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USGS2004

The microbial arsenic cycle in Mono Lake, California

Significant concentrations of dissolved inorganic arsenic can be found in the waters of a number of lakes located in the western USA and in other water bodies around the world. These lakes are often situated in arid, volcanic terrain. The highest concentrations of arsenic occur in hypersaline, closed basin soda lakes and their remnant brines. Although arsenic is a well-known toxicant to eukaryotes and prokaryotes alike, some prokaryotes have evolved biochemical mechanisms to exploit arsenic oxyanions (i.e., arsenate and arsenite); they can use them either as an electron acceptor for anaerobic respiration (arsenate), or as an electron donor (arsenite) to support chemoautotrophic fixation of CO 2 into cell carbon. Unlike in freshwater or marine ecosystems, these processes may assume quantitative significance with respect to the carbon cycle in arsenic-rich soda lakes. For the past several years our research has focused on the occurrence and biogeochemical manifestations of these processes in Mono Lake, a particularly arsenic-rich environment. Herein we review some of our findings concerning the biogeochemical arsenic cycle in this lake, with the hope that it may broaden the understanding of the influence of microorganisms upon the speciation of arsenic in more common, less “extreme” environments, such as drinking water aquifers.

California↗

USGS2019

The future of recreational fisheries: Advances in science, monitoring, management, and practice

Recreational fisheries (RF) are complex social-ecological systems that play an important role in aquatic environments while generating significant social and economic benefits around the world. The nature of RF is diverse and rapidly evolving, including the participants, their priorities and behaviors, and the related ecological impacts and social and economic benefits. RF can lead to negative ecological impacts, particularly through overexploitation of fish populations and spread of non-native species and genotypes through stocking. Hence, careful management and monitoring of RF is essential to sustain these ecologically and socioeconomically important resources. This special issue on recreational fisheries contains diverse research, syntheses, and perspectives that highlight the advances being made in RF research, monitoring, management, and practice, which we summarize here. Co-management actions are rising, often involving diverse interest groups including government and non-government organizations; applying collaborative management practices can help balance social and economic benefits with conservation targets. Technological and methodological advances are improving the ability to monitor biological, social, and economic dynamics of RF, which underpin the ability to maximize RF benefits through management actions. To ensure RF sustainability, much research focuses on the ecological aspects of RF, as well as the development of management and angling practices that reduce negative impacts on fish populations. For example, angler behavior can be influenced to conform to conservation-minded angling practices through regulations, but is often best accomplished through growing bottom-up social change movements. Anglers can also play an important role in fisheries monitoring and conservation, including providing data on fish abundance and assemblages (i.e., citizen science). The increasing impacts that growing human populations are having on the global environment are threatening many of the natural resources and ecosystem services they provide, including valuable RF. However, with careful development of research initiatives, monitoring and management, sustainable RF can generate positive outcomes for both society and natural ecosystems and help solve allocation conflicts with commercial fisheries and conservation.

Fisheries Research↗

USGS2023

Viability of side-scan sonar to enumerate Paddlefish, a large pelagic freshwater fish, in rivers and reservoirs

Recreational-grade side-scan sonar (SSS) has become an invaluable tool for inland fisheries, particularly when characterizing underwater habitat, but it is being increasingly used for enumerating large-bodied (> 1 m total length [TL]) aquatic fauna. We used SSS in river and reservoir environments to evaluate methods for identifying and counting Paddlefish Polyodon spathula , a large pelagic planktivore of recreational and economic importance that can exceed 2 m in length and weigh over 70 kg. We assessed accuracy and precision among readers to identify Paddlefish by assigning confidence scores (1–3; with 3 being more confident) to sonar images of a ballistics-gel filled fiberglass replica Paddlefish. Readers varied in their confidence scores for the replica Paddlefish and no reader could identify the target beyond 25 m from the transducer. Afterwards, we used SSS to survey several kilometers of a reservoir during summer residency and a large river during springtime spawning migrations. Two readers counted Paddlefish images in the SSS recordings and we estimated population size in the surveyed area with distance sampling. In the reservoir, the number of Paddlefish counted ranged from 172 to 184. In the river, the number of Paddlefish counted ranged from 165 to 617. The exponential model of distance was most-supported for detection in both environments, except there was support for a half-norm distribution for one reader in the river. In the reservoir, abundance estimates were statistically similar between readers at approximately 1500 (7/ha) in the total scanned area. In the river, similar abundance estimates were obtained with the half-norm model from one reader compared to the exponential model of the other reader, resulting in approximately 1500 individuals (30/ha) in the surveyed area. The application of SSS to count Paddlefish has some clear advantages to traditional methods, such as gill netting, and can be done at multiple times of the year. Distance sampling methods compensated for differences in counts among readers, indicating distance sampling can produce similar abundance estimates even when variation in counts exists among readers.

