Tributary Confluences Research Articles

Makrozoobenthos As A Bioindicator Of Water Quality In The Masang Kecil River In West Pasaman Regency

Sungai Masang Kecil is located in the middle of the PT Andalas Agro Industri (PT AAI) palm oil plantation and mill. This activity will have an impact on aquatic biota, especially benthos. Benthos occupies an important position in the food chain and lives permanently on the substrate to be used as a bioindicator of pollution. This study aimed to determine the Community Structure of Macrozoobenthos and the indicator species of water pollution in the Masang Kecil River around the PT AAI area, West Pasaman Regency. This research was conducted using a purposive sampling method with three sampling points, namely upstream and two downstream points after the Wastewater Treatment Plant (IPAL) and after the confluence of tributaries. Sampling using Surber net size 30 x 30 cm. The results of identifying the types of Bento's organisms as a whole identified as many as 45 species. Most species are found in Class Insecta. Based on the diversity index, the water quality in PT AAI's river basin was classified as unpolluted, and it could be concluded that the benthic condition was in good condition on a scale of 4. In the current study, the Diptera order as an indicator of polluted water was most commonly found among orders from other insect classes, namely, ten species. However, there were nine species from the Order Ephemeroptera as an indicator of clean waters and six species for Trichoptera.

Highest methane concentrations in an Arctic river linked to local terrestrial inputs

Abstract. Large amounts of methane (CH4) could be released as a result of the gradual or abrupt thawing of Arctic permafrost due to global warming. Once available, this potent greenhouse gas is emitted into the atmosphere or transported laterally into aquatic ecosystems via hydrologic connectivity at the surface or via groundwaters. While high northern latitudes contribute up to 5 % of total global CH4 emissions, the specific contribution of Arctic rivers and streams is largely unknown. We analyzed high-resolution continuous CH4 concentrations measured between 15 and 17 June 2019 (late freshet) in a ∼120 km transect of the Kolyma River in northeast Siberia. The average partial pressure of CH4 (pCH4) in tributaries (66.8–206.8 µatm) was 2–7 times higher than in the main river channel (28.3 µatm). In the main channel, CH4 was up to 1600 % supersaturated with respect to atmospheric equilibrium. Key sites along the riverbank and at tributary confluences accounted for 10 % of the navigated transect and had the highest pCH4 (41 ± 7 µatm) and CH4 emissions (0.03 ± 0.004 mmolm-2d-1) compared to other sites in the main channel, contributing between 14 % to 17 % of the total CH4 flux in the transect. These key sites were characterized by warm waters (T>14.5 ∘C) and low specific conductivities (κ<88 µS cm−1). The distribution of CH4 in the river could be linked statistically to T and κ of the water and to their proximity to the shore z, and these parameters served as predictors of CH4 concentrations in unsampled river areas. The abundance of CH4-consuming bacteria and CH4-producing archaea in the river was similar to those previously detected in nearby soils and was also strongly correlated to T and κ. These findings imply that the source of riverine CH4 is closely related with sites near land. The average total CH4 flux density in the river section was 0.02 ± 0.006 mmolm-2d-1, equivalent to an annual CH4 flux of 1.24×107 g CH4 yr−1 emitted during a 146 d open water season. Our study highlights the importance of high-resolution continuous CH4 measurements in Arctic rivers for identifying spatial and temporal variations, as well as providing a glimpse of the magnitude of riverine CH4 emissions in the Arctic and their potential relevance to regional CH4 budgets.

Indicators of Holocene high-stage flood events and tributary confluence migration in the lower Narmada Basin, western India

Indicators of Holocene high-stage flood events and tributary confluence migration in the lower Narmada Basin, western India

COVID-19 lockdown-driven changes in the Ganga River ecosystem in response to human perturbations.

