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Environmental influences on species' functional traits are important ecological issues to assess biodiversity. Relationships among fish abundance, their functional traits, and environmental conditions across different levels of anthropogenic impacts in a tropical Brazilian river were evaluated. We combined RLQ and fourth-corner methods, utilizing local environmental variables and the Human Footprint Index (HFI) as a human activities indicator. Three HFI levels (High, Intermediate, and Low) and short-term (1993–2009) impact changes at each location were assigned. Fish with internal fertilization and small body sizes were strongly associated with high HFI scores. Grass-dominated riparian areas were common in altered locations, whereas less altered localities exhibited the riparian cover dominated by trees. Highly altered areas showed high HFI, grass-covered riparian zones, and small-sized species with internal fertilization (e.g., Cyprinodontiformes like Poecilia vivipara, Poecilia reticulata, and Phalloceros caudimaculatus). In contrast, less altered areas had tree-lined riparian zones and medium to large-sized species with external fertilization and diverse traits. Underlying deterministic processes shape species distribution, tied to environment and traits. Filtering of traits in the most altered locations may favor small-sized species with internal fertilization. This approach, utilizing HFI and local variables to assess trait–environment relationships of riverine fish, facilitates understanding organisms' responses to environmental constraints. [ABSTRACT FROM AUTHOR]

Small streams dominate the hydrological network within Europe. In many regions, these waterbodies drain large areas of agricultural land and are vulnerable to pressures linked to livestock management, which can include direct livestock access. This study investigated the impacts of cattle access to watercourses on the contamination of streambed sediment with Escherichia coli (E. coli) in five agricultural catchments. Sediments were collected at cattle access sites and at areas upstream with no cattle access, in two time points in the livestock management cycle (mid-grazing and post-grazing season). Relatively high E. coli concentrations of 103 to 104 CFU g dry wt−1 were found at sites with no access in mid-grazing season. However, concentrations were significantly higher at sites with cattle access. E. coli was present, but in generally lower concentrations, in the post-grazing season. Additionally, the study found a significant negative relationship between the quality of the general riparian environment and E. coli bed sediment concentrations at the cattle access sites in the mid-grazing season, and a significant positive relationship between E. coli concentrations and estimated cattle density locally in post-grazing season. These findings indicate that allowing livestock access to watercourses can have implications for both water quality and human health. [ABSTRACT FROM AUTHOR]

Management measures targeting riverine macrophyte species often address dissolved nitrogen and phosphorus compounds. With recent reductions of nutrient pollution, effects of other variables have become more apparent. This study aims to shed light on the hierarchy of variables determining riverine macrophyte distribution, covering both surface water nutrients and a range of other variables, in a Central European landscape. We used a dataset of 1,371 monitoring samples to predict the presence and absence of 30 common macrophyte species with multiple random forest models. Besides surface water chemical variables (P-PO4, TN and pH), five reach hydromorphological variables (substrate, flow velocity, shading, width and depth) and a variable related to river size (distance from the river source) were use as predictors. The most important variables for the prediction of the species' presence and absence were substrate, distance from the river source and flow velocity. Additionally, P-PO4 and shade were also important, whilst TN, pH, width and depth played only a minor role. River hydromorphology was more important than surface water chemistry for the occurrences of individual riverine macrophyte species, in particular under less extreme eutrophic conditions. Species occurrences were related to multiple interacting variables, amongst which hydromorphology often prevailed. Presence/absence of species and composition of assemblages cannot be attributed to surface water nutrients alone, even when considering river typologies. Therefore, the results support the conjecture that a broader approach considering a range of stressors is necessary to design restoration measures for management and enhancement of macrophyte diversity. [ABSTRACT FROM AUTHOR]

Ranunculus species grouped in the section Batrachium (water crowfoots) indicate the most valuable fluvial habitat in Europe under the EU Habitats Directive, and recognition of their environmental preferences plays a crucial role in efficient conservation. Moreover, water crowfoots are used in various monitoring systems throughout Europe. The aim of this study was to identify the distribution patterns of two common water crowfoot species (Ranunculus fluitans, R. circinatus) and their hybrid (R. circinatus × R. fluitans) in relation to environmental variables in rivers. Various chemical and hydromorphological parameters were estimated for 54 river sites where 58 different Batrachium populations were recorded. Our study revealed the most distinct positive reaction of R. fluitans to rhithral conditions characterized by rapid currents and coarse substrate. R. circinatus × R. fluitans preferred larger channels, although this taxon also flourished in rhithral rivers. The preferences of R. circinatus were not so evident confirming its occurrence under a wide range of habitat conditions. The ecological reaction of the hybrid was compared with its parental species, revealing their ecological specificity, which is useful in designing appropriate conservation programmes. [ABSTRACT FROM AUTHOR]

Aquatic bryophytes are frequently used as bioindicators of water quality in rivers. Poor water quality increases physiological stress in moss, and stress levels can be estimated by measuring the concentrations of photosynthetic pigments and by calculating pigmentary indices. However, studies collecting many samples in a short time may need to store them until analysis. In the meantime, the pigments may suffer some degradation. Given the lack of studies on this problem for aquatic bryophytes, this one investigates the effect of three storage methods (refrigerated at 6 °C, frozen at − 20 °C and dried at room temperature) on the concentrations of chlorophyll a, chlorophyll b, pheophytin a and the following ratios: chlorophyll a/chlorophyll b, D430/D410, D665/D665a, D430/D665 and D480/D665 (where Dx is the absorbance at x nm) in the aquatic moss Fontinalis antipyretica. The results showed that refrigeration was the most suitable method, freezing might be suitable for some parameters, and drying was inadequate for this purpose. We recommend that all studies on photosynthetic pigments detail the time elapsed from collection to sample analysis, as well as the storage method used. [ABSTRACT FROM AUTHOR]

Understanding movement patterns and home range of rare species is challenging, especially aquatic fauna like fishes. The Sickle Darter Percina williamsi is a rare fish species endemic to the upper Tennessee River basin in eastern Tennessee, southwestern Virginia, and western North Carolina (USA). It has been listed as threatened by the states of Tennessee and Virginia and is being petitioned for federal listing under the United States Endangered Species Act. Little is known about the movement and home range of this species. A total of 8 Sickle Darters from the upper Emory River system were implanted with 8-mm PIT tags and released at the point of capture. The mean (± SD) total length and weight of all fish PIT tagged was 70.1 ± 3.4 mm and 3.08 ± 1.4 g. Movement of individuals was tracked every 2 weeks for 6 months (September–March) with a Biomark® HPR Plus reader and BP Plus portable antenna. Associated environmental data were collected throughout the study. Mean total effort for all the tracking events was 70 ± 39.4 min, mean catch-per-effort was 9.3 ± 6.6 (min/detection) and mean (± SE) detection was 69.5 ± 12%. Mean (± SD) distanced moved of all individuals throughout the study was 7.1 ± 4.5 m. Best sub-sets regressions modelling suggest that Sickle Darter movement is related to discharge (m/s3) at multiple temporal levels (1, 3, or 7-day). Home range for individuals varied in size. Median home range size was 157.5 (86.0–312.5) m2 and median (range) degree of overlap for estimated home range was 23.3 (6.2–34.0) %. The results from this study suggest that Sickle Darters exhibit strong site fidelity except when discharge is extremely high. Therefore, conservation measures that protect or attempt to reconnect fragmented habitats will need to factor in the low dispersal ability of this species. [ABSTRACT FROM AUTHOR]

