Downstream Stretch Research Articles

Boa Esperança's Dam Reservoir Ichthyofauna

Objective: The the present study investigated the composition and structure of the fish assemblage of the reservoir of Boa Esperança, located in the main body of the Parnaíba River, aiming to contribute to the expansion of knowledge on fish diversity of anthropic ecosystems and subsidizing management actions for the conservation of the diversity of inland waters. Method: Traps installation points were randomly chosen in order to include the greatest possible amount of aquatic microhabitats found in the Boa Esperança dam lake, on the Parnaíba river, in order to capture the greatest possible fish diversity. Samples were collected every two months, between September 2013 and October 2014 (SISBIO 42018-2 OF 12/12/2013), in which standardized gill nets were used (from 3 to 10 cm between opposite). Research results and discussions: The result of the fauna inventory was a total of 823 specimens, subdivided into 6 orders, 20 families and 39 species. The most abundant species upstream was the "Arenga" Pellona flavipinnis, with 198 specimens captured, accounting for 24% of the total capture in both systems. In the downstream stretch, it was the "Pacu" Myleus asterias, corresponding to 6.8% of the total capture in both systems, with 14 endemic species. Research implications: Implications of the research: The results obtained serve to show the impacts caused by the construction of the dam on the local ichthyofauna. Originality/Value: This study contributes to the understanding of the effect of dams on the maintenance, preservation and modification or not of the ichthyofauna existing in the rivers where they are implemented. It also serves as a basis for future analyses of the effects of dams on riverside populations that use the local ichthyofauna as a source of subsistence.

Water and Environment of Kangsabati River

The normal flow of the Kangsabati River, famous for its reservoir at Mukutmanipur, has been practically stopped due to damming on a temporary basis particularly in middle and downstream stretches. Although there are no significant towns on the riverbanks, water is polluted by mixing of waste materials in the river water from the non-point sources. The pollution level of this river is determined in the category of priority IV for BOD concentration 6.4 mg/l of the surface water samples near Midnapore town.

The late Pleistocene - Holocene sedimentary evolution in the Ba Lat River mouth area of the Red River Delta

The Ba Lat estuary is part of the downstream stretch of the Red River Delta, the second-largest Delta in Vietnam and the 12th largest in the world. This study analyses GAT borehole sediments in the Ba Lat estuary area to assess environmental changes during the Late Pleistocene - Holocene period. This entailed detailed analyses of 70 m-deep borehole data from the Ba Lat estuary area, including structural analysis of 70 m-deep sediment core samples, 230 samples of grain size, 49 samples of Foraminifera, five samples of petrographic thin slices, and four samples of radiocarbon dating.
 The data reveal nine sedimentary facies, including river channel sand facies, floodplain clayey silt facies, tidal flat sandy-silty facies, bay clayey silt facies, pro-delta clayey silt facies, delta front sandy-silty clay facies, mouth bar sand facies, tidal flat sandy - silty clay facies, and delta plain silty clay facies. The combined nine sedimentary facies formed sequentially in time, representing the evolution of the sedimentary environment from the Late Pleistocene to the Holocene and the evolutionary process from the continental to the estuarine and Delta environment.
 The results also enable the geographic identification and delineation of the incised valley in the Red River Delta during the Late Pleistocene to Holocene period. The sedimentation rate in the incised valley varies from period to period. In the sedimentation phase of the incised valley, the average accretion rate reached 11.64 mm/year. In contrast, during the open sea regime (shallow sea near the coast), the accretion rate was observed to be very low, with a rate of 1.27 mm/year and the period of delta formation had the highest accretion rate, reaching 13.41 mm/year.