Oklahoma↗

USGS2011

The contribution of competition to tree mortality in old-growth coniferous forests

Competition is a well-documented contributor to tree mortality in temperate forests, with numerous studies documenting a relationship between tree death and the competitive environment. Models frequently rely on competition as the only non-random mechanism affecting tree mortality. However, for mature forests, competition may cease to be the primary driver of mortality. We use a large, long-term dataset to study the importance of competition in determining tree mortality in old-growth forests on the western slope of the Sierra Nevada of California, U.S.A. We make use of the comparative spatial configuration of dead and live trees, changes in tree spatial pattern through time, and field assessments of contributors to an individual tree's death to quantify competitive effects. Competition was apparently a significant contributor to tree mortality in these forests. Trees that died tended to be in more competitive environments than trees that survived, and suppression frequently appeared as a factor contributing to mortality. On the other hand, based on spatial pattern analyses, only three of 14 plots demonstrated compelling evidence that competition was dominating mortality. Most of the rest of the plots fell within the expectation for random mortality, and three fit neither the random nor the competition model. These results suggest that while competition is often playing a significant role in tree mortality processes in these forests it only infrequently governs those processes. In addition, the field assessments indicated a substantial presence of biotic mortality agents in trees that died. While competition is almost certainly important, demographics in these forests cannot accurately be characterized without a better grasp of other mortality processes. In particular, we likely need a better understanding of biotic agents and their interactions with one another and with competition.

California↗

USGS2020

Carbon stock trends of baldcypress knees along climate gradients of the Mississippi River Alluvial Valley using allometric methods

Carbon stock trends of the knees of Taxodium distichum likely vary across climate gradients of the southeastern United States and contribute an unknown quantity of “teal” carbon to inland freshwater wetlands. Knee metrics (e.g., density, height, biomass) were measured in mixed T. distichum swamps across the Mississippi River Alluvial Valley (MRAV) from Illinois to Louisiana. Based on their geometric similarity to a cone, the biomasses of field knees were estimated by relating the volume of their measured field dimensions to lab-measured water displacement volume and biomass via volume/mass regressions (biomass (g) = 7.2230149 + 0.292902 × volume). Knees had greater height in flooded conditions (maximum height = 163 cm; Goose Lake, Arkansas), and also in climate normal environments of mid-range precipitation and temperature (p < 0.0001). Overall, knee biomass ha−1 was 7.5 times greater in flooded vs. not flooded conditions (34.6 ± 7.3 vs. 4.6 ± 1.0 Mg ha−1, respectively). The overall mean of knee carbon biomass stock was substantial (flooded vs. not flooded conditions: 18.1 ± 3.7 Mg C ha−1 to 2.9 ± 0.7 Mg C ha−1, respectively; knee/tree live standing biomass: 17.9–5.2%, respectively). Clearly, T. distichum knees should not be ignored in blue (teal) carbon discussions of wetlands. Because knees respond to climate normal conditions, hotter/drier environments in the MRAV could lead to a decline in the contribution of knee carbon stock in the southeastern United States.

Mississippi River Alluvial Valley↗

USGS2005

Direct observation of heavy metal-mineral association from the Clark Fork River Superfund Complex: Implications for metal transport and bioavailability

Two sets of samples from riverbeds and adjacent floodplains, separated by 80 river kilometers, were collected from the Clark Fork River Superfund Complex, Montana, (the largest Superfund site in the United States), and studied primarily with transmission electron microscopy (TEM) with several supporting techniques to determine heavy metal-mineral association. Seven of the eight samples studied were strongly influenced by material that once resided in mining and smelting dumps and impoundments; this material was transported downstream sometime during the last century and a half from the Butte/Anaconda areas. The eighth sample was from a deeper floodplain level and dates to premining days. The TEM observations afford a direct look, down to the nanometer level, at secondary mineral formation as a result of the breakdown of sulfides and silicates in the acid environment of this massive mine-drainage system. In the shallow, oxic floodplain sediments, heavy metals of concern in this system (As, Cu, Pb, and Zn) are taken up by the formation of sulfates (particularly Pb in jarosite), as well as hydrous metal oxides (As, Cu, Pb, and Zn in and on ferrihydrite, and a possibly new vernadite-like mineral). The oxides are long-lived in these systems, as they were also found in the anoxic riverbeds. Metals are also taken up by the formation of sulfides in sulfate-reducing environments as observed in the formation of nanoclusters of chalcopyrite and sphalerite. In all samples, clays make up between 5 and 20% of the sediment and carry significant amounts of Cu and Zn. The hydrous oxides, secondary sulfides, and clays provide several routes for metal transport downstream over long distances. Besides the potential bioavailability of heavy metals exchanged on and off the hydrous metal oxides and clays, nanometer-sized sulfides may also be highly reactive in the presence of biologic systems. Copyright ?? 2005 Elsevier Ltd.

