Main Thrust:
It is often viewed that soils are comprised of static organic matter and inorganic minerals that are subject to hydrological, chemical and biological processes. However, biogeochemical processes of minerals and organic matter and their interactions occur as they physically move on the earth surface at the wide range of spatial and temporal scales. My research goal is to quantitatively integrate the interactions among rocks, minerals, and organic matter in motion and to use this understanding to define and resolve fundamental questions in the geochemical and geomorphic evolution of soil covered landscapes and regional to global biogeochemical cycles.
My research approaches span across theoretical/mathematical, laboratory, and field investigations. Additionally, research activities in our group cover diverse locations: Delaware Coastal Plains, Pennsylvania Piedmont, Virginia Ridge and Valley, Sierra Nevada and Coastal Ranges in California, Great Lakes Region in Minnesota, and finally the Arctic Sweden.
Three Research Themes (Click for currently active projects):
WEATHERING
Active Research Projects
Field site in Sierra Nevada, California |
1. Theoretical and empirical integration of geochemical and morphologic evolution of soil covered hillslopes: responses to channel incision: In the Sierra Nevada California, I, in collaboration with Simon Marius Mudd at Univ. of Edinburgh, UK., am tracking down how tectonically driven river incision propagates upslope geochemically. This study will theoretically and empirically integrate the understanding of hillslope geomorphology based on a century of sediment budget-oriented research with a geochemistry-oriented understanding of soil spatial variation. We are looking for a highly motivated graduate student with strong backgrounds in bio/geochemistry, soil science, or geomorphology who will work on this NSF funded project. |
2. Theoretical integration among mineral geochemistry, soil formation, and geomorphology. I have been pursuing theoretical issues of soil formation and geomorphology in collaboration with Simon Marius Mudd at University of Edinburgh. There are two growing consensuses in geomorphology and geochemistry regarding the rates of chemical weathering that initiates terrestrial biogeochemical cycles. First, at watersheds to global scales, chemical weathering rate is limited by mineral supply (eg. tectonic uplift). Second, dissolution rates on mineral surface nonlinearly decrease with the increasing length of time that the minerals are exposed to chemical reaction. We are theoretically scaling up the mineral grain scale weathering rates to soil profiles to hillslopes and to watersheds. Recently, the issue of scaling in weathering has been identified as one of the most urgent issues in earth surface science.
Papers published on this topic:
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Yoo K. and S.M. Mudd, 2008, The Discrepancy between Mineral Residence Time and Soil Age: Implications for the Interpretation of Chemical Weathering Rates, Geology, v.36; no 1, 0.35-38 doi: 10.1130/G24285A
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Yoo, K., Mudd, S.M., (2008), Toward process-based modeling of geochemical soil formation across diverse landforms: A new mathematical framework, Geoderma, doi:10.1016/j.geoderma.2008.05.029
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Tennessee Valley, California |
3. Biogeochemical synthesis of soil, soil solute, and stream chemistry within a first order catchment in Coastal California. This is a collaborative effort among myself, Jon Sanderman (UC. Santa Cruz), Ronald Amundson (UC. Berkeley), and Simon Marius Mudd (University of Edinburgh, UK.). At Tennessee Valley in Coastal California, a series of biogeochemical and geomorphic studies have been conducted over the last three decades. The result is the tremendous amount of data set that can be found nowhere else on the globe. Using this data set, we are on the way to a landscape synthesis of soil geochemistry, geomorphic processes, and water chemistry of soil solutions and streams. |
Papers published on this topic:
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Glacial extent in North America.
The glaciated area has been devoid of earthworms until the recent invasion of European species. Although earthworms are known for their agricultural benefits, exotic earthworms are currently invading cold-temperate hardwood forests without native earthworms.
