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At least 325 records · Page 18Linked to original sources

USGS1974

Appraisal of operating efficiency of recharge basins on Long Island, New York, in 1969

Recharge basins on Long Island are unlined pits of various shapes and sizes excavated in surficial deposits of mainly glacial origin. Of the 2,124 recharge basins on Long Island in 1969, approximately 9 percent (194) contain water 5 or more days after a 1-inch rainfall. Basins on Long Island contain water because (1) they intersect the regional water table or a perched water table, (2) they are excavated in material of low hydraulic conductivity, (3) layers of sediment and debris of low hydraulic conductivity accumulate on the basin floor, or (4) a combination of these factors exists. Data obtained as part of this study show that (1) 22 basins contain water because they intersect the regional water table, (2) a larger percentage of the basins excavated in the Harbor Hill and the Ronkonkoma morainal deposits contain water than basins excavated in the outwash deposits, (3) a larger percentage of the basins that drain industrial and commercial areas contain water than basins that drain highways and residential areas, (4) storm runoff from commercial and industrial areas and highway: generally contains high concentrations of asphalt, grease, oil, tar, and rubber particles, whereas runoff from residential areas mainly contains leaves, grass cuttings, and other plant material, and (5) differences in composition of the soils within the drainage areas of the basins on Long Island apparently are not major factors in causing water retention. Water-containing basins dispose of an undetermined amount of storm runoff primarily by the slow infiltration of water through the bottoms and the sides of the basins. The low average specific conductance of water in most such basins suggests that evaporation does not significantly concentrate the chemical constituents and, therefore, that evaporation is not a major mechanism of water disposal from these basins.

Water Supply Paper↗

USGS1981

Eolian features produced by the December 1977 windstorm, southern San Joaquin Valley, California

High wind velocities during a windstorm in December of 1977 in the southern San Joaquin Valley, California, created eolian features and effects of a magnitude not previously reported in the literature. Three principal mechanisms of sediment movement by wind were studied by examining the size distribution of deposits in telephone poles (saltation and suspension), feeder pens and abandoned buildings (saltation and suspension), and gravel ripples (surface creep). The maximum grain sizes of rocks lodged in telephone poles at heights of 240, 160, and 80 cm are 7 mm X 11 mm X 6 mm, 10 mm X 15 mm X 6 mm, and 20 mm X 23 mm X 5 mm, respectively. In some areas with rocky soils, lag materials formed gravel ripples.

Journal of Geology↗

USGS2001

Vertical profiles of streambed hydraulic conductivity determined using slug tests in central and western Nebraska

Many issues of water-resources management rely on modeling of ground-water/surfacewater interactions, and streambed hydraulic conductivity is a key parameter controlling the water fluxes across the stream/aquifer interface. However, in central and western Nebraska, this parameter is generally undefined. The U.S. Geological Survey, in cooperation with the Nebraska Platte River Cooperative Hydrology Study Group, performed slug tests at 15 stream sites in the Platte, Republican, and Little Blue River watersheds to determine the hydraulic conductivity of streambeds in central and western Nebraska. Slug tests were completed at several discrete depth intervals using pneumatic or mechanical methods, and the water-level response was monitored on site using a pressure transducer and laptop computer. Responses were analyzed using either the Bouwer and Rice or Springer and Gelhar methods. Vertical profiles of hydraulic conductivity with depth were developed and were compared to available information on lithology. The profiles and corresponding lithology showed that different types of streambeds were tested and suggested that some streambeds display a large variability in hydraulic conductivity with depth. In some cases, hydraulic conductivity values associated with nonstreambed materials could be identified from nearby lithologic descriptions. Seven of 15 sites had streambed values that ranged over more than 3 orders of magnitude, and that variability increased significantly when the measurements considered to be from nonstreambed materials were included. Streambed profiles from the Platte and South Platte River sites generally were more homogeneous and of larger hydraulic conductivity than the other sites. No restrictive layers were detected at any of the streambed sites on the main stems or the flood plains of the main stems of their respective watersheds. Alternatively, the profiles characterized by a restrictive streambed layer at some depth below the streambed surface were all from tributary sites out of the main-stem flood plain. These profiles can be used to represent the streambed hydraulic conductivity in central and western Nebraska in various applications, including modeling ground-water/surfacewater interactions.

