Study On The Net Primary Productivity In Madika Wetland Reserve Based On Remote Sensing

Wetland is a natural complex of water and land interaction,playing an important role in global climate change and carbon balance.As the impact of global climate change and human activity intensifies,wetlands are threatened by shrinking biodiversity,declining biodiversity,water pollution and invasive species.The net primary productivity of wetland vegetation is the solar energy fixed by vegetation through photosynthesis,which reflects the productivity of wetland vegetation community and is also an important symbol of the carbon sequestration ability of wetland ecosystem.The Tibet Plateau has a large area of alpine wetland,which is of great significance for regulating climate,purifying water quality and maintaining species diversity.The Madika Wetland Reserve is located in the northern part of Lhari country in Naqu,Tibet.It is the most representative and typical highland lake swamp wetland in Tibet Plateau,and it is also the source of the Lhasa river.With the increasing impact of global warming and human activity,there have been serious problems such as shrinking wetlands and desertification.In order to better maintain wetland ecological safety,evaluate wetland health and effectively promote wetland ecological environmental protection,it is necessary to investigate the condition of wetland land cover in reserve and analyze the condition of net primary productivity of wetland vegetation.In this paper,the land cover status of Madika wetland in September 1988,1995,2004,2011and 2015 was extracted by object oriented classification method and analyze land use dynamic attitude;use of temperature,precipitation,solar radiation,NDVI data to build CASA model and estimate Madika wetland net primary productivity,analyze the temporal and spatial variation;explore the relationship between climate factors and net primary productivity.The results of the study are as following:?1?The type of land cover in Maidika wetland can be divided into 7 types:ice and snow,Tibetan grass meadow,alpine meadow,swamp wetland,sparse meadow,desert,and water;the area of land cover types in different research periods has changed in different amplitudes;the area of swamp wetland in protected areas has decreased.?2?The verification of the estimation results by field survey data shows that using the CASA model to estimate the Ntica of the Medika wetland has certain applicability?3?The characteristics of temporal and spatial distribution of NPP in protected areas are characterized by high northwest and low southeast;The buffer NPP value is 74.1 gC/m^-2,the core area is 69.28 gC/m^-2,and the experimental area is 67.34 gC/m^-2;from 1988 to 2015,the NPP showed an overall downward trend,and the five main types of land cover were swamp wetland>Tibetan grass meadow>Alpine grass meadow>Sparse grassland>desert;NPP decreased with elevation,elevation NPP decreases rapidly when it more than 5042 m.?4?NPP was positively correlated with temperature,precipitation and relative humidity,and negatively correlated with surface air temperature.Major vegetation types were related to climatic factors but not significant.