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Ceola S.,Ecole Polytechnique Federale de Lausanne | Bertuzzo E.,Ecole Polytechnique Federale de Lausanne | Mari L.,Ecole Polytechnique Federale de Lausanne | Mari L.,Polytechnic of Milan | And 7 more authors.
Ecohydrology | Year: 2014

We run a comparative study of the results of flume experiments and several dynamic models reproducing the effects of streamflow variability on biofilm (i.e. periphyton) temporal dynamics. During the experiment, two contrasting flow regimes, characterised by a constant and a time-varying discharge temporal sequence, and four different light conditions (from 90% to 27% transmission of incident light) were performed to test the effects of availability and temporal variability of light and streamflows on biofilm growth. Several model formulations, describing growth and loss dynamics, have been explored in order to assess the relevant processes that controlled biofilm temporal pattern. Model identification criteria were used to identify the most suitable model, in which the growth rate is found to be dependent on density-limitation dynamics coupled with a saturating light effect, while the loss rate is linearly proportional to the discharge conditions experienced in the flumes. This model formulation proved able to reproduce remarkably well the observed biofilm dynamics. In order to analyse the stationary behaviour of the best-performing model reproducing biofilm biomass dynamics, we also run a long-term simulation, where no significant biomass differences between the constant and stochastic flow regimes were detected. © 2012 John Wiley & Sons, Ltd. Source

Ribot M.,CSIC - Center for Advanced Studies of Blanes | Marti E.,CSIC - Center for Advanced Studies of Blanes | Von Schiller D.,Catalan Institute for Water Research | Sabater F.,University of Barcelona | And 3 more authors.
Freshwater Science | Year: 2012

Abstract. We investigated how dissolved inorganic N (DIN) inputs from a wastewater treatment plant (WWTP) effluent are processed biogeochemically by the receiving stream. We examined longitudinal patterns of NH4+ and NO3- concentrations and their 15N signatures along a stream reach downstream of a WWTP. We compared the 15N signatures of epilithic biofilms with those of DIN to assess the role of stream biofilms in N processing. We analyzed the δ15N signatures of biofilms coating light-and dark-side surfaces of cobbles separately to test whether light constrains functioning of biofilm communities. We sampled during 2 contrasting periods of the year (winter and summer) to explore whether changes in environmental conditions affected N biogeochemical processes. The study reach had a remarkable capacity for transformation and removal of DIN, but the magnitude and relevance of different biogeochemical pathways of N processing differed between seasons. In winter, assimilation and nitrification influenced downstream N fluxes. These processes were spatially segregated at the microhabitat scale, as indicated by a significant difference in the δ15N signature of light-and dark-side biofilms, a result suggesting that nitrification was mostly associated with dark-side biofilms. In summer, N processing was intensified, and denitrification became an important N removal pathway. The δ15N signatures of the light-and dark-side biofilms were similar, a result suggesting less spatial segregation of N cycling processes at this microhabitat scale. Collectively, our results highlight the capacity of WWTP-influenced streams to transform and remove WWTP-derived N inputs and indicate the active role of biofilms in these in-stream processes. © The Society for Freshwater Science. Source

Ceola S.,Ecole Polytechnique Federale de Lausanne | Ceola S.,University of Bologna | Hodl I.,University of Vienna | Adlboller M.,University of Vienna | And 10 more authors.
PLoS ONE | Year: 2013

The temporal variability of streamflow is known to be a key feature structuring and controlling fluvial ecological communities and ecosystem processes. Although alterations of streamflow regime due to habitat fragmentation or other anthropogenic factors are ubiquitous, a quantitative understanding of their implications on ecosystem structure and function is far from complete. Here, by experimenting with two contrasting flow regimes in stream microcosms, we provide a novel mechanistic explanation for how fluctuating flow regimes may affect grazing of phototrophic biofilms (i.e., periphyton) by an invertebrate species (Ecdyonurus sp.). In both flow regimes light availability was manipulated as a control on autotroph biofilm productivity and grazer activity, thereby allowing the test of flow regime effects across various ratios of biofilm biomass to grazing activity. Average grazing rates were significantly enhanced under variable flow conditions and this effect was highest at intermediate light availability. Our results suggest that stochastic flow regimes, characterised by suitable fluctuations and temporal persistence, may offer increased windows of opportunity for grazing under favourable shear stress conditions. This bears important implications for the development of comprehensive schemes for water resources management and for the understanding of trophic carbon transfer in stream food webs. © 2013 Ceola et al. Source

