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The objectives of my current research are to 1. Understand the water quality effects of fire, 2. Measure the effects of fire on the carbon cycle and other biogeochemical cycles, 3. Characterize the combustion products of wildfire, mainly ash and charcoal, and 4. Link post-fire responses and the composition, physical characteristics, and reactivity of ash and charcoal to measures of burn severity detected on the ground or using remotely-sensed data. The overarching objective of my research is to understand runoff, erosion, deposition, and water quality effects after wildfire.
To study the mechanisms, pathways, and rates of transformation of carbon and nitrogen compounds (natural and contaminant) mediated by microorganisms in aquatic habitats and identify factors controlling these transformations and to examine the effect that these transformations have upon other biogeochemical processes.
Our research seeks to evaluate and understand the processes that control and respond to changes in the level of CO 2 in the atmosphere. Our interests include the natural cycling of CO 2 and carbon through plants, soils, seawater, rocks, and sediments. We study the causes and effects of past geologic changes in atmospheric CO 2 levels, and the ongoing effects of human actions on CO 2 and climate.
The purpose of my research group is to develop new methods and applications of environmental isotopes to solve problems of national importance. In specific, the overall goal is to use environmental isotopes, combined with other biogeochemical measurements and hydrologic and biogeochemical modeling, to increase our understanding of biogeochemical and hydrological processes, nutrient and organic matter sources, subsurface flowpaths, and water age distributions in diverse environments. Many of our studies piggyback on the sampling efforts of major monitoring programs to investigate causes of hypoxia and food web problems. Our work provides critical scientific support for these monitoring programs. A long-term career...
I conduct research focused on understanding the role of microorganisms on both contaminated and pristine ecosystems. I carry out this work using a polyphasic approach that combines microbiology, molecular biology, and biogeochemistry to understand microbial processes. My work specifically aims to (1) assess the impact of microorganisms on the fate of organic and inorganic contaminants; (2) to investigate the microbial role in metal cycling, e.g., iron, uranium, and manganese cycling; (3) evaluate the potential of microbial populations to contribute to energy resources, either through coal bed methane production or mitigating contaminants due to nuclear energy production or unconventional oil and gas production;...
Robin Stewart's research is focused on identifying and understanding processes influencing the fate and bioavailability of selenium and mercury in food webs across a range of aquatic environments including estuaries, rivers, lakes and reservoirs.
Improve understanding of physical and biogeochemical processes affecting water quality of groundwater and surface water. Research focus includes multidisciplinary field and laboratory studies to determine factors affecting sources, movement, and fate of nutrients and reactive inorganic contaminants in the hydrologic cycle. Improve the usefulness of stable isotopes and other environmental tracers in hydrology and biogeochemistry by developing new techniques and approaches. Research topics include analytical techniques for stable isotopes in compounds separated from groundwater and surface water, stable isotope forensics, enriched isotope tracer experiments to quantify transport and reaction rates, field and...
The objectives are to 1) Quantify the hydrogeomorphic and ecological controls of nutrient and contaminant fluxes in wetland ecosystems; 2) Scale wetland fluxes from site to watershed scale; and 3) Identify the principals and modeling tools for managing wetland and river ecosystems. The focus will be on floodplain ecosystems, which are poorly studied due to the challenges of working in this environment and their inherent complexity.
I conduct research on the transport and fate of organic contaminants in aquatic systems (terrestrial and marine). This entails field investigations and laboratory experiments that are designed to advance our understanding of natural processes and the effects of these processes on the behavior, mobility, and geochemical fate of organic chemicals of concern. I develop and apply new sampling and analytical techniques, identify potential molecular tracers, and develop models to predict contaminant fate. The laboratory I supervise houses analytical instrumentation that is used for detailed characterization of complex mixtures of organic chemicals as well as quantitative determination of targeted substances at ultra-trace...
