The two-stage ditch is a river restoration technique that aims at improving the sediment regime and lateral channel connectivity by recreating a small floodplain alongside a stream reach. This study ...aimed to analyze the efficiency of a two-stage ditch in improving the stream sediment structure and functions under different hydrological conditions (baseflow, post-bankfull, post-flood). Stream sediments were collected in channel sections adjacent to the two-stage ditch, adjacent to a natural floodplain along channelized reaches without inundation areas. Grain sizes, organic matter content and phosphorous (P) fractions were analyzed along with functional parameters (benthic respiration rate and P adsorption capacity, EPC0). The reach at the two-stage ditch showed no changes in sediment texture and stocks, while the floodplain reach showed higher fines and organic matter content under all hydrological conditions. The sediments in degraded reaches were more likely to be P sources, while they were more in equilibrium with the water column next to the natural floodplains and the two-stage ditch. Only functional parameters allowed for assessing the restoration effects on improving the sediment stability and functionality. Due to its sensitivity, the use of P adsorption capacity is recommended in future studies aiming at evaluating the response of river sediments to restoration measures under different hydrological conditions.
Besides the importance of dissolved organic matter (DOM) in soil biogeochemical processes, there is still a debate on how agricultural intensification affects the leaching of terrestrial DOM into ...adjacent aquatic ecosystems. In order to close this linkage, we conducted a short-term (45 day) lysimeter experiment with silt loam and sandy loam undisturbed/intact soil cores. Mineral (calcium ammonium nitrate) or organic (pig slurry) fertilizer was applied on the soil surface with a concentration equivalent to 130 kg N ha.sup.-1. On average, amounts of leached DOC over 45 days ranged between 20.4 mg (silt loam, mineral fertilizer) and 34.4 mg (sandy loam, organic fertilizer). Both, mineral and organic fertilization of a silt loam reduced concentration of dissolved organic carbon (DOC) in the leachate and shifted its composition towards a microbial-like signature (BIX) with a higher aromaticity (Fi) and a lower molecular size (E2:E3). However, in sandy loam only mineral fertilization affected organic matter leaching. There, lowered DOC concentrations with a smaller molecular size (E2:E3) could be detected. The overall effect of fertilization on DOC leaching and DOM composition was interrelated with soil texture and limited to first 12 days. Our results highlight the need for management measures, which prevent or reduce fast flow paths leading soil water directly into aquatic systems, such as surface flow, fast subsurface flow, or drainage water. Keywords: Absorbance spectra; agricultural management; dissolved organic carbon (DOC); dissolved organic matter (DOM); fluorescence spectra; lysimeter; mineral; organic; soil pore water
Agriculture delivers significant amounts of dissolved organic matter (DOM) to streams, thereby changing the composition and biodegradability of the aquatic DOM. This study focuses on the interactive ...effects of DOM quality and biofilm composition on the degradation of DOM in a laboratory flume experiment. Half of the flumes were exposed to light to stimulate algal growth, the other half was shaded. Leachates of deciduous leaves, maize leaves, and cow dung were added to the flumes in a single pulse and changes of DOC (dissolved organic carbon) and nutrient concentrations, DOM composition (absorbance and fluorescence data), chlorophyll-a concentrations, bacterial abundances, and enzymatic activities were recorded over a week. DOM was taken up with rates of 50, 109, and 136 µg DOC L−1 h−1 for dung, leaf, and maize leachates, respectively, in the light flumes and 37, 80, and 170 µg DOC L−1 h−1 in the dark flumes. DOC uptake correlated strongly with initial SRP (soluble reactive phosphorus) and DOC concentrations, but barely with DOM components and indices. Algae mostly stimulated the microbial DOC uptake, but the effects differed among differently aged biofilms. We developed a conceptual model of intrinsic (DOM quality) and external (environmental) controlling factors on DOM degradation, with the microbial community acting as biotic filter.
