Gabriele Weigelhofer - Academia.edu (original) (raw)

Papers by Gabriele Weigelhofer

River Systems, Dec 19, 2003

The role of the hyporheic zone as a habitat for macrozoobenthos was investigated within the clogg... more The role of the hyporheic zone as a habitat for macrozoobenthos was investigated within the clogged sediments of a calcareous sandstone stream near Vienna. From September 1997 to October 1998 sediments were sampled for vertical distribution of grain size, organic matter and invertebrates to a depth of 60 cm every second month using the freeze-coring-technique with electropositioning. The amount of fine particles within the hyporheic zone was strongly influenced by channel morphology. Sediments at the deep and narrow run section accumulated significantly less fine particles down to 60 cm depth than at the riffle section. The degree of clogging strongly affected hyporheic colonization by stream biota. Invertebrate densities were significantly higher in sediments of the run than in those of the riffle section. Generally, hyporheic abundances of the mainly epigean fauna decreased with depth, although the decline was more distinct within the riffle section. Densities were strongly influenced by sediment depth and morphological subunit and significantly and negatively correlated with the percentage of fine particles, fine particulate organic matter and particulate nitrogen within the hyporheic zone.

Österreichische Wasser- und Abfallwirtschaft, Apr 29, 2019

$Research paper thumbnail of Flow history explains temporal and spatial variation of carbon fractionation in stream periphyton$

Limnology and Oceanography, Mar 1, 2005

We investigated factors that contribute to isotopic carbon fractionation in periphytic biofilms i... more We investigated factors that contribute to isotopic carbon fractionation in periphytic biofilms in a human-altered headwater stream with a flashy hydrograph. Water velocity had an important effect on periphyton ␦ 13 C, explaining both temporal and spatial variation. We found that water velocity averaged over a certain period before sampling, rather than the instantaneous water velocity, explained a high percentage of both temporal and spatial variation of the periphyton ␦ 13 C signature. The relationship between water velocity and periphyton ␦ 13 C signature was particularly influenced by individual flow events during the recent flow history. A simple model based on a flow history of 3-4 weeks reliably estimated the ␦ 13 C signature of periphyton from distinct reaches. The model clearly identified signature shifts caused by the deposition of activated sludge particles from a wastewater treatment plant onto the periphytic biofilms. We highlight the high spatial and temporal variability of periphyton ␦ 13 C signatures (i.e., up to 3-6‰) in a heterogeneous flow environment with inputs from a wastewater treatment plant, and we explore its implications for food web analysis.

International Review of Hydrobiology, Jul 1, 2003

Due to the erosiveness of their sediments, sandstone streams transport high loads of fine particl... more Due to the erosiveness of their sediments, sandstone streams transport high loads of fine particles. The catchment of the Weidlingbach, a 12 km long tributary of the Danube northwest of Vienna, is dominated by calcareous sandstone, marl and slate. Mean sediment grain size ranges from 29.3 to 31.0 mm, and mean pore volume is approximately 20%. The third order study site is divided into a wide, shallow riffle section with high accumulations of fine sediments in the hyporheic zone and a narrow, deep run section with a lower percentage of fine sediments. Invertebrates were sampled to a sediment depth of 60 cm every second month using the freeze-coring-technique with electropositioning. Hyporheic invertebrate densities were significantly higher in sediments of the run than in those of the riffle section. Generally, hyporheic abundances decreased with increasing depth; however, the decline was more distinct within the riffle than the run section. Furthermore, we observed a strong negative correlation between the percentage of fine sediments (<2 mm) and hyporheic invertebrate densities.

Water scarcity is one of the greatest challenges for stream management in the 21st century. Alrea... more Water scarcity is one of the greatest challenges for stream management in the 21st century. Already now, the majority of channel lengths of natural waterways are intermittent worldwide. Global warming will increasingly cause perennial streams to become intermittent also in temperate regions such as Austria. The project PURIFY (2018–21) aims at investigating the impacts of intermittency on the water quality and the self-purification capacity of streams in different regions in Austria. We want to identify factors, which significantly influence the resistance of in-stream processes towards desiccation. For this purpose, we sampled five perennial and five intermittent streams in Burgenland, Styria and Carinthia before and during the dry phase in 2018 to analyse the water quality and the activity of benthic microorganisms. Despite an extended dry period, we observed no significant differences in the microbial respiration, abundances, and enzymatic activities between perennial and intermittent reaches within the same region. We assume that dense shading by riparian trees and high accumulations of fine particles in the sediments helped to maintain a high humidity in the sediments and, thus, buffered the effects of drying on microbial processes. However, receding water levels in both intermittent and perennial reaches resulted in large fluctuations of nutrient concentrations. Extended field investigations combined with laboratory experiments and hydrodynamic modelling will clarify the short- and long-term effects of repeated drying on the microbial uptake of nutrients (self-purification capacity) and on the water quality in relation to stream type and degree of pollution.

