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Saline rivers are supposed to be 'hot spots' of high biological productivity in arid landscapes. To test this, we quantified the production of chironomid larvae, because river production is known to be transferred to arid landscapes primarily by birds fed on these larvae. In addition, we studied the potential biochemical quality of the larvae for birds based on the essential highly unsaturated fatty acid (HUFA) contents in their biomass. We studied species composition and measured production of chironomid larvae in two saline rivers (Volgograd region, Russia). We also evaluated the fatty acid composition and contents of the dominant taxa and estimated the flux of HUFA from the studied saline rivers to land via chironomid potential emergence. Average monthly production of chironomids measured for only 1 month, August, was quite comparable to annual production in some freshwater rivers. All the dominant chironomid larvae had comparatively high essential eicosapentaenoic acid contents, especially Cricotopus salinophilus, which showed the highest value, reported for Chironomidae. The monthly flux of HUFA from the studied rivers to land due to the chironomid potential emergence was roughly comparable to the global average estimation of annual water-land HUFA export via emerging insects. [ABSTRACT FROM AUTHOR]

Experimental studies evaluating the simultaneous effects of consumers, nutrients, and other biotic/abiotic factors on intact, natural food webs are rare, particularly among ecosystems of varying trophic conditions. We conducted a series of in situ studies that used nutrient-diffusing substrata with nitrogen (N) and phosphorus (P) concentrations in a full factorial design in three temperate, limestone streams in Pennsylvania across a trophic gradient (mesotrophic, eutrophic, and hypereutrophic streams). We assessed differences in algal and macroinvertebrate biomass, taxonomic composition, and functional groups relative to amended nutrients across the trophic gradient; as such, these results facilitated predictions about regulators of food web structure. All factors varied significantly among the streams (e.g., algal biomass P = 0.005, macroinvertebrate biomass P < 0.001, algal diversity P = 0.006, macroinvertebrate diversity P < 0.001, algal group P < 0.001, macroinvertebrate guilds P < 0.001); the streams, however, did not exhibit simple responses to nutrient amendment. Algal and macroinvertebrate biomass and diversity responded greatest in the mesotrophic stream while grazing seemed to be a strong factor preventing algal nutrient response in the eutrophic and hypereutrophic streams. Brillouin's Evenness Index was most influenced by nutrient amendment (nutrient effect on algae and macroinvertebrates P = 0.021). As such, we concluded that biomass and diversity were mediated by complexity within intermediate trophic levels. [ABSTRACT FROM AUTHOR]

Biological monitoring tools are largely lacking for many countries, resulting in adoption of tools developed from other countries/regions, but in many instances, their applicability to the new system has not been explicitly evaluated. The objective of the study was to test the applicability of the South African Scoring Systems Version 5 (SASS5) to urban streams in Zimbabwe. The study evaluated the relationship between water quality variables and SASS5 indices/metrics [(SASS and average score per taxon (ASPT)] and found high degree of concordance between water chemistry parameters and SASS5 metrics, indicating that both SASS and ASPT scores are sensitive to detect environmental changes. This result can be attributed to occurrence of ubiquitous macroinvertebrate taxa sharing similar environmental tolerances with those recorded for South African systems. The applicability of SASS5 metrics need to be tested across different geographical and climatic regions in the country (taking into consideration seasonal variations that are important drivers of benthic faunal assemblages in lotic systems) and disparities among the regions compared for the adoption of the index in the entire country. The SASS5 metrics can also be further strengthened by (a) taking into account the relative abundance of taxa and (b) also improving on its ability to reflect other forms of perturbations besides eutrophication and organic pollution such heavy metal pollution. [ABSTRACT FROM AUTHOR]

Litter decomposition in running water sometimes proceeds faster in small, cool tributaries than in warm, wide rivers because stenothermal, leaf-shredding invertebrates are more abundant in the cool streams. Evidence from eastern Canada suggests that the cold-stenothermal stonefly Leuctra has a disproportionate influence on rapid mass loss in upstream reaches of soft-water river systems, but is not replaced by an effective, warm-water shredder downstream. To test the generality of this observation, we compared litter decomposition rates in upstream (second or third order) and downstream (fourth or fifth order) reaches of a medium-size river system in Nova Scotia (Canada) and three river systems in Nordland (Norway). In all river systems, mass loss of nitrogen-rich speckled alder ( Alnus incana) leaves and nitrogen-poor red maple ( Acer rubrum) leaves proceeded faster at the upstream site only if water temperature there was significantly cooler than downstream. Decomposition rates in all systems were strongly correlated with abundance of Leuctra, and to a lesser extent the caddisfly Lepidostoma. The distribution of Leuctra seems to be driven primarily by water temperature, with a strong peak of abundance at 14°C, but may also be influenced by competition from other shredding species. [ABSTRACT FROM AUTHOR]

Streams and rivers in mediterranean-climate regions (med-rivers) are subjected to sequential, yet contrasting hydrologic disturbances of drying and flooding. Although seasonally predictable, these disturbances can vary in intensity and duration within and among mediterranean-climate regions (med-regions). Consequently, med-rivers differ in the permanence of their aquatic habitats. To persist, species have acquired matched resistance and resilience adaptations. They gain resistance either by enduring the stress or avoiding it. Community recovery (or resilience) is achieved with cessation of hydrologic stress that permits maximization of re-colonization and reproduction. Endurance strategies are usually disturbance-specific, but avoidance enables organisms to cope with both drying and flooding, and is the prevalent resistance strategy. Correspondingly, community persistence depends to a large extent on the integrity of refuges, an aspect that has so far been little explored. Existing information suggests that seasonal community succession becomes more pronounced with increasing aridity and declining water permanence. The invertebrate community in semi-arid med-rivers can therefore undergo succession through three to four identifiable assemblages, whereas in perennial streams the difference between wet and dry period assemblages is smaller. Community turnover is influenced by the intensity of the hydrologic disturbances and varies between wet and drought years. [ABSTRACT FROM AUTHOR]

Although the California mediterranean climate region is widely considered a biodiversity hotspot for terrestrial plants and vertebrates, freshwater biodiversity in this region is generally not well known. Using information from museum specimen databases, published literature, biological assessment surveys, and specialist's knowledge, we review freshwater biodiversity for several groups of stream organisms in the med-climate region of California, which includes 2,220 species in 292 families. The groups with the highest diversity of lotic species are aquatic insects and diatoms, which comprise 39 and 36 % of species in our lists, respectively. Sequential floods and drying periods limit the overall biodiversity of many stream organisms in California mediterranean rivers, and continued climate and land-use change may cause disproportionate biodiversity declines in the region. However, only 4 % of lotic species have been evaluated in the IUCN Red List of Threatened Species, and many assessments are outdated. Future development of online databases for botanical and zoological collections will significantly enhance biodiversity and distribution knowledge. This information will enable us to more accurately and efficiently assess the effects of global change on biodiversity of freshwater organisms, to evaluate conservation status of individual taxa, and to set conservation priorities for stream ecosystems. [ABSTRACT FROM AUTHOR]