Geochimica et Cosmochimica Acta↗

USGS2005

Control of Fe(III) site occupancy on the rate and extent of microbial reduction of Fe(III) in nontronite

A quantitative study was performed to understand how Fe(III) site occupancy controls Fe(III) bioreduction in nontronite by Shewanella putrefaciens CN32. NAu-1 and NAu-2 were nontronites and contained Fe(III) in different structural sites with 16 and 23% total iron (w/w), respectively, with almost all iron as Fe(III). Mo??ssbauer spectroscopy showed that Fe(III) was present in the octahedral site in NAu-1 (with a small amount of goethite), but in both the tetrahedral and the octahedral sites in NAu-2. Mo??ssbauer data further showed that the octahedral Fe(III) in NAu-2 existed in at least two environments- trans (M1) and cis (M2) sites. The microbial Fe(III) reduction in NAu-1 and NAu-2 was studied in batch cultures at a nontronite concentration of 5 mg/mL in bicarbonate buffer with lactate as the electron donor. The unreduced and bioreduced nontronites were characterized by X-ray diffraction (XRD), Mo??ssbauer spectroscopy, and transmission electron microscopy (TEM). In the presence of an electron shuttle, anthraquinone-2,6-disulfonate (AQDS), the extent of bioreduction was 11%-16% for NAu-1 but 28%-32% for NAu-2. The extent of reduction in the absence of AQDS was only 5%-7% for NAu-1 but 14%-18% for NAu-2. The control experiments with heat killed cells and without cells did not show any appreciable reduction (<2%). The extent of reduction in experiments performed with a dialysis membrane to separate cells from clays (without AQDS) was 2%-3% for NAu-1 but 5%-7% for NAu-2, suggesting that cells probably released an electron shuttling compound and/or Fe(III) chelator. The reduction rate was also faster in NAu-2 than that in NAu-1. Mo??ssbauer data of the bioreduced nontronite materials indicated that the Fe(III) reduction in NAu-1 was mostly from the presence of goethite, whereas the reduction in NAu-2 was due to the presence of the tetrahedral and trans-octahedral Fe(III) in the structure. The measured aqueous Fe(II) was negligible. As a result of bioreduction, the average nontronite particle thickness remained nearly the same (from 2.1 to 2.5 nm) for NAu-1, but decreased significantly from 6 to 3.5 nm for NAu-2 with a concomitant change in crystal size distribution. The decrease in crystal size suggests reductive dissolution of nontronite NAu-2, which was supported by aqueous solution chemistry (i.e., aqueous Si). These data suggest that the more extensive Fe(III) bioreduction in NAu-2 was due to the presence of the tetrahedral and the trans-octahedral Fe(III), which was presumed to be more reducible. The biogenic Fe(II) was not associated with biogenic solids or in the aqueous solution. We infer that it may be either adsorbed onto surfaces of nontronite particles/bacteria or in the structure of nontronite. Furthermore, we have demonstrated that natural nontronite clays were capable of supporting cell growth even in medium without added nutrients, possibly due to presence of naturally existing nutrients in the nontronite clays. These results suggest that crystal chemical environment of Fe(III) is an important determinant in controlling the rate and extent of microbial reduction of Fe(III) in nontronite. Copyright ?? 2005 Elsevier Ltd.

Geochimica et Cosmochimica Acta↗

USGS2009

Modeling aluminum-silicon chemistries and application to Australian acidic playa lakes as analogues for Mars