We examined 10 subsurface water, 5 benthic water and 19 sediment (02 cm) samples along a 518 km of the middle segment of the Ganga River to assess the possible improvements that resulted from the industrial shutdown during the COVID-19 pandemic. The sites included the main stem river, tributary confluences, and two point sources, one of which releases metal-rich effluents and the other flushes municipal sewage. We found significant declines in the carbon, nutrient and metal concentrations in both the water and sediment. Even the most polluted zones did not show hypoxia (dissolve oxygen; DO < 2.0 mg L−1) that had been observed in the previous year. Despite a significant decline in carbon and nitrogen as substrates, the activities of extracellular enzymes (EEs), such as β-D-glucosidase, FDAase and protease in sediment (0–2 cm depth), increased significantly (p < 0.05) in response to the declining metal concentrations resulting from the industrial shutdown. We found strong negative correlations between EE activity and the concentrations of metal pollutants measured in 2019, but the correlations between these variables appeared poor in 2020 (lockdown period). Also, we found large variances (low stability coefficients) during the period of strong anthropogenic effects (2019). The study indicates that industrial sources are important contributors of metal pollution in the Ganga River and has relevance exploring river ecosystem recovery windows for management decisions.

Vertically layered flow structure at confluence of a reservoir and tributary carrying high sediment loads

Enhanced understanding of flow structure at a river confluence is essential for predictions of sediment transport and morphological evolution. To date, however, the confluent flow structure of a reservoir and tributary carrying high sediment loads has remained poorly understood, and may be vertically layered sharply, featuring subaqueous sediment-laden flow, i.e., turbidity currents underneath subaerial clear water. Here a recently established 2D double layer-averaged model, able to resolve the formation, propagation, and recession of turbidity currents, is used to investigate a series of idealized laboratory-scale cases and a prototype case study of the Guxian Reservoir on the Yellow River, China. Four primary patterns of the stable, vertically layered flow structure at a reservoir-tributary confluence are identified: 1) single layers of sediment-laden inflow in both the main channel and tributary, sustained by sufficient vertical mixing; 2) a double layer in the main channel and a single layer of sediment-laden inflow in the tributary, when the sediment-laden flow in the tributary suffices to block intrusion of flow in the main channel; 3) a single layer of sediment-laden inflow in the main channel and a double layer in the tributary, induced by the intrusion of sediment-laden flow from the main channel into clear-water flow with small discharge in the tributary; and 4) double layers in both the main channel and tributary, which may be further divided into three subpatterns, as turbidity current exists in both the main channel and tributary, or in the main channel (tributary) intruding into the tributary (main channel). In response to unsteady discharge and sediment inputs from upstream, the vertically layered flow structure evolves in time, and may fall into one of the patterns identified above. Although bed deformation in the long term may modify the confluent flow, the vertically layered flow pattern remains so far as the present cases are concerned. The findings have implications for sediment transport and morphological evolution at a reservoir–tributary confluence, for which further studies are suggested to inform the optimization of reservoir operation schemes to mitigate capacity loss caused by sedimentation.

Experimental study on the mitigation effects of deflection walls on debris flow hazards at the confluence of tributary and main river

Experimental study on the mitigation effects of deflection walls on debris flow hazards at the confluence of tributary and main river

A field study of near-junction-apex flow at a large river confluence and its response to the effects of floodplain flow

• A field survey on flow at a large confluence of a compound tributary was conducted. • Kinetic energy and momentum correction coefficients at confluence were identified. • Floodplain flow decreased the size of stagnation zone and impacted its location. • Floodplain flow shifted the location of the mixing interface towards the centerline. • Floodplain flow was found to impact on the characteristics of the secondary flow. A field investigation was carried out in March 2019 at the large river confluence between the Yangtze River and the outflow channel with a large inner-side floodplain of Poyang Lake using acoustic Doppler current profiling (ADCP) and water quality sampling. The study was intended to complement previous field studies carried out under different flow conditions in August and December 2018 and to investigate the effects of the alternate flow mechanism (compound channel vs single channel) of the Poyang Lake outflow channel on confluence dynamics. The main hydrodynamics and morphodynamics features were identified and comparatively discussed with those from the previous field studies. The kinetic energy and momentum correction coefficients were found to peak near the confluence apex and decay farther downstream reflecting the gradual flow recovering process in the post-confluence channel. The alternate flow mechanism (compound channel vs single channel) of the Poyang Lake outflow channel and the change in momentum flux ratio M R were found to significantly impact on the characteristics of the stagnation zone, mixing interface and secondary flow at the confluence. The smallest and the largest stagnation zone were observed at the lowest M R and as the outflow channel acted as single channel, respectively, while also the location of the mixing interface was impacted. Furthermore, secondary flow consisting of dual counter-rotating helical cells and channel scale circulation were observed as the Poyang Lake outflow channel acted as compound channel and a single channel, respectively. These results provide novel information about confluence dynamics in large river systems where one tributary may have a floodplain flow in flooding conditions.