Aquatic-terrestrial interfaces may act as biogeochemical hotspots for greenhouse gas emissions, especially when exposed to frequent transitions between wet and dry phases. The study aimed to analyze ...the dynamics of nitrogen (N) processing along an inundation gradient from floodplain soils to river sediments and identify environmental factors affecting net nitrous oxide (N
2
O) production from different microbial sources. Intact soil and sediment cores were subject to two consecutive drying-rewetting cycles in laboratory experiments. The
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N isotope pairing technique was used to quantify N
2
O emissions sourced from denitrification and nitrification. We observed enhanced N
2
O emissions from both nitrification and denitrification following drying events. Sites exposed to frequent drying-rewetting cycles appear less affected by drying than hydrologically more stable habitats. Fluxes from nitrification were related to the organic matter content, while fluxes from denitrification were controlled by dissolved organic matter quality changes during the drying-rewetting cycles. This study shows the potential link between carbon metabolism and N
2
O production, combining the effect of drying-rewetting cycles.
The roles of dissolved organic matter (DOM) in microbial processes and nutrient cycles depend on its composition, which requires detailed measurements and analyses. We introduce a package for R, ...called staRdom (“spectroscopic analysis of DOM in R”), to analyze DOM spectroscopic data (absorbance and fluorescence), which is key to deliver fast insight into DOM composition of many samples. staRdom provides functions that standardize data preparation and analysis of spectroscopic data and are inspired by practical work. The user can perform blank subtraction, dilution correction, Raman normalization, scatter removal and interpolation, and fluorescence normalization. The software performs parallel factor analysis (PARAFAC) of excitation–emission matrices (EEMs), including peak picking of EEMs, and calculates fluorescence indices, absorbance indices, and absorbance slope indices from EEMs and absorbance spectra. A comparison between PARAFAC solutions by staRdom in R compared with drEEM in MATLAB showed nearly identical solutions for most datasets, although different convergence criteria are needed to obtain similar results and interpolation of missing data is important when working with staRdom. In conclusion, staRdom offers the opportunity for standardized multivariate decomposition of spectroscopic data without requiring software licensing fees and presuming only basic R knowledge.
This work addresses multiple human stressors and their impacts on fish assemblages of the Drava and Mura rivers in southern Austria. The impacts of single and multiple human stressors on riverine ...fish assemblages in these basins were disentangled, based on an extensive dataset. Stressor configuration, i.e. various metrics of multiple stressors belonging to stressor groups hydrology, morphology, connectivity and water quality were investigated for the first time at river basin scale in Austria. As biological response variables, the Fish Index Austria (FIA) and its related single as well as the WFD biological- and total state were investigated. Stressor-response analysis shows divergent results, but a general trend of decreasing ecological integrity with increasing number of stressors and maximum stressor is observed. Fish metrics based on age structure, fish region index and biological status responded best to single stressors and/or their combinations. The knowledge gained in this work provides a basis for advanced investigations in Alpine river basins and beyond, supports WFD implementation and helps prioritizing further actions towards multi-stressor restoration- and management.
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•Impacts of multiple stressors on river fish assemblages were investigated in Austria.•Seven stressor categories and up to 4 stressors at the same site were identified.•Of all sites, only 31% were unimpacted.•Impacted sites were affected by single stressors (26%) or multiple stressors (30%).•Decreasing ecological integrity with increasing number of stressors was identified.
Transport and transformation of inorganic nutrients are influenced by abiotic-biotic interactions and determine downstream water quality. Macrophytes play an important role in these complex ...ecological interactions. The role of macrophytes was studied in three reaches of the groundwater-fed, oligotrophic River Fischa with different macrophyte coverage and biomass. This was done by measuring metabolism and calculating changes in nutrient loading and concentrations, which were determined via an upstream-downstream mass balance approach. As the dominant autotrophs, we expected macrophytes (i) to have a direct effect by uptake and release, and (ii) an indirect effect by slowing down flow, which results in changed sedimentation patterns and altered conditions for heterotrophic microbial organisms implicating higher turnover and uptake rates.
