Stream Invertebrates Research Articles

Boulder ramps as a restoration measure: Increasing in the resilience of mountain freshwater ecosystems to environmental changes.

Mountain environments, as biodiversity hotspots, are subject to numerous anthropological pressures. In mountain areas, a common threat to stream biocenoses is the timber industry. Timber industry increases the fine sediment input into the mountain rivers; furthermore, timber transport requires the construction of low-water crossings across streams. Transversal barriers (weirs/fords/pipe culverts) may cause excessive erosion downstream and the accumulation of fine sediments upstream, thereby decreasing habitat heterogeneity. Moreover, mountain stream communities are sensitive to climate change; for e.g., climate change may result in increasing water temperature and decreasing flows. Boulder ramps are considered effective restoration measure for rivers; benthic macroinvertebrate community composition is an effective indicator of stream health. In this study, we selected two mountain streams catchment with forest management. The control was a stream without any objects in the streambed related to timber transport. The other stream contained weirs and pipe culverts. We considered an extensive study period that covered the stages before (2009) and after restoration (2014, 2017-2018, 2019). We present the hypothesis that boulder ramps can restore in-stream habitats, improve biodiversity, and increase the resilience of benthic macroinvertebrate communities to future environmental changes. Our study demonstrates the effectiveness of boulder ramps for mountain streams restoration. We indicated, that the habitat potential of the restored stream-reach for rheophilic and lithophilic invertebrates increased substantially. Moreover, the restored riffles allowed the streambed to be cleared of fine sediments, offering the microrefugia, which were beneficial for mountain stream invertebrates, thereby increasing the diversity and resilience of the benthic communities.

Introduction pages, Nova Geodesia 4(4), 2024

Nova Geodesia (https://novageodesia.ro), Issue 4, Volume 4, 2024: The papers published in this issue represent interesting novelties in different topics of geodetic science or related fields. Nova Geodesia publishes significant papers in geodesy and close topics related to cartography, engineering projects and construction, planetology, hydrography, geography, sociodemographic factors, urban administration, planning and environment, landscape, biodiversity, and ecology. Among the exciting articles, we invite readers to find news about: Evaluating the performance of various models for deriving orthometric heights using Global Navigation Satellite System (GNSS) data; Carbon stocks under different land cover types in the Hallaydeghe wildlife reserve, northeastern Ethiopia; Sorghum (Sorghum bicolor) yield and water use efficiency depending on planting techniques and soil mulching in drought-prone areas, Babile District, Ethiopia; Colour selection in Lantana camara L. blooms: A study on butterfly attraction; Assessment of treatment water effects on macrobenthic invertebrates in an urban stream; Influence of geographical provenance, biostimulatory treatments and their interaction on the seed germination of Quercus robur L.

In Situ Videography Quantifies Temporal and Spatial Variation in Prey Consumption and Energy Intake by Stream‐Dwelling Bull Trout (Salvelinus confluentus)

ABSTRACTIn stream ecosystems, invertebrates are a principal source of prey for many fishes, but their abundance as a food source depends on the predator's ability to exploit them in time and space. Although salmonid fishes are commonly thought of as daytime drift‐feeding predators of invertebrates in streams, they exhibit great flexibility in foraging behaviour and may also consume prey from the benthos and at night. Char species, (Salvelinus sp.), in particular, may be better adapted to forage under low light conditions due to greater scotopic sensitivity than other salmonids. In this study, we used in situ or in place videography to quantify the foraging behaviour of bull trout (Salvelinus confluentus) and determine when and where they capture prey. We found that bull trout were primarily daytime predators of invertebrates drifting in the water column, and that they rarely captured prey from the benthos or foraged at night. We did observe size‐related differences and seasonal declines in foraging rate from summer to fall months. A modelled estimate of energy intake indicates that daytime drift‐feeding by small size classes of bull trout was above that needed for a maximum daily ration under a range of assumptions about prey size and prey retention rates. Energy intake rates for larger fish were more dependent on assumptions of preferred prey size and prey retention rates. Our data indicate that daytime measures of invertebrate drift abundance and size are the most inclusive measure of food abundance for stream‐dwelling bull trout.

