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The shortgrass steppe is a semi-arid grassland, where elevated CO2 reduces stomatal conductance and promotes soil moisture storage. Enhanced biomass growth from elevated CO2 has been attributed in part to soil moisture effects. However, the influence of this soil moisture feedback on C cycling has received little attention. We used open-top chambers to increase atmospheric CO2 concentrations to twice-ambient for four growing seasons. Soil respiration rates and stable C isotopes of soil CO2 were measured during the third and fourth seasons. Elevated CO2 increased soil respiration rates by ?25% in a moist growing season and by ?85% in a dry season. Stable C isotope partitioning of soil respiration into its components...
Mining activities are a major source of land degradation in arid regions, and remediation methods developed for mesic sites may not be appropriate for arid sites. In climates where potential evapotranspiration exceeds precipitation, it might be possible to prevent the migration of contaminants away from a mine site by controlling the site water balance through vegetation, and allowing natural attenuation processes to reduce pollutant levels over time. We investigated the feasibility of remediating a nitrate-contaminated source-plume system in a desert environment using biological methods. The study site was a former uranium mill in Monument Valley, Arizona, where NO3? used in ore processing had leaked from the soil...
New paleomagnetic and stable isotopic results from the northeastern margin of the greater Green River Basin (South Pass, Wyoming) provide a refined geochronological context for the Wasatchian/Bridgerian Land Mammal Age boundary and suggest the existence of large amplitude Milankovich-scale carbon and oxygen isotopic oscillations in this area during the early Eocene. Analysis of 55 paleomagnetic sites through a 310 m section of Wasatch, Green River, and Bridger Formations indicates several reversals that can be correlated to the Geomagnetic Polarity Time Scale using radiometric age constraints. This correlation places the Wasatchian/Bridgerian boundary in Chron C23r at about 52 Ma, approximately two million years...
Anthropogenic activity is causing dramatic changes in the nitrogen (N) cycle in many ecosystems. Most research has focused on the increase in N input caused by atmospheric deposition and invasion of N-fixing species, and on their effects on resource availability and species composition. However, in contrast to many ecosystems experiencing large increases in N input, many arid ecosystems are experiencing loss of nutrients due to land-use change. An important component of many arid ecosystems on a worldwide basis is the microbiotic crust, a biological soil crust composed of lichens, cyanobacteria, mosses, and algae. Nitrogen fixation by lichens and cyanobacteria comprising the crust is the primary source of N input...
We propose a framework for hypothesis-testing of stable isotope ratios in ecological studies. Statistical procedures are based on analysis of nested linear models and a residual permutation procedure (RPP) that is employed to evaluate probabilities associated with test statistics. We used simulated examples and a real data set to illustrate the utility and generality of the method. First, we developed a test for differences in centroid location and dispersion of delta13C and delta15N values within and among groups of isotopic data. Second, we evaluated magnitude and direction of change in centroid position (termed "path") of a pair of isotopic samples separated in space/time relative to paths of other paired sample...
Spatial patterns of resource use by small-bodied fishes in the San Juan River were examined using stable isotopes. Using δ15N of fishes as an index of trophic position, our data suggest both native and non-native fishes primarily consumed macro-invertebrates. The δ13C of these fishes further suggested a detritus-based food web, from which most species fed on chironomids in low-velocity habitats. A two-way ANOVA revealed a significant interaction between trophic level of fish species and longitudinal position in the river. This interaction was primarily attributed to a decline in trophic level of non-native red shiner Cyprinella lutrensis, relative to other species, in upstream reaches of the river. In addition,...
Summary Drainage tiles buried beneath many naturally poorly drained agricultural fields in the Midwestern U.S. are believed to “short circuit” pools of NO 3 - -laden soil water and shallow groundwater directly into streams that eventually discharge to the Mississippi River. Although much is known about the mechanisms controlling this regionally pervasive practice of artificial drainage at the field-plot scale, an integrative assessment of the effect of drainage density (i.e., the number of tile drains per unit area) on the transport of nutrients and solutes in streams at the catchment scale is lacking. In this study, we quantified the flux and hydrological pathways of agricultural NO 3 - and road-salt Cl− from catchments...
