Benthic Invertebrate Communities Research Articles

The impact of microplastics on lake communities: A mesocosm study

Plastics are pervasive pollutants that are being produced at an increasing rate to meet consumer demands. After entering the environment, plastics can break down, creating smaller fragments, including secondary microplastics. Microplastic contamination in lakes has been recorded worldwide, and the ingestion of microplastics has been documented in zooplankton, macroinvertebrates, and fish. Microplastic ingestion and exposure can cause varying deleterious effects on these organism groups, but the impact of realistic microplastic concentrations on whole freshwater food webs requires further study. We addressed these knowledge gaps by conducting an 8-week experiment factorially crossing microplastic addition at a concentration of 1.5 particles/L with a fish predator (perch, Perca fluviatilus) presence in 1200-L outdoor mesocosms. Microplastic exposure had time-varying effects on zooplankton abundance, with a lower abundance of zooplankton in plastic treatments at the end of the experiment. Although microplastics had no impact on total macroinvertebrate abundance, there were effects on individual taxa. In the presence of microplastics, the cased caddisfly Triplectides spp. had a significantly lower abundance, which may have led to an increase in the snail Gyraulus spp. in week eight. Across the benthic and pelagic invertebrate communities, there were near-significant compositional differences between control and plastic treatments. These findings indicate that microplastic exposure may negatively impact freshwater invertebrate communities, even at low, field-realistic concentrations representative of the densities currently found in lakes.

Зообентос и зоопланктон малых рек бассейна реки Кобры (национальный парк «Койгородский»)

The studies were carried out on two small rivers – tributaries of the Kobra River (the Volga River basin), located on the territory of Koygorodsky National Park. The structure, quantitative development of zoobenthos and fauna of benthic invertebrates were studied. Hydrobiological sampling was carried out in June – July 2021. Standard methods were used for sampling. 87 species and taxa of a higher rank of invertebrates were found in the benthic fauna. The most diverse were caddisflies (21), mayflies (21), stoneflies (13) and oligochaetes (12 species). Quantitative development of the zoobenthos of the Kobra River basin is comparable to the average for the rivers of the Vyatka River basin as a whole and was 19 thous. ind./m2 and 74.6 g/m2 in the Suran River, and 14.1 thous. ind./m2 and 19.2 g/m2 in the Mytets River. The chironomids played a leading role in benthic invertebrate communities, and accounted for an average of 26.3–33.4% of the total zoobenthos abundance. Mayfly larvae and leeches dominated in the Suran River by biomass, as well as molluscs and caddisflies – in the Mytets River. The maximum quantitative characteristics were noted on the reaches of both rivers. The development of benthos was much poorer on the riffles. Three rare species from the orders of mayflies, stoneflies and dragonflies were identified. Zooplankton in the small tributaries of the Kobra River was studied using standard methods: in the Suran River on the early June and in the Mytets River – on the end of the July 2021. Plankton fauna was represented by 28 taxa, rotifers and copepods prevailed. Plankton species diversity, abundance and biomass were lower in the Suran River (the beginning of the vegetation season), which indicated the processes of zooplankton formation. The above indicators were higher in the middle of the summer season in the Mytets River, and indicated the stability of plankton communities. The presented data significantly expand the understanding of the biodiversity of aquatic ecosystems in the southern taiga zone.

