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Geology topics

M. L. Peterson

Publications and source records attributed to M. L. Peterson.

6 recordsLinked to original sources
USGS2005

Measurement and interpretation of low levels of dissolved oxygen in ground water

A Rhodazine-D colorimetric technique was adapted to measure low-level dissolved oxygen concentrations in ground water. Prepared samples containing between 0 and 8.0 μmoles · 1 -1 dissolved oxygen in equilibrium with known gas mixtures produced linear spectrophotometric absorbance with a lower detection limit of 0.2 μmoles · 1 -1 . Excellent reproducibility was found for solutions ranging in composition from deionized water to sea water with chemical interferences detected only for easily reduced metal species such as ferric ion, cupric ion, and hexavalent chromium. Such effects were correctable based on parallel reaction stoichiometries relative to oxygen. The technique, coupled with a downhole wire line tool, permitted low-level monitoring of dissolved oxygen in wells at the selenium-contaminated Kesterson Reservoir in California. Results indicated a close association between low but measurable dissolved oxygen concentrations and mobility of oxidized forms of selenium in the shallow aquifer which were in general electrochemical disequilibrium.

Groundwater↗
USGS1996

Reduction of aqueous transition metal species on the surfaces of Fe(II)-containing oxides

Experimental studies demonstrate that structural Fe(II) in magnetite and ilmenite heterogeneously reduce aqueous ferric, cupric, vanadate, and chromate ions at the oxide surfaces over a pH range of 1–7 at 25°C. For an aqueous transition metal m , such reactions are 3 [ Fe 2 + Fe 2 3 + ] O 4 (magnetite) + 2 / n m z → 4 [ Fe 2 3 + ] O 3 (magnetite) + Fe 2 + + 2 / n m z − n "> 3[Fe2+Fe23+]O4(magnetite)+2/nmz→4[Fe23+]O3(magnetite)+Fe2++2/nmz−n and 3 [ Fe 2 + Ti ] O 3 (ilmenite) + 2 / n m z → Fe 2 3 + Ti 3 O 9 (pseudorutile) + Fe 2 + + 2 / n m z − n , "> 3[Fe2+Ti]O3(ilmenite)+2/nmz→Fe23+Ti3O9(pseudorutile)+Fe2++2/nmz−n, where z is the valance state and n is the charge transfer number. The half cell potential range for solid state oxidation [Fe(II)] → [Fe(III)] is −0.34 to −0.65 V, making structural Fe(II) a stronger reducing agent than aqueous Fe 2+ (−0.77 V). Reduction rates for aqueous metal species are linear with time (up to 36 h), decrease with pH, and have rate constants between 0.1 and 3.3 × 10 −10 mol m −2 s −1 . Iron is released to solution both from the above reactions and from dissolution of the oxide surface. In the presence of chromate, Fe 2+ is oxidized homogeneously in solution to Fe 3+ . X-ray photoelectron spectroscopy (XPS) denotes a Fe(III) oxide surface containing reduced Cr(III) and V(IV) species. Magnetite and ilmenite electrode potentials are insensitive to increases in divalent transition metals including Zn(II), Co(II), Mn(II), and Ni(II) and reduced V(IV) and Cr(III) but exhibit a log-linear concentration-potential response to Fe(III) and Cu(II). Complex positive electrode responses occur with increasing Cr(VI) and V(V) concentrations. Potential dynamic scans indicate that the high oxidation potential of dichromate is capable of suppressing the cathodic reductive dissolution of magnetite. Oxide electrode potentials are determined by the Fe(II)/Fe(III) composition of the oxide surface and respond to aqueous ion potentials which accelerate this oxidation process. Natural magnetite sands weathered under anoxic conditions are electrochemically reactive as demonstrated by rapid chromate reduction and the release of aqueous Fe(III) to experimental solution. In contrast, magnetite weathered under oxidizing vadose conditions show minimum reactivity toward chromate ions. The ability of Fe(II) oxides to reduce transition metals in soils and groundwaters will be strongly dependent on the redox environment.

