Multiple sediment cores from reservoirs are needed to reconstruct recent watershed changes from stable isotopes (delta C-13 and delta N-15) and C/N ratios: case studies from the mid-western United States

作者：Kumar A; Hage Hassan J; Baskaran M^*; Miller C J; Selegean J P; Creech C T

来源：Journal of Paleolimnology, 2016, 56(1): 15-31.

DOI：10.1007/s10933-016-9888-0

• Pb-210 and Cs-137 chronology
• Sediment dating
• Stable carbon and nitrogen isotopes
• Reservoir sediment
• Paleoenvironmental changes

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 Cs-137 and Pb-210. Concentrations of organic carbon and nitrogen and their stable isotope compositions (delta C-13 and delta N-15) were measured to investigate past land-use changes. We used three excess Pb-210-based (Pb-210(xs)) sedimentation rate models (constant Pb-210 flux and sedimentation, constant rate of supply of Pb-210 and constant initial Pb-210 concentration) to develop core chronologies and compared them to the chronology obtained from the Cs-137 peak. Validation of the excess Pb-210-based chronology with(137)Cs-based chronology requires more than one Pb-210(xs)-based-model. That is, even in one watershed, output from more than one Pb-210(xs)-based model may have to be compared with an independent time marker. We compared C/N ratios, delta C-13 and delta N-15 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.

• 出版日期2016-6