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At least 631 records · Page 35Linked to original sources
USGS2013

Intercontinental dispersal of bacteria and archaea by transpacific winds

Microorganisms are abundant in the upper atmosphere, particularly downwind of arid regions, where winds can mobilize large amounts of topsoil and dust. However, the challenge of collecting samples from the upper atmosphere and reliance upon culture-based characterization methods have prevented a comprehensive understanding of globally dispersed airborne microbes. In spring 2011 at the Mt. Bachelor Observatory in North America (2.8 km above sea level), we captured enough microbial biomass in two transpacific air plumes to permit a microarray analysis using 16S rRNA genes. Thousands of distinct bacterial taxa spanning a wide range of phyla and surface environments were detected before, during, and after each Asian long-range transport event. Interestingly, the transpacific plumes delivered higher concentrations of taxa already in the background air (particularly Proteobacteria, Actinobacteria, and Firmicutes). While some bacterial families and a few marine archaea appeared for the first and only time during the plumes, the microbial community compositions were similar, despite the unique transport histories of the air masses. It seems plausible, when coupled with atmospheric modeling and chemical analysis, that microbial biogeography can be used to pinpoint the source of intercontinental dust plumes. Given the degree of richness measured in our study, the overall contribution of Asian aerosols to microbial species in North American air warrants additional investigation.

Applied and Environmental Microbiology↗
USGS1971

An evaluation of procedures used in computing chemical denudation rates

Computations of chemical denudation rates (that is, the average rate of lowering of the earth's crust by chemical processes) should be based only upon those components of dissolved loads of streams that are derived from chemical weathering of rocks and soils, even though identification of those components is difficult and imprecise. Past computations of chemical denudation rates exaggerated by 1.4 to 2.4 times the significance of this process because they were calculated from total dissolved loads. Identification of separate denudation and nondenudation components in a water analysis can be done most readily for streams in crystalline silicate rock terrane where commonly 25 to 55 percent of the dissolved solids are HCO 3 −1 , SO 4 −2 , Cl −1 , and NO 3 −1 that cannot be derived from the underlying rock; instead these ions are derived either directly from the atmosphere or from atmosphere-biosphere interactions. Most of the remaining solutes are derived from chemical weathering or rainfall, or both. Existing data are often insufficient to separate these two components, but atmospheric contributions to dissolved loads of dilute natural waters are substantial. The commonly observed increased concentration of dissolved solids in chemically polluted rivers is produced by concentration of natural dissolved loads by evaporation, and by addition of solutes not present in natural waters. Concentration of natural solutes represents a modification of natural denudation processes that does not change the rate of denudation. Addition of new solutes represents man-induced, accelerated chemical denudation. Extrapolation of modern chemical denudation rates to geologic situations is extremely imprecise because of uncertainties in assessing man's influence on present dissolved loads, in reconstructing the number and magnitude of past climatic changes, and in evaluating the effects of evolving flora and fauna.

Bulletin of the Geological Society of America↗
USGS2016

Response comment: Carbon sequestration on Mars

Martian atmospheric pressure has important implications for the past and present habitability of the planet, including the timing and causes of environmental change. The ancient Martian surface is strewn with evidence for early water bound in minerals (e.g., Ehlmann and Edwards, 2014) and recorded in surface features such as large catastrophically created outflow channels (e.g., Carr, 1979), valley networks (Hynek et al., 2010; Irwin et al., 2005), and crater lakes (e.g., Fassett and Head, 2008). Using orbital spectral data sets coupled with geologic maps and a set of numerical spectral analysis models, Edwards and Ehlmann (2015) constrained the amount of atmospheric sequestration in early Martian rocks and found that the majority of this sequestration occurred prior to the formation of the early Hesperian/late Noachian valley networks (Fassett and Head, 2011; Hynek et al., 2010), thus implying the atmosphere was already thin by the time these surface-water-related features were formed.

