Field-scale Variation in Colloid Dispersibility and Transport: Multiple Linear Regressions to Soil Physico-Chemical and Structural Properties

Abstract

Water-dispersible soil colloids (WDC) act as carriers for sorbing chemicals in macroporous soils and hence constitute a significant risk for the aquatic environment. The prediction of WDC readily available for facilitated chemical transport is an unsolved challenge. This study identifies key parameters and predictive indicators for assessing field-scale variation of WDC. Samples representing three measurement scales (1- to 2-mm aggregates, intact 100-cm rings, and intact 6283 cm columns) were retrieved from the topsoil of a 1.69-ha agricultural field in a 15-m by 15-m grid to determine colloid dispersibility, mobilization, and transport. The amount of WDC was determined using (i) a laser diffraction method on 1- to 2-mm aggregates and (ii) an end-over-end shaking method on 100-cm intact rings. The accumulated amount of colloids leached from 20-cm by 20-cm intact columns was determined as a measure of the integrated colloid mobilization and transport. The WDC and the accumulated colloid transport were higher in samples from the northern part of the field. Using multiple linear regression (MLR) analyses, WDC or amount of colloids transported were predicted at the three measurement scales from 24 measured, geo-referenced parameters to identify parameters that could serve as indicator parameters for screening for colloid dispersibility, mobilization, and transport. The MLR analyses were performed at each sample scale using all, only northern, and only southern field locations. Generally, the predictive power of the regression models was best on the smallest 1- to 2-mm aggregate scale. Overall, our results suggest that different drivers controlled colloid dispersibility and transport at the three measurement scales and in the two subareas of the field.

Prediction of the glyphosate sorption coefficient across two loamy agricultural fields

“…For all of the geographical scenarios, the increasing rate of R 2 with increasing parameter set size decreased after around four parameters suggesting that only four parameters need to be considered in defining a screening set. A similar result was found by Norgaard et al (2014b) for predicting colloid dispersibility and transport with a limited number of informative parameters that are feasible to measure at the field scale.…”

“…The analyses used in this paper follow directly those used to predict colloid dispersibility, mobility, and transport at the experimental site in Silstrup (Norgaard et al, 2014b). To examine the interactions among parameters, a multiple linear regression (MLR) analysis was performed to relate K d to every combination of nine measured soil properties (pH, EC, clay, sand, OC, Al OX Fe OX , P OX , and Olsen P).…”

“…We examined the combinations of properties in sets of varying size best able (defined by maximum R 2 ) to explain sorption of glyphosate in different scenarios: each field separately and both fields together. In addition, Silstrup was split into a northern and southern section, because this site showed marked differences between North and South in solute transport behavior and colloid dispersibility and leaching (Norgaard et al, 2014b).…”

“…For each subset of parameters considered, the goodness of the fit (R 2 ) and the significance level (p for significance, α = 0.05) were calculated. This analysis was applied previously to predict colloid dispersibility, mobilization and transport at different soil sample scales (Norgaard et al,2014b). Fig.…”

Pedogenesis significantly decreases the stability of water-dispersible soil colloids in a humid tropical region

“…The magnitude of F a and F r is controlled by the ΔpH (i.e. the difference between the pH of the suspension and the pH PZC of the colloids; pH PZC is the pH at which the net charge on the colloid surface is zero) and the solution ionic strength (Goldberg et al, 1988;Norgaard et al, 2014;Seta and Karathanasis, 1996). When Δ pH increases, F r also increases, thus leading to colloids stability (dispersion).…”