Effects of rainfall and vegetation change on soil erosion and sediment yield in typical small watershed in hilly area of central Sichuan Basin
FU Yan1, ZHENG Jiangkun1, REN Yuzhi1, WANG Wenwu1, ZEN Qianting1, XIANG Minghui2, CHENG Xin2, ZHANG Yunqi1, ZHAO Peng1
1. Key Laboratory of Soil and Water Conservation & Desertification Combating of Sichuan Provincial Colleges and Universities, College of Forestry, Sichuan Agricultural University, 611130, Chengdu, China;
2. Water and Soil Conservation Experiment Station of Suining City, 629006, Suining, Sichuan, China
Abstract：[Background] It is found that vegetation plays an important role in soil and water conservation. This paper is to understand the effect of vegetation change on soil erosion and sediment yield in Xiejiawan watershed,a small watershed in hilly area of central Sichuan Basin, under annual and individual rainfall scales.[Methods] Based on the data of rainfall and sediment yield of Xiejiawan watershed over 30 years, RUSLE model was used to calculate the rainfall erosivity of the small watershed. Combined Land-Use and Land-Cover Change (LUCC) with soil and water conservation engineering adjustment, the causes of soil erosion and sediment yield were quantitatively evaluated by the double cumulative curve method and the separation discriminant method during different periods in the small watershed.[Results] 1) During 1986-2016, rainfall and erosive rainfall in Xiejiawan watershed occurred mainly in June, July and August which accounted for 80% of that in all the year. Therefore,soil and water conservation projects should be strengthened in summer. 2) Interannual variability of rainfall and erosive rainfall were not obvious during 1986-2016, meanwhile, annual mean sediment modulus during 1990-2008 was obviously less than the values during 1986-1989 and 2009-2016. Soil erosion and sediment yield decreased dramatically when LUCC changed from farmland to orchard. The soil and water conservation engineering measures were destroyed seriously when the forest land was abandoned, resulting in the amount of soil erosion increased at initial stage of abandoned period and decreased gradually after the restoration of understory herbs at later stage of abandoned period. According to LUCC and the trend of double cumulative curve, the time period was divided into crop period (1986-1989), orchard period (1990-2008) and abandoned period (2009-2016). 3) Taking crop period as the base period, the contribution rates of vegetation and rainfall on sediment reduction were 78% and 22%, respectively when crop was transformed into orchard, which indicated that planting orchard effectively reduced the sediment transport modulus in the small watershed. This was mainly due to the increase of canopy coverage enhanced soil consolidation capacity of roots, and the strengthened repair and management of terrace ridges. 4) Taking orchard period as the base period, the contribution rates of vegetation change and rainfall on sediment increase were 88% and 12%, respectively in abandoned period. As the results of lacking land management and drainage, terrace ridges were damaged a lot, which increased sediment yield. Furthermore, sediment yield was positively correlated with rainfall during crop period. Sediment yield was directly related to vegetation coverage and the improvement of terrace ridge measures during orchard period and abandoned period. The sediment reduction effect of vegetation coverage was obvious in a certain range of rainfall erosivity. When the vegetation coverage exceeded the critical value, the sediment reduction effect of vegetation became weaker.[Conclusions] When other conditions remain unchanged, soil erosion and sediment yield is reduced significantly by increasing surface coverage. It plays an important guiding role in soil and water conservation in purple soil watershed by increasing tree and shrub layer, laying soil and water conservation projects, and effective field management.
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FU Yan, ZHENG Jiangkun, REN Yuzhi, WANG Wenwu, ZEN Qianting, XIANG Minghui, CHENG Xin, ZHANG Yunqi, ZHAO Peng. Effects of rainfall and vegetation change on soil erosion and sediment yield in typical small watershed in hilly area of central Sichuan Basin. SSWC, 2019, 17(4): 67-74.
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2019, Vol. 17 