The seasonal development of macrophytes in 2017 had a strong impact on gross primary production, but not on ecosystem respiration. Increase in macrophyte biomass led to higher GPP (max. 5.4 g O2m−2d−1). ER was highest in autumn in the reach with intermediate macrophyte biomass (max. 10.1 g O2m−2d−1). We observed that the autotrophic uptake of phosphorus accounted for 80–145% of the P-PO4-flux and concluded that P-uptake by macrophytes from the sediment is an important source of phosphate for macrophytes in the river. By accumulating fine sediment, macrophytes are improving the availability of phosphate for their own long-term development. N-NO3, represented >99% of the nitrogen flux. N-NO3 net uptake was higher in the reaches with more macrophytes (0.84 vs. 0.12 g m−2d−1), but in average only 21% of the net uptake could be related to autotrophic nitrogen uptake in the reach with high macrophyte biomass. Dissimilatory uptake by heterotrophic organisms, most probably denitrification, were of high relevance. Macrophytes supported microbial uptake and release by improving conditions and slowing down flow. In the River Fischa, an oligotrophic river with low variability of environmental parameters, macrophytes greatly affected nutrient uptake by direct and indirect pathways.
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•Macrophytes are playing a substantial role in river metabolism and net nutrient uptake•Impact of indirect effects of macrophytes (changed flow and sedimentation) are higher than direct effects (nutrient uptake)•Due to accumulation of fine sediment macrophytes maintain their main phosphorus source and improve their own habitat•By root uptake from the sediments, macrophytes enable a phosphate recycling pathway•Macrophytes enhance uptake rates of heterotrophic organisms (e.g. denitrification)
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.
River systems have undergone a massive transformation since the Anthropocene. The natural properties of river systems have been drastically altered and reshaped, limiting the use of management ...frameworks, their scientific knowledge base and their ability to provide adequate solutions for current problems and those of the future, such as climate change, biodiversity crisis and increased demands for water resources. To address these challenges, a socioecologically driven research agenda for river systems that complements current approaches is needed and proposed. The implementation of the concepts of social metabolism and the colonisation of natural systems into existing concepts can provide a new basis to analyse the coevolutionary coupling of social systems with ecological and hydrological (i.e., ‘socio-ecohydrological’) systems within rivers. To operationalize this research agenda, we highlight four initial core topics defined as research clusters (RCs) to address specific system properties in an integrative manner. The colonisation of natural systems by social systems is seen as a significant driver of the transformation processes in river systems. These transformation processes are influenced by connectivity (RC 1), which primarily addresses biophysical aspects and governance (RC 2), which focuses on the changes in social systems. The metabolism (RC 3) and vulnerability (RC 4) of the social and natural systems are significant aspects of the coupling of social systems and ecohydrological systems with investments, energy, resources, services and associated risks and impacts. This socio-ecohydrological research agenda complements other recent approaches, such as ‘socio-ecological’, ‘socio-hydrological’ or ‘socio-geomorphological’ systems, by focusing on the coupling of social systems with natural systems in rivers and thus, by viewing the socioeconomic features of river systems as being just as important as their natural characteristics. The proposed research agenda builds on interdisciplinarity and transdisciplinarity and requires the implementation of such programmes into the education of a new generation of river system scientists, managers and engineers who are aware of the transformation processes and the coupling between systems.
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•River systems have been massively transformed and are socio-ecohydrological systems.•A socio-ecohydrologically driven approach provides insights into coevolutionary processes.•Social metabolism and the colonisation of natural systems are underlying concepts.•Four research clusters analyse the transformation and coupling of society and nature.•Interdisciplinary and transdisciplinary approaches support the operationalization of the research agenda.
High-frequency water quality measurements in streams and rivers have expanded in scope and sophistication during the last two decades. Existing technology allows
automated measurements of water ...quality constituents, including both solutes and particulates, at unprecedented frequencies from seconds to subdaily sampling intervals. This detailed chemical information can be combined with measurements of hydrological and biogeochemical processes, bringing new insights into the sources, transport pathways, and transformation processes of solutes and particulates in complex catchments and along the aquatic continuum. Here, we summarize established and emerging high-frequency water quality technologies, outline key high-frequency hydrochemical data sets, and review scientific advances in key focus areas enabled by the rapid development of high-frequency water quality measurements in streams and rivers. Finally, we discuss future directions and challenges for using high-frequency water quality measurements to bridge scientific and management gaps by promoting a holistic understanding of freshwater systems and catchment status, health, and function.
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