Characteristics of the fish food supply of the Uglich reservoir

The work on assessing the feed base of the Uglich Reservoir was carried out within the framework of annual monitoring studies by the Branch for Freshwater Fisheries of the Federal State Budgetary Scientific Institution “VNIRO” (VNIIPRH). Samples were taken in July 2021 and 2022 on three sections. During the year, 10 samples of zooplankton and benthic invertebrate communities were collected and processed. The purpose of the study is to evaluate the fish food supply of the Uglich Reservoir according to the indicators of zooplankton and benthic invertebrate communities in the period 2021–2022. The tasks of the study: to determine the number and biomass of zooplankton of the Uglich Reservoir in 2021–2022; to determine the number and biomass of benthic invertebrate communities of the Uglich Reservoir in 2021–2022. The Uglich Reservoir belongs to the Upper Volga cascade of hydro nodes. Located in the territory of two regions and having a length of more than a hundred kilometers, it has differences in water temperature and oxygen content in the water by reaches. Oxygen conditions in 2021 in the bottom layers, and in 2022 — both in the surface and in the bottom horizons, were unfavorable: deviations from the water quality standard were observed. The studies showed that the productivity of the Uglich Reservoir also varies by reaches. The maximum indicators of zooplankton development were observed in the channel part of the Upper reach of the reservoir. During the observation period (with incomplete determination), 21 taxa of planktonic organisms were recorded, including: Rotifera — 5, Cladocera — 12, Copepoda — 3 and Bivalvia — 1 species. In the composition of the plankton fauna, Cladocera dominated in number and biomass. The benthic invertebrate communities of the Uglich Reservoir is mainly represented by oligochaetes, chironomid larvae and bivalve molluscs. By the magnitude of the summer biomass of zooplankton and benthic invertebrate communities, in accordance with the generally accepted classification of Pidgayko (1968), the Uglich Reservoir in 2021 can be assessed as a high-feed reservoir, and in 2022 — as a medium-feed reservoir.

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.

Factors of macrozoobenthos formation in low-mountain lakes of the Russian Altai

The current state of macrozoobenthos of six low-mountain lakes of the Russian Altai was studied in different hydrological seasons (May, July, September) 2022: Aya (Aiskoe), Beloe, Kireevo, Kolyvanskoe, Koksha, and Svetloe. The aim of the article is to study the factors of formation of benthic invertebrate communities of foothill lakes of the Russian Altai. In total 156 species from 9 classes of invertebrates were identified in the zoobenthos of the studied lakes, the highest percentage of occurrence was recorded for chironomids and oligochaetes. According to the taxonomic composition of macrozoobenthos, most of the studied lakes of the Russian Altai (Aya, Beloe, Kireevo and Kolyvanskoe) were close to flatland lakes. Two lakes (Koksha and Svetloe) combined characteristics of both flatland and highland lakes. The abundance and biomass of zoobenthos in lakes Aya and Kireevo corresponded to the oligotrophic level, in lakes Beloe and Kolyvanskoe to the mesotrophic level, and in lakes Koksha and Svetloye to the eutrophic level. The structural characteristics of macroinvertebrates are indicators of the state of lake ecosystems. Therefore, in order to maintain the health of lake ecosystems, it is important to determine the limiting factors for macroinvertebrate community composition and structure. The influence of environmental factors on the composition and structure of macrozoobenthos of foothill lakes of the Russian Altai was studied. The relationship of 10 main indicators of zoobenthos structure with 30 hydro physical and hydrochemical indicators was analyzed. Using principal component analysis, multiple regression method, correlation and canonical analyses, it was revealed that the greatest influence on the development of benthic invertebrate communities in the studied lakes of the Russian Altai was exerted by nutrients, permanganate oxidability and soil character and water temperature.

Risk Perception: Chemical Stimuli in Predator Detection and Feeding Behaviour of the Invasive Round Goby Neogobius melanostomus.

