1999-2012年三江源区植被净初级生产力及固碳释氧量测评

目的]估算近14 a三江源地区植被净初级生产力(net primary productivity,NPP)以及固碳释氧量,为河源区的生态环境建设以及制定碳减排与碳增汇政策提供科学依据.方法]基于遥感、气象、土地等数据,通过CASA模型、碳排放模型、Sen+ Mann-Kendall模型,分析三江源地区植被NPP及其固碳释氧量的时空变化特征.结果](1)三江源区植被NPP单位面积多年均值主要集中在0～750 g/(m2·a)之间,约占研究区81.72%;空间分布特征呈东南—西北递减规律,高值分布在海拔较低、河流密集以及林地地区,而高寒地区NPP值相对较低.(2) 1999-2012年研究区NPP物质量年际变化呈增加趋势,增速约为7.26 g/(m2·a),没有通过0.05显著水平检验;年际变化空间特征中,约23.64％呈下降趋势,其中通过0.05置信水平者约占2.3％,主要分布在人类活动较频繁的地区;在受人类活动影响较少且水资源丰富地区呈增加趋势,约占研究区的76.36％,其中30.58％通过0.05置信水平检验.(3)固碳释氧物质量变化中,耕地变化幅度较大,其次是林地和其他用地,牧草地变化波动性较小.与人类活动因素有关,人为因素作用越明显,其变化幅度就越大,反之亦然.结论]三江源高寒牧草地生态总体改善较好,受人类影响较少,而在海拔较低、河流密集以及人类活动频繁地区生态变化相对较复杂,局部地区存在退化现象,需要进一步加强该地区的生态环境保护建设.

Evaluation of Vegetation Net Primary Productivity and Its Carbon Sequestration Value in Three-river Headwaters Region During 1999-2012

Objective] The objective of this study is to analyze the spatial and temporal changes of vegetation NPP(net primary productivity) and carbon fixation and oxygen release in the three-river headwater region during the past 14 years in order to provide scientific basis for the ecological sustainable development in this area. Methods] NDVI, meteorological data, the land-use data and the remote sensing data were collected. The spatial and temporal variations in NPP and amounts of carbon fixation and oxygen release were analyzed based on CASA model, carbon emissions model and Sen+Mann-Kendall model. Results] (1) The mean value of NPP was ranged from 0 to 750 g/(m²·a), which accounted for 81.72% of the entire study area. The spatial distribution of average NPP presented a decreasing trend from southeast to northwest. And NPP in the lower altitude, rivers and dense woodland areas was higher than that in the alpine regions, which indicated that NPP was affected by altitude, rivers and land types. (2) The NPP showed an increasing trend in recent 14 years, with a growth rate of 7.26 g/(m²·a)(p>0.05). As to the inter-annual variation of NPP, about 23.64% of the study area showed a decreasing trend (2.3% of them p<0.05) while 76.36% showed an increasing trend (30.58% of them p<0.05). (3) As to the variation of carbon fixation and oxygen release, the cultivated land was larger than the forest land and other land use types. Variation of carbon fixation and oxygen release in forage land was small. Conclusion] The alpine grassland ecosystem in the three-river headwater region was good, as it was less influenced by human beings. However, ecosystem in the low altitude, river and human activities intensive areas was complex and the locally degraded, and ecological environment in those regions need to be protected.