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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↗

USGS1969

Mercury in soil gas and air--A potential tool in mineral exploration

The mercury content in soil gas and in the atmosphere was measured in several mining districts to test the possibility that the mercury content in the atmosphere is higher over ore deposits than over barren ground. At Cortez, Nev., the distribution of anorhalous amounts of mercury in the air collected at ground level (soil gas) correlates well with the distribution of gold-bearing rocks that are covered by as much as 100 feet of gravel. The mercury content in the atmosphere collected at an altitude of 200 feet by an aircraft was 20 times background over a mercury posit and 10 times background over two porphyry copper deposits. Measurement of mercury in soil gas and air may prove to be a valuable exploration tool.

Circular↗

USGS2004

Latitudinal variation in carbon storage can help predict changes in swamps affected by global warming

Plants may offer our best hope of removing greenhouse gases (gases that contribute to global warming) emitted to the atmosphere from the burning of fossil fuels. At the same time, global warming could change environments so that natural plant communities will either need to shift into cooler climate zones, or become extirpated (Prasad and Iverson, 1999; Crumpacker and others, 2001; Davis and Shaw, 2001). It is impossible to know the future, but studies combining field observation of production and modeling can help us make predictions about what may happen to these wetland communities in the future. Widespread wetland types such as baldcypress (Taxodium distichum) swamps in the southeastern portion of the United States could be especially good at carbon sequestration (amount of CO2 stored by forests) from the atmosphere. They have high levels of production and sometimes store undecomposed dead plant material in wet conditions with low oxygen, thus keeping gases stored that would otherwise be released into the atmosphere (fig. 1). To study the ability of baldcypress swamps to store carbon, our project has taken two approaches. The first analysis looked at published data to develop an idea (hypothesis) of how production levels change across a temperature gradient in the baldcypress region (published data study). The second study tested this idea by comparing production levels across a latitudinal range by using swamps in similar field conditions (ongoing carbon storage study). These studies will help us make predictions about the future ability of baldcypress swamps to store carbon in soil and plant biomass, as well as the ability of these forests to shift northward with global warming.

Fact Sheet↗

USGS1998

Geologic map of the MTM -85280 quadrangle, Planum Australe region of Mars

The polar deposits on Mars are of great interest because they probably record martian climate variations (Thomas and others, 1992). The area shown on this map includes polar layered deposits with distinct low-albedo features and a sharp boundary between the layered deposits and the moderately cratered unit that forms the floor of Chasma Australe. Detailed mapping of this quadrangle was undertaken to further investigate the geologic relations between the albedo features and the layered deposits and to better constrain the recent geologic history of the south polar region. Dark dunes in the north polar region appear to be derived from erosion of the layered deposits, but the source of dark material in the south polar region is less clear (Thomas and Weitz, 1989). The presence of dark material in the brighter, redder layered deposits is paradoxical (Herkenhoff and Murray, 1990a); resolving this paradox is likely to result in a better understanding of the origin and evolution of the layered deposits and, therefore, the mechanisms by which global climate variations are recorded. Published geologic maps of the south polar region of Mars have been based on images acquired by either Mariner 9 (Condit and Soderblom, 1978; Scott and Carr, 1978) or the Viking Orbiters (Tanaka and Scott, 1987). The extent of the layered deposits mapped previously from Mariner 9 data is different from that mapped using Viking Orbiter images, and the present map agrees with the map by Tanaka and Scott (1987): the floor of Chasma Australe is not mapped as layered deposits. The residual polar ice cap, areas of partial frost cover, the layered deposits, and two nonvolatile surface units - the dust mantle and the dark material - were mapped by Herkenhoff and Murray (1990a) at 1:2,000,000 scale using a color mosaic of Viking Orbiter images. This mosaic and an additional Viking color mosaic were used to confirm the identification of the nonvolatile Amazonian units for this map and to test hypotheses for their origin and evolution. The colors and albedos of these units, as measured in places outside this map area, are presented in table 1 and figure 1. Accurately measuring the color and albedo of the units in this map area was not possible due to low signal/noise in the part of the red/violet mosaic (corrected for atmospheric scattering) that includes this area (Herkenhoff and Murray, 1990a). However, color/albedo unit boundaries in this area are visible in color mosaics that have not been corrected for atmospheric scattering effects. Therefore, while the color and albedo of various units on this map cannot be precisely quantified and compared with the values in table 1 and figure 1, color/albedo units can still be recognized. Because the resolution of the color mosaics is not sufficient to map these units in detail at 1:500,000 scale, contacts between them were recognized and mapped using higher resolution black-and-white Viking and Mariner 9 images. Only two possible impact craters in the layered deposits have been found in the area mapped; both are slightly elongate rather than circular. One, 1.6 km in diameter at lat 86.6° S., long 268°, was recognized by Plaut and others (1988); the other, about 3 km in diameter, is at lat 82.8° S., long 277°. Although the crater statistics are poor (only 16 likely impact craters found in the entire south polar layered deposits), these observations generally support the conclusions that the south polar layered deposits are Late Amazonian in age and that some areas have been exposed for at least 120 million years (Plaut and others, 1988; Herkenhoff and Murray, 1992, 1994). However, the recent cratering flux on Mars is poorly constrained, so inferred ages of surface units are uncertain. The Viking Orbiter 2 images used to construct the base were taken during the southern summer of 1977, with resolutions no better than 180 m/pixel. (The "less than 100 m per picture element" in Notes on Base of the controlled photomosaic base [U.S. Geological Survey, 1986] is incorrect.) A digital mosaic of Mariner 9 images was also constructed to aid in mapping. The Mariner 9 images were taken during the southern summer of 1971-72 and have resolutions as high as 90 m/pixel. However, usefulness of the Mariner 9 mosaic is limited by incomplete coverage and atmospheric dust opacity.

