Study On Environmental Quality And Restoration Effects Of Mangrove Wetland In Shenzhen

With the rapid development of society and economy, human activities in coastal area exerted high pressures on coastal ecosystems. Coastal wetland, as one of the most important coastal ecosystems, has been impacting heavily by human activities for decades. It causes the degradation of the coastal wetland, which has become an important issue in the world. The restoration of wetlands thus attracts attentions of different countries, and numerous projects have been carried out to restore the degraded wetlands. The restored coastal wetland, especially the urban wetland, usually located in the special economic zones and in the region sensitive to the climate change. Consequently, the structure and function of the coastal wetlands are always in a dynamic equilibrium process and, are fragile to the external pressure. Thus, it is quite necessary to develop an effective method to evaluate the effect of the restoration of coastal wetlands, which is benefit for their management and functional maintenance.Mangrove wetlands, growing in the tropical and subtropical regions in the intertidal zone, have very important ecological functions, and play the key roles in supporting the marine fishery. In this study, mangrove forest-aquaculture coupling ecological restoration system in Water Resort Park at Shenzhen was selected. Environmental monitoring was conducted in Mar. 2013, Mar. 2014 and Aug. 2014. All the environmental samples were collected in different sampling sites including mulberry base pond, exhibition Park and the mangrove forest base, which were constructed in 2008, 2004 and 2002, respectively. The severely polluted river outside of the restoration area was selected as a negative reference, while a mulberry base pond without mangrove was selected as contrast. The investigation of environmental quality included the water, sediment under mangrove and sediment of the pond. Comparison between the results and the national water and sediment quality standards and also with the previous data in the same area were performed.The results showed that the p H values, dissolved oxygen(DO), nutrients and heavy metal concentrations in the water of restored sites are in a better state than those in river water. The concentrations of all heavy metals in the restored ponds were all significantly lower than those of other aquaculture ponds adjacent to Pearl River Delta. These results demonstrated that the restoration of mangrove wetlands could significantly improve the quality of water environment.The concentrations of soil nutrient and all heavy metals in the sediment are significant lower in restoration sites than those in the river site. These results showed that the growth of mangrove might effectively remove the heavy metals in the sediment. The nutrient concentrations in pond sediment, such as ammonia nitrogen and available phosphorus had significantly negative correlation with the corresponding environment factors, which might resulted from the transference of pollutant material. Furthermore, a severe pollution of heavy metals, especially the Cu and Cr, was observed in the pond sediment. Therefore, measures should be taken to protect the sediment quality of pond and prevent the cause of secondary pollution and the heap into a new base.Based on the above research results, the restoration of mangrove wetlands in Water Resort Park did achieve the initial objectives, including the protection of the ecological environment and the water purification for ecological aquaculture. The results of this study could be helpful in the evaluation of effect of ecological restoration of coastal wetland, and provide some recommendations on the management of coastal wetlands.