The round goby Neogobius melanostomus is a notoriously invasive fish originating from the Ponto-Caspian region that in recent decades has successfully spread across the globe. One of its primary impacts is direct predation; in addition, when entering new ecosystems, the round goby is likely to become a food resource for many higher native predators. However, little is known either about the indirect effects of predators on the round goby as prey or its feeding behaviour and activity. The non-consumptive effect of the presence of higher native predators presumably plays an important role in mitigating the impact of non-native round gobies as mesopredators on benthic invertebrate communities, especially when both higher- and mesopredators occupy the same habitat. We tested the food consumption probability and gut evacuation rates in round gobies in response to chemical signals from a higher predator, the European eel Anguilla anguilla. Gobies were placed individually in experimental arenas equipped with shelters and exposed to water from a tank in which (a) the higher predator had actively preyed on a heterospecific prey, earthworms Lumbricus sp. (the heterospecific treatment; HS); (b) the higher predator had fed on round gobies (the conspecific treatment; CS); or (c) the water was provided as a control treatment (C). To ensure exposure to the chemical stimuli, this study incorporated the application of skin extracts containing damaged-released alarm cues from the CS treatment; distilled water was used for the remaining treatments. No significant differences were observed in either the food consumption probability or gut evacuation rate in the tested treatments. Despite the lack of reaction to the chemical stimuli, round gobies did exhibit high evacuation rates (R = 0.2323 ± 0.011 h-1; mean ± SE) in which complete gut clearance occurred within 16 h regardless of the applied treatment. This rapid food processing suggests high efficiency and great pressure on resources regardless of the presence or not of a higher predator. These findings hint at the boldness of round gobies, which did not exhibit any pronounced threat sensitivity. This would seem to suggest great efficiency in food processing and a potential competitive advantage over local native species when colonising new ecosystems, irrespective of the presence of native predators. Our study did not detect any non-consumptive effect attributable to the higher predator, given that the feeding activity of the invasive round goby was not altered.

Invertebrate diversity in groundwater-filled lava caves is influenced by both neutral- and niche-based processes.

Understanding which factors shape and maintain biodiversity is essential to understand how ecosystems respond to crises. Biodiversity observed in ecological communities is a result of the interaction of various factors which can be classified as either neutral- or niche-based. The importance of these processes has been debated, but many scientists believe that both processes are important. Here, we use unique ecosystems in groundwater-filled lava caves near Lake Mývatn, to examine the importance of neutral- versus niche-based factors for shaping invertebrate communities. We studied diversity in benthic and epibenthic invertebrate communities and related them to ecological variables. We hypothesized that if neutral processes are the main drivers of community structure we would not see any clear relationship between the structure of community within caves and ecological factors. If niche-based processes are important we should see clear relationships between community structure and variation in ecological variables across caves. Both communities were species poor, with low densities of invertebrates, showing the resource limited and oligotrophic nature of these systems. Unusually for Icelandic freshwater ecosystems, the benthic communities were not dominated by Chironomidae (Diptera) larvae, but rather by crustaceans, mainly Cladocera. The epibenthic communities were not shaped by environmental variables, suggesting that they may have been structured primarily by neutral processes. The benthic communities were shaped by the availability of energy, and to some extent pH, suggesting that niche-based processes were important drivers of community structure, although neutral processes may still be relevant. The results suggest that both processes are important for invertebrate communities in freshwater, and research should focus on understanding both of these processes. The ponds we studied are representative of a number of freshwater ecosystems that are extremely vulnerable for human disturbance, making it even more important to understand how their biodiversity is shaped and maintained.

Ecological impact of heavy metal pollution on Limnodrilus cervix -abundance, bioaccumulation, and environmental dynamics in a perennial pond of Jammu, India

This study examines the ecological ramifications of heavy metal contamination on benthic invertebrate communities, with a focus on Limnodrilus cervix, in a perennial pond situated in the Raipur region of Jammu, India. The study identified 11,587 individuals of Limnodrilus cervix, showing seasonal variations in abundance. Through a multidisciplinary approach encompassing taxonomic analysis, heavy metal quantification, acute toxicity testing, and bioaccumulation assessments, the research explores the intricate dynamics between pollution and aquatic ecosystems. Findings reveal pronounced seasonal fluctuations in L. cervix populations, with copper emerging as the predominant metal. Acute toxicity tests underscore dose-dependent lead (Pb) toxicity with an LC50 value of 0.03 mg/L, while bioaccumulation experiments elucidate Pb absorption in worm tissue with a bioconcentration factor (BCF) of 0.4 at 0.005 mg/L and 0.7 at 0.01 mg/L. The study underscores the urgent need for informed management strategies to mitigate the ecological risks posed by heavy metal pollution and safeguard freshwater habitats and their inhabitants.

