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USGS2004

Using chromium stable isotope ratios to quantify Cr(VI) reduction: Lack of sorption effects

Chromium stable isotope values can be effectively used to monitor reduction of Cr(VI) in natural waters. We investigate effects of sorption during transport of Cr(VI) which may also shift Cr isotopes values, complicating efforts to quantify reduction. This study shows that Cr stable isotope fractionation caused by sorption is negligible. Equilibrium fractionation of Cr stable isotopes between dissolved Cr(VI) and Cr(VI) adsorbed onto γ-Al 2 O 3 and goethite is less than 0.04‰ ( 53 Cr/ 52 Cr) under environmentally relevant pH conditions. Batch experiments at pH 4.0 and pH 6.0 were conducted in series to sequentially magnify small isotope fractionations. A simple transport model suggests that adsorption may cause amplification of a small isotope fractionation along extreme fringes of a plume, leading to shifts in 53 Cr/ 52 Cr values. We therefore suggest that isotope values at extreme fringes of Cr plumes be critically evaluated for sorption effects. A kinetic effect was observed in experiments with goethite at pH 4 where apparently lighter isotopes diffuse into goethite clumps at a faster rate before eventually reaching equilibrium. This observed kinetic effect may be important in a natural system that has not attained equilibrium and is in need of further study. Cr isotope fractionation caused by speciation of Cr(VI) between HCrO 4 - and CrO 4 2 - was also examined, and we conclude that it is not measurable. In the absence of isotope fractionation caused by equilibrium speciation and sorption, most of the variation in δ 53 Cr values may be attributed to reduction, and reliable estimates of Cr reduction can be made.

Environmental Science & Technology↗

USGS2007

Incidence of the enterococcal surface protein ( esp ) gene in human and animal fecal sources

The occurrence of the enterococcal surface protein ( esp ) gene in the opportunistic pathogens Enterococcus faecalis and E. faecium is well-documented in clinical research. Recently, the esp gene has been proposed as a marker of human pollution in environmental waters; however, information on its relative incidence in various human and animal fecal sources is limited. We have determined the occurrence of the esp gene in enterococci from human ( n = 64) and animal ( n = 233) fecal samples by polymerase chain reaction using two primer sets: one presumably specific for E. faecium ( esp fm ) and the other for both E. faecalis and E. faecium ( esp fs/fm ). We believe that this research is the first to explore the use of esp fs/fm for the detection of human waste in natural environmental settings. The incidence in human sources was 93.1% esp fm and 100% esp fs/fm in raw sewage influent; 30% for both esp fm and esp fs/fm in septic waste; and 0% esp fm and 80% esp fs/fm in active pit toilets. The overall occurrence of the gene in animal feces was 7.7% ( esp fs/fm ) and 4.7% ( esp fm ); animal types with positive results included dogs (9/43, all esp fm ), gulls (10/34, esp fs/fm ; 2/34, esp fm ), mice (3/22, all esp fs/fm ), and songbirds (5/55, all esp fs/fm ). The esp gene was not detected in cat (0/34), deer (0/4), goose (0/18), or raccoon (0/23) feces. The inconsistent occurrence, especially in septic and pit toilet sewage, suggests a low statistical power of discrimination between animal and human sources, which means a large number of replicates should be collected. Both esp fm and esp fs/fm were common in raw sewage, but neither one efficiently differentiated between animal and other human sources.

Environmental Science & Technology↗

USGS2010

Natural chlorate in the environment: Application of a new IC-ESI/MS/MS method with a Cl18O3- internal standard

A new ion chromatography electrospray tandem mass spectrometry (IC-ESI/MS/MS) method has been developed for quantification and confirmation of chlorate (ClO 3 − ) in environmental samples. The method involves the electro-chemical generation of isotopically labeled chlorate internal standard (Cl 18 O 3 − ) using 18 O water (H 2 18 O). The standard was added to all samples prior to analysis thereby minimizing the matrix effects that are associated with common ions without the need for expensive sample pretreatments. The method detection limit (MDL) for ClO 3 − was 2 ng L −1 for a 1 mL volume sample injection. The proposed method was successfully applied to analyze ClO 3 − in difficult environmental samples including soil and plant leachates. The IC-ESI/MS/MS method described here was also compared to established EPA method 317.0 for ClO 3 − analysis. Samples collected from a variety of environments previously shown to contain natural perchlorate (ClO 4 − ) occurrence were analyzed using the proposed method and ClO 3 − was found to co-occur with ClO 4 − at concentrations ranging from <2 ng L −1 in precipitation from Texas and Puerto Rico to >500 mg kg −1 in caliche salt deposits from the Atacama Desert in Chile. Relatively low concentrations of ClO 3 − in some natural groundwater samples (<0.1 μg L −1 ) analyzed in this work may indicate lower stability when compared to ClO 4 − in the subsurface. The high concentrations of ClO 3 − in caliches and soils (3−6 orders of magnitude greater) as compared to precipitation samples indicate that ClO 3 − , like ClO 4 − , may be atmospherically produced and deposited, then concentrated in dry soils, and is possibly a minor component in the biogeochemical cycle of chlorine.

