| Urban wetlands are those wetland areas within a city or suburban area which have been integrated into the urban landscape and green system and, are capable of providing various ecosystem service functions for the city, including natural Rivers, lakes, ponds, swamps, floodplains, coastlines and a variety of artificial irrigation and water-based landscape areas. An urban wetland is a "nature-society-economy" complex ecosystem and provides a variety of important ecological service functions for the city.But within the last 30 years of high-speed urbanization and industrialization, urban wetlands in China are found under unprecedented stress from mankind. The city keeps expanding into urban wetlands, causing their rapid loss and heavy pollution. Most of those wetlands preserved within cities are providing irreplaceable service functions for urban residents, of which culture and tourism are the two most common of all.The West Lake and Xixi Wetland are two typical urban wetlands famous for their historic heritage and tourist attractions. Same as others, they are also subject to long-term human interference and coercion, and trace of human impacts can be found in all their natural, social, and economic aspects. Today, human interference of urban wetlands is more increasing than not, making the destiny of urban wetlands entirely dependent on the scientific protection and wise use of human-beings.Studies of urban wetlands are rarely found for the complexity of their ecosystems. But urban wetlands are closely related with urban residents'everyday life. We will lose those precious heritages if we failed to well protect and manage them, leaving a great pity for our future generations.In this study, Hangzhou's West Lake and Xixi Wetland are taken as cases for historical analysis of wetland changes by means of comparative study through historic data review, map overlapping, site inspection and deep conversation. Changes were measured in respect to geomorphology, hydrology, water environment, vegetation and such human input patches as buildings, roads, towns, fields and gardens, as well as social, cultural and economic elements. Drivers causing these changes were identified and their driving mechanism is analyzed. Based on the above results, values of West Lake and Xixi Wetland ecosystem services were assessed and compared.Multi-disciplined approach is taken to combine sociological and natural science methodologies in this study. Speed, scope and trend of changes are all measured for major natural, social and economic indicators with figures collected through historic data review, on-site investigation, data and image comparing. Methods of ecosystem function evaluation were explored as well. Methods of Travel Cost and Contingent Value were employed to assess the social and cultural ecosystem-service values of the two wetlands, and their value compositions were compared.Key findings of this study are summarized as bellow:1. An urban wetland is a complex ecosystem, and its ecosystem structure is distinctively different from natural wetlands for its long-term interference received from human-beings. Its ecosystem components, ecological process and ecosystem functions are all dominantly controlled by human-being.2. It is the irreplaceable ecological service functions West Lake provided at different ages that explain the existence of West Lake and the cares Hangzhou people gave it by constantly dredging and maintaining.In the last 30 years of Open-door and Reform policy, West Lake protection and maintenance were further strengthened. Its lake basin is 0.5 meter deeper, water area 0.66 km2 larger, and water quality is kept better than Class 4 until now.But the negative impacts are obvious from urban expansion and tourism development. Heavy pollutants from urban running water and tourism have destroyed the West Lake's self-cleaning ability and it's dependent on pumped water to dilute the polluted water, although the interception system enables no sewage water into the lake.Hydro-balance sheet shows 120 million cubic meters of water is pumped into West Lake every year,14 times of its precipitation supply.As one of the earliest State-level Scenic Areas, vegetation is well protected and reserved in West Lake. But with rapid urbanization and industrialization, construction of roads and service facilities with huge inflow of tourists have led to such problems as landscape fragmentation, forest damage and ecosystem deterioration.Total area of forest changed little, but fragmentation rate reached 36%; Construction of wide roads made hard-surface increased by 84%; although more and more residents have been moved out and buildings increased only 3% as a result of strict control, but number of building patches doubled, showing a trend of diversion. Garden patches increased by 26%, a fact that more forests have been transformed into leisure gardens. During the past 30 years, residential function is decreasing while tourism service is strengthened in West Lake. Economically, agriculture keeps steady, industry has decreased while service increased. Historic heritage and culture restoration and construction are never more emphasized.3. Xixi Wetland once was turned into an agricultural farmland for short of protection, and its water was heavily polluted with urbanization and agricultural production. Reed community and big water birds such as seagull and pelican were nowhere to be found any more.City expansion is the major cause of XiXi wetland loss. Wetland patches have decreased from 43 to 24 in 30 years. Wetland area decreased from over 50 km2 to 18.06 km2. The designated area reserved for Xixi Wetland Park is only 10.06 km2.Study shows building and road patches have greatly increased in Xixi watershed area. City expansion and road construction have made Xixi wetland into an isolated ecological island. Deterioration of surrounding water environment is the greatest threat to the ecological health of Xixi Wetland。Study shows Xixi Wetland has decreased by 23% in area and the protected area for Wetland Park is only one fifth of its original size. As a result of rapid urbanization in its watershed area, running water is now the major source of pollution and short in supply, Xixi Wetland is dependent on West Lake output as major source of water supply which is now 7 times of its watershed supply.Urbanization during the 30 years has caused a 32.4% increase of building area and 530% of road area. Social, economic and cultural changes resemble that of West Lake, but its tourism size is still a small part of its economy. Xixi Wetland is under the transformation from a farming wetland to one maintained for ecosystem service, leisure and tourism, and scientific education.4. Recognition of wetland ecosystem service function by urban residents is featured as closely time-related. Their needs of wetland ecosystem service are the direct drivers of their interference to wetland. The identification of ecosystem service functions of West Lake and Xixi proved that production function of the two urban wetlands has almost completely lost; regulating function is decreasing, too; cultural function is the most recognized, and residential environment improvement as a supporting function for human-being is the most important and wild-life habitation function is the least recognized.5. Based on the analysis of wetland ecosystem service functions, core functions for West Lake and Xixi wetlands have been identified, and then used for the assessment of their ecosystem services. Results show that West Lake has a total of 17.8 billion RMB as ecosystem service value every year, while Xixi has only 1.5 billion RMB. Considered in total value, West Lake is 11.8 times of Xixi's, far more valuable, but if divided by area, the former is only twice of the later.Among the four ecosystem functions, for West Lake, supporting function value is 98.6% of the total, while for Xixi, Cultural function 94.8% of the total. That explains that the ecosystem value of urban wetland is the long-term result of protection and cultural accumulation.
|
PDF Full Text Request