River Site Research Articles

Effects of Micro Plastics on Fishes of Hooghly River, India

Plastic pollution is now a concerning issue which destroying the riverine ecology silently. Excessive use of plastics & indifference to removing plastic waste after use gives birth to microplastics. Rivers are the major track way which can caught plastic debris from surrounding landside & contaminate the aquatic life without degraded the matter for a long time. The research was conducted on the Hooghly river near Barrackpore in the West Bengal region of India. The research explores the matter of microplastics contamination in various fish species of Hooghly river & effects of microplastics in the fish body according to the size, concentration, physical component & polymerase type of microplastic. Mainly 0.3 mm to 5 mm sizes microplastics have been noticed in both fish & shore sediments of this river site. Mostly the fiber & fragment type microplastics elements were damage the liver & gill of fish badly.

Phosphorus transport in a hotter and drier climate: in-channel release of legacy phosphorus during summer low-flow conditions

Abstract. “Legacy phosphorus” is the historical accumulation of phosphorus (P) in soils and sediments due to past human inputs. River networks represent a potential sink and/or source of legacy P, with many in-channel processes potentially governing the storage and mobilization of P over time. The objective of this study was to evaluate the potential contribution of the in-channel release of legacy P to bioavailable P transport in streams during summer low-flow conditions across a land use gradient in Minnesota, USA. We addressed this objective through the synthesis of (1) water quality and streamflow (Q) data collected for 143 gauged watersheds across the state of Minnesota between 2007–2021 (22 750 total samples); (2) water quality data from 33 additional ditch, stream, and river sites in Minnesota sampled under low-flow conditions in the summer of 2014; and (3) water quality data collected from tile drainage outlets for 10 monitored farm fields between 2011–2021. We used geospatial data and a random forest modeling approach to identify possible drivers of bioavailable P concentrations during summer low flows for gauged watersheds. During low flows in late summer, between one-third to one-half of the gauged watersheds we studied exhibited soluble reactive phosphorus (SRP) concentrations that were above previously identified thresholds for eutrophication of 0.02–0.04 mg L−1. For many of these watersheds, stream SRP concentrations in late summer were above those observed in tile drainage outlets. Elevated SRP concentrations during late-summer low flows weakened concentration–discharge relationships that would otherwise appear to indicate more strongly mobilizing SRP–Q responses across other seasons and flow conditions. While wastewater discharge likely contributed to elevated P concentrations for watersheds with high densities of treatment plants, many watersheds did not have substantial wastewater impacts. The most important variables for predicting bioavailable P concentrations during late-summer low-flow conditions in a random forest model were land use in riparian areas (particularly crop cover); soil characteristics including soil erodibility, soil permeability, and soil clay content; agricultural intensity (reflected via higher pesticide use, higher phosphorus uptake by crops, and higher fertilizer application rates); watershed precipitation; and stream temperature. These findings suggest that, for stream and river sites heavily impacted by past and current P inputs associated with agriculture and urbanization, biogeochemical processes mediated by climate and geology can result in the release of legacy P from in-channel stores during late-summer low-flow conditions. As summers become hotter and, at times, drier – which are predicted changes in this region – conditions for the release of legacy P stored in stream and river channels will likely become more prolonged and/or more acute, increasing eutrophication risk.

Population genomics of eastern oysters, Crassostrea virginica, in a well-mixed estuarine system: advancement and implications for restoration strategies

Eastern oysters, Crassostrea virginica, are historically a keystone species in many of the estuaries in which they reside, providing critical ecosystem services. Because oyster populations have been on the decline for the past century, restoration initiatives currently are underway in many estuarine systems, including Great Bay Estuary (GBE), New Hampshire. Results of prior studies of eastern oyster population genomics cannot be applied directly to GBE, as it is a well-mixed estuarine system that is relatively contained, and the sources of recruits are split among cultivated and native. This study aimed to identify the population genomic structure of eastern oysters in GBE to facilitate determination of effective population size and estimation of genetic differentiation among subpopulations. Results showed moderate genomic differentiation among native, cultivated, and restoration C. virginica subpopulations in the Bay. A small number of breeders (Ne=163–276) was found in all subpopulations except the Lamprey River site (Ne=995). This research provides a contemporary snapshot of eastern oyster subpopulation structure at the genomic level in GBE that will facilitate restoration and enhanced management.

