Search USGS⌕ Search

Geology topics

L.G. Miller

Publications and source records attributed to L.G. Miller.

28 records · Page 2Linked to original sources
USGS1995

A comparison of two nitrification inhibitors used to measure nitrification rates in estuarine sediments

Nitrification rates were measured using intact sediment cores from South San Francisco Bay and two different nitrification inhibitors: acetylene and methyl fluoride. Sediment oxygen consumption and ammonium and nitrate fluxes were also measured in these cores. Four experiments were conducted in the spring, and one in the fall of 1993. There was no significant difference in nitrification rates measured using the two inhibitors, which suggests that methyl fluoride can be used as an effective inhibitor of nitrification. Nitrification was positively correlated with sediment oxygen consumption and numbers of macrofauna. This suggests that bioturbation by macrofauna is an important control of nitrification rates. Irrigation by the tube-dwelling polychaete, Asychis elongata, which dominates the benthic biomass at this location, appears particularly important. Ammonium fluxes out of the sediment were greatest about one week after the spring bloom, while nitrification peaked about one month later.

FEMS Microbiology Ecology↗
USGS1995

Methylmercury oxidative degradation potentials in contaminated and pristine sediments of the Carson River, Nevada

Sediments from mercury-contaminated and uncontaminated reaches of the Carson River, Nevada, were assayed for sulfate reduction, methanogenesis, denitrification, and monomethylmercury (MeHg) degradation. Demethylation of [ 14 C]MeHg was detected at all sites as indicated by the formation of 14 CO 2 and 14 CH 4 . Oxidative demethylation was indicated by the formation of 14 CO 2 and was present at significant levels in all samples. Oxidized/reduced demethylation product ratios (i.e., 14 CO 2 / 14 CH 4 ratios) generally ranged from 4.0 in surface layers to as low as 0.5 at depth. Production of 14 CO 2 was most pronounced at sediment surfaces which were zones of active denitrification and sulfate reduction but was also significant within zones of methanogenesis. In a core taken from an uncontaminated site having a high proportion of oxidized, coarse-grain sediments, sulfate reduction and methanogenic activity levels were very low and 14 CO 2 accounted for 98% of the product formed from [ 14 C]MeHg. There was no apparent relationship between the degree of mercury contamination of the sediments and the occurrence of oxidative demethylation. However, sediments from Fort Churchill, the most contaminated site, were most active in terms of demethylation potentials. Inhibition of sulfate reduction with molybdate resulted in significantly depressed oxidized/reduced demethylation product ratios, but overall demethylation rates of inhibited and uninhibited samples were comparable. Addition of sulfate to sediment slurries stimulated production of 14 CO 2 from [ 14 C]MeHg, while 2-bromoethanesulfonic acid blocked production of 14 CH 4 . These results reveal the importance of sulfate-reducing and methanogenic bacteria in oxidative demethylation of MeHg in anoxic environments.

Nevada↗
USGS1994

Degradation of methyl bromide by methanotrophic bacteria in cell suspensions and soils

Cell suspensions of Methylococcus capsulatus mineralized methyl bromide (MeBr), as evidenced by its removal from the gas phase, the quantitative recovery of Br - in the spent medium, and the production of 14 CO 2 from [ 14 C]MeBr. Methyl fluoride (MeF) inhibited oxidation of methane as well as that of [ 14 C]MeBr. The rate of MeBr consumption by cells varied inversely with the supply of methane, which suggested a competitive relationship between these two substrates. However, MeBr did not support growth of the methanotroph. In soils exposed to high levels (10,000 ppm) of MeBr, methane oxidation was completely inhibited. At this concentration, MeBr removal rates were equivalent in killed and live controls, which indicated a chemical rather than biological removal reaction. At lower concentrations (1,000 ppm) of MeBr, methanotrophs were active and MeBr consumption rates were 10-fold higher in live controls than in killed controls. Soils exposed to trace levels (10 ppm) of MeBr demonstrated complete consumption within 5 h of incubation, while controls inhibited with MeF or incubated without O 2 had 50% lower removal rates. Aerobic soils oxidized [ 14 C]MeBr to 14 CO 2 , and MeF inhibited oxidation by 72%. Field experiments demonstrated slightly lower MeBr removal rates in chambers containing MeF than in chambers lacking MeF. Collectively, these results show that soil methanotrophic bacteria, as well as other microbes, can degrade MeBr present in the environment.