Streams and rivers in mediterranean-climate regions (med-rivers in med-regions) are ecologically unique, with flow regimes reflecting precipitation patterns. Although timing of drying and flooding is predictable, seasonal and annual intensity of these events is not. Sequential flooding and drying, coupled with anthropogenic influences make these med-rivers among the most stressed riverine habitat worldwide. Med-rivers are hotspots for biodiversity in all med-regions. Species in med-rivers require different, often opposing adaptive mechanisms to survive drought and flood conditions or recover from them. Thus, metacommunities undergo seasonal differences, reflecting cycles of river fragmentation and connectivity, which also affect ecosystem functioning. River conservation and management is challenging, and trade-offs between environmental and human uses are complex, especially under future climate change scenarios. This overview of a Special Issue on med-rivers synthesizes information presented in 21 articles covering the five med-regions worldwide: Mediterranean Basin, coastal California, central Chile, Cape region of South Africa, and southwest and southern Australia. Research programs to increase basic knowledge in less-developed med-regions should be prioritized to achieve increased abilities to better manage med-rivers. [ABSTRACT FROM AUTHOR]

Hydrologic alterations designed to provide a stable water supply and to prevent flooding are commonly used in mediterranean-climate river (med-rivers) basins, and these alterations have led to habitat loss and significant declines in aquatic biodiversity. Often the health of freshwater ecosystems depends on maintaining and recovering hydrologic habitat connectivity, which includes structural components related to the physical landscape, functionality of flow dynamics, and an understanding of species habitat requirements for movement, reproduction, and survival. To advance our understanding of hydrologic habitat connectivity and benefits of habitat restoration alternatives we provide: (1) a review of recent perspectives on hydrologic connectivity, including quantitative methods; and (2) a modeling framework to quantify the effects of restoration on hydrologic habitat connectivity. We then illustrate this approach through a case study on lateral hydrologic habitat connectivity that results from channel restoration scenarios using scenarios with different historic and climate-change flows to restore fish floodplain habitat in a med-river, the San Joaquin River, California. Case study results show that in addition to the channel alterations, higher flows are required to recover significant flooded habitat area, especially given reductions in flows expected under climate change. These types of studies will help the planning for restoration of hydrologic habitat connectivity in med-rivers, a critical step for mediterranean species recovery. [ABSTRACT FROM AUTHOR]

River and stream biofilms in mediterranean fluvial ecosystems face both extreme seasonality as well as arrhythmic fluctuations. The hydrological extremes (droughts and floods) impose direct changes in water availability but also in the quantity and quality of organic matter and nutrients that sustain the microbial growth. This review analyzes how these ecological pulses might determine unique properties of biofilms developing in mediterranean streams. The paper brings together data from heterotrophic and autotrophic community structure, and extracellular enzyme activities in biofilms in mediterranean streams. Mediterranean stream biofilms show higher use of peptides during the favorable period for epilithic algae development (spring), and preferential use of cellulose and hemicellulose in autumn as a response to allochthonous input. The drying process causes the reduction in bacterial production and chlorophyll biomass, but the rapid recovery of both autotrophs and heterotrophs with rewetting indicates their adaptability to fluctuations. Bacteria surviving the drought are mainly associated with sediment and leaf litter which serve as 'humid refuges'. Some algae and cyanobacteria show resistant strategies to cope with the drought stress. The resistance to these fluctuations is strongly linked to the streambed characteristics (e.g., sediment grain size, organic matter accumulation, nutrient content). [ABSTRACT FROM AUTHOR]

Forested headwater streams play an important role in watershed nutrient dynamics, and wood is thought to be a key factor influencing habitat structure and nitrate-nitrogen dynamics in many forested streams. Because wood in streams can promote nitrogen uptake through denitrification, we hypothesized that nitrate uptake velocities would decrease following wood removal. We measured stream characteristics and nitrate uptake velocities before and after wood manipulation experiments conducted at Hubbard Brook Experimental Forest, NH, and the Sleepers River watershed, VT. The mean size of stream substrates and the amount of riffle habitat increased following wood removal. In contrast to our expectations, summer nitrate uptake velocities increased in the wood removal treatments relative to the reference treatments, possibly because wood removal increased the availability of stable substrates for periphyton growth, therefore increasing nitrate demand in these streams. Our results highlight that effects of wood on stream ecosystems occur through multiple pathways and suggest that the relative importance of these pathways may vary seasonally. [ABSTRACT FROM AUTHOR]

Reduction of flow constitutes one of the most severe human alterations to rivers, as it affects the key abiotic feature of these ecosystems. While there has been considerable progress in understanding the effects of reduced flow on benthic macroinvertebrates, cascading effects of flow reduction on dissolved oxygen concentrations (DO) have not yet received much attention. We compared the macroinvertebrate composition between reference conditions and a situation after several years of discharge reduction in the Spree River (Brandenburg, Germany). Community composition shifted from rheophilic species to species indifferent to flow conditions. Filter feeders were partially replaced by collector/gatherers, which likely reduces the retention of organic matter, and thus the self-purification capacity of the river section. These shifts were associated with low discharge during summer, cascading into daily DO concentration minima of less than 5 mg l which prevailed 74% of the days in summer. This depletion of DO after flow reduction presumably caused the observed species turnover. Hence, flow reduction in lowland rivers may not only directly impair the ecological functions provided by benthic macroinvertebrates but may also act indirectly by depleting DO concentrations. [ABSTRACT FROM AUTHOR]

This resampling study in 338 semi-permanent plots analyses changes in river macrophyte diversity in 70 water courses (small streams to medium-sized rivers) from four regions of the northwest German lowlands during the last six decades. The total macrophyte species pool decreased between the 1950s and 2010/2011 by 28% (from 51 to 37 species), mean plot-level species richness by 19% (from 4.7 to 3.8 species per relevé) and the number of red-listed species by 40% (from 30 to 18 species). Species loss was associated with marked change in species traits: species with presumably higher mechanical stress tolerance (indicated by low specific leaf area and short leaf longevity) are more abundant today. Nearly, half of the species present in the 1950s had either disappeared or been replaced by other species in the recent relevés. The dramatic impoverishment is likely a consequence of continued nutrient input that drove oligo- and mesotraphent species to extinction, and of restructuring and maintenance works in the water courses that reduced stagnant and undisturbed river habitats, where stress-intolerant species can persist. Efficient measures to reduce the nutrient load and to re-naturalise stream and river beds are urgently needed to halt and reverse the loss of macrophyte diversity. [ABSTRACT FROM AUTHOR]

The damming of rivers and streams alters downstream habitat characteristics and biotic assemblages, and might thus alter stream functioning, although there is not much direct evidence of this impact. In this study we compared breakdown of alder leaves upstream and downstream from 4 small (<1 hm) dams in 4 Mediterranean mountain streams with no appreciable impact on water temperature and nutrient concentrations. Despite no effect on water characteristics, dams decreased leaf litter breakdown rates. Abundance and biomass of invertebrates and shredders and hyphomycete sporulation rates did not differ between upstream and downstream bags. However, the structure of invertebrate and hyphomycete assemblages did. Especially evident was a drop in limnephilids, which might explain the slower breakdown of leaf litter below dams. These results may help to explain some of the variability found in the literature on the effects of dams on decomposition rates. If dams increase water temperature and nutrient concentrations they may promote faster decomposition, but if dams do not change water characteristics, their impact on detritivore communities may cause slower decomposition rates. [ABSTRACT FROM AUTHOR]