DEVELOPMENT OF A GOOGLE EARTH ENGINE BASED APPLICATION TO MONITOR THE SEASONAL WATER SPREAD AREA OF RIVER GANGA

Abstract. The National River Ganga, home to the National aquatic animal, Gangetic dolphin along with species of critically endangered otters, gharial crocodile, turtles, waterbirds and numerous aquatic and semi aquatic life forms is of conservation importance to safeguard the biodiversity it harbors. Meanwhile, River Ganga is also the source of highly productive agricultural yield that satiates the nation’s food demands. The last few years have echoed demands for ‘e-flow’ regulations to be formalized and regularized to maintain healthy river conditions with adequate amount of water retained in the rivers while meeting the populations demand for water supply. Though e flow estimations are a complex science in itself, the simplest way is visualization. In this context, there needs to be a transparent mechanism to picturise and depict the ground conditions of the river stretches. Remote sensing provides ‘eyes in the sky’. The river receives water in the form of precipitation, snow melt and ground water recharge and the hydrological flux is evident in the surface water. Thus delineating the water spread area can provide a crude estimate of the water in the river. The Google Earth Engine platform provides a collection of satellite imageries, server side data processing and algorithms. The Landsat and Sentinel data catalogue offers good coverage of the river and its basin. Though sentinel data provides high ground resolution of 10m, Landsat provides multi temporal historic coverage at a good 30 m resolution, that works well for the main stem river. From the various available data processing methods, spectral decomposition technique of Modified Normalised Differential Water Index MNDWI was found to be most effective in delineating surface water. Data was filtered for the three major seasons of Pre monsoon, Monsoon and Post monsoon periods and MNDWI for the same was visualized. While Middle Ganga region through Uttar Pradesh shows seasonal flooding during the monsoon period, the Lower Ganga after the confluence of major tributaries of Son, Ghaghra, Gandak and Kosi flows in full bank width in the Post monsoon period. During the pre monsoon period many stretches of Ganga particularly the Upper middle stretch showed thin shallow channel and intermittent deep pools disconnected by dry sand beds. These regions result in disruption in the river flow and are priority sites to implement e flow regulations. Another key factor is the regulation of flow in the river from barrages. Sudden release of water can cause flooding resulting in disturbance to the life cycle of species that are tuned to the natural annual hydrological pulse of the river. This is because different aquatic species have different river width and depth requirements. Thus monitoring the seasonal variations in the water spread area helps to note the longitudinal and lateral connectivity of the river which is a prime characteristic for the health of a river. This study intended to create an application that offers to visualize the seasonal water spread in the Ganga river for the past years that can assist decision makers to monitor the river and make informed regulatory measures.

Basin-scale spatiotemporal distribution of ayu Plecoglossus altivelis and its relationship with water temperature from summer growth to autumn spawning periods

As climate warming progresses, it becomes necessary to study the effects of water temperature on the basin-scale dynamic distribution of riverine fish. This study examined the spatiotemporal distribution of Plecoglossus altivelis using the environmental DNA approach and its relationship with water temperature from summer growth to autumn spawning periods in the Nagara River basin, central Japan. The overall results of the spatiotemporal distribution of P. altivelis were consistent with the known life history: a wide-range distribution in the basin during summer and aggregation in the middle mainstem during autumn. Additionally, this study found three intriguing distribution patterns depending on water temperature. During summer (August), the warmest period, P. altivelis was distributed in the upper mainstem, one tributary, and the mainstem downstream of the tributary confluences in relation to the relatively colder water (< 25 °C). During early autumn (September–early October), it spread widely in the middle and upper mainstem without the constraint of the upper limit of water temperature. During late autumn (late October–November), it steadily aggregated to the middle mainstem because of downstream migration for spawning at water temperatures below 20 °C. This study suggests the importance of river connectivity for P. altivelis migration to suitable habitats during its freshwater life stages, upper mainstem and tributaries as summer growth habitats, and cooling effects of tributaries on the mainstem during mid-summer.

