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Flow refugia, locations that maintain substrate stability and low hydraulic stress during periods of high flow, can ensure riverine resilience in the face of increasing hydrological unpredictability. Despite their known importance, they have been overlooked in recent years with work on drought refugia currently seeing greater attention. Moreover, research on the role of flow refugia during artificial flood pulses in regulated rivers, where flood disturbances are no longer part of the hydrograph, is essentially absent. Here, we compared flow refugia for benthic macroinvertebrates among six habitats (main channel, side channel, riffle, margin, lentic including a floodplain pond, and inundated floodplain) within four different sites in response to an artificial flood pulse. We found that the grain-size distribution and macroinvertebrate community composition changed at each site following the flood. Macroinvertebrate assemblages became longitudinally homogeneous, but within-site beta diversity and taxa richness remained temporally stable following the flood pulse, suggesting the presence of flow refugia. In this respect, margin, inundated floodplain and lentic (a floodplain pond) habitats provided important flow refugia locations, particularly for the mobile mayfly Rhithrogena sp. In contrast, low substrate stability in riffle and side channels resulted in limited refugia potential for most taxa. Refuge use was however patchy with high levels of intra-habitat variability being evident for Rhithrogena sp. and the amphipod Gammarus fossarum in margin and side channel habitats. Further work is required to advance our knowledge of flow refugia in rivers with differing flow regimes to enable their integration into management and restoration schemes., River Research and Applications, 38 (4), ISSN:1535-1459, ISSN:1535-1467

Global environmental change is threatening freshwater biodiversity with ecological impacts predicted to be particularly severe in high-altitude regions. Despite this, an ecological understanding of high-altitude pond networks remains patchy, with only limited knowledge of the environmental and spatial predictors of taxonomic and functional diversity. Moreover, previous studies of pond ecosystems have focused primarily on taxonomic richness and largely overlooked functional diversity.This study examined the influence of local environmental and spatial factors on taxonomic and functional α and β diversity (including the turnover and nestedness-resultant components) of 17 high-altitude (~2,500 m above sea level) pond macroinvertebrate communities, in the Macun Cirque, Switzerland.Spatial processes (pond connectivity) were important drivers for taxonomic α diversity, while local environmental variables (pond permanence and surface area) were important determinants of functional α diversity. Species turnover was the most important component of β diversity for taxonomic composition, and functional composition demonstrated a nested spatial pattern.Variation in taxonomic and functional composition (and the turnover and nestedness components of β diversity) were determined by local environmental variables despite the limited environmental gradients within the pond network. No significant effects of spatial variables on community composition were recorded for either facet of diversity, indicating that compositional variation was determined at a local scale. Water temperature, depth and pond permanence were consistently the most important measured drivers of diversity.Given the importance of both spatial and environmental variables in structuring taxonomic and functional diversity, landscape-scale conservation and management activities that aim to improve or protect high-altitude freshwater biodiversity should focus on maintaining connectivity among ponds and environmental heterogeneity, particularly pond surface area, water depth, and hydroperiod. Understanding the mechanisms driving taxonomic and functional diversity will be critically important for the management and conservation of macroinvertebrate communities in high-altitude pond networks in the face of climatic warming.

This study aimed to experimentally examine how riverbed drying and different rates of water level reduction influenced the vertical movement of amphipods of various sizes into different subsurface sediment compositions. Using sediment columns (mesocosms) filled with different sized transparent substrates, we explored how varying speeds of drawdown affected vertical movement and stranding of individuals. We hypothesised that: (1) larger individuals would be less able to migrate within subsurface sediments compared to smaller ones; (2) smaller sediment particles would lead to more individuals becoming stranded and; (3) faster rates of water level drawdown would increase the likelihood of individuals becoming stranded above the waterline. Body size significantly influenced the final position of an individual, with smaller individuals accessing deeper sediments more readily. Larger amphipods were more likely to become stranded above the waterline. Amphipods migrated to greater depths during faster water level reduction rates with smaller individuals displaying greater overall movement. Sediment particle size did not influence the ability of amphipods to move vertically into subsurface sediments in response to water level reduction. The results indicate that subsurface sediments may serve as a refuge from surface drying but that both the size of individual invertebrates influences their ability to migrate vertically.