Small hydropower plants divert part of the water from wide and physically complex stream channels with active hyporheic areas to narrow and hydraulically simple concrete canals, and thus, might affect nutrient dynamics. We compared nutrient uptake in diversion canals and in stream channels in the Leitzaran Stream (Basque Country, northern Spain). We predicted that simple morphology in diversion canals will result in lower nutrient uptake in canals than in stream channels. Periphytic chlorophyll and biomass did not differ significantly between reach types. Water was significantly deeper and faster in canals than in stream channels, but the transient storage zone did not differ significantly between reach types. There were no significant differences between uptake length for neither phosphate nor ammonium between reach types. Uptake length in both stream channels and diversion canals decreased with discharge, in a pattern similar to that previously described for pristine rivers across the world. Uptake velocity and uptake rate for phosphate did not differ significantly between reach types, but in the case of ammonium both retention metrics were significantly larger in the diversion canals. Results suggest that although hydropower schemes have minor effects on nutrient retention, these depend on the proportion of flow diverted. [ABSTRACT FROM AUTHOR]

Flow and temperature are strongly linked environmental factors driving ecosystem processes in streams. Stream temperature maxima ( T) and stream flow minima ( Q) can create periods of stress for aquatic organisms. In mountainous areas, such as western North America, recent shifts toward an earlier spring peak flow and decreases in low flow during summer/fall have been reported. We hypothesized that an earlier peak flow could be shifting the timing of low flow and leading to a decrease in the interval between T and Q. We also examined if years with extreme low Q were associated with years of extreme high T. We tested these hypotheses using long-term data from 22 minimally human-influenced streams for the period 1950-2010. We found trends toward a shorter time lag between T and Q over time and a strong negative association between their magnitudes. Our findings show that aquatic biota may be increasingly experiencing narrower time windows to recover or adapt between these extreme events of low flow and high temperature. This study highlights the importance of evaluating multiple environmental drivers to better gage the effects of the recent climate variability in freshwaters. [ABSTRACT FROM AUTHOR]

Small hydropower plants (SHP) affect river flow and sediment transport and thus impact river morphology. Eight hydropower schemes were studied along the meandering middle and lower reaches of Aragón River (Spain) to assess their effects on channel morphology and sediment dynamics from 1927 to 2010. GIS tools were used to measure changes in fluvial surfaces, channel planform and lateral and vertical dynamics. Three periods (early, middle and late twentieth century) were analysed to discern the effects of the main pressures, such as changes in land use, large reservoirs upstream and SHPs. Results were combined with field and topographical measurements and hydrological analysis. Active channel width and channel migration suffered a clear reduction in the whole period. They started as a consequence of land cover changes in the drainage basin, but their speed increased after a large reservoir was built upstream. More recent changes occurred since most of the SHPs were put into operation in the 1990s, especially in their short-circuited reaches and in the four more downstream ones. These changes are interpreted as a consequence of reduced discharge, transitory sediment trapping and reactivation of sediment transport after weirs became filled as well as by the impact of flood hydrology. [ABSTRACT FROM AUTHOR]

We analysed, at a regional scale, the braiding pattern and the structure of the water channel habitats of 53 braided reaches located in the Rhône hydrographical district (France), in relation to three control factors: (i) spatial location along the network (i.e. slope, altitude), (ii) hydrological conditions and (iii) morphological conditions. This research is based on aerial orthophotos belonging to the French National Geographic Institute (IGN) taken between 2002 and 2006. We defined a regional typology of braided reaches based on the distribution of the variables listed above, and identified five hydro-geographical types of braided reaches. Following this regional classification, we compared the pattern of braided reaches by testing several parameters, which describe the physical characters of water channel habitats (such as braided index, channel sinuosity, or aquatic habitat diversity). We found that discharge appears to be less relevant than sediment supply or groundwater level in structuring the braided geometry and the channel habitat pattern in natural braided rivers at a regional scale. We discussed the importance of local factors, such as the position of the groundwater table and the width of the active channel, for explaining the intensity of the braided pattern. There are numerous cases where the discharge is very low but the braided index high. These findings support management and conservation recommendations of braided rivers for implementing the European Water Framework Directive (2000). [ABSTRACT FROM AUTHOR]

We compared habitat diversity and morphodynamics of 'actively' restored reaches (including removal of bank fixation, widening and large wood placement) with 'passively' restored reaches (abandonment of channel maintenance) and adjacent non-restored control reaches in medium-sized Central European mountain rivers. Habitat diversity and river morphology were mapped in two consecutive years and changes in habitat composition (channel features, substrates) and morphological changes (active depth and width) were quantified. In both years, habitat diversity was generally higher in the restored reaches compared to their non-restored counterparts, and significantly differed between restoration approaches, with average values in actively restored reaches being about 60% larger than in passively restored reaches. Channel feature composition differed significantly, both between restored and unrestored reaches, and between restoration approaches, whereas substrate composition was similar in all investigated reaches, indicating that restoration had a higher effect on mesohabitat than on microhabitat conditions. Interannual habitat dynamics in respect to channel feature composition were larger in the actively restored compared to the passively restored reaches, while substrate composition remained fairly constant in all reaches. Regarding morphodynamics, changes in depth and width of actively restored reaches differed significantly from changes in passively restored ones in three of the four elements compared. Our findings imply increased habitat richness, diversity and habitat dynamics in the restored reaches, especially in actively restored ones. Analysis of discharge data suggests that flood events exceeding critical shear stress of the bed material, and the time span since restoration determine the potential for morphological changes. [ABSTRACT FROM AUTHOR]

We present a new hydro-morphological index of diversity (HMID), a tool aimed for use in river engineering projects and firstly developed at gravel-bed streams in Switzerland, but intended for a broader use. We carried out field work with extensive hydraulic and geomorphic data collection, conducted correlation analysis with hydro-morphological variables, formulated the HMID, and analyzed the correlation between HMID and a visual habitat assessment method. The HMID is calculated by means of the coefficient of variation of the hydraulic variables flow velocity and water depth, which have been demonstrated to sufficiently represent the hydro-morphological heterogeneity of alpine gravel-bed stream reaches. Based on numerical modeling, the HMID can be calculated easily for a comparison of different alternatives in river engineering projects and thus achieves predictive power for design decisions. HMID can be applied at a reach-related scale in engineering programs involving geomorphic measures that aim at the enhancement of habitat heterogeneity of a stream. However, the application of HMID has to be integrated with evaluations of the long-term streambed evolvements that are considered at a catchment scale and strongly related to the sediment regime of the stream under study. [ABSTRACT FROM AUTHOR]

