Abstract: To explore the characteristics of soil erosion and nutrient loss in forestland since the implementation of the project of returning farmland to the forest in Dianchi lake watershed, Dongdahe small watershed located in the southwest of Dianchi Lake was selected as the study target area, and the soil erosion modulus of the forest land was estimated by the radionuclide¹³⁷Cs tracer technology. The change of nutrient content was analyzed and the effects of slope and vegetation coverage and soil particle composition on soil erosion were also discussed. The results showed that, the specific activity of¹³⁷Cs in the forestland soil profile decreased exponentially, and soil erosion was mainly affected by natural factors. The total erosion amount of the forest land in the basin was 69.28× 10³ t·a^-1, and the erosion intensity is mainly mild. The erosion modulus was 1 039.40 to 2 402.12 t·km^-2·a^-1.The total loss of TOC, TN and TP in the forestland of Dongdahe watershed was 1 963.5 t·a^-1, 209.1 t·a^-1, and 98.94 t·a^-1, respectively. The contents of TOC and TN in the soil were positively correlated with¹³⁷Cs (P<0.01), indicating that they had similar physical migration characteristics. The regularity of soil nutrient loss was consistent with that of soil erosion. The spatial differences in soil erosion intensity and nutrient loss were great. Soil clay content has a significant negative correlation with soil erosion (P<0.01). The effect of slope and vegetation coverage on soil erosion was obvious in a certain range. The erosion situation was relatively severe in woodlands with a slope of 10~25° and vegetation coverage of less than 0.4. The average erosion amount was about 1709.85 t·km^-2·a^-1. It is necessary to strengthen the protection of 10~25° mountain vegetation to reduce the local soil erosion and to restore the ecology. It provides a reference basis for promoting the project of returning farmland to forest and maintaining the benefit of soil and water conservation

Key words: Dongdahe small watershed, woodland, ¹³⁷Cs, nutrient loss, soil erosion

摘要： 为探究滇池流域自实施退耕还林工程以来的林地土壤侵蚀及养分流失特征,本研究以滇池西南部东大河小流域为研究靶区,利用放射性核素¹³⁷Cs示踪技术,对该区域内林地的土壤侵蚀模数进行估算,分析养分含量变化,并主要探讨了坡度、植被覆盖率及土壤颗粒组成对土壤侵蚀的影响。结果表明,林地土壤剖面中的¹³⁷Cs比活度呈指数下降趋势,以自然侵蚀为主。流域林地总侵蚀量为69.28×10³ t·a^-1, 侵蚀强度以轻度侵蚀为主,侵蚀模数介于1 039.40~2 402.12 t·km^-2·a^-1。东大河流域林地总有机碳(TOC)、总氮(TN)、总磷(TP)总流失量分别为1 963.5、209.1、98.94 t·a^-1,土壤TOC、TN含量与¹³⁷Cs比活度呈极显著正相关关系,物理迁移特征相似。土壤养分流失与土壤侵蚀规律较为一致。土壤侵蚀强度以及养分流失空间差异性较大。土壤黏粒含量与土壤侵蚀呈极显著负相关关系,坡度及植被覆盖率在一定范围内对土壤侵蚀的影响明显,坡度为10~25°以及植被覆盖率小于40%的林地中侵蚀状况相对严峻,平均侵蚀量约为1 709.85 t·km^-2·a^-1,需加强10~25°山地植被保护。本研究为减少当地水土流失,恢复生态以及继续推动退耕还林工程,保证退耕还林工程的效益提供了参考依据。

关键词: 东大河小流域, 林地, ¹³⁷Cs, 养分流失, 土壤侵蚀