Lipids in suspended matter from the human-disturbed Lanyang River, northeastern Taiwan

Due to anthropogenic disturbance such as mass road construction, the sediment yield in the Lanyang River, northeastern Taiwan has been reported to have increased substantially since 1976. Water samples were collected from the river on three occasions, and total suspended matter (TSM) was analyzed for aliphatic hydrocarbons and alkanols/sterols. Results show that the distribution of aliphatic hydrocarbons in the TSM is rather complicated during periods of normal flow, but is relatively simple during high flow and after a period of an extraordinarily high, daily mean discharge. Carbon preference index (CPI) values of n-alkanes (C-25-C-33) are comparatively low, ranging from 1.14 to 2.35, with an average of 1.62, when compared with a control station (CPI=5.88). Because there has been no anthropogenic fossil-fuel contamination in the study area in the past, the present results indicate a predominant hydrocarbon contribution from the old lipids derived from the bedrock (argillite-slate and meta-sandstone) due to massive road construction in 1975-1980, with a small contribution from modern vegetation. By using a two-end-member assumption, the percentage of old hydrocarbons in the TSM was estimated to be about 87%. The presence of a C-22 n-alkanol maximum is attributed mainly to bacterial contribution. Higher plants are considered a major source of the campesterol, stigmasterol, and sitosterol in the TSM.