Geochimica et Cosmochimica Acta↗
USGS1991

Chemical equilibrium and mass balance relationships associated with the Long Valley hydrothermal system, California, U.S.A.

Recent drilling and sampling of hydrothermal fluids from Long Valley permit an accurate characterization of chemical concentrations and equilibrium conditions in the hydrothermal reservoir. Hydrothermal fluids are thermodynamically saturated with secondary quartz, calcite, and pyrite but are in disequilibrium with respect to aqueous sulfide-sulfate speciation. Hydrothermal fluids are enriched in 18O by approximately 1??? relative to recharge waters. 18O and Cl concentrations in well cuttings and core from high-temperature zones of the reservoir are extensively depleted relative to fresh rhyolitic tuff compositions. Approximately 80% of the Li and 50% of the B are retained in the altered reservoir rock. Cl mass balance and open-system 18O fractionation models produce similar water-rock ratios of between 1.0 and 2.5 kg kg-1. These water-rock ratios coupled with estimates of reservoir porosity and density produce a minimum fluid residence time of 1.3 ka. The low fluid Cl concentrations in Long Valley correlate with corresponding low rock concentrations. Mass balance calculations indicate that leaching of these reservoir rocks accounts for Cl losses during hydrothermal activity over the last 40 ka. ?? 1991.

Journal of Volcanology and Geothermal Research↗
USGS1990

Sources and fractionation processes influencing the isotopic distribution of H, O and C in the Long Valley hydrothermal system, California, U.S.A.

The isotopic ratios of H, O and C in water within the Long Valley caldera, California reflect input from sources external to the hydrothermal reservoir. A decrease in δD in precipitation of 0.5‰ km −1 , from west to east across Long Valley, is caused by the introduction of less fractionated marine moisture through a low elevation embayment in the Sierra Nevada Mountain Range. Relative to seasonal fluctuations in precipitation (−158 to −35‰.), δD ranges in hot and cold surface and groundwaters are much less variable (−135 to −105‰.). Only winter and spring moisture, reflecting higher precipitation rates with lighter isotopic signatures, recharge the hydrological system. The hydrothermal fluids are mixtures of isotopically heavy recharge (δD = − 115‰, δ 18 O = − 15‰) derived from the Mammoth embayment, and isotopically lighter cold water (δD = −135‰, δ 18 O = −18‰). This cold water is not representative of current local recharge. The δ 13 C values for dissolved carbon in hot water are significantly heavier (− 7 to − 3‰) than in cold water (−18 to −10‰) denoting a separate hydrothermal origin. These δ 13 C values overlie the range generally attributed to magmatic degassing of CO 2 . However, δ 13 C values of metamorphosed Paleozoic basement carbonates surrounding Long Valley fall in a similar range, indicating that hydrothermal decarbonization reactions are a probable source of CO 2 . The δ 13 C and δ 18 O values of secondary travertime and vein calcite indicate respective fractionation with CO 2 and H 2 O at temperatures approximating current hydrothermal conditions.

California↗
USGS1980

Rate of mercury loss from contaminated estuarine sediments

The concentration of mercury in contaminated estuarine sediments of Bellingham Bay, Washington was found to decrease with a half-time of about 1.3 yr after the primary anthropogenic source of mercury was removed. In situ measurements of the mercury flux from sediments, in both dissolved and volatile forms, could not account for this decrease. This result suggests that the removal of mercury is associated with sediment particles transported out of the study area. This decrease was modeled using a steady-state mixing model. Mercury concentrations in anoxic interstitial waters reached 3.5 μg/l, 126 times higher than observed in the overlying seawater. Mercury fluxes from these sediments ranged from 1.2 to 2.8 × 10 −5 ng/cm 2 /sec, all in a soluble form. In general, higher Hg fluxes were associated with low oxygen or reducing conditions in the overlying seawater. In contrast, no flux was measurable from oxidizing interstitial water having mercury concentrations of 0.01-0.06 μ/l.

Geochimica et Cosmochimica Acta↗