Distribution Characteristics And Environmental Quality Of Heavy Metal Of The Yalu River Estuarine Intertidal Sediment, And Its Responses To Catchment Changes

Four sediment cores were collected at the western channel and the intertidal flats of the western Yalu River estuary in 2010 and 2011. We analyzed the 210Pb dating, grain size, total organic carbon (TOC), and heavy metal contents through the core to investigate the spatial distribution patterns and the sources of heavy metals in the west of intertidal flats of the Yalu River estuary. With the use of normalization approach and statistically analyzing method, the geochemical baseline of heavy metal elements in Yalu River is ascertained. Besides, several assessment methods were applied to assess the pollution degree and potential ecological risk of heavy metals in the intertidal surface and core sediments from Yalu River Estuay. Furthermore, we analyzed the effect of grain size on the distribution of heavy metal contents and discussed the responses of variation of grain size and heavy metal contents to catchment flow dynamic changes in different periods.The results indicated that the concentration of heavy metals in surficial sediments was high near the estuary, and decreased from east to west. In addition, grain size and heavy metal concentrations also represented decreasing trend with the elevation increasing in the intertidal flat. The different methods used to determine the geoehemieal baseline value made some difference and the geochemical baselines of seven heavy metal elements such as Cr、Ni、Cu、Zn、Cd and Pb were calculated to be 28.25 mg/kg、13.08 mg/kg、4.23mg/kg、48.32 mg/kg.0.12mg/kg、18.82 mg/kg, respectively. Based on the baselines, geoaccumulation indexes were calculated and assessment of pollution was acquired. The level sequence was obtained as Cu> Cr> Zn> Cd> Pb. The comparison of heavy metal contents from this study with that of Marine Sediment Quality showed that the overall average contents of all studies heavy metals in the intertidal sediments met the primary standard criteria. Comprehensive pollution index for marine sediment quality were used to assess the heavy metals pollution degree in intertidal zone. The results indicated that most surface sediments are in clean and noncontaminated. Also, the principal component analysis (PCA) and cluster analysis were applied to analyze the origin of heavy metal. Our observations show that the heavy metal Cu and Zn may originate from organic matter degradation. On the other hand, the sources of Cr and Ni are dominated by the rock erosion while Cd and Pb reflect the impacts of human activities. Further analysis indicate that, the distribution of heavy metal in the entire study area is mainly dominated by grain size effect, except that the contents of Cd and Pb are partly influenced by sources in the western intertidal flat of Yalu River Estuary. Moreover, the grain size variations are highly correlated to the catchment revolution, and the variations of heavy metal contents displayed remarkable response to anthropogenic activities and catchment fluid dynamic changes. Overall, the vertical distribution of heavy metal within the core sediments can be divided into four phases:before 1940,1941-1970,1971-1995, and 1996-2010. Before 1940s, the distribution of heavy metal was mainly subjected to a natural evolution; however, from 1940s to 2010s, human activities played a more important role in the distributions of heavy metals.