Small Streams Research Articles

Mobility of Sediment and Phosphorus in a Small Stream During Artificial Flood Wave

This study investigates the dynamics of sediment and phosphorus transport in small streams affected by recurrent flood waves. The experiments were carried out in two streams with contrasting conditions: one in an agricultural headwater section, which serves as a sediment source, and the other in a mid-water section influenced by fish ponds. High-frequency data on suspended sediment and phosphorus concentrations were collected during several flood waves to assess how floods affect the transport regime, including the role of small reservoirs. The results showed that even initially clear water can mobilize significant amounts of sediment from the riverbed when discharge increases. Sediment mobilization was strongest at the beginning of the flood wave, with concentrations peaking early and then decreasing. Successive floods without additional sediment input led to a decrease in sediment concentrations, as the stream had already flushed out the available sediments. Hysteresis loops showed that most of the sediment transport occurred during the rising part of the flood wave, indicating that the sediment originated from the nearby streambed areas. Phosphorus was mobilized simultaneously with the sediment, and an almost linear relationship was observed between sediment concentration and total phosphorus (r = 0.979, p < 0.0001). However, only a fraction of the phosphorus was dissolved, so most of the phosphorus was bound to the sediment particles. Soluble reactive phosphorus showed a weaker correlation with sediment concentration (r = 0.272, p = 0.047). This shows how important it is to consider both sediment dynamics and phosphorus mobilization in event-based flood models.

Synchronicity Between the Rates of Reaeration and Pollutants Degradation During Self-Purification in a Large River.

The pollutants after were discharged into the water can gradually degrade through the self-purification. The oxygen consumption and pollutant degradation rates characterize the self-purification of small and medium-sized streams, while the dynamics of the two characteristics for large rivers has not been reported yet. The in-situ investigation for 297 sites in the 1700km stream of the Yangtze River was conducted. The oxygen consumption rate was 0.003d- 1, and the degradation rate of organic pollutants was greater than that of inorganics. The degradation of anion surfactant was the fastest, while the degradation of TN was the slowest, with rates of 0.043 and 0.001 d- 1, respectively. The oxygen consumption rate was negatively correlated with the degradation rate of COD, anion surfactant, and TP, indicating the synchronicity between reaeration and degradation during the self-purification. This study highlighted the role of synchronicity in modelling of water quality and estimation of environmental capacity for large rivers.

Three-Dimensional Particle Tracking Velocimetry Investigation of Flow Dynamics Around Simplified Stones at Low Submergence: Implications for Instream Habitat

Shallow waterways such as rapids, tributaries and smaller streams can have important ecological functions in both free-flowing and regulated rivers. As more intermittent renewable energy is introduced to the energy system to reduce CO2 emissions, the operational conditions of hydropower plants are changing. This implies various flow scenarios that can lead to more locations with shallow depths and larger variations in water levels and velocities, resulting in increased impact on the riverine ecosystem. Accurate predictions of these impacts require an understanding of the flow dynamics near large roughness elements such as boulders or trees in shallow river regions. This study uniquely investigates the effect of relative submergence, i.e., water depth relative to boulder size, on the flow field, turbulence, and potential fish habitats around idealized stone shapes (hemispheres) in shallow open channel flow using time-resolved 3D particle tracking velocimetry. The results indicate that varying relative submergence significantly affects recirculation zones, velocity and vorticity distribution, as well as turbulent kinetic energy. Notably, larger regions of lower velocity downstream of the roughness elements were generated at lower submergences, which might be favorable for fish energy conservation. Valuable insights into ecohydraulic engineering and habitat restoration in shallow waterways can be gained by understanding the fundamental flow mechanisms at low submergence for the flow around large roughness elements.