The increasing number of taxa being translocated across the globe is leading to many non-native species encountering indigenous taxa as well as other non-native species. Environmental heterogeneity may strongly influence the spatial distribution, habitat use and refuge availability for these taxa. Using a series of 24-h mesocosm experiments we examined the predator–prey interactions between an invasive crayfish (Pacifastacus leniusculus) and four amphipod taxa, one indigenous (Gammarus pulex) and three non-native species (Crangonyx pseudogracilis, Dikerogammarus villosus and Gammarus tigrinus) to Great Britain. The potential mediating effect of physical habitat on predator–prey interactions was examined via the use of different substrate particle sizes; cobbles, gravels and, sand. Survivorship of amphipods in response to crayfish predation varied significantly with the highest rates recorded for the non-native species D. villosus, followed by G. tigrinus, and C. pseudogracilis, with the lowest survivorship recorded for the indigenous species G. pulex for all substrates except cobble. However, total biomass consumption of the indigenous G. pulex and the non-native D. villosus by P. leniusculus were similar suggesting that crayfish may have been satiated by larger D. villosus individuals. Substrate size had a significant influence on the predation success of P. leniusculus, with larger substrate clasts typically resulting in increased survivorship rates for all species except C. pseudogracilis, which displayed lower predation rates for sand substrates. The findings of this study highlight the risks that naïve indigenous taxa may face from new invasive species and the importance of characterising physical habitat (complexity and refugia potential) when considering the potential ecological effects of invaders on predation success.

Globally, excessive fine sediment (particles2 mm) deposition is acknowledged to have deleterious effects on aquatic biodiversity. However, the impacts are often equivocal possibly reflecting landscape context, although this is rarely considered. To address this, we examined the temporal response of macroinvertebrate taxonomic and functional diversity to experimental fine sediment clogging in a prealpine (Italy) and lowland setting (UK). Colonisation devices were installed insitu with either clean or clogged substrates and examined for short (7-14 days), medium (21-28 days) and long (56-63 days) timescales. Clogging resulted in altered taxonomic community composition in both the lowland and prealpine rivers and modified functional community composition in the prealpine river. Nestedness was consistently found to be the dominant process driving differences in taxonomic composition between the clean and clogged substrates in the prealpine environment, with clogged substrates forming a nested community. No dominant component structured lowland taxonomic communities. Functional community composition was driven by nestedness in both environments but was heavily dominant in the case of the prealpine river, possibly reflecting low functional redundancy. Widely employed community richness metrics (EPT, taxa and functional richness) only displayed a response to fine sediment loading in the prealpine environment but taxa characterized as sensitive to fine sediment as well as some functional feeding groups did exhibit differences in both settings. In the prealpine environment, the effects of fine sediment intensified over time for several community metrics. Although further research is required to corroborate our findings and extend our observations across more rivers and typologies, excessive fine sediment is a pervasive stressor affecting macroinvertebrate communities in prealpine and lowland environments. However, the biodiversity facets that responded to clogging differed between the two landscape settings probably reflecting wider environmental filtering. Monitoring and managing fine sediment loading likely requires context specific approaches to maximise ecological benefits.

Fine sediment availability and channel hydraulics are two of the primary controls on the ingress of fine sediment into gravel river beds. A novel dataset consisting of fine sediment ingress measurements coupled with high-resolution turbidity and discharge time series, was analysed to investigate relations between ingress, discharge and turbidity. Discharge and turbidity demonstrated a weak association with each other, and their relations with fine sediment ingress were relatively weak. An alternative, but widely applied ‘redundancy’ approach was investigated that focused on key metrics, or facets, of the discharge and turbidity time series and their association with fine sediment ingress. Principal component analysis was used to distil the most important facets driving variation in the discharge and turbidity datasets and these were then used as independent variables in regression models with sediment ingress as the dependent variable. These models accounted for a larger amount of the statistical variation in sediment ingress over time than discharge and turbidity time series. Facets of the turbidity time series were found to be the most effective explanatory variables. The results suggest that this approach could be valuable and justify its application and testing across a range of river types in different hydrological and sedimentary settings. Application of this method could improve our generic understanding of what controls ingress at larger spatial and temporal scales and therefore complements process-based approaches, which is vital for the development of fine sediment management strategies.

Foraging by benthivorous fish can affect bed material mobility and sediment flux. This paper collates evidence of benthic feeding effects at local scales and evaluates the possibility that large numbers of foraging fish, each of which accomplishes a small amount of geomorphic work when feeding, may have a cumulative effect across river systems. A first synthesis of research from several disciplines provides a deeper understanding of how fish disturb and condition bed materials with implications for sediment mobility. To evaluate the spatial extent of benthic feeding and therefore the potential for it to have a large-scale effect, the distribution of benthivorous fish is established across a large river network. After quality control, the dataset yields a comprehensive set of fish community information based on over 61,000 individuals and 30 species at 176 sites. The factors that are likely to mediate foraging and its geomorphological effectiveness are considered. A novel scoring system that incorporates three key controls (fish feeding behaviour, fish abundance and fish body size) is then applied across the river network to provide the first prediction of where geomorphologically effective benthic feeding is feasible and its possible relative magnitude. Our results demonstrate that the potential for zoogeomorphic impacts is widespread but variable in space as a function of community composition and the abundance of key benthivores. A preliminary calibration against measured field impacts suggests that benthic feeding may cause measurable geomorphological disturbance at more than 90% of sites. Together, previous work and this unique analysis suggest that benthic feeding is sufficiently effective and extensive to warrant additional research. Investigating the role of benthivorous fish in fluvial geomorphology is important because it may yield results that challenge the assumption that biota are irrelevant sources of energy in geomorphological systems. Key research questions and a roadmap to facilitate progress are identified.

