Stream Stretches Research Articles

Assessing water diversion impacts on the fish community size structure in headwater stream stretches

Water diversion for hydropower plants is one of the leading causes of habitat alteration and biotic homogenization. The impacts of small hydropower plants on fish communities are usually assessed using taxonomic composition and structure indicators. Size-based indicators are useful tools to evaluate the effects of environmental factors and anthropogenic perturbations on riverine ecosystems. In this study, we investigated the impact of water diversion on fish community body size structure in 16 small hydropower plants in the upper Ter River basin (NE Iberian Peninsula). We tested the use of multiple size-based metrics under different sampling intensities (one- vs. four-pass electrofishing) and compared control vs. diverted stream stretches. Results revealed that water diversion had a negative effect on fish community average and median length, while size spectrum and size diversity metrics showed no responses to the impact. Altitude was positively related with body size metrics and was the strongest natural driver affecting them. Moreover, we found that all the size-based metrics exhibited consistent values under different sampling efforts. Our findings suggest that size-based metrics could be useful indicators for bioassessment of river flow alteration and that one-pass electrofishing was robust enough to characterize the stream fish community size structure in our study.

Taxonomic and functional diversity patterns of stream fish assemblages from Brazilian Atlantic Rain Forest

Disentangling the hierarchical structure of river systems and multi-scale environmental effects is essential for understanding freshwater fish community structure and function. We sampled 70 stream stretches to investigate how the taxonomic and functional composition and diversity of fish assemblages responded to the environment considering a hierarchical organisation of streams in three Brazilian watersheds (Upper Sorocaba, Upper Paranapanema and Upper Ribeira de Iguape). Functional diversity indicated that stream fish community function was independent of the watershed. The most critical environmental variable was substrate gradient. In streams with a consolidated substrate, equitability and functional dispersion were low due to invertivores occurring in this type of substrate. Our results highlight the importance of local environmental filters for shaping streams fish assemblages across different basins. This shaping was more evident when functional descriptors of assemblages were analysed, thereby reinforcing the importance of an approach based on traits as a tool to elucidate local community assembly processes at broader spatial scales.

Protected areas and compositional diversity of fish from Serranias Costeiras of the Ribeira de Iguape River basin, Southeast Brazil

Abstract The Serranias Costeiras of the Ribeira de Iguape River basin comprise landscapes with steep slopes, where many streams are contained in protected areas. We evaluated the importance of these protected areas for stream fish diversity. We sampled the ichthyofauna during the dry season of 2010, 2018 and 2019 in 36 stream stretches. We used beta diversity measures and estimated species richness and dark diversity in streams from two types of protected areas (full protection, FP and sustainable use, SU) and outside (Out). The altitude-width and velocity gradient of the streams explained the species turnover. The PA type promoted the richness difference, with FP streams having less species richness than SU and outside. Streams from FP presented lower species richness and dark diversity. These results indicate that the few species in FPs are well protected. The FP streams contain a relevant proportion of the regional species pool and, therefore, are essential for conserving fish stream diversity in the study region. On the other hand, streams from SU or Out have higher species richness, but their fish fauna is more vulnerable. Due to longitudinal stream connectivity, we highlight the importance of rethinking the limits of protected areas.

Shortcuts for biomonitoring programs of stream ecosystems: Evaluating the taxonomic, numeric, and cross-taxa congruence in phytoplankton, periphyton, zooplankton, and fish assemblages.

Different biological groups can be used for monitoring aquatic ecosystems because they can respond to variations in the environment. However, the evaluation of different bioindicators may demand multiple financial resources and time, especially when abundance quantification and species-level identification are required. In this study, we evaluated whether taxonomic, numerical resolution and cross-taxa can be used to optimize costs and time for stream biomonitoring in Central Brazil (Cerrado biome). For this, we sampled different biological groups (fish, zooplankton, phytoplankton, and periphyton) in stream stretches distributed in a gradient of land conversion dominated by agriculture and livestock. We used the Mantel and Procrustes analyses to test the association among different taxonomic levels (species to class), the association between incidence and abundance data (numerical resolution), and biological groups. We also assessed the relative effect of local environmental and spatial predictors on different groups. The taxonomic levels and numerical resolutions were strongly correlated in all taxonomic groups (r > 0.70). We found no correlations among biological groups. Different sets of environmental variables were the most important to explain the variability in species composition of distinct biological groups. Thus, we conclude that monitoring the streams in this region using bioindicators is more informative through higher taxonomic levels with occurrence data than abundance. However, different biological groups provide complementary information, reinforcing the need for a multi-taxa approach in biomonitoring.

