Studies On Degradation And Vegetation Restoration Of Urban Lake Wetland In Wuhan

Urban wetland has important functions of ecosystem service. However, human activities such as urbanization and infrastructure construction, lead to shrinkage of wetland in area, structural fragmentation and functional decline. Wetland protection and restoration thus become an important issue in the region ecological sustainable development. With supporting of remote sensing and geographic information systems, this paper study the changes of landscape pattern, plant biological diversity and degradation mechanism of urban wetlands in Wuhan. We also focused on the Wuhan city wetland protection and recovery strategy. The main results are shown as followed:(1) Changes of Wuhan urban wetland landscapeUsing the multi-temporal Landsat remote sense images during 1991-2007, this study analyzed the landscape changes of Wuhan wetlands under the background of urbanization in recent 17 years. During the whole study period, the wetlands of Wuhan decreased in area with a mean annual decreasing rate of 1.38%, and annual decrement of 2751.42hm2. In particular, the annual-decreasing rate of wetlands during 1991a-1996a was larger than the mean decreasing rate in 17 years, and was synchronous with the area increase of Wuhan built-up area. During the study period, the area of natural wetland decreased, while constructed wetland increased. As a major wetland type of Wuhan, the lake wetlands had the fasted decline in area, being a direct cause of the wetland area decreasing in Wuhan. The increased area of constructed wetland did not prevent the decreasing trend of total wetland area. With rapid urbanization, the wetland in Wuhan showed the trends of the largest patch index and fractal and connectivity decreased and the fragmentation increased.(2) Plant diversity feature of Wuhan wetlandPlant resources in Wuhan lake wetlands were very abundant and included 361 vascular plant species, belonging to 82 families and 231 genera, in which the main category was angiosperm. Moreover, Graminea, Compositae, Leguminosa, and Cyperaceae are dominant families.The geographical composition the vascular plants surveyed is complex and widely associated with other florae thus showing both transitional and anciently originated characteristics. However, the endemic species were very rare. The pteridophytes of lake wetlands in Wuhan were rare with obviously intrazonality. The seed plants were rich. Additionally, the 14 areal-types had a large proportion of the cosmopolitan, pantropic and north-temperate distribution types. It indicates obviously subtropical flora characteristics. The dominant life-form of wetland plants was perennial herbaceous and annual herbaceous. This article take moisture as dominant factor-based in the survey of ecological adaptation of wetland plants classification in Wuhan water lakes, the results of showed that the typical vascular plants (164 species) ranked first, accounting for 45.4% of all species. This indicated that the direction of the succession of plant communities living tubes plant of wetland lakes in Wuhan.In this paper, exotic plant survey results showed that the lakes in Wuhan have been around the alien invasive plants. Invasive species has 24 species (12 families,17 genera), accounting for 77.4%of alien species. The remaining 22.6%of the total are basically cultivated species by human. These exotic plants had been a great threaten to plants biological diversity of lake wetlands in Wuhan.(3) Ecosystems degradation feature and mechanism of Wuhan wetlandAccording to biological, habitat and functional features of 23 emblematical lake wetlands in Wuhan, we got a lot of data referring to ecosystems degradation, which were dealt with hierarchical cluster analysis. We divided the 23 lake wetlands into 3 classes with degradation degree. Zhuyehu Lake wetland, Yandonghu Lake wetland, Beitaizihu Lake wetland and Qingtanhu Lake wetland are contained to the first class(Degraded Slightly), Nantaizihu Lake wetland, Yezhihu Lake wetland, Tazihu Lake wetland, Huangjiahu Lake wetland, Yehu Lake wetland, Qinglinghu Lake wetland, Longyanghu Lake wetland, Shahu Lake wetland, Nanhu Lake wetland, Zhangbihu Lake wetland, Yanxihu Lake wetland, Moshuihu Lake wetland, Beihu Lake wetland, Donghu Lake wetland, Wujiahu Lake wetland, and Sanjiaohu Lake wetland are contained to the second class(Degraded), the third class is degraded seriously lakes, such as Neishahu Lake wetland and Ziyanghu Lake wetland.City construction is one of the most remarkable symbols of human's effects to lake-wetlands. Urban construction affected the lake-wetlands by changing the land use type of environment around the lake-wetlands. The percent of construction coverage and agriculture coverage were the most remarkable differences among lakes of different degraded class. With the increasing of construction coverage percent and the decreasing of agriculture coverage percent, lake wetlands'degradation degree wound is increasingly serious. The results of degradation cause principal component analysis indicated that the primary degradation causes of lake wetlands were inning, breaking into and polluting the lake wetlands in Wuhan. (4) Classified protection mode of Wuhan lake wetlandThe change trends of species richness, plant diversity, ecological dominance, and evenness of vascular plants in lake wetlands in Wuhan are relative consistent. However, there were significant differences in plant diversity (abundance, diversity and evenness), association abundance and common wetland plants diversity (including percents of total common wetlands, abundance and dominance) among various fielded lakes. The spatial distribution of abundance of vegetation types, formation and association in different lakes are very consistent. Even though the vegetation communities are abundant in Donghu Lake, Yanxihu Lake, Qinglinghu Lake, Sanjiaohu Lake, Yandonghu Lake, and Chedunhu Lake, the majority of lakes still contain fewer plant community types. And the number of typical plant species had more obvious spatial variation.According to these characteristics, the lakes were classified into four classes, which included native vegetation lakes, secondary vegetation lakes, artificial vegetation lakes, and degraded vegetation lakes. In the native vegetation lakes, wetland natural reserves should be constructed so as to conserve the native wetland plants. The secondary vegetation lake is the most common type of lakes. Differentiated management measures should be developed according to their location. In urban area, vegetation buffer zones with the width of 30-100m should be considered to establish in order to promote restoration and development of wetland natural vegetations; while in agricultural areas, the government and managers should guide and regulate the mode of agricultural production around the lake to reduce disturbance of the human activities. Urban wetland parks should be constructed to protect the artificial vegetation lakes and promote the near-natural restoration of wetland vegetations. Some ecological engineering methods are also needed to improve wetland habitat of the degraded lakes as soon as possible, and then recover them with near-natural wetlands vegetation.The research of the Yandonghu Lake wetland plant communities along the moisture gradient demonstrated that the seasonal sweeper environment diversity index were all significantly higher than all other habitats community.As the lower of terrain, water increase, tree and shrub, mesophyte, mesophreatophyte, typical vascular plants of wetland plant, hydrophyte herbage plant seriatim appeared in particular space.(5) Typical wetland plants selection and recovery mode of Wuhan lake wetlandOn the basis of higher plants investigatation of 26 urban lake wetlands of Wuhan, summarize the Liangzi lake wetland and Donghu lake wetland historical plants situation changes by using TWINSPAN and DCA, analyze the type and structure of Yandonghu lake wetland higher plant communities, identified the Liangzihu(1998-2002), Donghu(1992-1993) and Yandonghu lakewetland plant as the reference target of Wuhan lake wetland vegetation restoration, guide Wuhan lake wetlands'restoration and reconstruction. Based on the evaluation of the Wuhan area typical wetland plants' different application, combined with the wetland function characteristics, environmental conditions, investigated lakes were classified into four models:ecological protection model, landscaping model, economic productive model and comprehensive efficiency model and probed its recovery mode respectively, choose a typical lake from each mode as the basis site of Wuhan area, based on the existing communities, submit their basic mode of restoration of wetland plants. It gives a theory and data support of Wuhan wetland protection and rehabilitation.