoff and diffuse infiltration occurred, the portions varied because of changing melting rates. Observed patterns indicated internal runoff dominated during frozen periods because recharge water moved as overland flow across a frozen surface to focused pathways. Diffuse infiltration became available during warmer periods because subsurface thawing allowed the snowmelt to penetrate the epikarst. Results of snowmelt monitoring in spring discharge indicated the transient nature of karst recharge.     

Apparent diameters of 172 B5V-A5V stars of the Catalogue of Geneva Observatory

The spectrophotometric method for computing the apparent stellar diameters, proposed by Chalonge and Divan (1950) and modified by Fracassini and Pasinetti (1967) has been applied to 172 B5V-A5V stars (single and belonging to galactic clusters) of the Catalogue of Geneva Observatory (Rufener, 1971). In the straight line diagrams log vsm, drawn for the stars of the same spectral type, it is possible to identify some peculiar stars (with peculiarities in the diameter or monochromatic brightness). The agreement with the values of the apparent diameters of Leo, Ori, Lyr and CMa, obtained by Hanbury Brownet al. (1967), is very good. The comparison with the diagramss _v vs (B-V)₀,R vs (B-V)₀ deduced by Wesselink (1969), seems satisfactory. The comparison with the results obtained by other authors and the great number of stars which will be observed in the photometric system in seven colors of Geneva, demonstrate the wide possibilities of this spectrophotometric method for determining the apparent stellar diameters.

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Sommario Il metodo spettrofotometrico di Chalonge e Divan (1950) per il calcolo dei diametri stellari apparenti, modificato da Fracassini e Pasinetti (1967), è stato applicato a 172 stelle B5V-A5V (isolate e in ammassi galattici) del Catalogo dell'Osservatorio di Ginevra (Rufener, 1971). Costruiti i diagrammi lineari log -m _v per i vari gruppi di stelle dello stesso tipo spettrale, è possibile identificare alcune stelle peculiari con diametri e brillanze monochromatiche anomale. Il confronto con i diametti apparenti di Leo, Ori, Lyr e CMa determinati da Hanbury Brownet al. (1967) mostra un accordo molto buono. Il confronto con le relazionis _v -(B-V)₀eR-(B-V) ₀ ottenute da Wesselink (1969) appare soddisfacente. Il confronto con i risultati ottenuti da altri autori e il grande numero di stelle che saranno osservate nel sistema fotometrico in sette colori di Ginevra, dimostrano le ampie possibilità di questo metodo spettrofotometrico per la determinazione dei diametri stellari apparenti.

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Thesis for the degree on Applied Physics.     

Dynamics of CO<Subscript>2</Subscript> fluxes and concentrations during a shallow subsurface CO<Subscript>2</Subscript> release

A field facility located in Bozeman, Montana provides the opportunity to test methods to detect, locate, and quantify potential CO₂ leakage from geologic storage sites. From 9 July to 7 August 2008, 0.3 t CO₂ day⁻¹ were injected from a 100-m long, ~2.5-m deep horizontal well. Repeated measurements of soil CO₂ fluxes on a grid characterized the spatio-temporal evolution of the surface leakage signal and quantified the surface leakage rate. Infrared CO₂ concentration sensors installed in the soil at 30 cm depth at 0–10 m from the well and at 4 cm above the ground at 0 and 5 m from the well recorded surface breakthrough of CO₂ leakage and migration of CO₂ leakage through the soil. Temporal variations in CO₂ concentrations were correlated with atmospheric and soil temperature, wind speed, atmospheric pressure, rainfall, and CO₂ injection rate.     

Multi-spectral imaging of vegetation for detecting CO<Subscript>2</Subscript> leaking from underground

Practical geologic CO₂ sequestration will require long-term monitoring for detection of possible leakage back into the atmosphere. One potential monitoring method is multi-spectral imaging of vegetation reflectance to detect leakage through CO₂-induced plant stress. A multi-spectral imaging system was used to simultaneously record green, red, and near-infrared (NIR) images with a real-time reflectance calibration from a 3-m tall platform, viewing vegetation near shallow subsurface CO₂ releases during summers 2007 and 2008 at the Zero Emissions Research and Technology field site in Bozeman, Montana. Regression analysis of the band reflectances and the Normalized Difference Vegetation Index with time shows significant correlation with distance from the CO₂ well, indicating the viability of this method to monitor for CO₂ leakage. The 2007 data show rapid plant vigor degradation at high CO₂ levels next to the well and slight nourishment at lower, but above-background CO₂ concentrations. Results from the second year also show that the stress response of vegetation is strongly linked to the CO₂ sink–source relationship and vegetation density. The data also show short-term effects of rain and hail. The real-time calibrated imaging system successfully obtained data in an autonomous mode during all sky and daytime illumination conditions.     