Species composition and seasonal succession of phytoplankton were analyzed in a lowland river located in South Banat (Ponjavica, Serbia). As a result of human activity, a network of irrigation channels was built on the Ponjavica River's upper and lower courses. These channels reduce the water level in the river and help to create favorable conditions for accelerated eutrophication processes. Eight phytoplankton divisions with 444 taxa were present. Physical and chemical testing of water, phytoplankton abundance and biomass, as well as chlorophyll a concentration showed a high level of eutrophication. Cyanobacterial biomass developed in 2002 with dominance of Microcystis aeruginosa and Aphanizomenon flos- aquae. Changes in phytoplankton composition were observed during 2008, characterized by the appearance and dominance of Cylindrospermopsis raciborskii when this species accounted for more than 85% of the total phytoplankton biovolume. The change in dominant phytoplankton functional groups was observed: codons H and M characterizing summer in 2002 were replaced by codons S and S in 2008. This study compares the presence of C. raciborskii with other phytoplankton species in relation to water quality parameters. High abundance of this species correlated positively with biochemical oxygen demand and turbidity, and negatively with NO-N concentrations during the study period. [ABSTRACT FROM AUTHOR]

This study compares the relative influences of physiography and anthropogenic pressures on river biota at catchment, riparian corridor, and reach scales. Environmental data, catchment and riparian corridor land use, anthropogenic modifications and biological data were compiled for 301 French sites sampled from 2005 to 2008. First, relationships between anthropogenic pressures and fish and macroinvertebrate assemblages were analysed using redundancy analysis. Second, the influences of physiography and the three scales of human pressures on biological assemblages were measured using variance partitioning. Distributions of fish and macroinvertebrate taxa along the pressure gradients agreed with bio-ecological knowledge. At the reach scale, assemblage variability among the 301 French sites was related to the presence of an impoundment and to poor water quality, while at larger scales it was linked to a gradient from forest to agricultural covers. In addition, a large proportion of the explained variability in assemblage composition was related to complex interactions among factors (~40%) and to physiographic variables (~30%). Furthermore, our results highlight that catchment land use better reflects local water quality impairments than hydromorphological degradations. Finally, this study supports the idea that human pressure effects on river communities are linked at several spatial scales and must be considered jointly. [ABSTRACT FROM AUTHOR]

The implementation of the Water Framework Directive has required intense research in applied aquatic ecology in Europe, and thus created challenges for data management in international research projects. In the project Waterbodies in Europe: Integrative Systems to assess Ecological status and Recovery (WISER), biological and environmental data from rivers, lakes, transitional and coastal waters in 26 European countries were collated. More than one million records of biological observations were stored in the project's central database, representing phytoplankton, macrophytes, macroalgae, angiosperms, phytobenthos, invertebrates and fish. The central database includes new data from the WISER field campaign in lakes and transitional/coastal waters during 2009-2010 (more than 6,000 biological samples from 58 waterbodies in 14 countries). The purpose of this paper is to provide an overview of the data collated within WISER, in order to facilitate future re-use of these data by other scientists. More specifically, the objectives are to (1) describe the data management in WISER, (2) describe the structure and content of the WISER central database and (3) share experiences and give recommendations for data management in large ecological research projects. [ABSTRACT FROM AUTHOR]

River restoration is a central issue of present-day River Basin Management. Unfortunately, many studies have shown limited ecological improvements, hypothesizing catchment influences and missing donor populations as main impeding factors. This study evaluates the ecological status after restoration at 46 river reaches in light of catchment influences upstream. Three groups of environmental parameters were investigated: (i) riparian land use and (ii) physical habitat quality in different lengths upstream of the restorations and (iii) land use in the whole catchment upstream. Ecological quality ratios of standardized fish, invertebrate and macrophyte samples were used as response variables. The results imply that sub-catchment variables influence the ecological status more than local habitat improvements. In particular, fish and invertebrate ecological status was positively linked to percent deciduous forest upstream of restored sites, while macrophytes revealed an opposite trend. Furthermore, we found a strong linkage of site-scale ecological status and physical habitat quality up to 5 km upstream of the restorations; the more natural were riparian land use and river habitat quality upstream, the higher was the chance of a good ecological quality in restored reaches. We conclude that site-scale restoration measures are likely to be unsuccessful, if the sub-catchment physical habitat upstream is degraded. [ABSTRACT FROM AUTHOR]

The EU-funded research project WISER ('Water bodies in Europe: Integrative Systems to assess Ecological status and Recovery') developed new assessment methods required by the EU Water Framework Directive (WFD) for lakes, coastal and transitional waters. WISER also addressed the recovery of biotic assemblages from degradation. The results are summarised in five key messages, supported by papers in this special issue and by WISER results published elsewhere: (1) Response to stress differs between organism groups, water types and stressors; a conceptual model is proposed summarising how the individual organism groups respond to different types of degradation in rivers, lakes, transitional and coastal waters. (2) The sources of uncertainty differ between BQEs and water types, leading to methodological suggestions on how to design WFD sampling programmes. (3) Results from about 300 current assessment methods indicate geographical variations in metrics but assessments are comparable at an aggregated level ('ecological status'). (4) Scale and time matter; restoration requires action at (sub)-basin levels and recovery may require decades. (5) Long-term trends require consideration; the effects of both degradation and restoration at the water body or river basin scales is increasingly superimposed by multiple stressors acting at large scales, in particular by climate change. [ABSTRACT FROM AUTHOR]

The European Water Framework Directive aims to improve ecological status within river basins. This requires knowledge of responses of aquatic assemblages to recovery processes that occur after measures have been taken to reduce major stressors. A systematic literature review comparatively assesses recovery measures across the four major water categories. The main drivers of degradation stem primarily from human population growth and increases in land use and water use changes. These drivers and pressures are the same in all four water categories: rivers, lakes, transitional and coastal waters. Few studies provide evidence of how ecological knowledge might enhance restoration success. Other major bottlenecks are the lack of data, effects mostly occur only in short-term and at local scale, the organism group(s) selected to assess recovery does not always provide the most appropriate response, the time lags of recovery are highly variable, and most restoration projects incorporate restoration of abiotic conditions and do not include abiotic extremes and biological processes. Restoration ecology is just emerging as a field in aquatic ecology and is a site, time and organism group-specific activity. It is therefore difficult to generalise. Despite the many studies only few provide evidence of how ecological knowledge might enhance restoration success. [ABSTRACT FROM AUTHOR]

In ecological sciences, the role of metadata (i.e. key information about a dataset) to make existing datasets visible and discoverable has become increasingly important. Within the EU-funded WISER project (Water bodies in Europe: Integrative Systems to assess Ecological status and Recovery), we designed a metadatabase to allow scientists to find the optimal data for their analyses. An online questionnaire helped to collect metadata from the data providers and an online query tool () facilitated data evaluation. The WISER metadatabase currently holds information on 114 datasets (22 river, 71 lake, 1 general freshwater and 20 coastal/transitional datasets), which also can be accessed by external scientists. We evaluate if generally used metadata standards (e.g. Darwin Core, ISO 19115, CSDGM, EML) are suitable for such specific purposes as WISER and suggest at least the linkage with standard metadata fields. Furthermore, we discuss whether the simple metadata documentation is enough for others to reuse a dataset and why there is still reluctance to publish both metadata and primary research data (i.e. time and financial constraints, misuse of data, abandoning intellectual property rights). We emphasise that metadata publication has major advantages as it makes datasets detectable by other scientists and generally makes a scientist's work more visible. [ABSTRACT FROM AUTHOR]

