The diatoms composition in the river suspended matter of the Mid-Amur (Russiun Far East)

Data on the suspended matter structure in the river waters are solitary, they are absent for the Amur River. First information on the diatoms composition in the suspended matter of the river in the vicinity of Khabarovsk taken in September of 2015 is presented. The samples reveal 16 species of diatoms, which refer to 10 genera, 6 families, 5 orders, and 3 classes. Generally, they are representatives of the class Coscinodiscophyceae. 6 species, Aulacoseira cf. pusilla, Discostella pseudostelligera, Navicula gregaria, Stephanodiscus invisitatus, Thalassiosira faurii, and T. cf. pseudonana, are noted as new for the Amur algoflora. Brief diagnoses and photos of the species are presented. The samples do not exhibit the earlier demonstrated for plankton of the Amur river species of the genus Aulacoseira, which surge in population development was characteristic of summer (Aulacoseira granulata) and winterautumn (A. islandica) periods. It is shown that considerable part of the diatoms suspended matter is involved in the formation of aggregations. The majority of the cells forming microaggregates falls to the species of the genus Stephanodiscus due to their morphology and life strategy, presence of spines, and their ability to be attached to other aggregates. The spines help them to hold on the particles of clay minerals. The polysaccharide exudates of diatoms promote participation of diatoms in aggregation. Species of the genera Cyclostephanos, Cyclotella and Thalassiosira are present in the suspended matter to a lesser degree. There occur Aulacoseira cf. pusilla, and also species of the genus Navicula (N. gregaria, N. cf. cryptotenella, Navicula sp.). Their companions are Diatoma moniliformis, Surirella angusta, S. helvetica, Ul-naria sp., Pinnularia sp., species of the Fragilariaceae family, and others. The dominant complexes divertion to unicellular centric ones, especially species of the Stephanodiscus genus, give evidence of the rapid development of eutrophication in the river due to both anthropogenic impact and the catastrophic flood of 2013.