Study On Dynamic Changes Of Wetland Landscape Pattern In Tianjin

Known as the kidney of the nature, Wetland is not only the most important living environment for human beings, but also the habitats for wildlives. As part of the Bohai Sea Coastal Area, Tianjin is of local, regional and international significance for south-north migratory birds in eastern Asia, and many of them are listed in the Red Book of China. However, due to human activities in recent decades, the decrease of wetland area seriously affected the wetland birds'habitat, migration and propagation. Supported by the remote sensing and geographical information system, this research used three periods of Tianjin TM images in1999,2003and2007as the data source to acquire the wetland patch data. The main classification and mapping method is traditional visual interpretation in combination with non-RS images and other materials with high resolutions. According to the study area's condition, the wetland was divided into two major categories and12sub-classes. The patch changes during three periods were analyzed by ARCMAP software and the dynamic change of wetland landscape pattern was processed by using Fragstats3.0and Excel software.The result shows that:the total area of wetland patch increased4.89%, from312088.725hm2in1999to328133.61hm2in2007, mainly attributing to the increase of constructed wetlands, especially salt fields. The salt fields increased significantly in8years from24043hm2to25699.57hm3, while other types of constructed wetlands and natural ones reduced. The natural wetlands lost7.38%on the contrary. Some important landscape pattern indices calculated show that in the spatial distribution the degree of the wetland landscape fragmentation was aggravated. Wetland patch types are getting more diversified, evenly distributed without apparent advantage ones. The main wetland type transition rule is natural wetlands to constructed ones, then to agricultural fields and forests, finally to development areas. Human development activities have shifted to inter-tidal zone, tide silt beach, river estuary, shallow sea water area, swamps and reservoir wetlands where human didn't touch before. The wetland landscape pattern changes led to big changes on waterfowl habitats.Based on the reliability of the information, the research selected20variables and divided then into2types to build up the driving factors indices system:social and natural ones. All indicators are standardized first because some are correlated to others. Then the research used "maximum variance orthogonal rotation" method to extract and filter the driving factors, analyze the driving weight and evaluate their impacts on landscape pattern change. The result shows:in the social driving factors, demographic and economic factors have significant impact on the changes of wetland landscape pattern. Further analysis explains that with fast economic development, the situation of the industrial structure is not improved. Population factor reflects that rapid urban population growth has led to urban physical expansion to intensive agricultural fields and wetlands. Food production increase was achieved via expanding the farmland to wetlands. New agricultural technology improvement helps improve the wetland landscape pattern. In the natural system, changes in temperature and precipitation caused by global climate change also affect the wetland landscape pattern, but the performance is not obvious because of the short time span of the study.Further, based on the wetland transition matrixes between1997and2003, the constrain factors and suitability set generated by MCE, this paper uses CA-Markov model to simulate wetland landscape pattern in2015and2023. The research shows that:the total area of Tianjin wetlands increase first then decrease in the future. The reason is, during the transition from natural wetlands to constructed wetlands, constructed wetlands to farmland and dry land, farmland and dry land to construction and industrial land use, the speed from natural wetlands to constructed wetlands has little change, while the constructed wetlands lose faster.Finally, this paper takes the Binhai New Area as case to discuss the wetland conservation principles and strategies. The wetland protect framework should base on the river corridor, the ancient shell dike and oyster beaches, and give priority to protect and restore the natural shape of the river corridor and ecological functions. Inter-regional water transportation will bring new water source, while rainwater collection, treatment and reuse are important as well. The wetland restoration also includes wetland plants restoration and waterfowl habitat restoration.