Continuous Flow Electrocoagulation System for Enhanced Phosphorous Removal in Decentralized Wastewater Treatment Systems

Decentralized wastewater treatment systems (DWTS) are significant contributors to the eutrophication of surface water bodies due to a lack of treatment mechanisms that target dissolved phosphorus removal. Existing advanced treatment systems are expensive to operate, large in nature, and require frequent maintenance, making them unattractive to DWTS owners. This study aims to investigate the development of a continuous flow treatment system that uses electrocoagulation (EC) to remove dissolved phosphorus from small wastewater streams such as septic tank effluent (STE). Operational parameters, including system hydraulic retention time (HRT), applied current density, and wastewater composition, were optimized to maximize total phosphorus (TP) removal most cost-effectively. Using an HRT of 10 min, an applied current density of 2.0 mA/cm2, and an influent concentration of 20 mg/L, the orthophosphate (OP) and TP removal percentages achieved were 99.9 and 88.1%, respectively. Under these conditions, the average effluent Al3+ concentration in the treated effluent was measured to be 1.0 mg/L while the total suspended solids concentration was measured to be 51 mg/L. The operation cost was estimated to be 0.056 CAD/m3. The results demonstrate that the EC reactor is effective in removing dissolved phosphorus from wastewater and is therefore a viable option in mitigating the risk of downstream eutrophication caused by inadequately treated STE.

Individual movement behaviour and habitat use of a small-sized cypriniform (Telestes muticellus) in a mountain stream

Knowledge about the biology and ecology of species is fundamental for their management and conservation. Despite this, many fish species and life stages are understudied, and there is a great need for research efforts to understand their ecology. Italian riffle dace (Telestes muticellus; order Cypriniformes) is a small-sized (< 15 cm) stream fish native to the Italian peninsula. There is a scarcity of research on its ecology and behaviour. In this study, we explored the movement ecology of Telestes muticellus in a Mediterranean mountain stream in Northern Italy using passive integrated transponder (PIT) telemetry. Over 15 months, 267 fish were located 2–27 times. Most fish remained stationary, while a few roamed over several hundreds of meters. Fish covered a larger linear range during spring and autumn than during other seasons. T. muticellus showed a strong preference for pools, and this preference was strongest during summer. We observed no differences in habitat use and movements between day and night, and fish size had no major effect. Within pools, many T. muticellus displayed remarkably small home ranges (median 8 m2). Fish increased their linear ranges over a period of flood events, indicating that high-flow events may be important for the downstream and upstream dispersal of T. muticellus in small mountain streams.

Reproductive intensity of fish assemblages from streams of the Contas river basin, State of Bahia, Northeastern Brazil.

Information about the reproductive biology of fish assemblages is limited, particularly for coastal basins in Northeast Brazil. However, this information is crucial for understanding species' life histories and informing conservation strategies and management actions. The scarcity of studies on the reproductive patterns of stream fish highlights a significant research gap, as this knowledge is essential for the effective conservation of these ecosystems. This study aimed to assess the reproductive intensity of fish assemblages from streams that are part of two drainages of the Contas River basin (Upper Contas and Gongogi River drainages), which are located in two distinct biomes (Caatinga and Atlantic Forest, respectively) in the Northeast Brazil. The fish were collected between November 2012 and November 2013 in four quarterly expeditions that encompassed one seasonal cycle. The captures were conducted by electric fishing in 18 sampling sites, nine in the Upper Contas River drainage and nine in the Gongogi River drainage. We obtained the reproductive intensity index (RII) of the studied assemblage, being the values compared between expeditions, drainages, and sampling sites. The highest values of RII were observed between November/December and February/March in both drainages, which demonstrated that the highest reproductive intensity was associated to the rainy season. In the Upper Contas River streams, the reproductive peak intensity seems to be synchronized to the beginning of the rainy season, while in the Gongogi River drainage streams, the reproductive intensity remains high throughout the entire rainy season. Regarding spatial variation, the highest RII values were observed in smaller streams, probably associated with a more restricted species distribution in these locations. Our results indicate that the assessed streams play a crucial role in the reproduction of many fish species, as evidenced by the high reproductive intensity observed, particularly within the fish assemblage of the Upper Contas River.

