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Micro-organisms alter the chemistry and productivity of aquatic environments by performing complex transformations of organic and inorganic molecules. In many cases, microbes can affect the speciation, mobility, bioavailability, and toxicity of toxic elements, such as Se, Hg, and As. The mechanisms by which these reactions proceed, the in situ rates of the transformation, their quantitative significance to element cycling, the responsible microorganisms and their physiology are only poorly understood. In this project, conceptual models of biogeochemical transformations will be developed by the combination of lab and field experimental work. Laboratory work will focus on identification of biochemical pathways, isolation...
Aqueous chemical models have become popular tools for the interpretation of natural water chemistry. Unfortunately, these models have deficiencies because of (1) incorrect or inconsistent thermodynamic data, (2) invalid assumption regarding the equilibrium state, (3) inappropriate or invalidated corrections for nonideality, (4) inadequate expressions for temperature dependence, (5) invalidated limitations for ionic strength, composition and temperature, and (6) lack of data on solid solution solubility. The plethora of models and databases has prompted federal agencies, especially hazardous waste and nuclear waste managers, to request geochemical code validation. Acid mine waters are a major source of water pollution...
I conduct long-term investigations on the fate and geochemical effect of organic contaminants in subsurface environments. I use a combined field and laboratory approach in a variety of hydrogeologic environments in order to meet these objectives. The principal questions being addressed by this project are: 1. How do long-term changes in biogeochemical processes affect the fate of organic and inorganic constituents in aquatic environments? and 2. Does availability of electron acceptors and electron donors control the progress of degradation reactions? My overarching objective is to increase our understanding of the transformation of contaminants from hydrocarbon spills, wastewaters from oil and gas development,...
My research objectives include characterization of dissolved and particulate natural organic acid influence on the reactivity, bioavailability, and mobility of metal ions and inorganic surfaces in aquatic environments. An important research objective of my project is examination of formation and dissolution rates of carbonate minerals. Biocalcification is a significant carbon sink in the world carbon budget and requires further investigation. I study aspects of biocalcification processes that proceed through a highly unstable calcium carbonate polymorph – amorphous calcium carbonate (ACC) stabilized by organic acids. I use chemical thermodynamics and kinetics to better describe and predict the fate and distribution...
The broad objective of my research is to determine rates and controls of organic carbon metabolism as a fundamental component of the terrestrial-aquatic-atmospheric exchange of carbon. I quantify the relative importance of intrinsic substrate properties and environmental variables to carbon metabolism, and the impact of climate change and other disturbances. I combine field and laboratory study approaches to understand the numerous controls on carbon cycling processes. Much of my research has focused on boreal and arctic systems, where nearly ½ of the global soil organic pool resides and is vulnerable to climate change. My research objectives in boreal and arctic regions include: 1) quantifying the release...
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The Gulf of Alaska is one of the most productive marine ecosystems on Earth, supporting salmon fisheries that alone provide large economic benefits to Southeast Alaska. The region also has a vibrant and growing tourism industry. Glaciers are central to many of the area’s natural processes and economic activities, but the rates of glacier loss in Alaska are among the highest on Earth. Glacier loss threatens to significantly change the amount and timing of nutrients delivered by streams to near-shore habitats. Changes in glacier runoff into the ocean may also impact coastal currents that contribute to vibrant nearshore marine ecosystems. Improving our understanding of how ecosystems depend on glaciers and what glacier...
Metals and metalloids occur in the environment both as natural constituents of water and as contaminants. The focus of my research is to identify and develop geochemical and particularly isotopic approaches to identifying the sources, transport mechanisms and fates of those metals and metalloids, and to use these novel tracer tools to study hydrologic and biogeochemical processes in varied field and laboratory situations. Examples of current research objectives are: 1) to use isotopes of the alkaline earth elements (Ca, Sr, Ba) to determine water flowpaths and solute sources in headwater catchments; 2) to use isotopes of Cr to understand Cr transport and contaminant remediation at industrial sites and in rivers;...
Most of my current efforts are committed to multi-catchment investigations designed to distinguish the roles of vegetation, climate, and land-cover change and to put these in a hydrologic and biogeochemical framework as well as to examine ecosystem costs and services focusing on water, carbon, and biodiversity. Two projects consume most of my efforts: (1) Work related to the Luquillo USGS Water, Energy, and Biogeochemical Budget (WEBB) Project in eastern Puerto Rico and parallel work in Panama is in the modeling and write-up phase (60% time). The objective is a comprehensive assessment of catchment hydrology and biogeochemistry in a humid-tropical landscape. In Puerto Rico we compare two rock types, quartzose and...
My research goals are (1) to develop reaction-transport models with varying levels of complexity and data requirements, providing guidelines for the appropriate application of these models given field conditions and limited resources; (2) to incorporate the effects of surface-chemistry phenomena into reaction-transport modeling; (3) to develop methods to identify and quantify important chemical and biological reactions affecting transport of inorganic and organic substances; and (4) to compile estimates of reaction rates and reaction-rate laws for chemical and biological reactions. In addition to model development, the project undertakes field, laboratory, and theoretical studies to investigate field-scale chemical...
map background search result map search result map Ice2O: A Continued Assessment of Icefield-to-Ocean Change in the Pacific Coastal Temperate Rainforest Ice2O: A Continued Assessment of Icefield-to-Ocean Change in the Pacific Coastal Temperate Rainforest