Lotic freshwater macroinvertebrate species distribution models (SDMs) have been shown to improve when hydrological variables are included. However, most studies to date only include data describing climate or stream flow-related surrogates. We assessed the relative influence of climatic and hydrological predictor variables on the modelled distribution of macroinvertebrates, expecting model performance to improve when hydrological variables are included. We calibrated five SDMs using combinations of bioclimatic (bC), hydrological (H) and hydroclimatic (hC) predictor datasets and compared model performance as well as variance partition of all combinations. We investigated the difference in trait composition of communities that responded better to either bC or H configurations. The dataset bC had the most influence in terms of proportional variance, however model performance was increased with the addition of hC or H. Trait composition demonstrated distinct patterns between associated model configurations, where species that prefer intermediate to slow-flowing current conditions in regions further downstream performed better with bC–H. Including hydrological variables in SDMs contributes to improved performance, it is however, species-specific and future studies would benefit from hydrology-related variables to link environmental conditions and diverse communities. Consequently, SDMs that include climatic and hydrological variables could more accurately guide sustainable river ecosystem management. [ABSTRACT FROM AUTHOR]

Four freshwater eel species (Anguilla spp.) occur in southern African rivers that are increasingly anthropogenically modified. Information on movements, habitat use and overlap by African eels is needed for their conservation. We carried out a preliminary investigation of the spatial ecology of three eel species in the Thukela River, South Africa, using radio-telemetry. Nineteen yellow-stage eels were surgically implanted with radio-tags, comprising A. mossambica (n = 2), A. bengalensis (n = 9) and A. marmorata (n = 8), and tracked from October 2018 to August 2019. Tagged eels exhibited high individual variability in space use. We recorded very small home ranges in winter for all species. A lack of apparent territoriality at inter- and intra-specific levels was observed. Eel species tended to use similar mesohabitats, especially glides, but habitat preference changed across seasons, and between species, suggesting fine-scale spatial and temporal niche partitioning. Given the breadth of flow typologies used by Thukela eels across the seasons, conservation of these long-lived species indicates that management of river flows needs to be sensitive to their habitat requirements all year round, but in many water-stressed South African rivers, this may be unlikely. Maintaining good habitat connectivity for these migrant species must be prioritised. [ABSTRACT FROM AUTHOR]

The intermediate disturbance hypothesis (IDH) has been thoroughly investigated, but much controversy has been found for supporting its assumptions, which rely largely on the nature of the disturbance, spatial scale, and biological predictors tested. In this paper, richness of native and non-native species along a suite of Neotropical aquatic ecosystems across a broad latitudinal and geographical range was used to test the IDH predictions. An extensive literature survey was performed to compile native species richness and the occurrence of several taxonomic groups listed as non-native for twenty-four coastal rivers and bays evenly distributed into three climatic zones (tropical, transitional, and subtropical). The climatic gradient was confirmed by NMDS and PERMANOVA, but IDH predictions were only significantly supported for native and total species richness in the coastal bays. The distribution patterns of non-native marine species showed a linear instead unimodal pattern of increase with latitudinal climatic gradient, but the responses are complex and dependent of many non-exclusive factors, such as the sampling effort per ecosystem and the potential interference of other disturbance gradients that should be further addressed to unravel the role of IDH for non-native species distribution. [ABSTRACT FROM AUTHOR]

The ability of macrophytes to indicate pressures in rivers was assessed by comparing metrics for nitrate (NO3), ammonia (NH4), soluble reactive phosphorus (SRP), dissolved oxygen saturation (DO), pH (PH) and siltation (SUBS) with direct estimates of the pressures at 810 sites in the Republic of Ireland, supplemented with General Linear Models (GLMs). The bivariate and rank correlation coefficients using the full data range and the first and fourth quartiles of the river pressures varied between 0.22 and − 0.39 for NO3 and DO; they were smaller or not significant for the other four metrics. The GLMs provided evidence for an independent association between NO3 and the nitrate concentration and SUBS and ammonia, indicating some specificity for these metrics. Discriminating sites in the first and fourth quartiles produced Type II errors between 37 (PH) and 69% (NH4), with a mean of 50. As the pressure-impact relationships are not precise enough (low correlation coefficients) that evidence from a single macrophyte metric is reliable, combining the metric with evidence from other biological groups at one site or from three or more sites may be the most useful approach. [ABSTRACT FROM AUTHOR]

Beta diversity typically increases with decreasing latitude, with explanations of this pattern often based on tropical origins of most clades. Black flies (Diptera: Simuliidae) are at odds with this trend, having a northern origin. Increasing β-diversity with decreasing latitude might also be a product of changes in causal mechanisms structuring local assemblages among biogeographical realms. We tested the hypotheses that (i) β-diversity of black flies in streams should be similar between the Nearctic and Neotropical realms, and (ii) causal processes influencing species composition do not differ between these areas. To this end, we examined two Nearctic (USA) and two Neotropical data sets (Ecuador, Venezuela). Results did not show distinct differences in β-diversity between Nearctic and Neotropical streams. Although stream conditions varied among regions, we provide evidence that several causal mechanisms of community structure are shared. We suggest that potentially similar causal mechanisms driving species composition contributed to the lack of distinct differences in β-diversity between Nearctic and Neotropical streams. In addition, dispersal appears to influence the β-diversity of larval black flies, a pattern different from many previous studies of stream invertebrates. The influence of taxon origins on β-diversity across biogeographic realms should be further investigated. [ABSTRACT FROM AUTHOR]

Proliferations of benthic mats dominated by anatoxin-producing Microcoleus autumnalis (basionym Phormidium autumnale) pose an increasing health risk to human and animals worldwide. This study assessed M. autumnalis mats in two in situ experiments undertaken at three spatial scales: (1) reach-scale along a river; (2) reach-scale, focusing on two sites upstream and downstream of a tributary with substantial differences in naturally occurring M. autumnalis; and (3) patch-scale differences in light intensity. Most studies exploring drivers of proliferation have surveyed natural populations with correlative analyses; these in situ experiments aimed to validate previously hypothesised drivers. In experiment one, M. autumnalis mat area and expansion tended to increase downstream. This longitudinal variation was partially associated with increases in dissolved inorganic nitrogen, fine sediment and associated biologically available phosphorus. M. autumnalis mat area differed markedly at sites above and below the most downstream tributary. A second experiment with additional parameters (metals, grazing and light) was undertaken in this reach. None of the parameters conclusively explained differences in mat area, although numerous metals were identified for further investigation with a controlled experimental approach. These results posit that there are multiple non-linear drivers of M. autumnalis proliferation and their hierarchy of importance varies amongst sites. [ABSTRACT FROM AUTHOR]