1. Sedimentation and clogging (colmation) of interstitial pore spaces with fine sediment particles is widely considered to be one of the most significant threats to lotic ecosystem functioning. This paper presents the results of a running water mesocosm study examining the effect of benthic and hyporheic fine sediment loading and particle size on the vertical movement and distribution of the freshwater amphipod Gammarus pulex. 2. A gradient of fine sediment loading and different particle sizes were used to examine the ability of G. pulex from two body size classes to access and migrate vertically within subsurface sediments. 3. We tested three hypotheses: i) sediment loading would modify the distribution of G. pulex by limiting vertical movement; ii) the deposition of large particles and heterogenous sediments would limit the vertical movement of individuals more than homogeneous fine grained sediments; and iii) large bodied individuals would be prevented from migrating vertically with increasing sediment loading and particle size / heterogeneity. 4. Sediment loading, particle size and heterogeneity of deposited sediment had a significant effect on the vertical movement of individuals, with heterogeneous sand (0.125 - 4 mm) acting as the strongest barrier to the vertical movement of individuals through the infilling and clogging of interstitial spaces followed by coarse (1 - 4mm) and fine sand (0.125 - 4 mm). 5. Fine sediment loading and particle size acted as a filter on body size and limited the ability of large bodied individuals to migrate vertically to a greater extent than small bodied individuals. 6. This study demonstrates that the effects of fine sediment on habitat availability and faunal movement is dependent on both sedimentological characteristics and an individual’s body size. The results illustrate the importance of both abiotic and biotic factors when evaluating the ecological 66 effects of fine sediment deposition.

Habitats that mitigate the effects of a disturbance event (e.g. flood) are referred to as refugia. Their occurrence in heavily impacted river systems is often limited, and their restoration rarely pursued. This paper presents the results of a combined laboratory and numerical modeling study to assess flood refugia availability to mobile aquatic organisms in the context of river restoration and dynamic river widening. We used a calibrated 2D hydrodynamic model based on eight topographies obtained in laboratory experiments to assess refugia availability by analyzing the hydro-morphological conditions under varying sediment supply. Overall, sediment equilibrium sustains more complex hydro-morphological conditions with low bed shear stress zones being maintained during elevated discharges. Furthermore, our results suggest that the floodplain is an important potential refuge that becomes accessible for discharges with a return period of approximately one year. Conversely, sediment deficit results in a homogeneous flow field with steadily increasing hydraulic forces for high flows and impaired lateral connectivity except for very large flood events of a 30- to 100-year return period. Dynamic river widening implemented in a channel with sediment equilibrium conditions as opposed to a sediment deficit is thus more likely to provide flood refugia.

Artificial drainage ditches are common features in lowland agricultural catchments that support a wide range of ecosystem services at the landscape scale. Current paradigms in river management suggest activities that increase habitat heterogeneity and complexity resulting in more diverse floral and faunal assemblages; however, it is not known if the same principles apply to artificial drainage ditch systems. We examined the effects of four artificial substrates, representing increasing habitat complexity and heterogeneity (bricks, gravel, netting and vegetation), on macroinvertebrate community structure within artificial drainage ditches. Each substrate type supported a distinct macroinvertebrate community highlighting the importance of habitat heterogeneity in maintaining macroinvertebrate assemblages. Each substrate type also displayed differing degrees of community heterogeneity, with gravel communities being most variable and artificial vegetation being the least. In addition, several macroinvertebrate diversity metrics increased along the gradient of artificial substrate complexity, although these differences were not statistically significant. We conclude that habitat management practices that increase habitat complexity are likely to enhance macroinvertebrate community heterogeneity within artificial drainage channels regardless of previous management activities.

