Abstract
Microbial communities promptly respond to the environmental perturbations, especially in the Arctic and sub-Arctic systems that are highly impacted by climate change, and fluctuations in the diversity level of microbial assemblages could give insights on their expected response. 16S rRNA gene amplicon sequencing was applied to describe the bacterial community composition in water and sediment through the sub-Arctic Pasvik River. Our results showed that river water and sediment harbored distinct communities in terms of diversity and composition at genus level. The distribution of the bacterial communities was mainly affected by both salinity and temperature in sediment samples, and by oxygen in water samples. Glacial meltwaters and runoff waters from melting ice probably influenced the composition of the bacterial community at upper and middle river sites. Interestingly, marine-derived bacteria consistently accounted for a small proportion of the total sequences and were also more prominent in the inner part of the river. Results evidenced that particular conditions occurring at sampling sites (such as algal blooms, heavy metal contamination and anaerobiosis) may select species at local scale from a shared bacterial pool, thus favoring certain bacterial taxa. Conversely, the few phylotypes specifically detected in some sites are probably due to localized external inputs introducing allochthonous microbial groups.
Highlights
Freshwater and brackish Arctic and sub-Arctic water systems are vulnerable to ongoing climate change
Contrary to sediments, whose bacterial diversity remained quite stable among the Pasvik watercourse (Shannon diversity showed variation between 6.78 in the sampling site 15s and 4.94 in the sampling site 18s), we found that the operational taxonomic units (OTU) richness in water peaked in the inner samples and quite gradually decreased towards middle and outer samples
The bacterial community was affected by different physicochemical properties, while in water it was mostly affected by oxygen concentration and in sediment by salinity and temperature
Summary
Freshwater and brackish Arctic and sub-Arctic water systems (e.g., estuaries, rivers, and fjords) are vulnerable to ongoing climate change. Arctic and sub-Arctic river flow dynamics depend on the increased amounts of glacial and snow meltwaters because of global warming as well as precipitation [1,2] This strongly affects the physico-chemical and biological features of their receiving water bodies (e.g., estuaries, ocean, and fjords), which can be enriched in particulate matter, allochthonous microorganisms and contaminants [3,4]. As freshwater bacterial communities are taxonomically distinct from marine estuarine and communities [8,9], the fluvial microorganisms may influence the native microbial communities in terms of both composition and metabolic functions causing alterations in biogeochemical cycles For this reason, the study of microbial communities inhabiting Arctic and sub-Arctic rivers can be fundamental to gain important insights on the biogeochemical processes in coastal and estuary ecosystems [2]. The bacterial community structure can largely vary at spatial scale, and be shaped at local scale, within the same freshwater system [3,10]
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