Microbiotic soil crusts in the Sahel of Western Niger and their influence on soil porosity and water dynamics

Microbiotic soil crusts are common features of the surface of fallow land in Western Niger. We investigated the interaction between these microbial covers and the porosity and water dynamics of soils at the surface of a Sahelian landscape. The soil pore system was examined by microscopic observations and mercury porosimetry. The soil water retention capacity was measured using a Richard pressure membrane apparatus. Runoff measurements were performed in situ at a 1 m2 scale under natural rainfall.Samples with dense cyanobacterial cover had microbially-originated pores ranging from 0.04 and 50 μm in size. These samples also showed higher total soil porosity and retained two to four times more water than samples with thin microbial cover. These properties are closely related to the hydrophobic nature of cyanobacterial components. Final runoff values obtained on densely covered surfaces were significantly higher compared to those measured on surfaces with thin microbial cover due to the geometry of the microbially-originated pore system and its functioning.