Nitrogen, sulfur, iron, and microbial communities co-shape the seasonal biogeochemical behaviors of As and Sb in coastal tidal flat wetlands associated with rivers

Arsenic (As) and antimony (Sb) are affected by complex biogeochemical processes in coastal ecosystems. However, the influence of N, S, Fe, and microbial communities on the biogeochemistry of As and Sb in coastal tidal flat wetlands remain uncertain, particularly when rivers flow into these areas. This study combined diffusive gradients in the thin-film technique with high-throughput sequencing to investigate the release and vertical distribution of As and Sb in river and coastal tidal flat wetland sediments. The results indicated a distinct stratification phenomenon in the As release at depths ranging from 20mm to −150mm. At river sites, the release of As occurred in the upper layer (above −40mm), with peak values of 4.3 and 9.3μg/L at HS and SY sites in summer, respectively, likely due to anaerobic ammonium oxidation. In the lower layer (below −40mm), both As and Sb were released, and this was possibly due to Fe reduction. However, at the coastal tidal flat sites, the release of As and Sb may have been driven by anaerobic ammonium oxidation, dissimilatory nitrate reduction to ammonium, sulfate reduction, and Fe reduction. At the river sites, As exhibited increased activity during the summer, and the residual forms were converted more easily into mobile forms. Sb remained relatively stable during both winter and summer. Conversely, both As and Sb primarily existed in residual forms and exhibited higher stability during summer in the coastal tidal flat sites. The microbial phyla Nitrospirota (3.6−7.0%) and Acidobacteriota (9.5−10.2%) were more prevalent at the river sites, whereas Desulfobacterota (8.8−12.0%) and Firmicutes (0.13−27.9%) were more prevalent at the coastal tidal flat sites. The bacterial genera involved in the N, S, and Fe transformation processes differed between the two sites, and they were primarily Thiobacillus, Limnobacter, and Sulfurovum at the river sites and Sva1033, Anaeromyxobacter, and Sva0485 at the coastal tidal flat sites. In this study, the microorganisms that mediated N, S, and Fe complex processes at various depths in the sediment–water interface were decoupled to elucidate the effect of these processes on the biogeochemical behavior of As and Sb as they move from rivers to coastal tidal flat wetlands. Environmental ImplicationCoastal wetlands have been experiencing heavy metal contamination, particularly in the estuarine regions affected by industrial activities. It is still not well understood how As and Sb behave biogeochemically in river and coastal tidal flat wetlands. This study provided an in-depth understanding of the effect of nitrogen, sulfur, iron, and microbial communities on the behavior of As and Sb in these areas. This study also highlights the eutrophication may increase As/Sb pollution in river areas. And these heavy metals may accumulate in seafood, potentially leading to heightened health risks of As and Sb poisoning in coastal tidal flat wetlands.

Evaluation of WSR-88D Level III and MRMS Rainfall Estimates Against Rain Gauge Observations at the Savannah River Site

Rainfall data for the Savannah River Site (SRS) has been historically measured by rain gauges. These instruments serve as ground truth for most climatological and weather applications; however, gauge measurements are prone to errors or biases under certain weather conditions. Rainfall estimates from radar reflectivity values have been developed and improved over the years and serve as an alternative or supplement for gauge measurements. This study compares measurements from tipping bucket rain gauges with rainfall estimates from the NOAA NWS WSR-88D Level III hourly rainfall product and the Multi-Radar Multi-Sensor (MRMS) gauge-corrected precipitation estimate. Results show good agreement between radar derived amounts and ground measurements, with MRMS values showing correlation coefficients of 0.60-0.95 and RMSE values of less than 1.0 cm (0.4 in). The WSR-88D Level III estimates result in correlation coefficients of 0.46-0.86 and RMSE values of less than 1.3 cm (0.5 in). Few outliers are observed for each data pair and are evaluated against precipitation classification products (WSR-88D Hybrid Hydrometeor Classification product and MRMS Precipitation Flag product). The rain gauges used in this study are not part of the Hydrometeorological Automated Data System (HADS) network used to correct the MRMS estimates and therefore, results of this work provide an independent validation of the MRMS gauge correction scheme.

