Macroscopic Evidence of Sources of Particles for Facilitated Transport during Intensive Rain

Abstract

Particulate transport of pesticides, heavy metals, and phosphate in soil is of interest when evaluating water contamination risk; however, researchers differ in their view of how and where the contaminated particles are mobilized. The main line of thought is that the particles originate in the soil, as a function of concentration differences between aggregate surfaces and surrounding immobile water, and move into mobile water by diffusion. Furthermore, material can be stored at the air–water interface. Low electrical conductivity enhances the formation of mobile particles. Other researchers consider the generation to take place close to the soil surface, as a side effect of splash erosion. By combining data on particle concentrations and the amounts of particle‐bound glyphosate [N‐(phosphonomethyl)glycine] from three leaching experiments with information about glyphosate on splashed material and the distribution of glyphosate in the soil, we concluded that the particles from the top 0.5 cm of the soil column contribute more than proportionally (up to 50%) to the particles in the leachate. The development in particle concentration with time and in columns with different properties indicated that particle generation took place both inside the column and as a result of the splash process. The leached particles that are generated inside the column probably stem from the flow‐active part of the plow layer, a volume that differs from column to column and between tillage treatments.