Environmental Science & Technology↗

USGS2023

Contaminant exposure and transport from three potential reuse waters within a single watershed

Global demand for safe and sustainable water supplies necessitates a better understanding of contaminant exposures in potential reuse waters. In this study, we compared exposures and load contributions to surface water from the discharge of three reuse waters (wastewater effluent, urban stormwater, and agricultural runoff). Results document substantial and varying organic-chemical contribution to surface water from effluent discharges (e.g., disinfection byproducts [DBP], prescription pharmaceuticals, industrial/household chemicals), urban stormwater (e.g., polycyclic aromatic hydrocarbons, pesticides, nonprescription pharmaceuticals), and agricultural runoff (e.g., pesticides). Excluding DBPs, episodic storm-event organic concentrations and loads from urban stormwater were comparable to and often exceeded those of daily wastewater-effluent discharges. We also assessed if wastewater-effluent irrigation to corn resulted in measurable effects on organic-chemical concentrations in rain-induced agricultural runoff and harvested feedstock. Overall, the target-organic load of 491 g from wastewater-effluent irrigation to the study corn field during the 2019 growing season did not produce substantial dissolved organic-contaminant contributions in subsequent rain-induced runoff events. Out of the 140 detected organics in source wastewater-effluent irrigation, only imidacloprid and estrone had concentrations that resulted in observable differences between rain-induced agricultural runoff from the effluent-irrigated and nonirrigated corn fields. Analyses of pharmaceuticals and per-/polyfluoroalkyl substances in at-harvest corn-plant samples detected two prescription antibiotics, norfloxacin and ciprofloxacin, at concentrations of 36 and 70 ng/g, respectively, in effluent-irrigated corn-plant samples; no contaminants were detected in noneffluent irrigated corn-plant samples.

Oklahoma↗

USGS2013

Association of toxin-producing Clostridium botulinum with the macroalga Cladophora in the Great Lakes

Avian botulism, a paralytic disease of birds, often occurs on a yearly cycle and is increasingly becoming more common in the Great Lakes. Outbreaks are caused by bird ingestion of neurotoxins produced by Clostridium botulinum, a spore-forming, gram-positive, anaerobe. The nuisance, macrophytic, green alga Cladophora (Chlorophyta; mostly Cladophora glomerata L.) is a potential habitat for the growth of C. botulinum. A high incidence of botulism in shoreline birds at Sleeping Bear Dunes National Lakeshore (SLBE) in Lake Michigan coincides with increasingly massive accumulations of Cladophora in nearshore waters. In this study, free-floating algal mats were collected from SLBE and other shorelines of the Great Lakes between June and October 2011. The abundance of C. botulinum in algal mats was quantified and the type of botulism neurotoxin (bont) genes associated with this organism were determined by using most-probable-number PCR (MPN-PCR) and five distinct bont gene-specific primers (A, B, C, E, and F). The MPN-PCR results showed that 16 of 22 (73%) algal mats from the SLBE and 23 of 31(74%) algal mats from other shorelines of the Great Lakes contained the bont type E (bont/E) gene. C. botulinum was present up to 15 000 MPN per gram dried algae based on gene copies of bont/E. In addition, genes for bont/A and bont/B, which are commonly associated with human diseases, were detected in a few algal samples. Moreover, C. botulinum was present as vegetative cells rather than as dormant spores in Cladophora mats. Mouse toxin assays done using supernatants from enrichment of Cladophora containing high densities of C. botulinum (>1000 MPN/g dried algae) showed that Cladophora-borne C. botulinum were toxin-producing species (BoNT/E). Our results indicate that Cladophora provides a habitat for C. botulinum, warranting additional studies to better understand the relationship between this bacterium and the alga, and how this interaction potentially contributes to botulism outbreaks in birds.