Geochemical characterization, its controlling factors, and comparison between the upstream and downstream segments of the Himalayan Satluj River basin, India

Satluj River Basin (SRB) has special economic significance, representing the country's most incredible hydro-structure with fresh water, a primary source of irrigation and hydroelectric power in Northern India. Therefore, SRB's geochemical characterization is vital for hydropower and agricultural sustainability. This study provides a preliminary characterization of the hydrogeochemical processes controlling the natural water evolution in SRB by observing the spatial variation and qualitative assessment of solute chemistry (major ions and trace/heavy elements) in the Satluj river, associated tributaries, and groundwater. Hydrochemical characteristics displayed the predominance of geogenic weathering processes with carbonates dissolution and silicate weathering as end members that could explain all the geochemical variability within the SRB. The results reveal that the chemical signature of the upstream segment is possibly influenced more by carbonate weathering than silicate weathering, and the trends reverse in the downstream section with the increasing influence of silicate weathering. Dissolved heavy metals (HMs) such as Mn, Cr, Fe, Co, Ni, Cu, Zn, As, Cd, and Pb showed large fluctuations among upstream and downstream sampling sites, indicating diverse environmental conditions. Human health risk assessment (HHRA) studies revealed less or no potential noncarcinogenic via HMs, except for the downstream stretch of tributaries inferring increased non-cancerous risk. Moreover, the HHRA with HMs (Cr, As, Cd, and Pb) manifested high carcinogenic risks for adults and children across the SRB. The finding of this study could be the baseline dataset for assessing the future status, effective management, and better utilization of water resources of the SRB.

Qualitative Risk Assessment of Microbial Indicators in the Lower Reaches of Meenachil River, Kerala, India

Pristine natural freshwater resources being severely contaminated by microbiological pollutants is still a big issue in many parts of the world. In the present study, water samples taken from the upstream, midstream, and downstream reaches of the Meenachil River were analysed for the presence of microbial pollution indicators such as faecal coliforms (FC), faecal streptococci (FS), and Eschericia coli. The E. coli isolates were subjected to antimicrobial susceptibility tests and the multiple antibiotic resistance (MAR) indexes were calculated so as to delineate the potential risk posed by infections to humans and animals using the river for routine potable and recreational purposes. E. coli was consistently isolated from all the samples collected from the different zones of the river. Other faecal coliforms such as Klebsiella oxytoca, Citrobacter koseri, Enterobacter, Proteus vulgaricus, and Shigella boydii were also identified. Higher FC/FS ratios were noticed for the midstream and the downstream sites indicating the contamination from high-risk sources such as human and anthropogenic domestic wastes. The MAR index values of E. coli isolates ranged from 0.33 upstream, 0.416 for midstream and 0.583 for the downstream reaches. Given that E. coli is an ideal indicator of faecal pollution, their existence and extended survival of multiple antibiotic resistance natural freshwater pose a potential risk for the consumers. Rapid urbanization and resultant waste drainage in the downstream stretches of the river might have accelerated the deterioration of the water quality up to a certain extent. Furthermore, the riverine system as it flows downstream loses its self-purification capacity due to the loss of natural water drifts. This may be attributed to the periodic shutdown of the salinity barrier, Thanneermukkam Bund in the confluence zone of the river which results in a temporary stagnation of the running waters in the lower stretches.

Effectiveness of Biomass/Abundance Comparison (ABC) Models in Assessing the Response of Hyporheic Assemblages to Ammonium Contamination

Abundance–Biomass Comparison (ABC) models, first described for marine benthic macrofauna, have been applied successfully to other marine and terrestrial/freshwater fauna but never to ecotonal communities. In particular, to our knowledge, ABC models have not been applied to hyporheic communities. This study represents the first application of ABC models to hyporheic assemblages. We aimed at testing the effectiveness of ABC models in describing the perturbation of hyporheic communities subjected to an existing/known disturbance. To this end, we applied the models to the hyporheic community of an Apennine creek, where the hyporheic waters of the upstream stretch were uncontaminated, whereas those of the downstream stretch were contaminated by ammonium. We also tested separated models for the summer and winter periods to account for potential variability due to season. ABC models provided a satisfactory description of the hyporheic community changes due to ammonium by showing the abundance dominance curve overlying that of the biomass in the downstream stretch contrarily to what was observed in the upstream stretch. However, ABC models did not highlight any significant seasonal effects. Our results showed that ABC models have the potential to be used as assessment tools for ecological quality of hyporheic zones in temperate regions.