Geology↗
USGS2013

Potential climate change impacts on temperate forest ecosystem processes

Large changes in atmospheric CO2, temperature and precipitation are predicted by 2100, yet the long-term consequences for carbon, water, and nitrogen cycling in forests are poorly understood. We applied the PnET-CN ecosystem model to compare the long-term effects of changing climate and atmospheric CO2 on productivity, evapotranspiration, runoff, and net nitrogen mineralization in current Great Lakes forest types. We used two statistically downscaled climate projections, PCM B1 (warmer and wetter) and GFDL A1FI (hotter and drier), to represent two potential future climate and atmospheric CO2 scenarios. To separate the effects of climate and CO2, we ran PnET-CN including and excluding the CO2 routine. Our results suggest that, with rising CO2 and without changes in forest type, average regional productivity could increase from 67% to 142%, changes in evapotranspiration could range from –3% to +6%, runoff could increase from 2% to 22%, and net N mineralization could increase 10% to 12%. Ecosystem responses varied geographically and by forest type. Increased productivity was almost entirely driven by CO2 fertilization effects, rather than by temperature or precipitation (model runs holding CO2 constant showed stable or declining productivity). The relative importance of edaphic and climatic spatial drivers of productivity varied over time, suggesting that productivity in Great Lakes forests may switch from being temperature to water limited by the end of the century.

Michigan;Minnesota;Wisconsin↗
USGS1993

Acid Rain

Acid deposition, or acid rain as it is more commonly referred to, has become a widely publicized environmental issue in the U.S. over the past decade. The term usually conjures up images of fish kills, dying forests, "dead" lakes, and damage to monuments and other historic artifacts. The primary cause of acid deposition is emission of S0 2 and NO x to the atmosphere during the combustion of fossil fuels. Oxidation of these compounds in the atmosphere forms strong acids - H 2 SO 4 and HNO 3 - which are returned to the Earth in rain, snow, fog, cloud water, and as dry deposition. Although acid deposition has only recently been recognized as an environmental problem in the U.S., it is not a new phenomenon (Cogbill & Likens 1974). As early as the middle of the 17th century in England, the deleterious effects of industrial emissions on plants, animals, and humans, and the atmospheric transport of pollutants between England and France had become issues of concern (Evelyn 1661, Graunt 1662). It is interesting that well over three hundred years ago in England, recommendations were made to move industry outside of towns and build higher chimneys to spread the pollution into "distant parts." Increasing the height of smokestacks has helped alleviate local problems, but has exacerbated others. In the U.S. the height of the tallest smokestack has more than doubled, and the average height of smokestacks has tripled since the 1950s (Patrick et al 1981). This trend occurred in most industrialized nations during the 20th century and has had the effect of transforming acid rain from a local urban problem into a problem of global scale.

Annual Review of Earth and Planetary Sciences↗
USGS1995

Two-year simulation of the Great Lakes region with a coupled modeling system

In this paper, we report on an experiment aimed at evaluating the feasibility of the application of our coupled regional climate modeling system to long-term climate simulations over the Great Lakes region. The simulation analyzed covers a continuous 24-month period beginning 1 September 1990 and extending to 1 September 1992. Many aspects of this simulation agreed well with observations. Compared with European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, area-averaged atmospheric temperature and moisture biases were generally small. The largest temperature biases were found in the simulated boundary layer, up to 1–1.5 K colder than observed in most months. Atmospheric moisture biases were of both signs and small in magnitude, almost universally less than 0.5 g kg −1 . Comparison of simulated surface air temperatures with station observations also indicated that model simulated temperatures generally display a cold bias. Simulated precipitation values agreed well with observations during the cold portions of the year while during warm months precipitation was overpredicted by 10%–50%. Spatial patterns of precipitation over the model domain agreed well with observations during the winter months but were not as well simulated during the other seasons. A one-dimensional lake model was coupled to the atmospheric component of the model to capture the effects of the Great Lakes on regional climate. Lake surface temperatures were generally well simulated by the lake model in the summer and fall seasons, and lake ice extent agreed well with the analysis over at least three of the five lakes. The greatest shortcomings in lake temperature simulation were the earlier-than-observed warm-up in the spring and warmer than observed peak temperatures in the summer over the northern portions of the lakes. Also, lake ice extent was generally overpredicted over Lake Superior and underpredicted over Lake Erie. In summary, the coupled modeling system described in this paper shows promise for use in climate simulators over regions where lakes are important such as the Great Lakes. It has been shown that many aspects of the simulation are in good agreement with available observations. Areas in which the results point to the need for further work are the model's convective parameterization, the eddy diffusivities in the lake model, and the treatment of clouds in the radiation package.