Modelling of nearshore microbial water quality at confluence of a local tributary in Lake St. Clair

Microbial water quality, measured asEscherichia coli(E. coli)concentration, at beaches along the southern shore of Lake St. Clair in Canada, often exceeds public safety guidelines. Belle River, located near a public beach and a drinking water intake, is one of the several smaller tributaries of the lake whose contribution to nearshore microbial water quality is currently unknown. A flexible mesh 3D coupled TUFLOW-FV and Aquatic Ecodynamic (AED2+) model was used to simulate the hydrodynamics and microbial water quality in Lake St. Clair. A higher resolution nested model was developed within the lake-wide TUFLOW-FV model for better spatial and temporal resolution in the local region surrounding Belle River. Regular and up to a factor of four difference in predictedE. coliconcentrations were observed with the nested and lake-wide models at the public beach next to Belle River, whereas the difference was marginal at the drinking water intake about a kilometre away from the shore. While theE. coliloading to Lake St. Clair from Belle River is considered negligible, >90% of the predicted dailyE. coliconcentration at the beach and > 50 % at the water intake were attributed to Belle River from amongst all watershed sources to Lake St. Clair considered in the model. The model results also show that the construction of a new 150 m jetty in 2018, replacing the older 25 m jetty separating Belle River from the public beach, is expected to significantly reduceE. coliconcentrations observed at the beach.

Variation of sediment grain size parameters, fish diversity, and phytoplankton richness in relation to sand and silt fractions in estuaries

ABSTRACT Estuaries are highly dynamic zones. They are confluence of sea, river, tributaries, effluents, and runoff water that modify constantly their physical conditions and affect growth, productivity, and survival of inhabiting biota. In the current study, we investigated the extent to which estuarine sediment fractions explain variation of grain size parameters (mean size: Mz, standard deviation: σI, skewness: Ski and kurtosis: KG), fish diversity, and phytoplankton richness in estuaries. We applied series of multivariate regression models and controlled for the effect of sediment origin, season, and measurement method. The models output showed that sand fraction explained consistently variation of all the four grain size parameters. However, silt fraction was significantly associated with Mz, Ski, and KG but not σI. We couldn’t detect any significant relationship between sand or silt fraction with fish diversity. In contrast, we found that high richness in phytoplankton species was associated with low sand and low silt conditions. We therefore conclude that it is possible to reliably estimate Mz, σI, Ski, KG, and phytoplankton richness from sand and silt fractions. Moreover, managing sand and silt fractions ejected in estuaries may be an alternative of protecting and restoring estuarine biodiversity.

Effects of hydrologic variability and remedial actions on first flush and metal loading from streams draining the Silverton caldera, 1992–2014

AbstractThis study examined water quality in the upper Animas River watershed, a mined watershed that gained notoriety following the 2015 Gold King mine release of acid mine drainage to downstream communities. Water‐quality data were used to evaluate trends in metal concentrations and loads over a two‐decade period. Selected sites included three sites on tributary streams and one main‐stem site on the Animas River downstream from the tributary confluences. During the study period, metal concentrations and loads varied seasonally and annually because of hydrologic variability and remedial actions designed to ameliorate the effects of acid mine drainage. Water‐quality data were divided into two periods based on the timing of remedial activities in the watershed. The first period includes active water treatment, surface reclamation and installation of bulkheads in adits; the second period includes the decade following these activities. Water‐quality data were used to estimate annual and monthly zinc loads using the Adjusted Maximum Likelihood Method (using LOADEST software) and U.S. Geological Survey streamflow data. This study presents one of the first applications of LOADEST focused on metal loads. Monthly flow‐weighted concentrations were analysed using a Mann‐Kendall trend test to determine the direction, magnitude, and significance of temporal trends in zinc loading in any given month and using t‐test comparisons between the two periods. Zinc loads estimated for the Animas River below the tributaries indicate decreased zinc loading during the rising limb of the hydrograph in the second period, perhaps reflecting a reduction of snowmelt‐derived zinc load following surface reclamation activities. In contrast, base‐flow zinc loading increased at the main‐stem site, perhaps because of the cessation of water treatment in tributary streams. Flow weighting of monthly load estimates yielded increased statistical significance and enabled more nuanced differentiation between the effects of hydrologic variability and remedial activities on zinc loading.

