New paper shows glacier size and hydrological drainage systems may influence the structure of exported microbial assemblages

Glacial meltwater streams export supra- and subglacially-derived microbial cells, along with terrestrial material from the ice-free landscape, and deliver them to downstream ecosystems. Despite the potential implications of these fluxes, studies addressing the formation and structure of exported assemblages are scarce, though vital to understanding the role of glaciers in regional biogeochemical cycling.

A new study, led by Jakub and published in FEMS Microbiology Ecology, shows that glacier size and hydrological drainage systems may influence the structure of exported microbial assemblages, and provides insights into their formation and fate in this current age of deglaciation.

In the summer 2015, we conducted a survey within a large catchment containing multiple glaciers on Qeqertarsuaq (Disko Island), west Greenland, to investigate whether meltwater-exported microbial assemblages in suspended sediments differ between glacial meltwater streams, and if they reflect corresponding bulk subglacial and extraglacial sediment communities. Using 16S rRNA gene amplicon sequencing, we found proglacial stream assemblages substantially differ from one another, despite their close spatial proximity. Furthermore, proglacial stream assemblages were composed of greater proportions of Cyanobacteria compared to bulk subglacial sediment communities, dominated by Betaproteobacteria, demonstrating large contributions of meltwater and microbial cells from supraglacial habitats. Corresponding physico-chemical characteristics of meltwater suggest that streams draining smaller glaciers had more equal contributions of both supra- and subglacial inputs compared with the main catchment outlet, aligning with observed changes in assemblage structure, such as the decreased proportion of Cyanobacteria.

These results suggest that microbial assemblages in glacial meltwaters are shaped through the mobilization of available source material, as reflected in the OTU overlap between suspended sediment and bulk subglacial sediment samples. Our findings improve our understanding of microbial export from glacierized catchments, and contribute to future efforts to delimitate the fate of microbial communities in the current age of deglaciation.

Žárský JD, Kohler TJ, Yde JC, Falteisek L, Lamarche-Gagnon G, Hawkings JR, Hatton JE, Stibal M (2018) Prokaryotic assemblages in suspended and subglacial sediments within a glacierized catchment on Qeqertarsuaq (Disko Island), west Greenland. FEMS Microbiology Ecology 94:fiy100 doi: 10.1093/femsec/fiy100

Upper left: Sediment of a temporary lake which developed after the surge of Kuannersuit glacier and drained some time before our visit. The pink flowers are the pioneering species Epilobium latifolium; lower left: The sharp border between the surge-affected and unaffected land is clearly visible in the field; upper center: Mosses are quickly colonising fine glacio-fluvial sediment close to the front of Kuannersuit Glacier; lower center: The rapidly melting “portal area” of the Kuannersuit Glacier terminus; upper right: Freshly exposed subglacial sediment layers formed during the Kuannersuit Glacier surge event; lower right: Tyler sampling bulk subglacial sediment for chemical analyses. Pieces of lignified vegetation stick out of the profile right above.