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At least 649 records · Page 36Linked to original sources
USGS2026

Widespread occurrence of Magnéli phases in wildland-urban interface fire ashes

The increasing activity of wildland–urban interface (WUI) fires has raised concerns regarding the potential environmental and human health impacts of residual ash remaining after burning. In this study, we investigated the concentration and speciation of titanium in WUI fire ash. Total titanium concentrations in WUI fire ash ranged from 0.53 to 80 g kg –1 . Synchrotron-based macro- and microscale X-ray absorption near-edge structure (XANES and μXANES, respectively) spectroscopy were used to quantify the relative abundance of major Ti phases in the fire ash, and the results were corroborated by high resolution-transmission electron microscopy (HR-TEM) measurements. Rutile (α-TiO 2 ), anatase (β-TiO 2 ), ilmenite (FeTiO 3 ), and titanium(III) oxide (Ti 2 O 3 ) were detected in all 20 ashes investigated by XANES and accounted for 0.26–0.83, 0.19–0.83, 0.33, and 0.17–0.72 of the spectral weight, respectively. Deeper analysis by μXANES of one sample demonstrated that Ti-bearing particles occurred as a mixture of rutile (α-TiO 2 ), anatase (β-TiO 2 ), ilmenite (FeTiO 3 ), and titanium(III) oxide Ti 2 O 3, with the absence of a pure Ti 2 O 3 phase. The presence of Ti 2 O 3 in the WUI fire ash is ascribed to the reduction of rutile and anatase to Magnéli titania (Ti n O 2 n– 1 , n = 4–9), which is estimated to be the dominant phase of titanium in the 20 WUI fire ashes investigated by XANES. The occurrence of Magnéli titania was corroborated by HR-TEM. Our findings demonstrate the impact of WUI fires on titanium speciation; fires convert titanium dioxides (e.g., rutile and anatase) to reduced titanium phases (e.g., Magnéli titania). Based on HR-TEM analyses, most of the titanium-bearing particles were less than 500 nm in size. Magnéli particles have been shown to be more toxic than rutile and anatase and have been linked to reduced lung function. Therefore, this study provides critical insights into the pollution characteristics and potential health risks of WUI fire ashes and associated particles, which are currently poorly understood.

California↗
USGS2018

Effect of calcium on the bioavailability of dissolved uranium(VI) in plant roots under circumneutral pH

We integrated field measurements, hydroponic experiments, microscopy, and spectroscopy to investigate the effect of Ca(II) on dissolved U(VI) uptake by plants in 1 mM HCO 3 – solutions at circumneutral pH. The accumulation of U in plants (3.1–21.3 mg kg –1 ) from the stream bank of the Rio Paguate, Jackpile Mine, New Mexico served as a motivation for this study. Brassica juncea was the model plant used for the laboratory experiments conducted over a range of U (30–700 μg L –1 ) and Ca (0–240 mg L –1 ) concentrations. The initial U uptake followed pseudo-second-order kinetics. The initial U uptake rate ( V 0 ) ranged from 4.4 to 62 μg g –1 h –1 in experiments with no added Ca and from 0.73 to 2.07 μg g –1 h –1 in experiments with 12 mg L –1 Ca. No measurable U uptake over time was detected for experiments with 240 mg L –1 Ca. Ternary Ca–U–CO 3 complexes may affect the decrease in U bioavailability observed in this study. Elemental X-ray mapping using scanning transmission electron microscopy–energy-dispersive spectrometry detected U–P-bearing precipitates within root cell walls in water free of Ca. These results suggest that root interactions with Ca and carbonate in solution affect the bioavailability of U in plants. This study contributes relevant information to applications related to U transport and remediation of contaminated sites.

