Distribution characteristics of heavy metals in surface sediments and core sediments of the Shenzhen Bay in Guangdong Province,China

The concentration of zinc, chromium, cadmium, nickel, lead and copper was measured on both surface sediments and core sediments in the Shenzhen Bay. The average contents of all metals have exceeded the background values in the coastal zone of Guangdong Province. Cadmium is a heavy pollution matter which indicates a strong pollution level according to the ecological risk coefficient method. The ecological risk index of the whole area is 299 which belongs to middle and strong level. The area with strong pollution level is the near shore area closing to the inside of Shenzhen Bay, Shakou area is in the middle level while the weak pollution level occurs in Shenzhenhe Estuary according to ecological risk index. The four sediment cores can be divided into two parts based on lead-210 dating, sediments size analysis and economic development period in surrounding areas since 1950 with strong human intervention. The sediment size, deposition rate and human activities have positive relationship with the contents of heavy metals which directly impact the pollution level of heavy metals in sediments in Shenzhen Bay.

Combining Decision Trees with Angle Indices to Identify Mangrove Forest at Shenzhen Bay, China

Mangroves are woody plant communities in the intertidal zone of tropical and subtropical coasts that play an important role in these zones. The infrared wave band is one of the key bands in the remote sensing identification of mangrove forest, and ALI（advanced land imagery） has a large number of infrared bands. Two angle indices were proposed based on liquid water absorption at band 5p and band 5 of EO-1 ALI, denoted as β1.25 and β1.65 respectively. A decision tree method was adopted to identify mangrove forest using remote sensing techniques for β1.25–β1.65 and NDVI（normalized difference vegetation index） for EO-1 ALI imagery acquired at Shenzhen Bay. The results showed that the reflectance of mangrove forests at band 5p and band 5 was significantly lower than that of terrestrial vegetation due to the characteristics of coastal wetlands of mangrove forests. This resulted in a greater β1.25–β1.65 value for mangrove forest than terrestrial vegetation. The decision tree method using β1.25–β1.65 and NDVI effectively identifies mangrove forest from other land cover categories. The misclassification and leakage rates were 4.29% and 5.11% respectively. ALI sensors with many infrared bands could play an important role in discriminating mangrove forest.

A Model for Environmental Impact Assessment of Land Reclamation

Land reclamation is a complex marine environmental engineering and has a huge impact on social, economic, and physical environment. Reclamation environmental impact assessment （REIA） is also a complicated project, including the assessment of social economic background, ocean engineering, coastal geomorphology, sediment transportation, marine hydrodynamics and marine ecosystem and so on. Nowadays, a large number of land reclaimed projects have been carried out or in the process of construction along the coastal zone, thus, it is necessary to build up a fnmlework on REIA to evaluate and quantify the environmental changes, to contribute to reclamation program, to reduce marine environmental disasters, and to sustain development of coastal zone. This article focuses on the research of REIA framework theory and puts forward a REIA model on land reclaimed evaluation, at the same time, applies this assessment system in Shenzhen City, which is a highly developed coastal city with an expectation of land reclamation. By use of the Remote Sensing （RS） and Geographic Information System （GIS） techniques, along with the topographic map and in situ survey in recla- mation area, it concludes that the area of 2680 hectares in total has been reclaimed in Shenzhen city by the end of the year 2000. Thus, reclamation is usually applied to meet the needs for infrastructure, such as harbors, industries and highways in Shenzhen City. However, some serious negative impacts have been created to the coastal environment shown clearly in the following aspects. Firstly, it caused the dramatic changes of tidal flat and channels along the western coast, made this area more unstable, which is threatening the function of the harbor in this area. Secondly, Tidal prism has decreased rapidly. During the 20 years of reclamation, the tidal prism has been reduced by 20% - 30% along the western coast in the Lingdingyang Estuary, and 15.6% in the Shenzhen Bay. As a result, the velocity of the tidal current has also declined, and the direction of the tidal current has changed, which is harmfid to the dilution and diffusion process of the contaminants. Thirdly, it has threatened the eco-environment finally. More than 147 hectares of mangrove area along the coast of Shenzhen Bay, accounting for 48.8% of the total mangrove reserve area in this region, has been reclaimed only during the short period from 1988 to 2000. Thus, the biodiversity is decreasing, and more and more plants and animals are disappearing. Based on the above analyses of the environmental impacts, strategies and suggestions for the future reclamation in this area have been put forward in order to support the sustainable development of the coastal zone.