Reducing hydraulic erosion of surficial sand layer by inoculation of cyanobacteria

Biological approaches have captured the attention of researchers regarding the beneficial effects of cyanobacteria inoculation in improving surficial soil stability. However, a gap exists in the literature regarding the impact of inoculation by individual cyanobacteria on stability of sand under intense surface-water erosion. This study assesses the improvements achieved in erosion resistance for biological soil crust (BC) formed on medium–coarse silica sand. Specimen groups were inoculated with Nostoc sp. and Calothrix sp., incubated for 32- or 48 day periods and then tested using an erosion function apparatus (EFA), investigating a wide range of flow velocities (hydraulic shear stresses). The significance of BC attachment to (or detachment from) the specimen container sidewall was also investigated in the EFA testing. Compared with untreated sand, inoculated specimens had a significantly greater erosion resistance that increased with the incubation period, with Nostoc inoculum producing greater reductions in erodibility coefficients (45–75%) compared with Calothrix (16–67%). Contrasting bond structures introduced by Nostoc and Calothrix are highlighted by scanning electron microscopy images that showed long Nostoc filaments were entangled more strongly in sand pore voids compared with short Calothrix filaments. In conclusion, this study supports the idea of using cyanobacteria inoculation as an eco-friendly, cost-benefit and effective technique for mitigating land degradation.