Environmental Science & Technology↗
USGS2013

A USANS/SANS study of the accessibility of pores in the Barnett Shale to methane and water

Shale is an increasingly important source of natural gas in the United States. The gas is held in fine pores that need to be accessed by horizontal drilling and hydrofracturing techniques. Understanding the nature of the pores may provide clues to making gas extraction more efficient. We have investigated two Mississippian Barnett Shale samples, combining small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) to determine the pore size distribution of the shale over the size range 10 nm to 10 μm. By adding deuterated methane (CD 4 ) and, separately, deuterated water (D 2 O) to the shale, we have identified the fraction of pores that are accessible to these compounds over this size range. The total pore size distribution is essentially identical for the two samples. At pore sizes >250 nm, >85% of the pores in both samples are accessible to both CD 4 and D 2 O. However, differences in accessibility to CD 4 are observed in the smaller pore sizes (~25 nm). In one sample, CD 4 penetrated the smallest pores as effectively as it did the larger ones. In the other sample, less than 70% of the smallest pores (<25 nm) were accessible to CD 4 , but they were still largely penetrable by water, suggesting that small-scale heterogeneities in methane accessibility occur in the shale samples even though the total porosity does not differ. An additional study investigating the dependence of scattered intensity with pressure of CD 4 allows for an accurate estimation of the pressure at which the scattered intensity is at a minimum. This study provides information about the composition of the material immediately surrounding the pores. Most of the accessible (open) pores in the 25 nm size range can be associated with either mineral matter or high reflectance organic material. However, a complementary scanning electron microscopy investigation shows that most of the pores in these shale samples are contained in the organic components. The neutron scattering results indicate that the pores are not equally proportioned in the different constituents within the shale. There is some indication from the SANS results that the composition of the pore-containing material varies with pore size; the pore size distribution associated with mineral matter is different from that associated with organic phases.

Texas↗
USGS2002

Oxidation of dimethylselenide by δMnO 2 : oxidation product and factors affecting oxidation rate

Volatile dimethylselenide (DMSe) was transformed to a nonvolatile Se compound in a ??-MnO2 suspension. The nonvolatile product was a single compound identified as dimethylselenoxide based on its mass spectra pattern. After 24 h, 100% of the DMSe added to a ??-MnO2 suspension was converted to nonpurgable Se as opposed to 20%, 18%, and 4% conversion for chromate, permanganate, and the filtrate from the suspension, respectively. Manganese was found in solution after reaction. These results imply that the reaction between manganese oxide and DMSe was a heterogeneous redox reaction involving solid phase ??-MnO2 and solution phase DMSe. Oxidation of DMSe to dimethylselenoxide [OSe(CH3)2] by a ??-MnO2 suspension appears to be first order with respect to ??-MnO2, to DMSe, and to hydrogen ion with an overall rate law of d[OSe(CH3)2 ]/dt = 95 M-2 min-1 [MnO2]1[DMSe]1[H+]1 for the MnO2 concentration range of 0.89 ?? 10-3 - 2.46 ?? 10-3 M, the DMSe concentration range of 3.9 ?? 10-7 - 15.5 ?? 10-7 M Se, and a hydrogen ion concentation range of 7.4 ?? 10-6 -9.5 ?? 10-8 M. A general surface site adsorption model is consistent with this rate equation if the uncharged |OMnOH is the surface adsorption site. DMSe acts as a Lewis base, and the manganese oxide surface acts as a Lewis acid. DMSe adsorption to |OMnOH can be viewed as a Lewis acid/ base complex between the largely p orbitals of the DMSe lone pair and the unoccupied eg orbitals on manganese oxide. For such a complex, frontier molecular orbital theory predicts electron transfer to occur via an inner-sphere complex between the DMSe and the manganese oxide. ?? 1995 American Chemical Society.

Environmental Science & Technology↗
USGS2002

Reductive dehalogenation of hexachloroethane, carbon tetrachloride, and bromoform by anthrahydroquinone disulfonate and humic acid

