title: Hydrologic linkages drive spatial structuring of bacterial assemblages and functioning in alpine floodplains.
abstract: Microbial community assembly and microbial functions are affected by a number of different but coupled drivers such as local habitat characteristics, dispersal rates, and species interactions. In groundwater systems, hydrological flow can introduce spatial structure and directional dependencies among these drivers. We examined the importance of hydrology in structuring bacterial communities and their function within two alpine floodplains during different hydrological states. Piezometers were installed in stream sediments and surrounding riparian zones to assess hydrological flows and also were used as incubation chambers to examine bacterial community structures and enzymatic functions along hydrological flow paths. Spatial eigenvector models in conjunction with models based on physico-chemical groundwater characteristics were used to evaluate the importance of hydrologically-driven processes influencing bacterial assemblages and their enzymatic activities. Our results suggest a strong influence (up to 40% explained variation) of hydrological connectivity on enzymatic activities. The effect of hydrology on bacterial community structure was considerably less strong, suggesting that assemblages demonstrate large functional plasticity/redundancy. Effect size varied between hydrological periods but flow-related mechanisms always had the most power in explaining both bacterial structure and functioning. Changes in hydrology should be considered in models predicting ecosystem functioning and integrated into ecosystem management strategies for floodplains.
authors.affiliation: Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology ETH Zurich, Dübendorf, Switzerland ; Institute of Integrative Biology ETH Zurich, Zürich, Switzerland ; Department of Biology, Institute of Molecular Health Sciences, Epigenetic Regulation and Cell Identity Control ETH Zurich, Zürich, Switzerland.
authors.forename: Remo
authors.initials: R
authors.lastname: Freimann
authors.affiliation: Department of Surface Waters - Research and Management, Eawag: Swiss Federal Institute of Aquatic Science and Technology ETH Zurich, Kastanienbaum, Switzerland.
authors.forename: Helmut
authors.initials: H
authors.lastname: Bürgmann
authors.affiliation: Cary Institute of Ecosystem Studies Millbrook, NY, USA.
authors.forename: Stuart E G
authors.initials: SE
authors.lastname: Findlay
authors.affiliation: Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology ETH Zurich, Dübendorf, Switzerland ; Institute of Integrative Biology ETH Zurich, Zürich, Switzerland.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Robinson
keywords: bacterial community dynamics; ecosystem functions; eigenvector maps; hydrologic connectivity