Abstract:
Background The sugarcane planting area expanded to the hilly land, which intensified the soil erosion intensity in the sugarcane plantation area of Guangxi. Driven by rainfall and runoff, eroding sediment and nutrients into the water, causing serious environmental pollution. However, there are few methods to determine the eroded sediment from sugarcane fields into river. Therefore, determining the appropriate method to the eroding sediment export load from sugarcane fields, which is of great significance to control soil erosion and select the reasonable soil and water conservation measures in sugarcane growth regions.
Methods In this study, a small sugarcane growing watershed in Guangxi was selected to determine the proportion of sugarcane eroding sediment contribution based on Compound Specific Stable Isotopes (CSSI). Soil loss were determined by field monitoring, 7Be tracer technique and RUSLE model under three heavy rainfall events during the early sugarcane planting period in 2020-2021. Sediment export load from sugarcane land were estimated by combinative use of field monitoring, 7Be tracer technique, RUSLE model and CSSI techniques, respectively.
Results 1) Eroding sediment from sugarcane land contributed 24.5% to 42.8% in Nala watershed, which was one of the main source of sediment into the river. 2) Soil loss measured by the three methods ranged from 0.18 to 5.57 t/hm2 under single rainfall event in the order of 7Be technique > RUSLE > Monitoring. 3) Sediment export load from sugarcane was between 0.04 and 1.07 t/hm2 determined by Monitoring-CSSI method. Compared with the results of Monitoring-CSSI method, the relative error of 7Be-CSSI method was 2.74% to 1672.63%, Nash-Sutcliffe (E) coefficient was –1.47. The relative error of RUSLE-CSSI method ranged from –16.42% to 208.41%, and E value was 0.8.
Conclusions Compared with the export load from sugarcane land measured by monitoring-CSSI method, the results of 7Be-CSSI method and RUSLE-CSSI method both have large error. Thus, those two methods are unsuitable for determining sediment export load from watershed.
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