Nebraska↗

USGS1991

Examination of micrinite concentrates from the Cannel City coal bed of eastern Kentucky: Proposed mechanism of formation

A high volatile B, micrinite-rich bituminous coal from Morgan County, Kentucky, was crushed and screened to −100 mesh, demineralized and subjected to density gradient centrifugation (DGC). In an initial density separation, micrinite concentration was increased from 52 vol% in the demineralized coal to a maximum of 67% in the 1.25–1.26 g/ml density fraction. Micrinite enriched fractions (1.21–1.29 g/ml) were combined to yield a sample containing ∼61% micrinite. This sample was crushed to −200 mesh in an attempt to enhance micrinite liberation then reprocessed by DGC. Reprocessing resulted in a slight increase in purity to 69 vol% in the 1.25–1.28 g/ml density fraction. The original −100 mesh sample was density separated a second time with the material recovered between 1.22 and 1.30 g/ml combined, crushed, screened past 325 mesh and reprocessed by DGC. Micrinite was recovered at a purity ranging up to 73% (1.27–1.28 g/ml) from the −325 mesh sample. A density of 1.26g/ml and H/C atomic ratio of 0.79 was calculated for micrinite in one of the higher purity micrinite fractions. These values are notably different than published fusinite values and are more similar to vitrinite values measured in high volatile-B coals. The results from this study suggest that the partitioning of micrinite to a density near that of vitrinite was governed by the inherent micrinite density and not particle aggregation. Transition of the micrinite precursors through a mobile liquid phase is proposed as an explanation for the discrepancy between chemical properties and reflectance as well as to account for the observed microlithological occurrences of micrinite in this sample.

Kentucky↗

USGS2022

Compression behavior of hydrate-bearing sediments

This work experimentally explores porosity, compressibility, and the ratio of horizontal to vertical effective stress ( K 0 ) in hydrate-bearing sandy silts from Green Canyon Block 955 in the deep-water Gulf of Mexico. The samples have an in situ porosity of 0.38 to 0.40 and a hydrate saturation of more than 80%. The hydrate-bearing sediments are stiffer than the equivalent hydrate-free sediments; the K 0 stress ratio is greater for hydrate-bearing sediments relative to the equivalent hydrate-free sediments. The porosity decreases by 0.01 to 0.02 when the hydrate is dissociated at the in situ effective stress. We interpret that the hydrate in the sediment pores is a viscoelastic material that behaves like a fluid over experimental time scales, yet it cannot escape the sediment skeleton. During compression, the hydrate bears a significant fraction of the applied vertical load and transfers this load laterally, resulting in the apparent increased stiffness and a larger apparent K 0 stress ratio. When dissociation occurs, the load carried by the hydrate is transferred to the sediment skeleton, resulting in further compaction and a decrease in the lateral stress. The viewpoint that the hydrate is a trapped viscous phase provides a mechanism for how stiffness and stress ratio ( K 0 ) are greater when hydrate is present in the porous media. This study provides insight into the initial stress state of hydrate-bearing reservoirs and the geomechanical evolution of these reservoirs during production.

Louisiana↗

USGS2006

Shallow-water pockmark formation in temperate estuaries: A consideration of origins in the western gulf of Maine with special focus on Belfast Bay

A systematic mapping program incorporating more than 5000 km of side scan sonar and seismic reflection tracklines in the western Gulf of Maine has identified more than 70 biogenic natural gas deposits, occupying 311 km 2 in nearshore muddy embayments. Many of these embayments also contain pockmark fields, with some exhibiting geologically active characteristics including the observance of plumes of escaping fluids and sediment. Pockmarks, hemispherically shaped depressions of various size and depths, formed through fluid escape of gas and/or pore water, are sometimes found within or outside gas fields, although many gas fields lack pockmarks altogether. Although the origin of the natural gas remains unclear, if coastal environments at times of lower sea level were similar to the present, numerous lake, wetland, valley fill and estuarine sources of organic-rich material may have formed on the inner shelf. If these deposits survived transgression and remain buried, they are potential gas sources. Intensive mapping of the Belfast Bay pockmark field in 1998 produced the first nearly continuous side scan sonar mosaic of a Gulf of Maine pockmark field with a corresponding 3-dimensional geological model generated from seismic data. Statistical analysis of pockmark geometry, gas deposit loci, and subsurface evidence for gas-enhanced reflectors suggest that gas migration from deeper lateral sources along permeable subsurface strata may be the mechanism for pockmark formation in areas lacking gas-curtain seismic reflections. The coarse-grained transgressive ravinement unconformity between Pleistocene glacial-marine mud and Holocene mud may act as a conduit for distributing methane to the field's margins. ?? 2005 Elsevier B.V. All rights reserved.

