Mitigation of aeolian erosion of loess soil by Bio-Stimulated microbial induced calcite precipitation

Abstract

Microbial-induced calcite precipitation (MICP) is a soil amelioration technique that addresses various environmental and engineering concerns. Here, we present a study focusing on aeolian erosion control of loess soil from the Negev Desert (Israel). Changes in the treated soil's chemical, physical, and microbial community (abundance and diversity) were characterized following bio-stimulation of native, urea-hydrolyzing soil bacteria to achieve MICP. Bio-stimulation of the loess soil was induced in liquid media (batch experiments) and by spraying soil trays with stimulation media (urea and yeast extract). These experiments showed that the Negev loess could be readily stimulated to induce bacterial urea hydrolysis. Three to four daily sprayings were sufficient to achieve effective bio-stimulation, evidenced by a high hydrolysis rate and an alkaline pH. Erodibility experiments on a decimeter scale (50 cm x 50 cm trays) were performed on loess sprayed with treatment media with varying concentrations of urea and CaCl2, with a constant 1:1 M ratio. The effectiveness of the treatments was studied in a wind tunnel and by image analysis of desiccation cracks. Upscaling of the experiments to the large trays revealed a more complicated reality with urease activity, community composition, and calcium carbonate precipitation depending on the concentration of the treatment medium. Specifically, we show that a twofold reduction in the area and length of the desiccation cracks can be achieved by spraying the soil with a 0.5 M solution, resulting in effective MICP or a high concentration treatment (>1M solution) without achieving MICP. Our results show that erosion mitigation in loess soil depends on an interplay between biotic and abiotic processes based on the treatment media concentration and provides a necessary step for upscaling the bio-stimulated MICP strategy for future field implementations.