Ecosystem functioning during biodiversity loss and recovery

Anthropogenic biodiversity loss can impair ecosystem functioning. Human activities are often managed with the aim of reversing biodiversity loss and its associated functional impacts. However, it is currently unknown whether biodiversity–ecosystem function (BEF) relationships observed during biodiversity recovery are the same as those observed during biodiversity loss. This will depend on how species extirpation and recolonisation sequences compare and how different species influence ecosystem functioning. Using data from a marine benthic invertebrate community, we modelled how bioturbation potential – a proxy for benthic ecosystem functioning – changes along biodiversity loss and recovery sequences governed by species' sensitivity to physical disturbance and recolonisation capability, respectively. BEF relationships for biodiversity loss and recovery were largely the same despite species extirpation and recolonisation sequences being different. This held true irrespective of whether populations were assumed to exhibit compensatory responses as species were removed or added. These findings suggest that the functional consequences of local biodiversity loss can be reversed by alleviating its drivers, as different species present at comparable levels of species richness during biodiversity loss and recovery phases have similar functional effects. Empirically verifying and determining the generality of our model‐based results are potential next steps for future research.

Benthic macroinvertebrate response to estuarine emergent marsh restoration across a delta-wide environmental gradient

Benthic invertebrates play vital roles in estuarine ecosystems, but like other taxa they have been excluded from former marshlands by diking and land use conversion. Dike removal is one way of restoring marsh, but the response of benthic invertebrates has been little studied. Also understudied is variation in benthic invertebrate communities across entire deltas, particularly in the Pacific Northwest of North America where deltas receive high flows and sediment loads for their size. Our goals were to evaluate invertebrate response to large-scale dike removal on the Nisqually River Delta in Puget Sound, Washington, U.S.A., characterize delta-wide invertebrate community variation, and relate invertebrate response and spatial variation to environmental conditions. We sampled invertebrates annually from one year before to three years after dike removal in restoring marsh, previously restored marsh, undisturbed reference marsh, and adjacent tidal flats. Marine taxa immediately colonized the area recently restored to tidal inundation and population size grew exponentially thereafter for several of them. Community composition and diversity recovered completely, and density and biomass were approaching recovery three years later. Invertebrate communities converged between restoring and pre-existing marsh (previously restored and reference), suggesting an influence of reestablished connectivity. Just offshore from the dike line, invertebrates declined one year after dike removal but then rebounded indicating resilience to short-term disturbance. Dike removal effects were not detected farther offshore. Near the offshore edge of the delta, invertebrate biomass and body size were greater than elsewhere and a diverse assemblage of crustaceans, polychaetes, and bivalves was present. Farther inshore, tidal flats were dominated by a few species of small-bodied polychaetes and had higher density but lower biomass and diversity. Facultative detritivores, which can also filter feed, were the dominant feeding guild everywhere on the tidal flats. Density, biomass, diversity, and community composition on the marsh were more similar to the inner than outer tidal flats. Environmental variables most associated with invertebrate community variation were elevation, salinity, and sediment grain size and organic content. Our results are relevant to assessing performance and setting expectations for future restorations and have broad implications for the role of benthic invertebrates in estuarine ecosystems.

