Grantee Research Project Results
Compositional and Biogeochemical Elucidation of UCM and Other Complex Environmental ContaminantsEPA Grant Number: U916230
Title: Compositional and Biogeochemical Elucidation of UCM and Other Complex Environmental Contaminants
Investigators: Drenzek, Nicholas J.
Institution: Massachusetts Institute of Technology
EPA Project Officer: Jones, Brandon
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $108,172
RFA: STAR Graduate Fellowships (2003)
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Chemistry and Materials Science
The objective of this research project is to assess the impact of drainage basin characteristics and land-use change on the rate and composition of organic matter (OM) delivered to the world's oceans.Approach:
Weathering of continents and subsequent delivery and burial of the liberated carbon to the sea floor represents a major component of the global carbon cycle and carries significant implications as a key factor in present and future climate variability. Moreover, urbanization and cultivation of natural landscapes has been implicated as a cause of increased erosion of continental material to the ocean. High-resolution sedimentary records of erosion rates, vegetation type, and ancient organic-rich rock (kerogen) weathering will be constructed for several marine sites using a suite of molecular and isotopic proxies. These areas include the Cariaco Basin, Saanich Inlet, Santa Barbara Basin, Pettaquamscutt River Basin, and the Eel River Margin. Each site receives terrestrial OM via fluvial and eolian mechanisms from proximal landmasses with characteristically different topographies, elevations, land-use histories, annual and seasonal temperatures and precipitation dynamics, and vegetative assemblages. Moreover, the high deposition rate and annually laminated nature of these sediments provide independent, high-resolution chronologies devoid of complicating factors associated with bioturbation and rapid oxic OM mineralization.
Specifically, down-core 14C measurements on individual compounds such as alkanes, alkanoic acids, alcohols, sterols, and lignin phenols will be taken to determine their terrestrial "residence time" and thus, erosion rates. As the transport mechanisms for these biomarkers vary from wind ablation and atmospheric dispersion (e.g., alkanes) to more sluggish riverine and groundwater flow (lignin phenols), residence times may span from weeks to millennia. Contemporaneous addition of significant amounts of ancient (radiocarbon dead) OM derived from shale weathering may increase this range even further. Compound-specific 13C profiles on the same lipids will help to elucidate the temporal variability in vegetation type by constraining the relative proportions of carbon fixed into grassland versus forest flora by the C4 and C3 metabolic pathways, respectively. Biomolecular D characterization should provide a sensitive record of aridity in the same region. These molecular level assays will complement one another and the associated bulk isotopic and compositional (e.g., percent organic carbon, carbon/nitrogen) characteristics when input into mass balance-based model simulations, whose ultimate goal will be the generation of a comprehensive, quantitative assessment of carbon cycle and land-use fluctuations.
Coupled down-core molecular 14C, 13C, and D profiles on lipid biomarkers extracted from sediment cores should provide a high-resolution multidecadal record of climate, land use, and weathering variability for an array of different sites.Supplemental Keywords:
fellowship, climate, land use, isotopes, global carbon cycle, biomarkers, radiocarbon, complex contaminants, mixtures.