Abstract
Preferential flow paths have been widely characterized by many visualization methods. However, the differences in preferential flow paths under various land uses and their relationships to hydraulic properties remain uncertain. The objectives of this study are to (1) characterize preferential flow paths under various land uses (forest and orchard) by combining drainage and dye-staining methods and to (2) build a connection between preferential flow paths and hydraulic-related parameters and extract the proportion of preferential flow paths from the compounding effects of matrix flow and preferential flow. The dye-staining experiments were conducted in five sandy soils and one sandy clay loam in situ, including four soils from forest and two soils from orchards. A total of 47 soil cores, 4 cm in height and 9 cm in diameter, were collected in each layer of the dye-stained soils for drainage experiments in the laboratory. Dye coverage and hydraulically equivalent macropore parameters (macroporosity, pore size distribution, and number of macropores) and their relationships were analyzed. The results show that the volume of preferential flow is partly affected by the total macropore volume. The effect of macropores on preferential flow varies by macropore size distribution. Dye coverage exhibited a significant (P < 0.01) correlation with macroporosity (correlation coefficient 0.83). Based on the value of macroporosity or steady effluent rates, the part of the dye coverage that was due to preferential flow on the surface dye-stained soil (resulting from both matrix and preferential flow) could be identified in this study. Compared with orchards, forestland has more preferential flow paths in both surface soil and subsoil. Further studies are needed to quantify the 3-D preferential flow paths and build a connection between preferential flow paths and hydraulic properties.
Highlights
The importance of preferential flow as a transport mechanism of water and solute is widely recognized [1,2,3,4]
They emphasized that land use has an important effect on the formation of preferential flow paths because root distribution and soil properties are quite different according to the type of land use
Dyestained proportions of the 1st soil layers in the A and B sites were greater than 80% (Figure 4). This result is similar to the results obtained by Öhrström [23], who reported dye coverage levels of close to 100% in the upper 5 to 10 cm soil layer
Summary
The importance of preferential flow as a transport mechanism of water and solute is widely recognized [1,2,3,4]. Land use and soil type are the main factors that influence the formation and distribution of preferential flow paths. Cheng [17] reported that vertically oriented preferential flow paths differed significantly under forestland, shrubland, and farmland. They emphasized that land use has an important effect on the formation of preferential flow paths because root distribution and soil properties are quite different according to the type of land use. Price [18] noted that soils under natural conditions generally exhibited higher macroporosity compared to soil impacted by human activities
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