Prokaryotic communities in sediments along the Pasvik River (Arctic Norway)

The Pasvik river is one of the largest river in the Northern Fennoscandia. Its water conditions are representative of Eastern European rivers. The river collects snowmelt, and it is typically a freshwater environment at its inner zone and brackish at its outer zone. Sediment samples were collected from 9 stations during two seasonal surveys (May and July 2014). Physical-chemical parameters were monitored at sampling time. Samples were analyzed for viable heterotrophic bacteria, total prokaryotic abundance, microbial enzymatic activity rates, and phylogenetic composition of bacterial community. Microbial enzymatic activities generally increased in July, but showed spatial and temporal variability. In May, leucin aminopeptidase showed the highest values at outer stations (9.37 mmol/g/h). The bacterial community resulted highly variable among the sampling stations with the predominance of the Proteobacteria, followed by the Actinobacteria and CF group of Bacteroidetes. In July, an increased abundance of the Acidobacteria was observed at St.1 (from 4.7 to 22.1%). This study highlights both seasonal (May and July) and spatial differences within the microbial community that inhabit sediments along the Pasvik river. This finding is probably strictly dependent on freeze-thaw cycles of the water body, with consequent organic inputs to sediments in July. The microbial community appears to be adapted to fluctuating conditions modulated by seasonality.