# Cyanobacterial Potential for Restoration of Loess Surfaces through Artificially Induced Biocrusts
## 3 Results
### Trapping of Particles  
The capturing and trapping of blown (or airborne) dust particles occurred during the simulated wet periods by a coherent cyanobacterial cover. Three types of particle trapping were observed, related to the morphology of the cyanobacterial colonies: 1. net-like trapping (Figure 8A,D); 2. carpet-like trapping (Figure 8B,E); and 3. trapping by pinnacles (Figure 8C,F).  
_Net-like trapping_: the net-like trapping (Figure 8A,D) was promoted by an extensive network of cyanobacterial filaments and the EPSs that covered, surrounded, and connected the particles (Figure 8D, arrow 1). Trapping of fine particles was also observed at the top of the EPS network (Figure 8D, arrow 2). The network pores (Figure 8D, arrow 3) further supported the trapping of particles.  
_Carpet-like trapping_: cyanobacterial colonies (Figure 8E, exemplified by arrow 3) and mostly their slime EPSs made a homogenous, amorphous surface, carpet-like biological cover by which particles were trapped (Figure 8B,E). Adhered particles were observed on the surface of the carpet-like biocover (Figure 8E, arrow 1). Wrapping of the individual particles by cyanobacterial filaments was not observed. Instead, amorphous mucilaginous  
Figure 7: Cross-section of a biocrust sample. There were three layers within the biocrust: one showing trapping particles by superficial cyanobacterial colonies (arrow 1), another showing particle accumulation in the cyanobacterial organic layer (arrow 2), and a third one showing deposition of particles below the cyanobacterial biofilm as a result of the migration of cyanobacteria to the upper layers (arrow 3).  
cyanobacterial colonies grew above the overlapping particles. The contours of the trapped particles are visible in Figure 8E, arrow 2.  
_Trapping by pinnacles_: vertical structures were identified in addition to the horizontal biological covers. Biocrusts that increased their own surface by joining filaments into bundles and growing upwards were observed (Figure 8C,F). The surface for trapping the particles was consequently also increased. Bundles of filaments and their sticky EPSs formed vertical bio-mineral aggregates (Figure 8C,F).  
The growth of cyanobacteria above the trapped particles led to their accumulation in a lower part of the topcrust layer (Figure 7, arrow 2). Cyanobacterial cover preserved and stabilized the particles within the active topcrust layer and served as a protective cover for the particles in the subcrust layer. The weathering of loess particles was observed in the contact zone between EPS and the particles (Figure 9A-C). The weathering led to cracking and breakage of some particles (Figure 9A, black arrows). Subsequent mineral precipitation occurred on the surface of the EPS (Figure 9A, thin white arrows), leading to the formation of organomineral structures in and around the contact zone of the EPS and particles (Figure 9A, thick white arrows; Figure 9B, arrows), which could improve the stabilization of the particles during dry periods. As shown in Figure 9C, the organomineral structures strengthen the bond between the EPS and the particles and thus could contribute to particle stabilization. Mineralized residues of EPSs were also observed in the subcrust layer (Figure 9D).