1. Invasive non-native species (INNS) threaten biodiversity and ecosystem functioning globally. However, there remains a pressing need to understand the environmental factors controlling the dispersal, successful establishment and subsequent ecological impacts of INNS for receiving ecosystems. Here, we examine how region-wide flow regime magnitudes facilitate the successful establishment of an invasive crayfish species (Pacifastacus leniusculus, signal crayfish) in England (UK). We also consider the interactive effects of invasive crayfish with flow regime variations on the structural and functional diversity of macroinvertebrate communities. 2. Low-flow magnitudes increased the likelihood of P. leniusculus establishment, with 80% of recorded invasion dates falling in years with flow magnitudes below average (low- and low-moderate flow classes), whilst only 1.6% occurred in high-flow years. 3. Temporal trajectories of structural and functional macroinvertebrate responses in invaded rivers demonstrated reduced diversity compared to control rivers. Lower taxonomic and functional richness measures typically coincided with periods of low discharge in invaded rivers and were greatest during regionally high-flows. 4. Macroinvertebrate communities displayed significant structural and functional responses to the interaction between invasive crayfish and flow regime variations. Specifically, a number of low- and high-flow indices yielded significant associations, highlighting the role of extreme hydrological events in shaping INNS effects on receiving ecosystems. We also detected greater ecological effects of invasive crayfish under hydrologically stable conditions. Importantly, and for the first time, we observed that invasive crayfish reversed macroinvertebrate community responses to flow regime cues (e.g. discharge fall rate and minimum flows in the preceding 180 days). 5. Synthesis and applications. Results from this study indicate that low-flow events facilitate the spread/establishment of invasive crayfish and correspond with greater ecological effects for receiving ecosystems. Given that low-flow events are predicted to increase in intensity, duration and frequency over the 21st century, our results highlight the potential threat that invasive crayfish may pose under future hydroclimatic changes. Managing river flow regimes effectively (including maintaining higher flow events and flow variability) is likely to be vital in conserving ecological diversity following crayfish invasion.

This study investigates the potential for physical damage caused by suspended fine sediment on gills of three macroinvertebrate species, Hydropsyche siltalai, Ephemera danica and Ecdyonurus venosus. Macroinvertebrate cadavers were exposed to three suspended sediment concentrations (control 3.5, low 83.7 and high 404.0 mg l−1) at two velocities (low 0.19 m s−1 and high 0.37 m s−1), for 6 h in a recirculating flume. Tracheal gill surfaces were subsequently examined for evidence of physical damage using scanning electron microscopy (SEM) images. Physical damage predominantly consisted of fine sediment coverage of gill surfaces, appearing as a deposited layer of sediment obscuring and potentially clogging the gill. For E. venosus, suspended sediment concentration influenced gill cover, but velocity had no significant effect. Coverage of H. siltalai gill surfaces increased significantly between low and high sediment concentrations but only at the higher flow velocity. Gill coverage of E. danica did not differ across any sediment concentration. The results were consistent with reported species sensitivities to fine sediment, despite the use of cadavers. However, we found limited evidence of physical abrasion as a direct physical effect of fine sediment under the experimental conditions used.

Two Ponto-Caspian amphipods, Dikerogammarus villosus and Dikerogammarus haemobaphes, have expanded their geographical ranges from eastern Europe into Great Britain in recent years. This study represents one of the first examining the distribution and habitat preferences of coexisting populations of D. haemobaphes and D. villosus via field and laboratory experiments in the UK. Field surveys of a recently invaded lowland reservoir in the UK are complimented with ex situ laboratory mesocosm experiments examining the substrate preferences of coexisting populations of D. villosus and D. haemobaphes. Results from the field study indicated that D. haemobaphes dominated the macroinvertebrate community within the reservoir and demonstrated a strong affinity for large cobble and artificial substrates. D. villosus occurred at lower abundances but displayed a strong preference for coarse cobble substrates. A third invasive amphipod, Crangonyx pseudogracilis, was largely confined to sand/silt habitats. Laboratory mesocosm experiments clearly supported the field observations of D. villosus and D. haemobaphes with both species demonstrating a preference for cobble substrates. Results from the study highlight the importance of characterising physical habitat when investigating biological invasions and suggest that habitat availability may influence the extent and speed at which range expansion of new amphipod invaders occurs.

Sediment transport in mountain streams can be a major hazard to downstream infrastructure. Consequently, sediment traps are a common feature in many high gradient streams to retain large volumes of sediment and protect settlements from major sediment transport events. Despite the wide application of these instream structures, there is little knowledge regarding the environmental and ecological effects on streams. Here, we investigated the hydromorphological effects of sediment traps on instream habitats and associated macroinvertebrate communities in four impacted and three non-impacted streams in Switzerland. Sediment traps significantly disrupted the sediment regime homogenising grain size percentiles compared to the natural stepwise downstream fining in control streams. This disruption in the sediment regime resulted in finer grain size distributions upstream of the sediment trap, and reduced substrate diversity in the sediment retention basin and just downstream of the trap. The reductions in substrate diversity resulted in an altered macroinvertebrate community composition. Further, the disconnection in sediment transport led to a lack of longitudinal correlation in macroinvertebrate communities. Refugia provision downstream of the sediment trap, and resource availability within the retention basin, were diminished, potentially reducing resilience of macroinvertebrate assemblages to instream disturbances. The effects of sediment traps were most likely localised in three of the four streams with substrate diversity recovering to comparable control values within 8 wetted widths (ca. 50 m) downstream of the trap associated with natural longitudinal fining. In contrast, ecological and environmental effects propagated downstream in one impacted stream with no recovery being evident. Sediment retention basins in the impacted streams provided a local artificially unique habitat of dynamic-braided channels. Our results indicate that sediment traps can significantly disrupt the sediment regime with important consequences for instream ecology and environmental conditions, although these effects can be system specific. Further work is needed to fully understand the effects of sediment traps in mountain streams to assist resource managers in the mitigation and future construction of these structures.

