Riverine Invertebrates Research Articles

Identifying freshwater invertebrate taxa susceptible to AChE-acting pesticides

Globally pesticide use has been associated with negative impacts on riverine invertebrate communities, but chronic exposure effects to most specific groups of pesticides are not well understood. In this paper, we sought to identify invertebrate species most vulnerable to effects of AChE-acting pesticides in UK rivers for potential application in environmental monitoring. We did this using a combination of the conservation of molecular target for AChE-acting pesticides (identified using the SeqAPass tool), laboratory-based toxicity data, and both biological traits and life history information. We then applied this information to assess for evidence of impacts on these riverine invertebrate communities in the Anglian region of England where there is high pesticide use. Sensitive genera to AChE-acting pesticides included Aedes, Anopheles, Cloeon, Ischnura, and the tolerant genera were Culex, Daphnia, Lymnaea. Using the UK Environment Agency's biota monitoring data spanning over period of 28 years (1984–2011) we evidence absence of the taxa most sensitive to AChE-acting pesticides (Ischnura, Aedes and Anopheles) but presence of AChE pesticide tolerant taxa (Lymnaea) at riverine sites in the Anglian region with high AChE pesticide use.

Ecological but Not Biological Traits of European Riverine Invertebrates Respond Consistently to Anthropogenic Impacts

ABSTRACTAimTo determine which riverine invertebrate traits respond consistently to anthropogenic impacts across multiple biogeographic regions.LocationEurope.Time Period1981–2021.Major Taxa StudiedRiverine invertebrates.MethodsWe compiled a database of riverine invertebrate community time series for 673 sites across six European countries spanning six freshwater ecoregions. We compared trait responses to anthropogenic impacts (quantified as changes in ‘ecological quality’) among regions for seven ‘ecological’ traits, which reflect habitat preferences, and nine ‘biological’ traits (e.g., morphology or life history), which represent taxon‐specific attributes that can influence ecosystem processes.ResultsFour ecological traits (current, microhabitat, salinity and trophic preferences) and one biological trait (dispersal mode) responded consistently across regions. These responses were primarily driven by spatial differences among poorer to better quality sites. Responses to temporal changes in quality were comparable but less pronounced.Main ConclusionsConsistent responses to anthropogenic impacts across multiple ecological traits indicate these traits may improve broader scale measurements, comparisons and predictions of community responses. However, we could not use ecological traits to identify the actions of specific stressors because multiple traits always responded as a group. Inconsistent responses across almost all biological traits indicated that these traits may be less predictive of impacts across regions. Predictions of how biological traits, and associated ecosystem processes, respond to anthropogenic impacts may be most effective at regional scales where responses are more consistent.

Predicting nature recovery for river restoration planning and ecological assessment: A case study from England, 1991–2042

AbstractThe Global Biodiversity Framework established ambitious goals for nature recovery which governments must now incorporate into national legislation. In England, legally binding targets require authorities to halt the decline in species abundance by 2030 and reverse the decline by 2042. Riverine invertebrates represent a substantial proportion of the species contributing towards the targets. Thus, understanding the response of these species to potential river restoration actions is key to target delivery. We model counts for 188 riverine invertebrate taxa using zero‐inflated generalized Poisson models, applying the models to both inform river restoration planning and set expected values for use in ecological assessment. We identify catchment‐specific restoration strategies that combine one or more actions involving the removal of channel modifications, reductions in nitrate concentrations and reductions in total dissolved phosphorus concentrations as the most likely to deliver species abundance targets across three joint climate–socioeconomic scenarios. By hindcasting species abundances under alternative target frameworks, we also demonstrate a new approach to setting expected values in ecological assessment, accounting for changes in water temperature and hydrology that confound historical reference models presently used by regulators. Our findings represent the first systematic attempt to prioritise major actions to deliver species abundance targets in England, providing valuable insights for policymakers, river restoration practitioners and authorities responsible for monitoring river ecosystems.

Multi-decadal improvements in the ecological quality of European rivers are not consistently reflected in biodiversity metrics.