An Annotated Checklist of Ichthyofaunal Diversity of the Potamon Zone of Thamirabarani River, South India

Background: Thamirabarani is a major east-flowing river originates from the Pothigai Hills of Southern Western Ghats (8°36'07.1"N 77°15'50.9"E) at an altitude of 2074 m with a catchment area of 5482 km2 and meanders through a distance of 120 km (24 km in hilly terrain and 96 km in plains) in Tirunelveli and Tuticorin districts and drains into the Bay of Bengal. Present paper provides information on abundance, distribution, human utility, Trophic level, Lm and IUCN status of the Thamirabarani River. Methods: The present study was conducted by monthly intervals on Ichythyofaunal diversity of the Potamon Zone of Thamirabarani River from November 2019 to October 2021, selecting seven sampling stations viz Cherenmahadevi, Vannarpettai, Murappanadu, Karungulam, Srivaikuntam, Eral and Authoor. Result: In the present study, a total of 57 species comprising 11 orders, 19 families and 38 genera were documented from downstream stretch of Thamirabarani River, of which three fish species namely Horadandia atukorali; Oreochromis mossambicus and Wallago attu are under vulnerable category and three fish species namely are Hypselobarbus dubius; Labeo fisheri and Dawkinsia tambraparniei endangered listed in the International Union for Conservation of Nature red list. Among the 11 orders reported, the order Cypriniformes (52%) was observed to have the highest contribution to the Ichthyofaunal diversity and the family Cyprinidae (32%) was recorded the highest contribution to the finfish diversity. The trophic level community structure of recorded fish species revealed the dominance of mid-level carnivores (48%). The human utility of recorded finfishes was found to be the highest was observed as edible (72%) and IUCN status was the highest with least concern (72%).

STUDY OF CORRELATION BETWEEN DOWNSTREAM STRETCHES AS STUDY SITES IN HOOGHLY RIVER AND LEAD CONTENT IN SEDIMENT AND MUSCLE OF FISH SPECIMEN (Mystus gulio HAM. - BUCH.)

The present study was conducted to detect a correlation between Pb content in sediment and muscle of fish (Mystus gulio Ham. - Buch.) and downstream stretches (three study sites) of the of the river Hooghly, West Bengal, India. The study sites were selected at Batanagar (Bt), Budge Budge (Bg) and Birlapur (Br) sites. The samples viz. sediment and muscle of fish were collected and estimated by using atomic absorption spectrophotometer. The Pearson correlation coefficient analysis was performed to know the association between these sites and sediment as well as muscle during pre-monsoon season. The study sites observed both significant positive (P is less than 0.05) and negative correlation with sediment of river Hooghly at downstream while significant (Pis less than0.05) positive correlation was observed between the study sites and muscle of the fish specimen (Mystus gulio). The findings pose the risk of accumulation may be lower in fish muscle due to positive correlation, but negative correlation may lead to harmful impact in the study site for sediment. In future, this study may be beneficial to determine the water and sediment quality status in different stations of river Hooghly as well as other metals content in different fish species.

Influence of the Salmo (trutta) trutta on the population structure, the growth, and the habitat preference of a Cottus gobio population

