Multiple sediment cores from reservoirs are needed to reconstruct recent watershed changes from stable isotopes (δ13C and δ15N) and C/N ratios: case studies from the mid-western United States

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• 作者：A. Kumar ; J. Hage-Hassan ; M. Baskaran ; C. J. Miller…
• 刊名：Journal of Paleolimnology
• 出版年：2016
• 出版时间：June 2016
• 年：2016
• 卷：56
• 期：1
• 页码：15-31
• 全文大小：1,129 KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Environment
  Environment
  Sedimentology
  Climate Change
  Physical Geography
  Hydrobiology
  Geology
  
• 出版者：Springer Netherlands
• ISSN：1573-0417
• 卷排序：56

文摘

Watershed land-use changes, including urbanization, have caused accelerated soil erosion, which in turn has increased sediment accumulation rates in most aging reservoirs in the mid-western United States (USA), thereby posing a threat to their longevity and productivity. We analyzed three sediment cores from each of two reservoirs in the mid-western USA, the Webber Dam impoundment in Michigan and Goshen Pond in Indiana. Core chronologies were established using 137Cs and 210Pb. Concentrations of organic carbon and nitrogen and their stable isotope compositions (δ13C and δ15N) were measured to investigate past land-use changes. We used three excess 210Pb-based (210Pb_xs) sedimentation rate models (constant 210Pb flux and sedimentation, constant rate of supply of 210Pb and constant initial 210Pb concentration) to develop core chronologies and compared them to the chronology obtained from the 137Cs peak. Validation of the excess 210Pb-based chronology with137Cs-based chronology requires more than one 210Pb_xs-based-model. That is, even in one watershed, output from more than one 210Pb_xs-based model may have to be compared with an independent time marker. We compared C/N ratios, δ13C and δ15N among three time horizons in each of the three cores from the reservoirs (corresponding to dates of 1950, 1970 and 2010). Within a reservoir, there can be large differences between cores for a given time horizon, indicating there could be spatial differences in sources of C and N and the processes that influence carbon and nitrogen isotopes. We conclude that multiple sediment cores from reservoirs should be analyzed if carbon and nitrogen isotopes in sediments are to be used for paleoenvironmental inference.Keywords210Pb and 137Cs chronologySediment datingStable carbon and nitrogen isotopesReservoir sedimentPaleoenvironmental changes