ABSTRACT
The Inner Lake is about 4 km in length and 2 km in width with an average surface area of 6.8 km2, water depth of 2.5 km and regulation storage of 1.6 × 107 m3. It is connected to the Yangtze River by the Leading Channel (3000 m in length and 300 m in width) and the Jiaonan Gate (300 m in width). There are two rivers, Yunliang River and Hongqiao Harbor, inflowing the Inner river, along with one river, Guyun River, outflowing the lake (Fig. 1). Because the Inner Lake is located in the middle-lower reaches of the Yangtze River, it is influenced by the tides of the Yangtze River twice a day with the rising tide lasting for 3.42 h and the ebb tide lasting for 9.25 h on average. The inflow of the Yangtze River, including not only the upstream runoff but also the tides, result in strong hydrodynamic conditions in the Inner Lake, which make it
1 INTRODUCTION
The Inner Lake, located in the north of Zhenjiang, Jiangsu Province, China, is not only an important scenic spot but also an emergency water source for the city. Influenced by excessive human activities including agriculture, industry and water amusement, the Inner Lake is receiving a large amount of pollutants. As a typical waterfront lake connected to the Yangtze River, the Inner Lake has much stronger water flow than common lakes (Wang et al. 2010). As a result, one kind of the pollutant, the heavy metal, which tend to deposit into the sediment finally after a series of migration and conversion processes in common lakes (Mao et al. 2010; Lei et al. 2013), is more likely to release from the sediment into the overlying water, accelerating the secondary pollution of the water. Currently, the government of Zhengjiang has conducted many water environmental protection projects in Inner Lake which have improved the water quality to a great degree, but the internal release of the sediment bring about threaten to the maintenance of water quality. Because heavy metals have the characteristics of high toxicity, persistence, hard degradation, easy accumulation, etc. (Zhao 2002; Fan et al. 2004), which may cause great damage to ecosystem, and endanger human health through food chain, it is of great importance to study the distribution characteristics of heavy metals in the
easier for heavy metal to release from the sediment. On the other hand, the frequent water exchange between the Inner Lake and the Yangtze River also bring about sediment deposition in the lake. Due to the weakened water sediment carrying capacity induced by the expansion of flow cross-section, large amount of suspended sediments sink to the bottom of the lake. With the increasing deposition, the sediment is containing more pollutants in vertical direction.