Recent Mars missions have stimulated considerable thinking about the surficial geochemical evolution of Mars. Among the major relevant findings are the presence in Meridiani Planum sediments of the mineral jarosite (a ferric sulfate salt) and related minerals that require formation from an acid-salt brine and oxidizing environment. Similar mineralogies have been observed in acidic saline lake sediments in Western Australia (WA), and these lakes have been proposed as analogues for acidic sedimentary environments on Mars. The prior version of the equilibrium chemical thermodynamic FREZCHEM model lacked Al and Si chemistries that are needed to appropriately model acidic aqueous geochemistries on Earth and Mars. The objectives of this work were to (1) add Al and Si chemistries to the FREZCHEM model, (2) extend these chemistries to low temperatures (<0 ??C), if possible, and (3) use the reformulated model to investigate parallels in the mineral precipitation behavior of acidic Australian lakes and hypothetical Martian brines. FREZCHEM is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach for the temperature range from <-70 to 25 ??C and the pressure range from 1 to 1000 bars. Aluminum chloride and sulfate mineral parameterizations were based on experimental data. Aluminum hydroxide and silicon mineral parameterizations were based on Gibbs free energy and enthalpy data. New aluminum and silicon parameterizations added 12 new aluminum/silicon minerals to this Na-K-Mg-Ca-Fe(II)-Fe(III)-Al-H-Cl-Br-SO 4 -NO 3 -OH-HCO 3 -CO 3 -CO 2 -O 2 -CH 4 -Si-H 2 O system that now contain 95 solid phases. There were similarities, differences, and uncertainties between Australian acidic, saline playa lakes and waters that likely led to the Burns formation salt accumulations on Mars. Both systems are similar in that they are dominated by (1) acidic, saline ground waters and sediments, (2) Ca and/or Mg sulfates, and (3) iron precipitates such as jarosite and hematite. Differences include: (1) the dominance of NaCl in many WA lakes, versus the dominance of Fe-Mg-Ca-SO 4 in Meridiani Planum, (2) excessively low K + concentrations in Meridiani Planum due to jarosite precipitation, (3) higher acid production in the presence of high iron concentrations in Meridiani Planum, and probably lower rates of acid neutralization and hence, higher acidities on Mars owing to colder temperatures, and (4) lateral salt patterns in WA lakes. The WA playa lakes display significant lateral variations in mineralogy and water chemistry over short distances, reflecting the interaction of acid ground waters with neutral to alkaline lake waters derived from ponded surface runoff. Meridiani Planum observations indicate that such lateral variations are much less pronounced, pointing to the dominant influence of ground water chemistry, vertical ground water movements, and aeolian processes on the Martian surface mineralogy. ?? 2009 Elsevier Ltd.

Geochimica et Cosmochimica Acta↗

USGS2010

Microbial carbon cycling in oligotrophic regional aquifers near the Tono Uranium Mine, Japan as inferred from δ13C and Δ14C values of in situ phospholipid fatty acids and carbon sources

Microorganisms are ubiquitous in deep subsurface environments, but their role in the global carbon cycle is not well-understood. The natural abundance δ 13 C and Δ 14 C values of microbial membrane phospholipid fatty acids (PLFAs) were measured and used to assess the carbon sources of bacteria in sedimentary and granitic groundwaters sampled from three boreholes in the vicinity of the Tono Uranium Mine, Gifu, Japan. Sample storage experiments were performed and drill waters analyzed to characterize potential sources of microbial contamination. The most abundant PLFA structures in all waters sampled were 16:0, 16:1ω7 c , cy 17:0, and 18:1ω7 c . A PLFA biomarker for type II methanotrophs, 18:1ω8 c , comprised 3% and 18% of total PLFAs in anoxic sedimentary and granitic waters, respectively, sampled from the KNA-6 borehole. The presence of this biomarker was unexpected given that type II methanotrophs are considered obligate aerobes. However, a bacterium that grows aerobically with CH 4 as the sole energy source and which also produces 56% of its total PLFAs as 18:1ω8 c was isolated from both waters, providing additional evidence for the presence of type II methanotrophs. The Δ 14 C values determined for type II methanotroph PLFAs in the sedimentary (−861‰) and granite (−867‰) waters were very similar to the Δ 14 C values of dissolved inorganic carbon (DIC) in each water (∼−850‰). This suggests that type II methanotrophs ultimately derive all their carbon from inorganic sources, whether directly from DIC and/or from CH 4 produced by the reduction of DIC. In contrast, δ 13 C values of type II PLFAs in the sedimentary (−93‰) and granite (−60‰) waters indicate that these organisms use different carbon assimilation schemes in each environment despite very similar δ 13 C CH 4 "> δ13CCH4 values (∼−95‰) for each water. The δ 13 C PLFA values (−28‰ to −45‰) of non-methanotrophic bacteria in the KNA-6 LTL water do not clearly distinguish between heterotrophic and autotrophic metabolisms, but Δ 14 C PLFA values indicate that >65% of total bacteria filtered from the KNA-6 LTL water are heterotrophs. Ancient Δ 14 C values (∼−1000‰) of some PLFAs suggest that many heterotrophs utilize ancient organic matter, perhaps from lignite seams within the sedimentary rocks. The more negative range of δ 13 C PLFA values determined for the KNA-6 granitic water (−42‰ to −66‰) are likely the result of a microbial ecosystem dominated by chemolithoautotrophy, perhaps fuelled by abiogenic H 2 . Results of sample storage experiments showed substantial shifts in microbial community composition and δ 13 C PLFA values (as much as 5‰) during 2–4 days of dark, refrigerated, aseptic storage. However, water samples collected and immediately filtered back in the lab from freshly drilled MSB-2 borehole appeared to maintain the same relative relationships between δ 13 C PLFA values for sedimentary and granitic host rocks as observed for samples directly filtered under artesian flow from the KNA-6 borehole of the Tono Uranium Mine.