Utilizing Insects as Bioindicators: An Approximation for Conservation in Urban Lentic Ecosystems in Central Chile.

This study considered using insect families as bioindicators to establish the health status of an ecosystem of lentic bodies. The water quality in urban lentic bodies in the Metropolitan Region, Chile, was evaluated from aquatic insect family assemblages and physicochemical variables for conserving aquatic life. Evaluations were carried out in parallel at four sampling stations of three water bodies (Batuco Wetland, Carén Lagoon, and Chada Reservoir) in a 2-3-year series, spring (2015, 2017, and 2018) and fall (2016 and 2018), with three replicates. Families were randomly sampled and aquatic insects were identified; abundance and richness differences were compared with non-parametric tests. Physicochemical variables were measured using portable multiparametric and laboratory chemical analyses to determine the water quality. A Canonical Correspondence Analysis was applied for insect families and the physical-chemical variable. In order to categorize the health of these water bodies based on aquatic insect composition and abundance, the Family Biotic Index (FBI), British Biological Monitoring Work Party (BMWP), and Stream Invertebrate Grade Number-Average Level (SIGNAL), adapted for Chile by Figueroa et al. (2007), were calculated. The eudominant insect families were Corixidae and Chironomidae in Batuco, Chironomidae and Corixidae in Carén, and Corixidae in Chada. Baetidae was dominant in Carén and Chada. The water bodies were classified in descending order of water quality by Chilean physicochemical standards: Chada > Carén > Batuco. The TSS (total suspended solids), phosphorus, and electrical conductivity were strongly positively correlated and negatively associated with dissolved oxygen. The TSS level was the most significant influential factor. The BMWP value and the SIGNAL differed from the FBI, but the first was more restrictive, contributing to the conservation of these ecosystems. Based on the nitrogen and phosphorus levels in the water bodies, all of them were eutrophic. Given the ecosystem diversity and complexity, studies should delve deeper into wetlands to establish methods that contribute to determining water quality, using insect families as bioindicators and physicochemical variables.

Spatial and temporal effects of heat waves on the diversity of European stream invertebrate communities

The frequency and magnitude of extreme events, such as heat waves, are predicted to increase with climate change. However, assessments of the response of biological communities to heat waves are often inconclusive. We aimed to assess the responses in abundance, taxonomic and functional diversity indices of stream invertebrate communities to heat waves using long-term monitoring data collected across Europe. We quantified the heat waves' magnitude, analyzed the spatial (i.e., long-term mean) and temporal (anomaly around the long-term mean) components of variation in the magnitude of heat waves, and their interaction with anthropogenic stressors (ecological quality and land cover). For the spatial component of variation, we found a negative association of the community indices to the increasing magnitude of heat waves. Sites undergoing heat waves of higher magnitude showed fewer species and lower trait diversity compared with sites experiencing lower magnitude heat waves. However, we could not detect an immediate temporal response of the communities to heat waves (i.e., the temporal component). Furthermore, we found that the effects of heat waves interacted with the ecological quality of the streams and their surrounding land cover. Diversity declined with increasing heat waves' magnitude in streams with higher ecological quality or surrounded by forest, which may be due to a higher proportion of sensitive species in the community. Heat waves' impacts on diversity were also exacerbated by increasing urban cover. The interaction between heat waves' magnitude and anthropogenic stressors suggests that the effects of extreme events can compromise the recovery of communities. Further, the predicted increase in heat waves will likely have long-term effects on stream invertebrate communities that are currently undetected.