Inter riverine variability in microplastic distribution among two tropical rivers – Chalakudy and Periyar, Southwest India

ABSTRACT The study intends to bridge the lack of baseline information on microplastic (MPs) contamination in two river systems (Periyar: the longest river, lifeline of the Kerala State and Chalakudy: the fifth longest river) and hence is highly relevant. Sampling was carried out twice during December 2020 and January 2021. Elevated level of contamination was recorded at midstream sites in Chalakudy and downstream sites at Periyar. Small-sized particles (<100 µm) constituted the majority (>45%) in both river systems resulting from the disintegration of larger particles or direct release of primary MPs. Prevalence of fragment shape, accounting for ≈48–71% across all sites in both rivers, resulted from the disintegration of meso or macro plastics. Preponderance of blue-coloured particles (≈33–67%) inferred potential risk to aquatic organisms. Low-density polyethylene emerged as the dominant polymer group, originated from packaging materials and bottles. Overall abundance and recovery rate in both rivers indicate that MPs occur at all sites, irrespective of land use patterns, sourced to the degradation of abandoned fishing gears, shipping, tourism activities, and untreated waste disposal. The high risk of microplastic pollution in the study area was endorsed by polymer hazard index and coefficient of microplastic impact index.

Disturbance by jet boating increases corticosterone concentrations in the black-backed gull (Larus dominicanus)

ABSTRACT Recreational activities such as jet boating have the potential to disturb native birds that rely on braided river habitats. To examine whether jet boating affects levels of glucocorticoid hormones, which can increase in animals under stress, we compared concentrations of corticosterone in the faeces of nesting black-backed gulls (Larus dominicanus) between days with differing levels of jet boat activity and to a nearby braided river site with no jet boating. The corticosterone titers of gull faeces sampled on the weekends (when jet boating activity was high) were almost twice that collected in the same area during the week (when jet boating activity was low). Corticosterone titers were also lower in the site without jet boating. Corticosterone levels were not significantly related to whether faeces were sampled in the centre or margin of the colony, nor did they vary significantly with number of birds in the colony. It is not known if increased concentrations of corticosterone have any negative effects on the survival or reproductive success of black-backed gulls, but our results suggest that the disturbance created by jet boating has the potential to alter hormone levels in this and perhaps other species that occur in braided river habitats.

Shotgun metagenomics analysis indicates Bradyrhizobium spp. as the predominant genera for heavy metal resistance and bioremediation in a long-term heavy metal-contaminated ecosystem.

Ten soil cores were collected from the long-term heavy metal-contaminated Savannah River Site (SRS) and studied using shotgun metagenomics. In-line with our previous reports, Bradyrhizobium spp. dominated the SRS soils, and thus we recommend that SRS bioremediation studies target the Bradyrhizobium genus.

Soft matter mechanics of baseball’s Rubbing Mud

Researchers looking for sustainable materials with optimal mechanical properties may draw inspiration from a baseball tradition. For nearly 100 y, a mysterious mud harvested from an undisclosed river site in New Jersey (USA) has been the agent of choice in the USA's Major League Baseball for "de-glossing" new baseballs. It is unclear, however, what makes this "Rubbing Mud" work. Here, we perform a multiscale investigation of the rheology and tribology of this mud material under baseball-relevant conditions and identify three mechanisms by which the mud alters the surface properties of the baseball. First, the mud creates a more uniform baseball surface by filling in pores in the leather; this is possible because of its relatively high cohesion (clays and organics) making the material remarkably shear thinning. Second, the residue of cohesive particles coating the baseball effectively doubles contact adhesion. Third, a sparse population of angular sand grains are bonded to the baseball by clay-sized particles, leaving a studded surface that enhances friction. The proportions of cohesive, frictional, and viscous elements in Rubbing Mud conspire to create a soft material with an unusual mix of properties, that could find other applications in the development of sustainable geomaterials. Our improved understanding of the flow and friction of natural muds may also find use in modeling natural hazards such as mudslides and for locomotion in muddy environments.