The reductive dehalogenation of hexachloroethane (C2Cl6), carbon tetrachloride (CCl4), and bromoform (CHBr3) was examined at 50??C in aqueous solutions containing either (1) 500 ??M of 2,6-anthrahydroquinone disulfonate (AHQDS), (2) 250 ??M Fe2+, or (3) 250 ??M HS-. The pH ranged from 4.5 to 11.5 for AHQDS solutions and was 7.2 in the Fe2+ solutions and 7.8 in the HS- solutions. The observed disappearance of C2Cl6 in the presence of AHQDS was pseudo-first-order and fit k??ccl4 = k0[A(OH)2] + k1[A(OH)O-] + k2[A(O)22-] where A(OH)2, A(OH)O-, and A(O)22- represent the concentrations of the three forms of the AHQDS in solution. The values of k0, k1, and k2 were ???0,0.031, and 0.24 M-1 s-1, respectively. The addition of 25 mg of C/L of humic acid or organic matter extracted from Borden aquifer solids to aqueous solutions containing 250 ??M HS- or Fe2+ increased the reduction rate by factors of up to 10. The logarithms of the rate constants for the disappearance of C2Cl6 and CCl4 in seven different experimental systems were significantly correlated; log k???ccl4 = 0-64 log k??? c2cl6 - 0.83 with r2 = 0.80. The observed trend in reaction rates of C2Cl6 > CCl4 > CHBr3 is consistent with a decreasing trend in one-electron reduction potentials. ?? 1994 American Chemical Society.

Environmental Science & Technology↗
USGS2002

In-situ evidence for uranium immobilization and remobilization

The in-situ microbial reduction and immobilization of uranium was assessed as a means of preventing the migration of this element in the terrestrial subsurface. Uranium immobilization (putatively identified as reduction) and microbial respiratory activities were evaluated in the presence of exogenous electron donors and acceptors with field push−pull tests using wells installed in an anoxic aquifer contaminated with landfill leachate. Uranium(VI) amended at 1.5 μM was reduced to less than 1 nM in groundwater in less than 8 d during all field experiments. Amendments of 0.5 mM sulfate or 5 mM nitrate slowed U(VI) immobilization and allowed for the recovery of 10% and 54% of the injected element, respectively, as compared to 4% in the unamended treatment. Laboratory incubations confirmed the field tests and showed that the majority of the U(VI) immobilized was due to microbial reduction. In these tests, nitrate treatment (7.5 mM) inhibited U(VI) reduction, and nitrite was transiently produced. Further push−pull tests were performed in which either 1 or 5 mM nitrate was added with 1.0 μM U(VI) to sediments that already contained immobilized uranium. After an initial loss of the amendments, the concentration of soluble U(VI) increased and eventually exceeded the injected concentration, indicating that previously immobilized uranium was remobilized as nitrate was reduced. Laboratory experiments using heat-inactivated sediment slurries suggested that the intermediates of dissimilatory nitrate reduction (denitrification or dissimilatory nitrate reduction to ammonia), nitrite, nitrous oxide, and nitric oxide were all capable of oxidizing and mobilizing U(IV). These findings indicate that in-situ subsurface U(VI) immobilization can be expected to take place under anaerobic conditions, but the permanence of the approach can be impaired by disimilatory nitrate reduction intermediates that can mobilize previously reduced uranium.

Environmental Science & Technology↗
USGS2002

Evaluating behavior of oxygen, nitrate, and sulfate during recharge and quantifying reduction rates in a contaminated aquifer

This study evaluates the biogeochemical changes that occur when recharge water comes in contact with a reduced aquifer. It specifically addresses (1) which reactions occur in situ, (2) the order in which these reactions will occur if terminal electron acceptors (TEAs) are introduced simultaneously, (3) the rates of these reactions, and (4) the roles of the aqueous and solid-phase portions of the aquifer. Recharge events of waters containing various combinations of O 2 , NO 3 , and SO 4 were simulated at a shallow sandy aquifer contaminated with waste fuels and chlorinated solvents using modified push−pull tests to quantify rates. In situ rate constants for aerobic respiration (14.4 day - 1 ), denitrification (5.04−7.44 day - 1 ), and sulfate reduction (4.32−6.48 day - 1 ) were estimated. Results show that when introduced together, NO 3 and SO 4 can be consumed simultaneously at similar rates. To distinguish the role of aqueous phase from that of the solid phase of the aquifer, groundwater was extracted, amended with NO 3 and SO 4 , and monitored over time. Results indicate that neither NO 3 nor SO 4 was reduced during the course of the aqueous-phase study, suggesting that NO 3 and SO 4 can behave conservatively in highly reduced water. It is clear that sediments and their associated microbial communities are important in driving redox reactions.

