Application of a Cellular Automaton Method to Model the Structure Formation in Soils Under Saturated Conditions: A Mechanistic Approach

Abstract

Soil functions are closely related to the structure of soil microaggregates. Yet, the mechanisms controlling the establishment of soil structure are diverse and partly unknown. Hence, the understanding of soil processes and functions requires the connection of the concepts on the formation and consolidation of soil structural elements across scales that are hard to observe experimentally. At the bottom level, the dynamics of microaggregate development and restructuring build the basis for transport phenomena at the continuum scale. By modeling the interactions of specific minerals and/or organic matter, we aim to identify the mechanisms that control the evolution of structure and establishment of stationary aggregate properties. We present a mechanistic framework based on a cellular automaton model to simulate the interplay between the prototypic building units of soil microaggregates quartz, goethite, and illite subject to attractive and repulsive electrostatic interaction forces. The resulting structures are quantified by morphological measures. We investigated shielding effects due to charge neutralization and the aggregate growth rate in response to the net system charge. We found that the fraction as well as the size of the interacting oppositely charged constituents control the size, shape, and amount of occurring aggregates. Furthermore, the concentration in terms of the liquid solid ratio has been shown to increase the aggregation rate. We further adopt the model for an assessment of the temporal evolution of aggregate formation due to successive formation of particle dimers at early stages in comparison to higher order aggregates at later stages. With that we show the effect of composition, charge, size ratio, time, and concentration on microaggregate formation by the application of a mechanistic model which also provides predictions for soil aggregation behavior in case an observation is inhibited by experimental limitations.

Explicit spatial modeling at the pore scale unravels the interplay of soil organic carbon storage and structure dynamics

“…by occlusion. The range of potential movement was characterized by a stencil, which was higher for small clay particles than that for large aggregates (Rupp et al, 2019; Zech et al, 2020). More precisely, stencil sizes between 10 μm, i.e.…”

“…The CAM enables the change of the explicit porous structure over time. The CAM rules were based upon the ones described previously (Ray et al, 2017;Rupp et al, 2018Rupp et al, , 2019Zech et al, 2020) for the reorganization of single solid pixels and building units. Compared with these publications, we here applied the CAM for the relocation of building units with realistic shapes based on experimental data and also POM particles and considered the impact of reactive and memory edges.…”

“…For this we used a cellular automaton method (CAM) which extends a process‐based mathematical model that was introduced by Ray et al (2017) and Rupp et al (2018). The CAM was successfully used to describe and study structure formation of microaggregates using minerals and oxides as idealized prototypic building units (Rupp et al, 2019; Zech et al, 2020). Zech, Ritschel, et al (2022) further adapted and applied the model to study microbial population dynamics and the turnover of POM in microaggregates based on static μCT images.…”

Accounting for soil architecture and microbial dynamics in microscale models: Current practices in soil science and the path ahead

“…Timeresolved methods to image the dynamics of soil architecture (e.g., Bottinelli et al, 2016) provide experimental data that can potentially be used as direct model inputs. Recent attempts to simulate the evolution of soil architecture as a result of microbial activity (Ray et al, 2017) or physicochemical processes (Rupp et al, 2019), together with research focusing on the role of roots in modifying the geometrical arrangement of soil particles (Aravena et al, 2014;Kolb, Legué, & Bogeat-Triboulot, 2007), will certainly open new avenues to bridge knowledge gaps.…”

Understanding the joint impacts of soil architecture and microbial dynamics on soil functions: Insights derived from microscale models

“…However, these models face a number of limitations in describing the complexity of soil architecture and microbial life. Most of them describe a static soil architecture although innovative studies have attempted to investigate the feedback loops between architecture and microbes (Crawford et al, 2012;Ray et al, 2017) or roots (Aravena et al, 2014;Kolb et al, 2017) and physico-chemical processes (Rupp et al, 2019). Regarding ecological interactions, a number of simplifications have been undertaken, such as, among others, a simplification of soil biodiversity and an omission of the role of living roots (Pot et al, 2021).…”