The effect of different logging regimes on the ecomorphological structure of stream fish assemblages in the Brazilian Amazon

AbstractWe evaluated the effects of changes in habitat structure resulting from conventional logging (CL) and reduced-impact logging (RIL) on the ecomorphological structure of stream fish assemblages in the eastern Brazilian Amazon, investigating (1) which habitat characteristics are influenced by different logging methods, (2) the differences in the ecomorphological structure of fish assemblages between two logging methods and undisturbed forest (UF), and (3) the relationships between ecomorphological traits of fish assemblages and habitat variables. We measured 13 habitat variables and characterized 11 ecomorphological traits of 55 fish species collected in 34 sampling sites (stream stretches) located in CL, RIL, and UF. In logged areas, the streams present a fine sediment increase and reduced vegetation cover, while in the UF a greater amount of natural shelter and more cover vegetation were observed. These environmental changes selected ecomorphological traits of stream fish assemblages, recording a greater relative width of the mouth in UF, higher ventral flattening index in RIL, or greater relative head length, and higher caudal peduncle compression index in CL. In this sense, we recommend that logging practices, including RIL, should be reviewed as a means of adopting better strategies to minimize human disturbances in streams.

A stream multimetric fish index in a large-sized city in south-eastern Brazil

Abstract: Aim Our study was carried out to develop a multimetric index suitable for urban wadeable streams in Sorocaba, a large-sized city from the Atlantic rainforest in south-eastern Brazil. Methods Twenty-seven stream stretches were selected for environmental and fish evaluation. Twenty ecological metrics were tested over an environmental gradient between the reference and degraded stretches. Candidate metrics were screened for range, responsiveness, and redundancy. We calculated a multimetric fish index (MFI) subdivided into five quality classes: reference ≥ 0.8, 0.6 ≤ good < 0.8, 0.4 ≤ moderate < 0.6, 0.2 ≤ poor < 0.4, and bad < 0.2. Results Four metrics were adequate for discriminating higher biotic quality from degraded stretches. Five stream stretches (18%) were classified as a reference or good, and 16 (60%) were poor or bad. Three reference stretches could be used for a hydromorphological restoration programme. Conclusion Our results indicated that biological integrity was altered, which was indicative of severe environmental degradation. Our study results may be useful for a management and restoration project of the Sorocaba/Médio Tietê hydrographic basin.

The identity of Rasbora neilgherriensis (Teleostei: Danionidae), with a re-description.

Rasbora neilgherriensis Day, long considered a synonym of Rasbora daniconius or Rasbora dandia, is re-described and shown to be a valid species based on an examination of type and recently-acquired topotypical specimens from the Western Ghats of India. The species is characterised by a complete lateral line with 32-34 pored scales on body, ½5-6/1/2½ scales in transverse line on body, a mid-lateral stripe that is 2½ scales wide anterior to the pelvic fin and 1-1½ scales wide on the caudal peduncle, and a caudal fin that is emarginate to forked with broadly rounded lobes. The species was recorded from the Cauvery River Basin in Kerala and Tamil Nadu, India, at elevations ranging from 710 m to 2015 m above sea level, in stream stretches with relatively denser riparian canopy cover.