Correction to “Individual and combined impacts of carbon dioxide enrichment, heatwaves, flow velocity variability, and fine sediment deposition on stream invertebrate communities”

Correction to “Individual and combined impacts of carbon dioxide enrichment, heatwaves, flow velocity variability, and fine sediment deposition on stream invertebrate communities”

Microplastics and riverine macroinvertebrate communities in a multiple-stressor context: A mesocosm approach

Growing use of synthetic materials has increased the number of stressors that can degrade freshwater ecosystems. Many of these stressors are relatively new and poorly understood, such as microplastics which are now ubiquitous in freshwater systems. The effects of microplastics on freshwater biota must be investigated further in order to better manage and mitigate their impacts. Our experiment provides the first empirical evaluation of stream invertebrate community dynamics in response to microplastics of different concentrations and sizes, in combination with fine sediment, a pervasive known stressor in running waters. In a 7-week streamside experiment using 64 flow-through circular mesocosms, we investigated the effects of exposure to three simulated microplastic influxes (polyethylene microspheres at four levels between 0 and 28,800 items/event) and the addition of fine sediment (to simulate a polluted stream environment). Invertebrate drift was monitored for 48 h immediately after each microplastic influx, and benthic invertebrate communities were sampled after 28 days of microplastic and sediment manipulations. Microplastic concentration, size and fine sediment all had significant factor main effects on several invertebrate drift response metrics, whereas few microplastic main effects were seen in the benthic community. However, interactive stressor effects were common in different combinations between sediment, microplastic size and concentration, suggesting multiple-stressor relationships between microplastics and fine sediment. Microplastic ingestion was witnessed in four of 12 taxa analysed: Hydrobiosidae, Deleatidium spp., Potamopyrgus antipodarum and Archichauliodes diversus. Our findings provide insights into how microplastics affect drift and benthic community dynamics of stream invertebrates in a field-realistic experimental setting and highlight areas requiring further study. These include investigations of invertebrate drift dynamics in response to other types of microplastics, the role invertebrate size may play in determining their vulnerability to microplastic pollution, and framing more microplastic research in a field-realistic multiple-stressor context.

Macroinvertebrate Community as Bioindicator of Water Quality of Tambis River, Palompon, Leyte, Philippines

Macroinvertebrates have been used globally as bioindicators of water quality of rivers due to their varying tolerance to pollution. The water quality of Tambis River in Palompon, Leyte, Philippines was determined using macroinvertebrates and selected physico-chemical and ecological assessments. Employing kick-sampling method, three sampling stations were established based on the surrounding land use (forested, agricultural, and near residential). Twenty-seven macroinvertebrate families were identified. Permutational multivariate analysis of variance (PERMANOVA) revealed a significant difference in the benthic macroinvertebrate families across three stations (p=0.001). There was a decrease in the abundance of pollution-sensitive families from the forested station towards the downstream, closest to the residential area. Sensitive Ephemerellidae and tolerant Thiaridae were the most abundant in the forested and downstream area respectively. The highest diversity and evenness were observed from the agricultural area. Stream Invertebrate Grade Number - Average Level (SIGNAL 2) scores were plotted declined in all quadrants, suggesting good water quality to moderately polluted. Water temperature, pH, and velocity were the most influencing environmental variables to the macroinvertebrate assemblage as revealed by the Canonical Correspondence Analysis (CCA). Overall, the water quality of Tambis River ranged from being of good quality to moderately polluted. The data obtained in this study could serve as a baseline in providing information to formulate and implement scientific-based regulatory measures towards the conservation of Tambis River.

Long-term climate and hydrologic regimes shape stream invertebrate community responses to a hurricane disturbance.