Determining transition reaches between torrents and downstream rivers using a valley morphology index in a mountainous landscape

AbstractDividing rivers into homogeneous reaches is key for river processes and watershed management. In contrast to downstream fluvially dominated rivers, upstream debris‐flow dominated torrents have steeper channel slopes and smaller valley width/depth ratios. Investigating transition reaches between torrents and fluvially dominated rivers, not only explores the structure of the landscape, but also contributes to hazard management. This study proposed a valley morphology index combining two variables, channel slope and valley width/depth ratio, to determine transition reaches between torrents and rivers. The methodology was applied to 41 mountain streams in Taiwan using a Geographic Information System (GIS)‐based topographic analysis. Plots of valley width/depth ratio versus channel slope were used to determine boundary values of the valley morphology index (Iv) separating torrents from rivers. The plots showed that about 80% of the river basins present “L‐shaped” curves, which indicate sharp decreases in slope for upstream sections and dramatic increases of valley width/depth ratio for downstream sections. Results further demonstrated an average value of Iv 0.0047 across the study sites. Spatial comparison between geographic regions indicated that transition reaches in eastern rivers tend to occur lower in the drainage basin due, in part, to higher terrain. Local factors, such as tributary confluences and landslides promote the transition from torrents to fluvially dominated rivers. Satellite images verified that the approach correctly identified transition reaches, suggesting that it may provide a useful reference for river management.

Estimation of the area of potential thermal refuges using generalized additive models and multivariate adaptive regression splines: A case study from the Ste‐Marguerite River

AbstractThermal refuges in rivers are becoming a critical habitat for ectotherm fish, including Atlantic salmon (Salmo salar). In this study, two statistical modelling approaches were used to estimate the areas of potential thermal refuges: generalized additive models (GAM) and multivariate adaptive regression splines (MARS). This allowed for the first development of a reliable statistical model that uses a few relevant predictors (air temperature, river discharge, main river, and tributary temperatures) to estimate tributary plume thermal refuge surface areas. GAM and MARS models were fitted independently for four sites on the Ste‐Marguerite River, (Quebec, Canada). Model performances were evaluated using the leave‐one‐out cross validation (LOOCV) approach and the following criteria: the Akaike information criterion (AIC), root‐mean‐square error (RMSE), relative root‐mean‐square error (rRMSE), Nash‐Sutcliffe efficiency coefficient (NASH), and finally the bias (BIAS). Using an array of thermographs deployed at the confluence of a cold tributary and the warmer main river stem, refuges were delineated at a daily time step. Model results indicate that the estimated areas are similar to the refuge surfaces interpolated using temperature measurements, with both models and for all sites. Results suggest that MARS performs better than GAM in terms of forecasting and estimating the variability of the area of thermal refuges at all study‐stations. This relatively simple approach will be of use to water resources managers faced with the challenge of protecting thermal refuges for fish.

Prognosis of metal concentrations in sediments and water of Paraopeba River following the collapse of B1 tailings dam in Brumadinho (Minas Gerais, Brazil)

In January 25, 2019, the B1 dam of Córrego do Feijão mine located in Brumadinho municipality (Minas Gerais, Brazil) collapsed and injected nearly 2.8 Mm3 of iron (Fe)- and manganese (Mn)-rich tailings in the Paraopeba River. This study assessed the contribution of tailings to the contamination of sediments and water by those metals. The dataset was built through daily to weekly samplings executed in the two years following the event, at 27 sites located along the Paraopeba plus 9 sites located at the confluence of main tributaries. The results evidenced a distinct contribution in the sectors “Anomalous” (8.6–63.3 km downstream from the dam) and “Natural” (115.8–341.6 km). The “Anomalous” sector presented large Fe/Al (12.2 ± 6.4) and Mn/Al (0.33 ± 0.19) ratios in sediments, thus being rich in tailings, while the “Natural” sector presented small ratios (2.4 ± 1.0; 0.06 ± 0.03) comparable to the natural sediments. A 500–700 m3/s stream flow discharge in the Paraopeba caused pronounced drops to the Fe/Al and Mn/Al ratios in the “Anomalous” sector, attributed to the mixture of contaminated sediments from the main water course with uncontaminated sediments injected by the tributaries during the event. Non-linear regressions showed Fe/Al and Mn/Al declines in the “Anomalous” sector, related with tailings mobilization downstream. The concentrations of Fe and Al in the sediments correlated positively with the corresponding concentrations in the Paraopeba water, conditioned by raising discharge rates and variations in the water pH. The contribution of tailings to the Fe correlation was demonstrated. No direct relation was established between the Mn concentrations in water and stream discharge, because manganese is associated with fine particles in the tailings that are mobilized to the water column even under low flows. The preliminary results of Seasonal Autoregressive Integrated Moving Average models predicted the return of Paraopeba to a pre-collapse condition in 7–11 years.