Tono Uranium Mine↗

USGS2015

Beyond temperature: Clumped isotope signatures in dissolved inorganic carbon species and the influence of solution chemistry on carbonate mineral composition

“Clumped-isotope” thermometry is an emerging tool to probe the temperature history of surface and subsurface environments based on measurements of the proportion of 13 C and 18 O isotopes bound to each other within carbonate minerals in 13 C 18 O 16 O 2 2- groups (heavy isotope “clumps”). Although most clumped isotope geothermometry implicitly presumes carbonate crystals have attained lattice equilibrium (i.e., thermodynamic equilibrium for a mineral, which is independent of solution chemistry), several factors other than temperature, including dissolved inorganic carbon (DIC) speciation may influence mineral isotopic signatures. Therefore we used a combination of approaches to understand the potential influence of different variables on the clumped isotope (and oxygen isotope) composition of minerals. We conducted witherite precipitation experiments at a single temperature and at varied pH to empirically determine 13 C- 18 O bond ordering (Δ 47 ) and δ 18 O of CO 3 2- and HCO 3 - molecules at a 25 °C equilibrium. Ab initio cluster models based on density functional theory were used to predict equilibrium 13 C- 18 O bond abundances and δ 18 O of different DIC species and minerals as a function of temperature. Experiments and theory indicate Δ 47 and δ 18 O compositions of CO 3 2- and HCO 3- ions are significantly different from each other. Experiments constrain the Δ 47- δ 18 O slope for a pH effect (0.011 ± 0.001; 12 ⩾ pH ⩾ 7). Rapidly-growing temperate corals exhibit disequilibrium mineral isotopic signatures with a Δ 47- δ 18 O slope of 0.011 ± 0.003, consistent with a pH effect. Our theoretical calculations for carbonate minerals indicate equilibrium lattice calcite values for Δ 47 and δ 18 O are intermediate between HCO 3 − and CO 3 2− . We analyzed synthetic calcites grown at temperatures ranging from 0.5 to 50 °C with and without the enzyme carbonic anhydrase present. This enzyme catalyzes oxygen isotopic exchange between DIC species and is present in many natural systems. The two types of experiments yielded statistically indistinguishable results, and these measurements yield a calibration that overlaps with our theoretical predictions for calcite at equilibrium. The slow-growing Devils Hole calcite exhibits Δ 47 and δ 18 O values consistent with lattice equilibrium. Factors influencing DIC speciation (pH, salinity) and the timescale for DIC equilibration, as well as reactions at the mineral–solution interface, have the potential to influence clumped-isotope signatures and the δ 18 O of carbonate minerals. In fast-growing carbonate minerals, solution chemistry may be an important factor, particularly over extremes of pH and salinity. If a crystal grows too rapidly to reach an internal equilibrium (i.e., achieve the value for the temperature-dependent mineral lattice equilibrium), it may record the clumped-isotope signature of a DIC species (e.g., the temperature-dependent equilibrium of HCO 3 − ) or a mixture of DIC species, and hence record a disequilibrium mineral composition. For extremely slow-growing crystals, and for rapidly-grown samples grown at a pH where HCO 3 - dominates the DIC pool at equilibrium, effects of solution chemistry are likely to be relatively small or negligible. In summary, growth environment, solution chemistry, surface equilibria, and precipitation rate may all play a role in dictating whether a crystal achieves equilibrium or disequilibrium clumped-isotope signatures.

Geochimica et Cosmochimica Acta↗

USGS2019

Effects of organic ligands and background electrolytes on barite dissolution

Barite dissolution rates and features were investigated under conditions that combine a variety of organic ligands with different background electrolyte solutions. The organic ligands included low molecular weight organic compounds (LMWO) that can be produced by halophilic bacteria and are common in natural environments, as well as synthetic chelators that were previously studied in barite dissolution. Background electrolyte solutions included deionized water, 0.72 M NaCl and 2 M NaCl solutions designed to simulate freshwater, seawater, and brine fluids, respectively. Barite dissolution rates and corresponding rate constants normalized for saturation states were calculated for most experiments. Equal or lower rates and rate constants for pure LMWO relative to controls at all background electrolyte concentrations and pH values indicated that LMWO do not promote barite dissolution. Synthetic chelators showed higher rates and rate constants at pH 10 at static conditions than controls, indicating enhanced barite dissolution. Distinctive etch pit morphologies on the barite (0 0 1) face were observed in the presence of synthetic chelators, suggesting a direct contact dissolution mechanism by synthetic chelators. The effect of synthetic chelators on barite dissolution was significantly reduced in the presence of 2 M NaCl and/or at pH 6.5 due to salting out effects. Under hypersaline conditions, barite dissolution rates and rate constants by bacterial activities were up to four times higher than those of synthetic chelators. The wide range of conditions studied in this work provides insights into prediction of barite dissolution behavior in various natural environments as well as in industrial treatment procedures.