Combining geostatistical and biotic interaction model to predict amphibian refuges under crayfish invasion across dendritic stream networks

AbstractAimBiological invasions are pervasive in freshwater ecosystems, often causing native species to contract into areas that remain largely free from invasive species impacts. Predicting the location of such ecological refuges is challenging, because they are shaped by the habitat requirements of native and invasive species, their biotic interactions, and the spatial and temporal invasion patterns. Here, we investigated the spatial distribution and environmental drivers of refuges from invasion in river systems, by considering biotic interactions in geostatistical models accounting for stream network topology. We focused on Mediterranean amphibians negatively impacted by the invasive crayfishes Procambarus clarkii and Pacifastacus leniusculus.LocationRiver Sabor, NE Portugal.MethodsWe surveyed amphibians at 168 200‐m stream stretches in 2015. Geostatistical models were used to relate the probabilities of occurrence of each species to environmental and biotic variables, while controlling for linear (Euclidean) and hydrologic spatial dependencies. Biotic interactions were specified using crayfish probabilities of occurrence extracted from previously developed geostatistical models. Models were used to map the distribution of potential refuges for the most common amphibian species, under current conditions and future scenarios of crayfish expansion.ResultsGeostatistical models were produced for eight out of 10 species detected, of which five species were associated with lower stream orders and only one species with higher stream orders. Six species showed negative responses to one or both crayfish species, even after accounting for environmental effects and spatial dependencies. Most amphibian species were found to retain large expanses of potential habitat in stream headwaters, but current refuges will likely contract under plausible scenarios of crayfish expansion.Main conclusionsIncorporating biotic interactions in geostatistical modelling provides a practical and relatively simple approach to predict present and future distributions of refuges from biological invasion in stream networks. Using this approach, our study shows that stream headwaters are key amphibian refuges under invasion by alien crayfish.

The effects of fisheries management on harvest rates of native and non‐native salmonid fish species

In central Europe, both brown trout Salmo trutta and European grayling Thymallus thymallus are threatened native salmonid species with high value in recreational angling and nature conservation. On the other hand, rainbow trout Oncorhynchus mykiss and brook trout Salvelinus fontinalis are intensively stocked non-native species of high angling value but no value for nature conservation. This study tested if harvest rates of native salmonids are negatively correlated to intensive stocking and harvest rates of non-native salmonids in inland freshwater recreational fisheries. Data were collected from 250 fishing sites (river and stream stretches) over 13 years using mandatory angling logbooks. Logbooks were collected from individual anglers by the Czech Fishing Union in the regions of Prague and Central Bohemia, Czechia (central Europe) and processed by the author of this study. In result, anglers harvested 200,000 salmonids with total weight of 80 tons over 13 years. Intensive stocking of multiple salmonid species lead to slightly lower harvests of native salmonids. Inversely, intensive harvests of multiple salmonid species lead to slightly higher harvest of native salmonids. Recapture rates of stocked salmonids were relatively low (0.6%–3.7%), proving fish stocking moderately ineffective. Since the effects of non-native salmonid stocking and harvest rates on native salmonid harvest were significant but not strong, it is suggested that rivers and streams that support fishing for non-native salmonids still support fishing for native salmonids. However, this idea does not apply for fishing sites with really high intensity of non-native salmonid stocking – harvest rates of natives were very low on these fishing sites.

An Assessment of Self-Purification in Streams

The territory of Lithuania is characterized by a prevailing moisture excess, therefore in order to timely remove excess water from arable lands, the drainage systems have long been installed. In order to drain excess water people used to dig trenches, to regulate (deepen or straighten) natural streams. The length of regulated streams has reached 46,000 km and they are deteriorated ecosystems. Investigations showed that the self-purification of streams from nitrates and phosphates is more effective in natural stretches than in stretches regulated for drainage purposes. Decrease in the average concentration of nitrates in natural and regulated stretches are 8.8 ± 5.0 and 3.0 ± 2.9 mg NO 3 − L−1, respectively. The average coefficient of nitrate self-purification, at a confidence level of 95% in natural stream stretches is 0.50 ± 0.22, and in regulated is −0.15 ± 0.21 km−1, and this difference is essential. The change in the average concentration of phosphates in natural and regulated stretches is almost the same, 0.2 ± 0.1 and 0.2 ± 0.2 mg PO 4 3 − L−1, respectively. The average coefficient of phosphate self-purification, at a confidence level of 95%, in natural stream stretches is 0.28 ± 0.12, in regulated −0.14 ± 0.12 km−1, and this difference is not essential. In terms of the need for the renovation of drainage systems it is suggested that soft naturalization measures are first applied in the streams of Western (Samogitian) Highlands, Coastal Lowlands, and South-Eastern Highlands to improve their self-purification processes.

