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Format:
Print
Author:
Burgess, Heather D.
Dept./Program:
Geology
Year:
2007
Degree:
MS
Abstract:
Geochemical analysis of organic matter (OM) preserved within lake sediments provides a record of changes in environmental conditions, within and around a lake. Several studies have examined the response of lacustrine ecosystems to anthropogenic inputs. These studies have determined that sediment OM provides a record of lacustrine ecosystem change, prior to available water quality monitoring data, and allows decadal to century scale baseline conditions to be determined. Seven sediment cores from Lake Champlain provide a geochemical record of ecological responses to events within the lake and surrounding catchment that dates back several centuries. In this study, the sedimentary record from Lake Champlain was used to: 1) Determine the pre-settlement geochemical conditions; 2) Record changes in postsettlement lacustrine productivity; and 3) Relate geochemical trends to specific land-use activities and other anthropogenic disturbances. Land-use changes within the surrounding watershed have been well documented within the historical record.
Multiple geochemical proxies used in this study to infer in-lake ecological responses include: percent total organic carbon (%Corg) percent total nitrogen (%TN; used to calculate C/N ratios) and stable carbon isotope composition of organic matter (ð¹³C) . Biogenic silica and phosphorous concentration data are included to aid in interpretations of these proxies. Total organic carbon is a good indicator of total organic matter within the sediment, and a useful proxy for biomass production. Carbon to nitrogen ratios reflect algal vs. tewestrial organic matter sources. Variations in paleoproductivity and organic matter sources are also indicated by carbon stable isotopic composition.
The results of geochemical analyses suggest that the sediment archive from Lake Champlain records three major trends: 1.) The oldest sediments, prior to European settlement, exhibit low productivity; 2.) Increases in %Corg and C/N, typically correspond to early settlement and deforestation, and are often accompanied by less negative shifts in ð¹³C; 3.) More pronounced increases in productivity, documented by increasing %Corg, and nutrients, decreasing C/N and more negative ð¹³C trends, occur during the second half of the 20th century, corresponding to large-scale suburban development and agriculture.