Applied and Environmental Microbiology↗
USGS1993

The geochemistry of methane in Lake Fryxell, an amictic, permanently ice-covered, antarctic lake

The abundance and distribution of dissolved CH4 were determined from 1987-1990 in Lake Fryxell, Antarctica, an amictic, permanently ice-covered lake in which solute movement is controlled by diffusion. CH4 concentrations were < 1 ??M in the upper oxic waters, but increased below the oxycline to 936 ??M at 18 m. Sediment CH4 was 1100 ??mol (1 sed)-1 in the 0-5 cm zone. Upward flux from the sediment was the source of the CH4, NH4 +, and DOC in the water column; CH4 was 27% of the DOC+CH4 carbon at 18 m. Incubations with surficial sediments indicated that H14CO3 - reduction was 0.4 ??mol (1 sed)-1 day-1 or 4?? the rate of acetate fermentation to CH4. There was no measurable CH4 production in the water column. However, depth profiles of CH4, NH4, and DIC normalized to bottom water concentrations demonstrated that a significant CH4 sink was evident in the anoxic, sulfate-containing zone of the water column (10-18 m). The ??13CH4 in this zone decreased from -72 % at 18 m to -76% at 12 m, indicating that the consumption mechanism did not result in an isotopic enrichment of 13CH4. In contrast, ??13CH4 increased to -55 % at 9 m due to aerobic oxidation, though this was a minor aspect of the CH4 cycle. The water column CH4 profile was modeled by coupling diffusive flux with a first order consumption term; the best-fit rate constant for anaerobic CH4 consumption was 0.012 yr-1. On a total carbon basis, CH4 consumption in the anoxic water column exerted a major effect on the flux of carbonaceous material from the underlying sediments and serves to exemplify the importance of CH4 to carbon cycling in Lake Fryxell. ?? 1993 Kluwer Academic Publishers.

Biogeochemistry↗
USGS1993

Selective inhibition of ammonium oxidation and nitrification-linked N2O formation by methyl fluoride and dimethyl ether

Methyl fluoride (CH 3 F) and dimethyl ether (DME) inhibited nitrification in washed-cell suspensions of Nitrosomonas europaea and in a variety of oxygenated soils and sediments. Headspace additions of CH 3 F (10% [vol/vol]) and DME (25% [vol/vol]) fully inhibited NO 2 - and N 2 O production from NH 4 + in incubations of N. europaea , while lower concentrations of these gases resulted in partial inhibition. Oxidation of hydroxylamine (NH 2 OH) by N. europaea and oxidation of NO 2 - by a Nitrobacter sp. were unaffected by CH 3 F or DME. In nitrifying soils, CH 3 F and DME inhibited N 2 O production. In field experiments with surface flux chambers and intact cores, CH 3 F reduced the release of N 2 O from soils to the atmosphere by 20- to 30-fold. Inhibition by CH 3 F also resulted in decreased NO 3 - + NO 2 - levels and increased NH 4 + levels in soils. CH 3 F did not affect patterns of dissimilatory nitrate reduction to ammonia in cell suspensions of a nitrate-respiring bacterium, nor did it affect N 2 O metabolism in denitrifying soils. CH 3 F and DME will be useful in discriminating N 2 O production via nitrification and denitrification when both processes occur and in decoupling these processes by blocking NO 2 - and NO 3 - production.

Applied and Environmental Microbiology↗
USGS1991

In situ bacterial selenate reduction in the agricultural drainage systems of western Nevada

Dissimilatory in situ selenate reduction to elemental selenium in sediments from irrigated agricultural drainage regions of western Nevada was measured at ambient Se oxyanion concentrations. Selenate reduction was rapid, with turnover rate constants ranging from 0.04 to 1.8 h -1 at total Se concentrations in pore water of 13 to 455 nM. Estimates of removal rates of selenium oxyanions were 14, 38, and 155 μ mol m -2 day -1 for South Lead Lake, Massie Slough, and Hunter Drain, respectively.

Nevada↗
USGS1987

Sources and flux of natural gases from Mono Lake, California

The ability to identify a formation mechanism for natural gas in a particular environment requires consideration of several geochemical factors when there are multiple sources present. Four primary sources of methane have been identified in Mono Lake. Two of these sources were associated with numerous natural gas seeps which occur at various locations in the lake and extend beyond its present boundary; the two other gas sources result from current microbiological processes. In the natural gas seeps, we observed flow rates as high as 160 moles CH 4 day −1 , and estimate total lakewide annual seep flux to be 2.1 × 10 6 moles CH 4 . Geochemical parameters ( δ 13 CH 4 , δDCH 4 , CH 4 /[ C 2 H 6 + C 3 H 8 ]) and δ 14 CH 4 measurements revealed that most of the seeps originate from a paleo-biogenic ( δ 13 CH 4 = about −70%.). natural gas deposit of Pleistocene age which underlies the current and former lakebed. Gas seeps in the vicinity of hot springs had, in combination with the biogenic gas, a prominent thermogenic gas component resulting from hydrothermal alteration of buried organic matter.

