The Spatial-Temporal Evolution Of Wetland And Its Driving Factors In Hangzhou

Western Hangzhou Wetland, as the largest wetland in Hangzhou, is located in the Hangjiahu Plain (Core region:Xixi wetland、Wuchang wetland and Hemu wetland). It has important geographical position and ecosystem service functions, and plays an important role in developing healthy city environment of Hangzhou. But its related research was weak. Under the support of RS and GIS, this paper carried out research on the information extraction and temporal-spatial evolution of Western Hangzhou Wetland area, with aerial photo data of 1955 and 1974, topographic map data of 1982, ALOS data of 2010. This study analyzed the space-time evolution from 1955 to 2010 wetland condition and driving factors, the main contents and results are as follows:(1) Establishment of Western Hangzhou Wetland classification system. The paper established the wetland classification system suitable for the study area, refereed to the wetland classification standard in the international important wetland classification system and principles and combined with the actual situation of Western Hangzhou Wetland. It contains natural and artificial wetland 2 categories, including lake, river, marsh, natural ponds, rice field, pond, and other land.(2)Information extraction of Western Hangzhou Wetland area. By using GIS software, this paper completed in 1982 topographic maps registration and correction. Combined with statistical data of Hangzhou, the research extracts wetland classification information and makes wetland distribution map in three periods.(3) Western Hangzhou Wetland distribution.1955-2010, the main type of Western Hangzhou Wetland is artificial wetland (rice field and ponds). It is distributed mainly in Yuhang. During the period of 55-74, the artificial wetland showed a trend of growth, particularly in central regions of Yuhang and western Gongshu. But along with the development of west region, artificial wetland was greatly reduced. From 1974 to 2010, its ratio is closer to the natural wetland, main distribution area only in the north and west. Natural wetland mainly include rivers, lakes, marsh, natural ponds. It is distributed mainly in Jiangcun, Xixi and Gudang. Compared with 1955, natural ponds in 2010 almost halved. But, Until 2010, within the region of rivers and tributaries almost entirely disappeared, part of the mainstream dried up, river becomes sparse. However, the change of Lake Wetland and marsh wetland is relatively small, Even some areas have increased.Lake wetlands and marshes are evenly distributed, located in the western and northern regions, Xixi Wetland is the main area of wetland distribution.(3)Scale dynamic changes of Western Hangzhou Wetland area. In terms of wetland scale change, from 1955 to 2010, the total area of the wetland showed a trend of increase after decreases first. Wetland areas were 238.31 square kilometers in 1955,247.66 square kilometers in 1974, finally reduced to 146.85 square kilometers in 2010. Natural wetland experienced sustained decrease from 86.23 to 68.41 to 56.29 square kilometers, artificial wetland experienced a decrease after the first increase from 152.07 to 179.25 to 90.5 square kilometers. In terms of wetland dynamic change, from 1955 to 1974, annual growth rates of natural and artificial wetland were -3.17 percent and 0.94 percent, the new rates were 11.62 percent and 2.08 percent, depletion rates were 11.38 percent and 1.14percent, respectively. From 1974 to 2010, annual growth rates of natural and artificial wetland were 2.79 percent and-1.37 percent, the new rates were 12.42 percent and 0.3 percent, depletion rates were 9.56 percent and 1.67 percent, respectively.(4) Transfer process of Western Hangzhou Wetland area. On the basis of the spatial analysis of wetland, the paper calculated indexes of wetland move in or out contribution rate by using wetland transfer matrix. Through the two period transfer matrix, although the transfer of all kinds of wetland characteristics, the amplitude is different. In addition to construction land and lake, roll out various types of land area is significantly higher than the reserve area.1955-1974, only lake, artificial wetland and the construction land into contribution rate is higher than its roll-out contribution, present growth trend.1974-2010, Lakes, marsh turn into the contribution rate is greater than its roll-out contribution due attention and protection of the lake. In addition, woodland and other lands into rate is higher than the transfer rate.Research shows that:over the past fifty years great changes have taken place in the west of Hangzhou wetland.The main driving factors in affecting the west wetland space-time evolution includes two aspects of natural and social, fewer natural factors and Social factors are the leading factors, among them mainly affected by human factors. Through to the west wetland for more than 50 years area and distribution of dynamic monitoring, we can be more accurate and timely grasp its spatial and temporal changes in the characteristics and laws, and then, for the management, development and protection of the west wetland provides reference value and the scientific basis.