The Evaluation Of Biocapacity Based On NPP In Shiyang River Basin

The theory and methodology of the biocapacity are a major matter of ecological economics, and the supporting theory for sustainable development. The comprehensive study of biocapacity theory, methodology and application not only can be of great scientific importance among the development of ecological economics, but also has been of real applying value for the establishment of a perfect regional sustainable development theory.Aming at the deficiency of the ecological footprint (EF) method in evaluation of bio-capacity, by using MODIS-1KM month-to-month NDVI date products as well as the meteorological dates (temperature, precipitation, total solar radiation, surface net radiation), the paper calculated the vegetation net primary productivity (NPP) of ecosystem according to CASA model. Then based on NPP date, with the basic principle of ecological footprint method for guidance, biocapacity conversion factors were calculated by using NPP as an index.. Finally, combined with present land use situation, this article estimated the bio-capacity in the whole basin. The main results are as follows:(1)Land useage and coverage features:desert takes over the largest area of basin, accounting for most of middlestream and downstream, followed by bare land and arable land; forest and grassland in high coverage mainly concentrate in the mountainous area, with distribution reatively small; as a key ecological factor, water resource is extremely scarce. So the naural condition in Shiyang river basin is complex, and the ecological environment is very vulnerable.(2)Vegetation net primaty productivity estimation:in 2009, the total NPP reached 4.36×1012gC/yr, with average unit area for 171.98gC/m2·yr. ①In space distribution, the NPP was degressive from the Qinlian mountain area to desert area. ②The biomass accumulation phase was chiefly among March and October of the whole year, in June up to highest, mainly related with photosynthetically active radiation intensity. ③For the contribution to the NPP accumulation, forest had the highest average level, reaching about 300gC/m2·yr, while the minimum for desert and bare land (0～50gC/m2-yr). Besides, the total NPP of arable land was the highest (1.59×1012gC/yr).(3) Biocapacity conversion factors determination:combined with the advantages of vegetation net primary productivity and ecolocogical footprint menthod in the evaluation of biocapacity, the paper took NPP as the important biological production index, and calculated the yield factor and equivalence factor in different types of land use.From the calculation results, on one hand, the equivalence factor of forest was 1.78, highest of all, followed by arable land (1.35), grassland (1.28), water land (0.42), while desert was the lowest (0.29); On the other hand, the yield factor of grassland was the largest, for 1.17, followed by arable land (0.57), forest (0.51), water land (0.49), desert (0.42). With the exception of grassland, the rest types were less than 1, reflecting the lower output relatively to the national level.(4)Biocapacity evaluation:in 2009, the total biocapacity of whole basin was 1751783.44nhm2, and per capita biocapacity was 0.77nhm2. ①From the constitution of per capita biocapacity, the grassland and arable land ranked the top two, accounting for 69.41%, both of which were the primary contribution elements to biocapacity of the whole basin; ②From the spatial distribution of biocapacity per unit area, it generally revealed a degressive trend from Qinlian mountain area in south to desert area in north, with pank value region appearing at mountain forest and meadow zone with an altitude of 2000 to 5000 meters, however, the low value sector distributed in desertification area of Minqin basin and Alxa Right Banner. ③According to the different region statistics, per capita biocapacity and biocapacity per unit area had both the highest value in Qinlian mountain area, and its total biocapacity took up 63.50% of whole basin, with the greatest contribution of forest and grassland to this region; Due to the bigger population density, in plains and hilly region of central part, the per capita biocapacity was just 0.42nhm2, besides, biocapacity per unit area was only 0.33nhm2, with farmland being the main body of the area; Biocapacity per unit area in northern desert was minimum, and also per capita biocapacity was very low.