California↗
USGS1986

Measurement of nitrous oxide reductase activity in aquatic sediments

Denitrification in aquatic sediments was measured by an N 2 O reductase assay. Sediments consumed small added quantities of N 2 O over short periods (a few hours). In experiments with sediment slurries, N 2 O reductase activity was inhibited by O 2 , C 2 H 2 , heat treatment, and by high levels of nitrate (1 mM) or sulfide (10 mM). However, ambient levels of nitrate (<100 &mu;M) did not influence activity, and moderate levels (about 150 &mu;M) induced only a short lag before reductase activity began. Moderate levels of sulfide (<1 mM) had no effect on N 2 O reductase activity. Nitrous oxide reductase displayed Michaelis-Menten kinetics in sediments from freshwater ( K m = 2.17 &mu;M), estuarine ( K m = 14.5 &mu;M), and alkaline-saline ( K m = 501 &mu;M) environments. An in situ assay was devised in which a solution of N 2 O was injected into sealed glass cores containing intact sediment. Two estimates of net rates of denitrification in San Francisco Bay under approximated in situ conditions were 0.009 and 0.041 mmol of N 2 O per m 2 per h. Addition of chlorate to inhibit denitrification in these intact-core experiments (to estimate gross rates of N 2 O consumption) resulted in approximately a 14% upward revision of estimates of net rates. These results were comparable to an in situ estimate of 0.022 mmol of N 2 O per m 2 per h made with the acetylene block assay.

California↗
USGS1985

Benthic fluxes in San Francisco Bay

Measurements of benthic fluxes have been made on four occasions between February 1980 and February 1981 at a channel station and a shoal station in South San Francisco Bay, using in situ flux chambers. On each occasion replicate measurements of easily measured substances such as radon, oxygen, ammonia, and silica showed a variability (??1??) of 30% or more over distances of a few meters to tens of meters, presumably due to spatial heterogeneity in the benthic community. Fluxes of radon were greater at the shoal station than at the channel station because of greater macrofaunal irrigation at the former, but showed little seasonal variability at either station. At both stations fluxes of oxygen, carbon dioxide, ammonia, and silica were largest following the spring bloom. Fluxes measured during different seasons ranged over factors of 2-3, 3, 4-5, and 3-10 (respectively), due to variations in phytoplankton productivity and temperature. Fluxes of oxygen and carbon dioxide were greater at the shoal station than at the channel station because the net phytoplankton productivity is greater there and the organic matter produced must be rapidly incorporated in the sediment column. Fluxes of silica were greater at the shoal station, probably because of the greater irrigation rates there. N + N (nitrate + nitrite) fluxes were variable in magnitude and in sign. Phosphate fluxes were too small to measure accurately. Alkalinity fluxes were similar at the two stations and are attributed primarily to carbonate dissolution at the shoal station and to sulfate reduction at the channel station. The estimated average fluxes into South Bay, based on results from these two stations over the course of a year, are (in mmol m-2 d-1): O2 = -27 ?? 6; TCO2 = 23 ?? 6; Alkalinity = 9 ?? 2; N + N = -0.3 ?? 0.5; NH3 = 1.4 ?? 0.2; PO4 = 0.1 ?? 0.4; Si = 5.6 ?? 1.1. These fluxes are comparable in magnitude to those in other temperate estuaries with similar productivity, although the seasonal variability is smaller, probably because the annual temperature range in San Francisco Bay is smaller. Budgets constructed for South San Francisco Bay show that large fractions of the net annual productivity of carbon (about 90%) and silica (about 65%) are recycled by the benthos. Substantial rates of simultaneous nitrification and denitrification must occur in shoal areas, apparently resulting in conversion to N2 of 55% of the particulate nitrogen reaching the sediments. In shoal areas, benthic fluxes can replace the water column standing stocks of ammonia in 2-6 days and silica in 17-34 days, indicating the importance of benthic fluxes in the maintenance of productivity. Pore water profiles of nutrients and Rn-222 show that macrofaunal irrigation is extremely important in transport of silica, ammonia, and alkalinity. Calculations of benthic fluxes from these profiles are less accurate, but yield results consistent with chamber measurements and indicate that most of the NH3, SiO2, and alkalinity fluxes are sustained by reactions occurring throughout the upper 20-40 cm of the sediment column. In contrast, O2, CO2, and N + N fluxes must be dominated by reactions occurring within the upper one cm of the sediment-water interface. While most data support the statements made above, a few flux measurements are contradictory and demonstrate the complexity of benthic exchange. ?? 1985 Dr W. Junk Publishers.

California↗