近10 a青海高原东部土地利用/覆被变化及碳效应

近年来在人类活动的影响下,青海高原东部土地覆盖变化显著,为揭示区域土地利用/覆被变化及其对环境的影响,促进区域可持续发展,以青海高原东部农业区为研究区,采用多时相Landsat TM卫星遥感数据,分析该区域1999－2009年的土地利用格局转变以及由此引起的碳效应变化,以期为青海高原东部土地利用结构与空间配置的低碳优化、科学管理与规划提供参考。首先,利用土地利用变化强度指数分析了青海高原海东市近10 a来的土地利用类型间的变化强度及方向;其次,对研究区主要的8种土地利用转移类型引起的碳效应进行了定量分析。研究结果表明：近10 a来,退耕还林/草等生态工程与西部开发战略的实施,使区域土地利用呈现"3增2减"的整体变化,即林地、建设用地和未利用地面积呈上升趋势,分别增加约67%、56%和1.14%,耕地、草地面积减少,分别减少30%和12%;由于建设用地的扩张,耕地非农化导致的碳排放量增加373.60万t,生态的正向演变（退耕还林/草;草地转林地）和建设用地的复垦退出引起的总碳汇量增加156.04万t,生态的逆向演变（林地/草地转变成耕地;林地转变成草地）引起的碳汇量损失22.85万t。近10 a来区域土地利用/覆被变化导致的碳排放增量高出碳汇增量240.41万t,说明自然和人文因素共同驱动的土地利用变化对青海高原东部的碳平衡和可持续发展产生显著影响。

Land use/cover change and its impact on soil carbon in eastern part of Qinghai Plateau in near 10 years

Abstract: In recent years, the rapid changes of land use pattern have taken placed in the eastern part of Qinghai plateau due to human activities. Therefore, it is of great significance to reveal the relationship between the regional land cover change and consequently impact on soil carbon. Using such relationship, we can optimize land use structure and spatial configuration in order to improve the regional environment and promote its sustainable development. It is reported in literature that the land use/cover change is one of the main factors which may influence the regional carbon balance, and it can change the ecosystem carbon cycle and alter the regional even global carbon balance among different carbon pools. Based on the multi-temporal remote sensing data from Landsat TM, in this paper, we used the agriculture area of Haidong city located in the eastern part of Qinghai Plateau as a case study to investigate land use/cover change and consequently its impact on the regional carbon balance. The research was to be used as a reference for balancing the relationship among economic development, eco-system protection and cultivated land conservation and pursuit of low-carbon land use. Firstly, the intensity and directions of different types of land use pattern on eastern region of Qinghai Plateau in the last decade was analyzed by using change of land use intensity index. Then, carbon effect caused by eight main types of land use change including: cultivated land into forest land, forest land into cultivated land, cultivated land into grass, grass into cultivated land, forest land into grass, grass into forest land, cultivated land into construction land and construction land into cultivated land was studied. The results indicated that the implement of "Grain for Green Project" and progress made from the Western Development Strategy from the central government significant changed land use/cover in Haidong from 1999 to 2009. There were three kinds of land use types including forest, construction land and unutilized land, which increased by 67%, 56% and 1.14%, respectively and two types including cultivated land and grassland which decreased by 30% and 12%, respectively. Besides, the decrease of cultivated land was caused by construction land expansion and cultivated land conversion to different land uses. As a convention, the land use type, such as cultivated, forests and grass, are mainly considered as carbon sinks, while construction land is considered to be carbon source for emissions. By use of the method of ecological system type, we estimated the incremental trend effect on carbon in the studied area from 1999 to 2009, which indicated that the increment of carbon emission was higher than carbon sink by 2.4041 million tons. Especially, the expansion of construction land has caused carbon emission 3.7360 million tons. The positive impact on ecosystem from land conversion to non-cultivated land increased carbon sinks by 1.5604 million tons and the negative impact on ecosystem decreased carbon sinks by 0.2285 million tons. In the last 10 years, the increment of carbon emission caused by land use/cover changes exceeded the carbon sink which indicated that land use changes driven by natural and human factors jointly can exercise remarkable impact on carbon balance and sustainable development in eastern region of Qinghai Plateau.