Fine sediment storage within gravel beds is a key component of catchment sediment budgets and affects the health of benthic and hyporheic habitats. Here, we assess the performance of two substrate infiltration traps for the characterization of fine sediment (

Invasive signal crayfish (Pacifastacus leniusculus) are considered to be the most prevalent non-native crayfish species in Europe. Where large populations become established they have significant and long-term effects on benthic macroinvertebrate communities. However, much less is known about how community effects associated with crayfish invasion change in the short-term as a function of varying activity levels during the summer months. We examined the macroinvertebrate community composition of two lowland UK rivers, one which supported a well-established non-native crayfish population (invaded) and one in which crayfish had not been recorded (control). Colonisation cylinders were deployed which recorded community composition over a 126-day time period. Results indicate that once the activity period commences, invasive crayfish consistently altered macroinvertebrate community structure regardless of substrate character. Invaded communities displayed reduced beta-diversity compared to control sites. However, effects on the macroinvertebrate assemblage varied over the period when crayfish were active probably reflecting the behavioural activity of crayfish (which intensifies with increasing water temperature and during the spawning season) and life histories of other macroinvertebrates. The results indicate that crayfish invasions modify macroinvertebrate community composition, but over shorter timescales, the effects vary associated with their activity levels.

Temporary streams constitute a significant proportion of rivers globally and are common in wet, cool, temperate regions. These heterogeneous ecosystems harbour high biodiversity associated with the dynamic turnover of taxa. Despite flow permanence being widely recognised as an important environmental control, few studies have characterised biotic responses to long‐term hydrological variability in temporary streams. We examined taxonomic and functional macroinvertebrate communities of perennial and nonperennial river reaches over a 26‐year period. Flow permanence resulted in spatial variation in taxonomic and functional macroinvertebrate communities. Nonperennial river reaches, which were characterised by dynamic habitat provision (lotic, lentic, and dry states) over the study period, supported more heterogeneous communities than perennial river reaches. Hydrological variables, in particular wetted width, water depth, and zero‐flow states, were instrumental in structuring taxonomic and functional communities, although the importance of substrate conditions increased in autumn. Hydrological conditions resulted in separation of perennial and nonperennial taxonomic communities regardless of season, whereas functional communities differed only in spring. Our results emphasise that understanding of community responses to hydrological variability is enhanced by analyses that concurrently explore taxonomic and functional responses to long‐term intraannual and interannual hydrological variability. Moreover, functional responses represent a robust method to test ecological responses to hydrological drivers. Further research that builds on our work is needed to inform the protection of both perennial and nonperennial streams as they adapt to ongoing environmental change.

The duration, intensity and frequency of hydrological droughts are predicted to increase significantly over the 21st century globally, threatening the long-term stability of lotic communities. In this paper we examine the recovery and recolonization of macroinvertebrate taxa in ephemeral and near perennial reaches of the River Lathkill (UK) after a supra-seasonal drought event. Following flow resumption, species accumulation (recolonization) occurred rapidly over a 4-month period, with a steady increase observed thereafter. Taxonomic richness was significantly higher in the section with near perennial flow after the first month of the study than the naturally ephemeral reach. Serial correlation was observed in the near perennial section but not in the upstream ephemeral reach. Serial correlation in the near perennial section may reflect: (1) the ongoing process of recovery or (2) the macroinvertebrate community following a new ecological trajectory. Our results suggest that supra-seasonal droughts may cause initial reductions in lotic diversity during stream desiccation events but may re-set ecological succession and/or temporarily provide new ecological niches, thereby supporting increased taxonomic diversity when the full range of hydrological conditions are considered. Quantifying the recovery of ecological communities following supra-seasonal drought can provide information to help develop ecologically effective conservation and management strategies.

Defining reference conditions is a crucial element in quantifying the extent of anthropogenic modification and for identifying restoration targets in riverine ecosystems. Despite palaeoecological approaches being widely applied in lakes to establish reference conditions, their use in lotic ecosystems remains limited. In this study, we examine contemporary, historical (1930 and 1972), and palaeoecological macroinvertebrate biodiversity and biomonitoring scores in Eastburn Beck, a headwater tributary of the River Hull (UK) to determine if palaeoecological approaches can be used to characterize lotic system reference conditions. Palaeoecological samples comprised a greater gamma diversity (18 taxa) than contemporary samples (8 taxa), samples taken in 1972 (11 taxa) and 1930 (8 taxa). Palaeoecological samples supported taxonomically different Gastropoda, Trichoptera, and Coleoptera (GTC) communities compared with contemporary and historical samples (1930 and 1972). Results from biomonitoring indices using the GTC community indicated that the palaeochannel had (a) similar invertebrate biological quality, (b) a less energetic flow regime, and (c) increased fine sediment deposits compared with the contemporary channel. The results clearly illustrate that palaeoecological data can provide a suitable method to characterize reference conditions for lotic habitats. However, it is important to recognize that faunal data from palaeochannel deposits provide a short-term “snapshot” of the conditions within the river immediately prior to its hydrological isolation. River restoration activities should therefore draw on multiple lines of evidence, including palaeoecological information where possible, to characterize a range of reference conditions to reflect the highly dynamic nature of lotic ecosystems.

