Biodiversity of a small water body during the initial filling phase (the Amazar River of the Amur River Basin, Russia)

In 2017, for the purposes of the Pulp and Saw Mill (PSM) “Polyarnaya”, the spillover dam was constructed on the Amazar River, a left tributary of the Amur River. Upon completion of the dam construction, the waters of the river formed a small river reservoir PSM “Polyarnaya”. This work covers findings on components and quantities of the newly formed reservoir at its initial stage and the data on biodiversity of its feeding flows. At this stage, the species composition of the flora and fauna in the reservoir falls in between the lacustrine and the riverine ones. The riverine conditions are observed in the upstream area of the reservoir; the middle area bears an intermediate status; while the limnetic zone near the dam features transformation of the river system into a lake-like running-water ecosystem. Seasonally, in the period from spring to autumn, phytoplankton showed a decreasing trend of the quantitative values; whereas the total abundance and biomass of zooplankton were increasing; zoobenthos featured lack of trends; macrophytes contents were different from season to season being abundant in the Amazar River near the urban settlement in spring and in the Amazar River downstream from the dam in autumn. Consequently, the initial stage of the formation of the reservoir is rather similar to original watercourses in the physical and chemical parameters and in the composition of flora and fauna as well.