# Cyanobacterial Potential for Restoration of Loess Surfaces through Artificially Induced Biocrusts
## 3 Results
### Ex Situ Particle Trapping and Stabilization Study
#### 3.2.2 Stabilization of Loess Particles by Cyanobacteria  
The SEM micrographs of biocrusts formed in the experimental chamber (Figure 6A,B) showed assemblies of various cyanobacterial colonies and their excreted polymeric substances. Superficial colonies of cyanobacteria immobilized dust particles by surrounding, binding and adhering the particles to this coherent organic layer. In this way, the dust particles that encountered the cyanobacterial biomass were stuck to the surface (Figure 6A,B, arrows), unlike the particles from the control chamber that did not interact with cyanobacteria (Figure 6C,D, arrows).  
Figure 4: Morphology of formed biocrusts. Morphologically different colonies covered the surface of the experimental chamber: smooth biocrusts (**A**); biocrusts consisting of pinnacle (**B**, arrow 1), curled (**B**, arrow 2) and smooth structures (**B**, arrow 3); pinnacle biocrusts (**C**, arrow).  
Figure 3: Formation of biocrusts. The interaction between the cyanobacterial biofilm (**A**) and particles resulted in biocrust development (**B**). A patchy structure was formed by pinnacle and curled biocrusts (**B**, arrow 1). Smooth biocrusts appeared between the patches later (**B**, arrow 2).  
Figure 5: The response of biocrusts to hydration. The appearance of biocrusts is different under dry conditions (**A**) and 15 min after wetting (**B**). The watering changed the appearance of the less colonized parts of the sediment (**A**) into a dark, continuous biofilm (**B**).  
Figure 6: Difference between colonized and uncolonized surfaces of experimental chamber (**A**,**B**) and control chamber (**C**,**D**), respectively. The scanning electron microscopy (SEM) micrographs show a cyanobacterial carpet-like structure (**A**) and a cyanobacterial network (**B**) adhering the airborne dust particles in the experimental chamber (arrows); the stereomicroscopic image (**C**) and the SEM micrograph (**D**) show loosely aggregated dust particles in the control chamber (arrows).  
The accumulation and stabilization of dust particles were most visible in cross-sections of the biocrusts (Figure 7). Stereomicroscopic examination revealed a vertical stratification of biocrusts and the presence of topcrust and subcrust layers. The topcrust comprised layers of living cyanobacteria colonies associated with dust particles, where the trapping (Figure 7, arrow 1) and accumulation (Figure 7, arrow 2) of new airborne material take place. The subcrust was represented by old topcrust layers and consisted of accumulated and stabilized loess particles and residual, partially mineralized EPS (Figure 7, arrow 3). The layering and particle accumulation and stabilization are the consequence of the cyanobacterial life-style. During simulated dust storms, metabolically active cyanobacteria of the topcrust layer were trapping dust particles and their subsequent burial by the particles led to the migration of these cyanobacteria towards the light source resulting in the accumulation of trapped particles in their organic layer. Growing upwards, cyanobacteria formed a new topcrust, while the \"old\" EPSs remained in deeper layers (see Results section _Accumulation and Stabilization of Particles_) which together with accumulated particles made a stabilized subcrust layer of deposited particles.