Declines in Freshwater Mussels and Loss of Mussel–Invertebrate Interactions in the Subtropical Waterbodies of Dhaka, Bangladesh

ABSTRACT Freshwater mussels are a globally threatened taxon, but little is known about population trajectories for species outside Europe and North America. To contribute to understanding of mussel conservation status outside these regions, we surveyed mussel and other invertebrate populations in waterbodies across Dhaka, Bangladesh, to assess population trends and the role of mussels in structuring benthic communities. We found that mussel populations in Dhanmondi Lake, our focal waterbody, have declined in density by approximately 90% between 2010 and 2023. Lamellidens marginalis declined by 90.8% from an average density of 47.9 ± SE 7.1 mussels 0.25 m−2 in 2010 to 4.4 ± SE 0.7 mussels 0.25 m−2 in 2023, while Indonaia caerulea declined by 89.4% from an average density of 6.6 ± SE 1.0 mussels 0.25 m−2 in 2010 to 0.7 ± SE 0.1 mussels 0.25 m−2 in 2023. Previously detected associations between mussels and other invertebrate taxa, and between mussels and community composition, have been lost. Non‐mussel invertebrates have also declined significantly, with an average decrease in abundance of 27%, alongside decreases in family richness and Shannon‐Wiener diversity. These declines occurred despite apparent improvements in water quality. Findings from other waterbodies across Dhaka also suggest the loss of mussel species including L. marginalis, I. caerulea and Parreysia corrugata from some locations, as well as the presence of the non‐native mussel Pilsbryoconcha exilis at river sites. Our results reflect a wider, global pattern of enigmatic declines in freshwater mussels and the possible loss of associated ecosystem functioning, which may be going unnoticed in less‐studied areas including the subtropics.

Zooplankton Community and their variation : A case study in Few rivers Across Nadia and North 24 Parganas, West Bengal

This study conducted to investigate the plankton diversity and abundance from the rivers at Nadia and North 24 Parganas to reveal the status. Samples were collected from seven sites of rivers Hooghly, Churni, Jalangi, Mathabhanga Bhagirathi, Ichamathi of West Bengal were carried out during March to May 2021. Enormous loads of wastes received from anthropogenic activities influences the living planktonic organisms which play the major role in food web dynamics in riverine ecosystem. pH, temperature, dissolved oxygen, dissolved carbon di-oxide, transparency, hardness, alkalinity, total dissolved solids, nitrate, nitrite, silicate and ammonia were analysed. 21 speciesof zooplankton including protozoa (2 species, 2 genera, 2 families, 1 order), rotifers (11 species, 6 genera, 4 families, 2 suborders), copepods (2 species, 2 genera, 2 families, 1 suborder), and Cladocera (5 species, 5 genera, 4 families, 1 suborder) and the variation in abundance were noticed from the study. The maximum representation of the zooplankton species belonging to rotifera (Family: Brachionidae) and copepodites and naupliar stages of cyclopoid copepods were found to be abundant.

Hydraulics of Time-Variable Water Surface Slope in Rivers Observed by Satellite Altimetry

The ICESat-2 and SWOT satellite earth observation missions have provided highly accurate water surface slope (WSS) observations in global rivers for the first time. While water surface slope is expected to remain constant in time for approximately uniform flow conditions, we observe time varying water surface slope in many river reaches around the globe in the ICESat-2 record. Here, we investigate the causes of time variability of WSSs using simplified river hydraulic models based on the theory of steady, gradually varied flow. We identify bed slope or cross section shape changes, river confluences, flood waves, and backwater effects from lakes, reservoirs, or the ocean as the main non-uniform hydraulic situations in natural rivers that cause time changes of WSSs. We illustrate these phenomena at selected river sites around the world, using ICESat-2 data and river discharge estimates. The analysis shows that WSS observations from space can provide new insights into river hydraulics and can enable the estimation of river discharge from combined observations of water surface elevation and WSSs at sites with complex hydraulic characteristics.

Distributions of Fecal Indicators at Aquaculture Areas in a Bay of Republic of Korea.