Marine Geology↗

USGS1997

Sr-isotopic evidence for leakage of pore water from clay-silt confining units to the Atlantic City 800-foot sand, Atlantic City, New Jersey

The evolution of water quality in confined aquifers in the New Jersey Coastal Plain may be affected by leakage of pore water from the adjacent confining units. We investigated the distribution and sources of solutes, particularly Sr, in pore water mechanically extracted from clay-silt core samples collected from depths of 552–840 ft (168–256 m) in the lower Miocene Kirkwood Formation at Atlantic City, New Jersey (Ocean Drilling Program Leg 150X). The sampled sediments consist of thin clay-silt stringers in the upper part of the Atlantic City 800-ft sand, a major aquifer, and the massive clay-silt units above and below it. The distribution of Sr and the ratio of 87 Sr to 86 Sr in the pore water and adjacent shell material were used to identify the possible sources of, and physical processes that may affect the distribution of, Sr in the pore water. Concentrations of Sr in 14 pore-water samples from the clay-silt unit above the aquifer and the clay-silt interbeds in the upper part of the aquifer ranged from 2.74 to 28.19 µM/L; those in the four pore-water samples from the clay-silt unit below the aquifer ranged from 0.52 to 7.30 µM/L. Concentrations of Sr in the samples varied with depth but correlated strongly with pore-water concentrations of Ca, Mg, Na, and SO4. Cation-exchange processes may be responsible, in part, for the lower concentrations of Sr, Ca, and Mg in pore water from the clay-silt unit below the aquifer than in that above the aquifer. 87 Sr/ 86 Sr values in 11 samples of aragonitic mollusk shells (bearing no visible evidence of recrystallization) collected from depths in the clay-silt unit similar to those from which the pore-water samples were collected ranged from 0.708468 to 0.708713 , and decreased (Sr in the shells was less radiogenic) with depth. This trend is consistent with the decrease in the 87 Sr/ 86 Sr value in seawater through time during the early Miocene. The 87 Sr/ 86 Sr values in 12 pore-water samples from the studied stratigraphic interval ranged from 0.708257 to 0.708527 and also decreased with depth. The Sr-isotope ratios in the pore water were lower than those in the shell material from nearby or adjacent sediments for all samples but one. Because the only known source of Sr with an isotope ratio this low is shell material from sediments deeper than the strata from which the pore-water samples were collected (including pre-Miocene stratigraphic units), the isotope ratio in the pore-water samples from the lower Miocene claysilt units may result from upward movement of pore water into lower Miocene strata through geologic time, which could create the observed difference in Sr isotope ratios between the pore water and shells.

New Jersey↗

USGS1992

Growth of grain contacts in halite by solution-transfer: Implications for diagenesis, lithification, and strength recovery

Lithification of a sediment to form a rock may involve cementation, diagenetic reactions, or compaction under load. In these experiments, convex halite lenses were pressed against fiat halite plates at 50° C in a specially designed microscope stage. A saturated brine surrounded the samples, which were observed during the experiment in transmitted and reflected light. No time-dependent convergence was observed between the two crystals, even at mean normal stresses of up to 14 M Pa at the contact. In all experiments, however, the contact (or neck) between the two crystals grew with time as material dissolved from the surrounding lens surfaces, diffused through the pore fluid, and precipitated at the neck. Neck growth rates did not appear to correlate with the applied load, but did systematically increase as the misorientation between the two crystals decreased. Our analysis of the shapes of fluid inclusions formed along the grain boundary within the neck suggests that the grain boundary energy is about 1.8 times greater than the fluid-solid interfacial energy. Neck growth appears to be driven by the reduction of interfacial energy rather than by mechanical loads. Assuming that the interfacial energy is isotropic, and incorporating some geometric simplifications, two models of neck growth were formulated. The rate-controlling steps in the models were either precipitation or diffusion in the pore fluid. The data fit either model equally well. Both models predict that neck growth rate will be rapid at first but will decrease with time, as was observed. Neck growth will lead to an increase in real area of contact between grains in a granular aggregate even without the introduction of supersaturated solutions and may be important in the induration of sediments and the strengthening of fault gouge.