Illinois, Indiana, Michigan, Minnesota, New York, ↗
USGS2012

Partly cloudy with a chance of migration: Weather, radars, and aeroecology

Aeroecology is an emerging scientific discipline that integrates atmospheric science, Earth science, geography, ecology, computer science, computational biology, and engineering to further the understanding of biological patterns and processes. The unifying concept underlying this new transdisciplinary field of study is a focus on the planetary boundary layer and lower free atmosphere (i.e., the aerosphere), and the diversity of airborne organisms that inhabit and depend on the aerosphere for their existence. Here, we focus on the role of radars and radar networks in aeroecological studies. Radar systems scanning the atmosphere are primarily used to monitor weather conditions and track the location and movements of aircraft. However, radar echoes regularly contain signals from other sources, such as airborne birds, bats, and arthropods. We briefly discuss how radar observations can be and have been used to study a variety of airborne organisms and examine some of the many potential benefits likely to arise from radar aeroecology for meteorological and biological research over a wide range of spatial and temporal scales. Radar systems are becoming increasingly sophisticated with the advent of innovative signal processing and dual-polarimetric capabilities. These capabilities should be better harnessed to promote both meteorological and aeroecological research and to explore the interface between these two broad disciplines. We strongly encourage close collaboration among meteorologists, radar scientists, biologists, and others toward developing radar products that will contribute to a better understanding of airborne fauna.

Bulletin of the American Meteorological Society↗
USGS2018

Growth and survival relationships of 71 tree species with nitrogen and sulfur deposition across the conterminous U.S.

Atmospheric deposition of nitrogen (N) influences forest demographics and carbon (C) uptake through multiple mechanisms that vary among tree species. Prior studies have estimated the effects of atmospheric N deposition on temperate forests by leveraging forest inventory measurements across regional gradients in deposition. However, in the United States (U.S.), these previous studies were limited in the number of species and the spatial scale of analysis, and did not include sulfur (S) deposition as a potential covariate. Here, we present a comprehensive analysis of how tree growth and survival for 71 species vary with N and S deposition across the conterminous U.S. Our analysis of 1,423,455 trees from forest plots inventoried between 2000 and 2016 reveals that the growth and/or survival of the vast majority of species in the analysis (n = 66, or 93%) were significantly affected by atmospheric deposition. Species co-occurred across the conterminous U.S. that had decreasing and increasing relationships between growth (or survival) and N deposition, with just over half of species responding negatively in either growth or survival to increased N deposition somewhere in their range (42 out of 71). Averaged across species and conterminous U.S., however, we found that an increase in deposition above current rates of N deposition would coincide with a small net increase in tree growth (1.7% per Δ kg N ha -1 yr -1 ), and a small net decrease in tree survival (-0.22% per Δ kg N ha -1 yr -1 ), with substantial regional and among-species variation. Adding S as a predictor improved the overall model performance for 70% of the species in the analysis. Our findings have potential to help inform ecosystem management and air pollution policy across the conterminous U.S., and suggest that N and S deposition have likely altered forest demographics in the U.S.

