Seasonal patterns of Potamoplankton in a Large Lowland River of Temperate zone (Upper Ob as a case study, Russia)

The paper presents the results of seasonal potamoplankton dynamics in a Siberian lowland river and its relationships with environmental variables. The sampling was carried out every 10-15 days from April to September 2001 at the left and right banks including the midstream of the Upper Ob River close to the big industrial center,Barnaul city(53?21’24"N, 83?47’14"E). Thepresence of 145 species (158 taxa) with predominance of diatoms (45.6% of total number of species) and green algae (35.8%) was noted. Remarkable seasonal potamoplankton variations were revealed using measures of inclusions and amultigraph. The correlation analysis indicated that physical factors (e.g. hydrological variables) and major nutrients (e.g. nitrates) were of equal importance for controlling the variation in structure and abundance of the large lowland Upper Ob River potamoplankton. Based on the regional trophic classification, the Upper Ob River can be currently characterized as oligo-mesotrophic since the total abundance and biomass of algae were less than 1260×103 cells/L and 780 mg/m³ throughout the sampling seasons. The results of the saprobiologic analysis showed that the greatest number of bioindicators belong to B-mesosaprobionts that is indicative of the B-mesosaprobic environment. Water qualitywas ranked among I-III classes.Our studypresents a baseline formonitoring theplanktonic component in the river ecosystem as a main factor of its stability. In spite of the regional aspect of the study, the investigation of potamoplankton in the environments of the south ofWest Siberiawill be useful for understanding of phytoplankton development in large unregulated lowland rivers.