Dübendorf, Switzerland
Dübendorf, Switzerland

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Bodmer P.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Bodmer P.,Free University of Berlin | Freimann R.,ETH Zurich | Freimann R.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | And 6 more authors.
Aquatic Sciences | Year: 2016

Natural floodplains comprise a spatial mosaic of habitat types that vary in successional development. The physical–chemical properties of soils and sediments in these habitats vary spatio-temporally with changes in hydrology, thereby influencing microbial dynamics and general floodplain functioning. The major goals of this study were to characterize the spatio-temporal variation of different floodplain habitats and elucidate microbial function as a mechanistic basis underlying floodplain functioning. Microbial functional parameters (i.e. soil-sediment respiration, enzyme activity) as well as a microbial state variable (i.e. bacterial abundance, BA) were assessed in conjunction with abiotic properties of respective soils and sediments in different floodplain habitats over an annual cycle. BA and respiration differed significantly among habitat types, being lowest in early successional gravel and stream channel habitats and highest in older successional habitats of mature forest, islands, and riparian pasture/grassland. Coarse-scale floodplain hydrology influenced the spatial variation in microbial measures within specific habitats. A non-metric multidimensional scaling clearly separated habitat types based on the functional activities of eight tested enzymes and specific microbial variables could be linked to soil-sediment respiration. These results document a high functional heterogeneity of soil and sediment microbial variables that complements the shifting habitat mosaic found in most natural floodplains. Moreover, the use of functional measures such as respiration enhances the understanding of complex floodplain functioning. © 2015, Springer Basel.

Simcic T.,Slovenian National Institute of Biology | Mori N.,Slovenian National Institute of Biology | Mori N.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Hossli C.,eQcharta GmbH | And 5 more authors.
Hydrological Processes | Year: 2015

The respiratory potential [i.e. electron transport system activity (ETSA)] of soils and sediments from five floodplain habitats (channel, gravel, islands, riparian forest and grassland) of the Urbach River, Switzerland, and actual respiration rate (R) of the same samples exposed to experimental inundation were measured. Measurements were carried out at three incubation temperatures (4°C, 12°C and 20°C), and ETSA/R ratios (i.e. exploitation of the overall metabolic capacity) were investigated to better understand the effects of temperature and inundation on floodplain functional heterogeneity. Furthermore, ETSA/R ratios obtained during experimental inundation were compared with ETSA/R ratios from field measurements to investigate the exploitation in total metabolic potential at different conditions. Lowest ETSA and R were measured in samples from channel and gravel habitats, followed by those from islands. Substantially higher values were measured in soils from riparian forest and grassland. Both ETSA and R increased with increasing temperature in samples from all habitats, while the ETSA/R ratio decreased because of a rapid response in microbial community respiration to higher temperatures. The metabolic capacity exploitation (i.e. ETSA/R) during experimental inundation was lowest in predominantly terrestrial samples (riparian forest and grassland), indicating the weakest response to wetted conditions. Comparison of experimentally inundated and field conditions revealed that in rarely flooded soils, the metabolic capacity was less exploited during inundation than during non-flooded conditions. The results suggest high sensitivity in floodplain respiration to changes in temperature and hydrological regime. ETSA/R ratios are considered good indicators of changes in metabolic activity of floodplain soils and sediments, and thus useful to estimate the impact of changes in hydrological regime or to evaluate success of floodplain restoration actions. © 2015 John Wiley & Sons, Ltd.

Cardenas M.B.,University of Texas at Austin | Doering M.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Doering M.,ETH Zurich | Doering M.,University of Zürich | And 6 more authors.
Journal of Hydrology | Year: 2014

Understanding the temperature dynamics of rivers is critical for their management and for ecological and biogeochemical aquatic processes. In proglacial rivers, there is typically a paucity of thermal observations which in turn limits the understanding of these sensitive and evolving environments. Here we collected ground-based thermal images, with approximately meter resolution and imaged every half hour for 24h, of a proglacial river and 2km2 of its floodplain and interpret the observations using a numerical energy balance model. The images revealed the longitudinal thermal pattern of the Urbach River in Switzerland - there was gradual cooling in the upstream half of the study section and then warming in the remaining downstream portion. This pattern persisted through the diurnal warming and cooling cycle. The spatio-temporal thermal pattern was explained by a model that included distributed thermal inputs of cooler water in the upstream half coming from alluvial fans and warmer water in the downstream half running off steep cliffs that warm snowmelt. The warm inputs from the cliffs were confirmed by the thermal imaging. These data and the associated modeling illustrated that distributed inflows can overwhelm the influence of atmospheric fluxes, and that their knowledge is critical for understanding stream temperatures. The combination of modeling and detailed time-lapse thermal imaging allowed for identification and quantification of processes critical to in-stream temperature dynamics in a proglacial river. © 2014 Elsevier B.V.

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