Characterizing temporary river ecosystem responses to flow regimes is vital for conserving their biodiversity and the services they provide to society. However, freshwater biomonitoring tools rarely reflect community responses to hydrological variations or flow cessation events, and those available have not been widely tested within temporary rivers. This study examines two invertebrate biomonitoring tools characterizing community responses to different flow‐related properties: the “Drought Effect of Habitat Loss on Invertebrates” (DEHLI) and “Lotic‐invertebrate Index for Flow Evaluation” (LIFE), which, respectively reflect community responses to habitat and hydraulic properties associated with changing flow conditions. Sub‐seasonal (monthly) variations of LIFE and DEHLI were explored within two groundwater‐fed intermittent rivers, one dries sporadically (a flashy, karstic hydrology—River Lathkill) and the other dries seasonally (a highly buffered flow regime—South Winterbourne). Biomonitoring tools were highly sensitive to channel drying and also responded to reduced discharges in permanently flowing reaches. Biomonitoring tools captured ecological recovery patterns in the Lathkill following a supra‐seasonal drought. Some unexpected results were observed in the South Winterbourne where LIFE and DEHLI indicated relatively high‐flow conditions despite low discharges occurring during some summer months. This probably reflected macrophyte encroachment, which benefitted certain invertebrates (e.g., marginal‐dwelling taxa) and highlights the importance of considering instream habitat conditions when interpreting flow regime influences on biomonitoring tools. Although LIFE and DEHLI were positively correlated, the latter responded more clearly to drying events, highlighting that communities respond strongly to the disconnection of instream habitats as flows recede. The results highlighted short‐term ecological responses to hydrological variations and the value in adopting sub‐seasonal sampling strategies within temporary rivers. Findings from this study indicate the importance of establishing flow response guilds which group taxa that respond comparably to flow cessation events. Such information could be adopted within biomonitoring practices to better characterize temporary river ecosystem responses to hydrological variations.

Sediment transport is regarded as an abiotic process driven by geophysical energy, but zoogeomorphological activity indicates that biological energy can also fuel sediment movements. It is therefore prudent to measure the contribution that biota make to sediment transport, but comparisons of abiotic and biotic sediment flux are rare. For a stream in the UK, the contribution of crayfish bioturbation to suspended sediment flux was compared with the amount of sediment moved by hydraulic forcing. During baseflow periods, biotic fluxes can be isolated because nocturnal crayfish activity drives diel turbidity cycles, such that night-time increases above day-time lows are attributable to sediment suspension by crayfish. On average, crayfish bioturbation contributed at least 36% (430 kg) to monthly baseflow suspended sediment loads; this biotic surcharge added between 4.7 and 13.54 t (0.19 to 0.55 t km-2 yr-1) to the annual sediment yield. As anticipated, most sediment was moved by hydraulic forcing during floods and the biotic contribution from baseflow periods represented between 0.43 and 1.24% of the annual load. Crayfish activity is nonetheless an important impact during baseflow periods and the measured annual contribution may be a conservative estimate because of unusually prolonged flooding during the measurement period. In addition to direct sediment entrainment by bioturbation, crayfish burrowing supplies sediment to the channel for mobilization during floods so that the total biotic effect of crayfish is potentially greater than documented in this study. These results suggest that in rivers, during baseflow periods, bioturbation can entrain significant quantities of fine sediment into suspension with implications for the aquatic ecosystem and baseflow sediment fluxes. Energy from life rather than from elevation can make significant contributions to sediment fluxes.

Invasive species represent one of greatest threats to aquatic biodiversity globally and are widely acknowledged to be instrumental in modifying native community structure. Despite this, little is known about how the increasing range expansion of invasive taxa may affect routine biomonitoring tools widely employed to measure or quantify environmental quality in lotic systems. This study examined the impact of an invasive freshwater crayfish on commonly employed riverine macroinvertebrate biomonitoring tools (scores and indices) designed to respond to a range of stressors. Data from long-term monitoring sites on both ‘control’ and invaded rivers in England were examined to assess changes to biomonitoring scores following invasion by signal crayfish ( Pacifastacus leniusculus ). Results indicate that routine biomonitoring tools used to quantify potential ecological stressors which are weighted by abundance, such as the Lotic-invertebrate Index for Flow Evaluation (LIFE) score and Proportion of Sediment-sensitive Invertebrates (PSI), were subject to significant inflation following invasion. In contrast, indices based simply on the presence of taxa, such as the Average Score Per-Taxon (ASPT – a derivative of BMWP), displayed no changes compared to control rivers; or in the case of the Biological Monitoring Working Party Score (BMWP), NTAXA and EPT richness, no consistent pattern following invasion. Season had a significant effect on the interaction of crayfish and LIFE and PSI scores. Autumn samples were subject to statistical inflation following crayfish invasion whilst spring samples exhibited no significant change. The results suggest that care should be taken when interpreting routine macroinvertebrate biomonitoring data where non-native crayfish are present, or in instances where their presence is suspected.