Environmental Science & Technology↗
USGS2006

Anaerobic biotransformation of roxarsone and related N-substituted phenylarsonic acids

Large quantities of arsenic are introduced into the environment through land application of poultry litter containing the organoarsenical feed additive roxarsone (3-nitro-4-hydroxyphenylarsonic acid). The objective of this study was to evaluate the bioconversion of roxarsone and related N-substituted phenylarsonic acid derivatives under anaerobic conditions. The results demonstrate that roxarsone is rapidly transformed in the absence of oxygen to the corresponding aromatic amine, 4-hydroxy-3-aminophenylarsonic acid (HAPA). The formation of HAPA is attributable to the facile reduction of the nitro group. Electron-donating substrates, such as hydrogen gas, glucose, and lactate, stimulated the rate of nitro group reduction, indicating a microbial role. During long-term incubations, HAPA and the closely related 4-aminophenylarsonic acid (4-APA) were slowly biologically eliminated by up to 99% under methanogenic and sulfate-reducing conditions, whereas little or no removal occurred in heat-killed inoculum controls. Arsenite and, to a lesser extent, arsenate were observed as products of the degradation. Freely soluble forms of the inorganic arsenical species accounted for 19-28% of the amino-substituted phenylarsonic acids removed. This constitutes the first report of a biologically catalyzed rupture of the phenylarsonic group under anaerobic conditions. ?? 2006 American Chemical Society.

Environmental Science & Technology↗
USGS2007

Spectroscopic evidence for uranium bearing precipitates in vadose zone sediments at the Hanford 300-area site

Uranium (U) solid-state speciation in vadose zone sediments collected beneath the former North Process Pond (NPP) in the 300 Area of the Hanford site (Washington) was investigated using multi-scale techniques. In 30 day batch experiments, only a small fraction of total U (???7.4%) was released to artificial groundwater solutions equilibrated with 1% pCO2. Synchrotron-based micro-X-ray fluorescence spectroscopy analyses showed that U was distributed among at least two types of species: (i) U discrete grains associated with Cu and (ii) areas with intermediate U concentrations on grains and grain coatings. Metatorbernite (Cu[UO2]2[PO 4]2??8H2O) and uranophane (Ca[UO 2]2[SiO3(OH)]2?? 5H 2O) at some U discrete grains, and muscovite at U intermediate concentration areas, were identified in synchrotron-based micro-X-ray diffraction. Scanning electron microscopy/energy dispersive X-ray analyses revealed 8-10 ??m size metatorbernite particles that were embedded in C-, Al-, and Si-rich coatings on quartz and albite grains. In ??- and bulk-X-ray absorption structure (??-XAS and XAS) spectroscopy analyses, the structure of metatorbernite with additional U-C and U-U coordination environments was consistently observed at U discrete grains with high U concentrations. The consistency of the ??- and bulk-XAS analyses suggests that metatorbernite may comprise a significant fraction of the total U in the sample. The entrapped, micrometer-sized metatorbernite particles in C-, Al-, and Si-rich coatings, along with the more soluble precipitated uranyl carbonates and uranophane, likely control the long-term release of U to water associated with the vadose zone sediments. ?? 2007 American Chemical Society.

Environmental Science & Technology↗
USGS2015

Using chromate to investigate the impact of natural organics on the surface reactivity of nanoparticulate magnetite

Chromate was used as a chemical probe to investigate the size-dependent influence of organics on nanoparticle surface reactivity. Magnetite–chromate sorption experiments were conducted with ∼90 and ∼6 nm magnetite nanoparticles in the presence and absence of fulvic acid (FA), natural organic matter (NOM), and isolated landfill leachate (LL). Results indicated that low concentrations (1 mg/L) of organics had no noticeable impact on chromate sorption, whereas concentrations of 50 mg/L or more resulted in decreased amounts of chromate sorption. The adsorption of organics onto the magnetite surfaces interfered equally with the ability of the 6 and 90 nm particles to sorb chromate from solution, despite the greater surface area of the smaller particles. Results indicate the presence of organics did not impact the redox chemistry of the magnetite–chromate system over the duration of the experiments (8 h), nor did the organics interact with the chromate in solution. Brunauer–Emmett–Teller (BET) and scanning electron microscopy (SEM) results indicate that the organics blocked the surface reactivity by occupying surface sites on the particles. The similarity of results with FA and NOM suggests that coverage of the reactive mineral surface is the main factor behind the inhibition of surface reactivity in the presence of organics.

