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Metabolism after drying and bedform migration in the Spree River in 2018/2019

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.

Community abundance after drying and bedform migration in the Spree River in 2018/2019

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.

Degradation of diatom-derived dissolved organic matter (DOM) in surface seawater

Stored surface seawater originally collected in the North Sea was amended with dissolved organic matter (DOM) obtained from the diatom Skeletonema marinoi by exposing the diatom culture to a hydrostatic pressure level of 40 MPa for 24 h. To this end, S. marinoi had been grown to stationary phase in L1 medium plus silicate (Guillard & Hargraves 1993) at 15°C under a light/dark regime of 14/10 h. Diatom-cell-free DOM was added to aliquoted seawater samples at initial concentrations of 250 µmol C/L. The microbial degradation of the added DOM and the microbial response to DOM-amendment at 15°C and in darkness was followed for 2 weeks. The seawater was subsampled at defined time intervals to analyze a number of variables.

Enzyme activity after drying and bedform migration in the Spree River in 2018/2019

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.

Long-term recovery of metabolism, enzyme activity and community abundance after drying and bedform migration in the Spree river 2018/2019

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.

Community composition

Metabolism

Nutrient dynamics

Metabolism, nutrient dynamics and community composition in sandy sediments - A microcosms experiment

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.

Does traditional Alpine farming alter greenhouse gas emissions and C-turnover in remote mountain streams? (Marie Heim-Voegtlin Beiträge)

Because inland waters only cover a small portion (6-15%) of the terrestrial surface they are often not regarded as an important component of the global carbon (C) cycle. However, as part of the terrestrial landscape these active, rather than passive, conduits receive and transform substantial amounts of organic C. In fact, the global carbon dioxide (CO2) emissions from inland waters was estimated to be about 1.4 Gt C year-1 corresponding to about 50 % of the terrestrial C sink. Together with methane (CH4) this results in C emissions from inland waters that correspond to about 75 % of the terrestrial sink. However, there is a large degree of uncertainty in these estimates as most studies on rivers and streams have focused on CO2 emissions, with little research performed on CH4 emissions and turnover processes. Furthermore, studies on C-fluxes and turnover processes in small streams are highly under-represented. Thus, the overall objective of this proposal is to study the dynamics of C fluxes (CO2 and CH4), and the pathways of CH4 production in Alpine streams influenced by managed Alpine pastures, thereby adding another puzzle piece to the understanding of C-cycling in small streams It is still common in Switzerland to drive livestock up into the Alps for summer farming and grazing. However, the associated fecal and urine deposits may strongly influence the species composition of the vegetation in mountain meadows, the quality of soil organic matter and thus dissolved organic matter quality entering adjacent streams. Once the organic matter enters the stream in particulate and/or dissolved form, it will be degraded by microbes either aerobically or anaerobically (or both) while producing CO2 and CH4. CH4 can be produced via acetate fermentation or CO2 reduction. Which of these two pathway used for CH4 production depends on the quality and age of the organic matter. The effect of Alpine summer farming on C emissions (CO2 and CH4) and C turnover processes will be investigated in headwaters draining intensely farmed Alpine/subalpine pastures. A field study will be performed based on 1) a stable isotope approach, 2) resolving CH4 and CO2 fluxes, 3) investigating the CH4 production pathways and 4) changes in microbial communities.

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