Spatiotemporal Pattern and Driving Factors of Soil Erosion in Hexi Region
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【Author in Chinese】 林锦阔；
【Author's Information】 兰州大学， 地理学·地球系统科学， 2020， 博士
【Abstract in Chinese】 土壤侵蚀造成近地表细小土壤颗粒持续流失,致使土壤持水力和生产力显著降低,这加剧了土地资源的稀缺趋势。该过程严重影响干旱、半干旱区域的农业生产、环境质量、生态安全以及社会经济的可持续发展。此外,附着于土壤团聚体上的氮、磷、钾及有机质等营养物质会随土壤侵蚀一并迁移,导致养分大量流失,这加快了土地沙漠化和荒漠化进程,威胁绿洲生态系统健康。因此,评估土壤侵蚀（风蚀、水蚀）的动态变化并探究其驱动因素,是水土流失防治的基础,也是实施生态环境保护工程的前提。本研究基于地理学研究理论,运用遥感技术、地理信息系统及野外调查手段,全面收集1982-2015年气象、地形、土壤等诸多资料,重建河西地区（92°13′E-104°46′E,36°31′N-42°57′N）关键要素的时空信息,尝试将修正水土流失方程（the revised universal soil loss equation,RUSLE）与泥沙有限传输公式（the transport limited sediment delivery,TLSD）整合并进行参数本地化校正,以此模拟河西地区水蚀速率,同时运用修正风蚀方程（the revised wind erosion equation,RWEQ）模拟其风蚀速率,揭示多因子耦合下土壤侵蚀的驱动因素。主要结果如下:RUSLE-TLSD模型模拟河西地区土壤水蚀过程具有较好效果。1982-2015年潜在水蚀速率介于6.24-31.01 t·ha-1·a-1,净水蚀速率呈下降态势且在土壤容许流失量的范围内。在空间上水力侵蚀多发于祁连山区,呈现南强北弱的特点。强烈侵蚀区多发生于海拔1500 m以上的陡坡地段（大于20°）,泥沙沉积多发生于陡坡的坡脚处。坡度、降水、NDVI是影响河西地区水蚀的关键因素,其中坡度的贡献最大。极端降雨会直接加剧局部地区的水蚀风险,在干旱、半干旱区应对其着重关注。“退耕还林”政策的实施有效降低了极端降雨对土壤的侵蚀,这在研究区产生了显著的水土保持效益。1982-2015年风蚀速率呈显著下降趋势(平均值为67.7 t·ha-1·a-1)。10月-次年5月（6-9月）为强（弱）风蚀时段。空间上风蚀速率表现为东西强、中部弱,北部强、南部弱的特点,95%的区域呈现降低趋势。位于马鬃山地区的肃北蒙古族自治县（肃北蒙古族自治县1）风蚀程度最严重,民乐县最轻。气候因子是抑制河西地区风蚀速率的决定因素,其中风速是风蚀强弱的主控因子,其与温度、大风日数、NDVI的耦合作用共同主导了风蚀速率的变化。虽然河西地区土地利用变化向着抑制风蚀的趋势发展,但是由于土地利用变化的总面积不足研究区的2%,且这些地区主要位于绿洲内部与绿洲荒漠过渡带附近,因此该过程对风蚀的抑制作用仅限于面积较小的绿洲区,短期内对风蚀速率没有产生显著影响。
【Abstract】 Soil erosion is a primary cause of the continuous loss of soil especially that of fine particles near the surface,and considerably decreases the soil water-holding capacity and productivity,aggravates the scarcity trend of land.This process severely affects the agricultural production,environmental quality,ecological security,and sustainable development in arid and semiarid regions.Moreover,nutrients（nitrogen,phosphorus,potassium and organic）are eroded along with these fine soil particles,leading to considerable loss in soil nutrients,soil degradation,and desertification,threatening the robustness of oasis ecosystems.Therefore,accurately evaluating the dynamic changes of soil erosion（wind and water erosion）and available nutrients,explaining the driving mechanism are the foundation of soil erosion prevention and control and the advance of implementing ecological environmental protection project.Based on remote sensing,geographic information system and field survey,the meteorological,topographic,soil and other data from 1982 to 2015 were comprehensively collected to reconstruct the spatial-temporal information of key elements in Hexi region（92°13′E-104°46′E,36°31′N-42°57′N）for 34 years.In order to simulate the water erosion rate,the revised universal soil loss equation（RUSLE）was integrated with the transport limited sediment delivery（TLSD）.The wind erosion rate was simulated by the revised wind erosion equation（RWEQ）.And the response characteristics of soil erosion and available nutrients under multi factor coupling were revealed.The main results of this study are as follows:The RUSLE-TLSD model could reliably simulate the soil erosion process in Hexi region.The potential water erosion rate was between 6.24 and 31.01 t·ha-1·a-1from 1982 to 2015,and the net water erosion rate showed a downward trend and in the range of soil loss tolerance.Spatially,the water erosion rate was strong in the south and weak in the north,mainly concentrated in the Qilian Mountains.The areas with strong erosion were mostly located on the steep slope section（more than 20°）above 1500 m sea level.Slope,precipitation and NDVI were the primary factors affecting water erosion in Hexi region,and the contribution of slope was the largest.Sediment deposition was mostly at the foot of steep slope.Extreme precipitation directly aggravated the water-erosion risk,and this factor should be given increased attention particularly in arid and semi-arid regions.The“Grain to Green Program”（GTGP）effectively reduced water soil erosion caused by extreme precipitation and improved water retention and soil consolidation in Hexi region.The Potential wind erosion rate（PWER）decreased remarkably from 1982 to2015(annual average of 67.7 t·ha-1·a-1 for the entire region).A severe and a mild wind erosion period occurred from October to May and from June to September,respectively.Spatially,the PWER was strong in the eastern,western,and northern regions（especially in the west）and less severe in the central and southern regions,and there was a decreasing tendency in 95%of the area.The PWER of Subei Mongolian Autonomous County was highest,while that of Minle was lowest.Climatic factors primarily determined the PWER in Hexi region,among which wind speed was the main factor controlling the intensity of wind erosion,and the coupling of temperature,gale days and NDVI jointly dominated the wind erosion rate in Hexi region.Meanwhile,the total area with a changing land cover was less than 2%of the study area,and mainly occurred in the inner oasis and near the oasis-desert transition zone.Therefore,the inhibiting effect of LUCC process on wind erosion was limited to the oasis with a small area and did not significantly affect the PWER in the short term.