Nutrient content in tissues of Groenlandia densa, Myriophyllum spicatum and Zannichellia palustris: an attempt to understand the intercompartmental relationships in a small stream in the Middle Atlas Mountains of Morocco

Research has long focused on the relative importance of leaves and roots as sources of nutrient supply for macrophytes, as well as the function each stream compartment plays in their growth and development. This study aims to expand the debate on aquatic ecology and to better understand the connection between compartments in aquatic systems by highlighting the relationship observed in rivers between nutrients in macrophytes tissues, water, and sediments. We measured the concentrations of P-PO4, N-NO3 and N-NH4 in three different compartments of the Amengous stream in the Middle Atlas of Morocco. Myriophyllum spicatum (L.), Groenlandia densa (L.) Fourr. and Zannichellia palustris (L.) were selected as plant species. Our results show that even if the species coexist in the same habitat, they respond differently to nutrient richness. G. densa has a higher nutrient accumulation capacity than M. spicatum and Z. palustris and prefers the water compartment as a nutrient source. Although M. spicatum can accumulate phosphate compounds from water and sediment, ammonium is not its preferred nitrogen source. Z. palustris shows a tendency to accumulate nitrogen compounds through the roots, while it prefers the assimilation of phosphorus compounds through the leaves rather than the roots.

Restoring streams with large wood: An analysis of geomorphic changes 7 years post‐restoration in small coastal streams

AbstractIntroducing large wood (LW) into streams for restoration purposes is a common practice, as it creates habitat through processes like scouring, deposition and sediment sorting. However, while monitoring often focuses on short‐term (&lt;3 years) or long‐term (&gt;10 years) changes in habitat features, there is a lack of understanding regarding annual geomorphic changes over relatively long periods. In this study, we investigated annual geomorphic adjustments (channel geometry and substrate size) over 7 years in three tributaries of the Mill Creek watershed (Oregon, USA). The 7‐year period included moderate to high flows, with peak annual flow exceeding bankfull flow (Qbf) 2–5 times and flows being above half Qbf on average 4–20 days per year. Data included topographic surveys and surface pebble counts collected from 2014 (1 year before LW) to 2021 (6 years after LW). We quantified scour and deposition and estimated sediment grain sizes and sorting from topographic surveys and pebble counts. Our analysis revealed that stream size influenced geomorphic adjustment, with smaller streams experiencing more scouring compared with larger streams over the 6 years. LW structures promoted increased scouring at the cross‐section scale, with a strong relationship found between volumetric blockage ratio and scour. In our case, the most significant scouring changes were associated with volumetric blockage ratios between 35% and 50%; further research is needed to investigate scouring for higher blockage ratios. Instream changes in scour and deposition peaked around 3–4 years after LW introductions but persisted until the end of the monitoring period. Sediment size dynamics were influenced more by time since restoration than by proximity to LW jams. While LW introductions increased sediment sorting into patches, the degree of sorting declined 5–6 years post‐restoration at all sites. Our findings offer insights into the long‐term persistence and magnitude of instream changes associated with LW introductions.

Biogas Purification by Methane and Acetate Manufacturing

ABSTRACTWastewater treatment plants have two persistent financial and energetic drains, the carbon dioxide content of biogas, which limits its commercial sale, and the presence of trace organics in the wastewater effluent, which damages the aquatic ecosystem, like the Great Barrier Reef. Biogas is a renewable methane resource that is underutilized due to the variable CO2 content (~40%). Biogas is energy intensive to purify and limited by the economy of scale (&gt; 8.85 GJ/h) to large‐scale purification methods, thus small‐scale processes require development. Electrocatalytic microbes native to wastewater have been shown to convert CO2 to CH4 and acetate, however complete conversion of the CO2 content to CH4 is energy intensive. Here we show a low power bioelectrochemical fuel cell design to purify biogas to pipeline quality methane (98%), manufacture methane and/or acetate, and remove trace organics, using HCO3− as the transport charge carrier from dissolved CO2 from the biogas through an anion exchange membrane. This decreased the power required to separate CO2 from methane in biogas on a molar basis, resulting in a net energy recovery similar to current industrial systems. Magnesium anode use resulted in an energy positive system. Tests evaluated the influence of cathode potential on the current density, HCO3− ion flux and the rates and efficiencies of methane production, resulting in optimization at −0.7 V versus standard hydrogen electrode (SHE). A techno‐economic analysis modeled a positive return on investment for scaled‐up production to purify small biogas streams that are otherwise financially unrecoverable. Carbon sequestration by production of methane, acetate and solid fertilizers demonstrated profitable and energy efficient waste‐to‐resource conversion.

