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Watershed-scale water quality and water availability are affected by the interaction between the landscape and surface and subsurface flows at multiple scales. Wide-spread agriculture leads to diffuse non-point sources of contamination by agricultural chemicals. Localized exchanges of surface water and groundwater through highly reactive streambeds can attenuate the impact of agricultural chemicals on water quality. Thus, understanding the patterns and trends in water quality within a watershed requires analyses at multiple scales to understand hydrologic processes and the integration of hydrology and water quality information. The main objective of my research is to develop a better understanding of the role of...
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.
During the March-May 2014 Colorado River Delta pulse flow, approximately 102??106 m3 (82,000 acre-feet) of water was released into the channel at Morelos Dam, with additional releases further downstream. The majority of pulse flow water infiltrated and recharged the regional aquifer. Using groundwater-level and microgravity data we mapped the spatial and temporal distribution of changes in aquifer storage associated with pulse flow. Surface-water losses to infiltration were greatest around the Southerly International Boundary, where a lowered groundwater level owing to nearby pumping created increased storage potential as compared to other areas with shallower groundwater. Groundwater levels were elevated for several...
Evaluate the hydrologic and geochemical processes that control nitrate fluxes in agricultural settings. Important questions remain about the overall regional and global importance of groundwater nitrogen fluxes, denitrification (microbial reduction of NO 3 − to N 2), and the sources of electron donors contributing to this microbial reaction. Studies are needed that apply robust methods for measuring nitrogen fluxes and denitrification among multiple sites to evaluate important factors affecting N fluxes. These results, in combination with novel methods for efficient estimation of fluxes in groundwater, facilitate estimates of N fluxes in across large regions such as the Corn Belt. Quantify the effects of complex...
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The “Hydroecology of Flowing Waters” project was initiated in 1998 with the aim to improve understanding of how stream and river corridors function naturally in ways that produce valuable ecosystem services (e.g. flood attenuation, carbon and nutrient storage and contaminant removal, habitat value for fish and wildlife, recreation). The research is increasingly focused on how aquatic ecosystem services can be better protected in the face of degradation resulting from accelerating land use and climate change. Central to the research is the investigation of interactions between physical and biological processes, e.g. how land use change affects hydraulics and channel geomorphology in ways that produce cascading...
Objectives are quantitative scientific examination of hydrologic processes in the near-stream environment to determine spatial and temporal patterns of stream exchanges with shallow ground, for the purpose of improved understanding of streambed exchanges and resulting impacts on water resources and stream ecology.
Coupled Transport and Geochemical Processes Determining the Fate of Chemicals in Surface Waters
This project investigates the spatial and temporal variability of ground-water surface-water exchange in response to changes in the geometry and hydrogeologic properties of this interface that are driven by episodic and sustained fluvial and hydrologic events. Episodic events are common and occur across a broad range of physical and climatic settings and are rarely accounted for in scientific investigations or resource management. Linkages between a dynamic sediment-water interface and the resulting fluxes between ground water and surface water need to be understood, quantified, and modeled to determine their influence on the quantity and quality of our Nation’s water resources as well as the ecological changes...
An important challenge of the 21st century is the global water challenge that is exacerbated by recent droughts and rapid population growth. Water shortages have led to increased reliance on groundwater and broad reductions in groundwater resources. As demands for water resources increase, our understanding of interconnections between the hydrologic cycle and our environment increasingly become more important. Moving into the future, approaches are needed for sustainable management of water resources in order to maintain robust water-dependent systems on earth. Our research aims to better understand local and regional hydrologic processes affecting humans and the environment. Our focus is on the development of...
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...
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...
Many hydrological and geochemical processes associated with lakes and wetlands are poorly understood. Characteristics of wind and vapor profiles over lakes, which are basic controls on evaporation, have been studied in detail for only a few large reservoirs in the western United States. Many commonly used methods of estimating surface runoff to lakes and wetlands, are inaccurate. Hydrogeologic controls on seepage to and from all surface-water bodies have not been studied adequately, either from theoretical or field perspectives. Research on these components of lake and wetland hydrology is especially critical to individuals responsible for management, protection, and restoration of these resources. The major objective...


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