The European Water Framework Directive (WFD) has led to an increase in hydromorphological restoration attempts in European rivers, but data on the ecological responses of rivers to these restoration attempts are scarce. We investigated the effects of 24 hydromorphological river restoration projects in Germany. We compared hydromorphological parameters and biological diversity of macroinvertebrates, fish, and macrophytes in restored reaches to nearby unrestored sections. We applied, for the first time, the WFD to assess the results of these restoration projects. While hydromorphology changed significantly in the restored sections, differences between restored and unrestored sections in terms of biological parameters were lower. Positive restoration effects were observed for fish (11 of 24 cases) only. Based on the synthesis of results from the different organism groups, only one of the 24 restored sections reached a 'good' Ecological Quality Class as demanded by the WFD. Our results indicate that stressors other than hydromorphological degradation still affect the biota in restored sections. We emphasize the need for advanced restoration strategies based on catchment analyses considering water pollution, source populations, and dispersal capacities of sensitive species, and recommend the inclusion of additional parameters, including societal and stakeholder perspectives, in assessing the initial success of restoration projects. [ABSTRACT FROM AUTHOR]

Clearfell, burn and sow (CBS) forestry can potentially alter stream environments by increasing available light and the input of woody debris. However, little is known about how CBS forestry affects in-stream processes such as nutrient uptake. We evaluate whether short-term (2-7 years) environmental changes (e.g. light availability and woody debris) associated with CBS forestry lead to differences in nutrient uptake metrics. To do this, we measured in-stream uptake of soluble reactive phosphorus (SRP) and ammonium (NH) in three old growth (OG) and four CBS-affected headwater stream reaches. The abundance of fine woody debris and light availability were significantly greater in CBS-affected than in OG reaches. Uptake velocities varied from 0.0880 to 0.951 mm min for NH and from 0.0383 to 1.06 mm min for SRP across all sites. The mean uptake of SRP, but not NH, was significantly greater (i.e. higher uptake velocities and lower uptake lengths) in CBS-affected than in OG reaches. These results suggest that CBS forestry altered the stream environment enabling greater SRP uptake relative to OG reaches. Our findings highlight the tight linkage between headwater streams and their surrounding terrestrial environment, which has direct implications for catchment-scale biogeochemical processes. [ABSTRACT FROM AUTHOR]

In addition to the effects of environmental conditions, biotic assemblages may exhibit spatial structure depending on the scale of study. We tested whether the dissimilarity of stream insect assemblages is related to two types of spatial distances (stream corridor and overland distance), and evaluated the relative importance of diversity components at multiple spatial scales. Field data included assemblages of Ephemeroptera, Plecoptera, and Trichoptera found in 16 streams in four microbasins. We evaluated the relationship of the dissimilarity of assemblages with the distance types, using Mantel tests. In addition, we evaluated the relationships among the diversity components at multiple spatial scales, using additive partitioning analysis. The biological dissimilarities were correlated only with the geographical distances. Additive partitioning showed that the values of richness observed in the β1 (among Surber), β2 (among riffles), β3 (among streams), and β4 (among microbasins) were higher than those expected. The highest variation of the richness was found in β3 (30.6%). We conclude that stream faunas are distributed in patches all over the studied spatial extent, causing a weak relationship of biological dissimilarity with distance but important beta components when compared to a completely homogenous distribution of the fauna. [ABSTRACT FROM AUTHOR]

We developed a methodology to predict brook trout ( Salvelinus fontinalis) distribution using summer temperature metrics as predictor variables. Our analysis used long-term fish and hourly water temperature data from the Dog River, Vermont (USA). Commonly used metrics (e.g., mean, maximum, maximum 7-day maximum) tend to smooth the data so information on temperature variation is lost. Therefore, we developed a new set of metrics (called event metrics) to capture temperature variation by describing the frequency, area, duration, and magnitude of events that exceeded a user-defined temperature threshold. We used 16, 18, 20, and 22°C. We built linear discriminant models and tested and compared the event metrics against the commonly used metrics. Correct classification of the observations was 66% with event metrics and 87% with commonly used metrics. However, combined event and commonly used metrics correctly classified 92%. Of the four individual temperature thresholds, it was difficult to assess which threshold had the 'best' accuracy. The 16°C threshold had slightly fewer misclassifications; however, the 20°C threshold had the fewest extreme misclassifications. Our method leveraged the volumes of existing long-term data and provided a simple, systematic, and adaptable framework for monitoring changes in fish distribution, specifically in the case of irregular, extreme temperature events. [ABSTRACT FROM AUTHOR]

Highly seasonal rivers can experience extended low flow, and often dry, periods. Macroinvertebrate and flow data were used to explore hypotheses on the effects of antecedent hydrology and the low-flow, dry-season period on macroinvertebrate assemblages in northern Australia. Composition differed between early and late dry seasons. Taxa were more sensitive to water quality and more rheophilous in the early dry season when their habitats were lotic than when habitats later became lentic. As flow magnitudes in the antecedent dry season and on the sampling day increased, the habitats became more oxygenated and, in turn, macroinvertebrate richness increased. Higher wet-season flow magnitudes, flow variability and rates of fall were correlated with lower richness in the following dry season. Alteration of the flow-disturbance regime that increases the likelihood of flow cessation in macroinvertebrate habitats, or extends the duration of the dry season beyond that previously experienced in these highly seasonal systems, may alter the resistance and resilience of assemblages such that the seasonal decline and recovery of biodiversity may no longer be so reliable. Given the projected increase in low-flow incidence in many regions of the world, future research needs to examine the effects of reduced flow, flow cessation and stream drying as multiple, interacting stressors on stream biota. [ABSTRACT FROM AUTHOR]

Land use changes have resulted in large environmental impacts, and in agricultural landscapes sometimes only forest fragments remain. Riparian forest remnants can positively influence stream water quality, and serve as refuges for aquatic species. We evaluated whether the presence of a riparian forest remnant influenced the structure and composition of macroinvertebrate communities in a rural stream in southeastern Brazil. We sampled three reaches upstream (within abandoned sugarcane cultivation) and nine downstream the remnant edge, until 600 m inside the forested area, using leaf litter bags. The abundances of Elmidae, Chironomidae, and total macroinvertebrates increased along the forest remnant, whereas the abundance of Baetidae, proportion of Ephemeroptera, Plecoptera, and Trichoptera (EPT), rarefied taxonomic richness, and diversity decreased. Taxon richness and EPT abundance did not vary along the forest remnant. Increases in Chironomidae and total abundance within the forest remnant can be related to moderate increases in nutrient concentrations, or to the availability of high quality leaf litter patches. Forest remnants can influence macroinvertebrate communities, although variation both in temperate and tropical studies can be related to local agricultural practices and land use at the watershed scale. Forest remnants are important in maintaining stream water quality in rural landscapes, and deserve attention in watershed management projects. [ABSTRACT FROM AUTHOR]