International Geophysics↗

USGS1990

Enzyme leaching of surficial geochemical samples for detecting hydromorphic trace-element anomalies associated with precious-metal mineralized bedrock buried beneath glacial overburden in northern Minnesota

One objective of the International Falls and Roseau, Minnesota, CUSMAP projects was to develop a means of conducting regional-scale geochemical surveys in areas where bedrock is buried beneath complex glacially derived overburden. Partial analysis of B-horizon soils offered hope for detecting subtle hydromorphic trace-element dispersion patterns. An enzyme-based partial leach selectively removes metals from oxide coatings on the surfaces of soil materials without attacking their matrix. Most trace-element concentrations in the resulting solutions are in the part-per-trillion to low part-per-billion range, necessitating determinations by inductively coupled plasma/mass spectrometry. The resulting data show greater contrasts for many trace elements than with other techniques tested. Spatially, many trace metal anomalies are locally discontinuous, but anomalous trends within larger areas are apparent. In many instances, the source for an anomaly seems to be either basal till or bedrock. Ground water flow is probably the most important mechanism for transporting metals toward the surface, although ionic diffusion, electrochemical gradients, and capillary action may play a role in anomaly dispersal. Sample sites near the Rainy Lake-Seine River fault zone, a regional shear zone, often have anomalous concentrations of a variety of metals, commonly including Zn and/or one or more metals which substitute for Zn in sphalerite (Cd, Ge, Ga, and Sn). Shifts in background concentrations of Bi, Sb, and As show a trend across the area indicating a possible regional zoning of lode-Au mineralization. Soil anomalies of Ag, Co, and Tl parallel basement structures, suggesting areas that may have potential for Cobalt/Thunder Baytype silver viens. An area around Baudette, Minnesota, which is underlain by quartz-chlorite-carbonate-altered shear zones, is anomalous in Ag, As, Bi, Co, Mo, Te, Tl, and W. Anomalies of Ag, As, Bi, Te, and W tend to follow the fault zones, suggesting potential for lode-Au deposits. Soil anomalies of Co, Mo, and Tl appear to follow northwest-striking structures that cross the shear zones, suggesting that Thunder Bay-type mineralization may have overprinted earlier mineralization along the shear zones.

Conference Paper↗

USGS1997

Effect of faulting on ground-water movement in the Death Valley Region, Nevada and California

This study characterizes the hydrogeologic system of the Death Valley region, an area covering approximately 100,000 square kilometers. The study also characterizes the effects of faults on ground-water movement in the Death Valley region by synthesizing crustal stress, fracture mechanics, and structural geologic data. The geologic conditions are typical of the Basin and Range Province; a variety of sedimentary and igneous intrusive and extrusive rocks have been subjected to both compressional and extensional deformation. Faulting and associated fracturing is pervasive and greatly affects ground-water flow patterns. Faults may become preferred conduits or barriers to flow depending on whether they are in relative tension, compression, or shear and other factors such as the degree of dislocations of geologic units caused by faulting, the rock types involved, the fault zone materials, and the depth below the surface. The current crustal stress field was combined with fault orientations to predict potential effects of faults on the regional groundwater flow regime. Numerous examples of faultcontrolled ground-water flow exist within the study area. Hydrologic data provided an independent method for checking some of the assumptions concerning preferential flow paths.

California, Nevada↗

USGS1970

Estimates of the mechanical properties of lunar surface using tracks and secondary impact craters produced by blocks and boulders

Estimates of bearing capacities of lunar surfaces using tracks and secondary impact craters produced by blocks and boulders shown in photographs taken by Lunar Orbiters II and III are the same order of magnitude as those reported by the Surveyor project, but they are generally less. Static analyses of 48 lunar blocks and boulders and their tracks yield friction angles between 10° and 30° and averaging about 17°. These values were computed using: (1) Terzaghi's bearing capacity equations for circular footings, (2) Meyerhof's dimensionless numbers for general shear on level surfaces, (3) a cohesion of 10 3 dynes per cm 2 , (4) a density of 1.35 gm per cm 3 for the near surface materials, (5) a density of 2.7 gm per cm 3 for the block or boulder, (6) spheroidal (triaxial) boulders unless definite shapes can be established, (7) footing radii equal to the half-width of the block or boulder, the half-width of the track, and(or) the half-width of the shadow near the base of the block or boulder. For 115 secondary impact craters and their corresponding blocks, dynamic strengths are estimated using: (1) the product of one-half the mass per unit area of the block and the normal component of velocity squared divided by the crater depth, and (2) the ratio of the kinetic energy of the block and the volume of the secondary crater. Velocities of the blocks are calculated using a ballistics equation and assuming an ejection angle of 45°. Block densities are taken as 2.7 gm per cm 3 . Dynamic strengths of the near surface materials using the first procedure average 25.2 x 10 5 dynes per cm 2 (37 psi); and, for the second procedure, they average 19.2 x 10 5 dynes per cm 2 (28 psi). Comparison between dynamic strengths and expected static strengths, computed for each block using the assumptions above, show that most of the dynamic strengths correspond to the static strengths when the friction angle is 30° and larger. Data on experimental low velocity impacts with natural targets are compared with the lunar data on secondary impacts. Nara's modified Poncelet equation for sand yields an average angle of internal friction near 34° using the appropriate block and soil constants mentioned above. Comparison of coefficients computed using the equations for sand of Clark and McCarty, Mortensen, and Moore for the lunar data with the corresponding constants for terrestrial data indicate the lunar coefficients are generally low. These low values can be brought into better agreement with terrestrial data on sand by increasing the assumed ejection angles to 60° or 70° and considering the effect of the low acceleration of gravity at the lunar surface.

