Glacial microbiota are hydrologically connected and temporarily variable.

Climate warming is leading to changes in the hydrology of glacier-fed catchments around the world. The influence of this on the export of microbial assemblages from glacial and downstream habitats 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 continued and elevated glacial melt may impact downstream environments. Here we report on the connectivity and temporal variability of microbiota sampled from a glacial catchment. We find that microbial habitats within glacial catchments are biologically connected through hydrological flow paths, leading to a cumulative system, with increased prokaryotic abundance and diversity as meltwaters travel downstream. 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 periglacial environment resulted in a flushing of soil assemblages into the riverine system. In contrast, ice and subglacial meltwaters remained relatively stable. Our results are indicative that changes in glacial melt will influence the abundance and diversity of microbial assemblages transported downstream.