AbstractThe bullhead Cottus gobio is a small‐sized fish whose range extends over most of the European continent, and it is listed in Annex II of EU “Habitat” Directive for its great conservation interest. In the last decades, bullhead populations suffered local decline. Among the factors that negatively affect bullhead populations, major threats are pollution, habitat deterioration, and the massive introduction of salmonids. This study aims to better understand in which way the presence of the Salmo (trutta) trutta affects Cottus gobio populations. The investigation was carried out in two stretches of a stream located in the Orobic Alps (Italy). The downstream stretch hosts a fish assemblage constituted of both bullhead and brown trout, while in the upstream stretch only bullhead is present. An insurmountable barrier isolates the upstream population of C. gobio from trout, while the environmental conditions of the two stretches proved to be fully comparable. We evaluated population structure, habitat preference, and body shape of bullhead populations in both stretches: the results indicate that the presence of trout decreases the number of bullhead adults, reduces the average adult body size, and induces a bullhead suboptimal habitat occupation. However, both populations of C. gobio showed a well‐structured population and good performance indexes, so trout do not seem to be a threat to the population survival.

Distribution patterns and transportation behavior of alkylphenol polyethoxylate degradation metabolites among river, port area, and coastal water bodies of Kaohsiung City, Taiwan

In this study, we conducted a comprehensive study of the distribution, transportation behavior and potential ecological risk of alkylphenol polyethoxylates (APnEOs) in the aquatic environments of Kaohsiung City, Taiwan because little information is available regarding the fate of APnEOs in the water bodies of a total environment. At Love River, APnEOs concentrations were much higher at upstream of interception stations L15 (27.33 ± 1.22 μg/L) and L16 (6.31 ± 0.14 μg/L) than at downstream of interception stations L1–L14 (0.69–2.54 μg/L). Additionally, the average ethoxy (EO) chain lengths of APnEOs at L15 and L16 were longer than at L1–L14. These observations were attributed to the sluice between L14 and L15 that intercepts and accumulates untreated sewage from upstream areas and to the infrastructure of the sewage system that prevents domestic sewage from flowing downstream in the river and to the Kaohsiung Port Area. At Kaohsiung Port Area, APnEO concentrations ranging from 0.63 to 6.50 μg/L were measured. The concentration range and average EO chain length of these APnEOs were similar to those of the downstream stretch of the river, which was attributed to the mixing efficiency of the Kaohsiung Port Area and Love River through tidal exchange. At Cijin Coastal Area, APnEO concentrations ranged from 0.14 to 18.77 μg/L. Notably, the APnEO concentration of surface waters was much higher than that of bottom waters. This observation was attributed to the sewage discharged from the ocean outfall buoying up to the surface instead of mixing with surrounding bottom waters. In potential ecological risk, 19 of 39 sampling points exceeded toxic equivalency of 1 μg/L, and approximately 48.7% of the sampling points would exceed the threshold. The result provides insight into the environmental implications of APnEOs contamination in aquatic environments and useful information for environmental policy and ecological risk assessments.

Dazed and confused: Behavioural constraints impose major challenges to fish passage in the neotropics

Abstract The role of fish translocation upstream of dams, for the conservation of migratory species, is controversial. An important but still unaddressed question is whether migratory patterns are affected, after the translocation events, by a hydropower dam. In existing dams, a useful means to test this might be to compare the behaviour of translocated fish with those in undammed river segments in the same region. The objective of this study was to evaluate the effectiveness of fish translocation in promoting access to spawning areas through a behavioural approach using Prochilodus costatus as a study model in the São Francisco River, south‐east Brazil. The reservoir acted as a barrier to the dispersal of translocated individuals with only a small fraction of the population able to locate lotic stretches in the tributaries. Individuals translocated to undammed stretches of river upstream of the reservoir exhibited movement behaviour that was markedly different from that of individuals native to this region. Translocated individuals mainly displayed an erratic pattern of movement between upstream and downstream stretches of river with no specific route. In contrast, local individuals made long‐distance upstream spawning migrations and downstream return migrations to feeding sites during specific periods of the year. The results indicate that translocating individuals upstream of Três Marias dam tends to be ineffective for the conservation of P. costatus in the region. The study showed that the behaviour of translocated individuals, a largely neglected factor for the tropical region, may be an additional barrier to the success of conservation programmes based on fish passage systems. For the population studied, the maintenance of a free‐flowing stretch where fish are able to complete their life cycle is a more viable and effective alternative for conservation.