Humans impact terrestrial, marine and freshwater ecosystems, yet many broad-scale studies have found no systematic, negative biodiversity changes (for example, decreasing abundance or taxon richness). Here we show that mixed biodiversity responses may arise because community metrics show variable responses to anthropogenic impacts across broad spatial scales. We first quantified temporal trends in anthropogenic impacts for 1,365 riverine invertebrate communities from 23 European countries, based on similarity to least-impacted reference communities. Reference comparisons provide necessary, but often missing, baselines for evaluating whether communities are negatively impacted or have improved (less or more similar, respectively). We then determined whether changing impacts were consistently reflected in metrics of community abundance, taxon richness, evenness and composition. Invertebrate communities improved, that is, became more similar to reference conditions, from 1992 until the 2010s, after which improvements plateaued. Improvements were generally reflected by higher taxon richness, providing evidence that certain community metrics can broadly indicate anthropogenic impacts. However, richness responses were highly variable among sites, and we found no consistent responses in community abundance, evenness or composition. These findings suggest that, without sufficient data and careful metric selection, many common community metrics cannot reliably reflect anthropogenic impacts, helping explain the prevalence of mixed biodiversity trends.

Monthly sampling reveals seasonal fine sediment fluctuations and riverine invertebrate community responses

Managing the impacts of anthropogenically enhanced deposited fine sediment levels in lotic ecosystems requires understanding of how catchment land-use changes have altered the natural sediment regime (erosion, transport, deposition) of rivers. Unfortunately, no existing studies have employed an appropriate sampling frequency over a period encompassing the full range of seasonal flow conditions expected to influence in-stream sediment dynamics. We determined the short-term (monthly) dynamics of deposited fine sediment and invertebrate communities over 12-months in 15 fourth- and fifth-order rivers draining catchments of low, medium and high land-use intensity in Southland, New Zealand to determine when and where fine sediment threatens stream health. We compared the Quorer resuspension method (suspendable inorganic sediment, SIS) and the in-stream visual sediment cover assessment method, and evaluated the effectiveness of four commonly-used invertebrate stream health metrics against their newly developed sediment-specific counterparts. Monthly variability in SIS was substantial across all land-use categories, but became more pronounced as land-use intensity increased. All 15 sites experienced a prolonged period of relatively stable flow which coincided with the largest short-term increase in SIS at 14 of the 15 sites. However, variability in SIS was not mirrored in macroinvertebrate metrics. These findings suggest that controlling inputs of fine sediment to rivers and streams will be most effective when targeted at periods of prolonged stable flow, particularly within high land-use intensity catchments. The resuspension method consistently outperformed visual estimates when considering its relationship with macroinvertebrate metrics, while sediment-specific metrics demonstrated a stronger association with fine sediment than commonly employed metrics e.g. (%EPT). We conclude that restoration/mitigation practices cannot be based solely on short-term, or even long-term, reductions in fine sediment, or on physical measures alone, but should be based on long-term recoveries of sediment-impacted invertebrate communities using concurrent measurements of both biotic and abiotic conditions.

Pesticide pollution associations with riverine invertebrate communities in England

Globally freshwater biodiversity has experienced major decline and chemical pollutants are believed to have played a significant role in this decline, but this has not been well quantified for most riverine invertebrate populations. Here we applied a biogeographically independent trait-based bioindicator, SPEARpesticides across sites across five regions (Northern, Midlands and Western, Anglian, Southeast, and Southwest) in England to investigate for associations specifically between pesticide use/pollution and riverine invertebrate communities over a 55-year period (1965–2019). Both spatially and temporally post-1990, the Anglian and Thames regions consistently showed the lowest SPEARpesticides scores, illustrating the presence of fewer pesticide sensitive species. The Anglian region had the highest pesticide use compared to all other regions from 1990 to 2018 and there were negative relationships between the level of pesticide/insecticide use and the regional SPEARpesticides score. Biochemical Oxygen Demand and ammonia, as measures of general water quality, were also negatively correlated with the SPEARpesticides scores across the regions, but these factors were not the driver for the lower SPEARpesticides scores seen in the Anglian region. Based on SPEARpesticides scores, riverine invertebrate communities in England have been most impacted in the Anglian region and we evidence chronic insecticide exposure is likely a significant factor in shaping the status of those invertebrate communities.