PLoS ONE↗
USGS2014

Variation in the terrestrial isotopic composition and atomic weight of argon

The isotopic composition and atomic weight of argon (Ar) are variable in terrestrial materials. Those variations are a source of uncertainty in the assignment of standard properties for Ar, but they provide useful information in many areas of science. Variations in the stable isotopic composition and atomic weight of Ar are caused by several different processes, including (1) isotope production from other elements by radioactive decay (radiogenic isotopes) or other nuclear transformations (e.g., nucleogenic isotopes), and (2) isotopic fractionation by physical-chemical processes such as diffusion or phase equilibria. Physical-chemical processes cause correlated mass-dependent variations in the Ar isotope-amount ratios ( 40 Ar/ 36 Ar, 38 Ar/ 36 Ar), whereas nuclear transformation processes cause non-mass-dependent variations. While atmospheric Ar can serve as an abundant and homogeneous isotopic reference, deviations from the atmospheric isotopic ratios in other Ar occurrences limit the precision with which a standard atomic weight can be given for Ar. Published data indicate variation of Ar atomic weights in normal terrestrial materials between about 39.7931 and 39.9624. The upper bound of this interval is given by the atomic mass of 40 Ar, as some samples contain almost pure radiogenic 40 Ar. The lower bound is derived from analyses of pitchblende (uranium mineral) containing large amounts of nucleogenic 36 Ar and 38 Ar. Within this interval, measurements of different isotope ratios ( 40 Ar/ 36 Ar or 38 Ar/ 36 Ar) at various levels of precision are widely used for studies in geochronology, water–rock interaction, atmospheric evolution, and other fields.

Pure and Applied Chemistry↗
USGS2026

New measurements indicate that natural geologic methane emissions from microseepage in the Michigan Basin are likely negligible

The magnitude of natural geologic methane (CH 4 ) emissions to the atmosphere (including emissions of fossil CH 4 from offshore and onshore gas and oil seeps, diffuse microseepage, mud volcanoes, volcanic vents, and geothermal areas) is highly uncertain. The largest component of geologic emissions is thought to be microseepage, which is the diffuse flux of CH 4 from soils across large areas of productive hydrocarbon basins. The accuracy of existing bottom-up estimates of microseepage is limited by low spatial coverage of published microseepage measurements. We present the first soil—atmosphere CH 4 flux measurements from Michigan Basin, USA. Results from 335 measurements taken during summer and winter seasons across a large portion of the basin suggest microseepage is nonexistent in the sampled region. Even areas with predictive features for microseepage (e.g., underlying mature, organically rich source rocks, proven gas accumulations, faults, and lineaments) yield null or negative fluxes, suggesting that CH 4 emissions from microseepage are negligible throughout our study region. A Monte Carlo method was used to place an upper limit on the regional-mean microseepage flux, in which synthetic patchy microseepage distributions were generated and tested against our observations to assess the impact of possible emission hot spots that were missed by our sampling strategy. Our analysis finds it is very unlikely that regional-mean emissions are as high as assumed in a previous global microseepage study. The observed lack of seepage may be explained by groundwater flow, active methanotrophy, glacial sediments, and bedded salt deposits, which could inhibit vertical gas migration and release to atmosphere.

Michigan↗
USGS2018

Variation in soil carbon dioxide efflux at two spatial scales in a topographically complex boreal forest

Carbon dynamics of high-latitude regions are an important and highly uncertain component of global carbon budgets, and efforts to constrain estimates of soil-atmosphere carbon exchange in these regions are contingent on accurate representations of spatial and temporal variability in carbon fluxes. This study explores spatial and temporal variability in soilatmosphere carbon dynamics at both fine and coarse spatial scales in a high-elevation, permafrost-dominated boreal black spruce forest. We evaluate the importance of landscape-level investigations of soil-atmosphere carbon dynamics by characterizing seasonal trends in soil-atmosphere carbon exchange, describing soil temperature-moisture-respiration relations, and quantifying temporal and spatial variability at two spatial scales: the plot scale (0–5 m) and the landscape scale (500–1000 m). Plot-scale spatial variability (average variation on a given measurement day) in soil CO 2 efflux ranged from a coefficient of variation (CV) of 0.25 to 0.69, and plot-scale temporal variability (average variation of plots across measurement days) in efflux ranged from a CV of 0.19 to 0.36. Landscape-scale spatial and temporal variability in efflux was represented by a CV of 0.40 and 0.31, respectively, indicating that plot-scale spatial variability in soil respiration is as great as landscape-scale spatial variability at this site. While soil respiration was related to soil temperature at both the plot- and landscape scale, landscape-level descriptions of soil moisture were necessary to define soil respiration-moisture relations. Soil moisture variability was also integral to explaining temporal variability in soil respiration. Our results have important implications for research efforts in high-latitude regions where remote study sites make landscape-scale field campaigns challenging.