We studied the effects of flow reduction on epibenthic algal assemblages by comparing up- and down-stream reaches of ten Hong Kong streams subject to different degrees of water abstraction during 2007-2008. Downstream discharge declined by 71 and 54% during the wet and dry seasons, respectively. Algal responses varied seasonally and according to morphological guild and reflecting reductions in discharge and current velocity, or changes in total nitrogen and phosphate, or their combined effects. Significant inter-reach assemblage differences were observed during the both seasons, but wet-season assemblage structure was not directly influenced by any flow-related variable. During the dry season, scouring-tolerant prostrate/adnate diatoms (especially Achnanthes, Cocconeis) were relatively abundant upstream, whereas intolerant stalked ( Eunotia, Gomphonema) and mobile diatoms were more numerous downstream. Both low- and high-profile (erect diatoms, Chamaesiphon, Calothrix) guilds were sensitive to changes in nutrients. Low-flow conditions downstream, surprisingly, enhanced algal diversity, and richness. Based on the linear response of Cocconeis (mainly C. placentula) to discharge reduction, we recommend that >65% of dry-season discharge should be maintained in downstream reaches in order to sustain near-natural algal assemblages; 32% of discharge is required to avoid substantial alterations in assemblage structure. [ABSTRACT FROM AUTHOR]

The light field and its relationship with biogeochemical variables were investigated in the Solimões, Negro, Amazon, Madeira, Uatumã, Trombetas, and Tapajós Rivers. In high suspended sediment rivers, total suspended matter is the primary control on light attenuation ( r = 0.8), with colored dissolved organic matter (CDOM) being secondary ( r = −0.6) due to scattering and absorption, respectively. Photosynthetically active radiation was the lowest (<100.0 μmol m s at the depth of half Z) and was limited to depths of less than 1.0 m and confined to red light. In low suspended sediment rivers, CDOM is the primary control on light attenuation ( r = 0.9). The concentrations of chlorophyll a (Chla) and CDOM cause variations among these rivers. High CDOM rivers, Negro and Uatumã, are depleted (<0.5% of incoming irradiance) of blue and green light at the depth of half Z. The light spectra of low CDOM and higher Chla waters, such as the Tapajós, Uatumã, and Trombetas Rivers at rising water stage, are restricted to green and red wavelengths, and marked by high absorption at 620 and 670 nm, due to the presence of Cyanophyceae. [ABSTRACT FROM AUTHOR]

Although disturbance and productivity are clearly strong influences on lotic diversity, rarely have their interactive effects been studied in running water systems. We hypothesised that the presence or absence of canopy cover in streams would alter productivity-disturbance-diversity relationships due to differential effects on the food base, and tested this hypothesis in 47 mountain streams in the central North Island of New Zealand. Canopy cover had no influence on algal biomass in these streams, but a link between disturbance and productivity was found in open canopy streams where taxonomic richness of invertebrates increased log-linearly with increasing algal biomass and peaked at intermediate levels of disturbance. Community evenness declined with disturbance, but only at closed canopy sites where both invertebrate taxonomic richness and Simpson's diversity index were higher. Although there was a peak in richness at intermediate rates of disturbance, our results do not directly match predictions of the dynamic equilibrium model which predicts that the level of disturbance maximising diversity interacts with habitat productivity. Rather, we suggest the combined effects of productivity and disturbance are additive rather than multiplicative such that productivity simply sets the upper limit to richness in streams. [ABSTRACT FROM AUTHOR]

For more than 100 years, the Werra River has been severely affected by intensive salinisation caused by potash fertilizer industries. We show considerable differences in macroinvertebrate assemblages between reaches without salinisation impact and downstream reaches with intense anthropogenic salinisation in the Werra. This is true for almost all biological metrics relevant for ecological status classification under the EU-Water Framework Directive (EU-WFD) (European Community, Directive /60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy, No. L 327/1, of 22 December 2000) and diversity measures (taxon richness, evenness). Macroinvertebrate assemblages at salinisation sites were completely dominated by three halophile neobiotic macroinvertebrate species ( Gammarus tigrinus, Corophium lacustre and Potamopyrgus antipodarum). We compared anthropogenically salinised sites from the Werra with disturbed but non-salinised sites from the Werra and other German rivers. We used biological metrics developed for classifying the ecological status according to the EU-WFD. This comparison indicated a severe degradation at salinisation sites on the Werra and these fell into the worst ecological status class 'bad' according to the EU-WFD. Multivariate statistical analyses revealed anthropogenic salinisation as a key factor causing the differences in composition of macroinvertebrate assemblages in the Werra between salinisation and reference sites. Analyses of the long-term presence-absence data of macroinvertebrate assemblages indicated no marked improvement in the ecological status in the past 20 years. [ABSTRACT FROM AUTHOR]

Relationships between environmental variables, ecosystem metabolism, and benthos are not well understood in sub-arctic ecosystems. The goal of this study was to investigate environmental drivers of river ecosystem metabolism and macroinvertebrate density in a sub-arctic river. We estimated primary production and respiration rates, sampled benthic macroinvertebrates, and monitored light intensity, discharge rate, and nutrient concentrations in the Chena River, interior Alaska, over two summers. We employed Random Forests models to identify predictor variables for metabolism rates and benthic macroinvertebrate density and biomass, and calculated Spearman correlations between in-stream nutrient levels and metabolism rates. Models indicated that discharge and length of time between high water events were the most important factors measured for predicting metabolism rates. Discharge was the most important variable for predicting benthic macroinvertebrate density and biomass. Primary production rate peaked at intermediate discharge, respiration rate was lowest at the greatest time since last high water event, and benthic macroinvertebrate density was lowest at high discharge rates. The ratio of dissolved inorganic nitrogen to soluble reactive phosphorus ranged from 27:1 to 172:1. We found that discharge plays a key role in regulating stream ecosystem metabolism, but that low phosphorous levels also likely limit primary production in this sub-arctic stream. [ABSTRACT FROM AUTHOR]

Rivers in urban locations frequently receive contaminated wastewater and particulate waste either directly from storm overflows or from sewage treatment facilities. Although many urban streams are now recovering from wide-scale historic pollution, lower-level effects on water chemistry, nutrients and biotic composition are still widespread. We aimed to determine whether such effects could be detected using stable isotope ratios (δN, δC and δS) in macroinvertebrates alone or in conjunction with traditional biomonitoring. Macroinvertebrates were collected upstream and downstream of 11 different secondary wastewater treatment works (WwTW) in South Wales and the Welsh borders (United Kingdom). Overall, mean invertebrate δN signatures downstream of the WwTW were significantly enriched despite variation amongst sites. Moreover, changes between upstream and downstream macroinvertebrate δN values were highly correlated with patterns in macroinvertebrate community composition, increased total macroinvertebrate abundance, and reduced Shannon Diversity and other biomonitoring indices (% EPT, % shredders and ASPT scores). Changes in invertebrate δN values also paralleled the consented discharge volumes and population equivalents from each WwTW. In contrast, isotopic ratios of δC and δS were unable to distinguish or quantify wastewater input into the rivers but differences were apparent amongst study streams. Overall, these results suggest that macroinvertebrate δN signatures can detect and quantify the effects of secondary sewage treatment inputs to riverine ecosystems. Moreover, the method potentially provides a sensitive means for tracing sewage-derived nutrients into food webs while inferring effects on aquatic communities where sewage-loads are subtle or confounded by other stressors. [ABSTRACT FROM AUTHOR]