Disturbances can produce a spectrum of short- and long-term ecological consequences that depend on complex interactions of the characteristics of the event, antecedent environmental conditions, and the intrinsic properties of resistance and resilience of the affected biological system. We used Hurricane Harvey's impact on coastal rivers of Texas to examine the roles of storm-related changes in hydrology and long-term precipitation regime on the response of stream invertebrate communities to hurricane disturbance. We detected declines in richness, diversity and total abundance following the storm, but responses were strongly tied to direct and indirect effects of long-term aridity and short-term changes in stream hydrology. The amount of rainfall a site received drove both flood duration and flood magnitude across sites, but lower annual rainfall amounts (i.e. aridity) increased flood magnitude and decreased flood duration. Across all sites, flood duration was positively related to the time it took for invertebrate communities to return to a long-term baseline and flood magnitude drove larger invertebrate community responses (i.e. changes in diversity and total abundance). However, invertebrate response per unit flood magnitude was lower in sub-humid sites, potentially because of differences in refuge availability or ecological-evolutionary interactions. Interestingly, sub-humid streams had temporary large peaks in invertebrate total abundance and diversity following recovery period that may be indicative of the larger organic matter pulses expected in these systems because of their comparatively well-developed riparian vegetation. Our findings show that hydrology and long-term precipitation regime predictably affected invertebrate community responses and, thus, our work underscores the important influence of local climate to ecosystem sensitivity to disturbances.

Individual and combined impacts of carbon dioxide enrichment, heatwaves, flow velocity variability, and fine sediment deposition on stream invertebrate communities.

Climate change and land-use change are widely altering freshwater ecosystem functioning and there is an urgent need to understand how these broad stressor categories may interact in future. While much research has focused on mean temperature increases, climate change also involves increasing variability of both water temperature and flow regimes and increasing concentrations of atmospheric CO2, all with potential to alter stream invertebrate communities. Deposited fine sediment is a pervasive land-use stressor with widespread impacts on stream invertebrates. Sedimentation may be managed at the catchment scale; thus, uncovering interactions with these three key climate stressors may assist mitigation of future threats. This is the first experiment to investigate the individual and combined effects of enriched CO2, heatwaves, flow velocity variability, and fine sediment on realistic stream invertebrate communities. Using 128 mesocosms simulating small stony-bottomed streams in a 7-week experiment, we manipulated dissolved CO2 (ambient; enriched), fine sediment (no sediment; 300 g dry sediment), temperature (ambient; two 7-day heatwaves), and flow velocity (constant; variable). All treatments changed community composition. CO2 enrichment reduced abundances of Orthocladiinae and Chironominae and increased Copepoda abundance. Variable flow velocity had only positive effects on invertebrate abundances (7 of 13 common taxa and total abundance), in contrast to previous experiments showing negative impacts of reduced velocity. CO2 was implicated in most stressor interactions found, with CO2 × sediment interactions being most common. Communities forming under enriched CO2 conditions in sediment-impacted mesocosms had ~20% fewer total invertebrates than those with either treatment alone. Copepoda abundances doubled in CO2-enriched mesocosms without sediment, whereas no CO2 effect occurred in mesocosms with sediment. Our findings provide new insights into potential future impacts of climate change and land use in running freshwaters, in particular highlighting the potential for elevated CO2 to interact with fine sediment deposition in unpredictable ways.

Two-stage channels can enhance local biodiversity in agricultural landscapes

Field drainage causes habitat loss, alters natural flow regimes, and impairs water quality. Still, drainage ditches often are last remnants of aquatic and wetland habitats in agricultural landscapes and as such, can be important for local biodiversity. Two-stage channels are considered as a greener choice for conventional ditches, as they are constructed to mimic the structure of natural lowland streams providing a channel for drainage water and mechanisms to decrease diffuse loading. Two-stage channels could also benefit local biodiversity and ecosystem functions, but existing information on their ecological benefits is scarce and incomplete. We collected environmental and biological data from six agricultural stream systems in Finland each with consequent sections of a conventional ditch and a two-stage channel to study the potential of two-stage channels to enhance aquatic and riparian biodiversity and ecological functions. Biological data included samples of stream invertebrates, diatoms and plants and riparian beetles and plants. Overall, both section types were highly dominated by few core taxa for most of the studied organism groups. Riparian plant and invertebrate communities seemed to benefit from the two-stage channel structure with adjacent floodplains and drier ditch banks. In addition, two-stage channel sections had higher aquatic plant diversity, algal productivity, and decomposition rate, but lower stream invertebrate and diatom diversity. Two-stage channel construction did not diversify the structure of stream channels which is likely one explanation for the lack of positive effects on benthic diversity. However, both section types harbored unique taxa found only in one of the two types in all studied organism groups resulting in higher local gamma diversity. Thus, two-stage channels enhanced local biodiversity in agricultural landscapes. Improvements especially in aquatic biodiversity might be achieved by increasing the heterogeneity of in-stream habitat structure and with further efforts to decrease nutrient and sediment loads.