Aquaculture products, such as clams, scallops, and oysters, are major vectors of fecal-derived pathogens. Male-specific and somatic coliphages are strongly correlated with human noroviruses, the major enteric viruses worldwide. Geographic information system with local land-use patterns can also provide valuable information for tracking sources of fecal-derived pathogens. We examined distributions of four fecal indicator microorganisms, i.e., male-specific and somatic coliphage, total coliform, and Escherichia coli (E. coli) in three river and seawater sampling sites located on the coast of Gomso Bay in the Republic of Korea during the sampling period (from March 2015 to January 2016). Geospatial analyses of fecal indicators and correlation between environmental parameters and fecal indicators or among fecal indicators were also performed. Overall, river water samples showed highest concentrations of both types of coliphage in summer (July 2015). High concentrations of both total coliform and E. coli were detected in river water during the period from July to September 2015. High concentrations of all fecal indicators were found at site GL02, located in the innermost part of Gomso Bay, which has high-density agriculture and residential areas. Environmental factors related to precipitation-cumulative precipitation on and from 3 days before the sampling day (Prep-0 and Prep-3, respectively)-and salinity were strongly correlated with concentrations of all fecal indicators. The present results suggest that investigations of multiple fecal indicators with a systemic geospatial information are necessary for precisely tracking fecal contaminations of aquaculture products.

Improving multiple stressor-response models through the inclusion of nonlinearity and interactions among stressor gradients.

Stressor-response models are used to detect and predict changes within ecosystems in response to anthropogenic and naturally occurring stressors. While nonlinear stressor-response relationships and interactions between stressors are common in nature, predictive models often do not account for them due to perceived difficulties in the interpretation of results. We used Irish river monitoring data from 177 river sites to investigate if multiple stressor-response models can be improved by accounting for nonlinearity, interactions in stressor-response relationships and environmental context dependencies. Out of the six models of distinct biological responses, five models benefited from the inclusion of nonlinearity while all six benefited from the inclusion of interactions. The addition of nonlinearity means that we can better see the exponential increase in Trophic Diatom Index (TDI3) as phosphorus increases, inferring ecological conditions deteriorating at a faster rate with increasing phosphorus. Furthermore, our results show that the relationship between stressor and response has the potential to be dependent on other variables, as seen in the interaction of elevation with both siltation and nutrients in relation to Ephemeroptera, Plecoptera and Trichoptera (EPT) richness. Both relationships weakened at higher elevations, perhaps demonstrating that there is a decreased capacity for resilience to stressors at lower elevations due to greater cumulative effects. Understanding interactions such as this is vital to managing ecosystems. Our findings provide empirical support for the need to further develop and employ more complex modelling techniques in environmental assessment and management.

Reptilian Diversity in Selected Riparian Systems in Misamis Occidental, Philippines

Reptiles are one of the most ecologically important organisms in the ecosystem. Studying their diversity is important in the conservation of the habitats to where each of these reptiles live. This study aimed to explore the diversity of reptiles in the areas around and within Labo and Clarin rivers, two of the most important river systems in the province of Misamis Occidental. Three sampling techniques were applied, which are visual encounter surveys, opportunistic encounters, and road-kill encounters. The results recorded a total of 21 species, including eleven endemic species, with nine Philippine endemic and two Mindanao endemic. Most notable among the species recorded was Lycodon ferroni, which is the second documented occurrence of the species and the first outside Samar Island. Labo River has the highest species richness, abundance and percent endemism of the two riparian systems, with the upstream sites of both rivers having the highest species richness and percent endemism. Studying the nearby riparian areas using other sampling techniques is recommended to fully understand the extent of reptilian diversity in the province and to effectively implement conservation and sustainability programs for the preservation not only of the reptile diversity but as well as the riparian ecosystem.