Molecular Identification and Description of the Tadpole of Leptobrachella melanoleuca (Matsui, 2006) (Amphibia: Anura: Megophryidae)

Identifying tadpoles will significantly enhance future studies on life histories, behavior, ecology, and distribution of amphibian species. This study provides a detailed morphological and buccopharyngeal description of Leptobrachella melanoleuca tadpoles, utilizing DNA barcoding for accurate identification. Ten tadpoles, measuring 15.0±1.22 mm (range: 12.0–16.6 mm) in body length, were collected from Khlong Saeng Wildlife Sanctuary, Surat Thani Province, southern Thailand. Mitochondrial gene sequences, including 12S rRNA, tRNA-Val, and 16S rRNA, showed less than 0.1% divergence from adult L. melanoleuca in GenBank and our adult specimens, confirming the identification. Both tadpoles and adults were found in a small rocky stream. The tadpoles exhibit dark brown coloration with brown blotches in life, while preserved specimens show significant fading. The tadpoles’ external morphology includes a translucent abdomen, darkened throat, and dark gray chest. The tail musculature is gray with light brown spots, and the fins are slightly transparent. Buccopharyngeal anatomy revealed a semicircular prenarial arena with knobby projections, narrow choanae, and a densely pustular buccal roof arena. The buccal floor features triangular tongue anlage, trapezoidal prelingual arena, and large buccal floor arena papillae. The Keratodont Row Formula (KRF) is recorded as 1:2–2/0 or 2+2/0, with black jaw sheaths. These findings contribute significantly to our understanding of tadpole morphology in the genus Leptobrachella, providing a crucial reference for future taxonomic and ecological studies of this and related species.

A Kick in the Headwaters: Evaluating a Macroinvertebrate Sampling Method for Ecological Condition Monitoring in Small Streams

ABSTRACTSmall streams dominate river networks and collectively support high biodiversity, but are rarely included in regulatory biomonitoring programmes. Macroinvertebrate communities are effective biomonitors of ecological condition and are routinely collected using 3‐min ‘kick’ samples. However, this 3‐min duration may not be suitable for small streams, which typically support fewer taxa at lower densities than larger rivers of equivalent condition. We evaluated the kick‐sampling method at 30 sites representing a national small stream monitoring network. At each site, we collected three 5‐min kick samples in 10 0.5‐min component parts. We used the families collected in 15 min to represent ‘total’ site‐scale taxonomic richness, then determined the duration needed to sample ≥ 65% of these taxa (a method and target comparable to those used in larger rivers). We also determined the sampling duration at which an average score per taxon (ASPT) biomonitoring index stabilized. Considering all streams, on average, 2.5‐min durations captured ≥ 65% of taxa, but 3.5 min was required to reach this target in temporary streams, because numerous taxa occurred at low abundance. Only 54% of samples contained ≥ 65% of taxa after 2.5 min, compared to 70% after 3 min. In most streams, the ASPT stabilized after 2 min, whereas 3 min was required to meet this target in temporary streams. Considering the variation around any estimate of capture rates introduced by natural variability, taxonomic resolution and operator error, we suggest 3 min as the most robust sampling duration to enable condition monitoring in individual small streams and comparison with larger rivers.

