The major objective of this research is to determine whether pollution trends could be reconstructed from sediment records at the downstream wetlands of the Huolin River. Sediment cores, representing a range of watershed characteristics and anthropogenic impacts, were collected from two marshes at the Xianghai Wetlands in order to trace the historical variation of heavy metals, accumulation rates, and chemical forms. Cores were 210Pb- and 137Cs-dated, and these data were used to calculate sedimentation rates and sediment accumulation rates that were compared with environmental change. Ranges of dry mass accumulation rates and sedimentation rates were 0.27–0.96g/ cm2 /yr and 0.27–0.90 cm/yr. After normalization to Al, the anthropogenic enrichment of Cu, Zn, Cr, and Pb occurred in the upper layer of sediments and indicated that heavy metal contamination coming from the hydrologic inputs primarily occurred after the 1980s. This result was consistent with two decades of surface coal-mining history within the upstream region of Huolin River. Sediment inputs of most heavy metals at Xianghai Wetlands began to increase over background levels at around 1885 and were generally consistent with the time of the Qing Dynasty's immigration settlement. The anthropogenic inputs of Cu, Zn, Fe, Mn, Cr, and Pb have been 1.20–3.67 times greater than values of their natural inputs after the 1980s, which may be a result of increased input of heavy metal-rich alluvial deposits derived from surface coal-mining activities in the watershed. Sequential extraction was used to describe partitioning of heavy metals among different mineralogical components in sediments, and results showed that heavy metals in sediment cores were mostly associated with the lithogenic bonding forms (residual fraction) and least with the exchangeable fraction (except Pb). The major fraction of Pb was in the Fe-Mn oxide fraction (mean: 40.7–48.6%), indicating that Pb in these sediments had greater mobility and suggested that it might be primarily from anthropogenic sources.
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Vol. 24 • No. 3