河湟谷地近20年耕地利用变化的土壤保持效应

Soil conservation effect of cropland use change in the Yellow River-Huangshui River Valley over the past 20 years

为了探究黄土高原-青藏高原过渡带河湟谷地在生态修复和城市建设共同发展下土壤保持对土地利用的响应,以退耕及西部大开发蓬勃发展的近20 a为研究时段,采用USLE模型,分析该区域近20 a来耕地利用变化的土壤保持效益,识别维持土壤保持功能的关键区域,为当地国土空间规划及水土保持方案设计提供科学依据。结果表明:1)2000-2018年,河湟谷地土地利用变化以耕地减少2145 km^(2)(6.08%)、林地和建设用地分别增多2846和511 km^(2)(8.06%和1.45%)为主,并伴随以耕地向草地、林地和建设用地转移为代表的多种地类转变方式;2)近20 a来土壤保持量持续增大,林地和草地共占研究区土壤保持总量的84%以上,耕地转移至草地和林地均引起土壤保持的正效益,2种转移模式以耕地转移至林地土壤保持价值更高,且脑山区耕地转移的土壤保持效益优于川水区和浅山区。未来应围绕耕地优化土地利用布局,以提高区域土壤保持功能。

[Background]Soil conservation is a regulatory service provided by ecosystems to reduce soil erosion.By altering the surface environment,soil conservation function has been greatly affected by human land use activities in recent years.Yellow River-Huangshui River Valley(YHV),the main agricultural area of Qinghai province,has had huge changes in the use of croplandand soil conservation under the dual drive of the project of returning farmland to forests and the large-scale development of the western region in the past two decades.The analysis of its soil conservation function and its dynamic soil conservation effect may provide a scientific basis for local land spatial planning and soil and water conservation program design and policy management.[Methods]In this study,cropland,abandoned cropland,and converted forestland from 2000 to 2010 and 2000 to 2018 in the YHV was extracted using supervised classification and normalized difference vegetation index(NDVI)time series changes.Then,by using rainfall datasets,soil property,digital elevation model(DEM),annual maximum NDVI and land use datasets,the soil conservation in YHV from 2000 to 2018 was simulated and the soil conservation effect of cropland change was analyzed based on Universal Soil Loss Equation(USLE).[Results]1)From 2000 to 2018,the land use change in the YHV was mainlythe decrease of cropland(6.08%),the increase of construction land and forest(1.45%and 8.06%).The loss of cropland was principally transferred to grassland,forest and construction land,which were mostly distributed in Qianshan area,the edge of Naoshan areas and river valleys,indicating that the change of cropland in the YHV in recent years was greatly affected by the project of converting cropland to forest and urbanization.2)In the past 20 years,the amount of soil conservation has continued to increase.Forest and grassland had accounted for more than 84%of the total soil conservation in the study area.The transfer of cropland to grassland and cropland to forest both resulted in soil conservation benefits,and the later had higher value because it mostly distributed in the Naoshan area with better water resources.Moreover,the soil conservation benefit of the cropland transfer in the Naoshan area was better than that in the Qianshan area,while the soil conservation amount of the cropland transfer plots in the flat terrain area such as river valley and loess tableland was even lower than that of the cropland in the same area.[Conclusions]Using RS technology and USLE model,the distribution and change characteristics of land use and soil conservation in the YHV from 2000 to 2018 were quantitatively assessed.In the YHV,the soil conservation effect of cropland change is obvious,and it is greatly affected by terrain and water resources.It will be the direction of soil and water conservation management in the future to adjust the structure of cropland and abandoned cropland and ensure the stable and long-term providing of vegetation and soil conservation function.