Y.W. Zhao

Equilibrium State of PAHs in Bottom Sediment-Water- Suspended Sediment System of a Large River Considering Freely Dissolved Concentrations

In natural waters, the equilibrium state of hydrophobic organic compounds among bottom sediment (BS), suspended sediment (SPS), and water is fundamental to infer their transfer flux and aqueous bioavailability. However, this type of information remains scarce and fragmented. This study systematically evaluated the equilibrium state of polycyclic aromatic hydrocarbons (PAHs) in the Yangtze River. Total and freely dissolved concentrations of the 16 priority PAHs in pore water and overlying water (including surface and near-bottom) of the Yangtze middle reaches were investigated, as were the concentrations of attached PAHs in SPS and BS. Results showed that concentrations of total/freely dissolved PAHs, dissolved organic carbon (DOC), and SPS in surface water were not statistically different from those in near-bottom water, and the DOC-water distribution coefficients of PAHs in pore water were not statistically different from overlying water. However, significant disequilibrium was found at the sediment-water interface; concentrations of total/freely dissolved PAHs in pore water were 1 to 2 orders of magnitude higher than those in overlying water. This study offers a complete analysis of the potential disequilibrium of PAHs in BS-water-SPS system of large rivers and suggests that distribution of hydrophobic organic compounds between BS and overlying water is essential in controlling their equilibrium state in the BS-water-SPS system of natural waters.

LONG-TERM PERIODIC STRUCTURE AND SEASONAL TREND DECOMPOSITION OF WATER LEVEL IN LAKE BAIYANGDIAN, NORTHERN CHINA

Water level, as an intuitive factor of hydrologic conditions, is of great importance for lake management. In this study, periodic structures of water level and its fluctuations in Lake Baiyangdian are analyzed based on wavelet analysis and seasonal-trend decomposition using local error sum of squares (STL). Data of monthly time series are divided into three types with emphasis on anthropogenic influence from water allocation. It is found that intra-annual characteristics of water level fluctuations are the common periodic structures. Water allocation alters the periodic structures by decreasing and weakening the oscillations of water level, compared with the slight effects of natural hydrologic water supplies and short-term climate changes. An irregular water level decline and short-term oscillation with irregular periodicity are deduced from seasonal-trend decomposition analysis using STL. With seasonality depicted monthly, the influence of water allocation implies irregular oscillations with high-frequency components, especially for monthly changes. The water level fluctuations are influenced by seasonal changes, as demonstrated by three types of time series. The impacts of water allocation on seasonality show the differences with continuous single-peak oscillations representing no influences and continuous double-peak oscillations representing frequent influences. Furthermore, the accumulation of water allocation shows a slight rising trend in average monthly level fluctuations over the last several years. The study helps understand periodic structures and long-term trend changes of water level fluctuations, which will facilitate lake management of Lake Baiyangdian.