Geochimica et Cosmochimica Acta↗

USGS2023

Intramolecular carbon isotope geochemistry of butane isomers from laboratory maturation and Monte-Carlo simulations of kerogen types I, II, and III

Position-specific (PS) carbon isotope compositions of light hydrocarbons such as propane and butane isomers (n-butane and i-butane) can provide a wealth of information on the history of natural gases in the subsurface reservoirs and other environments. For PS carbon isotope analysis of butane isomers, we have established a GC-pyrolysis-GC-isotope ratio mass spectrometry method with demonstrated accuracy. With this method, we analyzed PS δ 13 C values of butane isomers generated from the systematic laboratory pyrolysis experiments of three different kerogen types (I, II, and III) at temperatures of 310–430 °C with corresponding thermal maturity (Easy %R o ) ranging from 0.7 to 3.3. The observed evolution in the abundances of butane isomers can be interpreted and semi-quantitatively modeled based on the abundances of different C C bonds within the kerogens at low maturity and thermal degradation of butane isomers at high maturity. The δ 13 C values at the central sites of both nC 4 and iC 4 were heavier than those at the terminal positions, similar to our previous observations of propane. Their isotopic evolution with the maturity were controlled largely by kinetic isotope effects associated with breaking of different C C bonds during the generation and degradation of butane isomers. Kinetic Monte Carlo (kMC) simulations of n-butane generated from thermal cracking of model kerogens (I, II, and III) and an oil with a series of reactions (homolytic cleavage, β-scission, radical isomerization, H-abstraction, and termination by radical recombination) provided generally consistent results with the experimental observations, although the difference in PS δ 13 C values between the central and terminal positions are somewhat overestimated. On the other hand, the kMC simulation with homolytic cleavage and capping reactions alone produced significant deviations from the experimental results. Re-assessment of very limited data of PS δ 13 C values of natural butanes with our experimental and simulation results show that biodegradation significantly increased δ 13 C values at the central positions, not only of propane, but also of both butane isomers. This study lays a foundation and demonstrates the potential of PS isotope geochemistry of butane isomers to further improve our understanding of the sources, and geochemical and microbial processes of light hydrocarbons in the subsurface and other natural environments.

Geochimica et Cosmochimica Acta↗

USGS2020

Movements and habitat use of loons for assessment of conservation buffer zones in the Arctic Coastal Plain of northern Alaska

Oil and gas development in the Arctic Coastal Plain, Alaska, may pose threats to wildlife. Management guidelines within the National Petroleum Reserve-Alaska dictate buffer zones for coastal wildlife habitat and for breeding and foraging sites of yellow-billed loons (YBLOs; Gavia adamsii), a species of conservation concern. However, few data exist to assess the value of these buffer zones for YBLOs or for sympatrically breeding red-throated loons (RTLOs; G. stellata) and Pacific loons (PALOs; G. pacifica). We evaluated movements of these loons on the Arctic Coastal Plain to understand: 1) seasonal timing; 2) marine habitat use; and 3) spatial characteristics of breeding home ranges. We then used those findings to evaluate current management strategies in the context of loon biology. Compared to RTLOs and PALOs, YBLOs nested on larger lakes, stayed on them longer, had larger home ranges, but less frequently used the marine environment in summer. During autumn, YBLOs and PALOs were located farther from shore than during spring or summer, whereas RTLOs used the marine environment similarly during all three seasons. Management buffers established for YBLO nesting areas corresponded well with nest site space use of all three species, suggesting cross-taxa applicability of current management guidelines for nesting habitat. However, the majority of loon locations on the Arctic Coastal Plain were outside of coastal buffer zones established to protect fish and wildlife habitat within the National Petroleum Reserve-Alaska. These findings can inform assessment of conservation buffer zones to mitigate anthropogenic disturbance to loons in Alaska.

