Seasonal Snowmelt Drives Changes in Alpine Streambed Microbiome Structure and Function

The Science

Within the East River, near Crested Butte, Colo., a team of researchers examined seasonal patterns of surface and groundwater mixing, observing shifts in microbial composition and activity in both stream water and the streambed associated with the water mixing patterns. Their observations highlight the tight linkage between seasonal changes in hydrology and microbial community assembly and function. Specifically, rates of aerobic respiration increased during spring snowmelt, linked to the influx of abundant dissolved organic carbon. Moreover, strong river water downwelling into the riverbed had the additional effect of homogenizing microbial community composition across depth profiles through the bed.

The Impact

This work revealed multiple close linkages and feedbacks between physical, chemical, and microbiological processes in headwater streambed ecosystems and highlights the need for increased characterization of upland biogeochemical cycles under future climate change scenarios.

Summary

Seasonal changes in river discharge in upland watersheds affect patterns of surface and groundwater mixing in the hyporheic zone, the region in the riverbed where these two water sources interact. These changes impact how carbon compounds and dissolved metals are processed and exported from such catchments. This study focused on seasonal patterns of hyporheic mixing in the East River, Colo., watershed where seasonal snowmelt drives large fluctuations in the annual hydrograph. Using in situ depth-resolved temperature loggers and discrete sampling of pore fluids and riverbed sediments, researchers demonstrated that snowmelt-derived runoff drives increased downwelling of river water into the riverbed. Conversely, the riverbed experienced a greater influence from upwelling groundwater under low- and base-flow conditions. The movement of dissolved solutes was strongly correlated with seasonal changes in flow. Under high river discharge, increased dissolved oxygen concentrations in riverbed pore fluids stimulated aerobic heterotrophic metabolism. Conversely, this activity was depressed under baseflow conditions. Linked to changes in microbiome function, the research team demonstrated that this dynamic hydrology also influenced microbial community assembly; strong downwelling river water conditions had the effect of homogenizing microbial community composition across depth profiles through the riverbed.

Principal Investigator

Susan Hubbard
Lawrence Berkeley National Laboratory
[email protected]

Program Manager

Jennifer Arrigo
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This work was supported by the Subsurface Biogeochemical Research program, (now the Environmental System Science program) within the U.S. Department of Energy’s Office of Biological and Environmental Research.

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• Dataset Information

References