Environmental Science & Technology↗
USGS1996

Limestone characterization to model damage from acidic precipitation: Effect of pore structure on mass transfer

The pore structure of Salem limestone is investigated, and conclusions regarding the effect of the pore geometry on modeling moisture and contaminant transport are discussed based on thin section petrography, scanning electron microscopy, mercury intrusion porosimetry, and nitrogen adsorption analyses. These investigations are compared to and shown to compliment permeability and capillary pressure measurements for this common building stone. Salem limestone exhibits a bimodal pore size distribution in which the larger pores provide routes for convective mass transfer of contaminants into the material and the smaller pores lead to high surface area adsorption and reaction sites. Relative permeability and capillary pressure measurements of the air/water system indicate that Salem limestone exhibits high capillarity end low effective permeability to water. Based on stone characterization, aqueous diffusion and convection are believed to be the primary transport mechanisms for pollutants in this stone. The extent of contaminant accumulation in the stone depends on the mechanism of partitioning between the aqueous and solid phases. The described characterization techniques and modeling approach can be applied to many systems of interest such as acidic damage to limestone, mass transfer of contaminants in concrete and other porous building materials, and modeling pollutant transport in subsurface moisture zones.

Environmental Science & Technology↗
USGS1996

Comparison of Eh and H2 measurements for delineating redox processes in a contaminated aquifer

Measurements of oxidation-reduction potential ( E h ) and concentrations of dissolved hydrogen (H 2 ) were made in a shallow groundwater system contaminated with solvents and jet fuel to delineate the zonation of redox processes. E h measurements ranged from +69 to -158 mV in a cross section of the contaminated plume and accurately delineated oxic from anoxic groundwater. Plotting measured E h and pH values on an equilibrium stability diagram indicated that Fe(III) reduction was the predominant redox process in the anoxic zone and did not indicate the presence of methanogenesis and sulfate reduction. In contrast, measurements of H 2 concentrations indicated that methanogenesis predominated in heavily contaminated sediments near the water table surface (H 2 ∼ 7.0 nM) and that the methanogenic zone was surrounded by distinct sulfate-reducing (H 2 ∼ 1-4 nM) and Fe(III)-reducing (H 2 ∼ 0.1-0.8 nM) zones. The presence of methanogenesis, sulfate reduction, and Fe(III) reduction was confirmed by the distribution of dissolved oxygen, sulfate, Fe(II), and methane in groundwater. These results show that H 2 concentrations were more useful for identifying anoxic redox processes than E h measurements in this groundwater system. However, H 2 -based redox zone delineations are more reliable when H 2 concentrations are interpreted in the context of electron-acceptor (oxygen, nitrate, sulfate) availability and the presence of final products [Fe(II), sulfide, methane] of microbial metabolism.

Environmental Science & Technology↗
USGS1997

Bacterial oxidation of methyl bromide in Mono Lake, California

The oxidation of methyl bromide (MeBr) in the water column of Mono Lake, CA, was studied by measuring the formation of H14CO3 from [14C]MeBr. Potential oxidation was detected throughout the water column, with highest rates occurring in the epilimnion (5-12 m depth). The oxidation of MeBr was eliminated by filter-sterilization, thereby demonstrating the involvement of bacteria. Vertical profiles of MeBr activity differed from those obtained for nitrification and methane oxidation, indicating that MeBr oxidation is not simply a co-oxidation process by either nitrifiers or methanotrophs. Furthermore, specific inhibitors of methane oxidation and/or nitrification (e.g., methyl fluoride, acetylene, allyl sulfide) had no effect upon the rate of MeBr oxidation in live samples. Of a variety of potential electron donors added to Mono Lake water, only trimethylamine resulted in the stimulation of MeBr oxidation. Cumulatively, these results suggest that the oxidation of MeBr in Mono Lake waters is attributable to trimethylamine-degrading methylotrophs. Neither methyl chloride nor methanol inhibited the oxidation of [14C]MeBr in live samples, indicating that these bacteria directly oxidized MeBr rather than the products of MeBr nucleophilic substitution reactions.

