Changes in morphologic, hydraulic, and hydrodynamic properties of rill erosion due to surface inoculation of endemic soil cyanobacteria

Abstract

Rill erosion is one of the most important causes of land degradation, and it is caused by the flow concentration on the surface of the hillslopes. It, therefore, results in several times increase in the amount of soil loss and sediment yield. However, the biological control of the rill erosion using soil microorganisms has not been adequately endeavored. In this respect, soil microorganisms have been used and accepted as one of the latest methods for managing surface erosion. Following that, we evaluated the efficacy of soil cyanobacteria inoculation in controlling rill erosion components in the current study. To this end, inoculation of cyanobacteria in mid-sized plots with dimensions of 6 × 1 × 0.5 m, at a slope of 30%, was performed on marl soil and prone to rill erosion from Marzanabad Region, northern Iran. An artificial rainfall of 50 ± 7 mm h−1 was simulated after 40 days of cyanobacteria inoculation, along with a supplementary runoff of 2 ± 0.32 L min−1. Many different outflows and soil loss and runoff hydraulic and hydrodynamic properties were then measured to assess the effects of soil cyanobacteria inoculation compared to untreated conditions. The results showed that inoculation of cyanobacteria reduced runoff volume, runoff coefficient, soil loss, and sediment concentration by 42, 64, 82, and 62%, respectively. It also increased infiltration volume by 74% showing high water retention capacity of the treated soil. Also, the hydraulic and hydrodynamic components of the flow, including velocity, depth, Froude number, and Reynolds number, were significantly reduced (P < 0.05), in contrast, the shear stress and friction coefficient did not change significantly in treated plots. The statistical analyses further showed that soil surface cyanobacterisation considerably affected morphological factors of rill depth, rill mean width, rill maximum length, and rill density by 44.34, 54.25, 40.75, and 38.21%, respectively. Overall, the findings revealed that using cyanobacteria to mitigate rill erosion is a practical and effective method for the bio-conservation of soil and water resources in most arid and semiarid areas.