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Biocrusts and adjacent sediments were collected from the so-called loess plateau of Northern Iran and the loess deposits on the foothills of Alborz Mountains. The mineralogical and granulometric analyses characterized sediments as quartz-rich clayey or sandy silts. Cyanobacterial diversity, colony morphology and grain stabilization were studied by light and scanning electron microscopy, which showed glue-like layers of cyanobacterial EPS and dense networks of filamentous cyanobacteria immobilizing finer and bigger grains, respectively. Amorphous, tuft and globular cyanobacterial colony structures were also detected. 15 cyanobacterial genera were identified in the biocrust samples including Microcoleus vaginatus as the common species in all samples, Aphanocapsa, Aphanothece, Calothrix, Chroococcus, Chroococcidiopsis, Cyanosarcina, Hassallia, Homeothrix, Nostoc, Oculatella, Schizothrix, Scytonema, Tolypothrix and Trichocoleus. Two biocrust samples showed traces of toxicity in a protein phosphatase inhibition assay targeting microcystins and similarly acting compounds. The Artemia salina assay revealed an elevated toxic response in one sample. (C) 2016 Elsevier Ltd and INQUA. All rights reserved.