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At least 811 records · Page 45Linked to original sources
USGS1990

Climatic change and permafrost. Record from surficial deposits

The physical and chemical characteristics of surficial deposits and the floral and faunal remains they contain provide information that is useful for interpreting both paleoclimate and past permafrost conditions. Surficial deposits thus provide a record of climatic change and permafrost history. This record suggests that initiation of permafrost in lowland areas of the Southern Arctic Archipelago and continents of the northern hemisphere may have occurred about 2,400,000 years ago during the pronounced cooling that led to the first major glaciation of late Cenozoic time. Since then, climate has been relatively cold but cyclically variable, characterized by the growth and shrinkage of large, continental ice sheets. Permafrost has expanded and contracted in response to these climatic changes, and we can expect the present permafrost conditions to change in response to future climatic changes. To predict the response of permafrost and the landscape to future climatic change we should: (1) Define relations between climate and the modern landscape; (2) establish long‐term records of past climatic change and landscape response; and (3) determine the paleoenvironments of past warm periods as possible analogs for future global warming.

Journal of Cold Regions Engineering↗
USGS2001

Analysis of radiation-induced small Cu particle cluster formation in aqueous CuCl2

Radition-induced small Cu particle cluster formation in aqueous CuCl2 was analyzed. It was noticed that nearest neighbor distance increased with the increase in the time of irradiation. This showed that the clusters approached the lattice dimension of bulk copper. As the average cluster size approached its bulk dimensions, an increase in the nearest neighbor coordination number was found with the decrease in the surface to volume ratio. Radiolysis of water by incident x-ray beam led to the reduction of copper ions in the solution to themetallic state.

Journal of Chemical Physics↗
USGS2003

Relaxation of the structure of simple metal ion complexes in aqueous solutions at up to supercritical conditions

Recently x-ray absorption fine structure (XAFS) studies of various ions in aqueous solutions showed a variation of cation-ligand bond lengths, often coupled with other structure changes, with increasing temperatures. Thus, the variations of the structure of several metal ion complexes with temperature based on observations from the X-ray absorption fine structure (XAFS) studies in the hope that it will stimulate the development of either first- principles theory or molecular dynamics simulations that might adequately describes these results are discussed.

Journal of Chemical Physics↗
USGS1969

Oxygen isotope fractionation in divalent metal carbonates

Equilibrium fractionation factors for the distribution of 18 O between alkaline‐earth carbonates and water have been measured over the temperature range 0–500°C. The fractionation factors α"> α α can be represented by the equations CaCO3–H2O, 1000lnα = 2.78(106T−2)− 3.39,"> CaCO 3 – H 2 O , 1000 ln α = 2.78(10 6 T −2 )− 3.39, CaCO3–H2O, 1000lnα = 2.78(106T−2)− 3.39, SrCO3–H2O, 1000lnα = 2.69(106T−2)− 3.74,"> SrCO 3 – H 2 O , 1000 ln α = 2.69(10 6 T −2 )− 3.74, SrCO3–H2O, 1000lnα = 2.69(106T−2)− 3.74, BaCO3–H2O, 1000lnα = 2.57(106T−2)− 4.73."> BaCO 3 – H 2 O , 1000 ln α = 2.57(10 6 T −2 )− 4.73. BaCO3–H2O, 1000lnα = 2.57(106T−2)− 4.73. Measurements on MnCO 3 , CdCO 3 , and PbCO 3 were made at isolated temperatures. A statistical‐mechanical calculation of the isotopic partition function ratios gives reasonably good agreement with experiment. Both cationic size and mass are important in isotopic fractionation, the former predominantly in its effect on the internal vibrations of the anion, the latter in its effect on the lattice vibrations.

Journal of Chemical Physics↗
USGS1963

Antiferromagnetism of UO2⋅2H2O

Magnetic susceptibility measurements have been made on UO 2 · x H 2 O for x =1.78 to x =2.13, and from 77° to 375°K. As the value of x decreased the susceptibility increased. Both these data and structural arguments imply that the formula of this compound is U(OH) 4 rather than the dihydrate form. Based on this concept the data have been corrected for diamagnetism and also small amounts of UO 2 and H 2 O which were present. The molar susceptibility of U 4+ in U(OH) 4 is nearly an order of magnitude less than in other uranium compounds, and it is suggested that this is probably due to superexchange between adjacent uranium atoms through intervening oxygen atoms.

Journal of Chemical Physics↗
USGS2004

Lattice-Boltzmann simulation of coalescence-driven island coarsening

The first-order phase separation in a thin fluid film was simulated using a two-dimensional lattice-Boltzman model (LBM) with fluid-fluid interactions. The effects of the domain size on the intermediate asymptotic island size distribution were also discussed. It was observed that the overall process is dominated by coalescence which is independent of island mass. The results show that the combined effects of growth, coalescence, and Ostwald ripening control the phase transition process in the LBM simulations.