IMAP↗

USGS2003

Soil organic carbon on lands of the Department of the Interior

The stocks of soil organic carbon (SOC) on the landscape are an important element in the global carbon cycle. Changes in soil carbon can change the concentrations of greenhouse gases in the atmosphere. If carbon dioxide from the atmosphere, captured through photosynthesis, is ultimately stored in the soil to an enhanced degree, the resulting soil carbon sequestration may help delay some of the undesirable consequences of global warming. If the conditions affecting the balance of photosynthesis and decomposition are changed to favor decomposition, then soil carbon can be released to the atmosphere as carbon dioxide or methane, contributing to greenhouse warming. The Department of the Interior (DOI) is the largest land management agency in the United States, with jurisdiction influencing more than 2 million square kilometers of land--about 22 percent of the total land area of the country. Estimates using available data indicate that the DOI lands have nearly 18 petagrams (Pg; 1 Pg = 1015 g = 1 gigaton) of SOC, which is about 22 percent of the estimate for the country (81 Pg). The distribution is not uniform, and few areas of DOI lands reflect “average” conditions. Large areas of land with low biological productivity occur in the conterminous U.S. part of the DOI lands, and substantial areas with high SOC occur in Alaska. About 74 percent of the SOC on DOI lands is in Alaska. Details on amounts of SOC by DOI Bureau and location are shown in a series of tables and maps. For the conterminous United States, statistics are given by land cover type and soil depth ranges.

Open-File Report↗

USGS2011

Preliminary assessment of chloride concentrations, loads, and yields in selected watersheds along the Interstate 95 corridor, southeastern Connecticut, 2008-09

Water-quality conditions were assessed to evaluate potential effects of road-deicer applications on stream-water quality in four watersheds along Interstate 95 (I-95) in southeastern Connecticut from November 1, 2008, through September 30, 2009. This preliminary study is part of a four-year cooperative study by the U.S. Geological Survey (USGS), the Federal Highway Administration (FHWA), and the Connecticut Department of Transportation (ConnDOT). Streamflow and water quality were studied at four watersheds?Four Mile River, Oil Mill Brook, Stony Brook, and Jordan Brook. Water-quality samples were collected and specific conductance was measured continuously at paired water-quality monitoring sites upstream and downstream from I-95. Specific conductance values were related to chloride (Cl) concentrations to assist in determining the effects of road-deicing operations on the levels of Cl in the streams. Streamflow and water-quality data were compared with weather data and with the timing, amount, and composition of deicers applied to state highways. Grab samples were collected during winter stormwater-runoff events, such as winter storms or periods of rain or warm temperatures in which melting takes place, and periodically during the spring and summer. Cl concentrations at the eight water-quality monitoring sites were well below the U.S. Environmental Protection Agency (USEPA) recommended chronic and acute Cl toxicity criteria of 230 and 860 milligrams per liter (mg/L), respectively. Specific conductance and estimated Cl concentrations in streams, particularly at sites downstream from I-95, peaked during discharge events in the winter and early spring as a result of deicers applied to roads and washed off by stormwater or meltwater. During winter storms, deicing activities, or subsequent periods of melting, specific conductance and estimated Cl concentrations peaked as high as 703 microsiemens per centimeter (?S/cm) and 160 mg/L at the downstream sites. During most of the spring and summer, specific conductance and estimated Cl concentrations decreased during discharge events because the low-ionic strength of stormwater had a diluting effect on stream-water quality. However, peaks in specific conductance and estimated Cl concentrations at Jordan Brook and Stony Brook corresponded to peaks in streamflow well after winter snow or ice events; these delayed peaks in Cl concentration likely resulted from deicing salts that remained in melting snow piles and (or) that were flushed from soils and shallow groundwater, then discharged downstream. Cl loads in streams generally were highest in the winter and early spring. The estimated load for the period of record at the four monitoring sites downstream from I-95 ranged from 0.33 ton per day (ton/d) at the Stony Brook watershed to 0.59 ton/d at the Jordan Brook watershed. The Cl yields ranged from 0.07 ton per day per square mile (ton/d/)mi2) at Oil Mill Brook, one of the least developed watersheds, to 0.21 (ton/d)/mi2) at Jordan Brook, the watershed with the highest percentage of urban development and impervious surfaces. The median estimates of Cl load from atmospheric deposition ranged from 11 to 19 tons, and contributed 4.3 to 7.1 percent of the Cl load in streamflow from the watershed areas. A comparison of the Cl load input and output estimates indicates that less Cl is leaving the watersheds than is entering through atmospheric deposition and application of deicers. The lag time between introduction of Cl to the watershed and transport to the stream, and uncertainty in the load estimates may be the reasons for this discrepancy. In addition, estimates of direct infiltration of Cl to groundwater from atmospheric deposition, deicer applications, and septic-tank drainfields to groundwater were outside the scope of the November 2008 to September 2009 assessment. However, increased concentrations of ions were observed between upstream and downstream sites and could result from deicer appli