Erosion irregularities resulting from series of grade control structures: The Mszanka River, Western Carpathians

Grade control structures (GCSs) are one of the most often used hydraulic structures in a river regulation in mountain catchments. The purpose of their use is to reduce the river bed gradient and prevent downcutting. The aim of this study is to evaluate the influence of GCS on changes in river bed morphology. The study was conducted in a downstream stretch (5.66 km long) of the Carpathian river – the Mszanka, regulated with 25 GCSs. Research has shown that erosion is here a predominant process despite the use of GCSs. The river bed has been cut into bedrock along approximately 40% of a studied stretch. A total of 56 scour holes were identified, which vary substantially in terms of their depth, length, and mechanism of formation. The erosion depth depends mainly on the length of reaches between GCSs and on the water surface gradient. A surprising research discovery was scour holes found upstream of the crests of the GCSs – 16 such scour holes were found. The formation of these scour holes is explained through the drawdown profile characterized by the increasing of the velocity that favored the bed erosion. The studied river is characterized by deficit of sediment. The insufficient sediment supply and imbalance between the river's load and sediment transport are two of the greatest problems affecting the most Carpathian rivers. The novelty of this research is the analysis of such a long and complex reach of mountain river engineered with GCSs in terms of variances in erosion processes. Also a new knowledge presented here is an information about scour holes located upstream of GCSs and explanation of the mechanism of their formation. Results from this research could serve geomorphologists, engineers and ecologists as well as help river managers in decision-making processes when river regulation is planned.

Structure of aquatic macroinvertebrate communities in streams of a sub-basin in the Pampa Biome, Southern Brazil

The Piratinim River is located in the northwest of Rio Grande do Sul, and represents an important effluent from the Uruguay River, with streams located far from urbanized areas, in conditions similar to those of environmental integrity, but under the influence of agricultural activities. In this study, we aim at investigating the structure of the aquatic macroinvertebrate community in streams of the Piratinim river basin by observing both spatial and local scales. The sampling was carried out in six streams distributed in three regions (upper, middle and lower) of the basin, thus exploring its upstream, intermediate and downstream stretches, during spring and autumn. Macroinvertebrates were collected using aquatic dipnets and were identified at the family level; trophic-functional categories were established according to the classification adapted to the state of Paraná. The spatial and temporal variations of the groups and of the biotic attributes (density, richness, diversity and equitability) were subjected to Kruskal-Wallis non-parametric tests anda posterioriDunn’s tests. The abiotic variables were obtained to verify possible influence on the composition of the macroinvertebrate community, evaluated through a Canonical Correspondence Analysis. We sampled 11,564 macroinvertebrate individuals from 72 taxa, and found a predominance of the collector-filter trophic group. Abundance and richness were different between streams; the highest densities were found in the streams located in the upper region of the watershed (Chuní and Itú). The highest taxon richness was found in the lower region of the watershed (Guaracapa stream), and the lowest richness was found in the two streams for the intermediate region (Santana and Ximbocu). Diversity and equitability did not vary; temporal variations were not found. Canonical correspondence analysis explained 31.7% of the data variability. The main environmental variables that influenced macroinvertebrates distribution were temperature, electrical conductivity, dissolved oxygen, altitude and extension of the riparian forest. Seasonality and the longitudinal gradient along the basin represented determining factors for the structure and distribution of the macroinvertebrate community in the tributary streams of the Piratinim River.