Urbanisation is one of the greatest threats to freshwater biodiversity, with the area of land covered by towns and cities predicted to increase significantly in the future. Ponds are common features in the urban landscape and have been created for a variety of reasons ranging from ornamental/amenity purposes through to the detention of urban runoff and pollution. This paper aims to quantify the aquatic macroinvertebrate biodiversity associated with garden, ornamental and other urban ponds in Leicestershire, UK. We examined the macroinvertebrate biodiversity of 41 urban ponds (13 garden, 12 park and 16 other urban ponds) within the town of Loughborough, UK. Park ponds supported greater macroinvertebrate richness than garden or other urban ponds. Garden ponds were the most taxon poor. Pond size was strongly correlated with macroinvertebrate diversity. Collectively, urban ponds were found to be physically and biologically heterogeneous and were characterised by high community dissimilarity. Urban ponds provide a diverse range of habitats for a mixture of common and rare aquatic macroinvertebrate taxa and represent a valuable biodiversity resource within anthropogenically dominated landscapes. Recognition of the significant contribution of ponds to urban freshwater biodiversity is important for future aquatic conservation within anthropogenically dominated landscapes.

The distribution of lotic fauna is widely acknowledged to be patchy reflecting the interaction between biotic and abiotic factors. In an in-situ field study, the distribution of benthic and hyporheic invertebrates in the heads (downwelling) and tails (upwelling) of riffles were examined during stable baseflow conditions. Riffle heads were found to contain a greater proportion of interstitial fine sediment than riffle tails. Significant differences in the composition of benthic communities were associated with the amount of fine sediment. Riffle tail habitats supported a greater abundance and diversity of invertebrates sensitive to fine sediment such as EPT taxa. Shredder feeding taxa were more abundant in riffle heads suggesting greater availability of organic matter. In contrast, no significant differences in the hyporheic community were recorded between riffle heads and tails. We hypothesise that clogging of hyporheic interstices with fine sediments may have resulted in the homogenization of the invertebrate community by limiting faunal movement into the hyporheic zone at both the riffle head and tail. The results suggest that vertical hydrological exchange significantly influences the distribution of fine sediment and macroinvertebrate communities at the riffle scale.

Ponds are common and abundant landscape features in temperate environments, particularly on floodplains where lateral connectivity with riverine systems persists. Despite their widespread occurrence and importance to regional diversity, research on the ecology and hydrology of temperate ephemeral and perennial floodplain ponds lags behind that of other shallow waterbodies. This study examines the aquatic macroinvertebrate diversity of 34 ponds (20 perennial and 14 ephemeral) on two unregulated riverine floodplain meadows in Leicestershire, UK. Perennial ponds supported nearly twice the diversity of ephemeral ponds. Despite frequent inundation of floodwater and connectivity with other floodplain waterbodies, ephemeral ponds supported distinct invertebrate communities when compared to perennial ponds. When the relative importance of physical and chemical, biological and spatial characteristics was examined, physical and chemical characteristics were found to account for more variation in community composition than biological or spatial variables. The results suggest that niche characteristics rather than neutral colonisation processes dominate the structure of invertebrate communities of floodplain ponds. The maintenance of pond networks with varying hydroperiod lengths and environmental characteristics should be encouraged as part of conservation management strategies to provide heterogeneous environmental conditions to support and enhance aquatic biodiversity at a landscape scale.

Deposition of fine sediment that fills interstitial spaces in streambed substrates is widely acknowledged to have significant negative effects on macroinvertebrate communities, but the temporal consistency of clogging effects is less well known. In this study the effects of experimentally enhanced fine sediment content on aquatic invertebrates were examined over 126 days in two lowland UK streams. Taxonomic approaches indicated significant differences in macroinvertebrate community structure associated with sediment treatment (clean or sedimented substrates), although the effects were variable on some occasions. The degree of separation between clean and sedimented communities was strong within seven of the nine sampling periods with significant differences in community composition being evident. EPT taxa and taxon characterised as sensitive to fine sediment demonstrated strong responses to enhanced fine sediment loading. Faunal traits also detected the effects of enhanced fine sediment loading but the results were not as consistent or marked. More widely, the study highlights the temporal dynamics of sedimentation effects upon macroinvertebrate communities and the need to consider faunal life histories when examining the effects of fine sediment loading pressures on lotic ecosystems.

