title: Deterministic influences exceed dispersal effects on hydrologically-connected microbiomes.
abstract: Subsurface groundwater-surface water mixing zones (hyporheic zones) have enhanced biogeochemical activity, but assembly processes governing subsurface microbiomes remain a critical uncertainty in understanding hyporheic biogeochemistry. To address this obstacle, we investigated (a) biogeographical patterns in attached and waterborne microbiomes across three hydrologically-connected, physicochemically-distinct zones (inland hyporheic, nearshore hyporheic and river); (b) assembly processes that generated these patterns; (c) groups of organisms that corresponded to deterministic changes in the environment; and (d) correlations between these groups and hyporheic metabolism. All microbiomes remained dissimilar through time, but consistent presence of similar taxa suggested dispersal and/or common selective pressures among zones. Further, we demonstrated a pronounced impact of deterministic assembly in all microbiomes as well as seasonal shifts from heterotrophic to autotrophic microorganisms associated with increases in groundwater discharge. The abundance of one statistical cluster of organisms increased with active biomass and respiration, revealing organisms that may strongly influence hyporheic biogeochemistry. Based on our results, we propose a conceptualization of hyporheic zone metabolism in which increased organic carbon concentrations during surface water intrusion support heterotrophy, which succumbs to autotrophy under groundwater discharge. These results provide new opportunities to enhance microbially-explicit ecosystem models describing hyporheic zone biogeochemistry and its influence over riverine ecosystem function.
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: Emily B
authors.identifier: 0000-0002-4623-7076
authors.initials: EB
authors.lastname: Graham
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: Alex R
authors.identifier: 0000-0002-2443-6146
authors.initials: AR
authors.lastname: Crump
authors.affiliation: Geochemistry Department, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: Charles T
authors.initials: CT
authors.lastname: Resch
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Fansler
authors.affiliation: Environmental Compliance and Emergency Preparation, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: Evan
authors.identifier: 0000-0002-9209-5670
authors.initials: E
authors.lastname: Arntzen
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: David W
authors.identifier: 0000-0003-0763-501X
authors.initials: DW
authors.lastname: Kennedy
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: Jim K
authors.identifier: 0000-0001-5627-7496
authors.initials: JK
authors.lastname: Fredrickson
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: James C
authors.identifier: 0000-0001-9135-7424
authors.initials: JC
authors.lastname: Stegen
mesh_terms: D060587:Groundwater / Q000382:microbiology*; D064307:Microbiota; D045483:Rivers / Q000382:microbiology; D014871:Water Microbiology; D014872:Water Movements