EVALUATION OF MICROBIAL LOAD AND SELECTED HEAVY METALS CONTAMINATION IN THE RIVER BEAS (PUNJAB) INDIA

Aim: To analyse the heavy metal contamination and microbial load in upstream (Talwara), midstream (Urmar Tanda) and downstream (Harike Pattan) stretches of the river Beas in Punjab. Methodology: Month-wise samples were collected in triplicate during the period of May to December, 2019. Heavy metal parameters such as Arsenic, Cadmium, Nickel, Lead and Zinc were analysed by Atomic Inductively Coupled Plasma Mass Spectrometry following standard protocol. Microbial load in water samples was calculated in terms of Total Plate Count, Total Coliform and Faecal Coliform as per following standard protocol. Statistical analysis involved calculating Analysis of Variance at 5% significant level (p<0.05). Results: The study revealed that heavy metal parameters like Arsenic, Cadmium, Nickel, Lead and Zinc ranged in mgl from 0.0 to 0.009, 0.0 to 0.02, 0.0 to 0.004, 0.0 to 0.001, and 0.0 to 0.036 respectively. Total Plate Count ranged from 0.32 4 5 -1 -1 x10 to 3.2 x10 cfu ml whereas, Total Coliforms and Faecal Coliforms ranged from 4.0 to 1100 MPN 100 ml and 0.0 to -1 460 MPN 100 ml respectively. The mean concentrations of analysed metals were recorded in the order of Zinc > Cadmium > Arsenic >Nickel >Lead; and most of them were under the permissible limits; however, the presence of faecal coliforms in the water is alarmingly high at Harike Pattan. Interpretation: This investigation revealed that the river Beas water is suitable for supporting aquatic life, bathing, irrigation and other purposes. The microbial load and the heavy metal parameters need to be monitored regularly, so that their adverse effects on living beings or aquatic organisms may be minimized. River stretch near Harike Pattan and Urmar Tanda being an important habitat of endangered freshwater Dolphin (Platanista gangetica minor), Smooth-Coated Otter (Lutrogale perspicilliata) and Ghariyal (Gavialis gangeticus) is more vulnerable to the toxic levels of heavy metals and contamination of faecal coliform.

Textural and mineralogical maturities and provenance of sands from the Budhi Gandaki-Narayani Nadi, central Nepal

The Budhi Gandaki-Narayani Nadi in the Central Nepal flows across fold-thrust belts of the Tethys Himalaya, Higher Himalaya, Lesser Himalaya, and the Sub-Himalaya, and is located in sub-tropical to humid sub-tropical climatic zone. Within the Higher Himalayas and the Lesser Himalayas, a high mountain and hilly region give way the long high-gradient, the Budhi Gandaki Nadi in the northern region. At the southern region within the Sub-Himalayas, having a wide Dun Valley, gives way the long low-gradient Narayani Nadi. Sands from Budhi Gandaki-Narayani Nadi were obtained and analysed for textural maturity and compositional maturity. The textural analyses consisted of determining roundness and sphere city of quartz grains for shape, and determining size of sand for matrix percent and various statistical measures including sorting. The analysis indicates that the textural maturity of the majority of sands lies in sub mature category though few textural inversions are also remarkable. Sands from upstream to downstream stretches of the main stem river show depositional processes by graded suspension in highly turbulent (saltation) current to fluvial tractive current, as confirmed from the C-M patterns.
 The compositional variation includes quartz, feldspar, rock fragments, mica, etc. The quartz grain percent slightly increases from the mountains to the lower relief areas. The percent feldspar decreases rapidly whereas the percent rock fragment decreases gradually along the downstream transport of sediment. The Budhi Gandaki-Narayani Nadi sands range from sublitharenite to lithic arenite composition in QFL diagram, and are remarkably poorer in feldspar compared to rock fragment. Among the rock fragments, the high-grade metamorphic rock fragmentsare dominant in the upstream stretch of the main stem Narayani Nadi stretch while the sedimentary lithics are remarkable in the downstream stretch. The QFL plots also show that the studied sands belong to recycled orogeny provenance and agree with the current tectonic setting of the Himalayas. Mineralogically, the sands (MMI=100%–203%) are not as matured as the normal sands. MMI fluctuates along downstream distance due to mixing of sediments from the major tributaries at various places along the main stem river.