River Systems, 2003

Österreichische Wasser- und Abfallwirtschaft, Aug 10, 2022

Zusammenfassung Landwirtschaft führt zu einer Belastung von Bächen durch Nährsalze und Fäkalkeime... more Zusammenfassung Landwirtschaft führt zu einer Belastung von Bächen durch Nährsalze und Fäkalkeime. Das Ziel der Studie ist, das Potenzial von Ufergehölzen zu untersuchen, derartige Belastungen zu reduzieren und zu einer verbesserten Wasser-und Sedimentqualität zu gelangen. Wir analysierten, wie Ufergehölze die Sedimentstruktur, den Sauerstoffverbrauch, die Aufnahmekapazität für Phosphor und die Akkumulation von eingetragenen Fäkalkeimen beeinflussen. Dazu untersuchten wir die Wasser-und Sedimentqualität von 20 Bachabschnitten mit und ohne Ufergehölzen in landwirtschaftlichen Regionen in Niederösterreich. Die Proben wurden jeweils am Ende eines 1 km langen Abschnitts mit Ufergehölzstreifen sowie unmittelbar davor entnommen. Die Ergebnisse rangierten zwischen einer deutlichen Verbesserung der Sedimentqualität (reduzierte Feinsedi

Science of The Total Environment, Jul 1, 2018

Fine sediments and phosphorus concentrations increased with percent cropland. • Sediments of poll... more Fine sediments and phosphorus concentrations increased with percent cropland. • Sediments of polluted streams showed high potential for P adsorption. • Phosphatase activity in epilithic biofilms decreased with increasing SRP in water. • Phosphatase activity in epipsammic biofilms was highest in polluted streams. • Fine sediments restrict P exchange between water column and sediments.

EGU General Assembly Conference Abstracts, Apr 1, 2019

Oecologia, Aug 1, 2012

Phytoplankton play an important role as primary producers and thus can affect higher trophic leve... more Phytoplankton play an important role as primary producers and thus can affect higher trophic levels. Phytoplankton growth and diversity may, besides other factors, be controlled by seasonal temperature changes and increasing water temperatures. In this study, we investigated the combined effects of temperature and diversity on phytoplankton growth. In a controlled laboratory experiment, monocultures of 15 freshwater phytoplankton taxa (green algae, cyanobacteria, and diatoms) as well as 25 mixed communities of different species richness (2-12 species) and taxa composition were exposed to constant temperatures of 12, 18, and 24°C. Additionally, they were exposed to short-term daily temperature peaks of ?4°C. Increased species richness had a positive effect on phytoplankton growth rates and phosphorous content at all temperature levels, with maximum values occurring at 18°C. Overyielding was observed at almost all temperature levels and could mostly be explained by complementary traits. Higher temperatures resulted in higher fractions of cyanobacteria in communities. This negative effect of temperature on phytoplankton diversity following a shift in community composition was most obvious in communities adapted to cooler temperatures, pointing to the assumption that relative temperature changes may be more important than absolute ones.

Zenodo (CERN European Organization for Nuclear Research), Dec 15, 2022

Sturgeon hatchery practices and management for re lease. Guidelines FAO Fisheries and Aquaculture... more Sturgeon hatchery practices and management for re lease. Guidelines FAO Fisheries and Aquaculture Technical Paper No. 570, Ankara, 110 pp. Friedrich T, Eichhorn H (in prep): Durations of incubation & larval development of sterlets (A. ruthenus) in river water rearing under seminatural conditions Friedrich T, Ludwig A (in prep): Genetic population assessment of two sterlet populations in the Upper Danube, Austria.

Aquatic Sciences, Jun 30, 2021

EGUGA, Apr 1, 2013

ABSTRACT At different spatial and temporal scales, the connectivity of habitats within the four d... more ABSTRACT At different spatial and temporal scales, the connectivity of habitats within the four dimensional riverine environment has been recognized as a central element in structuring and sustaining aquatic and riparian communities and controlling biogeochemical cycling in riverine landscapes. Floodplains for example are controlled by the patterns of connectivity with the river channel and the adjacent landscape elements. They are seen as biodiversity and biogeochemical hotspots and bear a strategic importance for nature conservation and ecosystem management targets in river basins and from a socioeconomic point of view, floodplains provide a multitude of ecosystem services. The deterioration of river systems and their landscapes due to regulation and land use change has prompted restoration measures aiming to improve the ecological conditions of river systems. One of the aims is to improve the connectivity between these landscape elements and by that also enhance overall the spatial heterogeneity and temporal variability within the riverine landscape. Thus, the responses of changes in connectivity are key to predict and understand effects of restoration measures. Even more insights on how species development and population dynamics are impacted can be gained by linking concepts of meta community ecology with spatial analysis and the connectivity patterns at different spatial scales as well as seasonal and long-term effects. In this presentation different aspects of connectivity, the changes due to restoration and effects for biodiversity and biogeochemical cycles are highlighted for complex riverine landscapes.