Understanding the biotope requirements of the various aquatic biota is crucial for effective biomonitoring. Yet, the biotope preferences of macroinvertebrates in Afrotropical rivers have been poorly studied. In this study, we investigated the influence of human disturbance and flow-driven biotope changes on the β-diversity and biotope preferences of macroinvertebrates in the Mara River, Kenya. Macroinvertebrates were sampled from various biotopes at seven reference and nine impaired sites in wet and dry seasons. β-Diversity was determined (i) for each biotope and (ii) at the site scale, combining all biotopes sampled, and macroinvertebrate biotope preferences were assessed among biotopes between reference and impaired sites. Minor β-diversity differences were observed between reference and impaired sites based on relative abundance data, but differences were greater when the presence–absence data were used. There were no statistically significant changes in macroinvertebrate biotope preference due to human disturbance, but fidelity to preferred biotopes increased at impaired sites. In fast-flowing waters, Simuliidae, Baetidae, Tricorythidae, and Hydropsychidae dominated stable rocky substrates and were the most sensitive to flow alteration. This study adds valuable information on the effects of biotope reduction/loss and flow alteration on the diversity and biotope preferences of macroinvertebrates in Afrotropical rivers, and contributes to improvement of relevant bioassessment protocols and biodiversity conservation efforts. [ABSTRACT FROM AUTHOR]

River phytoplankton has been studied to understand its occurrence and composition since the end of the nineteenth century. Later, pioneers addressed mechanisms that affected river phytoplankton by "origin of plankton", "turbulent mixing", "flow heterogeneity", "paradox of potamoplankton maintenance" and "dead zones" as keywords along the twentieth century. A major shift came with the recognition that characteristic units in phytoplankton compositions could be linked to specific set of environmental conditions, known as the "Phytoplankton Functional Group concept" sensu Reynolds. The FG concept could successfully be applied to river phytoplankton due to its close resemblance to shallow lakes phytoplankton. The FG approach enables one to separate the effects of "natural constraints" and "human impacts" on river phytoplankton and to evaluate the ecological status of rivers. The FG classification has mainly been advocated in the context of how the environment shaped the functional composition of phytoplankton. It may be further developed in the future by a trait-based mechanistic classification of taxa into FGs, and by the exact quantification of FGs on ecosystem functioning. These improvements will help quantify how global warming and human impacts affect river phytoplankton and corresponding alterations in ecosystem functioning. [ABSTRACT FROM AUTHOR]

Specific concepts of fluvial ecology are well studied in riverine ecosystems of the temperate zone but poorly investigated in the Afrotropical region. Hence, we examined the longitudinal zonation of fish and adult caddisfly (Trichoptera) assemblages in the endorheic Awash River (1,250 km in length), Ethiopia. We expected that species assemblages are structured along environmental gradients, reflecting the pattern of large-scale freshwater ecoregions. We applied multivariate statistical methods to test for differences in spatial species assemblage structure and identified characteristic taxa of the observed biocoenoses by indicator species analyses. Fish and caddisfly assemblages were clustered into highland and lowland communities, following the freshwater ecoregions, but separated by an ecotone with highest biodiversity. Moreover, the caddisfly results suggest separating the heterogeneous highlands into a forested and a deforested zone. Surprisingly, the Awash drainage is rather species-poor: only 11 fish (1 endemic, 2 introduced) and 28 caddisfly species (8 new records for Ethiopia) were recorded from the mainstem and its major tributaries. Nevertheless, specialized species characterize the highland forests, whereas the lowlands primarily host geographically widely distributed species. This study showed that a combined approach of fish and caddisflies is a suitable method for assessing regional characteristics of fluvial ecosystems in the tropics. [ABSTRACT FROM AUTHOR]

Several Alpine streams are currently facing recurrent summer drying events with detrimental consequences on stream detritivores, i.e., shredders, due to negative effects via changes the organic matter (CPOM) availability. We examined the ecological requirements of three phylogenetically related shredder genera belonging to the family of Nemouridae (Plecoptera), namely Nemoura, Protonemura and Amphinemura, in 14 Alpine streams recently facing recurrent summer flow intermittency events. We evaluated the overlap among their ecological niches measured in terms of hydraulic stress, substrate composition, changes in CPOM availability and competition with other shredder taxa (i.e., presence of individuals of other shredders) and we examined potential changes in their ecological niches between permanent and intermittent sites. The ecological niches of Protonemura and Amphinemura overlap broadly, but not with Nemoura, suggesting only partial potential competition. The reduced CPOM availability decreased the individual abundance of the three genera in intermittent sites, where they consistently preferred microhabitats with high CPOM availability and low competition with other shredder taxa, possibly due to food limitation. Overall, our results emphasize how the negative effect of flow intermittency on shredders in Alpine streams is mainly due to the decrease in CPOM availability, with consequent potential bottom up effects on stream ecosystem functionality. [ABSTRACT FROM AUTHOR]

Spawning strategies of lowland river fishes include single spawning, where reproduction generally occurs in early spring to provide 0+ fish with an extended growth season through the summer, but with a high risk of stochastic mortality events occurring, such as early summer floods. This risk can be reduced by multiple or protracted spawning strategies, where 0+ fish are produced over an extended period, often into mid-summer, but with the trade-off being a shorter growth season. The spawning strategies of cypriniform fish were explored in the River Teme, a spate river in Western England, which has non-indigenous European barbel Barbus barbus present. Sampling 0+ fish in spring and summer and across three spawning periods, B. barbus, chub Squalius cephalus and minnow Phoxinus phoxinus always revealed multiple spawning events, with 0+ fish of < 20 mm present in samples collected from June to August. Fish below 20 mm in August remained relatively small by the end of their growth season (October). For dace Leuciscus leuciscus, only single spawning events were evident, but with 0+ dace always being relatively large. Therefore, multiple spawning appears to be a common strategy that provides resilience in 0+ fish against stochastic mortality events in lowland rivers. [ABSTRACT FROM AUTHOR]

Beta diversity quantifies changes in assemblages among sites and can identify how anthropogenic changes affect species distributions patterns. We investigated how spatial and temporal beta diversity of fish assemblages responded to recent environmental changes within an established agroecosystem and investigated whether the observed pattern of spatial and temporal beta diversity was different from null expectations. Fish assemblages in 38 streams were sampled in 2003 and 2013, and local and regional variables were quantified in both periods. Species were classified into functional groups based on 15 ecomorphological traits. We tested for relationships between spatial and temporal patterns of beta diversity and its components (turnover and nestedness) and environmental distances and degree of changes over time, and for differences with null expectations. Spatial beta diversity was mostly due to turnover and remained relatively unchanged between periods. Spatial beta diversity was not different from randomness. Temporal beta diversity was lower than expected by null models and not correlated with environmental changes. Past environmental filters related to a long history of agricultural development homogenized habitats and fish assemblages by selecting for habitat-generalist species. In this context, contemporary fish assemblage dynamics in these streams are driven primarily by stochastic processes, likely stochastic local species loss. [ABSTRACT FROM AUTHOR]

