基于GIS和RUSLE的拉萨河流域土壤侵蚀研究

Study on Soil Erosion in LaSa River Basin Based on GIS and RUSLE

通过识别土壤侵蚀关键区域,为开展拉萨河流域生态治理与水土保持提供依据.研究将修正通用土壤侵蚀方程（RUSLE）与空间信息技术（GIS和RS）相结合,以2010年TM遥感影像为数据源,得到拉萨河流域土地利用图,结合流域数字高程模型、土壤类型分布、归一化植被指数和多年降雨数据,计算得到RUSLE模型中各因子值的空间分布数据,利用地理信息系统软件ArcGIS栅格计算功能得到研究区土壤侵蚀强度空间分布情况.对拉萨河流域土壤侵蚀特征进行分析,结果表明,流域年土壤侵蚀量为10 006.2万t/a,平均土壤侵蚀模数为3 076.6 t/（km2·a）,中度侵蚀面积比例达59.0％,强烈以上侵蚀面积很小,但侵蚀量占比为14.3％,呈大部分区域中度侵蚀、局部区域强烈和轻度侵蚀的特征,中度以上侵蚀分别有24.2％,20.5％和16.8％分布在墨竹工卡县、林周县和嘉黎县.研究区土壤侵蚀强度与地形、土地利用和植被覆盖表现出很大的相关性,坡度每增加1个等级,土壤侵蚀模数平均增加861.6 t/（km2·a）,土壤侵蚀面积最大的为坡度15°～25°,其次为25°～35°;裸地、稀疏植被、旱地和草地的土壤侵蚀模数分别为7 949,5 621,2 816,2 505 t/（km2·a）,中度以上侵蚀面积比例超过50％,其中稀疏植被和裸地均大于70％;植被覆盖度低于10％和10％～30％时,中度以上侵蚀面积比例分别为76.8％和90.5％,植被覆盖度高于60％时,中度以上侵蚀面积比例降低到28.3％.流域水土保持本底较好,但土壤侵蚀现状仍不容忽视,应对15°～25°坡度地区重点防治,同时防范陡坡地发生高强度侵蚀;对土壤侵蚀模数高的用地类型采取封育措施,促进自然修复,坡耕地采取增加地表覆盖、保护性耕作和间作套种等措施以提高水土保持功能;防止植被退化,结合综合运用林草措施和农业耕作措施提高植被覆盖度,达到防治土壤侵蚀目的.

To provide scientific basis for ecological management and soil conservation in Lasa River basra, the critical areas of soil erosion needs to be investigated. In this study, by combining revised universal soil loss equation（RUSLE） and spatial information techniques（GIS and RS）, the land use map of LaSa River basin was acquired from remote sensing data in 2010. Then, the individual factors in RUSLE model were determined by digital elevation model, soil type distribution, the normalized differences vegetation index and the rainfall data of recent years. Finally, the spatial distribution of soil erosion intensity in research area was yielded from grid modulus in ArcGIS. The results showed that the amount of soil erosion in this area was 10 006.2 × 10^4 t/a and the average soil erosion modulus was 3 076.6 t/（km2 · a）. The area percentage of moderate erosion regions reached up to 59o/oo. Although the area percentage of severe erosion regions was very small, the amount of soil erosion of these regions reached 14.3%. Most regions of LaSa River basin were eroded moderately, while some regions were eroded intensively or slightly. 24.2%, 20.5 %and 16.8 % of moderate erosion regions were distributed in Mozhugongka, Linzhou and Jiali county, respectively. In research area, the intensity of soil erosion strongly correlated with geography, land use and vegetation coverage. The average soil erosion modulus increased by 861.6 t/（km2 · a） when geographic slope degree increased by 1°. The most severe soil erosion occurred when the degree of geographic slope ranged from 15° to 25°, and relative slighter erosion happened when the slope degree was in the range of 25°～35°. The average erosion modulus were 7 949, 5 621, 2 816, 2 505 t/（km2 ·a） in bare land, sparse vegetation land, upland and grassland, respectively. The area percentage of moderate and severe erosion regions was more than 50% of all the regions. For bare land and sparse vegetation land, the area percentage of moderate and severe erosion regions exceeded 70%, which even reached 76.8% and 90.5% when the vegetation coverage was lower than 10% in bare land and in the range of 10%～30% in sparse vegetation land, respectively. When vegetation coverage was higher than 60%, the area percentage of regions with moderate and severe erosion fell to 28.3%, but soil erosion should still be paid attention to. Effective measures should be applied in slope area where slope degree ranged from 15° to 25°. Moreover, efforts should be made in steep slope area to avoid severe soil erosion. In this context, it is suggested to use enclosure measures in regions with high soil erosion modulus to improve natural restoration. In slope cropland area, the vegetation coverage should be increased and proper cultivation measures such as conservation tillage and intercropping should be applied. To prevent vegetation degradation and increase vegetation coverage, the integrated application of forest, grass and tillage measures should be used to prevent soil erosion.