Long‐term environmental flows restore benthic invertebrate communities in a highly regulated river

The construction of dams and other in‐stream structures for human use has altered river ecosystems worldwide. Dams degrade rivers, and environmental flow releases aim to mitigate flow alterations and restore rivers downstream of dams by returning elements of the pre‐regulation flow regime, resulting in an ecosystem that resembles a more natural state. We examined the responses of benthic invertebrate communities in riffles and pool‐edge habitats to an environmental flow regime (EFR) in the highly regulated Snowy River over 17 years (2000–2016). Benthic invertebrate communities significantly changed in response to prolonged increases in the magnitude of all components of the flow regime. The composition of the benthos in the regulated river became more dissimilar to pre‐EFR communities and more closely resembled those of nearby unregulated rivers. These changes were apparent in both riffle and pool‐edge habitats and were most pronounced when flow magnitudes were highest. Scrapers increased as flows increased, and in contrast, the relative abundances of gatherers declined with prolonged high flows and could be attributed to increased daily flows and high flow events mobilizing fine sediment and scouring benthic substrates. These results indicated that the EFR altered abiotic conditions or resources that previously limited invertebrate abundances, facilitating changes to the benthic community. Community changes we observed were in response to a flow regime that remained drastically lower than natural, demonstrating that restoration targets can be achieved with small flow increases that mimic natural flow patterns.

Impact of artificial barriers on benthic macroinvertebrate functional diversity in estuarine ecosystems

AbstractFunctional diversity research enhances our understanding of ecosystems and both their functioning and their responses to environmental variations. This study investigated the biological trait responses of benthic invertebrate communities to various environmental conditions in estuarine habitats. We analyzed benthic macroinvertebrate communities in freshwater and estuarine environments to compare their characteristics between estuary sites with and without artificial barriers. Moreover, we combined taxonomic analyses (species richness, abundance, and four community indices) with functional diversity indices and biological trait analyses. The major results are as follows: (i) the most important environmental factors shaping species distribution in estuarine habitats were salinity and electrical conductivity; (ii) comparing functional diversity indices, tidal estuaries revealed that seawater intrusion induced changes in species distribution and the dispersion of benthic macroinvertebrates; (iii) the presence or absence of artificial barriers in estuaries affected biological traits owing to the influence of specific functional strategies of certain species. Consequently, the presence or absence of artificial barriers in estuaries can lead to significant changes in habitat connectivity and functional diversity related to ecosystem functions. These findings indicate that the presence of artificial barriers can significantly influence the ecological dynamics of estuarine ecosystems, thereby affecting species distribution, functional diversity and habitat connectivity. Understanding these effects contributes to a more comprehensive understanding of ecosystem functionings, as it complements existing taxonomic findings and integrates information about the functional aspects of diverse ecosystems.

How tolerances, competition and dispersal shape benthic invertebrate colonisation in restored urban streams

Biotic communities often respond poorly to river restoration activities and the drivers of community recovery after restoration are not fully understood. According to the Asymmetric Response Concept (ARC), dispersal capacity, species tolerances to stressors, and biotic interactions are three key drivers influencing community recovery of restored streams. However, the ARC remains to be tested. Here we used a dataset on benthic invertebrate communities of eleven restored stream sections in a former open sewer system that were sampled yearly over a period of eleven years. We applied four indices that reflect tolerance against chloride and organic pollution, the community's dispersal capacity and strength of competition to the benthic invertebrate taxa lists of each year and site. Subsequently, we used generalised linear mixed models to analyse the change of these indices over time since restoration. Dispersal capacity was high directly after restoration but continuously decreased over time. The initial communities thus consisted of good dispersers and were later joined by more slowly dispersing taxa. The tolerance to organic pollution also decreased over time, reflecting continuous improvement of water quality and an associated increase of sensitive species. On the contrary, chloride tolerances did not change, which could indicate a stable chloride level throughout the sampling period. Lastly, competition within the communities, reflected by interspecific trait niche overlap, increased with time since restoration. We show that recovery follows a specific pattern that is comparable between sites. Benthic communities change from tolerant, fast dispersing generalists to more sensitive, slowly dispersing specialists exposed to stronger competition. Our results lay support to the ARC (increasing role of competition, decreasing role of dispersal) but also underline that certain tolerances may still shape communities a decade after restoration. Disentangling the drivers of macroinvertebrate colonisation can help managers to better understand recovery trajectories and to define more realistic restoration targets.

