土地利用和植被覆盖变化对长汀县30多年土壤侵蚀变化的定量影响

土地利用和植被覆盖是人类活动对大自然改造的直接体现,为研究人类活动对土壤侵蚀的定量影响,以中国南方红壤典型水土流失区——福建省长汀县为研究区,利用每间隔3~4年的11个年份的遥感影像,基于USLE模型评估该县1988-2020年30多年来的土壤侵蚀时空变化特征,定量分析不同土地利用和植被覆盖度(fractional vegetation cover, FVC)变化对土壤侵蚀的影响。结果表明:(1)长汀县土壤侵蚀严重区域主要集中于县域中部河田镇、三洲镇和策武镇等地,30多年来,土壤侵蚀强度呈先增后减的趋势,1988-1994年土壤侵蚀状况逐渐严重,1994年的水土流失率高达30.49%,90年代中期后开始逐渐好转,至2020年水土流失率降为6.22%。(2)1988-1994年和1994-2001年2个时期,林地转化成裸地的面积最大,导致土壤侵蚀增加量平均约占每个时期增加量的93%;2001-2010年和2010-2020年2个时期,裸地转化成林地的面积最大,引起的土壤侵蚀减少量平均约占每个时期减少量的73%。(3)30多年来长汀县FVC呈先减少后增加的趋势,1988-1994年平均FVC从44%减少到35%,随后开始增加,至2020年,FVC增加至79%;土壤侵蚀量与FVC呈反比,FVC减少对土壤侵蚀量的影响更大,FVC平均每降低1%,土壤侵蚀量增加7.49万t;而FVC平均每增加1%,土壤侵蚀量减少3.75万t。(4)FVC对土壤侵蚀的敏感性与坡度呈正比,低坡度下土壤侵蚀随FVC变化较均匀,高坡度等级下,FVC低于60%时,对土壤侵蚀的敏感性高,FVC每增加10%,土壤侵蚀模数平均减少262.73 t/(km²·a)。研究结果有助于分析长汀县土壤侵蚀在长时间序列上的时空变化及人类活动对土壤侵蚀的影响,为长汀县未来的土地利用规划和生态保护提供重要的科学支持。

Quantitative Effects of Land Use and Vegetation Cover Changes on Soil Erosion in Changting County in Recent 30 Years

Land use and vegetation cover are direct manifestations of human activities in transforming nature. In order to quantitatively assess the impact of human activities on soil erosion, this study focuses on Changting County, a typical red soil erosion-prone area in southern China. Using remote sensing images from 11 years between 1988 and 2020 with 3- or 4-years interval, the USLE model was applied to evaluate the spatiotemporal characteristics of soil erosion in the county over the past 30 years, and the quantitative impact of different land use and Fractional Vegetation Cover (FVC) changes on soil erosion was analyzed. The results showed that:(1) The severe soil erosion in Changting County is mainly concentrated in the central areas of the county, including Hetian Town, Sanzhou Township, and Cewu Township. Over the past 30 years, the intensity of soil erosion showed an increasing trend followed by a decreasing trend. From 1988 to 1994, the situation of soil erosion became increasingly severe, with a soil erosion rate as high as 30.49% in 1994. Since the mid-1990s, the situation gradually improved, and by 2020, the soil erosion rate had decreased to 6.22%. (2) During the two periods of 1988-1994 and 1994-2001, the area of forest land converted to bare land was the largest, resulting in an average increase in soil erosion of about 93% for each period. During the two periods of 2001-2010 and 2010-2020, the area of bare land converted to forest land was the largest, resulting in an average reduction in soil erosion of about 73% for each period. (3) For over 30 years, the FVC in Changting County has shown a decreasing trend followed by an increasing trend. The average FVC decreased from 44% to 35% between 1988 and 1994, after which it began to increase. As of 2020, the FVC has increased to 79%. The soil erosion amount was inversely proportional to the FVC, and the impact of FVC reduction on soil erosion was greater. On average, for every 1% decrease in FVC, the soil erosion increased by 74 900 tons, while for every 1% increase in FVC, the soil erosion decreased by 37 500 tons. (4) The FVC in Changting County was negatively correlated with soil erosion intensity, and the sensitivity to soil erosion was positively correlated with slope. Under low slope conditions, soil erosion changed more uniformly with FVC, but under high slope conditions, when FVC was less than 60%, the sensitivity to soil erosion was high. For each 10% increase in FVC, the average soil erosion modulus in areas with a slope greater than 15° was reduced by 262.73 t/(km²·a). This study helps to analyze the spatiotemporal changes of soil erosion in Changting County over a long time series and the impact of human activities on soil erosion, providing important scientific support for future land use planning and ecological protection in Changting County.