Long term changes in soil structure of microbial crusts: quantification by X-ray Micro-CT and hydrological measurements

Highly eroded environments can be stabilised using plant structures which often produce crusted soil layers. Inthe steppified desert region of Shapotou (China) a vegetated protection system was progressively established sincethe 1950s up to 2004. Initially, a sand barrier was built with woven willow branches or bamboos to reduce winderosion. Behind the sand barrier, straw chequerboards (wheat or rice straw) were installed, usually with sectionsof 1 m2 area. The fixed sand surface led to the formation of very different microbial soil crusts although appliedon the same soil according to the age of the straw structures. In situ disc tension infiltrometer measurementsand X-ray Micro-CT scanning have been used in order to physically characterise three very different aggregatesrepresenting such long term structure evolution. Soil composition analysis of the stabilized dune sand with andwithout microbiotic soil crust have also been carried out.3D image reconstruction and analysis allowed to visualize and quantify internal structure changes of the aggregatesin terms of pore size distribution and connectivity. Hydraulic conductivity curves showed a strong correlation withpore size distribution from 3D image analysis.