Dramatic environmental changes and species invasions are increasingly threatening the diverse fish fauna of the Yellow River, China. This study examines temporal changes in the alpha and beta components of fish taxonomic, functional and phylogenetic diversity in relation to anthropogenic environmental changes over the past 50 years. We hypothesized that temporal trends in multifaceted components of diversity would be highly congruent, but that the relative importance of anthropogenic disturbances would differ in shaping spatial patterns of fish diversity. We found that all three components of alpha diversity increased over time but at different rates (19.1%, 21.3% and 15.3% for taxonomic, functional and phylogenetic diversity, respectively). Fish faunas of the Yellow River have also become homogenized over time, but this was much greater for functional and phylogenetic components of beta diversity than for taxonomic diversity (change in beta diversity = − 0.11, − 0.24 and − 0.02, respectively). Temporal changes in alpha and beta diversity were strongly related to invasion of non-native fish species and changes in temperature, sediment load, reservoir capacity and aquaculture area. Our results underscore the ongoing need for threat mitigation (particularly relating to dams and aquaculture) to conserve the unique biodiversity of one of the world's largest rivers. [ABSTRACT FROM AUTHOR]

The intensification of agricultural practices is impacting on Piedmont streams in Patagonia and concern exists regarding the integrity of aquatic ecosystems. This study investigated changes in water quality, habitat and riparian condition, and macroinvertebrate community attributes at three small streams during high- and low-water periods. The upper reaches of streams consisted of well-conserved riparian forest where agricultural impact was minimal, while different production systems affected lower stream-reaches. Significant changes in water quality were indicated by increases in nutrient levels, conductivity, total suspended solids, and bacteria (E. coli) at spatial scale. These were mostly associated with livestock, pasture, and horticulture production, though the most severe impacts on in-stream habitat and riparian ecosystem occurred at sites with livestock productions. A gradient of disturbance was highlighted by Canonical Community Ordination and macroinvertebrates were grouped accordingly. Among the metrics measured, EPT richness, number of insect families, density of tolerant taxa, abundance of collector-gatherers, and total invertebrate density displayed significant responses to water quality. The overriding stressor explaining community changes with regard to intolerant taxa (EPT) was ammonium. Mitigation measures should be directed towards reducing livestock intrusion on streams and riparian areas, maintenance and restoration of buffer zones, and regulation of application of fertilizers. [ABSTRACT FROM AUTHOR]

Human activities have disrupted the functioning of river ecosystems around the world. In the Amazon basin, hydropower expansion has affected diversity patterns, but no study has investigated how phytoplankton assemblages respond to impoundments. This study investigated the hypothesis that phytoplankton diversity is highly sensitive to river damming in large tropical rivers, declining in impoundment areas. We examined patterns of taxonomic diversity (i.e., richness, biovolume, and composition), functional diversity (Reynolds Functional Groups, RFGs), and functional redundancy (i.e., number of taxa in each RFG) along the Tocantins River, before and after the construction of Estreito Hydropower Dam. We monitored five sites along the river (ca. 260 km) between December 2009 and May 2013. The dam changed environmental conditions related to flow, nutrient supply, and depth. We recorded 140 taxa and 26 RFGs in the area. Taxa richness, biovolume, and the number of RFGs declined significantly after river regulation. Composition and abundance ranks changed over periods, and the codons C, Y, TC, W1, and LO were eliminated; functional redundancy declined significantly. These results show that phytoplankton diversity is sensitive to river regulation in large tropical rivers, where changes in hydrology and environmental filters lead to significant losses in taxonomic and functional diversity. [ABSTRACT FROM AUTHOR]

Flow intermittency occurs naturally in alpine streams. However, changing rainfall patterns and glacier retreat are predicted to increase the occurrence of flow intermittency in alpine catchments, with largely unknown effects on ecosystem structure and function. We conducted a flow manipulation experiment within a headwater stream of Val Roseg, a glacierized alpine catchment, to determine the effects of increased flow intermittency on aquatic macroinvertebrates, periphyton, benthic organic matter, and trophic structure. Compared to an adjacent reference channel, an increase in flow intermittency reduced macroinvertebrate density, taxa richness, and the proportion of rheophilic taxa. Density and richness remained low in the manipulated channel after resumption of natural flow. Flow intermittency did not affect organic matter standing stocks, but increased assimilation of periphyton by aquatic macroinvertebrates. Predation on aquatic invertebrates by riparian spiders also increased. We attribute many of these patterns to the timing of drying, which likely excluded summer-growing cohorts of rheophilic, aerial dispersers. This study suggests that reductions in summer glacial melt and rainfall events might increase flow intermittency and lead to fundamental changes in diversity and function of alpine fluvial networks. [ABSTRACT FROM AUTHOR]

The River Continuum Concept (RCC) predicts that aquatic insect communities undergo predictable changes in composition from headwaters to downstream regions relative to changes in habitat. An important aspect of this change is stream temperature. Studies have been conducted on thermal partitioning of chironomids within the RCC and across streams with different thermal regimes; however, few have focused on effects of fine-scale within-stream temperature variability on winter chironomid composition. Our objectives were to characterize thermal heterogeneity within a small headwater trout stream during winter using slope and Y-intercepts from linear regressions of air–water temperatures and to document patterns of chironomid emergence and taxonomic composition relative to mean water temperatures, regression slopes, and Y-intercepts along stream length. We developed air–water temperature regressions using mean daily air and water temperatures for three headwater trout streams. We assessed similarity in taxonomic composition across sites by collecting and analyzing chironomid surface floating pupal exuviae. We demonstrate that regressions of mean daily air and water temperatures can characterize fine-scale thermal heterogeneity within and among headwater trout streams during winter. We also demonstrate that chironomid taxonomic composition varied at spatial scales substantially less than a kilometer within a stream that possessed significant thermal heterogeneity. [ABSTRACT FROM AUTHOR]

Estimating changes in organic matter flow from resource to consumer using trophic basis of production (TBP) is a way to examine resource limitation effects on ecosystem function. We examined diet shifts and production of insect detritivores to assess changes with reduced detrital inputs to a forested headwater stream. Organic matter was excluded for 7 years using a canopy net. Small and large wood were removed from the stream after the 3rd and 5th year, respectively. Detritivore production declined after 3 years of litter exclusion. After wood removal, production of detritivores declined again. Steepest declines in Pycnopsyche gentilis production occurred within year 1. Tipula spp. and Tallaperla spp. production declined after wood removal. Diets shifted from leaves to wood to fine particulate organic matter (FPOM) for Tipula spp. and Tallaperla spp., but not for P. gentilis. Resource flows to detritivores shifted in the exclusion stream from leaves to wood to FPOM after leaf standing crops declined and wood removal. Small wood was an important food resource. TBP results showed shifts in food resource use by two detritivores with terrestrial input reduction. These findings suggest that maintaining diverse riparian inputs of organic matter is important for detritivore productivity in forested headwater watersheds. [ABSTRACT FROM AUTHOR]