Great Lakes↗

USGS1975

Earthquake shaking and damage to buildings

Ground shaking close to the causative fault of an earthquake is more intense than it was previously believed to be. This raises the possibility that large numbers of buildings and other structures are not sufficiently resistant for the intense levels of shaking that can occur close to the fault. Many structures were built before earthquake codes were adopted; others were built according to codes formulated when less was known about the intensity of near-fault shaking. Although many building types are more resistant than conventional design analyses imply, the margin of safety is difficult to quantify. Many modern structures, such as freeways, have not been subjected to and tested by near-fault shaking in major earthquakes (magnitude 7 or greater). Damage patterns in recent moderate-sized earthquakes occurring in or adjacent to urbanized areas, however, indicate that many structures, including some modern ones designed to meet earthquake code requirements, cannot withstand the severe shaking that can occur close to a fault. It is necessary to review the ground motion assumed and the methods utilized in the design of important existing structures and, if necessary, to strengthen or modify the use of structures that are found to be weak. New structures situated close to active faults should be designed on the basis of ground motion estimates greater than those used in the past. The ultimate balance between risk of earthquake losses and cost for both remedial strengthening and improved earthquake-resistant construction must be decided by the public. Scientists and engineers must inform the public about earthquake shaking and its effect on structures. The exposure to damage from seismic shaking is steadily increasing because of continuing urbanization and the increasing complexity of lifeline systems, such as power, water, transportation, and communication systems. In the near future we should expect additional painful examples of the damage potential of moderate-sized earthquakes in urban areas. Over a longer time span, however, we can significantly reduce the risk to life and property from seismic shaking through better land utilization, improved building codes and construction practices, and at least the gradual replacement of poor buildings by more resistant buildings. Progress toward reducing risk from seismic shaking through better building design is slowed by deficiencies in our knowledge about the nature of damaging ground motion and the failure mechanisms in structures. For example, lacking observational data, seismologists must rely on simplified theoretical and numerical models of the earthquake process to estimate near-fault ground motion, especially for earthquakes as large as magnitude 7 and 8. Because such models have not been adequately tested against data, their reliability is unknown. Engineers lack detailed information about failure processes in structures during an earthquake. Although many structures have been instrumented to measure their response to an earthquake, few records have been obtained from buildings that actually sustained significant structural damage and few structures are properly instrumented to measure all the modes of deformation that are likely to contribute to failure. Moreover, the fact that many structures have withstood ground motion more intense than that assumed in their design indicates that conventional methods of design do not take into account important contributions to earthquake resistance by nonstructural elements and by the ability of structural elements to deform inelastically without necessarily causing failure of the structure. It is fortunate when such reserve resistance exists, but better understanding of the sources of reserve strength is needed to determine how large a margin of safety they confer and how they might be affected by changes in construction practices and materials with time. In the next few years we look forward to significant advances in knowledge and to more effective application of what is already known, largely because of substantial funding of research related to seismic engineering by the National Science Foundation . The increasing number of strong-motion seismographs operating in seismically active regions will likely provide for the first time a number of records of damaging levels of ground motion. Significant effort is being directed toward obtaining near-fault records, although many probable sites of future large earthquakes remain inadequately instrumented, especially outside the conterminous United States. New and more complete information on building response and damage mechanisms will be obtained by improved instrumentation of structures and through laboratory investigations of failure in structures and structural elements. Further developments in computer technology and in computer modeling techniques will permit more realistic simulations of the seismic response of soils and structures that take into account their inelastic behavior and their strain-dependent properties. Earthquake design codes will continually be revised to better utilize existing knowledge concerning the nature of strong ground motion and the dynamic behavior of buildings during earthquakes and to incorporate new knowledge and also experiences gained from future earthquakes. We believe that application of new knowledge, improvements in earthquake-resistant design and construction, and remedial strengthening or replacement of weak existing structures can significantly reduce our current level of exposure to earthquake hazards.

