HR: 1340h
AN: B23B-1047    [Abstracts]
TI: Lead Isotopic Chronologies From Inland Lakes: Evidence for Watershed Scale Sources of Lead in the Great Lakes Region
AU: * Benedict, M L
EM: benedi41@msu.edu
AF: Geological Sciences, Michigan State University, 206 Natural Science, East Lansing, MI 48824 United States
AU: Long, D T
EM: long@msu.edu
AF: Geological Sciences, Michigan State University, 206 Natural Science, East Lansing, MI 48824 United States
AU: Patino, L C
B23B-1047 AF: Geological Sciences, Michigan State University, 206 Natural Science, East Lansing, MI 48824 United States
AU: Yohn, S S
B23B-1047 AF: Geological Sciences, Michigan State University, 206 Natural Science, East Lansing, MI 48824 United States
AU: Parsons, M J
B23B-1047 AF: Geological Sciences, Michigan State University, 206 Natural Science, East Lansing, MI 48824 United States
AB: In the Great Lakes region, overall anthropogenic Pb input to the environment has decreased from the mid 1970's to the present as a result of environmental regulations. However, Pb concentration profiles from inland lake sediment cores in Michigan show that the rates of decrease to natural background concentrations of Pb differ spatially. One hypothesis to explain this spatial disparity is that watershed scale sources are the dominant contributor of Pb. To investigate this hypothesis, lake sediment cores from inland lakes in Michigan are used as a temporal record of Pb input to the environment. Sediment Pb isotopic ratios are used to evaluate the influence of various sources for lead other than what is expected as background both locally and regionally. Sediment cores used in this study were dated with Pb 210 and Cs 137. Stable Pb concentrations were also determined. The cores were analyzed for their isotopic composition (²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb) by HEX-ICP-MS. Results show that 1) Pb 207/ 206 ratios range from 0.805- 0.835, 2) temporal Pb isotopic profiles from the lake cores do not directly correlate with concentration profiles from those lakes, 3) isotopic profiles from different inland lakes appear to show dissimilar temporal isotopic trends and 4) the Pb isotopic profiles do not closely follow Pb isotopic profiles recorded in large lakes (e.g., Lake Michigan). The differences between the Pb isotopic profiles from the large lakes and the inland lakes may be due to the integration of the isotopic signal in large lakes from a larger area with more of a variety of sources. These preliminary results suggest that sources of Pb within a watershed are more important than regional Pb sources for inland lakes. These results also indicate that isotopic studies from inland lakes can provide an important compliment to those from large lakes.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0461 Metals
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4870 Stable isotopes (0454, 1041)
SC: Biogeosciences [B]
MN: Fall Meeting 2005