Diatoms have been widely used in stream health assessments as they are highly sensitive to water quality. There is no standardised method for diatom-based stream health assessments causing many substrates, both natural and artificial, to be used. Few studies have investigated the impact of substrate type on diatom assemblages in streams with highly variable water levels. To determine if the substrate type affects these assessments, diatoms were analysed from an artificial substrate (rope), rock and mud, from 17 sites in the Mount Lofty Ranges, South Australia. Rope has been advocated as a substrate as it mimics aquatic plants, while having advantages of artificial substrates (e.g. standardised habitat). We found that substrate type did not affect the stream health assessment based on the Diatom Species Index for Australian Rivers and hence the additional cost of deploying ropes in such studies is unlikely to be warranted. However, substrate type influenced diatom–nutrient relationships, with no relationship between nutrients in the stream water and diatoms in the mud substrate—possibly due to the nutrient subsidy provided by mud. Therefore, by contrast, the absence of nutrients provided by the rope substrate indicates it is suited to studies of nutrient status and sensitivity in streams. [ABSTRACT FROM AUTHOR]

We measured nitrate in water (n = 4762) and nitrogen stable isotopes (δ15N) (n = 353) of macroalgae and macroinvertebrates at different sites in a French karst river (Loue River) which has moderate nitrogen loading (~ 23 kg nitrogen ha−1 year−1). The main objective was to estimate whether nitrate in water and nitrogen stable isotopes of the biota could allow identification of the spatial and temporal variations in agriculture-related nitrogen losses to the river. Highest nitrate concentrations (> 90% quantile) increased significantly over the last three decades but mean nitrate concentrations did not change significantly. Nitrate and biota δ15N values tended to increase from upstream to downstream, although the δ15N values decreased in the most downstream sites. Generalized additive mixed models allowed the identification of clear matching annual patterns of nitrate and biota δ15N values characterized by recurrent autumn to winter maxima, supporting that agricultural nitrogen export and its assimilation within the river biota would mostly occur during the autumn and winter seasons. Overall, our results highlight the high vulnerability of karst river to nitrogen-related eutrophication. [ABSTRACT FROM AUTHOR]

The aim of this research was to investigate the diversity patterns of benthic insects and functional feeding groups by assessing the contribution of α and β diversity components over 1 year. Temporal diversity variation as a function of the diversity components and regional rainfall in subterranean streams was also verified. Diversity components varied significantly at different spatial scales. In general, α diversity tended to be smaller and less varied temporally than the β diversity components. In addition, we detected a higher contribution of β2, indicating the importance of the regional species pool. Finally, for all significant models relating diversity values with rainfall, the relationship was negative. Intense flows leached organisms, leading to homogenization of communities. On the other hand, despite this negative effect, each functional feeding group responds differently to the hydrological stress, which makes it difficult to develop community predictability models after a disturbance. [ABSTRACT FROM AUTHOR]

Anthropogenic impact can alter food web structure through changes in species interactions. In this study, we explored the food web of three Mediterranean stream reaches (two seasonal and one permanent) along an anthropogenic impact gradient to test the hypothesis that increasing impact simplifies food webs. To test this, we applied the isotopic (δ13C and δ15N) niche concept to compare reaches using isotopic metrics (isotopic richness, divergence, dispersion, evenness, and redundancy). The isotopic indices were useful to identify differences in food web architecture among the three reaches. The least impacted site had the highest isotopic richness, dispersion, and isotopic redundancy, suggesting higher ecological resilience at this site. The effect of disturbance in the remaining two sites was masked by the presence of invasive crayfish, which increased isotopic divergence and was responsible for higher food-chain length in the most impacted reach, but not in the moderately impacted reach. Consumers displayed generalistic feeding habits, with Bayesian mixing models indicating that they relied primarily on a mixture of periphyton, other macroinvertebrates, and to a lesser extent, detritus. Some taxa displayed changes in their dietary habitats depending on the site, indicating that the same type of taxa fed on distinct foods at each stream reach. [ABSTRACT FROM AUTHOR]

Shredders play a crucial role in litter decomposition in streams. However, in oceanic islands, many streams have low shredder density and richness, and microbes seem to be the main litter decomposers. Here, we evaluate the effects of shredders and aquatic hyphomycetes on litter decomposition in insular streams. Three leaf species differing in physical and chemical characteristics, Alnus glutinosa, Clethra arborea, and Cryptomeria japonica, were enclosed in bags of coarse and fine mesh to allow and avoid macroinvertebrate access to the litter, respectively, and incubated in six streams along a gradient of Limnephilus atlanticus (Trichoptera) density in São Miguel Island. In streams with higher L. atlanticus density, leaf mass loss was higher in coarse than fine mesh bags. However, no difference in litter mass loss was found between bag types in streams with no L. atlanticus, despite the presence of other shredder taxa. These results suggest that when L. atlanticus are present at relatively high densities, they significantly contribute to litter decomposition, while litter decomposition is mainly driven by microbes when L. atlanticus density is low, or they are absent. Moreover, litter decomposition depends on litter quality, with leaves with high nutrient concentration and low concentration of secondary compounds being preferred by shredders. [ABSTRACT FROM AUTHOR]

Temporary streams are submitted to high seasonal hydrological variations which induce habitat fragmentation. Global change promotes longer non-flow periods, affecting hydrological continuity and the distribution of biological assemblages in river networks. We aimed to investigate the effects of hydrological discontinuity on phototrophic biofilm assemblages in a Mediterranean stream, at both network and habitat scales. At the network scale during basal flow conditions, mostly nitrate and DOC concentrations were associated to the taxonomical and trait distribution of algae and cyanobacterial assemblages. Cyanobacteria dominated at the upstream and downstream sites of the network, while green algae and diatoms were abundant in its middle part. At the habitat scale, hydrological discontinuity promoted large changes in biofilm composition between riffles and pools, where pools were inhabited preferentially by green algae and riffle habitats by cyanobacteria. Our findings emphasize the myriad of factors affecting the spatial distribution of phototrophic biofilms, which become more heterogeneous according to water flow interruption. Under the predicted climate change scenarios, spatial heterogeneity in temporary streams may increase, which will lead to change phototrophic biofilm assemblages. [ABSTRACT FROM AUTHOR]

The aim of our study was to analyze dissolved organic carbon processing at a reach of a productive Pampean stream and to determine DOM retention efficiencies under a wide range of hydrological conditions. This study was carried out in Las Flores stream, a third-order stream located in the Luján River basin in the northeast of the Buenos Aires province, Argentina. We selected a 2.2 km reach of Las Flores stream. On each sampling occasion, we collected water samples at the end of the reach, at two upstream tributaries, and at the potential hydrological contributors (end members) to stream flow. We determined DOC concentration and DOM optical properties in the stream and end members by combining absorbance–fluorescence spectroscopy techniques. The reach acts as a reactor for DOC concentration at baseflow condition, when in situ production processes prevailed. However, DOC is passively transported downstream at high flow condition. We found that humic and more degraded compounds predominate in DOM at the end of the reach. According to this, we proposed that both protein-like and humic-like compounds are produced at the study reach through in situ production processes, such as biological production from periphyton and macrophytes decomposition. [ABSTRACT FROM AUTHOR]