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4. Accelerated mineral chemical weathering rate by biophysical soil mixing along an earthworm invasion chronosequence: Earthworms vertically mix soil profiles which are not optimized for maximum chemical weathering because mineral dissolution is most intense near the ground surface where weathering susceptible minerals are often depleted. Along a well documented earthworm invasion chronosequence in Minnesota, we test a hypothesis: Rates of mineral dissolution and subsequent inorganic nutrient release are proportional to mixing rates. This work is a collaborative effort with Anthony Aufdenkampe at Stroud Water Research Center and Cindy Hale at University of Minnesota, Duluth.
We are looking for a highly motivated graduate student with backgrounds in bio/geochemistry, soil science, and geomorphology who will work on this USDA funded project.
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COUPLED CYCLES OF CARBON AND MINERALS
Active Research Projects
1. Accelerated organic matter-mineral complexation by biophysical soil mixing along an earthworm invasion chronosequence: Earthworms vertically mix soil profiles which are not optimized for maximum carbon storage: organic matter is most abundant in the surface, but carbon free minerals, which protect the organic matter by forming aggregates and carbon-mineral sorption, are more abundant in the subsoil. Our goal is to understand how and to what degree earthworms, by mixing soils, accelerate the carbon-mineral association by reducing the limiting conditions. Although earthworms are known for their agricultural benefits, exotic earthworms are currently invading cold-temperate hardwood forests without native earthworms. Along a well documented earthworm invasion chronosequence in Minnesota, we test a hypothesis: organic matter becomes associated with minerals at faster rates with increasing biophysical mixing. This work is a collaborative effort with Anthony Aufdenkampe at Stroud Water Research Center and Cindy Hale at University of Minnesota, Duluth. For the weathering component of this study, see above.
We are looking for a highly motivated graduate student with backgrounds in bio/geochemistry, soil science, and geomorphology who will work on this USDA funded project.
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Temperature and precipitation gradient in Sweden. |
2. Release of metal contaminants accumulated in organic soil layers: response to climate change: Dr. Jonatan Klaminder, who is supported by the postdoctoral fellowship from Swedish Research Council, is studying the impact of ongoing and projected climate change on the fates of heavy metals that have accumulated in the organic-rich soils in the Arctic Zone. It was hypothesized that accelerated decomposition of the organic matter due to climate change may result in releasing organically-complexed metals.
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Papers published on this research project:
- Klaminder J., K. Yoo, Reiner Giesler, pending revision, Permafrost degradation and its implication for the export of mercury in sub-arctic peat lands: interpreting mercury pools along four erosion gradients.
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Typical stream bank in Piedmont. These stream banks are probably the remnants of sediments behind mill dams, and the materials are from the accelerated soil erosion associated with early agricultural settlement in 16-18th century. We are currently working on coupling the accelerated erosion to carbon and metal cycles. |
3. Erosion induced changes in organo-metal-mineral complexation at landscape scales: This is a Ph.D. project of Chunmei Chen. In the Piedmont and Coastal Plains,rapid deforestation to agricultural fields occurred in the 17th century. Those changes have resulted in dramatic and widespread changes in the magnitude and sign of soil erosion and deposition for upland soils and fluvial systems. In such settings, we are integrating three well established findings : (1) the soil organic matter is one of the largest reservoirs of trace metals, (2) the bioavailability of the soil organic matter is significantly reduced by its complexation onto mineral surfaces, and (3) the organo-mineral complexation in biologically productive terrestrial and aquatic ecosystems are largely limited by the available C-poor mineral surfaces. Our collaborators on this project are Anthony Aufdenkampe at Stroud Water Research Center and James Pizzuto at University of Delaware.
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4. Impacts of land use change on the coupled cycles of carbon and metals: Junling Ji is finishing her MS thesis on this work. We are investigating how and what degree land use types (forests vs. agricultural field) affect the complexation between metals and organic matter. |
SHORT LIVED RADIO ISOTOPES
In pursuing the research projects listed above, we actively engage the measurements of short-lived isotopes (210Pb and 137 Cs) as a geophysical tracer of soil mixing and sediment transport. Our lab is equipped with four alpha spectrometers and one low energy level gamma detector with full sample preparation lines.
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