Fe isotopic fractionation during mineral dissolution with and without bacteria

Fe released into solution is isotopically lighter (enriched in the lighter isotope) than hornblende starting material when dissolution occurs in the presence of the siderophore desferrioxamine mesylate (DFAM). In contrast, Fe released from goethite dissolving in the presence of DFAM is isotopically unchanged. Furthermore, Δ⁵⁶Fe_{solution-hornblende} for Fe released to solution in the presence of ligands varies with the affinity of the ligand for Fe. The extent of isotopic fractionation of Fe released from hornblende also increases when experiments are agitated continuously. The Fe isotope fractionation observed during hornblende dissolution with organic ligands is attributed predominantly to retention of ⁵⁶Fe in an altered surface layer, while the lack of isotopic fractionation during goethite dissolution in DFAM is consistent with the lack of an altered layer. When a siderophore-producing soil bacterium is added to the system (without added organic ligands), Fe released to solution from both hornblende and goethite differs isotopically from Fe in the bulk mineral: Δ⁵⁶Fe_{solution-starting material} = −0.56 ± 0.19 (hornblende) and −1.44 ± 0.16 (goethite). Increased isotopic fractionation is attributed in this case to the fact that as bacterial respiration depletes the system in oxygen and aqueous Fe is reduced, equilibration between aqueous ferrous and ferric iron creates a pool of isotopically heavy ferric iron that is assimilated by bacterial cells. Adsorption of isotopically heavy ferrous iron (Fe(II) enriched in the heavier isotope) or precipitation of isotopically heavy Fe minerals may also contribute to observed fractionations.To test whether these Fe isotope signatures are recorded in natural systems, we also investigated extractions of samples of soils from which the bacteria were isolated. These extractions show variability in the isotopic signatures of exchangeable Fe and Fe oxyhydroxide fractions from one soil sample to another, but exchangeable Fe is observed to be lighter than Fe in soil Fe oxyhydroxides and hornblende. This observation is consistent with isotopically light Fe-organic complexes in soil pore water derived from the Fe-silicate starting materials in the presence of growing microorganisms, as documented in experiments reported here. The contributions from phenomena including organic ligand-promoted nonstoichiometric dissolution of Fe silicates, uptake of ferric iron by organisms, adsorption of isotopically heavy ferrous iron, and precipitation of iron minerals should create complex isotopic signatures in soils. Better understanding of these processes and the timescales over which they contribute to fractionation is needed.     

New Constraints on Ages of Glasses Proposed as Reference Materials for Fission-Track Dating

New analyses have been performed in order to enhance the data-set on the independent ages of four glasses that have been proposed as reference materials for fission-track dating. The results are as follows. Moldavite - repeated ⁴⁰Ar/³⁹Ar age determinations on samples from deposits from Bohemia and Moravia yielded an average of 14.34 ± 0.08 Ma. This datum agrees with other recent determinations and is significantly younger than the ⁴⁰Ar/³⁹Ar age of 15.21 ± 0.15 Ma determined in the early 1980s. Macusanite (Peru) -four K-Ar ages ranging from 5.44 ± 0.06 to 5.72 ± 0.12 Ma have been published previously. New ⁴⁰Ar/³⁹Ar ages gave an average of 5.12 ± 0.04 Ma. Plateau fission-track ages determined using the IRMM-540 certified glass and U and Th thin films for neutron fluence measurements agree better with these new ⁴⁰Ar/³⁹Ar ages than the previously published ages. Roccastrada glass (Italy) - a new ⁴⁰Ar/³⁹Ar age, 2.45 ± 0.04 Ma, is consistent with previous determinations. The Quiron obsidian (Argentina) is a recently discovered glass that has been proposed as an additional reference material for its high spontaneous track density (around 100 000 cm^-2). Defects that might produce "spurious" tracks are virtually absent. An independent ⁴⁰Ar/³⁹Ar age of 8.77 ± 0.09 Ma was determined and is recommended for this glass. We believe that these materials, which will be distributed upon request to fission-track groups, will be very useful for testing system calibrations and experimental procedures.     