Journal of Chemical Physics↗
USGS1982

Pyridine radical cation and its fluorine substituted derivatives

The spectra and relaxation of the pyridine cation and of several of its fluorinated derivatives are studied in low temperature Ne matrices. The ions are generated by direct photoionization of the parent compounds. Of the compounds studied, laser induced → and → fluorescence is observed only for the 2, 6‐difluoropyridine cation. The analysis of the spectrum indicates that the ion is planar both in the and states. The large variety in the spectroscopic and relaxation behavior of fluoropyridine radical cations is explained in terms of their electronic structure and of the differential shifts of the individual electronic states caused by the fluorine substitution.

Journal of Chemical Physics↗
USGS2013

2D IR spectra of cyanide in water investigated by molecular dynamics simulations

Using classical molecular dynamics simulations, the 2D infrared (IR) spectroscopy of CN − solvated in D 2 O is investigated. Depending on the force field parametrizations, most of which are based on multipolar interactions for the CN − molecule, the frequency-frequency correlation function and observables computed from it differ. Most notably, models based on multipoles for CN − and TIP3P for water yield quantitatively correct results when compared with experiments. Furthermore, the recent finding that T 1 times are sensitive to the van der Waals ranges on the CN − is confirmed in the present study. For the linear IR spectrum, the best model reproduces the full widths at half maximum almost quantitatively (13.0 cm −1 vs. 14.9 cm −1 ) if the rotational contribution to the linewidth is included. Without the rotational contribution, the lines are too narrow by about a factor of two, which agrees with Raman and IR experiments. The computed and experimental tilt angles (or nodal slopes) α as a function of the 2D IR waiting time compare favorably with the measured ones and the frequency fluctuation correlation function is invariably found to contain three time scales: a sub-ps, 1 ps, and one on the 10-ps time scale. These time scales are discussed in terms of the structural dynamics of the surrounding solvent and it is found that the longest time scale (≈10 ps) most likely corresponds to solvent exchange between the first and second solvation shell, in agreement with interpretations from nuclear magnetic resonance measurements.

Journal of Chemical Physics↗
USGS2017

Response of fish population dynamics to mitigation activities in a large regulated river

Extensive water development in large rivers has precipitated many negative ecological effects on native fish populations. Mitigation for such development often focuses on restoring biological integrity through remediation of the physical and chemical properties of regulated rivers. However, evaluating and defining the success of those programs can be difficult. We modeled the influence of mitigation-related environmental factors on growth and recruitment of two ecologically important native fish species (Largescale Sucker Catostomus macrocheilus and Mountain Whitefish Prosopium williamsoni ) in the Kootenai River, Idaho. Artificial nutrient (phosphorus) addition best predicted the variability in annual growth of both species. Nutrient addition was positively related to Largescale Sucker growth but negatively related to Mountain Whitefish growth. The best model explained 82% of the annual variability in incremental growth for Largescale Suckers and 61% of the annual variability for Mountain Whitefish. Year-class strength of Largescale Suckers was not closely related to any of the environmental variables evaluated; however, year-class strength of Mountain Whitefish was closely associated with nutrient addition, discharge, and temperature. Most research has focused on biotic assemblages to evaluate the effects of mitigation activities on fishes, but there is an increased need to identify the influence of rehabilitation activities on fish population dynamics within those assemblages. Here, we demonstrate how fish growth can serve as an indicator of rehabilitation success in a highly regulated large river. Future fish restoration projects can likely benefit from a change in scope and from consideration of an evaluation framework involving the response of population rate functions to mitigation.

Idaho↗
USGS2009

Water, something peculiar

Some chemical and physical properties of water are discussed and compared with those of other fluids. For instance, the boiling point is much higher than one would expect considering the molecular weight of water. The heat capacity is also much higher but the viscosity is not. The dielectric constant is exceptionally high. These and other properties of water can be explained by the geometry of the water molecule and the structure of water or ice.

