纸坊沟小流域近80年来土地利用变化及其土壤保持效应

Land Use Change and Soil Conservation Effect in Zhifanggou Watershed in Recent 80 Years

[目的]小流域综合治理驱动的土地利用变化可显著影响流域产沙过程,探究纸坊沟小流域不同治理阶段土地利用动态变化特征及土壤保持效应,为黄土高原生态服务功能的改善提供科学支撑。[方法]基于CSLE模型,系统评估纸流域近80年5个治理时段土地利用变化及其土壤保持效应的时空特征。[结果](1) 1938年植被破坏前流域林草植被占88.55%,植被破坏后1958年林草植被占比降为32%,林地、草地和耕地比例为1∶244∶433,1978年土地利用变化平缓;小流域综合治理实施后,1999年和2020年林草植被占比分别为64.73%和86.55%,2020年林草植被占比与1938年破坏前基本持平,但林地占比还是略小,草地略高,林地、草地和耕地比例为7.6∶5∶1。(2)流域5个时期土壤保持量分别为24.85万t, 18.86万t, 22.88万t, 23.62万t, 24.60万t,植被破坏后土壤保持量有所下降,小流域综合治理后土壤保持量有所增加,由于林地面积仍低于破坏前,2020年土壤保持量仍低于1938年0.01%。(3)受土地流转驱动,不同时期林地、草地和耕地土壤保持量分别较1938年增加或减少了-99.80%~-17.86%,23.90%~69.18%和-25.06%~664.66%,园地土壤保持量在1999年达到最大值,后于2020年降至7 511.14 t。[结论]纸坊沟小流域的植被覆盖已基本恢复至1938年破坏前的水平,说明黄土高原生态恢复在纸坊沟小流域取得了显著成效。

[Objective]The land use change driven by comprehensive management of small watershed can significantly affect the process of sediment yield in the watershed.The aims of this study are to explore the characteristics of land use dynamic change and soil conservation effect in different management stages of Zhifanggou small watershed,and to provide scientific support for the improvement of ecological service function in the Loess Plateau.[Methods]Based on the CSLE model,the spatial and temporal characteristics of land use change and soil conservation effect in the five management periods of the Zhifanggou watershed in the past 80 years were systematically evaluated.[Results](1)Before the vegetation destruction in 1938,the forestland and grassland in the watershed accounted for 88.55%.In 1958,the proportion of forest and grass vegetation decreased by only 32%.In 1978,the land use change was gentle.After the implementation of comprehensive management of small watersheds,the proportion of forest and grass vegetation in 1999 and 2020 was 64.73%and 86.55%,respectively.The proportion of forest and grass vegetation in 2020 was basically the same as that before the destruction in 1938,but the proportion of forestland was still slightly smaller.(2)The amount of soil conservation in the five periods of the watershed was 2.485×105 t,1.886×105 t,2.288×105 t,2.362×105 t and 2.460×105 t,respectively.The amount of soil conservation decreased after vegetation destruction,and the amount of soil conservation increased after comprehensive management of small watersheds.Because the area of forestland was still lower than that before destruction,the amount of soil conservation in 2020 was still lower than 0.01%in 1938.(3)Driven by land transfer,the soil conservation of woodland,grassland and cultivated land in different periods increased or decreased by-99.80%~-17.86%,23.90%~69.18%and-25.06%~664.66%,respectively,compared with that in 1938.[Conclusions]The vegetation coverage of Zhifanggou watershed has been basically restored to the level before the destruction in 1938,indicating that the ecological restoration of the Loess Plateau has achieved remarkable results in Zhifanggou.