Arctic, Antarctic, and Alpine Research↗
USGS1964

Origin of precambrian iron formations

A statistical study of the chemical composition of the Precambrian iron formations of the Canadian Shield affords a new approach to the origin of these unusual formations . The average total iron content of 2,200 samples from the literature and from unpublished mining company analyses is 26.7 percent Fe. The average Fe content for 16 iron formations in the United States and Canada ranges from 24.5 to 34.1 percent. Low contents of A1203, Ti02, P2O5, and CaO characterize the Precambrian iron formations compared to the relatively large amounts of these constituents in the post- Precambrian iron -bearing sediments. The chemical data emphasize that whereas iron , manganese, and silica were transported and deposited together in the cherty iron formations of the Precambrian , these same elements were chemically differentiated in younger geological time in large but separate deposits of iron and silica. Isotopic age determinations indicate that cherty iron formations were deposited during a long interval of geologic time from approximately 1,700 to 3,000 million years ago. A model is proposed to explain the origin of the iron formations of the Lake Superior type based on the absence or marked deficiency of free oxygen in the atmosphere prior to the Late Precambrian . Lateritic weathering under these conditions permitted the transport of iron and manganese together with silica. The weathered mantle effectively retained aluminum, titanium, phosphorus, and colloidal clay. Graphitic material of biogenic origin is closely associated with the Precambrian iron formations . Although it is uncertain whether iron was precipitated directly through biologic processes, the removal of C02 and the liberation of oxygen to the sea water through photosynthesis of primitive plants undoubtedly influenced the energy relationships among the iron minerals. As a result of the variable conditions the iron formations commonly are characterized by nonequilibrium mineral assemblages. In Late Precambrian time a critical level of free oxygen in the atmosphere was attained permitting a marked acceleration in plant growth and in accretion of oxygen. This stage in the development of an oxygenated atmosphere was reached at least 1,200 million years ago and effectively curtailed the development of cherty iron formations of the Lake Superior type.

Economic Geology↗
USGS1965

The system arsenic-antimony

The one atmosphere isobaric phase relations have been determined for the system As-Sb, using a simple experimental arrangement where a low melting temperature alkali halide melt acts as a reaction vessel. The one atmosphere univariant temperature, where a liquid of composition 45.5 mol % As, plus a solid of composition 62 mol % As and a gas of composition 89 mol % As coexist, is 666° ± 3° C. The one atmosphere sublimation point of As was measured as 611° ±2° C. Arsenic and antimony are hexagonal isostructural compounds with a complete solid solution series between them. The a cell edge and volume of the unit cell vary linearly with composition in mol percent. The c edge changes in a markedly nonlinear manner with composition. The measured unit-cell parameters at 25° C are: As, a = 3.760 ± 0.001 A, c = 10.555 ± 0.003A, V = 129.2A3; Sb, a = 4.310 ± 0.001 A, c - 11.279 ± 0.003A, V = 181.4A3.