Responses of macroinvertebrate communities to land use specific sediment food and habitat characteristics in lowland streams

The input of land use specific organic matter into lowland streams may impact sediment characteristics in terms of food resources and habitat structure, resulting in differences in macroinvertebrate community composition. Therefore, we investigated to what extent land use specific sediment food and habitat characteristics structure macroinvertebrate communities. To this purpose linear multiple regression models were constructed, in which macroinvertebrate biotic indices were considered as response variables and sediment characteristics as predictor variables, analysed in 20 stream stretches running through five different land use types. Sediment characteristics and macroinvertebrate community composition were land use specific. The carbon/nitrogen (C/N) ratio, woody debris substrate cover and the origin of fatty acids influenced macroinvertebrate community composition. Shannon-Wiener diversity was better explained by fatty acids origin, such as in grassland streams, where a higher relative content of plant derived fatty acids related to a higher macroinvertebrate diversity. In cropland and wastewater treatment plant (WWTP) streams with a low C/N ratio and dominated by microbial derived fatty acids, higher abundances of Oligochaeta and Chironomus sp. were observed. Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness was positively related to woody debris substrate cover, which only occurred in forest streams. Hence, macroinvertebrate community composition was influenced by the origin of the organic material, being either allochthonous or autochthonous and when autochthonous being either autotrophic or heterotrophic. It is therefore concluded that sediment food and habitat characteristics are key ecological filters.

Particularities of Grey Alder (Alnus incana) Stands in Riparian Galleries Along Streams of the Southern Transylvanian Tableland (Romania)

Abstract Grey Alder (Alnus incana (L.) Moench.) stands are distributed in the Carpathian area on alluvial deposits with sediments of different grain size as galleries along rivers and streams of the sub-montane to the middle montane level. The geological structure (Tertiary sedimentary deposits) in relation to the hydromorphological processes is the base for the structure of the stream valleys, which are in part very deep. Under the special microclimate of these deeper stream stretches with lower temperatures there are favourable conditions for the development of grey alder stands.

Astronomers track dwarf galaxies to better understand the Milky Way’s make-up and evolution

At the turn of this century, astronomers were confident they understood the Milky Way’s relationship with its galactic neighbors. Our home galaxy is the second-largest member of the Local Group, an assembly of more than 50 galaxies that spans roughly 10 million light-years. Many of the group’s smaller galaxies are satellites of the Milky Way—two of the closest companions are the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). Streams of gas and dust ripped from these dwarf galaxies seemed to show that they had made several trips around the Milky Way, bearing witness to the destruction wrought by our galaxy. By studying the masses and movements of nearby galaxies, astronomers may collect details that rewrite the story of our own galaxy’s evolution. In this combined radio and visible-light image, a ribbon of gas called the Magellanic Stream (pink) stretches halfway around the Milky Way (light-blue band). Nearby galaxies known as Magellanic Clouds appear in the bottom right as white spots. Image courtesy of Nidever, et al. (Montana State University/NOAO), NRAO/AUI/NSF and Meilinger, Leiden-Argentine-Bonn Survey, Parkes Observatory, Westerbork Observatory, Arecibo Observatory. But this neat picture was upended almost a decade ago when researchers used NASA’s Hubble Space Telescope to precisely measure the clouds’ motion. Suddenly, it became clear that the LMC and SMC are actually making their first orbit around the Milky Way. Since then, researchers have been trying to pin down the masses and movements of the clouds, details that could rewrite the story of our own galaxy’s evolution. This year, the European Space Agency (ESA) space telescope Gaia has provided some vital clues in that quest. Gaia found that the LMC itself boasts several ultra-faint dwarf galaxies as satellites, observations that are helping constrain the masses of the cloud and the Milky Way. They also provide strong …

Tropical lotic primary producers: Who has the most efficient photosynthesis in low‐order stream ecosystems?

