Increasing magnetic susceptibility of the suspended particles in Yangtze River and possible contribution of fly ash

The magnetic properties of soil have been increasingly applied as a rapid and economic way to monitor environment pollution. Sediments from a growing islet in the lower reach of Yangtze River as well as the suspended particles in the surrounding river water were used to identify anthropogenic influence on the magnetic susceptibility (MS) of the Yangtze River sediment. Results show that newly deposited sediments in 2004 have significantly higher MS (~ 150 × 10−8 m3 kg−1) on average than that of the ancient deposit (~ 50 × 10−8 m3 kg− 1). Scanning electron microscope (SEM) of the extracted magnetic particles from newly deposited sediments and fly ash samples indicates large contribution of fly ash for the samples with elevated MS. Dependence of MS on grain size is evident, which enable calculation of the MS of suspended particles from river sediment. A value of 32 × 10−8 m3 kg− 1is inferred for the suspended particles in ancient Yangtze River. The records from 2004 to 2010 indicate progressive increase in the MS of the suspended particles in Yangtze River from 67 to 96 × 10−8 m3 kg− 1, which is much higher than that of the ancient. Mass balance calculation based on the increasing MS suggests that at least 7% of the fly ash produced within the catchment of Yangtze River was released into the environment.

Research highlights► The magnetic susceptibility (MS) of river sediment is a strong function of grain size. ► The MS of the suspended particles in Yangtze River increase over the past decades. ► The increasing MS is caused by anthropogenic pollution of fly ash. ► MS can be used as a dating tool for the recent sediments of Yangtze River. ► MS of Yangtze River sediment can monitor the overall fly ash emission of China.