The size–abundance spectrum (SAS) of phytoplankton is controlled by the interplay of physical and biological factors whose particular relevance varies between ecosystems. Here we report the results of a study of phytoplankton SAS in a system of eight estuarine shallow, eutrophic lagoons (Guadalhorce river, South Spain). SAS were obtained through a combination of flow cytometry and image analysis microscopy techniques covering six orders of magnitude from picoplankton to microplankton. Cell numbers were classified into a log2 scale of cell volume to model the log–log relation between cell abundance (cells/mL) and cell volume (μm3). The resulting averaged phytoplankton SAS can be described by a log–log transformed, power model with a slope of – 0.62 (that is, there is an allometric relation between the size and abundance of cells). The distribution of biovolume (μm3/l) in broader size categories is characterized by the dominance of nanoplankton (67.4%), followed by microplankton (30.1%) and picoplankton (2.5%). The minor relative contribution of picoplankton to total biovolume can be explained by a combination of high and variable rates of nutrient inputs, light stress and grazing. The biomass dominance of intermediate-size cells (nanoplankton) is coherent with experimental findings describing the unimodal size scaling of growth rate, with maximum values centered in this size category. [ABSTRACT FROM AUTHOR]

The relative importance of allochthonous and autochthonous resources in fueling tropical headwater streams remains an open topic. We combined estimates of secondary production and assessment of its trophic basis to determine which resources were responsible for animal production. We studied benthic insect assemblages in two streams in the Luquillo Experimental Forest, Puerto Rico. Habitat-weighted production estimates were similar in both streams (528.5 and 591.5 mg m−2 year−1), but production was over twice as high in pool versus riffle habitats. The mayfly Neohagenulus (Leptophlebiidae) was a major contributor to total production (259.1 and 352.2 mg m−2 year−1). All taxa relied heavily on amorphous detritus and plant tissue. Aquatic insect production was similar to that reported for shrimp assemblages in the same study area, but low relative to temperate region estimates. The trophic basis of production appears to be allochthonous organic matter, which agrees with the small size and closed canopy cover over the study streams. This is the first study quantifying the production and trophic basis of the non-shrimp macroinvertebrate assemblage in tropical island streams. We also provide support for the importance of riparian vegetation as the main energy sources for stream tropical stream food webs. [ABSTRACT FROM AUTHOR]

Light, temperature, and discharge control stream metabolism, but the response of gross primary production (GPP) and ecosystem respiration (ER) to seasonal variation in these physical drivers may differ in accordance with the types of human activities present in the catchment. Our study examined three mid-order streams in southern Ontario, Canada that differed in anthropogenic nutrient sources (i.e., sewage treatment plant effluent, sewage lagoon effluent, and agriculture), but had comparable light, temperature, and discharge regimes. For each stream, GPP and ER were estimated daily from June through November. Comparisons of paired daily metabolic rates revealed pairwise differences among all streams, with streams receiving sewage effluent having greater rates and variability of GPP and ER than the stream draining agricultural land. The two sewage influenced streams differed only in ER. Temporal patterns of GPP and ER were correlated for all streams throughout the study period and were most affected by seasonal variation in temperature, whereby effluent receiving streams responded more rapidly to increases in temperature. Our findings suggest that managers may need to balance effects of human activities with regional environmental constraints on stream metabolism to maintain and enhance the ecological condition and services of stream ecosystems. [ABSTRACT FROM AUTHOR]

Coffee farming is an important practice in the tropics, but studies addressing its effect on streams, especially at high elevations in high productivity regions, are limited. We evaluated streams draining the high-elevation coffee farming region of Tarrazú, Costa Rica, in terms of water quality and benthic macroinvertebrates over the course of a year. We compared our observations to regulatory benchmarks to determine overall condition, and compared our sites in terms of riparian vegetation (i.e., canopy cover, and riparian width) to determine the role of this management practice. Overall, we found that most streams fell within recommended water quality criteria and supported high proportion of pollution-sensitive taxa. Nevertheless, we found high levels of conductivity during the drier period of the year, which may signal agrochemical pollution. Also during the drier period, we found significantly higher diversity, % scrapers, and % predators, which suggests a boost in basal food sources associated to the observed high conductivity levels. We found that riparian buffer widths were not associated to improvements in water quality indicators or bio-integrity parameters on our sites. However, canopy cover was positively correlated to % shredders and family diversity, and negatively correlated to certain tolerant taxa. Our findings help to better characterize a system that is of great economic importance in the tropics, but that remains relatively under studied. It also helps inform management practices to enhance the potential of coffee agroforestry systems in promoting tropical biodiversity conservation within aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Despite the importance of shredders in organic matter processing in streams, information about the habitat specificities of different taxa is scarce. Herein, we evaluated the habitat preferences of invertebrate shredders in tropical forest streams. A total of 72 leaf patches were sampled in three Atlantic Forest streams (SE Brazil). For each sample, 20 environmental variables were measured, including water properties and characteristics of the leaf patch. We used an Outlying Mean Index analysis to evaluate the niche breadth and overlap of each taxon found as well as habitat preferences. In total, we found 14 shredder taxa in 68 leaf patches, and the gradient of environmental conditions influenced the distribution of most taxa. Considering taxa that occurred in atypical habitats in the study sites, Blaberidae (semiaquatic cockroaches) and Trichodactylus fluviatilis (Decapoda) showed niche segregation, while Macrobrachium potiuna (Decapoda), Tupiperla (Plecoptera), and Nectopsyche (Trichoptera) showed niche overlap. On the other hand, Heterelmis (Coleoptera), Stenochironomus (Diptera), Phylloicus major, and Triplectides gracilis (Trichoptera) occurred in typical habitats. These results showed that shredder taxa had different habitat preferences. The observed differences in niche breadths and habitat specificities among taxa probably result in different leaf processing rates across leaf patches in Atlantic Forest streams. [ABSTRACT FROM AUTHOR]

A growing interest in the importance of simuliids in health and animal welfare in certain areas in Europe, such as around the Mediterranean basin, together with the fact that there is fragmentary ecological information on the pre-imaginal stages of these dipterans has led to the need to carry out further research. We studied the abundance and distribution of pre-imaginal stages—mainly the pupae—of simuliid species, and examined their assemblages in relation to environmental gradients identified in Mediterranean basins of eastern Spain. We report a total of 21 black fly species from the set of studied streams, where largely the most common species were Simulium (Simulium) intermedium and Simulium (Simulium) ornatum, two species of medical and veterinary concern. We found that pre-imaginal simuliid assemblages were strongly related to elevation, water temperature and turbidity, dissolved oxygen concentration and water velocity. The analysis of the optima and tolerances for these environmental factors suggests differences in ecological requirements of the pre-imaginal stages of the reported simuliid species. Likewise, it was found that the pupae of some species were strongly associated with specific substrates. We hope that our research results on autoecology of black fly species will contribute to the improvement of pest management programs. [ABSTRACT FROM AUTHOR]