Sulfur stable isotopes as a tracer of insect migration and consumption by fish predators

Resource flows between freshwater ecosystems can greatly affect foodweb dynamics. The seasonal movement of a family of aquatic insects, water boatmen, or corixids (Hemiptera: Corixidae) represents an important transfer of resources between wetland and river ecosystems. Corixids migrate en masse from wetlands in the North American prairies to rivers every autumn to overwinter. In the North and South Saskatchewan rivers, Saskatchewan, Canada, several fish species prey upon these migratory corixids. Here, we examined the utility of the stable isotope ratio of sulfur, δ34S, in tracing the migration of corixids between wetlands and the North and South Saskatchewan rivers. We also assessed the extent to which riverine fish use migratory corixids as a dietary subsidy. We found that both corixids and other wetland invertebrates exhibited a mean δ34S value of −10.5 ± 5.8‰, lower than riverine invertebrates at −4.1 ± 4.1‰. Specifically, riverine invertebrates from the South Saskatchewan River were more depleted in 34S than those from the North Saskatchewan River, with means of −5.1 ± 4.1‰ and −1.4 ± 2.8‰, respectively. In summer, corixid-feeing and noncorixid-feeding fish exhibited similar δ34S values in liver tissue, whereas in spring and autumn, corixid feeders exhibited more negative δ34S values. Isotope mixing models indicated that corixid-feeding species may have derived 34 to 65% of liver tissue from wetland sources in spring, 15 to 34% in summer, and 41 to 78% in autumn, whereas contributions to noncorixid-feeding species ranged from 4 to 17% across all seasons. We conclude that δ34S has the potential to trace insect movement and consumer use between isotopically distinct freshwater systems.

Environmental filtering and habitat (mis)matching of riverine invertebrate metacommunities

AbstractAimMetacommunities are assembled through a combination of local and regional processes, with the relative importance of the drivers of assembly depending on ecological context. Global change can alter community assembly at both local and regional levels, potentially shifting communities into disequilibrium with their local environmental conditions. We evaluated the spatial variation in environmental filtering and habitat matching of 1078 riverine macroinvertebrate communities distributed across nine ecoregions.LocationConterminous United States.TaxonFreshwater macroinvertebrates.MethodsPatterns in environmental filtering, habitat matching and functional trait diversity were compared among ecoregions. Boosted regression trees were used to identify (1) functional trait predictors of environmental filtering and habitat matching and (2) environmental, landscape and network variables that predict functional trait abundances.ResultsEnvironmental filtering but not habitat matching varied strongly by ecoregion. Functional trait diversity varied by ecoregion, but not as strongly as the signatures of environmental filtering. Functional trait predictors of environmental filtering and habitat matching were not consistent, with trait predictors instead varying by individual traits, trait categories and ecoregions. Notwithstanding inconsistent trait predictors, environmental filtering was primarily influenced by habitat preference traits, whereas habitat matching was primarily influenced by both habitat preference and dispersal traits. Predictors of functional traits also varied by trait category and ecoregion, with habitat preference and dispersal traits primarily influenced by network variables.Main conclusionsOur study demonstrates the contingent patterns and drivers of environmental filtering and habitat matching on a macroecological scale. We provide the foundation on which trait–environment relationships can be further quantified and causal explanations established in the context of community disequilibrium and applied to conservation and management of freshwater systems.

How far can EPTs fly? A comparison of empirical flying distances of riverine invertebrates and existing dispersal metrics

The species composition of a community is driven by the dispersal capacity of the species forming that community and their ecological niche. While the ecological niches of EPTs (Ephemeroptera, Plecoptera and Trichoptera) are well-studied due to their wide use as indicators for the ecological status of freshwater ecosystems, their dispersal capacity has not yet been accurately characterized. Dispersion of the merolimnic EPT species during the terrestrial aerial adult stage is of special importance because the distance dispersed by active flight or passive wind drift is usually much larger compared to dispersion during the aquatic larval stage by active crawling or by drifting downstream.The aerial dispersal distance has been directly measured for only a small number of EPT species. For most other species, the dispersal capacity is assessed indirectly using species’ traits that are mainly based on expert judgement and dispersal indices derived from trait information. In this study, we compiled a database of European EPTs’ aerial dispersal distances reported in empirical studies and compared them to the dispersal capacity of the species as described by five different dispersal indices (original and modified versions of Li’s Dispersal Capacity Metric DCM and Sarremejane’s Species Flying Propensity SFP as well as relative wing length).The database included empirical data on 180 species, comprising 9.3% of European EPT species. Most data came from trap experiments with traps located at different distances from the assumed emergence point. Since the distance classes differed between studies and had to be translated to a fixed set of four distance classes here, several species had to be assigned to more than one class. To account for this uncertainty, five ordered logistic regression models, each one with a dispersal index as predictor and the ordinal-scaled aerial dispersal distance as response, were bootstrapped 10,000 times. In each run, species belonging to several distance classes were randomly assigned to a single class out of all possible classes. Since wing length had no significant effect on aerial dispersal distance in any of the 10,000 bootstrap runs, we question the use of this anatomical trait as an indicator for the aerial dispersal capacity. In contrast, a modified version of the DCM index was consistently related to the aerial dispersal distances (96%). The original SFP index had a significant effect in 100% of the model runs, indicating that this index is very well-suited as an indicator for the aerial dispersal capacity of European EPT species.This study facilitates the assessment of European EPT flying distances by providing a compilation of empirical data on the topic and by recommending an accurate indirect method when empirical data is not available.