Alaska↗

USGS2005

Animating the biodynamics of soil thickness using process vector analysis: A dynamic denudation approach to soil formation

This paper expands the dynamic denudation framework of landscape evolution by providing new process insights and details on how soil and its signature morphological feature, the biomantle, form and function in the environment. We examine soils and their biomantles from disparate parts of the world, from the tropics through midlatitudes and hyperarid through perhumid, a range that exhibits varying environments for, and of, life. We then explicate the process pathways that cause soils to thicken and thin, and to even disappear, then reform. We do this by examining thickness relationships, where soil thickness stand biomantle thickness bt are functions of upbuilding u and deepening d minus removal r processes, hence st/bt=f(u+d-r). Upbuilding has two subsets, u1, which includes all exogenous (allochthonous-outside) mineral and/or organic inputs to the soil system, and u2, which includes all endogenous (autochthonous-in situ) processes and productions, including weathering. Exogenous u1 inputs include eolian and slopewash inputs (sedimentations) of mineral and organic materials, mass wasting accumulations and the like. Endogenous u2 processes and productions include the sum of in situ bioturbations, biosynthetic productions, organic accumulations, biovoid productions, weathering and volume increases caused by their sum. Endogenous upbuildings, which dominantly occur in the biomantle, are basically biodynamic bd processes and productions, hence u2=bd. Therefore, if exogenous upbuildings u1 are minimal or zero, then biomantle thickness bt is expressed by bt=f(u2-r) or bt=f(bd-r). Drawing on these relationships, we employ a graphic-conceptual device called process vector analysis in a digital animation (see supplementary materials or cf. https://netfiles.uiuc.edu/jdomier/www/temp/ biomantle.html) that illustrates the main pathways that form both Earth's soil and its unique epidermis, the biomantle. We then discuss the main elements of the animation using still frames that represent thickness turning points. We end by encouraging researchers, instructors and students to view Earth's landforms and soils as integrated dynamic entities that are constantly coevolving elements of a global subaerial-subaqueous continuum. ?? 2004 Elsevier B.V. All rights reserved.

Geomorphology↗

USGS2011

Hillslope chemical weathering across Paraná, Brazil: a data mining-GIS hybrid approach

Self-organizing map (SOM) and geographic information system (GIS) models were used to investigate the nonlinear relationships associated with geochemical weathering processes at local (~100 km 2 ) and regional (~50,000 km 2 ) scales. The data set consisted of 1) 22 B-horizon soil variables: P, C, pH, Al, total acidity, Ca, Mg, K, total cation exchange capacity, sum of exchangeable bases, base saturation, Cu, Zn, Fe, B, S, Mn, gammaspectrometry (total count, potassium, thorium, and uranium) and magnetic susceptibility measures; and 2) six topographic variables: elevation, slope, aspect, hydrological accumulated flux, horizontal curvature and vertical curvature. It is characterized at 304 locations from a quasi-regular grid spaced about 24 km across the state of Paraná. This data base was split into two subsets: one for analysis and modeling (274 samples) and the other for validation (30 samples) purposes. The self-organizing map and clustering methods were used to identify and classify the relations among solid-phase chemical element concentrations and GIS derived topographic models. The correlation between elevation and k-means clusters related the relative position inside hydrologic macro basins, which was interpreted as an expression of the weathering process reaching a steady-state condition at the regional scale. Locally, the chemical element concentrations were related to the vertical curvature representing concave–convex hillslope features, where concave hillslopes with convergent flux tends to be a reducing environment and convex hillslopes with divergent flux, oxidizing environments. Stochastic cross validation demonstrated that the SOM produced unbiased classifications and quantified the relative amount of uncertainty in predictions. This work strengthens the hypothesis that, at B-horizon steady-state conditions, the terrain morphometry were linked with the soil geochemical weathering in a two-way dependent process: the topographic relief was a factor on environmental geochemistry while chemical weathering was for terrain feature delineation.

