Hydrological behavior of microbiotic crusts on sand dunes: Example from NW China comparing infiltration in crusted and crust-removed soil

Biological soil crusts are important microbiotic communities which are considered a key factor in combating desertification in terms of sand dune remobilitation. Because of their greater concentration of clay, silt and hydrophobic organic matter, they create a physical discontinuity in surface profile which potentially contribute to variability in soil hydrology of arid and semiarid land and should be considered in the development of hydrological and erosion models. However, until recently limited inconclusive research has been conducted to determine the functional relationship between soil and microbiotic crusts. We investigated the influence of microbiotic crust on hydrological behaviour of crusted sand dunes in NW China. The infiltration data on a crusted and crust-removed sand dune were obtained with dish permeameter which was not moved during the measurement at a sequence of nominal pressure head values, h, of -1, -4, -7, -10, -18 cm. Hydraulic conductivity K(h) was measured by steady-state infiltration experiments and piece-wise application of the exponential relation between K and h, according to Wooding's analytical solution of a three-dimensional flow field. The transient experimental infiltration data, along with initial and final water contents were used for numerical analysis within sand prfiles without and with microbiotic crust. Specifically, we provided evidences that the main physical and hydrological consequences occurring locally, always cause lower unsaturated fluxes in the sand beneath the crusted layer. Nevertheless, due to the effective rainfalls regime, it has insignificant effects on the local soil water regimes with unchanged storage and deep fluxes.