Freshwater Biology, Aug 16, 2022

The hyporheic zone (HZ) is a hotspot of carbon processing in stream ecosystems as a consequence o... more The hyporheic zone (HZ) is a hotspot of carbon processing in stream ecosystems as a consequence of the mixing of organic matter and nutrients from ground water and surface waters. However, major knowledge gaps exist regarding the drivers of microbial activity and carbon processing in the HZ among stream ecosystems with different carbon sources and sediment properties. We investigated the impact of algal dissolved organic matter (DOMalgal) and inorganic phosphorus (P) on the degradation of soil DOM (DOMsoil) by hyporheic microorganisms in two laboratory experiments. In our first experiment, we explored the influence of different ratios of DOMalgal to DOMsoil with and without P additions on microbial respiration and DOM composition in laboratory hyporheic microcosms under oxic conditions. Here, we used glass beads colonised by stream microorganisms resembling a pristine stream system. As the addition of DOMalgal increased P concentrations, we added P to adjust the P concentrations to the same level of the pure DOMalgal in a second batch. In our second experiment, we determined the aerobic microbial respiration of HZ‐sediments from 20 streams along a land‐use gradient in Austria incubated with DOMsoil. Again, we performed the experiments with and without P additions to see whether effects on microbial respiration depended on the ambient P concentrations of the streams. Aerobic microbial respiration in the hyporheic microcosms decreased with increasing DOMsoil proportions. When P concentrations were adjusted to the P level of the DOMalgal, aerobic microbial respiration rates were similar between the different DOM mixtures in the microcosms, mainly stimulating the degradation of humic‐like DOM fractions. This highlights the stimulating effects of the P additions on hyporheic microbial respiration and humic‐like DOM degradation in pristine streams. However, P additions caused a significant increase in microbial respiration in only one of 20 natural HZ‐sediments, suggesting that aerobic microbial respiration rates rarely were controlled by P availability in the investigated streams. We conclude that nutrient pulses can, but do not necessarily, stimulate microbial activity and terrestrial carbon degradation in the HZ of streams. Nevertheless, at low ambient nutrient concentrations (i.e., in pristine streams) terrestrial carbon degradation in the HZ can be accelerated when nutrient pulses occur, which has consequences for CO2 outgassing and the organic matter quality in the stream and its export to downstream sections.

Biogeosciences, May 25, 2021

Uptake and release patterns of dissolved organic matter (DOM) compounds and co-transported nutrie... more Uptake and release patterns of dissolved organic matter (DOM) compounds and co-transported nutrients are entangled, and the current literature does not provide a consistent picture of the interactions between the retention processes of DOM fractions. We performed plateau addition experiments with five different complex DOM leachates in a small experimental stream impacted by diffuse agricultural pollution. The study used a wide range of DOM qualities by including leachates of cow dung, pig dung, corn leaves, leaves from trees, and whole nettle plants. We measured changes in nutrient and dissolved organic carbon (DOC) concentrations along the stream course and determined DOM fractions by fluorescence measurements and parallel factor (PARAFAC) decomposition. To assess the influences of hydrological transport processes, we used a 1D hydrodynamic model. We developed a non-linear Bayesian approach based on the nutrient spiralling concept, which we named the "interactions in nutrient spirals using Bayesian regression" (INS-BIRE) approach. This approach can disentangle complex interactions of biotic and abiotic drivers of reactive solutes' uptake in multi-component DOM sources. It can show the variability of the uptake velocities and quantify their uncertainty distributions. Furthermore, previous knowledge of nutrient spiralling can be included in the model using prior probability distributions. We used INSBIRE to assess interactions of compound-specific DOM and nutrient spiralling metrics in our experiment. Bulk DOC uptake varied among sources, showing decreasing uptake velocities in the following order: corn > pig dung > leaves > nettles > cow dung. We found no correlations between bulk DOC uptake and the amounts of proteinlike compounds or co-leached soluble reactive phosphorus (SRP). The fastest uptake was observed for SRP and the tryptophan-like component, while the other DOM components' uptake velocities more or less resembled that of the bulk DOC. Almost all DOM components showed a negative relationship between uptake and concentration, known as efficiency loss. Furthermore, we observed a few negative and (weak) positive interactions between the uptake and the concentration of different components, such as a decreased uptake of protein-like compounds at high concentrations of a high-molecular-weight humic-like compound. We also found an influence of the wetted width on the uptake of SRP and a microbially derived humic substance, which indicates the importance of the sediment-water interface for P and humic C cycling in the studied stream. Overall, we show that bulk DOC is a weak predictor of DOC uptake behaviour for complex DOM leachates. Individual DOM compound uptake, including co-leached nutrients, is controlled by both internal (quality-related) and external (environmental) factors within the same aquatic ecosystem. We conclude that the cycling of different C fractions and their Published by Copernicus Publications on behalf of the European Geosciences Union. 3104 M. Pucher et al.: Interactions of in-stream DOM and nutrient spiralling mutual interaction with N and P uptake in streams is a complex, non-linear problem, which can only be assessed with advanced non-linear approaches, such as the presented INS-BIRE approach.

