Replacing the (inefficient) manual runoff sampling method used in Brazil – a prototype sample splitter

ABSTRACT The method used to sample the runoff collected from soil erosion plots can be a significant source of error. In this study, we performed a laboratory experiment to evaluate the efficiency of the runoff sampling method most commonly used in Brazil. It is based on the manual homogenization and sampling of the collected runoff. Using soil material with 583 g kg–1 of sand and 89 g kg–1 of clay, the manual sampling method was tested for its ability to produce representative samples of artificial suspensions with a concentration of 2, 10 and 50 g L–1 of total solids. An underestimation of 30 % or more of the concentration of total solids was observed, with a variation of the same magnitude (CV between 20 and 45 %). We then developed a prototype sample splitter to replace the manual sampling method and tested it using the same artificial suspensions. The splitter was efficient in producing samples representative of the artificial suspensions, even without altering the particle size distribution of the total solids. Both absolute percentage errors (|< 5 %|) and the variation between five replicates (CV < 3 %) were small. The problems with the manual method are due to the inefficient homogenization that facilitates the differential sedimentation of particles of different sizes. If these problems are also found in other areas, then the prototype that we developed is a reasonable alternative.

摘要 从土壤侵蚀小区采集径流的采样方法，可能是引入误差的重要来源。本研究通过室内试验，对巴西最常用的径流采样方法的效能开展评估。该方法依托对采集所得径流的人工均质化处理与采样流程。本研究采用砂粒含量583 g·kg⁻¹、黏粒含量89 g·kg⁻¹的土壤材料，针对总固体浓度分别为2、10、50 g·L⁻¹的人工悬浮液，检验该人工采样方法能否获取具有代表性的样品。研究观测到总固体浓度被低估30%及以上，且离散程度与之相当（变异系数Coefficient of Variation，CV介于20%~45%）。随后，本研究研发了一款原型分样器以替代人工采样方法，并采用同款人工悬浮液对其开展测试。该分样器可有效获取具备代表性的人工悬浮液样品，且不会改变总固体的粒径分布。绝对百分比误差（绝对值<5%）与五次重复样品间的变异程度（CV<3%）均处于较低水平。人工采样方法的上述问题，源于均质化效率不足，进而导致不同粒径颗粒发生差异沉降。若其他领域也存在同类问题，则本研究研发的原型分样器可作为合理替代方案。