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Data set includes water Sr:Ca, Ba:Ca, and δ18O for the Mississippi River and tributaries, and otolith Sr:Ca, Ba:Ca, and δ18O data from bigheaded carp (Silver Carp and BIghead Carp) collected in navigation pools 16-19 of the Upper Mississippi River in 2016 to 2018. Bigheaded carp (Bighead Carp and Silver Carp) are invasive species in the US and have spread throughout most of the lower Mississippi River Basin. Population abundance upstream of Lock and Dam 19 (LD19) on the Upper Mississippi River (UMR) has likely been limited by the high-head dam at this location, which restricts all upstream fish passage to the lock chamber. To determine early-life environments of adult bigheaded carp captured upstream LD19 at the...
This dataset contains carbon (δ13C) and nitrogen (δ15N) isotope values, and C:N ratios, from eggshell tissue samples of Arctic terns (Sterna paradisaea), Common terns (S. hirundo), and Roseate terns (S. dougalii) nesting on seven islands located along the coast of Maine in 2016, 2017, and 2018.
In desert ecosystems a large proportion of water and nitrogen is supplied in rain-induced pulses. It has been suggested that competitive interactions among desert plants would be most intense during these pulse periods of high resource availability. We tested this hypothesis with three cold desert shrub species of the Colorado Plateau (Gutierrezia sarothrae, Atriplex confertifolia, and Chrysothamnus nauseosus), which differ in their distribution of functional roots. In a three-year field study we conducted a neighbor removal experiment in conjunction with simulated 25-mm precipitation events and the addition of a nitrogen pulse in either spring or summer. We measured predawn water potential (?), gas exchange, leaf...
The Summitville Au?Ag?Cu deposit is a classic volcanic dome-hosted high-sulfidation deposit. It occurs in the Quartz Latite of South Mountain, a composite volcanic dome that was emplaced along the coincident margins of the Platoro and Summitville calderas at 22.5�0.5 Ma, penecontemporaneous with alteration and mineralization. A penecontemporaneous quartz monzonite porphyry intrusion underlies the district and is cut and overlain by pyrite?quartz stockwork veins with traces of chalcopyrite and molybdenite. Alteration and mineralization proceeded through three hypogene stages and a supergene stage, punctuated by at least three periods of hydrothermal brecciation. Intense acid leaching along fractures in the quartz...
We used dual labelled stable isotope (13C and 15N) techniques to examine how grassland plant species with different growth strategies vary in their ability to compete with soil microbes for different chemical forms of nitrogen (N), both inorganic and organic. We also tested whether some plant species might avoid competition by preferentially using different chemical forms of N than microbes. This was tested in a pot experiment where monocultures of five co-existing grassland species, namely the grasses Agrostis capillaris, Anthoxanthum odoratum, Nardus stricta, Deschampsia flexuosa and the herb Rumex acetosella, were grown in field soil from an acid semi-natural temperate grassland. Our data show that grassland...
Organic carbon (C) and nitrogen (N) are essential for heterotrophic soil microorganisms, and their bioavailability strongly influences ecosystem C and N cycling. We show here that the natural (15)N abundance of the soil microbial biomass is affected by both the availability of C and N and ecosystem N processing. Microbial (15)N enrichment correlated negatively with the C : N ratio of the soil soluble fraction and positively with net N mineralization for ecosystems spanning semiarid, temperate and tropical climates, grassland and forests, and over four million years of ecosystem development. In addition, during soil incubation, large increases in microbial (15)N enrichment corresponded to high net N mineralization...
The mobility and bioavailability of Se depend on its redox state, and reduction of Se oxyanions to less mobile, reduced species controls transport of this potentially toxic element in the environment. Stable isotope fractionation of Se is currently being developed as an indicator of Se immobilization through reduction. In this study, Se isotope fractionation resulting from reduction of Se(VI) and Se(IV) oxyanions by natural microbial consortia was measured in sediment slurry experiments under nearly natural conditions, with no substrate added. Experiments were conducted with a wide range of initial Se concentrations and with sediment and water from three locations with contrasting environmental settings. The products...