Ecohydrology and Hydrobiology, 2006

Water bodies within floodplains are strongly governed by their hydrological connectivity with the... more Water bodies within floodplains are strongly governed by their hydrological connectivity with the main river (Heiler et al. 1995). Connectivity is decisive for the general ecosystem characteristics and the balance between input and output of nutrients and organic carbon sources. A major determinant is the abundance of macrophytic vegetation, which is controlled by through-flow, dry-falling and scouring effects. The autochthonous primary production is strongly augmented by local terrestrial carbon sources and by the riverine transport in form of dissolved and particulate organic matter. The significance of these different sources depends on hydrology. Flood pulses represent a disturbance to pelagic communities (followed by successions) and a source of nutrients. High loads of inorganic nutrients produce conditions for prolific algal growth. High availability of allochthonous organic carbon provides the basis for a prolific bacterial secondary production. Our data emphasize that the stimulus of local aquatic primary production enhances carbon utilization by bacteria.

We assess the &#8220;macronutrient-balance hypothesis,&#8221; wh... more We assess the &#8220;macronutrient-balance hypothesis,&#8221; which we define as: &#8220;Aquatic heterotrophic nutrient assimilation is controlled by the balance between the bioavailable DOC : reactive macronutrient stoichiometry and the microbial stoichiometric macronutrient demand.&#8221; Here we define the reactive macronutrients as the sum of dissolved inorganic nitrogen, soluble-reactive phosphorus (SRP), and dissolved bioavailable organic N (bDON) & P (bDOP). A global meta-analysis of monitoring data from various freshwaters suggests this hypothesis, yet clear experimental support is missing.We assessed this hypothesis in a proof-of-concept experiment for waters from four different small agricultural streams. We used seven different bioavailable DOC (bDOC) : reactive N and bDOC : reactive P ratios, induced by seven different levels of alder leaf leachate addition. With these treatments and a stream-water specific bacterial inoculum, we conducted a separate 3-day experiment, with three independent replicates per combination of stream water, treatment and sampling occasion. Here, we extracted dissolved organic matter (DOM) fluorophores by measuring excitation-emission matrices with subsequent parallel factor decomposition (EEM-PARAFAC). We assessed the true bioavailability of DOC, DON, and the DOM fluorophores as solute concentration difference between the beginning and end of each experiment. Separately, we predicted bDOC and bDON concentrations based on the bioavailable fluorophores, which we compared to their true bioavailability measured before. Due to very low DOP concentrations, the DOP determination uncertainty was high, and we had to neglect DOP as part of the reactive P.For bDOC and bDON, the bioavailability measurements agreed with the same fractions calculated indirectly from bioavailable DOM fluorophores (bDOC r&#178;&#8196;=&#8196;0.96, p&#8196;<&#8196;0.001; bDON r&#178;&#8196;=&#8196;0.77, p&#8196;<&#8196;0.001), hence we could predict bDOC and bDON concentrations based on the molecular composition of DOM. Moreover, we found that bDOC : reactive nutrient ratios at specific ranges (molar bDOC&#8196;:&#8196;reactive N&#8196;=&#8196;2&#8197;&#8722;&#8197;17; molar bDOC&#8196;:&#8196;reactive P&#8196;=&#8196;50&#8197;&#8722;&#8197;300) control microbial heterotrophic nutrient uptake.In summary, the results of our simple laboratory experiment provide first proof that the bDOC : reactive macronutrient ratio strongly controls heterotrophic reactive macronutrient uptake. Combined with the previous large-scale monitoring evidence, our study implies that the &#8220;macronutrient-balance hypothesis&#8221; holds in many aquatic ecosystems. However, this hypothesis needs to be corroborated by further experiments with different DOC sources and assessments of changes in bDOC : reactive macronutrient ratios on freshwater carbon and nutrient cycles.

International Research in Geographical and Environmental Education