Science↗

USGS2014

Three-dimensional imaging, change detection, and stability assessment during the centerline trench levee seepage experiment using terrestrial light detection and ranging technology, Twitchell Island, California, 2012

A full scale field seepage test was conducted on a north-south trending levee segment of a now bypassed old meander belt on Twitchell Island, California, to understand the effects of live and decaying root systems on levee seepage and slope stability. The field test in May 2012 was centered on a north-south trench with two segments: a shorter control segment and a longer seepage test segment. The complete length of the trench area measured 40.4 meters (m) near the levee centerline with mature trees located on the waterside and landside of the levee flanks. The levee was instrumented with piezometers and tensiometers to measure positive and negative porewater pressures across the levee after the trench was flooded with water and held at a constant hydraulic head during the seepage test—the results from this component of the experiment are not discussed in this report. We collected more than one billion three-dimensional light detection and ranging (lidar) data points before, during, and after the centerline seepage test to assess centimeter-scale stability of the two trees and the levee crown. During the seepage test, the waterside tree toppled (rotated 20.7 degrees) into the water. The landside tree rotated away from the levee by 5 centimeters (cm) at a height of 2 m on the tree. The paved surface of the levee crown had three regions that showed subsidence on the waterside of the trench—discussed as the northern, central, and southern features. The northern feature is an elongate region that subsided 2.1 cm over an area with an average width of 1.35 m that extends 15.8 m parallel to the trench from the northern end of the trench to just north of the trench midpoint, and is associated with a crack 1 cm in height that formed during the seepage test on the trench wall. The central subsidence feature is a semicircular region on the waterside of the trench that subsided by as much as 6.2 cm over an area 3.4 m wide and 11.2 m long. The southern feature is an elongate region that has a maximum subsidence of 3.5 cm over an area 0.75 m wide and 8.1 m long and is associated with a number of small fractures in the pavement that are predominately north-south-trending and parallel to the trench. We determined that there was no significant motion of the levee flank during the last week of the seepage test. We also determined biomorphic parameters for the landside tree, such as the 3D positioning on the levee, tree height, levee parallel/perpendicular cross sectional area, and canopy centroid. These biomorphic parameters were requested to support a University of California Berkeley team studying seepage and stability on the levee. A gridded, 2-cm bare-earth digital elevation model of the levee crown and the landside levee flank from the final terrestrial lidar (T-Lidar) survey provided detailed topographic data for future assessment. Because the T-Lidar was not integrated into the project design, other than an initial courtesy dataset to help characterize the levee surface, our ability to contribute to the overall science goals of the seepage test was limited. Therefore, our analysis focused on developing data collection and processing methodology necessary to align ultra high-resolution T-Lidar data (with an average spot spacing 2–3 millimeters on the levee crown) from several instrument setup locations to detect, measure, and characterize dynamic centimeter-scale deformation and surface changes during the seepage test.

California↗

USGS2000

Sorption of selected organic compounds from water to a peat soil and its humic-acid and humin fractions: Potential sources of the sorption nonlinearity

The sorption isotherms of ethylene dibromide (EDB), diuron (DUN), and 3,5-dichlorophenol (DCP) from water on the humic acid and humin fractions of a peat soil and on the humic-acid of a muck soil have been measured. The data were compared with those of the solutes with the whole peat from which the humic-acid (HA) and humin (HM) fractions were derived and on which the sorption of the solutes exhibited varying extents of nonlinear capacities at low relative concentrations (C(e)/S(w)). The HA fraction as prepared by the density-fractionated method is relatively pure and presumably free of high- surface-area carbonaceous material (HSACM) that is considered to be responsible for the observed nonlinear sorption for nonpolar solutes (e.g., EDB) on the peat; conversely, the base-insoluble HM fraction as prepared is presumed to be enriched with HSACM, as manifested by the greatly higher BET- (N2) surface area than that of the whole peat. The sorption of EDB on HA exhibits no visible nonlinear effect, whereas the sorption on HM shows an enhanced nonlinearity over that on the whole peat. The sorption of polar DUN and DCP on HA and HM display nonlinear effects comparable with those on the whole peat; the effects are much more significant than those with nonpolar EDB. These results conform to the hypothesis that adsorption onto a small amount of strongly adsorbing HSACM is largely responsible for the nonlinear sorption of nonpolar solutes on soils and that additional specific interactions with the active groups of soil organic matter are responsible for the generally higher nonlinear sorption of the polar solutes.

