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The Reaction-Transport Modeling Group provides environmental managers and policy makers with the understanding and tools needed to predict how decisions made today can improve the amount of clean water available to both society and to nature in the future. In support of the project goals, I have developed the Water, Energy, and Biogeochemical Model (WEBMOD). WEBMOD integrates the latest understanding of hydrologic processes with the full gamut of geochemical simulations available in PHREEQC to simulate conservative and reactive transport of solutes that cycle between the atmosphere, the soils, and bedrock.
The soil emission rates (fluxes) of nitrous oxide (N2O) and nitrogen oxides (NO + NO2 = NOx) through a seasonal snowpack were determined by a flux gradient method from near-continuous 2-year measurements using an automated system for sampling interstitial air at various heights within the snowpack from a subalpine site at Niwot Ridge, Colorado. The winter seasonal-averaged N2O fluxes of 0.047-0.069 nmol m-2 s-1 were ~15 times higher than observed NOx fluxes of 0.0030-0.0067 nmol m-2 s-1. During spring N2O emissions first peaked and then dropped sharply as the soil water content increased from the release of snowpack meltwater, while other gases, including NOx and CO2 did not show this behavior. To compare and contrast...
This paper discusses the important limitations in several areas of element interaction research and highlights the discrepancies between model formulations and observable ecosystem properties, including carbon dynamics in soils and element ratios and threshold effects. Some difficulties in sampling of individual species within microbial communities and in determining the flexibility of microbial stoichiometry are discussed. Also covered are the new approaches and recent advancements in element cycling research, e.g., resolving the chemical identity of element observations, element analysis for individuals and species, and scaling element interactions from sites to regions. Finally, some elements of a proposed experimental...
Laboratory incubations of15N-amended soils from a sagebrush steppe in south-central Wyoming indicate that nutrient turnover and availability have complex patterns across the landscape and between microsites. Total and available N and P and microbial C and N were highest in topographic depressions characterized by tall shrub communities. Net and gross N mineralization rates and respiration were also highest in these areas, but microbial efficiencies expressing growth relative to respiration cost were highest in soils of exposed ridgetop sites (prostrate shrub communities). Similar patterns occurred between shrub and intershrub soils, with greater nutrient availability under shrubs, but lower microbial efficiencies...
Reactive solute transport models are useful tools for analyzing complex geochemical behavior resulting from biodegradation of organic compounds by multiple terminal electron acceptors (TEAPs). The usual approach of simulating the reactions of multiple TEAPs by an irreversible Monod rate law was compared with simulations that assumed a partial local equilibrium or kinetically controlled reactions subject to the requirement that the Gibbs free energy of reaction (ΔG) was either less than zero or less than a threshold value. Simulations were performed using a single organic substrate and O2, FeOOH, SO4−2 and CO2 as the terminal electron acceptors. It was assumed that the organic substrate was slowly and completely...
Geochemical mass balances were computed for water years 1992–1997 (October 1991 through September 1997) for the five watersheds of the U.S. Geological Survey Water, Energy, and Biogeochemical Budgets (WEBB) Program to determine the primary regional controls on yields of the major dissolved inorganic solutes. The sites, which vary markedly with respect to climate, geology, physiography, and ecology, are: Allequash Creek, Wisconsin (low-relief, humid continental forest); Andrews Creek, Colorado (cold alpine, taiga/tundra, and subalpine boreal forest); Río Icacos, Puerto Rico (lower montane, wet tropical forest); Panola Mountain, Georgia (humid subtropical piedmont forest); and Sleepers River, Vermont (humid northern...
