Metal cation leaching affects soil aggregate stability via altering soil internal forces governed by specific ion effects during dry-wet cycles
Description
Research hypothesis We hypothesised that metal cation leaching induced by dry-wet cycles can affect soil internal force, thereby reducing aggregate stability, and specific ion effects playing critical roles throughout. In this study, both drainage and non-drainage conditions were employed to elucidate the mechanisms of metal cation leaching on soil aggregate stability via altering soil internal forces during dry-wet cycles. Overall, our findings indicate that soil aggregate stability decreased as the metal cation are leached during dry-wet cycles. Specifically, metal cation leaching reduces the quantity of metal cations adsorbed onto soil colloid surfaces, thereby enhancing the net force between soil particles and consequently decreasing aggregate stability during dry-wet cycles. Repeated dry-wet cycles lead to the stabilization of metal cation leaching and the net forces of soil internal forces, which directly govern soil aggregate stability. Additionally, significant specific ion effects on soil aggregate stability were observed during dry-wet cycles, mediated by cationic non-classical polarization that alters soil internal forces. In summary, metal cation leaching affects soil internal force, thereby reducing aggregate stability during dry-wet cycles, with specific ion effects playing critical roles throughout.
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Steps to reproduce
To quantitatively evaluate the impact of soil internal forces and specific ion effects on soil aggregate stability, soil samples were saturated by replacing the originally adsorbed heterogeneous ions with specific ion specie. To modulate the specific ion effects in soil, three monovalent cations (Li+, Na+, and K+) were selected due to their identical coulombic interactions and significantly different polarizabilities (Chen et al., 2020). In this study, soil samples were pretreated according to the procedure described by Liu et al. (2022). Briefly, air-dried soil samples were first exchanged with an XCl solution (X = Li, Na, or K), then washed with deionized water to remove excess X+ (X+ = Li+, Na+, or K+), oven-dried at 60 °C, and finally crushed and sieved to obtain pretreated soils (1-5 mm in diameter) for the dry-wet cycle simulation experiments. To indicate the effects of dry-wet cycles on soil aggregate stability, the pretreated soil samples were subjected to 9 dry-wet cycles. Each cycle was consisted of 24 h of wetting by immersion of the soil samples in water at 20 °C, followed by drying in an oven at 40 °C. Moreover, to indicate the differences between drainage and non-drainage conditions, two control experiments were conducted with and without leaching, and the leached solutions were collected to determine the electrolyte concentration of the respective cations (Fig. S1). In the experiment, various electrolyte solutions (i.e., LiCl, NaCl, or KCl at electrolyte concentrations of 1, 10-1, 10-2, 10-3, or 10-4 mol L-1) were applied to disintegrate soil aggregates. These solutions, at varying electrolyte concentrations, were used to modify soil internal forces. Additionally, distinct electrolyte solutions were employed to evaluate the specific ion effects on soil aggregate stability throughout the dry-wet cycles.
Institutions
- Chongqing Jiaotong University