A magnetic record of heavy metal pollution in the Yangtze River subaqueous delta.
The rapid industrial development in the Yangtze River watershed over the last several decades has drawn great attention with respect to heavy metal pollution to the Yangtze River estuary and nearby coastal areas. In this study, a 236 cm long sediment core was retrieved from the Yangtze River subaqueous delta (122°36' E, 31°00' N) in 2008 and analyzed for magnetic properties and geochemical compositions to investigate heavy metal pollution history. The activity of (137)Cs peaked at depth 140 cm, with a broad plateau between 120 cm and 140 cm, suggesting an average sedimentation rate of 3.11 cm yr(-1) for the upper 140 cm layer. Magnetic susceptibility (χ), saturation isothermal remanent magnetization (SIRM), anhysteretic remanent magnetization (χARM) and heavy metal enrichment factors (EF) all showed an upward increase trend above depth 140 cm, suggesting that increased ferrimagnetic mineral concentration was accompanied by heavy metal enrichment in the sediment. Geochemical and granolumetric analyses showed that sediment sources and particle sizes played minor roles in the variations of magnetic properties. The effect of diagenesis, which can lead to the selective removal of magnetic minerals, was noticeable in the lower part of the core (140-236 cm). Co-variation between magnetic properties (χ, SIRM and χARM) and EF of Cu and Pb suggests that the elevated ferrimagnetic mineral concentration can be used as an indicator of heavy metal pollution in the reconstruction of environmental changes in estuarine and coastal settings.
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China.
Chenyin
C
Dong
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China. Electronic address: wgzhang@sklec.ecnu.edu.cn.
Weiguo
W
Zhang
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China.
Honglei
H
Ma
Department of Earth and Environmental Studies, Montclair State University, NJ 07043, USA.
Huan
H
Feng
Department of Geography, College of Resources and Environmental Science, East China Normal University, Shanghai 200241, China.
Honghua
H
Lu
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China; Institute of Geographic Engineering Technology, School of Geographical Science, Nantong University, Nantong 226007, China.
Yan
Y
Dong
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China.
Lizhong
L
Yu
D004784:Environmental Monitoring; D060328:Magnetic Phenomena; D008280:Magnetics; D019216:Metals, Heavy / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*
D019216:Metals, Heavy; D014874:Water Pollutants, Chemical
Diagenesis; Heavy metal pollution; Magnetic properties; Particle size; Yangtze River subaqueous delta