There is practically no stream or river without non-native beaver impact, past or current, in Tierra del Fuego (TDF), Argentina. In this study, we evaluated the effect of beaver activity on water quality and algal composition in forested streams and rivers from TDF. We sampled five streams and rivers with current beaver activity during the austral summers of 2016 and 2017. Also, three streams which have had beaver activity in the past but with no activity since several years ago (ca. 10 years) were included in the study. Sampling was performed in a paired design upstream and downstream the beaver dam or the site where it used to be located. Physical and chemical variables as well as phytoplankton and epilithon chlorophyll-a and algal composition were monitored. Results show a decrease in dissolved organic carbon concentration and an increase in both phytoplankton abundance and periphyton taxa richness downstream the dam. The diatom Hannaea arcus was present in both communities only in impacted sites, thus influencing the clustering. In this study, we show that beaver activity influences periphyton richness and composition, and phytoplankton abundance in impacted streams and rivers, though it exerted a minor influence on water physical and chemical variables. [ABSTRACT FROM AUTHOR]

Epilithic algal community structure and function are important indicators of stream ecosystem health and are sensitive to ambient environmental changes. In this study, we examined the impact of light and nutrients on epilithic algal community structure and function by an in situ nutrient addition and shaded canopy experiment in subtropical streams in China. Epilithic algae structure, dominated by diatoms, was significantly different with nutrient addition and light reduction. Nutrient addition increased the epilithic algae and diatom density, colonial life-forms, planktonic diatoms, and high-profile diatoms but decreased the low-profile diatoms. The shaded canopy increased the low-profile diatoms but decreased the adnate life-forms, planktonic diatoms, and high-profile diatoms. Epilithic metabolism, including gross primary production (GPP), net daily metabolism (NDM), and production/respiration (P/R) increased with nutrient addition, while respiration (R) only increased when the canopy was open with nutrient addition. Epilithic GPP had a significant positive correlation with diatom density (P < 0.01, R2 = 0.9425). Our results indicated that changes in epilithic algae structure due to changes in riparian canopy coverage and nutrients could affect epilithic algal community function. Quantifying the impacts of such drivers on community structure and function is vital to effective river management. [ABSTRACT FROM AUTHOR]

The river discontinuity caused by damming can modify both the availability of production sources and the energy flow in riverine food webs. We hypothesized the carbon source support food web would vary among the reaches in response to changing in hydrogeomorphic conditions, and this variability further caused food web structure changes. To test our hypothesis, three different river reaches in the lower Jinsha River, China, were selected and the stable isotope ratios of basal sources and dominant consumers were analyzed in three seasons 2015. The relative importance of basal sources showed temporal and spatial difference to varying degrees. Seston were the most important carbon sources in supporting all consumers and the contributions increased from upstream to downstream. Riparian C3 plants played an important supplementary role in both reaches above the dam or only in the high flow period. Dam-induced flow alteration changed the trophic basis and the composition of food webs, resulting in a difference in the food web structures, and widening but with lowest complexity food web occurred in the downstream reach. The results further confirm that the differences in the hydrogeomorphologic conditions caused by dam construction can exert potential influence on riverine food web structures. [ABSTRACT FROM AUTHOR]

Our study characterized the food web of a shaded stream to investigate consumer food choices and food source quality. We measured fatty acids (FA) and elemental carbon (C), nitrogen (N), and phosphorus (P) of autochthonous and allochthonous resources and macroinvertebrates (Hydropsyche sp., Ephemerella sp., Rhyacophila sp., and crayfish-Cambaridae). We examined trophic links using FAs and identified food source quality based on essential fatty acids (EFAs) and elemental nutrients. Autochthonous food sources had greater EFA content (20:5ω3 in periphyton, 20:4ω6 in bryophyte Hygrohypnum) than terrestrial matter. FAs confirmed the grazing nature of Ephemerella. Periphyton may release this invertebrate from N and P limitation, and FA biochemical constraints. Limitation by elemental nutrients, but not FAs, may exist for Hydropsyche if feeding solely on transported matter. Crayfish FA signature suggests consumption of the bryophyte Hygrohypnum as well as terrestrial matter. Our data demonstrate that autochthonous sources are crucial for many invertebrates in shaded streams, despite limited light availability. However, detrital food sources can also be important and their contribution to stream food webs should not be overlooked. Our study highlights the importance of measuring nutrient and biochemical constraints in order to understand factors driving secondary production in streams. [ABSTRACT FROM AUTHOR]

Forestry-related land use can cause increasing instream sedimentation, burying and eradicating stream bryophytes, with severe ecological consequences. However, there is limited understanding of the relative roles and overall importance of the two frequently co-occurring stressors, increased fine sediments and loss of bryophytes, to stream biodiversity and ecosystem functions. By using random forest modeling and partial dependence functions, we studied the relative importance of stream bryophytes and fine sediments to multiple biological endpoints (leaf-decaying fungi, diatom, bryophyte, and benthic macroinvertebrate communities; leaf decomposition) using field survey data from headwater streams. Stream bryophyte abundance and richness were negatively related to fine sediment cover, highlighting the detrimental effect of sedimentation on bryophytes. However, bryophyte abundance was consistently more important a determinant of variation in community composition than was fine sediment cover. Leaf decomposition was influenced by shredder abundance, water temperature and, to a lesser degree, stream size. Our results suggest that the loss of stream bryophytes due to increasing sedimentation, rather than fine sediments per se, seems to be the key factor affecting multiple biological responses. Enhancing the re-establishment of bryophyte stands could partly compensate for the negative impacts of sedimentation on bryophytes and, consequently, on several other components of boreal stream ecosystems. [ABSTRACT FROM AUTHOR]

The study of variation of species composition among sites is key to understanding community ecology, but few studies have assessed beta diversity patterns in highly dynamic stream networks in the Neotropical region. We assessed aquatic insect patterns of local contribution to beta diversity (LCBD) and species contribution to beta diversity (SCDB) in a Neotropical drainage network composed of both perennial and intermittent streams in a dry period. We evaluated if environmental and/or spatial predictors drive patterns of LCBD. We sampled aquatic insects in 12 intermittent headwater streams and 34 perennial streams. The intermittent compared to perennial streams had higher LCBDs and lower richness. The pure environmental component significantly explained 19% of the variation of LCBD, while the pure spatial components were not significant. Forty-six taxa contributed to beta diversity above the mean of the 199 taxa. We detected the association of oxygen tolerant and good dispersal ability taxa to intermittent streams and species riffle-adapted taxa as indicators of perennial streams. We showed a disproportional contribution of intermittent streams to the regional species pool. In summary, we demonstrated that when streams dry out, compositional uniqueness may increase during the dry period making them critical to conservation planning of dynamic stream networks. [ABSTRACT FROM AUTHOR]

This study was designed to survey zonation and ion compartmentalization of mangroves in relation to water salinity along a freshwater-dominated river to reveal controlling factors of mangrove distribution, and to define differences in the mechanisms of adaptation to fluctuating salinity between true mangroves and mangrove associates. The water salinity along the river exhibited significant spatial and temporal variations, and true mangroves did not occur where freshwater was permanent. Both the true mangrove Aegiceras corniculatum and mangrove associate Hibiscus tiliaceus showed signs of preferential uptake of Cl− and K+ at low-salinity sites, and Cl− and Na+ exclusion at high-salinity sites. However, they differed in their selectivity for K+ over Na+: A. corniculatum preferentially absorbed K+ via root absorption, whereas H. tiliaceus preferentially controlled Na+ and promoted the transport of K+ from roots to stems. These findings indicate that, under fluctuating salinity, mangroves along the river maintained ion homeostasis in their tissues via preferential uptake of Cl− and K+ under low salinity and exclusion of Cl− and Na+ under high salinity. Water salinity regime and salt tolerance of mangrove species can explain the mangrove distribution along rivers. [ABSTRACT FROM AUTHOR]

