Differences in organic matter and bacterioplankton between sections of the largest Arctic river: Mosaic or continuum?

Abstract

We studied biogeochemical characteristics, including organic carbon and nitrogen contents, fatty acid (FA) composition, stable isotope ratios, and primary production in conjunction with species composition of bacterioplankton, using next generation sequencing, in the Yenisei River along a distance ∼1800 km. Basing on FA composition of particulate organic matter (POM) and on other indicators of sources of POM, the river was subdivided into four sections. The upper section 1, situated in mountain region, was the net source of high‐quality autochthonous organic matter, produced primarily by diatoms and partly consumed by specialized bacteria species. Section 2 in plain taiga was net sink of high quality allochthonous and autochthonous organic matter, produced by cyanobacteria and green algae. Section 3 was net sink of organic matter, primarily allochthonous, consumed by the specialized species of bacteria. The lowest section 4, situated in tundra, was primarily the conduit of recalcitrant terrestrial organic matter, but also the net source of autochthonous organic matter, produced by diatoms. Biogeochemical traits of sections of the Yenisei River evidently shaped dominant species composition of bacterioplankton of these sections. Regarding the biogeochemical and microbiological data, we concluded that the Yenisei River ecosystem complexly combines features of river mosaic, river continuum, and “neutral pipe.”

Fatty Acid Composition and Contents of Seven Commercial Fish Species of Genus Coregonus from Russian Subarctic Water Bodies

“…Hence, the above result seems to be in a good agreement with data of other authors on higher content of PUFA in fish from oligotrophic water bodies [22,65]. Moreover, C. lavaretus from Lake Onega had the highest level of arachidonic acid 20:4n-6, which is regarded as marker of allochthonous (terrestrial) organic matter of comparatively low nutritive value [31]. Thus, the lowest content of EPA + DHA of C. lavaretus from Lake Onega among the studied fish was likely determined by the low quality of its food sources.…”

“…Fish food chains in inland waters are known to be based on autochthonous resources, microalgae and, to some extent, on allochthonous (terrestrial) organic matter. Moreover, C. lavaretus from Lake Onega had the highest level of arachidonic acid 20:4n-6, which is regarded as marker of allochthonous (terrestrial) organic matter of comparatively low nutritive value [31]. In our study, all water bodies were oligotrophic, diatomdominated rivers and lakes, except the mesotrophic Lake Onega.…”

“…Indeed, C. autumnalis had the highest level of the sum of 20:1 fatty 1 3 acids. Moreover, C. autumnalis had the lowest proportion of the marker of low-quality terrestrial organic matter, 20:4n-6 [31]. Evidently, this species assimilated organic matter of marine origin, which seemed to be of very high nutritive value.…”

“…All sampled water bodies (Table 1) were oligotrophic (except nearly mesotrophic Lake Onega) and had low water temperature, 6.5-15 °C. Dominant phytoplankton taxa were Bacillariophyta [31,38,39]. A map of the sampled water bodies is given in Fig.…”

Fungal community demonstrates stronger dispersal limitation and less network connectivity than bacterial community in sediments along a large river

“…Moreover, it is notable that both bacterial and fungal communities in midstream may experience stronger effect of geographic distance but weaker effect of environmental heterogeneity than those in upstream and downstream (Table 1). One possible explanation is attributed to the construction of six cascading dams in the midstream section, which likely cause the spatial isolation of sediments and homogenization of environmental condition in the impounded region (Ruiz-Gonzalez et al, 2013), thus greatly impacting on species distribution pattern (Gladyshev et al, 2015). Both dam and water depth could obviously cause stronger spatial isolation for microbial distributions in a large river.…”