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A discrete sample introduction module (DSIM) was developed and interfaced to a cavity ring-down spectrometer to enable measurements of methane and CO2 concentrations and 13C values with a commercially available cavity ring-down spectrometer (CRDS). The DSIM-CRDS system permits the analysis of limited volume (5 - 100-ml) samples ranging six orders-of-magnitude from 100% analyte to the lower limit of instrument detection (2 ppm). We demonstrate system performance for methane by comparing concentrations and 13C results obtained by the DSIM and traditional methods for a variety of sample types, including low concentration (nanomolar) seawater and high concentration (> 90%) natural gas. The expansive concentration range...
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Despite being one of the most prevalent forms of consumerism in ecological communities, parasitism has largely been excluded from food-web models. Stable isotope analysis of consumers and their diets has been widely used in the study of food-webs for decades. However, the amount of information regarding parasite stable isotope ecology is limited, restricting the ability of ecologists to use stable isotope analysis to study parasites in food-webs. This study took advantage of distinct differences in the feeding ecology and trophic position of different species of fish known to host the same common micropredatory gnathiid isopod, to study the effects of host stable isotope ecology on that of the associated micropredator....
The growing awareness that plants might use a variety of nitrogen (N) forms, both organic and inorganic, has raised questions about the role of resource partitioning in plant communities. It has been proposed that coexisting plant species might be able to partition a limited N pool, thereby avoiding competition for resources, through the uptake of different chemical forms of N. In this study, we used in situ stable isotope labeling techniques to assess whether coexisting plant species of a temperate grassland (England, UK) display preferences for different chemical forms of N, including inorganic N and a range of amino acids of varying complexity. We also tested whether plants and soil microbes differ in their preference...
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Populus fremontii (Fremont cottonwood) was once a dominant species in desert riparian forests but has been increasingly replaced by the exotic invasive Tamarix ramosissima (saltcedar). Interspecific competition, reduced flooding frequency, and increased salinity have been implicated in the widespread decline of P. fremontii. To elucidate some of the multiple and interacting mechanisms of this decline, we examined ecological processes in a control stand of P. fremontii along the Colorado River in Utah, USA, as well as a disturbed stand characterized by high groundwater salinity and invasion of T. ramosissima. Sap flux data showed that P. fremontii at the saline site experienced large reductions in afternoon canopy...
map background search result map search result map Elevated atmospheric CO 2 effects and soil water feedbacks on soil respiration components in a Colorado grassland Ecohydrology in a Colorado River riparian forest: implications for the decline of Populus fremontii Data for Analysis of Endocrine Disrupting Compounds in Lake Mead National Recreation Area near Las Vegas, Nevada Host feeding ecology and trophic position significantly influence isotopic discrimination between a generalist ectoparasite and its hosts: implications for parasite-host trophic studies Pre-breeding foraging ecology of three tern species nesting in the Gulf of Maine Otolith microchemistry of adult bigheaded carp for determining early-life environments in the Upper Mississippi River 2016-2018 Comparison of methane concentration and stable carbon isotope data for natural samples analyzed by discrete sample introduction module - cavity ring down spectroscopy (DSIM-CRDS) and traditional methods Nearshore Fish Isotope Values, Beaufort Sea, Alaska, 2017-2019 Ecohydrology in a Colorado River riparian forest: implications for the decline of Populus fremontii Host feeding ecology and trophic position significantly influence isotopic discrimination between a generalist ectoparasite and its hosts: implications for parasite-host trophic studies Elevated atmospheric CO 2 effects and soil water feedbacks on soil respiration components in a Colorado grassland Otolith microchemistry of adult bigheaded carp for determining early-life environments in the Upper Mississippi River 2016-2018 Data for Analysis of Endocrine Disrupting Compounds in Lake Mead National Recreation Area near Las Vegas, Nevada Nearshore Fish Isotope Values, Beaufort Sea, Alaska, 2017-2019 Pre-breeding foraging ecology of three tern species nesting in the Gulf of Maine Comparison of methane concentration and stable carbon isotope data for natural samples analyzed by discrete sample introduction module - cavity ring down spectroscopy (DSIM-CRDS) and traditional methods