坡面径流小区集流桶含沙量测量方法对比

Comparison of measurement methods of sediment concentration in collecting tanks of slope runoff plots

准确测量坡面径流小区集流桶含沙量是定量精准监测坡面土壤侵蚀的关键,野外径流小区观测方法测量精度、影响因素及其适用性的研究是实际应用的基础。该研究以第四纪红土为研究对象,采用室内模拟试验,对比不同含沙量(1.05、5.07、10.49、50.72、101.45、439.10 kg/m^3)、不同水深(30、60、90 cm)下4种集流桶含沙量测量方法的精度,并对测量结果进行修正。结果表明:1)在60cm水深、不同含沙量下,4种测定方法中,以机械+全剖面法测量误差总体最低;2)水深和含沙量是影响坡面径流小区集流桶取样测量误差的重要因素。总体而言,含沙量越高,测量误差越大;不同含沙量下,水深对测定误差影响程度不一,当含沙量小于50.72kg/m^3时,水深对机械+全剖面法测量精度无显著影响;3)4种方法的测量值与真实值均呈极显著正线性相关,含沙量测量值经过方程修正后相对误差明显降低。4)在含沙量小于5.07 kg/m^3时,人工搅拌法可以应用于野外径流小区观测;当含沙量大于等于101.45 kg/m^3后,全剖面法可以直接用于野外径流小区观测;机械法、机械+全剖面法在野外径流小区观测中可以直接使用。研究结果为集流桶含沙量取样测量方法在红壤区应用提供依据。

The accurate measurement of sediment concentration in collecting tanks of slope runoff plots is a key to quantitatively monitor slope soil erosion.The researches on measuring accuracy,influencing factors and applicability of field runoff plot observation methods are needed.In this study,four methods of sediment concentration were compared.The test was taken in quaternary red earth.The soil samples were taken from surface of farmland(0-20 cm).Six sediment concentrations(1.05,5.07,10.49,50.72,101.45 and 439.10 kg/m^3)were designed based on the measured sediment concentration range from 2012 to 2016 in slope farmland.Three water depths were set up including 30,60 and 90 cm.Four methods included Artificial Method(AM),Mechanical Method(MM),Dept Profile Method(PM)and MM+PM.The measurement accuracy was evaluated by relative error.Each treatment was replicated three times.The results show that compared with the true value,the measurement accuracy of different method for determining sediment concentration was low.The averages of absolute relative error for the AM,MM,PM and MM+PM were 37%,24%,38%and14%,respectively.The measurement accuracy of different methods was 14%or above.Among them,the accuracy of MM+PM was the highest.In general,the relative error of each method was large under the condition of high sediment concentration.The depth of water had different influence on different sampling methods.Comparatively,the measurement error of AM was most significantly affected by water depth.Under low sediment concentration,when the water depth increased to 60 cm,the measurement error significantly increased,but when the water depth continued to increase,the measurement error did not increase.When the sediment concentration was 101.45 kg/m^3,the relative error of MM only increased significantly after the water depth increased to 90 cm.When the sediment concentration was 59.72 kg/m^3,no obvious relationship was found between the measurement accuracy of the PM method and the water depth.When the sediment concentration was more than 5.07 kg/m^3,the measurement accuracy of the MM+PM method was almost not affected by water depth.The linear equation was used to modify the sediment concentration measurement results of the four methods.All R^2 were greater than 0.99(P<0.01),and the root-mean-square error was 4.53-11.37 kg/m^3,which indicated the reliability of the linear regression equation and the equation could be used to calibrate the measured values of each method.The relative error of the measured values of each method was significantly reduced and the measurement accuracy was significantly improved.The practical range of these equations was 1.05-439.10 kg/m^3 and the water depth was 60 cm.The results of this study could support the selection of sampling methods under different conditions.The results of this study could be used to revise the sediment concentration in collecting tanks of slope runoff plots in red soil area.