Effects of Soil Composition on Zn Speciation in Drainage Waters from Agricultural Soils

The influence of Zn speciation on Zn transport by drainage from different soils to surface water is examined in a stream catchment in an agricultural area. Drainage waters were collected from two types of soils, a mineral soil (MS) and a soil rich in organic matter (OS) by means of artificial drainage pipes. The speciation of dissolved Zn in the stream and the drainage waters was determined using ligand-exchange and voltammetry. About 50–95% of dissolved Zn is bound in strong complexes, and the free Zn²⁺ ion concentration is in the range of 1–16% of dissolved Zn. A substantial part of Zn is present in weaker organic or inorganic complexes. The simulated Zn speciation using the WHAM VI model is compared to the determined speciation. Free Zn²⁺ concentrations predicted by the WHAM VI model are generally higher than the analytically determined free Zn²⁺, but are mostly within the same order of magnitude. Effects of different soil organic matter content on Zn speciation and transport are discussed. Zn speciation in the drainage at the OS site is influenced by the distribution of organic matter between the solid and solution phase. The abundant organic Zn complexes in solution contribute to facilitate Zn transport from soil into surface waters, through the drainage at the OS site. Drainage from the OS site contributes about twice as much Zn input to the receiving water as the MS soil, as related to specific area. The mineral soil contains much lower organic matter, and a part of Zn bound with inorganic phases can hardly be released by dissolved organic ligands, leading to much higher Zn retention at the MS site.     

Petrogenesis of Quebrada de la Mina and Altar North porphyries (Cordillera of San Juan,Argentina): Crustal assimilation and metallogenic implications

We investigate the geology of Altar North (Cu–Au) and Quebrada de la Mina (Au) porphyry deposits located in San Juan Province (Argentina), close to the large Altar porphyry copper deposit (995 Mt, 0.35% Cu, 0.083 g/t Au), to present constraints on the magmatic processes that occurred in the parental magma chambers of these magmatic-hydrothermal systems. Altar North deposit comprises a plagioclase-amphibole-phyric dacite intrusion (Altar North barren porphyry) and a plagioclase-amphibole-biotite-phyric dacite stock (Altar North mineralized porphyry, 11.98 ± 0.19 Ma). In Quebrada de la Mina, a plagioclase-amphibole-biotite-quartz-phyric dacite stock (QDM porphyry, 11.91 ± 0.33 Ma) crops out. High Sr/Y ratios (92–142) and amphibole compositions of Altar North barren and QDM porphyries reflect high magmatic oxidation states (fO₂ = NNO +1.1 to +1.6) and high fH₂O conditions in their magmas. Zones and rims enriched in anorthite (An_37–48), SrO (0.22–0.33 wt.%) and FeO (0.21–0.37 wt.%) in plagioclase phenocrysts are evidences of magmatic recharge processes in the magma chambers. Altar North and Quebrada de la Mina intrusions have relatively homogeneous isotopic compositions (⁸⁷Sr/⁸⁶Sr_(t) = 0.70450–0.70466, ε_Nd(t) = +0.2 to +1.2) consistent with mixed mantle and crust contributions in their magmas. Higher Pb isotopes ratios (²⁰⁷Pb/²⁰⁴Pb = 15.6276–15.6294) of these intrusions compared to other porphyries of the district, reflect an increase in the assimilation of high radiogenic Pb components in the magmas. Ages of zircon xenocrysts (297, 210, 204, 69 Ma) revealed that the magmas have experienced assimilation of Miocene, Cretaceous, Triassic and Carboniferous crustal rocks.Fluids that precipitated sulfides in the Altar deposit may have remobilized Pb from the host rocks, as indicated by the ore minerals being more radiogenic (²⁰⁷Pb/²⁰⁴Pb = 15.6243–15.6269) than their host intrusions. Au/Cu ratio in Altar porphyries (average Au/Cu ratio of 0.14 × 10^?4 by weight in Altar Central) is higher than in the giant Miocene porphyry deposits located to the south: Los Pelambres, Río Blanco and Los Bronces (Chile) and Pachón (Argentina). We suggest that the increase in Au content in the porphyries of this region could be linked to the assimilation of high radiogenic Pb components in the magmas within these long-lived maturation systems.