Linking pore network characteristics extracted from CT images to the transport of solute and colloid tracers in soils under different tillage managements

A new method to trace colloid transport pathways in macroporous soils using X‐ray computed tomography and fluorescence macrophotography

“…Following this approach, in a previous article (Soto‐Gómez, Pérez‐Rodríguez, Vázquez‐Juiz, López‐Periago, & Paradelo, ) we reported significant correlations among macroscopic descriptors of CT porosity, soil physical properties and some parameters of the advection–diffusion equation with dual porosity. These correlations suggested the importance of particle trapping on the macropore walls.…”

“…The general procedures for soil sampling, CT scanning and breakthrough experiments were described in Soto‐Gómez et al (); therefore, they are only briefly explained here. In the present study, 16 undisturbed soil columns (100‐mm height × 84‐mm diameter) were sampled from two adjacent experimental plots (Centro de Desenvolvemento Agrogandeiro, Ourense, NW Spain, coordinates 42.099 N–7.726 W WGS84): eight columns from a plot devoted to organic agriculture with more and less earthworm activity deduced in the field from the signs of surface alteration (named Org.…”

“…The water content of columns during breakthrough was close to saturation with an effective saturation of 0.92 ± 0.03, and the flow boundary conditions were a constant flux at the upper boundary with a flow rate of ~10 mL hr ‐1 (5.1 mm hr ‐1 ) and a seepage face at the bottom. The flow rate was reduced in some columns (nos 9, 10, 15 and 19) to avoid surface ponding resulting from the decrease in infiltration at late stages of the breakthrough (for further information, see Soto‐Gómez et al ()). Water and microsphere suspensions were distributed dropwise at random points across the topsoil surface by a robotic arm attached to a dripper connected to a peristaltic pump (Minipuls III pump, Gilson Inc., Middleton, WI, USA).…”

Colloid transport through soil and other porous media under transient flow conditions—A review

“…Synchrotron radiation X‐ray fluorescence has been used to measure the in situ colloid concentration and moisture content in soil column experiments (DiCarlo et al, 2006). More recently, X‐ray computed tomography (CT) has been used to extract macropore networks in soil columns (Carrel et al, 2017, 2018; Soto‐Gómez, Pérez‐Rodríguez, Vázquez‐Juiz, López‐Periago, & Paradelo, 2018) allowing to link the characteristics of the extracted macropore networks to the transport characteristics of colloids. Development and wider application of existing as well as new techniques such as the 19‐port sampling system by Mohanty, Bulicek, et al (2015) (Figure 6) to visualize and measure in situ moisture content and colloid concentration in porous media (Crist et al, 2004; DiCarlo et al, 2006; Keller & Auset, 2007; Soto‐Gómez et al, 2018, 2019), and to differentiate different flow pathways and colloid attachment sites (Auset & Keller, 2006; Baumann & Werth, 2004; Lanning & Ford, 2002; Zhang, Hassanizadeh, Liu, Schijven, & Karadimitriou, 2014) offer promising methods and technologies to advance understanding of the fate and transport of colloids in transient flow systems.…”

Reflection on Jarvis (2007), “Review of non‐equilibrium water flow and solute transport in soil macropores: Principles, controlling factors and consequences for water quality”. European Journal of Soil Science, 58, 523–546

“…I thought that more research was needed to: assess the significance of macropore flow for leaching of strongly adsorbing contaminants, especially the role of small‐scale processes such as rates of biodegradation and kinetic sorption effects in macropores and colloid‐bound transport Since 2007, research has shown that the quantitative contribution of colloid‐bound transport to leaching of strongly adsorbing contaminants varies greatly depending on soil and compound properties and management practices (e.g., Andersson, Bergström, Djodjic, Ulén, & Kirchmann, ; Kjaer et al, ; Ulén, Gunborg, Kreuger, Svanbäck, & Etana, ; Vendelboe, Moldrup, Heckrath, Jin, & de Jonge, ). The use of novel colloidal tracers has also provided new insights into the mechanisms of colloid and particle transport and retention in soil macropores under both field and laboratory conditions (e.g., Cey, Rudolph, & Passmore, ; Koch, Kahle, & Lennartz, ; Soto‐Gómez, Pérez‐Rodríguez, Vázquez Juiz, López‐Periago, & Paradelo, ; Soto‐Gómez, Pérez‐Rodríguez, Vázquez Juiz, López‐Periago, & Paradelo Perez, ). Enhanced degradation rates of pesticides have been measured in soil sampled from macropore linings, but the empirical evidence is still too limited to draw general conclusions (Dechesne, Badawi, Aamand, & Smets, ).…”