Riparian ground beetles in gravel bed rivers: validation of Invertebrate Bankfull Assessment method

Bankfull Assessment Method (IBA method) applies riverine invertebrate community of ground beetles as a biotic indicator of bankfull variation in a dynamic river. IBA index is calculated as a proportion of small sized individuals (1–6 mm) to large size individuals (18–24 mm) of ground beetles in given sample site. The aim of the study was to validate the IBA bankfull discharge method with 135 carabid assemblages collected in gravel-bed rivers of various modifications of channel morphology in the Polish Carpathians. Constrained canonical correspondence analysis revealed that biotic factors such as IBA, plant cover and plant height described most of the variation of small and large sized species abundance. The IBA index variation confirmed earlier expectation of the mean IBA values. Mean value of the index for the lowest bench is about 5, for the middle bench about 2 and it never exceeds 1 for the highest bench. The bankfull calculated using morphometric methods (Wolmann) was located between the first and second bench on each river. Values of the IBA for the lowest bench depend significantly on channel incision whereas modifications of vegetation affect the values for all three benches. The study presents high value of IBA method in estimating bankfull discharge which is considered to be important supporting flow predicting morphological changes responsible for river channel shape with direct connection to living organisms occupying river banks as well as to river environmental quality. Proposed simple method could be important for local watershed managers for prediction of bank embankments level (e.g. maximum level of rip-rap or gabions) or for maximum level of low head hydraulic structures when they are necessary in terms of river engineering works but when they are still built as environmental friendly hydraulic structures.

Broad-scale effect of herbicides on functional properties in benthic invertebrate communities of rivers: An integrated analysis of biomonitoring and exposure evaluations

We conducted a broad-scale ecological effect assessment of agricultural chemicals where we combined biomonitoring databases of riverine invertebrate communities with predictions of environmental concentrations of chemicals, based on an exposure evaluation model for Japanese rivers. One of the difficulties of broad-scale assessment arises from the use of biomonitoring databases for which the monitoring sites are often spread across different geographic regions, with varying species compositions and heterogeneous environmental factors. This problem was circumvented using a trait-based approach, which extracts patterns of ecological properties of species response to changes in either chemical concentration or environmental factors. We identified groups of species that had particular trait categories that were negatively correlated with herbicide pollutants (the predicted concentration divided by the acute toxic concentration). Numerical abundances of species groups classified by trait categories had more sensitive responses to herbicide pollutants than total species abundance. However, a finding that trait diversity and species diversity indexes in the communities examined did not change with herbicide pollutants means that the two indexes showed resistance to chemical stresses. We inferred that the reason for the greater resistance in terms of trait and species diversity was that compositional changes of species caused by increasing herbicide pollutions were simply a shift from communities composed of susceptible species to those composed only of tolerant species.