Environmental Science & Technology↗

USGS2020

Trophodynamics of per- and polyfluoroalkyl substances in the food web of a large Atlantic slope river

Per- and polyfluoroalkyl substances (PFASs) have attracted scientific and regulatory attention due to their persistence, bioaccumulative potential, toxicity, and global distribution. We determined the accumulation and trophic transfer of 14 PFASs (5 short-chain and 9 long-chain) within the food web of the Yadkin-Pee Dee River of North Carolina and South Carolina, US. Food web components and pathways were determined by stable isotope analyses of producers, consumers, and organic matter. Analyses of water, sediment, organic matter, and aquatic biota revealed that PFASs were prevalent in all food web compartments. Biofilm, an aggregation of bacteria, fungi, algae, and protozoans and a basal resource for the aquatic food web, showed high PFAS accumulation (in 10 of 14 compounds), particularly for perfluorooctanoic acid, with the greatest mean concentration of 463.73 ng/g. The food web compartment with the most detections and greatest concentrations of PFASs was aquatic insects; all 14 PFASs were detected in individual aquatic insect samples (range of <limit of detection [<LOD] to 1670.10 ng/g of wet weight [WW]). These findings may suggest a trophic link between biofilm PFASs and aquatic insect PFASs. Individual fish tissue samples ranged from <LOD to 797.00 ng/g of WW, where perfluorooctanesulfonate (PFOS) was the dominant PFAS among all samples (64%). The ova of an imperiled fish, the robust redhorse ( Moxostoma robustum ), had concentrations of 10 PFASs (range of <LOD to 482.88 ng/g of WW) and the highest PFOS concentration (482.88 ng/g of WW), indicating a likely maternal transfer. The trophic magnification factors (TMFs) calculated in this study showed that various taxa accumulated PFAS compounds differently. PFBS, a short-chain PFAS compound that would presumably exhibit lesser TMFs, had nine values among our compartments and organisms >1.0 (range of 0.57 to 2.33); it is possible that an unmeasured PFBS precursor may be accumulating in biota and metabolizing to PFBS, leading to a higher than expected TMFs for this compound. Our findings demonstrate the prevalence of PFASs in a freshwater food web with potential implications for ecological and human health.

North Carolina, South Carolina↗

USGS2017

Expanded target-chemical analysis reveals extensive mixed-organic-contaminant exposure in USA streams

Surface water from 38 streams nationwide was assessed using 14 target-organic methods (719 compounds). Designed-bioactive anthropogenic contaminants (biocides, pharmaceuticals) comprised 57% of 406 organics detected at least once. The 10 most-frequently detected anthropogenic-organics included eight pesticides (desulfinylfipronil, AMPA, chlorpyrifos, dieldrin, metolachlor, atrazine, CIAT, glyphosate) and two pharmaceuticals (caffeine, metformin) with detection frequencies ranging 66–84% of all sites. Detected contaminant concentrations varied from less than 1 ng L –1 to greater than 10 μg L –1 , with 77 and 278 having median detected concentrations greater than 100 ng L –1 and 10 ng L –1 , respectively. Cumulative detections and concentrations ranged 4–161 compounds (median 70) and 8.5–102 847 ng L –1 , respectively, and correlated significantly with wastewater discharge, watershed development, and toxic release inventory metrics. Log 10 concentrations of widely monitored HHCB, triclosan, and carbamazepine explained 71–82% of the variability in the total number of compounds detected (linear regression; p -values: < 0.001–0.012), providing a statistical inference tool for unmonitored contaminants. Due to multiple modes of action, high bioactivity, biorecalcitrance, and direct environment application (pesticides), designed-bioactive organics (median 41 per site at μg L –1 cumulative concentrations) in developed watersheds present aquatic health concerns, given their acknowledged potential for sublethal effects to sensitive species and lifecycle stages at low ng L –1 .