Economic Geology↗
USGS1992

The stable isotope geochemistry of acid sulfate alteration

Acid sulfate wall-rock alteration, characterized by the assemblage alunite + kaolinite + quartz + or - pyrite, results from base leaching by fluids concentrated in H 2 SO 4 . Requisite amounts of H 2 SO 4 can be generated by different mechanisms in three principal geologic environments: (1) by atmospheric oxidation of sulfides in the supergene environment, (2) by atmospheric oxidation at the water table in the steam-heated environment of H 2 S released by deeper, boiling fluids, and (3) by the disproportionation of magmatic SO 2 to H 2 S and H 2 SO 4 during condensation of a magmatic vapor plume at intermediate depths in magmatic hydrothermal environments in silicic and andesitic volcanic terranes. In addition, coarse vein alunite may form in a magmatic steam environment from rapid release of an SO 2 -rich magmatic vapor phase at high temperature and low pressure or from the oxidation of a more reduced magmatic vapor by entrained atmospheric oxygen in the carapace of a volcanic edifice.Alunite [KAl 3 (SO 4 ) 2 (OH) 6 ] contains four stable isotope sites and complete analyses (delta D, delta 18 O (sub SO 4 ) , delta 18 O OH , and delta 34 S) are now possible. Except for delta 18 O OH in magmatic hydrothermal alunites, primary values are usually retained. In cooperation with many colleagues, over 500 measurements have been made on nearly 200 samples of alunite and associated minerals from 23 localities, and 55 additional analyses have been taken from the literature. This survey confirms that kinetic factors play an important role in the stable isotope systematics of alunite and acid sulfate alteration. To a very large extent they form the isotopic basis for distinguishing between environments of acid sulfate alteration, and they provide important insights into attendant processes. Stable isotope analyses of alunite, often in combination with those on associated sulfides and kaolinite, permit recognition of environments of formation and provide information on origins of components, processes (including rates), physical-chemical environments, and temperatures of formation.Supergene acid sulfate alteration may form over any sulfide zone when it is raised above the water table by tectonics or exposed by erosion. It may overprint earlier acid sulfate assemblages, particularly the magmatic hydrothermal assemblages which are pyrite rich such as at El Salvador, Chile; Rodalquilar, Spain; and Goldfield, Nevada. Supergene alunite normally has delta 34 S values virtually identical to precursor sulfides unless bacteriogenic reduction of aqueous sulfate takes place in standing pools of water. delta D values are close to that of local meteoric water unless extensive evaporation occurs. delta D and delta 18 O OH values of supergene alunites from a range of latitudes fall in a broad zone parallel to the meteoric water line much the way delta D and delta 18 O values of associated halloysite-kaolinite fall near the kaolinite line of Savin and Epstein (1970). delta 18 O (sub SO 4 ) values are kinetically controlled and will reflect the hydro-geochemistry of the environment. delta 18 O (sub SO 4 -OH) alues are grossly out of equilibrium and large negative values are definitive of a supergene origin.In steam-heated environments, such as those at the Tolfa district, Italy, and Marysvale, Utah, and numerous modern geothermal systems, acid sulfate alteration zones are characterized by pronounced vertical zoning. Such acid sulfate alteration may occur over adularia-sericite-type base and precious metal ore deposits such as the one at Buckskin, Nevada. Initial delta 18 O (sub SO 4 ) and delta 34 S values are kinetically controlled, but delta 18 O (sub SO 4 ) values usually reach equilibrium with fluids, and even delta 34 S values may reflect partial exchange with H 2 S where the residence time of aqueous sulfate is sufficient. Most alunites of steam-heated origin have delta 34 S values the same as those of precursor H 2 S (and as related sulfides, if present) and delta D values similar to that of local meteoric water. In the samples analyzed, most delta 18 O (sub SO 4 -OH) values give reasonable temperatures of 90 degrees to 160 degrees C, indicating that delta 18 O (sub SO 4 ) and delta 18 O OH values reflect a close approach to equilibrium with the fluid. The delta 18 O (sub SO 4 ) and delta 18 O OH values also reflect the degree of exchange of the meteoric fluids with wall rock. Coeval kaolinites typically have delta 18 O and delta D values to the left of the kaolinitc line.Magmatic hydrothermal, acid sulfate alteration zones in near-surface epithermal deposits such as Summitville, Colorado. Julcani, Peru, and Red Mountain and Lake City, Colorado, are characterized by vertical orientation and horizontal zoning, the presence of coeval pyrite, PO 4 analogues of alunite, zunyite, and later gold, pyrite and enargite, and often other Cu-As-Sb-S minerals. Acid sulfate alteration assemblages also occur as late stages in the porphyry-copper deposit at E1 Salvador, Chile. In the examples studied, magmatic hydrothermal alunites have delta D values close to those for magmatic water. delta 34 S values are 16 to 28 per mil larger than those for associated pyrite, reflecting equilibrium between aqueous H 2 S and SO 4 formed by the disproportionation of magmatically derived SO 2 . delta 18 O (sub SO 4 ) values are usually 8 to 18 per mil and vary systematically with delta 34 S values, reflecting variations in temperature and/or H 2 S/SO 4 fluid ratios. Further variation in delta 18 O (sub SO 4 ) values may result if SO 2 condenses in mixed magmatic meteoric water fluids. delta 18 O (sub SO (sub 4-) OH) values of magmatic hydrothermal alunites are generally unsuitable for temperature determinations because of retrograde exchange in the OH site, but delta 34 S (sub alunite-pyrite) values provide reliable temperature estimates.Magmatic steam environments appear to occur over a range of depths and are characterized by monomineralic veins of coarse alunite in variably alunitized and kaolinized wall rocks containing minor pyrite. Alunite formed in the magmatic steam environment can usually be recognized by delta 34 S near delta 34 S (sub Sigma S) values and delta D and delta 18 O (sub SO 4 ) values near magmatic values. Magmatic steam alunite differs from magmatic hydrothermal alunite by having delta 34 S close to delta 34 S (sub Sigma S) values of the system. delta 18 O (sub SO (sub 4-) OH) values of most magmatic steam alunite give temperatures ranging from 90 degrees to 210 degrees C but, for reasons which are not understood, some temperatures as well as calculated delta 18 O (sub H 2 O) values are too low for presumed precipitation from a magmatic vapor phase. Magmatic steam environments may occur over porphyry-type mineralization as at Red Mountain, Colorado, and Alunite Ridge, Utah, and over or adjacent to adularia-sericite-type deposits in volcanic domes as at Cactus, California.