Temporal thermal refugia and seasonal variation in upper thermal limits of two species of riverine invertebrates: the amphipod, Paramelita nigroculus, and the mayfly, Lestagella penicillata

Understanding the response of aquatic organisms to elevated water temperatures offers insight into the ecological consequences of climate change on riverine species. Upper thermal limits were determined for two riverine invertebrates, the amphipod Paramelita nigroculus (Paramelitidae) and the mayfly Lestagella penicillata (Teloganodidae), in two rivers in the south-western Cape, South Africa. Limits were estimated using the critical thermal method (reflected as the critical thermal maxima—CTmax) and the incipient lethal temperature method (reflected as the incipient lethal upper limit—ILUT). Thermal signatures of these rivers were characterized using hourly water temperatures. CTmax for seasonally acclimatized and laboratory-acclimated P. nigroculus varied significantly amongst months and acclimation temperature. CTmax for seasonally acclimatized L. penicillata varied significantly amongst months, but not with acclimation temperature. 96-h ILUT values for seasonally acclimatized individuals varied significantly amongst months for both species. CTmax values, 96-h ILUT and Maximum Weekly Allowable Temperature thresholds were lower for P. nigroculus compared to L. penicillata. Seven-day moving averages of daily mean and maximum water temperatures were significantly correlated with upper thermal limits for seasonally acclimatized L. penicillata but not P. nigroculus. The proportion of time within a 24-h period that chronic thermal stress thresholds are not exceeded provides a measure of monthly or seasonal chronic thermal stress, and reflects the quantity of temporal thermal refugia for vulnerable organisms. Further testing of these relationships for other species, rivers and regions is recommended, to evaluate the potential for stream temperature averaging statistics to serve as proxies for biological thresholds.

An index to track the ecological effects of drought development and recovery on riverine invertebrate communities

In rivers, the ecological effects of drought typically result in gradual adjustments of invertebrate community structure and functioning, punctuated by sudden changes as key habitats, such as wetted channel margins, become dewatered and dry. This paper outlines the development and application of a new index (Drought Effect of Habitat Loss on Invertebrates – DEHLI) to quantify the effects of drought on instream macroinvertebrate communities by assigning weights to taxa on the basis of their likely association with key stages of channel drying. Two case studies are presented, in which the DEHLI index illustrates the ecological development of drought conditions and subsequent recovery. These examples demonstrate persistent drought effects months or several years after river flows recovered. Results derived using DEHLI are compared with an established macroinvertebrate flow velocity-reactive index (Lotic-invertebrate Index for Flow Evaluation – LIFE score) and demonstrates its greater sensitivity to drought conditions. Data from a number of rivers in south east England were used to calibrate a statistical model, which was then used to examine the response of DEHLI and LIFE to a hypothetical multi-year drought. This demonstrated a difference in response between sampling seasons, with the spring model indicating a lagged response due to delayed recolonisation and the autumn model differentiating habitat loss and flow velocity-driven responses. The application of DEHLI and the principles which underlie it allow the effects of drought on instream habitats and invertebrates associated with short or long term weather patterns to be monitored, whilst also allowing the identification of specific locations where intervention via river restoration, or revision of existing abstraction licensing, may be required to increase resilience to the effect of anthropogenic activities exacerbated by climate change.

Whole‐landscape modelling of compositional turnover in aquatic invertebrates informs conservation gap analysis: An example from south‐western Australia

Abstract Freshwater aquatic ecosystems are in decline due to intensifying land use, salinisation, water abstraction and climate change. Understanding compositional patterns in aquatic biota is a useful step towards better management of aquatic ecosystems. We used generalised dissimilarity modelling (GDM) to predict compositional turnover in riverine invertebrate fauna (primarily insects) as a function of environment. Conceptual understanding of major drivers of aquatic invertebrate species distribution helped decide which predictor variables to source and include. Five groups of environmental variables—waterscape, local habitat, climate, landscape and disturbance—were derived from either spatial layers or in situ (site) measurements. Predictive models and variance partitioning tests of variable groups demonstrated the importance of representing all conceptual drivers of ecological pattern and process. As expected, waterscape variables were independently the most important group, followed by local habitat and landscape variables; with complex interactions between groups. Climate variables independently contributed the least. To determine the information content for mapping patterns, we investigated the independent and combined contribution of site‐measured and spatial predictors. Even though predictive models developed using only site‐measured variables or only spatial variables explained around the same amount of deviance (DE), combined they increased explained model DE by 11.2%. Compositional dissimilarities between the 51 surveyed site pairs predicted by the model using only spatial variables were highly correlated (r2 = .85) with dissimilarities predicted using site and spatial variables. These results support the use of the spatial model for conservation decisions. The spatial model was used to evaluate representativeness of both the conservation reserve network and biological monitoring locations. The location of aquatic monitoring sites was uneven, with comprehensive coverage south and coastward, and less representative of inland environments. Proportional protection of ecological environments (scaled by riverine invertebrate taxa) was found to vary between 20% and 30%, being higher in southern parts where more land has been allocated to reserves and less in northern and inland parts. This demonstrated local progress towards achieving the Convention on Biological Diversity's Aichi Target 11 for inland waters. These results provide a focus for improving the robustness of information used in decisions affecting the conservation of aquatic biodiversity, including places to target to fill gaps in the reserve network and additional aquatic monitoring locations (supporting Convention on Biological Diversity's Aichi Target 19). The GDM‐based approach to characterising ecological environments, provided a first quantitative foundation for comprehensively evaluating the conservation status of freshwater ecosystems in south‐western Australia. Potential future applications include assessing the ecological implications of land use and climate change.

