基于土地利用/覆被变化的流域景观格局与水沙响应关系研究

Land use/cover change based relationship between landscape,runoff,and sedimentation

以黄河流域的2个典型流域为研究对象,借助GIS和Fragstats平台与长系列水沙数据,分析流域景观格局和水沙变化特征,并探讨景观指数与径流输沙的关系。结果表明:(1)两个流域优势景观类型为草地,1985—2010年间变化最大的景观类型分别为未利用土地(25a变幅为453.94 km^2)和耕地(25a变幅为52.85 km^2);(2)秃尾河流域景观均向规则、高连通和高度聚集的方向发展。孤山川控制流域内景观多样性和聚集度逐渐增加,整体向好。秃尾河流域景观稳定性指数高于孤山川流域,两流域草地和未利用土地地稳定性均呈增加趋势,而城乡工矿用地则相反。(3)流域年径流量和泥沙量均呈现逐年同步减小的趋势。秃尾河年径流量明显高于孤山川,但孤山川流域泥沙量与秃尾河流域相近。两流域径流泥沙相关关系显著,秃尾河流域相关系数(0.48)明显低于孤山川流域(0.85)。(4)景观指数与径流量、泥沙量呈显著线性相关,其中景观多样性相关的指数SHDI、SIDI、SHEI和SIEI均与径流呈极显著正相关,而泥沙仅与CONTAG、COHESION呈显著负相关。

Serious soil erosion by the Yellow River has not only led to ecological deterioration, but also heightened the risk of floods downstream. Land use change is the main factor responsible for the ecological and environmental issues. Sedimentation and runoff variation caused by land use change has emerged as one of the popular topics of discussion. Researchers usually select landscape pattern as an important indicative factor of land use for analyzing the tense relationship between the socioeconomic system and natural ecosystem. The purpose of this study was to determine the characteristics of landscape patterns, runoff, and sedimentation changes, and discuss the relationship between landscape indices （LIs）, runoff, and sedimentation. Two typical watersheds （Tuweihe and Gushanchuan watersheds） in the Yellow River basin were selected as the study sites. Long-term historical land use, runoff, and sediment data （1985-2010） were analyzed relying on geographic information system and Fragstats software. Landscape indices included NP （number of patches）, PD （patch density）, LPI （largest patch index）, LSI （landscape shape index）, PAFRAC （perimeter area fractal dimension）, CONTAG （contagion index）, COHESION （patch cohesion index）, DIVISION （landscape division index）, and SHDI （Shannon＇s diversity index）. The following results were obtained：（1） Grassland was the dominant landscape in the two watersheds. Unused land in Tuweihe watershed and farmland in Gushanchuan watershed experienced the greatest changes with areas of 453.94 km2 and 52.85 km2, respectively, from 1985 to 2010. Deforestation and reconversion of cultivated land to forest and grassland were the main reasons for the land cover change. （2） The calculation of coefficient of variation （CV） revealed that LPI of Tuweihe watershed had intermediate variability （CV=27.29%）, while all the others including LIs of Gushanchuan watershed had little variability （CV〈10%）. The landscape in Tuweihe watershed tended to become regular, connected, and aggregate, indicating that with time, the influences of human activities on the area were growing. The diversity and aggregation index increased and the landscape pattern improved. For grassland and unused land, the landscape stability had been increasing gradually but decreased as farmland and urban and rural land became increasingly affected by human activities. The landscape stability of Tuweihe watershed was higher than that of Gushanchuan watershed. （3） The annual runoff and sediments decreased gradually. The runoff in Tuweihe watershed was greater than that in Gushanchuan watershed, and the sediment yields of the two watersheds were similar owing to the bigger area of farmland in Gushanchuan watershed and more check dams in Tuweihe watershed. A Pearson correlation analysis showed that there was a significant relationship between annual runoff and sedimentation （P〈0.01）. The coefficient of determination in Tuweihe watershed （0.48） was obviously lower than that in Gushanchuan watershed. （4） The Pearson correlation analysis showed that the LIs were in significant linear relationship with runoff and sedimentation （P〈0.01）. SHDI, SIDI, SHEI, and SIEI were positively correlated with annual runoff, whereas CONTAG and COHESION were negatively correlated with annual sedimentation. Compared to annual sedimentation, the correlation coefficients for LIs and runoff were higher, indicating that the land use/cover change affected runoff more than it affected sedimentation. Our results suggest that discussing the relationship between the LIs and runoff and sedimentation could provide scientific basis for the prevention and treatment of water loss and soil erosion.