SEDIMENT DYNAMICS AND STABILITY STATUS OF THE KARRA KHOLA, HETAUDA DUN VALLEY, CENTRAL NEPAL SUB-HIMALAYA

The Karra Khola in Hetauda, Siwalik region, originates within the Dun Valley, and contributes the Rapati Nadi in Hetauda Metropolitan city. The stability status of the river is of main concern because of rapid growing of the river corridor and peripheral land areas into suburban city. The river was surveyed for hydraulic parameters, sediment characteristics, and sediment loads. Rate of sediment transport and sediment yields were computed, and competency of the river was evaluated using Shield’s parameters and Reynolds numbers. The results show that the river sediments are sandy gravel to gravelly sands, and are moderately to very poorly sorted. The total sediment yield of the whole basin near the outlet is around 2% of the maximum total sediment yield. The specific stream power (SSP) ranges from 20.98 to 2866.34 Wm-2. The dimensionless boundary shear stress to dimensionless critical shear stress ratio exceeds unity, revealing that the river is competent enough to transport its bed material loads, except in downstream stretch before the river confluences with the Rapati Nadi. The Karra Khola clearly exhibits status of degradation in the upstream stretch, high rates of transportation due to lateral erosion in the midstream stretch, and aggradation in the downstream stretch.

Crowd-Based Observations of Riverine Macroplastic Pollution

Macroplastic pollution (> 0.5 cm) negatively impacts aquatic life and threatens human livelihood on land, in oceans and river systems. Reliable information on the origin, fate and pathways of plastic in river systems is required to optimize prevention, mitigation and reduction strategies. Yet, accurate and long-term data on plastic transport are still lacking. Current macroplastic monitoring strategies involve labor intensive sampling methods, require investment in infrastructure, and are therefore infrequent. Crowd-based observations of riverine macroplastic pollution may potentially provide frequent cost-effective data collection over a large geographical range. We extended the CrowdWater citizen science app for hydrological observations with a module for observations of plastic in rivers. In this paper, we demonstrate the potential of crowd-based observations of floating macroplastic and macroplastic on riverbanks. We analyzed data from two case studies: (1) floating plastic measured in the Klang (Malaysia), and (2) plastic on riverbanks along the Rhine (the Netherlands). Crowd-based observations of floating plastic in the Klang yield similar estimates of plastic transport (2,000–3,000 items h−1), cross-sectional distribution (3–7 percent point difference) and polymer categories (0–6 percent point difference) as reference observations. It also highlighted the high temporal variation in riverine plastic transport. The riverbank observations provided the first data of macroplastic pollution on the most downstream stretch of the Rhine, revealing peaks close to urban areas and an increasing plastic density toward the river mouth. The mean riverbank density estimates are also similar for the crowd-based and reference methods (573–1,033 items km−1). These results highlight the value of including crowd-based riverine macroplastic observations in future monitoring strategies. Crowd-based observations may provide reliable estimations of plastic transport, density, spatiotemporal variation and composition for a larger number of locations than conventional methods.

Effects of Focal Axonal Swelling Level on the Action Potential Signal Transmission.

Focal axon swelling refers to localized swelling in axons that may occur because of trauma (e.g., traumatic brain injury) or neurodegenerative diseases (e.g., Alzheimer's disease). Since the swelling region can be many times larger than its original axon size, many researchers hypothesize that the swelling can alter the action potential (AP) signal. This article discusses the results of a series of newly developed computational studies to elucidate the possible intervention or blockage of AP signals due to swelling in the brain. We argue that the spherical geometry of the swelling site with its enlarged conducting interior causes the entering electric currents to spread evenly over the entire swelled membrane. As such, when the swelled surface becomes larger than the threshold size, the electric current will spread too thin to trigger the AP to spike. In this study, we have used a hybrid membrane model to simulate AP propagation across axons of different radii and swelling radii. We used an integrated model where a cylindrical symmetric 2D model is used to examine the electric current inside a spherical swelling site. In addition, two 1D models are used to capture the current flows along the upstream and downstream stretch before and after the swelling site. The parameters for this model are obtained from literature dedicated to modeling the experimental outcomes of mammal neurons. We observed two factors, which simultaneously affect AP transmission across a swelled axon: a) the axon radius and b) the ratio of the swelled and unswelled axon radii. In general, a thicker axon needs a smaller swelling size and axon ratio to block AP transmission. On the other hand, a thinner axon will reach the threshold at a larger swelling size and axon ratio. When only swelling size is considered, then thinner axons will block AP transmission at a smaller swelling radius. The AP transmission delay inside the swelled region determines whether the AP transmits forward or not. Notably, the blockage is worse if the AP fires at a high frequency. An increase in the charging and reset time due to swelling appears to be the main reason for the variation in axonal response.