Environmental Science & Technology↗

USGS2006

History of the Fort Collins Science Center, U.S. Geological Survey

The U.S. Geological Survey’s Fort Collins Science Center ("the Center") has been a nucleus of research, technology development, and associated scientific activities within the Department of the Interior for more than 30 years. The Center’s historical activities are deeply rooted in federal biological resources research and its supporting disciplines, particularly as they relate to the needs of the U.S. Department of the Interior and its resource management agencies. The organizational framework and activities of the Center have changed and adapted over the years in response to shifts in the scientific issues and challenges facing the U.S. Department of the Interior and with the development of new strategies to meet these challenges. Thus, the history of the Center has been dynamic. The Center has been nested within the U.S. Geological Survey since 1996. From 1993 to 1996 the Center was a major unit of the National Biological Service (named the National Biological Survey at its inception). This was a period of great organizational flux. During that time the Center comprised multiple field stations and science functions that prior to 1993 had been scattered among the U.S. Bureau of Land Management, the U.S. Bureau of Reclamation, the National Park Service, and the U.S. Fish and Wildlife Service. In 1993, certain biological research components of these agencies were assigned to join with the National Ecology Research Center, formerly one of the major research and development hubs of the U.S. Fish and Wildlife Service. This was the year when biological resources research in the U.S. Department of the Interior was consolidated by the Secretary of the Interior, who in an April 1993 memo explaining his intentions wrote, "Our Department has, without doubt, the best biologists in the world." Soon after formation of the new agency, the Center was re-named the Midcontinent Ecological Science Center, reflecting its geographic location within the new Midcontinent administrative region of the National Biological Service (the other three original administrative regions were the eastern, western, and southern). The change in name to the Fort Collins Science Center took place in 2002, soon after the center moved to new facilities on the Colorado State University Natural Resources Research Campus. At various times during the period when it was part of the National Biological Service (1993–96), the Center served as the administrative and programmatic home base for a wide number of science activities in numerous Western states (table 1). This reflected the previous fragmentation of biological and related science efforts across resource management agencies in the U.S. Department of the Interior. The organization of the 2 Center within the National Biological Service was a manifestation of the desire of the Secretary of the Interior to consolidate its biological science activities in administratively independent entities that would ensure that the science retained its objectivity. Congress later recognized the need to maintain a hierarchical independence between biological science and resource management in the Department. However, Congress also saw that the U.S. Geological Survey, with its long history of objective science support to the nation in geology, water resources, geography, and remote sensing, was a suitable alternative home for these biological science functions. Thus, in 1996 Congress transferred the biological resources functions of the National Biological Service to the U.S. Geological Survey. Detailed overviews and opinions about the history and policy issues surrounding the formation and subsequent fate of the National Biological Service can be found elsewhere (for example Cohn, 1993, 2005; Kaufman, 1993; Kreeger, 1994; Pulliam, 1995, 1998a,b; Reichhardt, 1994; Wagner, 1999)

Open-File Report↗

USGS2002

Characterization and copper binding of humic and nonhumic organic matter isolated from the South Platte River: Evidence for the presence of nitrogenous binding site

Humic substances typically constitute 40−60% of the dissolved organic matter (DOM) in surface waters. However, little information is available regarding the metal binding properties of the nonhumic hydrophilic portion of the DOM. In this study, humic and nonhumic DOM samples were isolated from the South Platte River (Colorado, DOC = 2.6 mg·L - 1 , SUVA 254 = 2.4 L/mg·m) using a two-column array of XAD-8 and XAD-4 resins. The three major isolated fractions of DOM, which accounted for 57% of the bulk DOM, were characterized using a variety of analytical tools. Proton and copper binding properties were studied for each fraction. The main objective of this work was to compare the structural and chemical characteristics of the isolated fractions and test models describing DOM reactivity toward metal ions. The characterization work showed significant structural differences between the three isolated fractions of DOM. The hydrophobic acid fraction (i.e., humic substances isolated from the XAD-8 resin) gave the largest C/H, C/O, and C/N ratios and aromatic carbon content among the three isolated fractions. The transphilic acid (TPHA) fraction (“transphilic” meaning fraction of intermediate polarity isolated from the XAD-4 resin) was found to incorporate the highest proportion of polysaccharides, whereas the transphilic neutral (TPHN) fraction was almost entirely proteinaceous. The gradual increase of the charge with pH for the three DOM fractions is most likely caused by a large distribution of proton affinity constants for the carboxylic groups, as well as a second type of group more generally considered to be phenolic. In the case of the DOM fraction enriched in proteinaceous material (i.e., TPHN fraction), the results showed that the amino groups are responsible for the charge reversal. For low copper concentrations, nitrogen-containing functional groups similar to those of amino acids are likely to be involved in complexation, in agreement with previously published data.