Economic Geology↗
USGS1984

Causes of acidification of four streams on Laurel Hilld in southwestern Pennsylvania

Atmospheric deposition, soils developed from bedrock, a natural bog, gas wells, and a ski area were all investigated as possible sources of water quality degradation for four streams on Laurel Hill in southwestern Pennsylvania where fish kills have been reported since 1960. An intensive study of the chemistry of atmospheric deposition, soil leachate, and stream water and fish populations was conducted on these basins during 1980–1981 with emphasis on dormant season periods with runoff from snowmelt and rain. Although bedrock geology was found to control the natural buffering capacity of these streams, only acid precipitation could be linked to sharp drops in pH and increases in total Al concentrations observed during stormflows in the poorly buffered streams. Three poorly buffered streams exhibited drops to pH 4.4 to 4.5 and increases in total Al concentrations up to 1.5 mg/L during observed peak flows. Mineral soil leachate from the three major soil series on the basins during this time exhibited a low pH of 4.3 and mean total Al concentrations of 3.6 mg/L, indicating stream response during storms was closely linked to chemistry of soil leachate. Poorly buffered streams did not support reproducing populations of trout ( Salmonidae sp.) or other fishes. In contrast, one well-buffered stream (20 mg/L CaCO 3 ) exhibited drops to pH 5.5 during peak flow and supported reproducing trout and sculpin ( Cottus bairdi ) populations. The acidification of the four streams studied was attributed to atmospheric deposition.

Journal of Environmental Quality↗
USGS2014

Soil, plant, and terrain effects on natural perchlorate distribution in a desert landscape

Perchlorate (ClO 4 − ) is a contaminant that occurs naturally throughout the world, but little is known about its distribution and interactions in terrestrial ecosystems. The objectives of this Amargosa Desert, Nevada study were to determine (i) the local-scale distribution of shallow-soil (0–30 cm) ClO 4 − with respect to shrub proximity (far and near) in three geomorphic settings (shoulder slope, footslope, and valley floor); (ii) the importance of soil, plant, and terrain variables on the hillslope-distribution of shallow-soil and creosote bush [ Larrea tridentata (Sessé & Moc. ex DC.) Coville] ClO 4 − ; and (iii) atmospheric (wet plus dry, including dust) deposition of ClO 4 − in relation to soil and plant reservoirs and cycling. Soil ClO 4 − ranged from 0.3 to 5.0 μg kg −1 . Within settings, valley floor ClO 4 − was 17× less near shrubs due in part to enhanced leaching, whereas shoulder and footslope values were ∼2× greater near shrubs. Hillslope regression models (soil, R 2 = 0.42; leaf, R 2 = 0.74) identified topographic and soil effects on ClO 4 − deposition, transport, and cycling. Selective plant uptake, bioaccumulation, and soil enrichment were evidenced by leaf ClO 4 − concentrations and Cl − /ClO 4 − molar ratios that were ∼8000× greater and 40× less, respectively, than soil values. Atmospheric deposition ClO 4 − flux was 343 mg ha −1 yr −1 , ∼10× that for published southwestern wet-deposition fluxes. Creosote bush canopy ClO 4 − (1310 mg ha−1) was identified as a previously unrecognized but important and active reservoir. Nitrate δ 18 O analyses of atmospheric deposition and soil supported the leaf-cycled–ClO 4 − input hypothesis. This study provides basic data on ClO 4 − distribution and cycling that are pertinent to the assessment of environmental impacts in desert ecosystems and broadly transferable to anthropogenically contaminated systems.