Local factors drive the richness, biomass and composition of benthic invertebrate communities in Neotropical reservoirs

Local factors drive the richness, biomass and composition of benthic invertebrate communities in Neotropical reservoirs

Functional Traits Drive the Changes in Diversity and Composition of Benthic Invertebrate Communities in Response to Hydrological Regulation

Of all the environmental elements that influence the biological communities of rivers, water flow characteristics are undoubtedly the most important. Unfortunately, natural hydrological characteristics are increasingly threatened by human activities, especially in alpine or high mountain areas where there are numerous hydropower plants. In this study, we analysed the impact of hydrological alterations on the macroinvertebrate community of a lowland river in NW Italy. Specifically, we analysed the macroinvertebrate communities of an unaffected site by comparing them with those of a site subject to hydrological alteration. We adopted an approach that is not only taxonomic but also functional, allowing us to study a component of biodiversity that is generally less known. Our results show that the flow-altered site hosted a benthic community with lower species and functional diversity than the control site. Interestingly, we also detected a number of significant differences between the summer and autumn samples. In particular, examination of community-weighted mean (CWM) trait values reveals significant variation in body size, voltinism, substrate, locomotion, feeding habits and other traits between sites and seasons. The integration of taxonomic and functional approaches provides a comprehensive understanding of how human-induced hydrological variations can affect aquatic biodiversity and ecological functions.

Full year seasonality of benthos in the nearshore of Lake Superior

Relatively little is known about the full-year dynamics of benthic invertebrates in seasonally-freezing lakes. In this study, we describe the seasonal variability in benthic invertebrate abundance and coarse-level taxonomic composition across five nearshore locations in Lake Superior, with a focus on the winter period. We found that benthos abundances were relatively stable across the year, with similar winter (2294 ± 987 SD ind. m−2) and summer densities (2710 ± 1445 SD ind. m−2) across all stations. Community composition was also relatively stable across the year at our study stations, with Hexagenia sp., chironomids, and oligochaetes dominating our shallowest station (Duluth Harbor) and oligochaetes, Diporeia sp., and clams (Sphaeriidae) dominating deeper locations. Across all stations, diversity was similar across seasons, with the highest number of taxa observed in the fall (5.4 ± 1.8) and lowest number in the summer (4.5 ± 1.4). We found that the winter-spring period was an important time for the reproduction of the Lake Superior keystone amphipod Diporeia sp. Finally, we show that community structure was more variable across sites than across seasons. This is one of very few studies of winter benthos in the Great Lakes and suggests that benthic invertebrate communities show muted seasonal variability compared to planktonic organisms.

Parallels of quantum superposition in ecological models: from counterintuitive patterns to eco-evolutionary interpretations of cryptic species

BackgroundSuperposition, i.e. the ability of a particle (electron, photon) to occur in different states or positions simultaneously, is a hallmark in the subatomic world of quantum mechanics. Although counterintuitive at first sight, the quantum world has potential to inform macro-systems of people and nature. Using time series and spatial analysis of bird, phytoplankton and benthic invertebrate communities, this paper shows that superposition can occur analogously in redundancy analysis (RDA) frequently used by ecologists.ResultsWe show that within individual ecosystems single species can be associated simultaneously with different orthogonal axes in RDA models, which suggests that they operate in more than one niche spaces. We discuss this counterintuitive result in relation to the statistical and mathematical features of RDA and the recognized limitations with current traditional species concepts based on vegetative morphology.ConclusionWe suggest that such “quantum weirdness” in the models is reconcilable with classical ecosystems logic when the focus of research shifts from morphological species to cryptic species that consist of genetically and ecologically differentiated subpopulations. We support our argument with theoretical discussions of eco-evolutionary interpretations that should become testable once suitable data are available.