Re‐Connection of Oxbow Lakes as an Effective Measure of River Restoration

Six years after re‐connection of an oxbow lake from periodically to permanently connected to the main channel, the restoration success was assessed. This permanently connected oxbow lake was compared with the main channel of the Elbe River and with a periodically connected oxbow lake by means of comparisons of the aquatic macroinvertebrates, fish and aquatic macrophyte communities. The permanently connected oxbow was suited as important replacement habitat for riverine invertebrates, especially for clubtails (Odonata) and unionid mussels (Bivalvia). The periodically connected oxbow lake was colonized by typical species for shallow lakes. As expected, riverine species did not occur. Meanwhile, the invertebrate community in the main channel was poor and dominated by invasive species (Dikerogammarus villosus, Dreissena polymorpha). The results concerning fish showed a clear dominance of the rheophilic species spined loach (Cobitis taenia) in the permanently connected oxbow lake and of the indifferent species roach (Rutilus rutilus) and European perch (Perca fluviatilis) in the periodically connected oxbow lake. However, species number was highest in the main channel. For macrophytes, quantity, number of taxa and growth forms and diversity were lower in the permanently compared to the periodically connected oxbow lake. In conclusion, the re‐connection of oxbow lakes to main channels can be an important measure for native species conservation, especially macroinvertebrates, and hence for the implementation of the Water Framework Directive.

A closer look at the main actors of Neotropical floodplain food webs: functional classification and niche overlap of dominant benthic invertebrates in a floodplain lake of Paraná River

Functional classification of animals is necessary to enhance the predictive power of food web models. However, while there is a large database for functional classification of benthic invertebrates (Functional Feeding Groups, FFG) in the temperate zone, the attribution of individual species of riverine invertebrates is still in its infancies in the Neotropical Region. Different authors hypothesized that diet breadth was larger in the Tropics, however detailed analysis are scarce. In the present study we aimed at classifying dominant benthic taxa of the Middle Parana River floodplain (Argentina) into trophic guilds by diet and niche overlap analyses. We sampled twelve taxa of benthic invertebrates from a floodplain lake during low water season and performed a gut content analysis as a baseline for FFG classification. We also used available diet information of other common taxa for statistical analysis. Then, we compared the variance of niche overlap, using Pianka's index, with that of simulated null model. After that we grouped taxa using Morisita similarity index with a threshold of 0.6 and compared niche overlap with null models within and between FFGs. Observed variance of niche overlap was greater than expected by chance, confirming the presence of FFGs among analyzed taxa. Considering trophic similarity of species, we identified four FFGs: collectors, omnivores, herbivores and predators. Niche overlap was greater than expected by stochastic null models within FFGs, and smaller between FFGs. Nearly one third of analyzed taxa were classified in a different FFG than their congeners of the Holarctic region. This result indicates that classifications performed in the Holarctic region should be used with care in the Neotropical region, even in subtropical systems

Community–environment relationships of riverine invertebrate communities in central Chinese streams

Chinese rivers are both highly biodiverse and highly under pressure, hence an urgent need exists to understand ecological drivers and disentangle different scales of stressors to support water management. Our aims were to (1) determine the most influential variables for benthic invertebrate occurrence, (2) compare results related to communities as opposed to metrics and (3) examine the role of spatial scales with relevance to management. Benthic invertebrate sampling was performed at 37 sites in selected tributaries of the middle reaches of the Yangtze, covering an environmental gradient with a focus on organic pollution (stratified sampling design). Ten metrics commonly used in biomonitoring were derived and analysed in parallel to assemblage data. Environmental variables covered 74 parameters from three different spatial scales, namely local, reach and catchment scale. We ran a CCA with each of the three subsets to find out the significant determining/explanatory variables, followed by pCCA and pRDA (for metric data) with these variables with forward selection to determine single variables important for each subset; we further used variation portioning for benthic invertebrate data. A high percentage of overall variability (70 %) of the assemblage structure was explained, with catchment- and local-scale variables being almost equally important. Small-scale variables tended to be more important than large-scale variables for the metric-based approach but not for the assemblage approach. Our results emphasise the need for spatially explicit regional studies in freshwater systems and suggest testing multi-metric assessment approaches to tackle water management and environmental health questions in China.