Influence of hydrological characteristics and nutrient concentrations on phytoplankton was investigated in four large rivers (Mura, Drava, Danube and Sava) in the Pannonian ecoregion in Croatia to understand how phytoplankton of rivers can be explained by the 'different functional group approach'. To gain a clearer understanding of the factors that affect river phytoplankton, the present study examined phytoplankton biomass and composition in relationship with physical and chemical parameters assessed in detail by preparing self-organising maps using functional groups and morpho-functional groups. Total nitrogen along with water residence time showed to be the best predictor to determine phytoplankton biomass and chlorophyll a. Phytoplankton diversity increased with higher water discharge, but it had the consequence of diluting algae and decreasing biomass. Bacillariophyceae and Chlorophyceae species dominated the phytoplankton assemblages in all rivers. Diatoms predominated in rivers with shorter residence time. Dominant diatom codons of functional groups were C, D and TB while morpho-functional groups were represented by only diatom group VI. As residence time increased, the proportion of chlorococcalean green algae, represented by functional group codon T and morpho-functional group IV grew in summer. Since potamoplankton is dominated by diatoms, functional groups with its fine partition of diatom codons proved to be excellent descriptor of the potamoplankton. Application of morpho-functional groups originally developed from the lake data, showed to be limiting because of the predominating presence of only one diatom group. [ABSTRACT FROM AUTHOR]

The seasonal dynamics of river phytoplankton was analyzed using succession rate indices based on data collected from year-round observations of two small plain rivers in the Upper Ob Basin (Western Siberia). The study revealed a generally clear seasonal pattern of structural changes in the phytoplankton of the lower reaches of the studied rivers. The dynamics of succession rate indices reflects the key events in the life of phytoplankton in the Bolshaya Losikha and Barnaulka Rivers, showing mainly changes in the dominant species during the main phases of the hydrological cycle. The most significant changes in phytoplankton structure tend to occur in the period between the spring flood decline and the beginning of summer-autumn low water. These changes coincide with the most drastic changes in both environmental conditions and phytoplankton successional stages. Use of succession rate indices to analyze the seasonal dynamics of phytoplankton allowed us to distinguish between periods of abrupt change and periods of comparatively low-intensity changes in plankton composition in small lowland temperate rivers. [ABSTRACT FROM AUTHOR]

One of the most striking features of the diatom Didymosphenia geminata, which has increased markedly in abundance in a number of countries in recent years, is the very large branched stalks. In order to help understanding their role, an ultrastructural study was carried out on two populations, one from a stream in northern England and the other from a river on Vancouver Island, Canada. In both cases, the main part of the stalk had a central reticulate core surrounded by an outer region with dense fibres. A longitudinal structure in the uppermost part of the stalk just under the collar surrounding the base of the cell may perhaps correspond to a tube. The structure of the septa formed where branches divide is also described. Phosphomonoesterase activity known to be present in the stalks was shown to occur in the inner peripheral layers of the stalks and especially in the collar area. The results show that stalks have a complex structure suggesting their importance for their phosphatase activity to overcome low inorganic phosphate concentrations. Their large surface may function in herbivory avoidance, a better exposure of cells to turbulent conditions to increase nutrient uptake, adsorption of limiting elements and gas exchange. [ABSTRACT FROM AUTHOR]

In 2009, seventeen analysts participated in a pan-European diatom ring-test (intercalibration), analyzing nine samples from seven countries following the European standard EN 14407. The objective of this exercise was to agree on practical conventions on diatom identification to facilitate future intercalibration work and to assess the extent to which national differences in sample analysis (counting protocol and identification conventions) contribute to variability in EU-level comparisons of diatom-based methods. Differences in the reported taxa lists were large, but not a major source of variation in values of a common metric (the phytobenthos Intercalibration Common Metric, ICM). Therefore, every country can apply its own identification conventions for national assessments, and still be fairly confident that the ICM reflects the national classification of its streams. Part of the index variation was due to differences in counting protocols and care should be taken when handling broken valves, girdle views and small taxa. More work at both national and European level is needed to provide a harmonized way of using diatoms for ecological status assessments in the future. [ABSTRACT FROM AUTHOR]

Diatoms are major contributors to global carbon fixation and constitute a significant portion of biofilms found in lotic ecosystems. Despite their widespread abundance and the fact that extensive studies have been performed on morphological features of frustules, molecular tools for the identification of diatoms are not commonly available. This study focuses on the development of oligonucleotide probes for the detection of diatom species relevant to water quality assessment. The selected panel of diatoms covers all the species found in water of varying quality from the rivers of central-East Apennine (Italy). Small subunit rRNA-targeted probes were applied to a microarray platform as well as to a new technique termed Primer-Probe, with the aim of obtaining a molecular tool suitable for accurate identification of both single and mixed species diatom populations. The Primer-Probe technique together with dot-blot assays proved to be ideal for the preliminary screening of a large set of DNA oligonucleotides designed by ARB software. It was shown that microarrays, as a promising technology for rapid and simultaneous detection of a wide range of species-specific genetic markers, can be adapted to monitor changes within a diatom community. It is suggested that microarrays will provide a molecular basis for microbial identification to support standard microscopy techniques used by ecologists and environmental scientists for monitoring water quality. [ABSTRACT FROM AUTHOR]

Intercalibration of ecological status class boundaries between member states is a requirement of the European Union's Water Framework Directive. Although a preliminary intercalibration of boundaries established for phytobenthos has been performed, a number of questions remain, including the extent to which variations in taxonomic concepts used in different member states influences the position of these boundaries. In this paper, the robustness of the diatom-based metrics used for intercalibration is assessed. Whilst use of genus-level identification led to a loss of ecological information, merging representatives of closely-related taxa has little effect on these metrics. Similarly, taxa that occur only rarely or never have high relative abundances in a dataset can also be ignored without the loss of ecological information. Similar results were obtained when modern taxonomic concepts were compared with concepts in use 80 years ago. Fine scale taxonomy may play a valuable role within member states; however, our results suggest that, at a continental scale, a simplified approach to diatom taxonomy should not affect intercalibration results. [ABSTRACT FROM AUTHOR]

