Access Type

Open Access Thesis

Date of Award

January 2015

Degree Type

Thesis

Degree Name

M.S.

Department

Geology

First Advisor

Mark M. Baskaran

Abstract

Large-scale watershed land use changes, including urbanization, have resulted in accelerated soil erosion and sediment accumulation rates, which in turn have posed a threat to the longevity and productivity of a majority of the aging dams in the mid-western United States. In this study, we collected and analyzed 3 sediment cores each from two dams from the Mid-western United States: Webber Dam in Michigan and Goshen Pond Dam in Indiana. Cores were analyzed for 137Cs and 210Pb to establish chronology, as well as concentrations and isotopic composition of organic carbon and nitrogen to investigate the land use changes as preserved in the sedimentary records. We used three existing excess 210Pb-based (210Pbxs) sedimentation rate models (constant 210Pb flux and sedimentation (CFCS), constant rate of supply of 210Pb (CRS) and constant initial 210Pb concentration (CIC)) to obtain the chronology and compared it to the 137Cs-peak based chronology. The validation of 137Cs peak-based chronology requires more than one 210Pbxs-based-models for a given a reservoir and hence even in one watershed, more than one 210Pbxs-based model may have to be applied to compare with another independent time marker. We compared the 13C and 15N and C/N ratios in three time horizons in each of three cores (surface 0-1 cm corresponding to 2010, year 1970 and 1950) and our results sometimes show large variations between the three cores for a given time horizon indicating that the sources of C and N and the processes that result in changes of carbon and nitrogen isotopes could differ. This study indicates that more than one sediment core analysis is required from lakes for quantitative reconstruction of carbon and nitrogen isotopes for paleo-climatic and environmental studies.

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