Nevada↗
USGS2004

Transport and time lag of chlorofluorocarbon gases in the unsaturated zone, Rabis Creek, Denmark

Transport of chlorofluorocarbon (CFC) gases through the unsaturated zone to the water table is affected by gas diffusion, air–water exchange (solubility), sorption to the soil matrix, advective–dispersive transport in the water phase, and, in some cases, anaerobic degradation. In deep unsaturated zones, this may lead to a time lag between entry of gases at the land surface and recharge to groundwater. Data from a Danish field site were used to investigate how time lag is affected by variations in water content and to explore the use of simple analytical solutions to calculate time lag. Numerical simulations demonstrate that either degradation or sorption of CFC-11 takes place, whereas CFC-12 and CFC-113 are nonreactive. Water flow did not appreciably affect transport. An analytical solution for the period with a linear increase in atmospheric CFC concentrations (approximately early 1970s to early 1990s) was used to calculate CFC profiles and time lags. We compared the analytical results with numerical simulations. The time lags in the 15-m-deep unsaturated zone increase from 4.2 to between 5.2 and 6.1 yr and from 3.4 to 3.9 yr for CFC-11 and CFC-12, respectively, when simulations change from use of an exponential to a linear increase in atmospheric concentrations. The CFC concentrations at the water table before the early 1990s can be estimated by displacing the atmospheric input function by these fixed time lags. A sensitivity study demonstrates conditions under which a time lag in the unsaturated zone becomes important. The most critical parameter is the tortuosity coefficient. The analytical approach is valid for the low range of tortuosity coefficients (τ = 0.1–0.4) and unsaturated zones greater than approximately 20 m in thickness. In these cases the CFC distribution may still be from either the exponential or linear phase. In other cases, the use of numerical models, as described in our work and elsewhere, is an option.

Rabis Creek↗
USGS2002

Comparative effects of climate on ecosystem nitrogen and soil biogeochemistry in U.S. national parks. FY 2001 Annual Report (Res. Rept. No. 94)

In 1998, the USGS Global Change program funded research for a network of Long-Term Reference Ecosystems initially established in national parks and funded by the National Park Service. The network included Noland Divide, Great Smoky Mountains National Park, Tennessee; Pine Canyon, Big Ben National park, Texas; West Twin Creek, Olympic National Park, Washingtona?? Wallace Lake, Isle Royale National Park, Michigan; and the Asik watershed, Noatak National Preserve, Alaska. The watershed ecosystem model was used since this approach permits additional statistical power in detection of trends among variables, and the watershed in increasingly a land unit used in resource management and planning. The ecosystems represent a major fraction of lands administered by the National Park Service, and were chosen generally for the contrasts among sites. For example, tow of the site, Noland and West Twin, are characterized by high precipitation amounts, but Noland receives some of the highest atmospheric nitrogen (N) inputs in North America. In contrast, Pine Canyon and Asik are warm and cold desert sites respectively. The Asik watershed receives <1% the atmospheric N inputs Noland receives. The Asik site is at the northern extent (treeline) of the boreal biome in the North America while Wallace is at the southern ecotone between boreal and northern hardwoods. The research goal for these sites is to gain a basic understanding of ecosystem structure and function, and the response to global change especially atmospheric inputs and climate.

Report↗