ABSTRACT
Concentrations and distribution of n-alkanes (n-C14 to n-C33) in Lake Wanghu sediment core were analyzed to investigate the environmental changes in the lake during the past~100 years. Relatively higher concentrations of mid-and long-chain n-alkanes with a strong odd-over-even carbon number predominance indicated organic matter contributions dominated by aquatic macrophytes and terrestrial plants. The lower values of 2n-C31/(n-C27+n-C29) highlighted a type of landscape dominated by woody plants. The environmental changes that have been happening over the past 100 years in Lake Wanghu can be divided into three stages, based on the organic matter sources inferred from the changes in n-alkane parameters in the sediments. Before the 1950s, higher values of terrigenous/aquatic ratio (TAR) and high-/low-molecular weight n-alkanes (H/L) indicated vascular, plant-derived sediments deposited during a low-nutrient, clear-water phase with frequent water exchange between the lake and the Yangtze River. Between the 1950s and 1980s, decrease in values of H/L and TAR, and increase in the proportion of mid-and short-chain n-alkanes indicated a shift towards mid-and shorter-chain components likely associated with the increasing contribution of macrophytes and algae. Lower 2n-C17/(n-C23+n-C25) values indicated a relatively low algal abundance. In that stage, the lake trophic state increased slightly with the decreasing influence of the Yangtze River flow. After the 1980s,H/L and TAR values increased and then decreased, total n-alkane concentrations and 2n-C17/(n-C23+n-C25) increased significantly, especially after 2000s, suggesting the main contributor to high organic matter input most likely shifted to algae because of the eutrophication caused by anthropogenic activities.
ABSTRACT
The vertical distributions of 16 polycyclic aromatic hydrocarbons (PAHs) were investigated from a sediment core in the Lake Bosten, Xinjiang. Meanwhile, the possible source and risk assessment of PAHs in Lake Bosten were also discussed. The total PAHs concentration in the sediment core ranged from 37.5 ng x g(-1) to 184.5 ng x g(-1), and Naphthalene and Phenanthrene were the dominant compounds throughout the core. Over the one hundred year, the vertical profile of PAHs underwent significant changes around 1950s. The vertical distributions of PAHs had little change and low molecular weight PAHs were dominant PAHs before 1950s. Since then, the high molecular weight PAHs appeared and increased with fluctuations. A sharp increase in PAHs level and individuals was observed especially after 1990s and a maximum was found in the surface sediment. The results suggested PAHs in Lake Bosten were from the local sources, which were dominated by the low temperature combustion. Besides, the abundance of PAHs from high temperature combustion processes, such as combustion of industrial coal and vehicle emission, increased significantly in recent years. However, based on the results of risk assessment, the PAHs may not induce adverse biological effects on the aquatic ecosystem in Lake Bosten.
