HR: 0800h
AN: B31B-0326    [Abstracts]
TI: The Biogeochemical Dynamics of a Large-lake Ecosystem and Past Environmental Changes Recorded by a Sediment Core From Lake Erie, 1900-2003
AU: * Lu, Y
EM: luyuehan@umich.edu
AF: Department of Geological Sciences, University of Michigan, 1100 N University 2534 CC little, ann arbor, MI 48109,
AU: Meyers, P A
EM: pameyers@umich.edu
AF: Department of Geological Sciences, University of Michigan, 1100 N University 2534 CC little, ann arbor, MI 48109,
AU: Brian, E
EM: brian.eadie@noaa.gov
AF: Great Lakes Environment Research Lab, NOAA, 2205 Commonwealth Blvd, ann arbor, MI 48105,
AU: Robbins, J
EM: John.Robbins@noaa.gov
AF: Great Lakes Environment Research Lab, NOAA, 2205 Commonwealth Blvd, ann arbor, MI 48105,
AB: We have examined the sedimentary organic matter accumulation record and its changes in isotopic compositions in response to changes in trophic status in Lake Erie between 1900 to 2003. Del 13C values of organic matter showed a strong positive correlation with total organic carbon (TOC) contents (r= 0.847), and both displayed temporal patterns corresponding with the documented changes of P loadings, suggesting TOC and C isotopes are reliable proxies for primary productivity and trophic status of the lake. Although CN atomic ratios indicated phytoplankton as the primary sources for the TOC in the sediment, TOC also showed positive correlations with interannual variations of precipitation at Erie, suggesting external carbon sources brought by precipitation was also an important source for TOC in sediment of Lake Erie. The positive correlation between CN atomic ratios and the annual precipitation variations provided collateral evidence by showing that the proportions of terrestrial organic matter is higher with an increase of precipitation. Calcite concentrations in the sediment showed a strong negative relation with TOC and did not show any apparent correlations with P loadings, temperature or precipitation, suggesting calcite dissolution caused by the remineralization of TOC played the major role in modifying calcite sedimentation. However, the carbon isotopic composition of calcite was primarily controlled by the primary productivity by demonstrating strong correlations with both TOC and organic carbon isotopic values. Nitrogen isotopic values increased in response to the increased primary productivity but did not show an apparent response to the decreases of productivity after the P abatement program. However, the positive correlation between nitrogen and carbon isotopic compositions (r=0.288) suggests that the primary productivity played an important role in the nitrogen isotopic variations. The uncertainty of del 15N in reflecting primary productivity were attributed to the external N sources and the changes in lake ecosystems, such as shifts in food chains and changes in phytoplankton communities.
DE: 0400 BIOGEOSCIENCES
DE: 0428 Carbon cycling (4806)
DE: 0432 Contaminant and organic biogeochemistry (0792)
DE: 0469 Nitrogen cycling
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting