Study On Terrestrial Ecosystem NEP In Gannan Based On Romte Sense Technology

As the significant mark of organic carbon’s balance of terrestrial ecosystem, NEP(Net Ecosystem Production) gave a qualitative and quantificational description the ability of carbon source and carbon sink of terrestrial ecosystem directly. NEP had much significance to studying the carbon cycle and climate change all over the world. With developing of computer and remote sensing technology rapidly, the datas of satellite remote sensing had been applied to long-term surveys of land surfaces, biosphere, seas and oceans currently, and played an important role in the research of the dynamic changes of land use and terrestrial ecosystem production. Ganan was located in the transiton zone of the Tibetan Autonomous Prefecture and Loess Plateau. Owing to the condition of complicated terrain and vegetation type, it was certain difficulty to estimate the NEP in the area accurately. Therefore, the study on the NEP had important reference value to the research of the NEP of the large scale areas and even the earth in Ganan from 2005 to 2014.Based on the improved light use efficiency model and combined with remote sensing data and meteorological data, this study estimated the vegetation net primary productivity and heterotrophic respiration in Gannan from 2005 to 2014, and set up a model for estimated the vegetation NEP. Meanwhile we analysed the temporal change and spatial distribution of the NPP and its process factors in Gannan. The conclusions were as following:(1) For different vegetation patters, improved light use efficiency model took different εmax and the highest and lowest temperature threshold; For the proportion of environmental factors restrictions, we took ecology minimum rule algorithm and considered vegetation autotrophic respiration. By the comparison validation with the observed data and others estimated results, this model improved simulation accuracy and could be used to estimate NEP in Gannan.(2) Yearly average NPP was 1.78×1013 g C·a-1 in Gannan from 2005 to 2014, and average NPP was 487.42 g C·m-2·a-1 per unit area. NPP showed a gradual decreasing trend in 10 years. For the NPP, high value areas were mainly distributed in the southeastern mountain, low value areas were mainly distributed in northern rural areas, farming-pastoral zone and southwest high altitude where vegetation was sparse. Gannan’s vegetation types were mainly grassland and forest, NPP of deciduous broadleaf forest was maximum, and the NPP of grassland was 427.48 g C·m-2·a-1. NPP increased at first and then decreased during the year, and the maximum was in July. The relationship between vegetation NPP and terrain factors was close, With the altitude and aspect increasing, NPP increased at first and then reduced; Among all the aspects of the slope, NPP was the highest on the south slope, while it was the lowest on the north slope.(3) The vegetation average RH was 3.09×1012 g C·a-1 in Gannan from 2005 to 2014, and average RH was 84.86 g C·m-2·a-1 per unit area. The spatial distribution had obvious zone. RH was high in the southern Mindie-go-mountains and the eastern hills and mountains and was low in the northwest meadow steppe, and as a whole showed a decreasing trend from southeast to northwest. RH increased at first and then decreased during the year, and the maximum was in July. For different vegetation types, forest > shrubland > cropland > grasslad. RH showed a fluctuation and slowly rising trend from 2005 to 2014.(4) The vegetation average NEP was 1.47×1013g C·a-1 in Gannan from 2005 to 2014, and average RH was 402.56 g C·m-2·a-1 per unit area. The area of carbon source was about 0.39% of the total area and mainly distributed in Maqu’s highest mountain and Mindeigo mountains where were little or no vegetation cover. NEP was high in the Zhouqu of southern Mindie-go-mountains and Diebu, Zhuni, Lintan’s woodland; while NEP was low in the western alpine meadow which included Maqu, Luqu, Hezuo and Lintan that was in the pastoral transitional zone. NEP showed a downward trend but the area of carbon source increased slowly in Gannan from 2005 to 2014.