Copyright © 2017 John Wiley & Sons, Ltd. Excess fine sediment is a global cause of lotic ecosystem degradation. Despite historic interest in identifying sediment sources and quantifying instream dynamics, tackling fine sediment problems remains a key challenge for river managers and a continued focus of international research. Accordingly, a national meeting of the British Hydrological Society brought together those working on fine sediment issues at the interface of hydrology, geomorphology, and ecology. The resulting collection of papers illustrates the range of research being undertaken in this interdisciplinary research arena, by academic researchers, environmental regulators, landowners, and consultants. More specifically, the contributions highlight key methodological advancements in the identification of fine sediment sources, discuss the complexities surrounding the accurate quantification of riverbed fine sediment content, demonstrate the potential utility of faunal traits as a biological monitoring tool, and recognize the need for improved mechanistic understanding of the functional responses of riverine organisms to excess fine sediment. Understanding and mitigating the effects of fine sediment pressures remains an important and multifaceted problem that requires interdisciplinary collaborative research to deliver novel and robust management tools and sustainable solutions.

Sedimentation and clogging of benthic and hyporheic zone substrata is increasingly being recognised as one of the greatest threats to the ecological integrity of riverine ecosystems globally. This ex situ study examined the influence of sedimentation (surface and subsurface) and pattern of hydrological exchange on the vertical distribution of the freshwater shrimp Gammarus pulex within the experimental substrata of running water mesocosms. Six sediment treatments representing a continuum from a clean gravel substratum to heavy sediment loading of both surface (benthic) and subsurface (hyporheic) substrata were used to examine the distribution of G. pulex in relation to the direction of hydrological exchange (downwelling, upwelling and no exchange). The distribution of G. pulex between the sediment layers was dependent on the pattern of hydrological exchange, sediment treatment and the interaction between these two factors. Sedimentation of the surface layer under no-exchange conditions resulted in a lower proportion of G. pulex being recorded in the benthic sediments, whilst there were no significant differences under downwelling and upwelling flow conditions. Sedimentation of multiple layers of the column (benthic and subsurface) reduced the ability of individuals to utilise the subsurface layers of the substratum (i.e. the hyporheic zone) under no-exchange and upwelling conditions. However, with downwelling conditions, the abundance of G. pulex declined with depth regardless of the fine sediment distribution or volume. This study demonstrates that faunal movement, and use of benthic and hyporheic substrata, may be influenced by sedimentation and modified by the pattern of vertical hydrological exchange. Severe sedimentation (colmation) has the potential to prevent benthic fauna from accessing the hyporheic zone and its resources which may ultimately lead to a reduction in stream diversity and metabolism, thereby limiting overall productivity and lotic ecosystem resilience.

Fine sediment deposition and infiltration into the bed of lotic ecosystems, such as sedimentation, siltation and colmation, has been widely recognised as one of the most important causes of degradation within lotic ecosystems. The impact of increased fine sediment loading as a result of agricultural practices, urban development and channel management activities for flood defence purposes, have been widely acknowledged but poorly quantified. This chapter quantifies the influence of increasing sediment input that is sediment loading on the benthic invertebrate community inhabiting an artificial channel with an impervious concrete bed. This approach provided highly controlled conditions but also reflected channel and habitat characteristics typical of many highly modified and managed urban streams. Significant advances have been made recently in the development of biomonitoring tools which quantify fine sediment impacts on instream communities and which facilitate identification of vulnerable locations within river channels.

Non-native species represent a significant threat to indigenous biodiversity and ecosystem functioning worldwide. It is widely acknowledged that invasive crayfish species may be instrumental in modifying benthic invertebrate community structure, but there is limited knowledge regarding the temporal and spatial extent of these effects within lotic ecosystems. This study investigates the long term changes to benthic macroinvertebrate community composition following the invasion of signal crayfish, Pacifastacus leniusculus, into English rivers. Data from long-term monitoring sites on 7 rivers invaded by crayfish and 7 rivers where signal crayfish were absent throughout the record (control sites) were used to examine how invertebrate community composition and populations of individual taxa changed as a result of invasion. Following the detection of non-native crayfish, significant shifts in invertebrate community composition were observed at invaded sites compared to control sites. This pattern was strongest during autumn months but was also evident during spring surveys. The observed shifts in community composition following invasion were associated with reductions in the occurrence of ubiquitous Hirudinea species (Glossiphonia complanata and Erpobdella octoculata), Gastropoda (Radix spp.), Ephemeroptera (Caenis spp.), and Trichoptera (Hydropsyche spp.); although variations in specific taxa affected were evident between regions and seasons. Changes in community structure were persistent over time with no evidence of recovery, suggesting that crayfish invasions represent significant perturbations leading to permanent changes in benthic communities. The results provide fundamental knowledge regarding non-native crayfish invasions of lotic ecosystems required for the development of future management strategies.