Abstract Photosynthetic performance was assessed for the main groups of primary producers of low‐order tropical streams, comprising macroalgae (11 taxa of Chlorophyta, Rhodophyta and Xanthophyta plus Cyanobacteria), bryophytes (2), angiosperms (3), and the periphytic community, by means of the Chl‐a fluorescence and oxygen evolution techniques. Samples of primary producer were collected in nine stream reaches within the same drainage basin that were characterised as open or partially shaded. Low values of compensation irradiance (Ic) were found for all species tested, suggesting that they are able to maintain an autotrophic metabolism even under very low irradiances. Parameters derived from photosynthesis–irradiance curves revealed high values of the saturation parameter (Ik), associated with relative low values of photosynthetic efficiency (αETR) and photoinhibition (βETR) for species of Chlorophyta and the periphyton, suggesting adaptation to high irradiance conditions. Species of Rhodophyta, Xanthophyta, Bryophyta and angiosperms showed, in general low values of Ik and moderate to high values of αETR and βETR, indicating typical photosynthetic responses of shade‐adapted plants. Chlorophyta and the periphyton showed high photosynthetic efficiency in high irradiance, and rhodophytes, bryophytes and angiosperms seemed to be more efficient in shaded stream stretches. Considering that Cyanobacteria showed high values of the photosynthesis/respiration (P/R) ratio, we suggest that this group is the most efficient primary producer in a wide range of low‐order tropical streams. This physiological trait could be a feature that favours the abundance of Cyanobacteria in the benthic primary producer community, as is often reported in the literature.

High β‐diversity maintains regional diversity in Brazilian tropical coastal stream fish assemblages

AbstractUnderstanding spatial patterns of species diversity and the variables that structure biological communities is critical to successful ecosystem management. Regional diversity (γ) can be considered a combination of local diversity (α) and among sites variation (β). Using abundance data of fish species in 19 stream stretches, an analysis of diversity partitioning was used to determine the contribution of α‐ and β‐diversity to γ‐diversity. Redundancy analysis was applied to find the contribution of environmental variables and spatial configuration to species composition. Intersite variation contributed significantly to γ‐diversity. Spatial configuration and instream heterogeneity (coarse substrate, channel width, water velocity and shading) and riparian vegetation were related to local fish abundances. Conservation actions should consider that all streams are important, and prioritisation of just a small number of the richest sites is not appropriate.

Temporary pools provide stability to fish assemblages in Amazon headwater streams

AbstractTemporal variations in the environment may function as disturbances that affect population processes and change the structure and composition trajectories of communities. The presence of refuges may buffer such variations and also support the recovery of communities after disturbances. In this study, we tested the effect of temporary pools as seasonal refuges for the ichthyofauna in upland forest streams in the Brazilian Amazon. We sampled environmental characteristics and fish in five occasions over one seasonal cycle in eight stream stretches and their adjacent temporary pools in Reserva Ducke, Manaus. We recorded 27 fish species, 13 of which occurred in both habitats and represented 81% of the total fish abundance in the stream–pool system (3695 records of fish, 54% made in pools). During rainy periods, fish abundance in pools was higher than in the channels. Total number of records varied inversely among habitats over time with a reduction in the pools and an increase in the channels as the pools gradually desiccated. The number of species exhibited a similar pattern. When data from pools and channels were pooled, representing the entire flood zone, fluctuations in all the measured variables along the time were smoothed. The variability in fish assemblage composition was associated with variability in the volume of water in the entire system. These results indicate that temporary pools are an important habitat component of upland forest streams, providing resources and spatial refuges for the fish during rainy periods, and regulating the stability of these communities.

Do non-native pumpkinseed Lepomis gibbosus affect the growth, diet and trophic niche breadth of native brown trout Salmo trutta?