Environmental Science & Technology↗
USGS2002

Direct conversion of terpenylalkanolamines to ethylidyne N -nitroso compounds

A series of mono- and diterpenylalkanolamines bearing isopropylidene functionality on the terpene group was reacted with sodium nitrite in aqueous acetic acid to yield ethylidyne N -nitroso analogues. The key feature of this direct conversion involved initial N-nitrosation followed by apparent elimination of a "CH 4 " unit (not necessarily methane) from the isopropylidene double bond. The product distribution data for ethylidyne nitrosamines derived from tertiary terpenyl alkanolamines reflect the conformational outcome of the nitrosative dealkylation process. For &beta; , &gamma; -unsaturated allylic diterpenylethanolamines, electronic effects appeared to be important for controlling the product distribution of ethylidyne nitrosamines in light of the highly selective &alpha; -cleavage observed in the nitrosation reactions.

Journal of Organic Chemistry↗
USGS2003

CO2 hydrate: Synthesis, composition, structure, dissociation behavior, and a comparison to structure I CH4 hydrate

Structure I (sI) carbon dioxide (CO 2 ) hydrate exhibits markedly different dissociation behavior from sI methane (CH 4 ) hydrate in experiments in which equilibrated samples at 0.1 MPa are heated isobarically at 13 K/h from 210 K through the H 2 O melting point (273.15 K). The CO 2 hydrate samples release only about 3% of their gas content up to temperatures of 240 K, which is 22 K above the hydrate phase boundary. Up to 20% is released by 270 K, and the remaining CO 2 is released at 271.0 plusmn; 0.5 K, where the sample temperature is buffered until hydrate dissociation ceases. This reproducible buffering temperature for the dissociation reaction CO 2 ·nH 2 O = CO 2 (g) + nH 2 O(1 to s) is measurably distinct from the pure H 2 O melting point at 273.15 K, which is reached as gas evolution ceases. In contrast, when si CH 4 hydrate is heated at the same rate at 0.1 MPa, >95% of the gas is released within 25 K of the equilibrium temperature (193 K at 0.1 MPa). In conjunction with the dissociation study, a method for efficient and reproducible synthesis of pure polycrystalline CO 2 hydrate with suitable characteristics for material properties testing was developed, and the material was characterized. CO 2 hydrate was synthesized from CO 2 liquid and H 2 O solid and liquid reactants at pressures between 5 and 25 MPa and temperatures between 250 and 281 K. Scanning electron microscopy (SEM) examination indicates that the samples consist of dense crystalline hydrate and 50-300 μm diameter pores that are lined with euhedral cubic hydrate crystals. Deuterated hydrate samples made by this same procedure were analyzed by neutron diffraction at temperatures between 4 and 215 K; results confirm that complete conversion of water to hydrate has occurred and that the measured unit cell parameter and thermal expansion are consistent with previously reported values. On the basis of measured weight gain after synthesis and gas yields from the dissociation experiments, approximately all cages in the hydrate structure are filled such that n ≈ 5.75.

Journal of Physical Chemistry B↗
USGS1998

Diel variability of mercury phase and species distributions in the Florida Everglades