Parana↗

USGS2015

Plugs or flood-makers? the unstable landslide dams of eastern Oregon

Landslides into valley bottoms can affect longitudinal profiles of rivers, thereby influencing landscape evolution through base-level changes. Large landslides can hinder river incision by temporarily damming rivers, but catastrophic failure of landslide dams may generate large floods that could promote incision. Dam stability therefore strongly modulates the effects of landslide dams and might be expected to vary among geologic settings. Here, we investigate the morphometry, stability, and effects on adjacent channel profiles of 17 former and current landslide dams in eastern Oregon. Data on landslide dam dimensions, former impoundment size, and longitudinal profile form were obtained from digital elevation data constrained by field observations and aerial imagery; while evidence for catastrophic dam breaching was assessed in the field. The dry, primarily extensional terrain of low-gradient volcanic tablelands and basins contrasts with the tectonically active, mountainous landscapes more commonly associated with large landslides. All but one of the eastern Oregon landslide dams are ancient (likely of order 10 3 to 10 4 years old), and all but one has been breached. The portions of the Oregon landslide dams blocking channels are small relative to the area of their source landslide complexes (0.4–33.6 km 2 ). The multipronged landslides in eastern Oregon produce marginally smaller volume dams but affect much larger channels and impound more water than do landslide dams in mountainous settings. As a result, at least 14 of the 17 (82%) large landslide dams in our study area appear to have failed cataclysmically, producing large downstream floods now marked by boulder outwash, compared to a 40–70% failure rate for landslide dams in steep mountain environments. Morphometric indices of landslide dam stability calibrated in other environments were applied to the Oregon dams. Threshold values of the Blockage and Dimensionless Blockage Indices calibrated to worldwide data sets successfully separate dam sites in eastern Oregon that failed catastrophically from those that did not. Accumulated sediments upstream of about 50% of the dam sites indicate at least short-term persistence of landslide dams prior to eventual failure. Nevertheless, only three landslide dam remnants and one extant dam significantly elevate the modern river profile. We conclude that eastern Oregon's landslide dams are indeed floodmakers, but we lack clear evidence that they form lasting plugs.

Oregon↗

USGS2022

Tracking geomorphic changes after suburban development with a high density of green stormwater infrastructure practices in Montgomery County, Maryland

Stream morphology is affected by changes on the surrounding landscape. Understanding the effects of urbanization on stream morphology is a critical factor for land managers to maintain and improve vulnerable stream corridors in urbanizing landscapes. Stormwater practices are used in urban landscapes to manage runoff volumes and peak flows, potentially mitigating alterations to the flow regime that drive changes in channel morphology. However, there remains a paucity of long-term studies assessing watershed-scale relationships between urbanization and effects on stream morphology where green stormwater infrastructure exists in high densities. This paper evaluates the geomorphic changes across four headwater catchments in the Chesapeake Bay Watershed over the course of >10 yr and relates these changes to urban development. Annual cross-sectional surveys conducted from 2002 to 2019 in one forested catchment, one agricultural catchment, and two treatment catchments were used to understand the relationship between urbanization and changes in stream morphology. Six cross-sectional geomorphic metrics were calculated and compared with development timelines and high flow events. A channel evolution model was then used to understand the status of morphologic stability at sites within the study. Results suggest downstream environments in developing areas are more impacted during early phases of suburban construction. Channel change during construction could be a result of sediment and erosion control efforts' limitations on preventing and controlling overland sediment mobilization or of increased discharge causing widening and thus bank-derived sediment to move to the streambed. Results demonstrate that geomorphic metrics are highly variable within a small area and are not always accurate representations of broader landscape changes but rather of the more localized environment at a specific stream segment. Despite a high density of stormwater management facilities in urban catchments, substantial alterations to cross sections were found at multiple locations in each catchment including the controls.

Maryland↗

USGS2021

Acute oral toxicity and tissue residues of saxitoxin in the mallard (Anas platyrhynchos)

Since 2014, widespread, annual mortality events involving multiple species of seabirds have occurred in the Gulf of Alaska, Bering Sea, and Chukchi Sea. Among these die-offs, emaciation was a common finding with starvation often identified as the cause of death. However, saxitoxin (STX) was detected in many carcasses, indicating exposure of these seabirds to STX in the marine environment. Few data are available that describe the effects of STX in birds, thus presenting challenges for determining its contributions to specific mortality events. To address these knowledge gaps, we conducted an acute oral toxicity trial in mallards ( Anas platyrhynchos ), a common laboratory avian model, using an up-and-down method to estimate the median lethal dose (LD 50 ) for STX. Using an enzyme-linked immunosorbent assay (ELISA), we tested select tissues from all birds and feces from those individuals that survived initial dosing. Samples with an ELISA result that exceeded approximately 10 µg 100 g −1 STX and randomly selected ELISA negative samples were further tested by high-performance liquid chromatography (HPLC). Tissues collected from mallards were also examined grossly at necropsy and then later by microscopy to identify lesions attributable to STX. The estimated LD 50 was 167 µg kg −1 (95% CI = 69–275 µg kg −1 ). Saxitoxin was detected in fecal samples of all mallards tested for up to 48 h after dosing and at the end of the sampling period (7 d) in three birds. In those individuals that died or were euthanized <2 h after dosing, STX was readily detected throughout the gastrointestinal tract but only infrequently in heart, kidney, liver, lung, and breast muscle. No gross or microscopic lesions were observed that could be attributable to STX exposure. Given its acute toxicity, limited detectability, and frequent occurrence in the Alaska marine environment, additional research on STX in seabirds is warranted.

Harmful Algae↗