Hydrological Sciences Bulletin↗
USGS2012

Stable isotope deltas: Tiny, yet robust signatures in nature

Although most of them are relatively small, stable isotope deltas of naturally occurring substances are robust and enable workers in anthropology, atmospheric sciences, biology, chemistry, environmental sciences, food and drug authentication, forensic science, geochemistry, geology, oceanography, and paleoclimatology to study a variety of topics. Two fundamental processes explain the stable isotope deltas measured in most terrestrial systems: isotopic fractionation and isotope mixing. Isotopic fractionation is the result of equilibrium or kinetic physicochemical processes that fractionate isotopes because of small differences in physical or chemical properties of molecular species having different isotopes. It is shown that the mixing of radioactive and stable isotope end members can be modelled to provide information on many natural processes, including 14C abundances in the modern atmosphere and the stable hydrogen and oxygen isotopic compositions of the oceans during glacial and interglacial times. The calculation of mixing fractions using isotope balance equations with isotope deltas can be substantially in error when substances with high concentrations of heavy isotopes (e.g. 13C, 2H, and 18O ) are mixed. In such cases, calculations using mole fractions are preferred as they produce accurate mixing fractions. Isotope deltas are dimensionless quantities. In the International System of Units (SI), these quantities have the unit 1 and the usual list of prefixes is not applicable. To overcome traditional limitations with expressing orders of magnitude differences in isotope deltas, we propose the term urey (symbol Ur), after Harold C. Urey, for the unit 1. In such a manner, an isotope delta value expressed traditionally as−25 per mil can be written as−25 mUr (or−2.5 cUr or−0.25 dUr; the use of any SI prefix is possible). Likewise, very small isotopic differences often expressed in per meg ‘units’ are easily included (e.g. either+0.015 ‰ or+15 per meg can be written as+15 μUr.

Isotopes in Environmental and Health Studies↗
USGS2001

Rehabilitation of gypsum-mined lands in the Indian desert

The economic importance of mining in the Indian Desert is second only to agriculture. Land disturbed by mining, however, has only recently been the focus of rehabilitation efforts. This research assesses the success of rehabilitation plans used to revegetate gypsum mine spoils within the environmental constraints of the north-west Indian hot-desert ecosystem. The rehabilitation plan first examined both mined and unmined areas and established assessments of existing vegetative cover and the quality of native soils and mine spoils. Tests were made on the effect of the use, and conservation, of available water through rainwater harvesting, amendment application (for physical and chemical spoil modification), plant establishment protocols, and the selection of appropriate germ plasm. Our results show that the resulting vegetative cover is capable of perpetuating itself under natural conditions while concurrently meeting the needs of farmers. Although the mine spoils are deficient in organic matter and phosphorus, they possess adequate amounts of all other nutrients. Total boron concentrations (>5.0 mg kg-1) in both the topsail and mine spoil indicate potentially phytotoxic conditions. Electrical conductance of mine spoil is 6-10 times higher than for topsail with a near-neutral pH. Populations of spoil fungi, Azotobactor, and nitrifying bacteria are low. The soil moisture storage in rainwater harvesting plots increased by 8% over the control and 48% over the unmined area. As a result of rehabilitation efforts, mine spoils show a steady buildup in organic carbon, and P and K due to the decomposition of farmyard manure and the contribution of nitrogen fixation by the established leguminous plant species. The rehabilitation protocol used at the site appears to have been successful. Following revegetation of the area with a mixture of trees, shrubs, and grasses, native implanted species have become established. Species diversity, measured in terms of species richness, increased after one year and then gradually declined over time; the decline was the result of the loss of annual species. The study not only develops methods of gypsum mine land rehabilitation but also helps in understanding processes of rehabilitation success in arid regions and emphasizes the importance of long-term monitoring of rehabilitation success. Copyright ?? 2001 Taylor & Francis.

Arid Soil Research and Rehabilitation↗
USGS2003

Supraglacial sulfur springs and associated biological activity in the Canadian high arctic - signs of life beneath the ice

Unique springs, discharging from the surface of an arctic glacier, release H2S and deposit native sulfur, gypsum, and calcite. The presence of sulfur in three oxidation states indicates a complex series of redox reactions. Physical and chemical conditions of the spring water and surrounding environment, as well as mineralogical and isotopic signatures, suggest biologically mediated reactions. Cell counts and DNA analyses confirm bacteria are present in the spring system, and a limited number of sequenced isolates suggests that complex communities of bacteria live within the glacial system.

Astrobiology↗
USGS2020

Petrologic insights into rift zone magmatic interactions from the 2011 eruption of Kīlauea Volcano, Hawaiʻi

