石羊河尾闾绿洲的景观变化与生态恢复对策

Landscape changes and ecological reconstruction in Minqin Huqu oasis

利用G IS技术和景观结构分析软件FRAG STATS,在对民勤湖区绿洲景观格局动态变化以及土地利用格局的空间转化分析的基础上,从水资源利用以及政策和市场经济等方面分析了湖区景观变化的驱动因素,结果表明:(1)耕地和沙地斑块数量减少,平均斑块面积增加,空间连片趋势加剧;蔓延度指数变大,边缘密度和多样性指数降低;(2)沙地和耕地面积分别增加5171.85 hm2和2640.33hm2,它们的增加以牺牲林、草地为代价;(3)湖区地表水净利用量近10a来降幅达50%,到20世纪90年代后期仅有0.22×108m3,使得地下水净利用量近年来年均高达0.80×108m3;(4)以耐盐性较强的经济作物占绝对优势的单一经济结构,降低了农业生产对市场风险的抵御能力,农户收入急剧下降。通过以上分析,提出了湖区生态恢复途径与措施。

The development and utilization of water and land resources in Shiyang river is the highest of the 3 watersheds in Hexi Corridor of Gansu province, northwestern China. Huqu oasis in Minqin county is a typical dry delta formed from inland river, and surrounded by desert on the west, north and east. Due to overuse of water resource in the upper and middle reaches, salt was accumulated in the Huqu delta. Consequently, shortage of water resource and overabundance of salt have become the biggest problem in Huqu oasis. The ecological environment degraded dramatically. Using GIS and landscape structure analysis program FRAGSTATS, based on the TM image of Huqu in Minqin oasis in the lower reaches of Shiyang river Watershed in 1987 and 2001, this paper calculated and analyzed the landscape metrics of study area in 1987 and 2001 at class level and landscape level respectively ,as well as the transformation matrix of the landscape mosaics. Also the driving forces of landscape changes were analyzed, including the dynamics of runoff and groundwater resource and their exploitation, and influences of policies and market economy. The results showed that： （1） Patch number of farmland and desert decreased, but their mean patch area increased, indicating that reclamation and desertification was very serious in the study area. Contagion index for oasis increased and edge density and landscape diversity reduced. （2） Area of farmland and desert have enlarged by 1520.46 hm^2 and 4941.27 hm^2 respectively, and their increase was at the cost of wood land and grassland, which shrank by 1520.46 hm^2 and 4941.27 hm^2, respectively. （3） The net utilization of surface water decreased by 50% in the last 10 years, and dropped to 22.3 ×10^6m^3in later 1990s. Thus the exploitation of groundwater enhanced remarkably, up to 80 ×10^6m^3 per year in the last 5 years. （4） The capability of economic structure standing against the market economy has depressed distinctly because of the simplified planting pattern which is dominated by salinity enduring cash crops such as cotton. Based on the above analysis, strategies of ecological reconstruction in Huqu were put forwarded, including adjustment of agricultural planting pattern, improvement of water use efficiency, decrease of groundwater exploitation, emigration of population, adjustment of water use prices, allotment of water resource in the whole watershed, and transfer of water from other watersheds.