Mussmann M.,University of Vienna | Ribot M.,CSIC - Center for Advanced Studies of Blanes | von Schiller D.,CSIC - Center for Advanced Studies of Blanes | von Schiller D.,Catalan Institute for Water Research | And 8 more authors.
FEMS Microbiology Ecology | Year: 2013

Effluents from wastewater treatment plants (WWTPs) containing micro-organisms and residual nitrogen can stimulate nitrification in freshwater streams. We hypothesized that different ammonia-oxidizing (AOB) and nitrite-oxidizing (NOB) bacteria present in WWTP effluents differ in their potential to colonize biofilms in the receiving streams. In an experimental approach, we monitored biofilm colonization by nitrifiers in ammonium- or nitrite-fed microcosm flumes after inoculation with activated sludge. In a field study, we compared the nitrifier communities in a full-scale WWTP and in epilithic biofilms downstream of the WWTP outlet. Despite substantially different ammonia concentrations in the microcosms and the stream, the same nitrifiers were detected by fluorescence in situ hybridization in all biofilms. Of the diverse nitrifiers present in the WWTPs, only AOB of the Nitrosomonas oligotropha/ureae lineage and NOB of Nitrospira sublineage I colonized the natural biofilms. Analysis of the amoA gene encoding the alpha subunit of ammonia monooxygenase of AOB revealed seven identical amoA sequence types. Six of these affiliated with the N. oligotropha/ureae lineage and were shared between the WWTP and the stream biofilms, but the other shared sequence type grouped with the N. europaea/eutropha and N. communis lineage. Measured nitrification activities were high in the microcosms and the stream. Our results show that nitrifiers from WWTPs can colonize freshwater biofilms and confirm that WWTP-affected streams are hot spots of nitrification. © 2013 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved. Source

Funk A.,University of Natural Resources and Life Sciences, Vienna | Funk A.,Interuniversity Center for Aquatic Ecosystem Research | Schiemer F.,University of Vienna | Reckendorfer W.,University of Natural Resources and Life Sciences, Vienna | Reckendorfer W.,Interuniversity Center for Aquatic Ecosystem Research
Freshwater Biology | Year: 2013

Metacommunity ecology predicts the relative importance of environmental and spatial processes in the structure of species assemblages. Such processes may act differentially on subsets of the community characterised by specific traits. To gain a deeper insight into these mechanisms, we supplemented a common method of studying metacommunities with an analysis of individual species and their traits. River floodplains are challenging environments for metacommunity analysis due to their spatial heterogeneity, temporal stochasticity and configurations of the networks of waterbodies. An analysis of aquatic gastropods showed that both environmental and spatial factors had significant influence. Within the spatial variables tested, the configuration of the floodplain network upstream of a sampling site was particularly important. An analysis of individual species revealed that traits related to niche breadth and drift propensity were significant for structuring the assemblages: species with a broad niche width (i.e. generalist, or neutral species) and a high drift propensity were governed more by the spatial configuration, whereas environmental conditions mainly determined the distribution of specialists having traits that prevented drift. These results can be interpreted as a trade-off between habitat specialisation and colonisation ability: specialists succeed locally due to competitiveness and a strategy of reducing risks by preventing drift, whereas generalists may succeed regionally due to a strategy of spreading risks, by high levels of reproductive output, dispersal rates and adaptability. Our findings have implications for schemes to restore river floodplains that affect the aquatic network, with subsequent effects on community assembly and thus on biodiversity. © 2013 John Wiley & Sons Ltd. Source

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