The perennially ice-covered Lake Enigma, Antarctica supports unique microbial communities

Northern Foothills of Victoria Land, Antarctica contains numerous hydrological formations, ranging from small surface streams and ponds fed by glacial or snow meltwater to permafrost lakes containing briny pockets. Here we describe the discovery of a massive body of unfrozen stratified oligotrophic water in Lake Enigma, a permanently ice-covered lake previously thought to be frozen from top to bottom. A remarkable feature of the Lake Enigma microbial ecosystem is the presence, and sometimes even dominance, of ultrasmall bacteria belonging to the superphylum Patescibacteria, a group apparently absent from Antarctic lakes in the well-studied McMurdo Dry Valleys. Cyanobacteria are virtually absent from Lake Enigma ice and water column although they are well represented in its extensive and diverse benthic microbial mats. Collectively, these features reveal a new complexity in Antarctic lake food webs and demonstrate that in addition to phototrophic and simple chemotrophic metabolisms, both symbiotic and predatory lifestyles may exist.

Effects of Channelization on Macroinvertebrate Assemblages in a Small Stream: The Case of Awetu in Jimma City, Ethiopia

Freshwater ecosystems are increasingly modified worldwide by anthropogenic activities. Land use change is one of the leading factors responsible for stream ecosystem degradation. Physical habitat disturbance due to channelization is among the factors responsible for the loss of biodiversity and degradation of river water quality worldwide. Since 2020, Jimma City municipality has been beautifying the city and one of the activities is channelizing using concrete embankment, a part of the Awetu stream that runs through the city. The main aim of this study is to assess the effect of channelization on macroinvertebrate assemblages and the water quality of the Awetu stream. A cross-sectional study was conducted in April 2022. Macroinvertebrates, water samples, and habitat data were collected from 21 sampling sites along the three segments of the stream (upstream, channelized, and downstream). Data were analyzed for different macroinvertebrate metrics and water quality parameters. Canonical Correspondence Analysis was used to examine the overall relationship between macroinvertebrate assemblages and water quality parameters. The upstream site has better macroinvertebrate assemblages than channelized and downstream sites (p<0.05). The downstream site showed better assemblage compared to the channelized site, though it was not significant. Regarding water quality parameters, a significant variation was observed between channelized and, un-channelized sites (upstream and downstream) (p<0.05). The habitat condition score varied from 47 (poor) at channelization to 150 (suboptimal) upstream. Upstream sites were found to have relatively better macroinvertebrate assemblages, better water quality, and good habitat conditions. The downstream sites had lower macroinvertebrate assemblages, poor habitat conditions, and degraded water quality compared to the upstream sites. The channelized segment had the poorest habitat, with poor macroinvertebrate assemblages and water quality. Thus, the conservation of habitat conditions along the channelized segments of the Awetu stream is recommended to improve the water quality and macroinvertebrate assemblage.

Five new species of the genus Grouvellinus Champion, 1923 from Guizhou Province, China (Coleoptera, Elmidae).

The genus Grouvellinus Champion, 1923 comprises 60 described species distributed across the Oriental and Palearctic regions. Species diversity is very high in mainland China, with 28 recorded species. Here, the results of the aquatic beetle survey in Guizhou Province are presented; they began in 2021, when we collected more than 5000 specimens of riffle beetle. All specimens come from small ravine streams where inhabited submerged stones. Using morphological characters of adults such as body form and size, coloration, elytral, pronotal and ventral surface structures, and forms of male and female genitalia, five new species were discovered and are described: Grouvellinusloong sp. nov., G.buyi sp. nov., G.wangmoensis sp. nov., G.lihaitaoi sp. nov., G.muyinlini sp. nov. The species descriptions contain illustrations of diagnostic characters and measurements of metric characters such as body length, pronotal length, pronotal width, elytral length and width, and head length and width. The females are, on average, larger and have only slight differences in external morphology compared to the males. The comparative diagnoses discuss characters of the new and already known species. The results show that the existing species diversity requires more detailed research focusing on larger areas of South China in the future.

