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Sandy streambed sediments that had been exposed to either intense drying (90-day without rainfall) or bedform migration (periodically moving ripples) were placed in 250 µm mesh bags to the Spree River in Northeastern Germany on October 22, 2018, to initiate the recovery process from drying or migration stress. Subsamples from the recovering sediments were collected at eight dates within eight months and taken to the laboratory for further analysis. Community respiration and Net Community Production of sediment associated biofilms were measured as dissolved oxygen concentrations from sediment pore water in inundated microcosms. The aim of the experiment was to observe the long-term recovery of microbial communities in lowland streams from drying and bedform migration and to identify if stress effects persisted as legacy after the stress period.
Sandy streambed sediments that had been exposed to either intense drying (90-day without rainfall) or bedform migration (periodically moving ripples) were placed in 250 µm mesh bags to the Spree River in Northeastern Germany on October 22, 2018, to initiate the recovery process from drying or migration stress. Subsamples from the recovering sediments were collected at eight dates within eight months and taken to the laboratory for further analysis. Community abundance was assessed on a heterotrophic (amplified bacterial and fungal gene copies) and on an autotrophic level (Chlorophyll a concentration and diatom cell count). The aim of the experiment was to observe the long-term recovery of microbial communities in lowland streams from drying and bedform migration and to identify if stress effects persisted as legacy after the stress period.
Sandy streambed sediments that had been exposed to either intense drying (90-day without rainfall) or bedform migration (periodically moving ripples) were placed in 250 µm mesh bags to the Spree River in Northeastern Germany on October 22, 2018, to initiate the recovery process from drying or migration stress. Subsamples from the recovering sediments were collected at eight dates within eight months and taken to the laboratory for further analysis. Potential extracellular enzyme activities (Beta-Glucosidase, Xylosidase, Chitinase, Phosphatase, Leucine-Aminopeptidase, Phenol-Oxidase, and Peroxidase) were assessed by measuring fluorescence and absorbance after extraction from sediments. The aim of the experiment was to observe the long-term recovery of microbial communities in lowland streams from drying and bedform migration and to identify if stress effects persisted as legacy after the stress period.
Sandy streambed sediments that had been exposed to either intense drying (90-day without rainfall) or bedform migration (periodically moving ripples) were placed in 250 µm mesh bags to the Spree River in Northeastern Germany on October 22, 2018, to initiate the recovery process from drying or migration stress. Subsamples from the recovering sediments were collected at eight dates within eight months and taken to the laboratory for further analysis. Community respiration and Net Community Production of sediment associated biofilms were measured as dissolved oxygen concentrations from sediment pore water in inundated microcosms. Potential extracellular enzyme activities (Beta-Glucosidase, Xylosidase, Chitinase, Phosphatase, Leucine-Aminopeptidase, Phenol-Oxidase, and Peroxidase) were assessed by measuring fluorescence and absorbance after extraction from sediments. Community abundance was assessed on a heterotrophic (amplified bacterial and fungal gene copies) and on an autotrophic level (Chlorophyll a concentration and diatom cell count). The aim of the experiment was to observe the long-term recovery of microbial communities in lowland streams from drying and bedform migration and to identify if stress effects persisted as legacy after the stress period.
Sandy streambeds can be mobilized at base flow and sediments are transported as bedload, more specifically as migrating ripples. Within migrating ripples, microbial communities experience an erosion-resting cycle of sediment grains. Besides, small changes in discharge can results in frequent transitions between migrating ripples and no-transport. Despite the ubiquity of both migrating ripples and sediment transport transition, their effect on streambed functioning and microbial community composition remain unclear. We performed a microcosm experiment mimicking two sediment transport conditions, namely ripple and no transport (i.e., stable), and their transition to observe the response of sediment community function and composition. Both net community production (NCP) and community respiration (CR) were suppressed in ripple sediments compared to stable sediments. In ripples, a combination of mechanic stress, advective supply and light limitation likely hampered microbial metabolism. Sediment stability likely facilitated an active community of autotrophs, mainly diatoms, as indicated by high NCP, high rates of DOC release and Si-SiO2 retention. Retention of nitrate and the high DIN : SRP ratio indicated efficient resource utilization in stable sediments. After the transition, microbial communities from each treatment responded differently to sediment transport, most likely as a result of the interaction between their previous environmental conditions and functional status in response to the new conditions. Our data indicate that sediment transport in the form of migrating ripples at low flow can strongly modulate streambed metabolism, and discharge oscillations (transitions) will result in a mosaic of metabolism and communities that will emerge at larger scales determining reach scale metabolism.
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