Bottom Sediments of Surface Watercourses of the Malmyzhsky Mountain Range

Using the methods of X-ray fluorescence, electron microscopic, sedimentation analysis, and laser diffractometry, the composition of bottom sediments of surface watercourses in the Malmyzhskaya Ridge section allocated for the construction of a mining and processing enterprise (Khabarovsk krai, Russia) was studied. It was established that the bottom sediments of the coastal zone of the watercourses of the studied region are characterized by a similar gross composition and physical and chemical properties (pH, solid phase density, total carbon content, contact angle CAW). They are mainly represented by a fine soil with a high portion of suspended sediments, in the composition of which the coarse silt fraction prevails (particle size <2 mm, <0.1 mm, and 0.01–0.05 mm, respectively). It was demonstrated 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 portion of suspended sediments up to 90%) in the upper reaches. The effect of afforestation on the dispersion of sediments fades downstream with the distance from the felling sites. The content of suspended sediments decreases to the values typical for watercourses, on the catchment area of which no deforestation was carried out. A significant microaggregation of the suspended sediments of watercourses was detected, and the involvement of microbiota (testate amoebae of xenosomic taxa, diatoms, and Fe-reducing bacteria) was diagnosed in the formation of microaggregates. The latter are involved in the formation of vivianite on the surface of ferruginous–clay microaggregates with an increased content of phosphates after fires. A mechanism for the formation of toroidal microforms of vaterite in the bottom sediments with the involvement of cyanobacteria from the Spirulinaceae family was proposed.