Pesticide presence in stream water, suspended sediment and biofilm is strongly linked to upstream catchment land use and crop type

Pesticide pollution can present high ecological risks to aquatic ecosystems. Small streams are particularly susceptible. There is a need for reproducible and readily available methods to identify aquatic regions at risk of pesticide contamination. There is currently a limited understanding of the relationship between upstream catchment land use and the presence of pesticides in multiple aquatic matrices. The aim of this study was to develop empirical relationships between different land uses and the levels of pesticides detected in multiple aquatic matrices. The inclusion of biofilm and suspended sediment as monitoring matrices has recently been proven effective for the characterization of pesticide exposure in stream ecosystems. Ten streams in Ontario, Canada with a variety of upstream catchment land uses were sampled in 2021 and 2022. Water, suspended sediment and biofilm were collected and analyzed from each site for the presence of approximately 500 different pesticides. Each of the three matrices exhibited distinctive pesticide exposure profiles. We found a significant relationship between the percentage of agriculture and urban land use and the detection of multiple pesticides in water, sediment and biofilm (logistic regressions, P<0.05). Statistically significant probabilistic models capable of predicting pesticide detections based on upstream catchment land use were developed. High-resolution cover crop maps identified soybeans, corn and other agriculture (e.g., vegetables, berries, canola) as the key variables associated with individual pesticide detection frequencies in each of the three matrices (linear regressions, P<0.05). Soybean land use was also the strongest predictor of site-wide pesticide pollution. This modelling approach using upstream catchment land use variables has the potential to be a powerful tool to identify streams at risk of pesticide pollution.

Population characteristics, seasonal distribution, and suppression potential of introduced Northern Pike in a Great Plains stream

AbstractObjectiveThe objectives of this study were to describe the population dynamics, reproductive characteristics, and movement of Northern Pike Esox lucius in the Niobrara River drainage of Wyoming. This information was used to estimate the necessary level of suppression to meaningfully reduce their abundance and thereby facilitate persistence of native nongame fishes.MethodsIn 2019 and 2020, Northern Pike were sampled to describe population size structure, age structure, growth, and mortality. An additional 42 gravid female Northern Pike were collected across 2020–2023 to determine a length–fecundity relationship. Vulnerability to recruitment overfishing was modeled with a static spawning potential ratio model. Finally, 15 mature fish were implanted with radio transmitters in 2021 and 2022 and tracked for 1 year to determine seasonal dispersal and spawning locations.ResultSampled Niobrara River drainage Northern Pike (n = 213) varied from 127 to 749 mm total length. Estimated ages of fish were between 0 and 8 years, and total annual mortality was estimated at 42% (95% confidence interval = 36–48%) in the presumed absence of fishing mortality. Recruitment was extremely stable, and growth was relatively fast through age 2. Some females matured at age 1, and all females were mature by age 2 and spawned annually. Estimated total fecundity for females between 297 and 914 mm total length varied from 3573 to 154,877 eggs. Most telemetered fish moved little throughout the year, but movements as large as 5.9 river kilometers were observed. Modeling suggests that exploitation of age‐1 and older Northern Pike should exceed 42% and exploitation of age‐2 and older fish should exceed 85% to meaningfully reduce the population's reproductive potential.ConclusionNorthern Pike growth and reproductive potential at older ages may be more limited in small prairie streams than within their native range. Observed annual home range was small, and spawning occurred annually in consistent locations. The necessary intensity of mechanical removal to achieve meaningful suppression in this system will likely require an intensive and ongoing interstate effort.

Lowland Interior-Forest Stream Habitat of Galictis vittata (Carnivora: Mustelidae) on the Las Piedras Tributary, Southeastern Peru.

Records of Galictis vittata (Greater Grison) from the Amazon basin are sparse, particularly in the Madre de Dios region, where only three records have been published. This study elaborates on seven observations of Galictis vittata within and near small interior forest streams of the Las Piedras tributary in Madre de Dios, Peru. While G. vittata inhabits terrestrial environments, it has also been observed in association with aquatic habitats in parts of its range. Although limited to seven observations, all documented sightings of G. vittata in the Las Piedras region have been associated with stream ecosystems. Based on our records, prior research from the region, and known natural history of the species, we hypothesize that streams are a preferred habitat in Amazon rainforests. Additionally, we provide behavioral notes associated with the encounters.

