Glacial microbiota are hydrologically connected and temporally variable

Abstract

Summary Glaciers are melting rapidly. The concurrent export of microbial assemblages alongside glacial meltwater is expected to impact the ecology of adjoining ecosystems. Currently, the source of exported assemblages is poorly understood, yet this information may be critical for understanding how current and future glacial melt seasons may influence downstream environments. We report on the connectivity and temporal variability of microbiota sampled from supraglacial, subglacial and periglacial habitats and water bodies within a glacial catchment. Sampled assemblages showed evidence of being biologically connected through hydrological flowpaths, leading to a meltwater system that accumulates prokaryotic biota as it travels downstream. Temporal changes in the connected assemblages were similarly observed. Snow assemblages changed markedly throughout the sample period, likely reflecting changes in the surrounding environment. Changes in supraglacial meltwater assemblages reflected the transition of the glacial surface from snow‐covered to bare‐ice. Marked snowmelt across the surrounding periglacial environment resulted in the flushing of soil assemblages into the riverine system. In contrast, surface ice within the ablation zone and subglacial meltwaters remained relatively stable throughout the sample period. Our results are indicative that changes in snow and ice melt across glacial environments will influence the abundance and diversity of microbial assemblages transported downstream.

Active and dormant microorganisms on glacier surfaces

“…Some members of Bacteroidota are known to have the ability to degrade high molecular weight organic C compounds, including polysaccharides (Cottrell & Kirchman, 2000 ), and are potentially utilizing algal necromass as a carbon and energy source (Teeling et al, 2012 ) enabling their growth and proliferation through the snowpack and across the ice surface. Additionally, Bacteroidota are known to be dominant in cryoconite holes (Edwards et al, 2013 , 2014 ), which, although were not sampled as part of this study, are dynamic and hydrologically connected to adjacent supraglacial habitats (Cameron et al, 2020 ). Although Bacteroidota may be passively dispersed throughout the glacier surface ecosystem, they may be better suited to (and therefore more metabolically active in) cryoconite holes rather than the bare ice or snow surface.…”

“…Ice surfaces are dynamic environments that are both hydrologically connected and temporally variable, and accordingly, glacial surface microbiota are continually responding to environmental fluctuations (Cameron et al, 2020 ). The high variability of the active fraction of cells – particularly from Langjökull ice samples incubated under ex‐situ conditions (Figure 4 ), is perhaps reflective of this.…”

Catchment characteristics and seasonality control the composition of microbial assemblages exported from three outlet glaciers of the Greenland Ice Sheet

“…Here, active prokaryotic life is represented by facultatively anaerobic heterotrophs utilizing legacy organic carbon substrates ( Vinšová et al, 2022 ) as well as chemolithoautotrophs ( Boyd et al, 2011 , 2014 ) and methanogens ( Boyd et al, 2010 ; Stibal et al, 2012b ; Dieser et al, 2014 ). As glaciers seasonally melt, these different habitat types become hydrologically connected ( Cameron et al, 2020 ), and entrained microbial cells are exported from the glacial habitat and into proglacial streams.…”

Spatially consistent microbial biomass and future cellular carbon release from melting Northern Hemisphere glacier surfaces

“…Fluctuations in OC delivery from glaciers can, however, result in complex ecological responses in mountain waters 10 . One component of glacially-derived OC is the active microbial ecosystem found on melting glacier surfaces 11 , which furnishes meltwater with dissolved and particulate organic carbon (DOC and POC respectively) and microbial assemblages [12][13][14] . In Greenland, recent estimates suggest 250 g km −2 of cellular carbon is released each day from the ice surface to supraglacial streams 15 , but no equivalent assessments exist for any other glaciers or ice sheets.…”

“…Despite estimates of ~10 26 microbial cells harboured within Earth's seasonally exposed weathering crust ecosystem 18 , assessments of community activity 20 and associated production, storage and transfer of OC 21,22 across glacier ice surfaces remain sparse. The hydrologically active weathering crust 23,24 connects the glacier surface habitats with downstream environments via the supra-, en-and sub-glacial hydrological networks 13 ; yet this hydraulic connection, and its role in regulating the transport of biomass and OC across the surface of mountain glaciers, remains poorly understood.…”