Colorado↗

USGS2007

A gel probe equilibrium sampler for measuring arsenic porewater profiles and sorption gradients in sediments: I. Laboratory development

A gel probe equilibrium sampler has been developed to study arsenic (As) geochemistry and sorption behavior in sediment porewater. The gels consist of a hydrated polyacrylamide polymer, which has a 92% water content. Two types of gels were used in this study. Undoped (clear) gels were used to measure concentrations of As and other elements in sediment porewater. The polyacrylamide gel was also doped with hydrous ferric oxide (HFO), an amorphous iron (Fe) oxyhydroxide. When deployed in the field, HFO-doped gels introduce a fresh sorbent into the subsurface thus allowing assessment of in situ sorption. In this study, clear and HFO-doped gels were tested under laboratory conditions to constrain the gel behavior prior to field deployment. Both types of gels were allowed to equilibrate with solutions of varying composition and re-equilibrated in acid for analysis. Clear gels accurately measured solution concentrations (??1%), and As was completely recovered from HFO-doped gels (??4%). Arsenic speciation was determined in clear gels through chromatographic separation of the re-equilibrated solution. For comparison to speciation in solution, mixtures of As(III) and As(V) adsorbed on HFO embedded in gel were measured in situ using X-ray absorption spectroscopy (XAS). Sorption densities for As(III) and As(V) on HFO embedded in gel were obtained from sorption isotherms at pH 7.1. When As and phosphate were simultaneously equilibrated (in up to 50-fold excess of As) with HFO-doped gels, phosphate inhibited As sorption by up to 85% and had a stronger inhibitory effect on As(V) than As(III). Natural organic matter (>200 ppm) decreased As adsorption by up to 50%, and had similar effects on As(V) and As(III). The laboratory results provide a basis for interpreting results obtained by deploying the gel probe in the field and elucidating the mechanisms controlling As partitioning between solid and dissolved phases in the environment. ?? 2008 American Chemical Society.

Environmental Science & Technology↗

USGS2012

Examining spring wet slab and glide avalanche occurrence along the Going-to-the-Sun Road corridor, Glacier National Park, Montana, USA

Wet slab and glide snow avalanches are dangerous and yet can be particularly difficult to predict. Wet slab and glide avalanches are presumably triggered by free water moving through the snowpack and the subsequent interaction with layer or ground interfaces, and typically occur in the spring during warming and subsequent melt periods. In Glacier National Park (GNP), Montana, both types of avalanches can occur in the same year and affect the spring opening operations of the Going-to-the-Sun Road (GTSR). We investigated the timing of wet slab and glide avalanche occurrence along the GTSR from 2003 to 2011 using meteorological and snowpack data from two high-elevation weather stations, one SNOTEL site, and an avalanche database to characterize 55 wet slab and 182 glide avalanches. Daily wet slab and glide avalanche occurrence were combined to represent an avalanche day and were compared to non-avalanche days (no avalanche occurrence) for 60 variables (both direct and derived measurements) using a univariate analysis. A classification tree (CART) was then trained to capture the most important variables for examining specific meteorological and snowpack variables that contribute to these types of wet snow avalanches. The CART was 10-fold cross validated using the data for 2003–2010 seasons and resulted in overall predictive accuracy of 73%. We then used the statistically optimal CART as a predictive model for the spring avalanche season of 2011, which resulted in an overall predictive accuracy of 82% for both avalanche and non-avalanche days, and a predictive accuracy of 91% for avalanche days. The results suggest that the role of air temperature and snowpack settlement appear to be the most important variables in wet slab and glide avalanche occurrence. When applied to the 2011 season, the results of the CART model are encouraging and they enhance our understanding of some of the required meteorological and snowpack conditions for wet slab and glide avalanche occurrence.