Geochemical Footprint of Megacities on River Sediments: A Case Study of the Fourth Most Populous Area in India, Chennai

An intensive surface sediment survey was carried out over 24 locations from the upstream to downstream sections of two large rivers (Adyar and Cooum) in Chennai (India) during the February dry season of 2015. Trace element concentrations were assessed on a <63 µm fraction using the Geoaccumulation Index (Igeo) and the newly proposed Geochemical Urban Footprint Index (GUFI), which can be performed to determine the pollution status of any megacity river influenced by urban development. The sediment quality of Chennai’s rivers was also compared to worldwide megacity pollution using sediment quality guidelines (SQGs), and a new megacity pollution ranking was determined. The Igeo results indicate that the Chennai rivers studied are strongly to extremely polluted regarding trace element content of sediment. Silver (Ag), Cadmium (Cd) and Mercury (Hg) are the most significant tracers of urban contamination. Chromium (Cr) concentrations show an industrial contamination gradient in relation to levels of other trace elements (As, Cu, Ni, Pb, and Zn) at the Chennai megacity scale. The GUFI ranges from moderate to extreme contamination, particularly in the downstream stretches of the two rivers. This spatial trend is related to various point sources and identified at specific sampling stations, with a lack of identifiable buffer zones. According to the worldwide comparison of megacity pollution, Chennai is ranked in fifth position. The present position can be attributed to a number of explanations: a population explosion associated with the unplanned growth of the city and non-controlled point sources of pollution in Chennai’s waterways.

Detailed engineering geological assessment of a shotcrete lined pressure tunnel in the Himalayan rock mass conditions: a case study from Nepal

The complex topography, geology, and tectonic environment prevailing in the Himalaya are the main challenges while applying the unlined or shotcrete lined pressure tunnel concept for hydropower projects. In addition, rock masses in the Himalayan region are influenced by faulting, folding, schistosity, and jointing to a varying degree representing geological complexity. Similarly, frequent occurrence of large scale earthquakes changes in situ stress dynamics. In spite of these challenges, an unlined/shotcrete lined pressure tunnel is being constructed at the headrace tunnel system of Upper Tamakoshi Hydroelectric Project (UTHP) in the Nepal Himalaya. This article studies the unlined or shotcrete lined pressure tunnel in terms of the topographical conditions, in situ stress state, and overall rock engineering aspects. First, the pressure tunnel alignment is assessed using the Norwegian confinement criteria. Second, the minimum principal stress state is assessed using numerical simulation by validating measured in situ stress conditions. Finally, a comprehensive assessment on the rock engineering aspects of the headrace tunnel is carried out. It has been found that if there exist good quality rock mass with tight joints, it is possible to apply the unlined/shotcrete lined pressure tunnel system in the Himalaya provided that the stress requirement is fulfilled. It was also found that the Norwegian confinement criteria are too optimistic for direct use in the design of high pressure headrace tunnel alignment. The detailed rock engineering assessment and stress state analysis indicated that there are some critical locations along the Upper Tamakoshi headrace tunnel alignment. This is specially the case for an about 700 m downstream stretch of the headrace tunnel from where there is a risk of hydraulic jacking, which may possibly lead to excessive water leakage during power plant operation.