Brown trout Salmo trutta Linnaeus, 1758, is a priority species for conservation and management efforts in many European countries. In its native range, interactions with non-native fishes often adversely affect somatic growth rates and population abundances. Consequences of introduced North American pumpkinseed Lepomis gibbosus (Linnaeus, 1758) for native S. trutta were examined in stream stretches with and without L. gibbosus. Data for somatic growth rates and trophic niche breadth (using stable isotope analyses) provided little evidence of L. gibbosus presence being detrimental for S. trutta. Shifts in S. trutta diet at all sites were associated with increased piscivory with increasing body length, with no evidence to suggest that interspecific resource competition with L. gibbosus structured the food web or affected trophic positions. Three years later, and following L. gibbosus removal, data revealed slight shifts in the food web at each site, but these related to shifts in resources at the bottom of the food chain rather than a response to L. gibbosus removal. Consequently, the ecological consequences of L. gibbosus for S. trutta in the study stream were minimal, with S. trutta populations responding more to natural mechanisms regulating their populations than to the presence of this non-native fish species.

Anuran Communities in Different Riparian Habitats: Native Forest, Secondary Forest, and Sugarcane

Abstract. This study aimed to test the influence of different riparian habitats on the structure of anuran communities in southeastern Brazil. Nine stream stretches were selected representing three different riparian habitat types: Native Forest, Secondary Forest, and Sugarcane. A total of 223 individuals of 17 species and five families were captured. The Chao1 richness index indicated that after standardizing the sampling effort the Native Forest sites had higher richness than the Secondary Forests and Sugarcane sites, which presented similar richness. The Abundance and Biomass Curves for the Native Forest sites showed an overlap of the weight and abundance curves, suggesting that these sites presented lower disturbance levels. A disturbance gradient from Native Forest towards Sugarcane sites was observed. The Bray-Curtis similarity index showed a significant effect of riparian condition on species composition. Our results suggest that Sugarcane and Secondary Forest sites limit the distribution of certai...

Alpha and beta diversity of phytoplankton in two subtropical eutrophic streams in southern Brazil

This paper reports the alpha and beta diversity of phytoplankton communities of two streams differing in land use. We analyzed which environmental conditions affect diversity of the phytoplankton communities and tested the hypothesis that stream stretches protected by forests will have lower species richness, whereas higher beta-diversity would occur among the non-protected stretches. Samples were taken quarterly, from February to November 2012, in nine stretches, including four non-protected stretches, two partially protected stretches and three totally forest-protected stretches. Eleven abiotic variables and their coefficients of variation were analyzed. Phytoplankton was analyzed for species richness (alpha diversity), frequency of occurrence and beta-diversity. Species richness was calculated by first and second order jackknife indexes. Biotic data were submitted to Sorensen similarity analysis. A total of 429 infrageneric taxa were reported, representing 88% of the estimated expected species richness. The phytoplankton composition was typical for lotic environments with high richness values of Bacillariophyceae (66.0%). High phytoplankton richness values occurred in all the sampled stretches, even though beta-diversity was moderate and indicated similarity between the sampled stretches, therefore only a part of the original hypothesis was corroborated.

The Magellanic Stream: Circumnavigating the Galaxy

The Magellanic Clouds are surrounded by an extended network of gaseous structures. Chief among these is the Magellanic Stream, an interwoven tail of filaments trailing the Clouds in their orbit around the Milky Way. When considered in tandem with its Leading Arm, the Stream stretches over 200° on the sky. The Stream is thought to represent the result of tidal interactions between the Clouds and ram-pressure forces exerted by the Galactic corona, and its kinematic properties reflect the dynamical history of the pair of dwarf galaxies closest to the Milky Way. The Stream is a benchmark for hydrodynamical simulations of accreting gas and cloud/corona interactions. If the Stream survives these interactions and arrives safely in the Galactic disk, its cargo of over a billion solar masses of gas has the potential to maintain or elevate the Galactic star-formation rate. In this article, we review the current state of knowledge of the Stream, including its chemical composition, physical conditions, origin, and fate. We also review the dynamics of the Magellanic System, including the proper motions and orbital history of the Large and Small Magellanic Clouds, the first-passage and second-passage scenarios, and the evidence for a Magellanic Group of galaxies.