The literature on monitoring rivers using benthic algal communities is reviewed, especially that for Europe during the past 20 years. In particular, papers in a series of symposia at approximately 3-year intervals are considered to assess the extent to which aims and methods have shifted. A variety of methods were being tested in the early 1990s, and some put to practical use. However, the requirements of the EU Urban Waste Water Directive in 1991 have gradually narrowed procedures in most countries outside Scandinavia to the use of indices based on benthic diatoms to monitoring nutrients, especially phosphate. Most countries in Europe now adopt one of a few indices. The same indices are being used to deal with the requirements of the EU Water Framework Directive introduced in 2000 to achieve good ecological status by 2015. It is argued, however, that features of upland river sites require the development of revised indices for this purpose. Features of many sites include highly variable nutrient concentrations and ratios, and the greater importance of organic phosphate. Two possible approaches are suggested to developing a revised index. One is a diatom index which incorporates information about the environmental features important here. The other is to use an index which incorporates data on genera from all algal phyla, with emphasis on those which are long-lived. [ABSTRACT FROM AUTHOR]

Nutrients and light are the most determinant factors for microbial benthic assemblages in oligotrophic forested streams. We investigated the importance of nutrients and light availability on the structure and the function of epilithic biofilms in a Mediterranean forested stream (Fuirosos, Spain). Biofilms grew on artificial substrata in both enriched and unenriched reaches where shade conditions were simulated. Four different treatments were generated: higher light unenriched, lower light unenriched, higher light enriched (HL-E) and lower light enriched. Chlorophyll a, bacterial density, extracellular polymeric substances (EPS), extracellular leucine aminopeptidase (LAmP) and alkaline phosphatase (APase) activities were analysed during the colonisation at days 4, 9, 16, 22 and 52. At day 52, confocal laser scanning microscopy (CLSM) was used to determine differences in biofilm architecture. CLSM evidenced differences in thickness and structural complexity of biofilms grown in different conditions. Biofilms in HL-E were the thickest and had the most complex structure. The CLSM highlighted that the EPS was agglomerated in the upper layer of enriched-grown biofilms, but evenly distributed through the biofilm in unenriched biofilms. CLSM 3D images suggested that cyanobacteria increased under higher nutrient conditions. Nutrient enrichment caused the decrease of APase activity. Interaction between the two factors affected LAmP activity. HL-E had the highest LAmP and the lowest APase activities, an indication that biofilm responses to nutrients mostly occurred with high-light availability. Our results revealed that the conjoint availability of light and nutrients caused the highest changes in biofilm spatial organisation, microbial structure and functioning in oligotrophic forested streams. [ABSTRACT FROM AUTHOR]

Understanding the interactions between physical habitat and aquatic biodiversity has become a key research objective in river management. River research and management practitioners are increasingly seeking new methodologies and techniques for characterizing physical habitat heterogeneity. The physical biotope has been widely employed as the standard mesoscale unit in river surveys. However, few surveys have quantified the combined physical heterogeneity at the meso- and microscale scale via a single technique. This paper describes a new field methodology for assessing variations in hydraulic habitat and retention across different channel types (e.g. step-pool, bedrock, plane-bed and pool-riffle). Hydraulic habitat and retention was measured by timing 100 flow tracers across a 100-m stream length, and recording the types of trapping structures. The pattern of flow tracers and retention varied significantly between channel types and structures. Rocks (boulders and cobbles) were more important retentive structures than eddies and snags (woody material and vegetation). The results indicate the importance of a diverse hydraulic environment, woody material and channel substrate character in increasing physical heterogeneity within a stream reach. The findings suggest that the field methodology may be an effective tool to assess differences in physical heterogeneity pre and post river restoration activities. [ABSTRACT FROM AUTHOR]

Human-induced reductions in species richness might alter the quality of ecosystem services when the remaining species are not able to substitute the functions provided by extirpated species. We examined how human disturbances (nutrient enrichment, land use intensification, instream habitat degradation and the presence of alien species) influence the species richness of stream invertebrates. Stream invertebrates (425 native species) were collected by kick and sweep sampling technique at 274 stream sites covering the entire area of Hungary. We measured the species richness, functional richness (i.e. number of unique functional roles provided by community members) and functional redundancy (i.e. the functional insurance of the community) using information on the feeding habits of each species. To remove the effect of natural variability, we tested the effect of stressors on the residuals of models relating species richness, functional richness and functional redundancy with natural environmental gradients. Our results showed that species richness was negatively influenced by instream habitat degradation and nutrient enrichment. Independent of the way of quantifying functional richness and functional redundancy, we found that functional richness is more sensitive to human impact than functional redundancy of stream invertebrates. The finding that a reduction of species richness is associated with a loss of unique functional roles (functional richness) is important for conservation issues, because the number of unique functional roles is usually regarded as driver of ecosystem functioning. [ABSTRACT FROM AUTHOR]

Environmental flow rules are developed to provide a flow regime necessary to maintain healthy river and floodplain ecosystems in rivers regulated for human uses. However, few studies have experimentally assessed potential ecological mechanisms causing declines in the health and productivity of freshwater fish assemblages in regulated rivers to inform the development of appropriate environmental flows. We tested whether an experimental flow release in a regulated tributary of the Hunter River, Australia, altered the diet of two widely distributed fish species (Australian smelt Retropinna semoni and Cox's gudgeon Gobiomorphus coxii) compared with data from unregulated reference and regulated control tributaries. Neither species had significant differences in the number of prey taxa ingested, gut fullness or composition of gut contents due to the environmental flow release (EFR). The diet of R. semoni did not differ significantly between regulated and unregulated tributaries in either catchment. However, the diet of G. coxii differed in only one of the two pairs of rivers consistently across all sample times. Assuming the EFR was sufficient to alter the composition of prey available for consumption by the fish species studied, our findings imply that functional indicators, such as the diet of generalist higher-order consumers, may be more suitable indicators of long-term flow regime change rather than short-term flow events. [ABSTRACT FROM AUTHOR]

Fish are important in the structuring of other communities and may have large effects on the functioning of aquatic ecosystems. The structure of fish communities, in turn, seems to differ with climate. We compared the characteristics of fish assemblages in lowland streams located in two contrasting climates (cold-temperate Europe and subtropical South America) by use of published and unpublished data on streams of similar depth, width, and slope ( n total = 91 streams). We also selected a subset of seven comparable little-affected streams in the two contrasting climates: temperate (Denmark, 55°-57°N, Dk) and subtropical (Uruguay, 30°-35°S, Uy) and compared the fish community structures in relation to environmental characteristics. We then analysed a series of potential explanatory factors behind the patterns observed, in particular the effect of ambient temperature, by comparing temperature-corrected community metabolism. Significantly higher species richness, higher densities, lower biomass, smaller mean body size, and lower mean weight of fish were observed for the subtropical streams than for the temperate streams, both in the literature review and in the subset of streams. Several characteristics of fish assemblages in streams may be explained by direct and indirect effects of temperature. Accordingly, fish in subtropical systems had a temperature-corrected community metabolism I m equal to that of fish in temperate systems, indicating that temperature, besides historical factors, is an important driver of different size structures. Our findings concur with differences previously found in littoral areas of shallow lakes, suggesting that these patterns are not restricted to running waters. Our results elucidate how fish community structure might be affected by increases in temperature triggered by climate warming. [ABSTRACT FROM AUTHOR]