Open-File Report↗

USGS1998

Dispersal of mimetic seeds of three species of Ormosia (Leguminosae)

Seeds with ‘imitation arils’ appear wholly or partially covered by pulp or aril but actually carry no fleshy material. The mimetic seed hypothesis to explain this phenomenon proposes a parasitic relationship in which birds are deceived into dispersing seeds that resemble bird-dispersed fruits, without receiving a nutrient reward. The hard-seed for grit hypothesis proposes a mutualistic relationship in which large, terrestrial birds swallow the exceptionally hard mimetic seeds as grit for grinding the softer seeds on which they feed. They defecate, dispersing the seeds, and abrade the seed surface, enhancing germination. Any fruit mimicry is incidental. Fruiting trees of Ormosia spp. (Leguminosae: Papilionoideae) were observed to ascertain mechanisms of seed dispersal and the role of seemingly mimetic characteristics of the seeds in that dispersal. Seed predation and seed germination were also examined. Ormosia isthamensis and O. macrocalyx (but not O. bopiensis ) deceived arboreally-foraging frugivorous birds into taking their mimetic seeds, although rates of seed dispersal were low. These results are consistent with the mimetic seed hypothesis. On the other hand, the rates of disappearance of seeds from the ground under the Ormosia trees, hardness of the seeds, and enhancement of germination with the abrasion of the seed coat are all consistent with the hard-seed for grit hypothesis.

Journal of Tropical Ecology↗

USGS1996

Granular-flow rheology: Role of shear-rate number in transition regime

This paper examines the rationale behind the semiempirical formulation of a generalized viscoplastic fluid (GVF) model in the light of the Reiner-Rivlin constitutive theory and the viscoplastic theory, thereby identifying the parameters that control the rheology of granular flow. The shear-rate number ( N ) proves to be among the most significant parameters identified from the GVF model. As N → 0 and N →∞, the GVF model can reduce asymptotically to the theoretical stress versus shear-rate relations in the macroviscous and grain-inertia regimes, respectively, where the grain concentration ( C ) also plays a major role in the rheology of granular flow. Using available data obtained from the rotating-cylinder experiments of neutrally buoyant solid spheres dispersing in an interstitial fluid, the shear stress for granular flow in transition between the two regimes proves dependent on N and C in addition to some material constants, such as the coefficient of restitution. The insufficiency of data on rotating-cylinder experiments cannot presently allow the GVF model to predict how a granular flow may behave in the entire range of N ; however, the analyzed data provide an insight on the interrelation among the relevant dimensionless parameters.

Journal of Engineering Mechanics↗

USGS2004

Macroscopic and microscopic observations of particle-facilitated mercury transport from New Idria and Sulphur Bank mercury mine tailings

Mercury (Hg) release from inoperative Hg mines in the California Coast Range has been documented, but little is known about the release and transport mechanisms. In this study, tailings from Hg mines located in different geologic settings-New Idria (NI), a Si-carbonate Hg deposit, and Sulphur Bank (SB), a hot-spring Hg deposit-were characterized, and particle release from these wastes was studied in column experiments to (1) investigate the mechanisms of Hg release from NI and SB mine wastes, (2) determine the speciation of particle-bound Hg released from the mine wastes, and (3) determine the effect of calcinations on Hg release processes. The physical and chemical properties of tailings and the colloids released from them were determined using chemical analyses, selective chemical extractions, XRD, SEM, TEM, and X-ray absorption spectroscopy techniques. The total Hg concentration in tailings increased with decreasing particle size in NI and SB calcines (roasted ore), but reached a maximum at an intermediate particle size in the SB waste rock (unroasted ore). Hg in the tailings exists predominantly as low-solubility HgS (cinnabar and metacinnabar), with NI calcines having >50% HgS, SB calcines having >89% HgS, and SB waste rock having ???100% HgS. Leaching experiments with a high-ionic-strength solution (0.1 M NaCl) resulted in a rapid but brief release of soluble and particulate Hg. Lowering the ionic strength of the leach solution (0.005 M NaCl) resulted in the release of colloidal Hg from two of the three mine wastes studied (NI calcines and SB waste rock). Colloid-associated Hg accounts for as much as 95% of the Hg released during episodic particle release. Colloids generated from the NI calcines are produced by a breakup and release mechanism and consist of hematite, jarosite/alunite, and Al-Si gel with particle sizes of 10-200 nm. ATEM and XAFS analyses indicate that the majority (???78%) of the mercury is present in the form of HgS. SB calcines also produced HgS colloids. The colloids generated from the SB waste rock were heterogeneous and varied in composition according to the column influent composition. ATEM and XAFS results indicate that Hg is entirely in the HgS form. Data from this study identify colloidal HgS as the dominant transported form of Hg from these mine waste materials.

