Yangtze River Estuary Environmental Study

The Yangtze River Estuary is one of the world’s largest estuaries, home to over 15 million people (Chen et al., 2001a). Due to urbanization and industrial development, metal contamination in the Yangtze River Estuary has received great attention (Xu et al., 1997; Chen et al., 2001b; Zhang, 1999; Zhang et al., 2001). Although several studies have been conducted in the Yangtze River Estuary, very few studies focused on trends of metal contamination in the intertidal zone. This information is critical to coastal zone management along with the industrial development and urbanization. This is especially true when a study is done near a major sewage outlet. Sediments near a point source of contaminants (e.g., a major sewage outlet) could preserve a record of contamination from the source and, therefore, metal concentration in the sediment could reflect environmental impact due to urbanization. A preliminary study is conducted in the Yangtze River high, middle and low tidal flats affected by the Southern (Nanqu) Sewage Outlet, one of the three largest municipal sewage outlets in Shanghai, China, to examine the trends of metal contamination due to fast urbanization. Three short sediment cores (<20 cm) were collected in the high, middle and low tidal flats in the Yangtze River Estuary near the Southern (Nanqu) Sewage Outlet (Fig. 1a). All samples were analyzed for Al, Cu, Pb, Zn, ²¹⁰Pb and ⁷Be. The ²¹⁰Pb_xs profile shows a non-steady-state sedimentation pattern in the study area and ⁷Be is only found in upper 1 cm layer of sediment in high and middle tidal flats. In this study, we found that Cu, Pb and Zn contaminants are present in the upper 20 cm of the tidal flat sediment (Fig. 1b). Relationships between metal (Cu, Pb and Zn) enrichment factor and ²¹⁰Pb_xs activity suggest that contamination increases with time (Fig. 1c). Factor analysis shows that the differences in sediment grain size have insignificant effects on Cu and Pb concentrations but have some influence on Zn concentration in the study area (Feng et al., 2004). This preliminary study shows that urbanization and recent coastal wetland reclamation have had a significant environmental impact on this area.

Fig. 1. a) Map showing the study area in the Yangtze River Estuary. The sampling sites are in the intertidal zone, where is about 1800 m south to the Southern (Nanqu) Sewage Outlet in Bai Long Gang, Shanghai. Station BLGH is in the high tidal flat, Station BLGM is in the middle tidal flat and Station BLGL is in the low tidal flat, b) Heavy metal (Cu, Pb and Zn) concentrations in the high (Station BLGH), middle (Station BLGM) and low (Station BLGL) tidal flats. The profiles show that heavy metal contamination existing nearly at all depths. As shown, contamination is more striking in the in the upper layer. The vertical lines represent these metal background values. The vertical error bars represent the sediment sample intervals analyzed, c) Relationship between metal (Cu, Pb and Zn) enrichment factors and ²¹⁰Pb_xsactivity. The trends suggest an increasing metal contamination with time in this area. Symbols are designated (l) for the high tidal flat, (n) the middle tidal flat and (▲) for the low tidal flat, respectively.