Distinct food-web transfers of 137Cs to fish in river and lake ecosystems: A case study focusing on masu salmon in the Fukushima evacuation zone

This study was conducted to elucidate the spatial and size variations, and food-web transfer of 137Cs in freshwater fish in the upper reaches of the Ukedo River system, a highly contaminated river system flowing through the Fukushima evacuation zone. Fish collection and environmental surveys were conducted in the summer of 2020 at five forest rivers and at the Ogaki Dam reservoir (an artificial lake) with different air dose rates (mean 0.20–3.32 μSv/h). From the river sites, two salmonid species (masu salmon and white-spotted charr) were sampled, with masu salmon generally exhibiting higher 137Cs concentrations, ranging widely (10.6 Bq/kg-wet to 13.0 kBq/kg-wet) depending on the fish size (size effect) and site. The 137Cs concentrations in masu salmon were explained by the air dose rates, 137Cs concentrations in water, sediments (excluding the lake site), and primary producers, with site-specific variations. In the rivers, masu salmon (fluvial type with parr marks) mainly fed on terrestrial insects with higher 137Cs concentrations compared with those of aquatic insects, indicating that 137Cs was transferred mainly to fish through the allochthonous forest food-web during summer. In the lake, masu salmon (lake-run type with larger size and silvery body coloration) mainly preyed on smaller fish with lower 137Cs concentrations, demonstrating that 137Cs is transferred to fish through the autochthonous lake food-web with biomagnification. Differences in 137Cs concentrations among masu salmon (mean 441 Bq/kg-wet) and other fish species (mean 74.8 Bq/kg-wet to 2.35 kBq/kg-wet) were also found in the lake. The distinct 137Cs transfers to river and lake fish were supported by stable isotope analysis: δ15N and δ13C values enriched stepwisely through the food-webs were, respectively, higher and lower in the lake. Our results obtained using multiple approaches clearly revealed the distinct food-web transfer of 137Cs in river and lake ecosystems. These findings can contribute to prediction of radioactive contamination in freshwater fish in the Fukushima evacuation zone.

Per- and Polyfluoroalkyl Substances in the Duluth, Minnesota Area: Exposure to and Biomarker Responses in Tree Swallows Relative to Known Fire-Fighting Foam Sources.

Tree swallow nest boxes were deployed at sites proximal to two putative aqueous film forming foam (AFFF) sources in the Duluth, MN area, as well as along the St. Louis River and a reference lake for comparative purposes in 2019, 2020 and 2021. The two AFFF sites were the current Duluth Air National Guard Base (ANG) and the Lake Superior College Emergency Response Training Center. Between 13 and 40 per- and polyfluoroalkyl substances (PFAS), depending on year, were detected and quantified in tree swallow egg, nestling carcasses, and stomach contents. Assessments were made of oxidative stress and ethoxyresorufin-O-dealkylase activity in liver tissue, thyroid hormone levels in plasma and thyroid glands, DNA damage in red blood cells, and two measures of immune response (haptoglobin-like activity and immunoglobulin) in plasma of the nestlings. Additionally, other contaminants, such as polychlorinated biphenyls, legacy organochlorine pesticides, and trace elements, were assessed at sites with no previous data. Total egg PFAS concentrations at the ANG site and north of that site were 30-40 times higher than at the reference lake, while nestling PFAS concentrations were 10-15 times higher. In contrast, the St. Louis River sites had slightly, but non-statistically significant, elevated egg and nestling PFAS concentrations relative to the reference lake (2-5 times higher). One PFAS, perfluorohexane sulfonate (PFHxS), was higher, as a proportion of total PFAS, at sites with a known AFFF source compared to the reference lake, as well as compared to sites along the St. Louis River with mainly urban and industrial sources of PFAS. The ratio of total carboxylates to total sulfonates also distinguished between PFAS sources. There were few to no differences in biomarker responses among sites, and no association with PFAS exposure.

Evaluation of Lead, Copper and Iron Concentrations in Cyprus papyrus and Rivers in Iraq

