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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.
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.
Phytoplankton photosynthesis drives many biogeochemical and ecological processes in lakes, estuaries, and the ocean. For example, dynamic changes in pH, trace metal speciation, and concentrations of dissolved gases (oxygen, carbon dioxide, methane), inorganic nutrients (nitrate, phosphate, silicate), and organic compounds (amino acids, organosulfur compounds) are all closely associated with fluctuations in phytoplankton photosynthesis. Trophic linkages also exist, between the phytoplankton as primary producers and populations of consumer organisms including bacteria, zooplankton, benthic invertebrates, and fish. Our scientific understanding of lakes and estuaries as dynamic ecosystems is therefore dependent upon...
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...
The overall objective of this project is to determine the role of chemical processes associated with dissolved organic carbon (DOC) on the transport and reactivity of both naturally occurring and anthropogenic compounds. Defining the roles of DOC in environmental and geochemical processes is critical to understanding the nature and quality of the Nation’s water resources, and is important for future management of these resources. This field of study has increased in relevancy as numerous environmental problems have been linked to processes involving organic matter. My project attempts to meet these needs by focusing on the chemical mechanisms controlling the fate, transport, and reactivity of naturally occurring...
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.
Many hydrogeomorphic processes are poorly understood. Botanical evidence studies can improve flood or debris flow prediction for streams with short or no gaging-station records. Improvement of our understanding of the relations among fluvial geomorphology, sedimentation, mass wasting, plant chemistry, and plant ecology will provide insight into such problems as assessment of water quality, wetland loss, long-term effects of climatic variation, and the frequency and magnitude of destructive hydrogeomorphic phenomena. Botanical and geomorphic analyses may provide substantial information about variable source areas of runoff production and ground-water recharge. The general objectives of this project include: 1) the...
<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...
The overall objective of this project is to determine the nature of natural organic carbon and organic nitrogen during its biogeochemical cycling through the environment and its interactions with anthropogenic compounds. Emerging techniques in liquid chromatography/mass spectrometry, liquid chromatography/tandem mass spectrometry, infrared spectroscopy and other means will be used to gain new insights into dominant processes responsible for fate, transport, and reactivity. Field- and laboratory-based experiments will enable direct application to current environmental problems such as disinfection byproduct formation potential, long-term effects of forest fires, and sustainability of agricultural soils. The chemical,...
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 goal of our research is to understand how climate and land use change will alter soil function including nutrient, carbon and water cycling.
The objectives of my research are to quantify mercury export and yields from multi-scaled watershed systems and to compare and contrast different forms of Hg (i.e. methylmercury) to understand the processes governing the dynamics of Hg transport and cycling. I also aim to determine an accurate understanding of the estimates of Hg stored in permafrost.
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 &frac12; 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...
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...