Global patterns of allochthony in stream-riparian meta-ecosystems.

Ecosystems that are coupled by reciprocal flows of energy and nutrient subsidies can be viewed as a single "meta-ecosystem." Despite these connections, the reciprocal flow of subsidies is greatly asymmetrical and seasonally pulsed. Here, we synthesize existing literature on stream-riparian meta-ecosystems to quantify global patterns of the amount of subsidy consumption by organisms, known as "allochthony." These resource flows are important since they can comprise a large portion of consumer diets, but can be disrupted by human modification of streams and riparian zones. Despite asymmetrical subsidy flows, we found stream and riparian consumer allochthony to be equivalent. Although both fish and stream invertebrates rely on seasonally pulsed allochthonous resources, we find allochthony varies seasonally only for fish, being nearly three timesgreater during the summer and fall than during the winter and spring. We also find that consumer allochthony varies with feeding traits for aquatic invertebrates, fish, and terrestrial arthropods, but not for terrestrial vertebrates. Finally, we find that allochthony varies by climate for aquatic invertebrates, being nearly twice as great in arid climates than in tropical climates, but not for fish. These findings are critical to understanding the consequences of global change, as ecosystem connections are being increasingly disrupted.

The impacts of within-stream physical structure and riparian buffer strips on semi-aquatic bugs in Southeast Asian oil palm

Despite the diverse ecosystem services that forested stream margins (“riparian buffer strips”) can provide in agricultural landscapes, understanding of their biodiversity impacts in the tropics is lacking. Stream invertebrates support many ecosystem functions and several groups are valuable bioindicators of environmental conditions. Semi-aquatic bugs (insects in Hemiptera that inhabit the water surface) are important within the aquatic food chain, acting as predators of other invertebrates and prey for larger animals. Since they inhabit the water surface, semi-aquatic bugs are potentially valuable indicators of within-stream health. Focusing on the impacts of conditions at the small-scale, we investigated how within-stream physical structure and the presence of riparian buffer strips affected the abundance, total biomass, richness, and community composition of semi-aquatic bugs in oil palm plantations in Sabah, Malaysia. We also assessed the effects on the proportion of juveniles and females of Ptilomera sp. (a common genus). Our focus on the small-scale make findings applicable for management both within smallholder and large-scale plantations. At the small-scale (10-m transect), oil palms streams with riparian buffers contained twice as many semi-aquatic bugs as those without (average richness in streams with buffers 3.55 (SE ± 0.42) compared to 1.40 (SE ± 0.22) in streams without). We found a total of 14 morphospecies in streams with buffers, compared to just seven in those without. There was no difference in total biomass or the proportion of female Ptilomera sp. in streams with or without buffers. There was a significantly higher abundance of semi-aquatic bugs in streams with wider wetted width, more isolated pools, shallower slopes, and lower percentage of deadwood. The proportion of juveniles was higher in streams with higher canopy openness, higher percentage of deadwood, lower percentage of pebbles, and narrower wetted widths. This study demonstrates that small-scale differences in stream conditions within oil palm can influence semi-aquatic bugs, opening up the possibility that oil palm management could be tailored to improve environmental conditions for stream communities. As our findings are based on only a few streams and at measurements collected at a single time-point, more studies are needed to validate what we have found.