Recent increases in the atmospheric concentrations of carbon dioxide and methane have emphasized the need for a more complete understanding of the processes that control carbon transfer among air, land, and water. Knowledge of the amount, rate and chemical form of carbon transfer across environmental interfaces, such as the land-air and water-air interfaces, is of particular importance. These fluxes are commonly controlled by a combination of physical, biological, and chemical processes at or near the interface. Isolation of the primary mechanisms that determine carbon transfer across the interface allows for development of process-based models that can be used for carbon mass transfer estimates at the ecosystem...
This project seeks to quantify, predict, and project the relative role of plant physiology, among other ecosystem drivers, on carbon, nutrient, and trace-metal biogeochemistry. Approaches span landscape-to-molecular scales as necessary to understand how human and stochastic alterations of wetland structure influence wetland function. Research sites represent a wide range of salinity and management conditions, from rice agriculture to coastal and restored wetlands. Primary goals include evaluating management and modeling approaches to quantify wetland carbon sequestration, greenhouse gas budgets and/or mercury methylation and export.
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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...
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.
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.
The objectives of my work are to better understand nutrient sources and cycling in specific environments to aid in resource management and pollution abatement and to improve and develop isotopic analytical methodologies.
<p>The overall objective of my research is to understand the movement and quality of surface and groundwater using geochemical approaches. Some key issues that are considered in this research are the environmental aspects of energy and mineral resources, climate change, and carbon cycling and sequestration. The geochemical approaches that are used in this research include the use of isotopic tracers, trace elements, and radioisotopes. My research has focused on the sampling and analysis of produced waters from geologic carbon sequestration studies, geochemical characterization of sediment transport in the coastal zone, the environmental chemistry of mercury in coastal regions, and water quality analysis for samples...
General objectives are to 1) add to the fundamental understanding of Se biogeochemistry; 2) document Se sources and assess the environmental impacts of Se contamination; 3) construct and validate an ecosystem-scale Se methodology that connects dissolved Se to bioaccumulated Se within an occurrence of Se exposure; and 4) develop scenarios to illustrate ecosystem foodwebs and hydrologic settings that control Se exposure within a watershed or site as an ecologically consistent management approach for Se. Within that framework, the specific objectives are to 1) quantitatively apply ecosystem-scale Se modeling on a site-specific basis in support of fish and wildlife management or protection through collaboration with...
I study biogeochemical cycling in aquatic ecosystems. Current projects include 1) Trends in alkalinity and acidity in coastal rivers of the US and potential effects on coastal acidification (USGS NAWQA Trends Team). 2) Continental-scale synthesis of stream metabolism and its links to water quality and the aquatic carbon cycle (USGS Powell Center; USGS NAWQA; USGS NRP). 3) Carbon transport and cycling in the Upper Mississippi River basin (USGS LandCarbon). 4) Long-term trends in acidification of the Delaware River Estuary (Penn State University). 5) Hyporheic exchange in contrasting headwater streams of the Colorado Front Range (with Colorado School of Mines).
The purpose of my research group is to develop new methods and applications of environmental isotopes to solve problems of national importance. In specific, the overall goal is to use environmental isotopes, combined with other biogeochemical measurements and hydrologic and biogeochemical modeling, to increase our understanding of biogeochemical and hydrological processes, nutrient and organic matter sources, subsurface flowpaths, and water age distributions in diverse environments. Many of our studies piggyback on the sampling efforts of major monitoring programs to investigate causes of hypoxia and food web problems. Our work provides critical scientific support for these monitoring programs. A long-term career...
To advance understanding of the factors controlling the environmental fate of elements which may be toxic or of other concern (e.g. greenhouse gases). For instance, microbes influence the partitioning of group 15 and 16 elements (Phosphorus, Arsenic, and Antimony; Sulfur, Selenium, and Tellurium) between dissolved and adsorbed phases, strongly affecting the quality of drinking water in aquifers around the world. On another topic, it is well known that methane and nitrous oxide are strong absorbers of IR radiation and act as greenhouse gases near the Earth’s surface. Bacteria in lakes, wetlands, and soils both facilitate and mitigate the flux of these gases and in so doing, shape our world. The primary goal of the...


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