Estuarine Pettaquamscutt River is a unique habitat 10 km in length with physical and biogeochemical characteristics analogous to a miniature fjord. Its meromictic upper basins are characterized by a permanent oxic–anoxic vertical gradient in which a well-oxygenated upper layer overlies a deeper, anoxic reservoir, with persistent blooms of phototrophic anoxygenic bacteria (Chromatium, Chlorobium) at the oxic–anoxic transition layer. A diverse assemblage of nanoplanktonic, centric diatoms (Cyclotella caspia, Thalassiosira pseudonana, cf. Cyclotella cryptica) dominated the seasonal phytoplankton cycle in the aerobic layer, similar to comparable meromictic habitats elsewhere. This assemblage of nano-centric diatoms appears to be trait-separated from other species clusters and is potentially useful as a functional group flora with ecophysiology diagnostic of marine estuarine rivers and meromictic habitat niche structure. The most conspicuous phytoplankton feature, however, was the year-round occurrence of the photoautotrophic euglenid Euglenaformis (Euglena) proxima, restricted in its upper water column distribution to the O2–H2S boundary layer where it formed a consortium with the photosynthetic green and purple sulfur bacteria community. The association of E. proxima with meromixis, H2S, and phototrophic anoxygenic bacteria is similar to that reported previously in a brackish Norwegian oyster poll and a brackish loch in Scotland. [ABSTRACT FROM AUTHOR]

While most anurans have limited vagility and local fidelity, there are some exceptions. In the present study, we used Boana boans, a large treefrog found throughout most of the Amazon basin, as a model organism. We investigated the possible isolation of the B. boans demes located on opposite margins of the Juruena River and their population structure. We sampled 14 individuals of B. boans and analyzed the mitochondrial D-Loop to verify whether the river or Euclidean distance is acting as barrier to the dispersal of this frog. The sequencing revealed 12 haplotypes, with global Fst values of − 0.079, K2P values ranging from − 0.187 to 0.054, and primarily intrapopulation (81.78%) genetic diversity, with only 18.22% of the variation being found among populations. Analysis of molecular variance and Bayesian cluster analysis detected a lack of genetic structuring within the study area. The model species presented a capacity for dispersal over long distances in comparison with most other amphibians, which, together with its resistance to desiccation and reproductive mode, enable this treefrog to disperse across rivers and overland. In the specific case of Juruena River, many fluvial islands present within the study area may also be favorable to the dispersal of the species. [ABSTRACT FROM AUTHOR]

Experimental streams are bounded and partly enclosed lotic units that facilitate the simulation of certain aspects of natural stream ecosystems under controlled conditions. We summarized the current knowledge regarding experimental streams in order to support researchers in designing and undertaking future studies using experimental streams. We observed an increase in the number of such studies since 1975. The geographically uneven distribution of studies suggests that the generalization of findings to global scale may not be straightforward. Our results indicate that macroinvertebrates, fish, and algae are the most frequently studied organisms and that the size of the experimental streams was related to the focal organism group(s) studied. The size of the units decreased over time, while the number of treatments, interpreted as the combination of the levels of factors, increased. These results suggest that biologically complex studies have gradually been replaced by biologically less complex ones. In contrast, the experimental complexity (the number of treatments) and the statistical power (number of replication) increased. Finally, we identified a number of important, but poorly documented pieces of information regarding experimental stream systems and experimental protocols and made recommendations for future research. [ABSTRACT FROM AUTHOR]

Headwater streams impacted by surface coal mining in the central Appalachian region of the eastern USA have characteristics not shared by reference-quality streams. These include elevated salinity, often measured using specific conductance (SC) and cited as a primary stressor of benthic macroinvertebrate communities. The study objective was to assess influence by mining-origin stressors on benthic macroinvertebrate community structure in headwater streams. Stream habitat characteristics were measured and benthic macroinvertebrates were sampled from 12 central Appalachian streams, 9 of which were influenced by mining. Multiple benthic macroinvertebrate community metrics, including Ephemeroptera density, richness, and composition were correlated negatively with watershed mining extent and with SC. Predator density and scraper richness were correlated negatively with watershed mining, stream-water selenium, and SC. Clinger richness was correlated positively with stream substrate characteristics including large cobble-to-fines ratios and relative bed stability, and was correlated negatively with watershed mining and SC. Relationships of predator density and scraper richness with selenium concentrations, and relationships of clinger richness with stream substrate characteristics, are consistent with stress mechanisms revealed by prior studies. Improved understanding of how habitat features are altered by mining and influence community structure in headwater streams can inform water resource management in mining areas. [ABSTRACT FROM AUTHOR]

Headwater streams drain large proportions of landscapes and represent a large proportion of stream habitat. Understanding their ecology requires more comparative data from the smallest streams. We describe dynamics of benthic organic material (BOM) and invertebrate assemblages in an order-2 Australian tropical stream and compare samples from orders-1 and 2 sites. Litterfall and, especially, stream discharge determined BOM standing stock. Most material was in the > 1 mm fraction, pools stored more than riffles, and order-1 sites more than order-2. BOM increased in the dry season but was depleted by wet-season spates. Retention was greater in years without major spates, when riffle-pool stream sections were largely ecologically isolated. Invertebrate richness was greater in riffles than pools and in order-2 than order-1 sites, with overlap in composition. Current velocity was the primary variable determining distributions in order-2 sites, with particulate organic matter (63–250 µm) the main variable in order-1 sites. However, explanatory relationships were weak because of unusually benign conditions during the sampling period. We need more globally comprehensive spatially explicit assessment of the ecosystem dynamics of headwater streams to predict effects of environmental change. Assessments over extended periods are necessary to capture the variability of even apparently predictable systems. [ABSTRACT FROM AUTHOR]

Available research is inconclusive on how circatidal habitat use and cross-shore distribution of aquatic epibenthic predators may affect the vertical zonation of infauna in muddy, soft-bottom substrates in estuaries. We placed fyke traps at different heights on the intertidal mudflat to assess the circatidal density of epibenthic predators. Infauna was sampled across the same tidal gradient. The abundance of epibenthic predators in the fykes decreased with elevation (decreasing inundation time), yet for the shrimp Palaemon longirostris abundance did not change with elevation in autumn. When corrected for inundation time, predator density was equal over the tidal range or higher on the high mudflat in some instances, indicating that predators evenly distributed over the mudflat or moved to the highest part during a high tide. The density of epibenthic predators did not correlate with the density of infauna, whereas the latter did show a close relationship with sediment characteristics. Our data suggest epibenthic predator density does not shape the present distribution of infauna across the tidal gradient on the oligohaline mudflats in the Scheldt. [ABSTRACT FROM AUTHOR]