Trout and invertebrate assemblages in stream pools through wildfire and drought

Abstract Climate change is increasing the frequency, severity, and extent of wildfires and drought in many parts of the world, with numerous repercussions for the physical, chemical, and biological characteristics of streams. However, information on how these perturbations affect top predators and their impacts on lower trophic levels in streams is limited. The top aquatic predator in southern California streams is native Oncorhynchus mykiss, the endangered southern California steelhead trout (trout). To examine relationships among the distribution of trout, environmental factors, and stream invertebrate resources and assemblages, we sampled pools in 25 stream reaches that differed in the presence (nine reaches) or absence (16 reaches) of trout over 12 years, including eight reaches where trout were extirpated during the study period by drought or post‐fire flood disturbances. Trout were present in deep pools with high water and habitat quality. Invertebrate communities in trout pools were dominated by a variety of medium‐sized collector–gatherer and shredder invertebrate taxa with non‐seasonal life cycles, whereas tadpoles and large, predatory invertebrates (Odonata, Coleoptera, Hemiptera [OCH]), often with atmospheric breather traits, were more abundant in troutless than trout pools. Structural equation modelling of the algal‐based food web indicated a trophic cascade from trout to predatory invertebrates to collector–gatherer taxa and weaker direct negative trout effects on grazers; however, both grazers and collector–gatherers also were positively related to macroalgal biomass. Structural equation modelling also suggested that bottom‐up interactions and abiotic factors drove the detritus‐based food web, with shredder abundance being positively related to leaf litter (coarse particulate organic matter) levels, which, in turn, were positively related to canopy cover and negatively related to flow. These results emphasise the context dependency of trout effects on prey communities and of the relative importance of top‐down versus bottom‐up interactions on food webs, contingent on environmental conditions (flow, light, nutrients, disturbances) and the abundances and traits of component taxa. Invertebrate assemblage structure changed from a trout to a troutless configuration within a year or two after trout were lost owing to post‐fire scouring flows or drought. Increases in OCH abundance after trout were lost were much more variable after drought than after fire. The reappearance of trout in one stream resulted in quick, severe reductions in OCH abundance. These results indicate that climate‐change induced disturbances can result in the extirpation of a top predator, with cascading repercussions for stream communities and food webs. This study also emphasises the importance of preserving or restoring refuge habitats, such as deep, shaded, perennial, cool stream pools with high habitat and water quality, to prevent the extirpation of sensitive species and preserve native biodiversity during a time of climate change.

Temporal partitioning of Chironomidae emergence in an insular, tropical rainforest stream

Annual water temperature variation strongly influences larval growth of aquatic insects in streams located in temperate regions or at high elevations, which produces cohorts with highly synchronized emergence periods and short average annual durations of emergence. Studies of Chironomidae in tropical streams indicate that species in these habitats have longer average durations of emergence due to reduced annual variation in water temperature. We used emergence trap data collected over one year from Quebrada Prieta (El Verde Field Station, Puerto Rico) to test the prediction that chironomids of an insular rainforest stream should have longer average annual durations of emergence than chironomids in both temperate streams and mainland streams in continental tropical regions. Taxa richness was relatively low with twenty-eight Chironomidae taxa collected from Quebrada Prieta. Emergence patterns of the most common taxa demonstrated some seasonally with the highest emergence generally occurring during the dry season (January through April). The estimated average emergence duration of Chironomidae in Quebrada Prieta was 205 days/species/year, which was greater than estimates of average durations for chironomids of three streams in Pennsylvania, USA (70 days/species/year), 6 streams in Minnesota, USA (89 days/species/year), and four streams in Guanacaste National Park in northwestern Costa Rica (116 days/species/year). The emergence duration for the chironomid community in Quebrada Prieta was most similar to another tropical, mountain stream in the Democratic Republic of the Congo (255 days/species/year). Although many taxa emerged throughout the one-year sampling period, some taxa in Quebrada Prieta had distinct emergence peaks. This demonstrates that although environmental conditions are stable enough to allow for emergence throughout the year for many species, there is some seasonality in the development of chironomid taxa in this tropical stream. These results are consistent with predictions that invertebrates in tropical streams will have longer, less synchronous emergence periods than species in temperate regions with high annual fluctuations in temperature. However, this research is also similar to several other studies that have identified seasonal emergence peaks in tropical chironomids which demonstrates a need to better understand the exogenous cues that affect these patterns.

