Aliphatic hydrocarbons in sediments of Lake Washington1

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Abstract
The distribution of aliphatic hydrocarbons in sediments from several locations in Lake Washington have been determined by gas chromatographic, radiocarbon, and stable carbon isotope analyses. Most surface sediments contain an average of about 1,400 µg g‒1 dry wt total aliphatic hydrocarbons, of which about 10 µg g‒1 are n‐paraffins. Gas chromatograms of these hydrocarbons and radiocarbon ages of about 18,000 years B.P. for the aliphatic hydrocarbon fraction suggest the presence of a large component of petroleum hydrocarbons. By contrast, sediments at depth in the sediment column and deposited before about 1880 contain only about 30 µg g‒1 total aliphatics and about 5 µg g‒1 n‐paraffins. These hydrocarbon levels are believed to represent the aged natural background concentrations in Lake Washington. A number of cores analyzed in detail show an increase in hydrocarbon levels after 1880, which corresponds to the start of a period of growth for the adjacent metropolitan area.