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Our research focuses on assessing the components of the Net Ecoystem Carbon Balance using the eddy covariance approach to measure atmospheric fluxes of heat, energy, carbon dioxide and methane and testing equipment and techniques to measure the tidal exchange of dissolved organic (DOC) and inorganic carbon (DIC). The atmospheric flux tower is located south of Solano Land Trust's Rush Ranch, a working ranch encompassing 2,070 acres of marsh and rolling grasslands that provides both recreational and educational experiences for the public (http://www.solanolandtrust.org/RushRanch.aspx). Lateral fluxes are being collected at the San Francisco Bay National Estuarine Research Reserve First Mallard water quality station...
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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...
This report describes the progress made by the Integrated Ecosystem Model (IEM) for Alaska and Northwest Canada Project for the full duration of the project (September 1, 2011 through August 31, 2016).This primary goal in this project was to develop the IEM modeling framework to integrate the driving components for and the interactions among disturbance regimes, permafrost dynamics, hydrology, and vegetation succession/migration for Alaska and Northwest Canada. The major activities of the project include (1) development and delivery of input data sets, (2) model coupling, (3) evaluation and applications of fire and vegetation dynamics, (4) evaluation and application of ecosystem carbon and energy balance, (5) evaluation...
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In order to determine the effect of increased nitrogen inputs on fluxed of N2O and CH4 from alpine soils, we measured fluxes of these gases from fertilized and unfertilized soils in wet and dry alpine meadows. In the dry meadow, the addition of nitrogen resulted in a 22-fold increase in N2O emissions, while in the wet meadow, we observed a 45-fold increase in N2O emission rates. CH4 uptake in the dry meadow was reduced 52% by fertilization; however, net CH4 production occurred in all the wet meadow plots and emission rates were not significantly affected by fertilization. Net nitrification rates in the dry meadow were higher in fertilized plots than in non-fertilized plots throughout the growing season; net mineralization...
Abstract (from http://www.nature.com/nature/journal/v520/n7546/full/nature14338.html): Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to...
We investigated the relationship between plant nitrogen limitation and water availability in dryland ecosystems. We tested the hypothesis that at lower levels of annual precipitation, aboveground net primary productivity (ANPP) is limited primarily by water whereas at higher levels of precipitation, it is limited primarily by nitrogen. Using a literature survey of fertilization experiments in arid, semi-arid, and subhumid ecosystems, we investigated the response of ANPP to nitrogen addition as a function of variation in precipitation across geographic gradients, as well as across year-to-year variation in precipitation within sites. We used four different indices to assess the degree of N limitation: (1) Absolute...
Roots influence root litter decomposition through multiple belowground processes. Hydraulic lift or redistribution (HR) by plants is one such process that creates diel drying?rewetting cycles in soil. However, it is unclear if this phenomenon influences decomposition. Since decomposition in deserts is constrained by low soil moisture and is stimulated when dry soils are rewetted, we hypothesized that diel drying?rewetting, via HR, stimulates decomposition of root litter. We quantified the decomposition of root litter from two desert shrubs, Artemisia tridentata ssp. tridentata and Sarcobatus vermiculatus, during spring and summer in field soil core treatments designed to have abundant roots and high magnitude HR...
Patterns and processes involved in litter breakdown on desert river floodplains are not well understood. We used leafpacks containing Fremont cottonwood (Populus deltoides subsp. wislizenii) leaf litter to investigate the roles of weather and microclimate, flooding (immersion), and macroinvertebrates on litter organic matter (OM) and nitrogen (N) loss on a floodplain in a cool-temperate semi-arid environment (Yampa River, northwestern Colorado, USA). Total mass of N in fresh autumn litter fell by 20% over winter and spring, but in most cases there was no further N loss prior to termination of the study after 653 days exposure, including up to 20 days immersion during the spring flood pulse. Final OM mass was 10?40%...
A number of studies have shown that dust delivers essential nutrients that sustain terrestrial productivity over millennia. Dust, however, contains a range of elements ranging from base cations, N and P, to heavy metals. Some of these elements will stimulate primary productivity over the time scale of soil development while others, such as metals, could inhibit biological activity. As dust accumulates, it also influences water flux and availability by altering soil texture. We are examining the ecological impacts of dust accumulation in Canyonlands National Park in Utah. Using magnetic susceptibility as a proxy for far-traveled dust, we have established transects in sandy surficial deposits (50-90% sand) in which...
