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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.

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.

Klasz G.,Vienna University of Technology | Reckendorfer W.,University of Natural Resources and Life Sciences, Vienna | Reckendorfer W.,Interuniversity Center for Aquatic Ecosystem Research | Gabriel H.,DonauConsult Ingenieurburo GmbH | And 3 more authors.
Geomorphology | Year: 2014

We investigated overbank deposition and natural levee formation along the Danube east of Vienna based on airborne laserscan data (ALS) combined with historical information. The analyses of equally spaced cross sections, hypsographic curves and point elevations revealed the significance of the distance from the river bank, the floodplain width and the floodplain flow situation (inflow/outflow sections) for the spatial variability of sediment deposition. Deposition was high near the banks (natural levee formation), in wide floodplain sections and in inflow areas. The overall pattern was modified by the presence of side-channels and the micro-relief of the floodplain. From the derived sedimentation rates (averaged for the past 120years over the reach) of about 11.0mmyr-1 at the natural levee and about 0.3mmyr-1 at the flood protection dyke, we can estimate an overbank deposit rate of 416,000m3yr-1 for the entire free-flowing reach (between river-km 1921 and 1880), that is, between 18 and 20% of the annual transported suspended load. An analysis of historical cross sections showed that there was no natural levee along the riverbanks shortly after the regulation, about 100. years ago. We thus assume that natural levee formation is a consequence of the Danube regulation in the late 19th century. Under natural conditions overbank deposition was balanced and limited by side erosion and lateral channel migration. After stabilization of the banks the overbank deposits were not eroded, and distinct 'natural' levees formed. These levees will develop and grow further and affect flood protection and floodplain ecology. We discuss the interplay between floodplain deposition and lateral bank migration under the concept of dynamic equilibrium. © 2014 Elsevier B.V.

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.

Reckendorfer W.,Interuniversity Center for Aquatic Ecosystem Research | Funk A.,Interuniversity Center for Aquatic Ecosystem Research | Gschopf C.,Vienna University of Technology | Hein T.,University of Natural Resources and Life Sciences, Vienna | Schiemer F.,University of Vienna
Journal of Applied Ecology | Year: 2013

We used an isolated floodplain of the river Danube as a model system to gain an understanding on the functioning of retention areas to predict future developments and to sustain their ecological services. We applied correlation analysis and spline regression models to assess the effects of geomorphology, hydraulics, and seasonality on sediment characteristics, suspended solids, hydrochemistry and primary producers. The spatio-temporal connection to the river is the primary factor influencing the hydrochemical characteristics and sediments. Allochthonous processes such as nutrient and sediment input during high waters dominate in connected parts of the floodplain, whereas autochthonous processes, for example, the release of phosphorus from the sediments and internally driven eutrophication, dominate in isolated parts. These conditions also affect the dominating primary producers, biodiversity, the degree of floodplain aggradation and thus the potential life span of aquatic habitats. Measures to improve the functional basis for ecological services may use both allochthonous and autochthonous processes as a starting point, that is, minimizing sediment storage and nutrient input and improving the water balance to prolong the life span of isolated waters, and thus maximizing water body diversity and associated biodiversity. Based on the results of our analysis and literature, eight alternative management measures have been evaluated. As a result, we propose a stepwise adaptive approach beginning with a controlled water supply with low sediments and nutrient loads. If these measures prove insufficient to sustain ecological functions and conservation value, more radical steps must be considered. Synthesis and applications The increasing problems with catastrophic flooding have forced decision makers to seek basin-wide solutions with focus on 'more room for the river' and the reintegration of former floodplains as retention basins. Such reintegrations also represent opportunities to improve the ecological conditions for nature development in addition to their principal function, that is, the storage of water during floods. The results of our study can serve as an effective tool to predict the effects of alternative management options and to establish and define the design criteria of water retention areas with regard to their ecological functions, life spans and biodiversity. The increasing problems with catastrophic flooding have forced decision makers to seek basin-wide solutions with focus on 'more room for the river' and the reintegration of former floodplains as retention basins. Such reintegrations also represent opportunities to improve the ecological conditions for nature development in addition to their principal function, that is, the storage of water during floods. The results of our study can serve as an effective tool to predict the effects of alternative management options and to establish and define the design criteria of water retention areas with regard to their ecological functions, life spans and biodiversity. © 2012 British Ecological Society.

Baart I.,University of Vienna | Baart I.,Interuniversity Center for Aquatic Ecosystem Research | Hohensinner S.,University of Vienna | Zsuffa I.,Environmental Protection and Water Management Research Institute VITUKI | And 2 more authors.
Environmental Science and Policy | Year: 2013

The presented case study deals with the hydromorphological alterations over a period of nearly 400 years and their ecological effects as shown by macrophytes in the urban floodplain Lobau along the Danube River within the city limits of Vienna for a period of about 160 years. Socio-economic pressures, such as flood protection (especially the Vienna Danube Regulation between 1869 and 1875), navigation and hydropower production, have modified the natural channel network in this anabranching river section into a shallow lake system in which habitat aging and sediment accumulation proceed. The aquatic and semi-aquatic habitats and their rich biodiversity would become reduced severely without any restoration measures promoting enhanced surface water exchange. The effects of restoration measures approaching pre-regulation conditions were evaluated for the macrophyte vegetation, a key ecosystem component. To collect monitoring data of the pre-regulation conditions, detailed literature data and mappings since 1846 up to recent surveys including the long-term development of aquatic vegetation patterns and aquatic habitat composition in the floodplain Lobau were analyzed. The potential effects were evaluated by analyzing how hydraulic parameters (water velocity and suitable habitat area for macrophytes) have controlled macrophyte composition and development. The study aimed at assessing the differences between the current and the historic situation caused by human impacts at different spatial scales and changes over time. By evaluating these differences we discussed intended as well as unintended effects of potential restoration measures.Primarily due to the loss of aquatic habitats the species diversity of aquatic vegetation is currently endangered and would decline without any restoration measures. However, a complete upstream reconnection of the remaining floodplain area Lobau to the Danube main channel (maximum achievable restoration goal) could also have unintended negative effects such as facilitation of the dispersal of non-native invasive species, decline of palaeopotamal species, and exposure of the floodplain to the present, altered water regime. Considering these alterations, the design of restoration projects would need to be adapted accordingly. In the presented case study Lobau, a partial reconnection instead of a complete reconnection might be the option optimizing the given management goals best. © 2012 Elsevier Ltd.

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.

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.

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