Environmental Science & Technology↗

USGS2010

Hydrogeomorphic segments and hydraulic microhabitats of the Niobrara River, Nebraska— With special emphasis on the Niobrara National Scenic River

The Niobrara River is an ecologically and economically important resource in Nebraska. The Nebraska Department of Natural Resources’ recent designation of the hydraulically connected surface- and groundwater resources of the Niobrara River Basin as “fully appropriated” has emphasized the importance of understanding linkages between the physical and ecological dynamics of the Niobrara River so it can be sustainably managed. In cooperation with the Nebraska Game and Parks Commission, the U.S. Geological Survey investigated the hydrogeomorphic and hydraulic attributes of the Niobrara River in northern Nebraska. This report presents the results of an analysis of hydrogeomorphic segments and hydraulic microhabitats of the Niobrara River and its valley for the approximately 330-mile reach from Dunlap Diversion Dam to its confluence with the Missouri River. Two spatial scales were used to examine and quantify the hydrogeomorphic segments and hydraulic microhabitats of the Niobrara River: a basin scale and a reach scale. At the basin scale, digital spatial data and hydrologic data were analyzed to (1) test for differences between 36 previously determined longitudinal hydrogeomorphic segments; (2) quantitatively describe the hydrogeomorphic characteristics of the river and its valley; and (3) evaluate differences in hydraulic microhabitat over a range of flow regimes among three fluvial geomorphic provinces. The statistical analysis of hydrogeomorphic segments resulted in reclassification rates of 3 to 28 percent of the segments for the four descriptive geomorphic elements. The reassignment of classes by discriminant analysis resulted in a reduction from 36 to 25 total hydrogeomorphic segments because several adjoining segments shared the same ultimate class assignments. Virtually all of the segment mergers were in the Canyons and Restricted Bottoms (CRB) fluvial geomorphic province. The most frequent classes among hydrogeomorphic segments, and the dominant classes per unit length of river, are: a width-restricted valley confinement condition, sinuous-planview pattern, irregular channel width, and an alternate bar configuration. The Niobrara River in the study area flows through a diversity of fluvial geomorphic settings in its traverse across northern Nebraska. In the Meandering Bottoms (MB) fluvial geomorphic province, river discharge magnitudes are low, and the valley exerts little control on the channel-planview pattern. Within the CRB province, the river flows over a diversity of geologic formations, and the valley and river narrow and expand in approximate synchronicity. In the Braided Bottoms (BB) fluvial geomorphic province, the river primarily flows over Cretaceous Pierre Shale, the valley and channel are persistently wide, and the channel slope is generally uniform. The existence of vegetated islands and consequent multithread channel environments, indicated by a higher braided index, mostly coincided with reaches having gentler slopes and less unit stream power. Longitudinal hydrology curves indicate that the flow of the Niobrara River likely is dominated by groundwater as far downstream as Norden. Unit stream power values in the study area vary between 0 and almost 2 pounds per foot per second. Within the MB province, unit stream power steadily increases as the Niobrara gains discharge from groundwater inflow, and the channel slope steepens. The combination of steep slopes, a constrained channel width, and persistent flow within the CRB province results in unit stream power values that are between three and five times greater than those in less confined segments with comparable or greater discharges. With the exception of hydrogeomorphic segment 3, which is affected by Spencer Dam, unit stream power values in the BB province are generally uniform. Channel sinuosity values in the study area varied generally between 1 and 2.5, but with locally higher values measured in the MB province and at the entrenched bedrock meanders of hydrogeomorphic segment 18 in the CRB province. The differences in channel morphology and hydraulic geometries between fluvial geomorphic provinces are evident in the types, relative abundance, and response