My primary objective is to characterize the hydrology and water chemistry of watersheds and how they are affected by both natural factors and disturbance. I study the role of precipitation type, intensity, and spatial distribution in driving runoff and transport of sediment, carbon, nutrients, and major ions in both disturbed and undisturbed sites. My research incorporates field research and existing climate, hydrologic, and water-quality data to distinguish between the roles of climate, land-cover change, and disturbance in driving watershed processes. I strive to communicate research findings to scientists, regulators, and the public in order to support the management of water resources.
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The dataset documents the spatial and temporal variability of nutrients and related water quality parameters at high spatial resolution in the North Delta, Central Delta, and the Western Delta out to Suisun Bay in the Sacramento-San Joaquin River Delta of California, USA. The dataset includes nitrate, ammonium, phosphate, dissolved organic carbon, temperature, conductivity, dissolved oxygen, and chlorophyll as well as information about phytoplankton community composition. Data-collection cruises were conducted under three different environmental/flow conditions in May, July, and October of 2018. The data release consists of a xml document, 13 text/csv documents, and a zip file. Descriptions for each document and...
Abstract (from http://link.springer.com/article/10.1007/s10021-014-9777-1): The Coast Mountains of southeast Alaska are currently experiencing some of the highest rates of glacier volume loss on Earth, with unknown implications for proglacial stream biogeochemistry. We analyzed streamwater for δ18O and dissolved organic matter (DOM) biogeochemistry (concentration, δ13C-dissolved organic carbon (DOC), and fluorescence characterization) during the 2012 glacial runoff season from three coastal watersheds in southeast Alaska that ranged in glacier coverage from 0 to 49% and a glacier outflow stream. Our goal was to assess how DOM biogeochemistry may change as receding glaciers are replaced by forests and glaciers contribute...
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The Hells Canyon Complex (HCC) is comprised of a series of three consecutive reservoirs (Brownlee, Oxbow, and Hells Canyon) along a 145 km reach of the Snake River bordered by Idaho to the east and Oregon to the west. Due to concerns regarding mercury (Hg) contamination within the HCC, in cooperation with Idaho Power Company, the U.S. Geological Survey has been leading an investigation into the sources, transport, microbial transformations, chemical speciation and bioaccumulation of Hg in this complex river-reservoir environment. This data release is focused on the sediment component of this larger effort and includes data collected between 2014 and 2018 from shallow surface sediment (≤ top 5 cm) and from sectioned...
map background search result map search result map Fluxes of nitrous oxide and methane from nitrogen-amended soils in a Colorado alpine ecosystem Cottonwood Lake Study Area - Water Chemistry - Wells Suisun Marsh, CA: Net Ecosystem Carbon Balance Assessing spatial variability of nutrients and related water quality constituents in the California Sacramento-San Joaquin Delta at the landscape scale: 2018 High resolution mapping surveys (ver. 2.0, October 2023) Biogeochemical Data for Mercury and other Constituents in Surface Sediment and Deep Cores from the Hells Canyon Reservoir Complex, Idaho and Oregon 2014-2018 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 Cottonwood Lake Study Area - Water Chemistry - Wells Fluxes of nitrous oxide and methane from nitrogen-amended soils in a Colorado alpine ecosystem Suisun Marsh, CA: Net Ecosystem Carbon Balance Biogeochemical Data for Mercury and other Constituents in Surface Sediment and Deep Cores from the Hells Canyon Reservoir Complex, Idaho and Oregon 2014-2018 Assessing spatial variability of nutrients and related water quality constituents in the California Sacramento-San Joaquin Delta at the landscape scale: 2018 High resolution mapping surveys (ver. 2.0, October 2023) 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