Connecticut↗

USGS2013

Mercury bioaccumulation in fishes from subalpine lakes of the Wallowa-Whitman National Forest, northeastern Oregon and western Idaho

Mercury (Hg) is a globally distributed pollutant that poses considerable risks to human and wildlife health. Over the past 150 years since the advent of the industrial revolution, approximately 80 percent of global emissions have come from anthropogenic sources, largely fossil fuel combustion. As a result, atmospheric deposition of Hg has increased by up to 4-fold above pre-industrial times. Because of their isolation, remote high-elevation lakes represent unique environments for evaluating the bioaccumulation of atmospherically deposited Hg through freshwater food webs, as well as for evaluating the relative importance of Hg loading versus landscape influences on Hg bioaccumulation. The increase in Hg deposition to these systems over the past century, coupled with their limited exposure to direct anthropogenic disturbance make them useful indicators for estimating how changes in Hg emissions may propagate to changes in Hg bioaccumulation and ecological risk. In this study, we evaluated Hg concentrations in fishes of high-elevation, sub-alpine lakes in the Wallowa-Whitman National Forest in northeastern Oregon and western Idaho. Our goals were to (1) assess the magnitude of Hg contamination in small-catchment lakes to evaluate the risk of atmospheric Hg to human and wildlife health, (2) quantify the spatial variability in fish Hg concentrations, and (3) determine the ecological, limnological, and landscape factors that are best correlated with fish total mercury (THg) concentrations in these systems. Across the 28 study lakes, mean THg concentrations of resident salmonid fishes varied as much as 18-fold among lakes. Importantly, our top statistical model explained 87 percent of the variability in fish THg concentrations among lakes with four key landscape and limnological variables— catchment conifer density (basal area of conifers within a lake’s catchment), lake surface area, aqueous dissolved sulfate, and dissolved organic carbon. The basal area of conifers within a lake’s catchment was by far the most important variable explaining fish THg concentrations, with an increase in THg concentrations of more than 400 percent across the forest density spectrum. Across all study lakes, fish THg concentrations ranged from 0.004 to 0.438 milligrams per kilogram wet weight (mg/kg ww). Only a single individual fish sample exceeded the U.S. Environmental Protection Agency’s (USEPA) human health tissue residue criteria of 0.3 mg/kg ww. However, 54 percent of fish (N=177) exceeded the more stringent tissue residue criteria (0.04 mg/kg ww) adopted by the Oregon Department of Environmental Quality to better protect subsistence fishers. Additionally, 2 and 10 percent of fish exceeded levels associated with reduced common loon reproduction and behavior, respectively. Whereas 25 and 68 percent of fish sampled exceeded concentrations deemed protective of mink and kingfisher, respectively. These results suggest that THg concentrations may be present in these lakes at levels associated with ecological risk. It is important to note however, that accurate inference on potential impairment cannot be made within the context of this study design and further research is needed to better quantify these risks.

Oregon;Idaho↗

USGS2015

Water-level measurements in Dauphin Island, Alabama, from the 2013 Hurricane Season

This report describes the instrumentation, field measurements, and processing methods used by the U.S. Geological Survey to measure atmospheric pressure, water levels, and waves on Dauphin Island, Alabama, in 2013 at part of the Barrier Island Evolution Research project. Simple, inexpensive pressure sensors mounted in shallow wells were buried in the beach and left throughout the hurricane season. Additionally, an atmospheric pressure sensor was mounted on the porch of a private residence to provide a local atmospheric pressure measurement for correcting the submerged pressure records.

Alabama↗

USGS2015

Water-level and wave measurements in the Chandeleur Islands, Louisiana, 2012 and 2013

This report documents measurements of atmospheric pressure, water levels, and waves made by the U.S. Geological Survey in the Chandeleur Islands, Louisiana, during 2012 and 2013 as part of the Barrier Island Evolution Research project. Simple, inexpensive pressure sensors mounted in shallow wells were buried in the beach and left for one hurricane season and one winter-storm season. Gauges with rapid-sampling pressure sensors that provided nondirectional wave data and water-level data were mounted on rugged mounts on the Chandeleur Sound side and at the base of a tower at the northern end of the island chain. Additionally, an atmospheric pressure sensor was mounted on the tower to provide a local atmospheric pressure measurement for correcting the submerged pressure records.

Louisiana↗