of hydraulic microhabitats to changing discharges. The four gaging stations chosen for hydraulic microhabitat analysis are distributed among three different fluvial geomorphic provinces. In the MB province, the smaller channel and lower discharges resulted in the dominance of shallow and intermediate-depth hydraulic environments with the vast majority of hydraulic microhabitat restricted to shallow categories even during upper-decile discharges. In the CRB province, intermediate depth hydraulic conditions, particularly intermediate-swift, dominate over all ranges of discharge. Hydraulic microhabitat conditions were most diverse in the BB province, with most hydraulic microhabitat categories present over the entire range of discharges analyzed. The calculated differences in hydraulic microhabitat distributions, abundance, and adjustments between streamflow-gaging stations were the result of differences in physical structure of the channel and subsequent channel hydraulic geometry. At the reach scale, field measurements made in water years 2008 and 2009 in four study reaches within the Scenic Reach were used to (1) characterize the elevation and geomorphic processes associated with fluvial landforms, (2) build hydraulic geometry relations, (3) examine flow hydraulics over a range of discharges, and (4) examine the types and responses of hydraulic microhabitats to a range of flow magnitudes. Four landform groups were identified and named in order of increasing elevation: low flood plains, intermediate flood plains, low terraces, and high terraces. The terraces were poorly characterized because the surveys did not extend across the full width of the alluvial valley bottom. The two lowest fluvial landforms are likely active in the modern hydroclimatic regime. Sediment samples obtained in the study reaches indicate that the primary bed material in the active channel ranged in size from coarse silt to coarse sand. Grain-size distributions from samples also indicate that the bed of the Niobrara River among the study reaches coarsens and has increasing grainsize variability in the downstream direction. Values of at-a-station hydraulic geometry exponents indicate that the Niobrara River in the study reaches adjusts its geometry to changing discharges primarily through increases in flow depth and velocity. Relations at one cross section indicated that, at least locally, changes in width were also an important channel adjustment mechanism. Hydraulic behavior over the range of flows measured was not consistent among all study reaches, but two general modes of hydraulic behavior were observed in the reaches with substantial coverage of the bed by fine sediment. At the Sunny Brook and Muleshoe study reaches, average boundary-shear stress remained approximately constant, and hydraulic resistance decreased, for discharges below 900 cubic feet per second (ft 3 /s). Above 900 ft 3 /s, average boundary shear stress and hydraulic resistance both increased. The Rock Barn study reach did not exhibit the same two-mode hydraulic behavior observed at the Sunny Brook and Muleshoe reaches. The coincident increase in boundary shear stress above 900 ft 3 /s observed at the Sunny Brook and Muleshoe study reaches represents a potential hydraulic threshold above which bedload transport rates were likely to increase markedly. No consistent bed-adjustment pattern (scour or fill) was identified in the study reaches over the range of flows or over the measurement season. Analysis of hydraulic microhabitats over the range of discharges measured at the study reaches indicates that some percentage of most habitat niche categories was available for at least one discharge condition, but the majority of hydraulic habitat available was within the intermediate-swift and deepswift habitat niche categories. Deep-swift conditions dominated nearly all study reaches under all measured discharge conditions. Slight differences in habitat distributions were observed between the study reaches with substantial coverage of the bed by fine sediment—Sunny Brook, Muleshoe, and Rock Barn—and the bedrock-dominated reach, Crooked Creek. Although the four study reaches occupy three different hydrogeomorphic segments, the types, relative abundance, and response of hydraulic microhabitat niche distributions to changing discharge conditions generally were similar among all reaches.