A bold new purpose for an old method: Using invertebrate kick‐netting to improve monitoring of microplastic pollution in running waters

AbstractFreshwaters are impacted by many pollutants. Scientists and resource managers need to reliably detect and monitor these pollutants by employing appropriate sampling techniques to quantify and mitigate their impacts. Emerging freshwater contaminants such as microplastics are difficult to monitor as effective sampling techniques have not been fully developed and lack standardization. Here, we propose a novel method, adapted from stream invertebrate kick‐net sampling, which can be employed for long‐term, standardized microplastic monitoring. We hypothesized that invertebrate kick‐net sampling would be effective at collecting microplastics, capturing higher microplastic concentrations than standard microplastic sampling, due to collecting suspended and benthic microplastics simultaneously. We sampled 28 streams for microplastics using standard drift and sediment microplastic collection methods and invertebrate kick‐netting. As predicted, kick‐netting captured microplastics at higher concentrations than conventional sampling, regardless of whether values were expressed per volume of water (as in drift samples), per kg of sediment or per area sampled (as in benthic samples). Consequently, kick‐net sampling has the potential to be a time‐ and cost‐efficient tool for monitoring microplastic pollution. We recommend the employment of invertebrate kick‐netting as a new, standardized means to investigate and routinely monitor microplastic concentrations worldwide. This would generate a more robust dataset of global freshwater microplastic pollution, making it possible to answer unresolved questions pertaining to changes in microplastic pollution profiles. Standardized, long‐term records of microplastic concentrations in freshwaters would also allow a more accurate assessment of the ecological risks of microplastic pollution. Finally, long‐term microplastic data could be used to inform much‐needed regulatory decisions pertaining to microplastic pollution.

Climatic effects on the synchrony and stability of temperate headwater invertebrates over four decades.

Important clues about the ecological effects of climate change can arise from understanding the influence of other Earth-system processes on ecosystem dynamics but few studies span the inter-decadal timescales required. We, therefore, examined how variation in annual weather patterns associated with the North Atlantic Oscillation (NAO) over four decades was linked to synchrony and stability in a metacommunity of stream invertebrates across multiple, contrasting headwaters in central Wales (UK). Prolonged warmer and wetter conditions during positive NAO winters appeared to synchronize variations in population and community composition among and within streams thereby reducing stability across levels of ecological organization. This climatically mediated synchronization occurred in all streams irrespective of acid-base status and land use, but was weaker where invertebrate communities were more functionally diverse. Wavelet linear models indicated that variation in the NAO explained up to 50% of overall synchrony in species abundances at a timescale of 4-6 years. The NAO appeared to affect ecological dynamics through local variations in temperature, precipitation and discharge, but increasing hydrochemical variability within sites during wetter winters might have contributed. Our findings illustrate how large-scale climatic fluctuations generated over the North Atlantic can affect population persistence and dynamics in inland freshwater ecosystems in ways that transcend local catchment character. Protecting and restoring functional diversity in stream communities might increase their stability against warmer, wetter conditions that are analogues of ongoing climate change. Catchment management could also dampen impacts and provide options for climate change adaptation.

