Turbidity And Sediment Response And Its Influencing Factors Based On Watershed Monitoring Technology

The intensification of sugarcane plantation slope farmland in Guangxi,the long-term monocropping of sugarcane and excessive fertilization accelerated the local soil erosion and nutrient loss,resulting in serious surface water pollution.At present,many scholars have conducted research on soil erosion in sugarcane areas in Guangxi,so it is particularly important to estimate the soil erosion status of sugarcane areas.Turbidity and sediment on-line monitoring system can timely and accurately grasp the situation of soil erosion,and provide a key basis for soil erosion control.In this study,the small watershed of Nachao District,the water source of Kelan Reservoir,Zuojiang Basin,Guangxi,was taken as the research object.The online monitoring platform of sediment and turbidity in the basin was used to monitor for two years(January 1,2021 to December 31,2022).Information of sugarcane at different growth stages(seedling stage,tillering stage,elongation stage,maturity stage),vegetation cover,rainfall and runoff were collected to explore the response relationship between turbidity and sediment and its influencing factors at small watershed scale.To provide basic scientific basis and data support for the control of agricultural non-point source pollution in this area.The main results and conclusions are as follows:(1)In 2021 and 2022,a total of 37 rainfall events were monitored and a total of 1920 sediment samples were collected.The total runoff in 2021 was less than that in 2022,but the sediment loss in 2021 was greater than that in 2022.The total mean turbidity and total mean sediment concentration decreased over time.The total mean turbidity in 2022 was 47.3%lower than that in 2021,and the total mean sediment concentration was 60.9%lower than that in 2021.(2)There was a significant correlation between turbidity and sediment in the whole growth period of sugarcane in the Nanla small watershed,and the relationship was y=0.0009x-0.005,R~2=0.9063,δ=±12.379%.(3)The measured total mean turbidity in 2021 and 2022 was substituted into the equation to check the calculation,and the relative error in 2021 and 2022was 8.235%and 4.066%.After substituting the measured total mean turbidity of the three sub-basins in two years,the relative errors of the three sub-basins in2021 are-8.809%,-15.035%and 18.018%,respectively,and those of the three sub-basins in 2022 are-11.563%,-22.829%and-31.869%,respectively.The results show that the turbidity and sediment technology monitoring platform can accurately reflect the relationship between turbidity and sediment,and can accurately estimate the soil loss of sugarcane during the whole growth period.(4)The rainfall runoff depth was positively correlated with the R~2 values of turbidity and sediment concentration(p<0.01),the total coverage of the basin was not significantly correlated with the R~2 values of turbidity and sediment concentration(p<0.01),and the vegetation coverage in 2021 was negatively correlated with the R~2 values of turbidity and sediment concentration(P<0.01).There was a significant negative correlation between vegetation coverage and the R~2 values of turbidity and sediment concentration in 2022(p<0.05).