Nebraska↗

USGS1996

Mechanism of molybdenum removal from the sea and its concentration in black shales: EXAFS evidence

Molybdenum K-edge EXAFS (extended X-ray absorption fine structure) spectra yield new structural information about the chemical environment of Mo in high-Mo black shales and sediments. Two spectral types are found. The less common one, associated with Mo ores developed in shale in China, is that of a MoS2 phase, possibly X-ray amorphous jordisite. The other, associated with Cretaceous deep sea sediments and with other black shales, is characterized by short Mo-O distances (1.69-1.71 A??), by Mo-S distances of 2.30-2.38 A??, and in some cases by second shell Mo and Fe interactions, which suggests that some Mo resides in transition metal-rich phases. EXAFS spectra of synthetic amorphous materials, prepared by scavenging Mo from HS solutions with Fe(II), FeOOH, and humic acid, suggest that the second spectral type arises from Mo present chiefly in two forms. One is a compact, Mo-Fe-S "cubane" type compound with Mo-S distances of ???2.36 A?? and Mo-Fe distances of ???2.66 A??, while the other is probably an organic form containing some Mo-O double bonds (???1.69 A??). Laboratory products, that were prepared by scavenging dissolved Mo from sulfidic solutions with humic acid, yield spectra quite similar to the second spectral type observed in shales and sediments, including unexpected indications of Mo-Fe interactions. Molybdenum L-edge spectra indicate that the mean oxidation state in the sediments and shales lies between IV and VI. This work demonstrates the merit of EXAFS for obtaining structural information on natural materials containing X-ray amorphous components which defeat conventional mineralogical characterization. The implications of these findings regarding Mo scavenging from sulfidic natural waters are considered. We introduce the concept of a geochemical switch, in which HS- transforms the marine behavior of Mo from that of a conservative element to that of a particle reactive element. The action point of the HS- switch is calculated to be, aHS- = 10-3.6 - 10-4.3. When aHS- approaches the action point, Mo becomes reactive to particles containing transition metals (e.g., Fe). We conjecture that thiols, including humic-bound thiol groups, also switch Mo behavior. In contrast to previous ideas, our model for Mo scavenging deemphasizes the role of reduction from Mo(VI) to Mo(V) as the initial step in scavenging; instead, we emphasize the ease with which Mo forms covalent bonds to transition metals and organic molecules via S bridges.

Geochimica et Cosmochimica Acta↗

USGS2018

Plant and microbial biomarkers suggest mechanisms of soil organic carbon accumulation in a Mojave Desert ecosystem under elevated CO2

We investigated how properties of soil organic matter (SOM) were altered after 10 years exposure to elevated atmospheric CO 2 concentration ([CO 2 ]) in a Mojave Desert ecosystem, using plant and microbial biomarkers. We focused on roles of Larrea tridentata , the dominant evergreen shrub which form islands of fertility, and biological soil crusts which have extensive cover in plant interspace. Soils to 5 cm in depth were collected under L. tridentata and plant interspace, and biological soil crusts to 0.5 cm in depth under three cover types, Pleuraphis rigida , a C 4 grass, shrubs and plant interspace. Soil organic carboncontents were not significantly different between elevated and ambient [CO 2 ]. However, significantly higher abundance of n -alkanes, a major constituent of foliage wax material, occurred in the elevated compared to ambient [CO 2 ] plots in the soils collected under L. tridentata , but no such difference was found in the soils at plant interspace or the biological soil crusts. There was no significant difference in abundance of microbial phospholipid fatty acids between the CO 2 treatments in the soils of either cover types. However, neutral lipid fatty acid abundance was significantly higher under elevated than ambient [CO 2 ] in the soils under L. tridentata , whereas no such significant difference was observed at plant interspace. These results emphasize important roles of the dominant shrubs in SOM formation under elevated [CO 2 ] in arid ecosystems. Elevated [CO 2 ] stimulated growth of L. tridentata in wet years, and aboveground litter deposition via senescence contributed to SOM formation in islands of fertility. In addition, elevated [CO 2 ] stimulated soil microbial turnover rates in rhizosphere of L. tridentata , which left more soil microbial necromass, a major SOM source. We concluded that responses of dominant shrubs to elevated [CO 2 ] can stimulate SOM formation in arid ecosystems, but biological soil crusts may have limited capacity.

Soil Biology and Biochemistry↗

USGS2014

Densovirus associated with sea-star wasting disease and mass mortality

Populations of at least 20 asteroid species on the Northeast Pacific Coast have recently experienced an extensive outbreak of sea-star (asteroid) wasting disease (SSWD). The disease leads to behavioral changes, lesions, loss of turgor, limb autotomy, and death characterized by rapid degradation (“melting”). Here, we present evidence from experimental challenge studies and field observations that link the mass mortalities to a densovirus (Parvoviridae). Virus-sized material (i.e., <0.2 μm) from symptomatic tissues that was inoculated into asymptomatic asteroids consistently resulted in SSWD signs whereas animals receiving heat-killed (i.e., control) virus-sized inoculum remained asymptomatic. Viral metagenomic investigations revealed the sea star-associated densovirus (SSaDV) as the most likely candidate virus associated with tissues from symptomatic asteroids. Quantification of SSaDV during transmission trials indicated that progression of SSWD paralleled increased SSaDV load. In field surveys, SSaDV loads were more abundant in symptomatic than in asymptomatic asteroids. SSaDV could be detected in plankton, sediments and in nonasteroid echinoderms, providing a possible mechanism for viral spread. SSaDV was detected in museum specimens of asteroids from 1942, suggesting that it has been present on the North American Pacific Coast for at least 72 y. SSaDV is therefore the most promising candidate disease agent responsible for asteroid mass mortality.

Proceedings of the National Academy of Sciences of↗