HR: 0830h
AN: B21D-0738    [PDF]
TI: Ancient Organic Matter Sources to the Hudson-Mohawk River System: Implications of Riverine Transport of Ancient Organic Matter for the Global Biogeochemical Carbon Cycle
AU: * Longworth, B E
EM: brettl@geo.umass.edu
AF: Dept. Geosciences, University of Massachusetts-Amherst, 611 N. Pleasant St., Amherst, MA 01003 United States
AU: Petsch, S T
EM: spetsch@geo.umass.edu
AF: Dept. Geosciences, University of Massachusetts-Amherst, 611 N. Pleasant St., Amherst, MA 01003 United States
AU: Raymond, P A
EM: peter.raymond@yale.edu
AF: School of Forestry and Env. Studies, Yale University, 205 Prospect St., New Haven, CT 06511 United States
AB: The connection between erosion of rocks on the continents and deposition of marine sediments is riverine transport. Rivers are an important component of both the contemporary and long-term geologic carbon cycles. They erode ancient organic matter [OM] buried in sedimentary rock, carbon stored in soils, and carbonate bearing rock. Current understanding is that ancient OM is chemically and biologically reactive during weathering and riverine transport. However, while much OM exposed during weathering and transport is oxidized to CO$_2$, a significant portion is not remineralized, but instead is delivered downstream and reburied in marine sediments. This riverine conduit potentially allows ancient organic carbon to remain chemically distinct from pools of the contemporary carbon cycle. If a significant portion of ancient organic carbon remains sequestered in reduced form via this mechanism, there are important implications for the global carbon cycle over geologic time. These include carbon isotope effects, reservoir sizes and turnover rates, and ultimately, the composition of earth's atmosphere over geologic time. The Ordovician and Devonian shales of the Hudson-Mohawk watershed in upstate New York, USA, provide an ideal location to study the behavior of OM in a river system. In this study, we quantify sources of the dissolved and particulate organic carbon load of headwater streams draining these organic rich black shales using isotopic and molecular tracers of organic matter source. These tracers include stable isotopes of carbon and nitrogen, radiocarbon isotope ratios, and chromatographic signatures produced by pyrolysis-GC. We employ a GIS-based matrix of field sites in watersheds of contrasting lithology (OM-rich shales vs. OM-free crystalline basement) and surface cover, under the assumption that the two main controls on riverine carbon under similar climatic conditions are land use and underlying rock type. Samples include stream waters as well as endmember soils, rocks and plants. Together, these data provide the necessary information to construct a mixing model and determine the relative contribution of ancient sedimentary OM to the river system.
DE: 0400 Biogeosciences
DE: 1055 Organic geochemistry
DE: 1615 Biogeochemical processes (4805)
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1655 Water cycles (1836)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting