Natural and anthropogenically driven changes in the n-alkanols of lake sediments and implications for their use in paleoenvironmental studies of lakes

Abstract

In order to examine how natural backgrounds and anthropogenic activities influenced the n-alkanol profiles of lake sediments, abundances and compositions of n-alkanols were determined in sediment cores taken from four lakes with notable differences in depth, nutrient level, transparency, water residence time and human impact. The results indicate the short-chain n-alkanols (C14, C16 and C18) are generally more abundant in sediments from eutrophic lakes than in oligotrophic bodies, due to greater inputs from algae and zooplankton. In individual lakes, however, high levels of short-chain n-alkanols were not always recorded in sediments of relatively eutrophic phases because contributions from zooplankton can be significant even if the lake remains relatively oligotrophic. The >C20n-alkanol profiles varied markedly between shallow and deep lakes. A prevalence of long-chain compounds (C26, C28, C30 and C32) was observed in shallow lakes and is attributable to terrestrial organic matter (OM) carried by inflowing rivers, whose relatively huge annual input is evidenced by the short water residence time in these lakes. Sediments from deep lakes were dominated by middle-chain n-alkanols (C20, C22 and C24) as a result of significant input from submersed macrophytes, which achieve high productivity in the clear, sunlit water. In shallow lakes, (C26 + C28)/(C22 + C24) n-alkanol ratios in sediments were greatly dependent on anthropogenic eutrophication and aquaculture via their influence on the productivity of submersed macrophytes.