Diet‐tissue fractionation of δ15N by consumers from streams and rivers

Variation in the diet‐tissue fractionation of stable nitrogen isotopes (Δ15N) is a major source of uncertainty in mixing model outputs and the calculation of trophic level in food web studies in aquatic systems. Using δ15N and δ13C of algae and consumers collected from a broad range of streams and rivers in Australia and New Guinea, we calculated Δ15N using a gradient approach, and compared these estimates with those from the literature. Riverine invertebrates and fishes from this region have δ15N diet‐tissue fractionation at the low end of the range of values reported for literature summaries, but different trophic groups had different Δ15N estimates. Source‐consumer regressions based on δ13C had lower slope estimates and lower R2 values compared with those based on δ15N. This implies that although consumers on average obtain a portion of their organic carbon from higher plants, they derive most of their organic nitrogen from N‐rich algae. Use of appropriate Δ15N for riverine consumers will lead to more satisfactory results with isotope mixing models, and the uncertainty associated with Δ15N estimates can be incorporated in the latest iterations of these models that are probabilistic rather than deterministic.

Disturbance and riverine benthic communities: What has it contributed to general ecological theory?

AbstractDisturbance from floods and/or low flows is a pervading force in almost all benthic riverine communities around the world. As such the study of disturbance effects on benthic communities has been a dominant theme of research in benthic river ecology. Many of these studies have been phenomenological or have evaluated hypotheses developed in other areas of ecology. These studies have provided considerable weight to move the common view of ecological communities in general as deterministically structured, to one where stochastic disturbances can be the dominant structuring force in many communities. Benthic river studies investigating the link between disturbance and diversity have generally failed to find support for single variable hypotheses, such as the intermediate disturbance hypothesis, from other areas of ecology, however, river ecologists have been among the first to embrace multivariate models of diversity. The highly mobile, larval life history stage of many riverine invertebrates makes many of the hypotheses generated in general ecology inappropriate for benthic river communities; however, the recently popularized neutral models may prove to be good descriptors of these communities. Food web structure studies indicate riverine webs respond differently to disturbance from the way predicted by ecological theory. The contribution of studies of disturbance in benthic ecology to general ecology has to date been rather limited with some notable exceptions. However, the ubiquity of floods in rivers worldwide offers fertile ground for future contributions that could substantially advance this area of ecology. Benthic river ecologists need to resist the temptation to simply show general ecological models often do not work in streams, and need to develop their own models, which in turn may feed back to wider ecology. Copyright © 2009 John Wiley & Sons, Ltd.

Low flow controls on benthic and hyporheic macroinvertebrate assemblages during supra‐seasonal drought

AbstractDespite the widely accepted importance of the hyporheic zone as a habitat for stream macroinvertebrates during floods, few data exist regarding community composition and distribution during periods of low flow or drought in perennial streams. Integrating research on hyporheic invertebrates with results from a long‐term study of a UK river provided the opportunity to examine how benthic and hyporheic macroinvertebrate communities respond to inter‐annual variability in river flow and periods of groundwater drought. Changes in the riverine macroinvertebrate community associated with low flow included a reduction in species richness and the number of individuals per sample, particularly aquatic insects. The hyporheic community was characterized by a relatively homogeneous composition during a period of severe low flow, punctuated by short‐term changes associated with variation in water temperature rather than changes in discharge. We present a conceptual model of the processes influencing benthic and hyporheic invertebrates under low‐flow conditions. Previous studies have seldom integrated these two assemblages and their interactions. The model presented highlights the potential importance of surface water and hyporheic zone linkages for riverine invertebrate communities under a range of flow conditions. Copyright © 2009 John Wiley & Sons, Ltd.