Responses by benthic invertebrate community composition to dissolved organic matter in lakes decline substantially above a threshold concentration

Abstract Dissolved organic matter (DOM), often measured as dissolved organic carbon (DOC), plays a fundamental role in influencing the structure and function of lake ecosystems. Due to the myriad ecosystem effects of DOM, widespread observations of long‐term increasing DOM concentrations have received much attention from ecologists. DOM positively influences primary production and consumer production at low concentrations due to the fertilising influence of bound nutrients. However, beyond a unimodal peak in production, a reduced light environment may result in a negative effect on production. This unimodal model has been largely developed and tested in lakes with low to moderate DOM concentrations (i.e., typically ≤10 mg/L DOC). To understand ecological responses in lakes across a larger range in DOM concentrations, we examined the response of benthic invertebrate communities in 148 Swedish lakes with DOM concentrations ranging between 0.67 and 32.77 mg/L DOC. We found that increasing DOM concentrations had a strong effect on invertebrate community composition below c. 10 mg/L. Across this range, abundances of individual taxa both increased and decreased, probably in response to environmental change induced by DOM. However, in lakes above this concentration, increasing DOM had minimal influence on community composition. As DOM concentrations continue to increase, faunal communities in lakes below this 10 mg/L DOC threshold are likely to undergo substantial change whereas those above this threshold are likely to be minimally impacted.

Effects of large dams on the aquatic food web along a coastal stream with high sediment loads

The contribution of two basal energy sources – detrital organic matter and primary producers – as part of aquatic food webs varies typically along river continua. A host of barriers to river flow increase the water residence time and sediment and nutrient retention in reservoirs worldwide, and potentially alter the balance between detritus-based and algae-based energy pathways in the downstream food webs. We explored this issue on the Sélune River (Normandy, France), a small coastal stream that drains an agricultural catchment with high sediment runoff. Seasonal measurements of the following parameters were compared upstream and downstream of the reservoirs of two large dams (16 m and 36 m high): sediment fluxes, nutrient and chlorophyll a concentrations, algal communities in the epilithic biofilm (taxonomic composition, biomass and growth), and benthic invertebrate communities (abundance and trophic guild structure). As anticipated, annual sediment fluxes were much lower downstream of the reservoirs, where significant decreases in water turbidity, phosphate and silicate concentrations were recorded. A higher chlorophyll a concentration in water and a higher contribution of pelagic algae taxa to the photosynthetic biofilm suggested drifting and deposition of reservoir-borne phytoplankton downriver. Photosynthetic biofilm growth was higher downstream of the reservoirs in spring and fall, and so was the abundance of herbivores in the invertebrate community, notably scrapers and algae eaters. Energy pathways within riverine food webs were traced using stable isotope analyses of carbon (C) and nitrogen in the tissues of aquatic consumers (invertebrates and fish). Mixing models revealed a discontinuity in the origin of the C entering the food webs along the river continuum, confirming a greater contribution of algal C to aquatic consumers downstream of the reservoirs. These results illustrate mechanisms whereby large reservoirs can modulate C flow in food webs along a small coastal river with high sediment loads, and make it possible to anticipate the effects of dam removal on the future river ecosystem.

Structural Indices of the Communities of Benthic and Phytophilous Invertebrates in Water Bodies Differing in the Dose Rate of Ionizing Radiation

The structural indices of the communities of benthic and phytophilous invertebrates were studied in water bodies differing in the levels of external radiation dose rate within the Chornobyl exclusion zone. The macrofauna of invertebrates of all studied water bodies was characterized by low species richness, numbers, and biomass. The obtained results suggest that the benthic and phytophilous invertebrate fauna of the cooling pond of the Chornobyl Nuclear Power Plant differs in its structure from the fauna of other water bodies of the Chornobyl exclusion zone more significantly than these water bodies differ from each other in terms of dose load levels on the biota. We consider the main reason for these differences to be the succession processes in the ecosystem caused by the transformation of the cooling pond of the Chornobyl Nuclear Power Plant. There is no reason to claim that the influence of external ionizing radiation determines the change in the structural indices of the communities of benthic and phytophilous invertebrates in water bodies of the Chornobyl exclusion zone.