Cold Regions Science and Technology↗

USGS2006

Perchlorate in pleistocene and holocene groundwater in North-Central New Mexico

Groundwater from remote parts of the Middle Rio Grande Basin in north-central New Mexico has perchlorate (ClO 4 - ) concentrations of 0.12−1.8 μg/L. Because the water samples are mostly preanthropogenic in age (0−28 000 years) and there are no industrial sources in the study area, a natural source of the ClO 4 - is likely. Most of the samples have Br - , Cl - , and SO 4 2 - concentrations that are similar to those of modern bulk atmospheric deposition with evapotranspiration (ET) factors of about 7−40. Most of the ET values for Pleistocene recharge were nearly twice that for Holocene recharge. The NO 3 - /Cl - and ClO 4 - /Cl - ratios are more variable than those of Br - /Cl - or SO 4 2 - /Cl - . Samples thought to have recharged under the most arid conditions in the Holocene have relatively high NO 3 - /Cl - ratios and low δ 15 N values (+1 per mil (‰)) similar to those of modern bulk atmospheric N deposition. The δ 18 O values of the NO 3 - (−4 to 0 ‰) indicate that atmospheric NO 3 - was not transmitted directly to the groundwater but may have been cycled in the soils before infiltrating. Samples with nearly atmospheric NO 3 - /Cl - ratios have relatively high ClO 4 - concentrations (1.0−1.8 μg/L) with a nearly constant ClO 4 - /Cl - mole ratio of (1.4 ± 0.1) × 10 - 4 , which would be consistent with an average ClO 4 - concentration of 0.093 ± 0.005 μg/L in bulk atmospheric deposition during the late Holocene in north-central NM. Samples thought to have recharged under wetter conditions have higher δ 15 N values (+3 to +8 ‰), lower NO 3 - /Cl - ratios, and lower ClO 4 - /Cl - ratios than the ones most likely to preserve an atmospheric signal. Processes in the soils that may have depleted atmospherically derived NO 3 - also may have depleted ClO 4 - to varying degrees prior to recharge. If these interpretations are correct, then ClO 4 - concentrations of atmospheric origin as high as 4 μg/L are possible in preanthropogenic groundwater in parts of the Southwest where ET approaches a factor of 40. Higher ClO 4 - concentrations in uncontaminated groundwater could occur in recharge beneath arid areas where ET is greater than 40, where long-term accumulations of atmospheric salts are leached suddenly from dry soils, or where other (nonatmospheric) natural sources of ClO 4 - exist.

Environmental Science & Technology↗

USGS2003

Effects of dissolved carbonate on arsenate adsorption and surface speciation at the hematite-water interface

Effects of dissolved carbonate on arsenate [As(V)] reactivity and surface speciation at the hematite−water interface were studied as a function of pH and two different partial pressures of carbon dioxide gas [ P CO 2 = 10 - 3.5 atm and ∼0; CO 2 -free argon (Ar)] using adsorption kinetics, pseudo-equilibrium adsorption/titration experiments, extended X-ray absorption fine structure spectroscopic (EXAFS) analyses, and surface complexation modeling. Different adsorbed carbonate concentrations, due to the two different atmospheric systems, resulted in an enhanced and/or suppressed extent of As(V) adsorption. As(V) adsorption kinetics [4 g L - 1 , [As(V)] 0 = 1.5 mM and I = 0.01 M NaCl] showed carbonate-enhanced As(V) uptake in the air-equilibrated systems at pH 4 and 6 and at pH 8 after 3 h of reaction. Suppressed As(V) adsorption was observed in the air-equilibrated system in the early stages of the reaction at pH 8. In the pseudo-equilibrium adsorption experiments [1 g L - 1 , [As(V)] 0 = 0.5 mM and I = 0.01 M NaCl], in which each pH value was held constant by a pH-stat apparatus, effects of dissolved carbonate on As(V) uptake were almost negligible at equilibrium, but titrant (0.1 M HCl) consumption was greater in the air-equilibrated systems ( P CO 2 = 10 - 3.5 atm) than in the CO 2 -free argon system at pH 4−7.75. The EXAFS analyses indicated that As(V) tetrahedral molecules were coordinated on iron octahedral via bidentate mononuclear (≈2.8 Å) and bidentate binuclear (≈3.3 Å) bonding at pH 4.5−8 and loading levels of 0.46−3.10 μM m - 2 . Using the results of the pseudo-equilibrium adsorption data and the XAS analyses, the pH-dependent As(V) adsorption under the P CO 2 = 10 - 3.5 atm and the CO 2 -free argon system was modeled using surface complexation modeling, and the results are consistent with the formation of nonprotonated bidentate surface species at the hematite surfaces. The results also suggest that the acid titrant consumption was strongly affected by changes to electrical double-layer potentials caused by the adsorption of carbonate in the air-equilibrated system. Overall results suggest that the effects of dissolved carbonate on As(V) adsorption were influenced by the reaction conditions [e.g., available surface sites, initial As(V) concentrations, and reaction times]. Quantifying the effects of adsorbed carbonate may be important in predicting As(V) transport processes in groundwater, where iron oxide-coated aquifer materials are exposed to seasonally fluctuating partial pressures of CO 2 (g).

Environmental Science & Technology↗