The high frequency of historical eruptions at Kīlauea Volcano presents an exceptional opportunity to address fundamental questions related to the transport, storage, and interaction of magmas within rift zones. The Nāpau Crater area on Kīlauea’s East Rift Zone (ERZ) experienced nine fissure eruptions within 50 years (1961–2011). Most of the magma intruded during these frequent eruptions remained stored within the rift zone, creating a potential magma mixing depot within the ERZ. The superbly monitored and sampled 2011 eruption (Puʻu ʻŌʻō episode 59) presents an extraordinary opportunity to evaluate magma mixing processes within the ERZ. Whole-rock, glass, and olivine compositions were determined, not only for lava from the 2011 eruption, but also for a new suite of Nāpau Crater area samples from the 1963, 1965, 1968, 1983, and 1997 eruptions, as well as the previously undocumented 1922 eruption. Whole-rock XRF data revealed two geochemically distinct magma batches for episode 59: one less evolved (∼6·6 wt % MgO, 0·46 wt % K2O) than the other (∼6·2 wt % MgO, 0·58 wt % K2O). Episode 59 lava is remarkably aphyric (∼0·1 vol. % phenocrysts), making use of mineralogy to identify parent magma affinities problematic. Linear compositional trends of whole-rock major and trace elements, and reversely zoned olivine crystals indicate episode 59 lavas underwent magma mixing. Least squares regression calculations and plots of major and trace element data, were used to evaluate whether the episode 59 samples are products of mixing summit-derived magma with residual magma from previous Nāpau Crater area eruptions. The regression results and trace element ratios are inconsistent with previously proposed mixing scenarios, but they do support mixing between summit-derived magma and residual magma from the 1983 and 1997 Nāpau Crater area eruptions. These magmas were stored in physically and chemically distinct pods at depths of 1·6–3·0 km prior to mixing with new magma intruded from the summit to produce the episode 59 lava. One pod contained a fractionated equivalent of 1983 lava, and the other a hybrid of compositions similar to 1983 and 1997 lavas. The petrology of episode 59 lava demonstrates that magmas from two previous eruptions (1983 and 1997) were available to mix with magma intruded from the summit region. This study clarifies the pre-eruptive history of the mixed episode 59 lava, and elucidates the evolution of the volcano's magmatic system in a region of frequent eruptions.

Hawaii↗
USGS1986

Shuttle imaging radar: Physical controls on signal penetration and subsurface scattenng in the Eastern Sahara

SIR-A signal penetration and subsurface backscatter within the upper meter or so of the sediment blanket in the Eastern Sahara of southern Egypt and northern Sudan are enhanced both by radar sensor parameters and by the physical and chemical characteristics of eolian and alluvial materials. Interpretation of SIR-A images by McCauley et al. [1], [2] dramatically changed previous concepts of the role that fluvial processes have played over the past 10000 to 30000000 years in shaping this now extremely flat, featureless, and hyperarid landscape. In the present paper we summarize the near-surface stratigraphy, the electrical properties of materials, and the types of radar interfaces found to be responsible for different classes of SIR-A tonal response. The dominant factors related to efficient microwave signal penetration into the sediment blanket include a) favorable distribution of particle sizes, b) extremely low moisture content and c) reduced geometric scattering at the SIR-A frequency (1.3 GHz). The depth of signal penetration that results in a recorded backscatter, here called "radar imaging depth," was documented in the field to be a maximum of 1.5 m, or 0.25 of the calculated "skin depth," for the sediment blanket. Radar imaging depth is estimated to be between 2 and 3 m for active sand dune materials. Diverse permittivity interfaces and volume scatterers within the shallow subsurface are responsible for most of the observed backscatter not directly attributable to grazing outcrops.

IEEE Transactions on Geoscience and Remote Sensing↗
USGS2024

Global assessment of aquatic Isoëtes species ecology

Isoëtes are iconic but understudied wetland plants, despite having suffered severe losses globally mainly because of alterations in their habitats. We therefore provide the first global ecological assessment of aquatic Isoëtes to identify their environmental requirements and to evaluate if taxonomically related species differ in their ecology. The assessment resulted in an extensive new database on aquatic Isoëtes , ecological niche analyses, and descriptive species accounts. We compiled a global database that includes all known environmental data collected from 1935 to 2023 regarding aquatic Isoëtes. We then evaluated the environmental drivers of 16 species using 2,179 global records. Additionally, we used hypervolume analysis to quantify the ecological niches of the two species with the greatest number of records, finding significant differences and evidence that Isoëtes echinospora occupies a wider ecological niche than Isoëtes lacustris . Fifty-nine species (30% of the c. 200 Isoëtes species known today) were categorised as aquatic and were mainly reported in the Americas and northern Europe. About 38% of the aquatic species are threatened with extinction or are endemic to a small region, according to the International Union for Conservation of Nature's Red List in 2023. Many species were determined to be sensitive to certain water physical and chemical factors, generally preferring oligotrophic conditions such as low total phosphorus, moderate total nitrogen, moderate to low pH, and low conductivity. This analysis includes ecological data in the assessment of rare/threatened aquatic plants globally. This new database and the ecological analyses completed defined the ecological requirements of several species and identified knowledge gaps, which can aid management actions and future research. This paper highlights ecological significance and environmental sensitivities of aquatic Isoëtes . The current level of knowledge is inadequate for a large proportion of known taxa. We affirm the extreme need to support global, collaborative initiatives on which to build future conservation strategies.

Freshwater Biology↗