1:45 PM - 2:00 PM
[AGE34-01] Relationship between soil erodibility by concentrated flow and particle-particle interactions of a Shimajiri Maaji soil with a cationic polyelectrolyte
★Invited Papers
Keywords:soil erosion, erodibility, rill erosion, shear strength, aggregation, soil particles interaction
Soil water erosion causes not only soil degradation of a field but also aquatic contamination and sedimentation in a basin. Therefore, predicting and preventing soil erosion is crucial for sustainable land use and environmental conservation. To clarify the governing parameters of soil erodibility, many previous studies have focused on the relationship between soil erodibility and physical properties of soil such as size distribution, organic matter content, and dry bulk density. On the other hand, a small number of studies have been conducted on the effects of physicochemical properties on soil erodibility, and their effectiveness is not fully understood. In this study, the relationship between soil erodibility of Shimajiri Maaji soil under concentrated flow and soil particle-particle interactions was examined through systematic rill erosion experiments with different soil particles interactions.
Shimajiri Maaji soil, collected from a sugarcane field on Ishigaki Island, Okinawa, was used for this study. The interactions of Shimajiri Maaji soil particles were tuned by adding a poly(diallyldimethylammonium chloride) (PDADMAC), a strong cationic polyelectrolyte, as a soil conditioner. Soil particle-particle interactions were evaluated by measuring the soil shear strength and light transmission of the supernatant of soil suspension with PDADMAC. Furthermore, the interaction mechanisms were examined by measuring the electrophoretic mobility (EPM). The rill erosion experiment was performed using a small model flume as a function of the mass ratio of PDADMAC to Shimajiri Maaji soil. Erodibility was represented by using rill erodibility parameters, rill erodibility and critical shear stress, in the excess shear stress model for rill erosion.
The EPM of Shimajiri Maaji soil particles increased from negative to positive with increasing the mass ratio of PDADMAC to Shimajiri Maaji soil. The increase in the mass ratio of PDADMAC to Shimajiri Maaji soil increased the transmission of soil suspensions to a maximum, which is located around the isoelectric point. Further additions of PDADMAC decreased the transmissions. These results show that Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions govern the aggregation and dispersion behavior of Shimajiri Maaji soil.
The shear strength monotonically increased with an increasing the mass ratio of PDADMAC to Shimajiri Maaji soil, even when soil particles were positively charged and electric double layer repulsion was in effect. The difference in trends between shear strength and transmission shows that shear strength is more sensitive to non-DLVO forces than transmission. This should be because shear strength, which is attributed to the broken/retract process, has a smaller characteristic length than transmission, which is attributed to the collision/approaching process.
Rill erodibility decreased with increasing shear strength, even when Shimajiri Maaji soil was positively charged. Furthermore, rill erodibility could be represented by a linear function of shear strength. These results clearly show that strong soil particle-particle attractions decrease rill erodibility. In other words, the high attractive force between soil particles prevents soil particles/aggregates from peeling off by increasing the shear stress from flowing water. Additionally, particle-particle interactions should be estimated with a parameter that is attributed to the retraction/broken process. Measuring shear strength is usually easier than measuring rill erodibility. Therefore, our results could potentially be used for a quick estimation of the effect of soil conditioners on the reduction of rill erodibility.
Shimajiri Maaji soil, collected from a sugarcane field on Ishigaki Island, Okinawa, was used for this study. The interactions of Shimajiri Maaji soil particles were tuned by adding a poly(diallyldimethylammonium chloride) (PDADMAC), a strong cationic polyelectrolyte, as a soil conditioner. Soil particle-particle interactions were evaluated by measuring the soil shear strength and light transmission of the supernatant of soil suspension with PDADMAC. Furthermore, the interaction mechanisms were examined by measuring the electrophoretic mobility (EPM). The rill erosion experiment was performed using a small model flume as a function of the mass ratio of PDADMAC to Shimajiri Maaji soil. Erodibility was represented by using rill erodibility parameters, rill erodibility and critical shear stress, in the excess shear stress model for rill erosion.
The EPM of Shimajiri Maaji soil particles increased from negative to positive with increasing the mass ratio of PDADMAC to Shimajiri Maaji soil. The increase in the mass ratio of PDADMAC to Shimajiri Maaji soil increased the transmission of soil suspensions to a maximum, which is located around the isoelectric point. Further additions of PDADMAC decreased the transmissions. These results show that Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions govern the aggregation and dispersion behavior of Shimajiri Maaji soil.
The shear strength monotonically increased with an increasing the mass ratio of PDADMAC to Shimajiri Maaji soil, even when soil particles were positively charged and electric double layer repulsion was in effect. The difference in trends between shear strength and transmission shows that shear strength is more sensitive to non-DLVO forces than transmission. This should be because shear strength, which is attributed to the broken/retract process, has a smaller characteristic length than transmission, which is attributed to the collision/approaching process.
Rill erodibility decreased with increasing shear strength, even when Shimajiri Maaji soil was positively charged. Furthermore, rill erodibility could be represented by a linear function of shear strength. These results clearly show that strong soil particle-particle attractions decrease rill erodibility. In other words, the high attractive force between soil particles prevents soil particles/aggregates from peeling off by increasing the shear stress from flowing water. Additionally, particle-particle interactions should be estimated with a parameter that is attributed to the retraction/broken process. Measuring shear strength is usually easier than measuring rill erodibility. Therefore, our results could potentially be used for a quick estimation of the effect of soil conditioners on the reduction of rill erodibility.