Migration patterns, habitat use and genetic origins of sea trout (Salmo trutta) in Norfolk chalk streams: implications for management of a mixed stock fishery

Sea trout, the anadromous ecotype of the species Salmo trutta, are subject to multiple threats, including exploitation and aquaculture impacts in the marine environment, habitat fragmentation and pollution in freshwaters, loss of genetic resilience due to interbreeding with hatchery strains and environmental change. Small streams contribute relatively little biomass to European sea trout stocks but are thought to be important in maintaining genetic diversity and therefore wider population resilience. The current study combined data from acoustic telemetry, stable isotopes, genetics and scalimetry to assess the current status of sea trout in the rivers Stiffkey and Glaven, two locally important chalkstreams in East Anglia, UK, to provide an evidence base for future management. The incidence of anadromy was low, and most sea trout were near migrants, residing in the lower reaches of rivers and close to the tidal outfalls. A small number migrated to the North Sea where they were vulnerable to exploitation in the coastal fishery, which comprises a mixed stock. Straying between the two rivers was recorded among 10% of sea trout, leading to apparent high gene flow. Nonetheless, genetic data also demonstrated structuring of River Glaven trout into two distinct groups. Quantification of patterns of freshwater and estuarine habitat use, and of passage at cross-channel obstructions, was used to identify where remedial measures such as habitat restoration would be most effectively targeted. Findings are discussed in the context of local supplementary stocking and the potential impact of the nearshore fishery on limited and vulnerable small stream anadromous trout populations.

The impact of repeated pyrethroid pulses on aquatic communities

Pesticides are considered to be one of the main causes of the decline in macroinvertebrate biodiversity in small streams. In particular, pyrethroids are detected in agricultural surface waters worldwide and pose a high risk to aquatic invertebrates. Due to their knock-down effect, even short pyrethroid exposure pulses can have significant short- and long-term effects on macroinvertebrate communities. Therefore, it is necessary to consider more realistic exposure scenarios for the environmental risk assessment of pyrethroids and, consequently, to obtain more realistic effect data by using multi-stressor test systems.In an experimental setup with artificial indoor streams (AIS), four pyrethroid pulses simulated the exposure scenario of heavy rainfall events. Effects of these 12 h-exposures at different concentrations of deltamethrin (0.64 ng/L, 4 ng/L, 16 ng/L, 64 ng/L) with intervening recovery periods of six days were assessed on an aquatic community consisting of Gammarus pulex, Ephemera danica, Lumbriculus variegatus and Potamopyrgus antipodarum with various lethal and sub-lethal endpoints.The mortality rate of G. pulex significantly increased with increasing deltamethrin concentrations, whereas the mean number of offspring significantly decreased (NOECoffspring: 16 ng/L, LOECoffspring: 64 ng/L). The biomass of L. variegatus decreased with increasing deltamethrin concentrations (NOECdry weight: 16 ng/L, LOECdry weight: 64 ng/L).The findings of this study clearly demonstrate that 12 h-deltamethrin pulses at environmentally relevant concentrations adversely affect an aquatic community. Based on the results of this study a RAC value of 5.33 ng/L is assumed, which is below the concentrations measured in rivers of up to 58.8 ng/L. Unacceptable effects on the entire freshwater environment can therefore not be ruled out. The experimental AIS approach is a useful tool for assessing the effects of repeated pulse exposures that occur during surface runoff events.

Flow analysis and optimization study of main components of flow-type small hydro turbine system

Abstract Small hydro power generation refers to the production of electricity by harnessing the kinetic energy of water in small rivers or streams, typically generating up to 10 MW of power. The optimal shape combination of the watercone and turbine, according to the water flow rate, is crucial for maximizing the power generated. In this study, flow analysis using computational fluid dynamics was performed on Kaplan turbines to examine the effects of blade angle, volume flow rate and rotational speed on power generation. To ascertain the impact of variables on power generation, the internal flow field was examined. The findings demonstrated that an increased blade angle perpendicular to the flow direction resulted in a reduced incidence of vortices and cavitation formations within the turbine wake. A predictive model was generated using a design of experiment and response surface methodology to generate a predictive model to find the power generation for flow rates, blade angles and rotational speed within the experimental range.