Preliminary studies of mercury (Hg) cycling in the Everglades revealed that dissolved gaseous mercury (DGM), total mercury (Hg(T)), and reactive mercury (Hg(R)) show reproducible, diel trends. Peak water-column DGM concentrations were observed on or about noon, with a 3 to 7 fold increase over night-time concentrations. Production of DGM appears to cease during dark periods, with nearly constant water column concentrations that were at or near saturation with respect to the overlying air. A simple mass balance shows that the flux of Hg to the atmosphere from diel DGM production and evasion represents about 10% of the annual input from atmospheric deposition. Production of DGM is likely the result of an indirect photolysis reaction that involves the production of reductive species and/or reduction by electron transfer. Diel variability in Hg(T) and Hg(R) appears to be controlled by two factors: inputs from rainfall and photolytic sorption/desorption processes. A possible mechanism involves photolysis of chromophores on the surface of a solid substrate (e.g., the periphyton mat) giving rise to destabilization of sorbed mercury and net desorption during daylight. At night, the sorption reactions predominate and the water-column Hg(T) decreases. Methylmercury (MeHg) also showed diel trends in concentration but were not clearly linked to the solar cycle or rainfall at the study site.

Biogeochemistry↗
USGS2002

Use of an extensive radio receiver network to document Pacific lamprey (Lampetra tridentata) entrance efficiency at fishways in the Lower Columbia River, USA

We used an extensive network of more than 170 radio receiving stations to document fine-scale passage efficiency of adult anadromous Pacific lamprey at Bonneville and The Dalles Dams in the lower Columbia River in the northwestern U.S.A. Each spring from 1997 to 2000, we released 197-299 lamprey with surgically implanted radio transmitters. Unique transmitter codes and the date and time of reception at each antenna site were downloaded electronically, and initial processing was conducted to eliminate false positive signals. The resulting large Oracle database was analyzed using an Arc View-based coding protocol. Underwater antennas positioned outside the fishway entrances detected lamprey approaches, and antennas positioned immediately inside the entrances indicated successful entries. Entrance efficiency (the number of lamprey that successfully entered a fishway divided by the number that approached that fishway) was compared for different types of entrances (main entrances versus orifice entrances) and entrance locations (powerhouse versus spillway). Lamprey used orifice-type entrances less frequently than main entrances, and passage success was generally low (< 50%) at all entrances to fishways at Bonneville Dam (the lowest dam in the system). Lamprey activity at the entrances was highest at night, and entrance success was significantly higher at The Dalles Dam (the next dam upstream from Bonneville Dam) than at Bonneville Dam. In 1999 and 2000, construction modifications were made to Bonneville Dam spillway entrances, and water velocity at these entrances was reduced at night. Modifications to increase lamprey attachment at the entrances improved lamprey entrance efficiency, but entrance efficiency during reduced velocity tests was not significantly higher than during control conditions.

Conference Paper↗
USGS2001

Mars Color Imager (MARCI) on the Mars Climate Orbiter

The Mars Color Imager, or MARCI, experiment on the Mars Climate Orbiter (MCO) consists of two cameras with unique optics and identical focal plane assemblies (FPAs), Data Acquisition System (DAS) electronics, and power supplies. Each camera is characterized by small physical size and mass (∼6×6×12 cm, including baffle; <500 g), low power requirements (<2.5 W, including power supply losses), and high science performance (1000×1000 pixel, low noise). The Wide Angle (WA) camera will have the capability to map Mars in five visible and two ultraviolet spectral bands at a resolution of better than 8 km/pixel under the worst case downlink data rate. Under better downlink conditions the WA will provide kilometer-scale global maps of atmospheric phenomena such as clouds, hazes, dust storms, and the polar hood. Limb observations will provide additional detail on atmospheric structure at 1/3 scale-height resolution. The Medium Angle (MA) camera is designed to study selected areas of Mars at regional scale. From 400 km altitude its 6° FOV, which covers ∼40 km at 40 m/pixel, will permit all locations on the planet except the poles to be accessible for image acquisitions every two mapping cycles (roughly 52 sols). Eight spectral channels between 425 and 1000 nm provide the ability to discriminate both atmospheric and surface features on the basis of composition. The primary science objectives of MARCI are to (1) observe Martian atmospheric processes at synoptic scales and mesoscales, (2) study details of the interaction of the atmosphere with the surface at a variety of scales in both space and time, and (3) examine surface features characteristic of the evolution of the Martian climate over time. MARCI will directly address two of the three high-level goals of the Mars Surveyor Program: Climate and Resources. Life, the third goal, will be addressed indirectly through the environmental factors associated with the other two goals.

Journal of Geophysical Research E: Planets↗