Effects of altered streamflow on macroinvertebrate taxonomic richness and composition in the Goulburn River, Australia

River systems have been stressed by the construction of dams and regulation structures which influence aquatic ecosystem integrity. Previous studies considered the general significance of regional streamflow regimes for aquatic communities, but they did not investigate the influence of specific components of flow regimes on aquatic ecosystems under the combined impact of regulation and extreme drought events, limiting our ability to design and implement precise environmental flow management strategies. This study aims to quantify the relationship between macroinvertebrate biotic indices and ecologically important streamflow characteristics derived from five natural flow regime components by investigating the spatiotemporal variation in the macroinvertebrate assemblage in regulated and unregulated reaches and identifying specific flow indices that have a direct impact on macroinvertebrates in the Goulburn basin in Victoria, Australia during the Millennium Drought period. The relationship between dominant flow metrics and macroinvertebrates indices was investigated using boosted regression trees (BRT). The results revealed a significant difference in hydrological variability between regulated and unregulated reaches. The regulated reaches demonstrated reduced hydrological variability during low flow periods, and rapid increase in discharge during high flow periods when compared to unregulated reach. Unregulated reach had 38% more taxa richness than regulated reach impacted by hydropeaking. Eight indicator taxa were identified in the unregulated reach, and they exhibited a higher Stream Invertebrate Grade Number Average Level (SIGNAL 2) score, indicating that they were highly sensitive species. The maximum flow in June was the most important flow parameter that influences the macroinvertebrate indices as per the BRT model. Better management of environmental flows will benefit from identifying which aspects of the natural flow regime impact stream ecosystems and predicting the consequences of altered flow regimes on aquatic ecosystems.

Short-term insecticide exposure amid co-occurring stressors reduces diversity and densities in north-east Indian experimental aquatic invertebrate communities

Globally, river pesticide concentrations are associated with regional and local stream invertebrate diversity declines. Pesticides often co-occur with elevated nutrients (e.g. nitrogen and phosphorus) and sediments related to agriculture, making their individual effects difficult to disentangle. These effects are also less well studied in Asia, than in other geographic regions. Within Asia, India is one of the largest producers and users of pesticides and has approximately 60% of total land mass used for agriculture. Here we examine the responses of Indian river invertebrate communities subjected to malathion, nutrients, and sediment additions in a semi-orthogonal design, in three sequential (through time) short-term (120 h) mesocosm experiments. Additionally, a series of single-species toxicity tests were run that used 24 h exposure and 72 h recovery to examine the sensitivity of 13 local invertebrate taxa to malathion, and 9 taxa to cypermethrin, comparing these results to those from other biogeographic regions. Mesocosm results indicate that malathion exposure had a major effect compared to other stressors on communities, with a lesser effect of nutrients and/or sediments. In mesocosms, taxa richness, total abundance and the abundance of sensitive species all declined associated with malathion concentrations. Comparisons of organism sensitivities from other geographic locations and those in the current paper suggest taxa in India are relatively tolerant to malathion and cypermethrin. Our results further reinforce that the high observed aquatic pesticide concentrations known to occur in Asian freshwater ecosystems are likely to be negatively affecting biodiversity, homogenising biota towards those most stress tolerant.

Slow recovery of stream invertebrates on subantarctic Macquarie Island after eradication of introduced rabbits and regrowth of vegetation

Context Streams on subantarctic Macquarie Island were first sampled for freshwater invertebrates in 1992 when rabbit numbers were low. Then an average 11.6 taxa per site were recorded. Between 2000 and 2011, vegetation was overgrazed as rabbit numbers increased. In 2008 and 2010, 7.4–8.4 taxa per site were recorded, abundance of most taxa had decreased and greatest compositional changes occurred at sites exposed to moderate or severe vegetation damage. Rabbits were eradicated in 2011 and substantial regrowth of vegetation was evident by 2016. Aims Sites were resampled in 2016 to determine the extent to which the invertebrate communities had changed after rabbit removal. Methods In all, 13 of the original 15 sites sampled in 1992 were resampled. Five kick samples were taken at each site. Key results Mean taxon richness (8.2 taxa per site) and community composition at individual sites remained, in 2016, very similar to that recorded in 2008 and 2010 when the island was heavily grazed. Conclusions Recovery of stream invertebrate communities appeared to be slow, possibly because few refuges were available. Minor changes in climate and water quality did not influence recovery. Implications Stream invertebrate communities could take a decade or more to recover.