In February 2023, samples were gathered from the research location. Five samples were taken from each leaf of the aquatic plant Cyprus papyrus, which is a member of the Cyperaceae family, as well as from the Tigris and Euphrates rivers. The primary heavy metals detected were lead (Pb), iron (Fe), and copper (Cu). Samples were collected from various areas in Iraq, including the Diyala River site, AL Rustamiya site, Karbala site, Babylon site, and AL-Rashdiya site as a control. The samples collected from each site consisted of water and Cyprus papyrus. The ICP-AES analysis successfully determined the concentration of elements in the samples. The results indicated that the Pb average concentration in plants varied across different sites, with the highest levels recorded in Diyala River, followed by AL Rustamiya, Babylon, Karbala, and Rashdiya sites (Control) at 3.67, 2.11, 0.55, 1.26, and 0.046 ppm, respectively. These values were compared with the UNEP standard of 0.01 ppm. Similarly, water samples also exhibited elevated levels of Pb average concentration in the same order of sites, with values of 2.97, 0.48, 0.41, 0.35, and 0.0891 ppm, compared with the UNEP standard of 0.005 ppm. Furthermore, the analysis of Fe average concentrations in plants revealed the highest levels in Diyala River, Babylon site, AL Rustamiya site, Karbala site, and Rashdiya (Control) at 0.5, 0.4, 0.3, and 0.1 ppm respectively. In water samples, Fe average concentrations were also found to be elevated in the same order of sites, with values of 1.3, 0.07, 0.06, 0.03, and 0.01 ppm. The presence of Cu was not detected in any of the samples collected from either plants or rivers. The aim of this study was to evaluate the levels of heavy metals in the Iraqi environment and examine their impact on living organisms.

Long-term effects of an early-life exposure of fathead minnows to sediments containing bitumen. Part II: Behaviour, reproduction, and gonad histopathology

The oil sands area of northern Alberta has river sediments that contain natural bitumen. Eggs and fish in these rivers may be exposed to bitumen-related chemicals early in life. This paper assesses a short embryo-larval fish exposure to oil sands sediment and follows the fish behaviour as they mature in clean water and examines their breeding success as adults (5 months afterwards). The three different oil sands river sediments tested were: a sediment collected outside of the bitumen deposit (tested at 3 g/L, Reference sediment from upstream Steepbank River site), and two sediments collected within the deposit (each tested at low (1 g/L) and high (3 g/L) concentrations). The sediments within the bitumen deposit were from the Ells and Steepbank (Stp) Rivers, and both contained significant total PAHs (>170 ng/g wet weight sediment) and alkylated PAHs (>4480 ng/g). Fish were exposed to these sediments for 21 days (as eggs and larval fish), and then transferred permanently to clean water to mature and breed. There was a significant decrease in the number of egg clutches produced by fish exposed early in life to Stp downstream high sediment (compared to Reference sediment). There was also a decrease in overall cumulative egg production, with fish from Stp downstream high sediment producing just over 1000 eggs in total while fish exposed to Ref sediment produced nearly 6900 eggs. The fish with reduced egg production were also less social than expected as they matured, and they had a lower % of early vitellogenic eggs in their ovaries. Overall, the exposure shows that a single, brief exposure during early life stages to natural bitumen can affect fish in adulthood. Naturally occurring bitumen-derived PAHs can reduce fish reproductive output by complex mechanisms, measurable as lower ovary maturity and changes in social behaviour.

Identifying Key Environmental Drivers of Reach‐Scale Salmonid eDNA Recovery With Random Forest

ABSTRACTEnvironmental DNA (eDNA) sampling from rivers has emerged as a promising new method for monitoring freshwater organisms of management concern. However, eDNA sampling cannot yet offer reliable estimates of a target species' abundance/biomass or confident determinations of a species' absence from a river segment. To unlock these abilities—and thereby greatly improve eDNA as a tool for management decision‐making—the influence of local environmental factors on eDNA fate must be better understood. At nine river sites across the central California coast, we added a known quantity of novel eDNA (Brook Trout, Salvelinus fontinalis) and collected eDNA at sequential downstream distances for qPCR analysis. We then used random forest modeling to identify the most important environmental factors to reach‐scale (≤ 200 m) sampling outcomes and characterize salmonid eDNA fate. Our final model identified six factors important to sampling outcomes, including five environmental factors (discharge, local catchment calcium oxide content, average depth of the sampling cross‐section, presence of pools, and impervious cover of the watershed) and one factor regarding our experimental design (the number of qPCR technical replicates). Our results highlight the notable effects of cross‐sectional area, turbulence, and catchment geology on eDNA fate, and we suggest the discharge and presence of pools as useful proxies for evaluating a site's favorability for eDNA recovery.