土地利用变化对生态系统服务功能的影响 ——以密云水库流域为例

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Ecosystem services are the goods and services provided by ecosystems to people.Ecosystem services are important basis of human existence and strongly related to human well-being,and the sustainable provision of multiple services is essential for the sustenance of human societies.There are a series of factors driving ecosystem services,one of which is the change of land use pattern,and it is drawing more and more attention of ecologists. Miyun reservoir,which is the only surface water source for domestic water in Beijing,plays the key role for the ecological security of the capital.Miyun reservoir watershed is a vital water source region of Beijing city,and it has many important ecosystem services.The water yield and water quality of reservoir strongly depend on Miyun reservoir watershed′s condition,therefore,the conservation and improvement of ecosystem services in Miyun reservoir watershed has vital significance for local and Beijing′s ecological security.However,how the land use change influenced ecosystem services during the past decades is not clear yet,which may block the comprehensive development of watershed. So we take Miyun reservoir watershed as example,analyze the change of land use and ecosystem services between 1990 and 2009.We set up a two-grade classify system of land use and interpreted the remote sensing images of 1990,2000 and 2009 respectively,and then apply Integrated Valuation of Ecosystem Services and Tradeoffs(InVEST model),which is a space explicit model and based on land use,to map the ecosystem services,and analyze the influence of Land Use to ecosystem services during study period.The sub models we apply in this research contain Water Yield,Sediment Retention and Water Purification,and before running these sub models,we verify them with observed data. The results of image interpretation show that farmland,forest and grassland are main type of land use of watershed,and these areas account for more than 95% of the whole watershed.There are sharp changes of land use during study period,and conversion of land use types distributed more widely after 2000.The general trend in study period is farmland and grassland decreased by 30%,48% respectively,when forest increased by 30%,and another change cannot be neglected is residential area expanded by more than 280% during the past 20 years. The changes of land use have affect on the pattern of ecosystem services and there are trade-offs among different ecosystem services in question.During the study period,the decreasing of farmland and increasing of forest and grassland improved the ability of sediment retention,and this service increased by 46% in the past 20 years.But forest expansion caused more evapotranspiration,which reduced water yield of watershed by 3% at the same time.Because the nutrient loading of residential area is much higher than other types of land use,the large-scale expansion of residential area decreased water purification service sharply after 2000 although the expansion of forest and decrease of farmland can improve this service to a certain degree,and this service declined by 55% in the past 20 years.With the expansion of forest,carbon sequestration service increased about 19%.So with the goal to get overall improvement of ecosystem services in watershed,we suggest that manages should strengthen the control of forest and residential areas. Understanding the relationship between land use and ecosystem services,the department of decision-making can control and reduce the trade-off between ecosystem services and achieve the sustainable development through appropriate land use plan.Although the approach and process of evaluation still need more improvement,our research can provide scientific foundation for decision-making in Miyun reservoir watershed.