Vladimir Ilyich Kim

X-ray fluorescence, electron microscopic, sedimentation analyses and laser diffractometry methods were used to study the composition of bottom sediments of surface watercourses of the Malmyzhskaya Ridge section allocated for the construction of a mining and processing plant (Khabarovsk region, Russia). It is established that the bottom sediments of the coastal zone of the watercourses of the studied area are characterized by a similar gross composition and physical and chemical properties (pH, solid phase density, total carbon content, wetting edge angle CAW). They are mainly represented by fine earth with a high proportion of suspended sediments, in which the fraction of coarse silt prevails (particle size <2,0 mm, <0,1 mm and 0,01–0,05 mm, respectively). It is shown that deforestation in the sources of watercourses accompanied by soil erosion leads to a significant increase in the dispersion of sediments (an increase in the proportion of suspended sediments up to 90%) in the upstream. Downstream, with the distance from the felling sites, the influence of deforestation on the dispersion of deposits fades. The content of suspended sediment is reduced to values characteristic of watercourses in the catchment area of which deforestation has not been carried out. Significant microaggregation of suspended sediments of watercourses was revealed, the participation of microbiota (testate amoebas of xenosome taxa, diatoms and Fe-reducing bacteria) in the formation of microaggregates was diagnosed. The latter are involved in the formation of vivianite on the surface of ferruginous-clay microaggregates with an increased content of phosphates after fires. The mechanism of formation of toroidal microforms of vaterite in bottom sediments with the participation of cyanobacteria of the Spirulinaceae family is proposed.