Influences of natural salinity sources and human actions on the Shapour River salinity during the recent streamflow reduction period.

The Shapour River, with a catchment area of 4254 km2, is a major river system in southern Iran. While the upstream river flow (the upper Shapour River) is fresh, it becomes extremely salinized at the downstream confluence of the Shekastian saline tributary and the entering nearby Boushigan saline spring. Then, the river passes via the Khesht plain and finally discharges into Raeisali-Delvari storage dam which went into operation in 2009. Over the 2006-2019 period, reduced precipitation and over-utilization of freshwater resources resulted in ~ 72% streamflow reduction in the Shapour River. Due to not using the saline waters for irrigation, drinking, and industrial purposes, the ratio of saline-outflow of Shekastian tributary and Boushigan spring to fresh-outflow of upper Shapour River increased by ~ 3 times; consequently, river salinity fluctuation domain at the Khesht plain inlet dramatically increased from 2.1-4.0 dS m-1 to 3.7-26.0 dS m-1. It resulted in major economic damages to the agricultural sector of middle Shapour River. On the seasonal timescale, consecutive processes of salt accumulation during irrigation season of the Khesht plain date orchards and then salt drainage during the rainy season have adjusted salinity fluctuation domain from 3.7-26.0 dS m-1 at the plain inlet to 5.2-8.9 dS m-1 at the plain outlet. In the lower Shapour River, storage/mixing of fresh/saline inflow waters in the Raeisali-Delvari reservoir has adjusted strong river salinity fluctuation domain from 0.9-10.7 dS m-1 at the reservoir inlet to 3.6-5.5 dS m-1 at the reservoir outlet. The success of the Raeisali-Delvari reservoir for salinity adjustment is due to its suitable location on the Shapour River, by being situated downstream of all main river tributaries with natural saline/fresh sources of water.

Effects of garbage salvaging and suspended crossbar on microplastic pollution along a typical urban river.

Microplastic pollution has been considered as a global environmental issue that potentially threatens human health. However, research about microplastic pollution in urban rivers is still insufficient. This study analyzed the abundance and distribution of microplastics in surface water of the Nanfei River in Hefei, China. Microplastic concentrations ranged from 0.8 to 27 items/L along the studied river. The small size (50-333μm) (47.58-84.89%) and white (55.65-88.89%) were predominant among all samples, except that collected from the source reach. Pellet was a typical and abundant microplastic type and accounted for 60.30%. PE and PP were the major polymers, occupying 55.24% and 22.86%, respectively. The results showed that traditional environmental management practices including salvaging surface garbage regularly and setting wooden suspended crossbars at tributary confluences could significantly mitigate the pollution degree of microplastics. The polymer risk index was calculated to describe the potential risk of microplastics, and the pollution level was still at high risk under various management practices. This study provides a valuable finding for future research on microplastics in urban city rivers, which may improve the knowledge that how to control and prevent microplastic pollution.

Organophosphate flame retardants, tetrabromobisphenol A, and their transformation products in sediment of e-waste dismantling areas and the flame-retardant production base

Due to the prohibition of polybrominated diphenyl ethers, organophosphate flame retardants (OPFRs) and tetrabromobisphenol A (TBBPA) have become emerging flame retardants. However, knowledge about their occurrence, especially their transformation products, is still limited. This study collected sediment samples from two rivers, i.e., Lianjiang River (located at an e-waste dismantling area) and Xiaoqing River (situated at a flame retardant production base), to investigate the occurrence, composition, and spatiality distribution of OPFRs, TBBPA, and their transformation products. Both targets were detected in the Lianjiang River in the range of 220–1.4 × 104 and 108–3.1 × 103 ng/g dw (dry weight) for OPFRs and TBBPA, and 0.11–2.35 and 4.8–414 ng/g dw for their respective transformation products, respectively. The concentrations of OPFRs and TBBPA in the Xiaoqing River ranged from 4.15 to 31.5 and 0.76–2.51 ng/g dw, respectively, and no transformation products were detected. Different compositional characteristics of OPFRs and distinct spatial distribution from mainstream and tributary observed between the two rivers are attributed to the difference in the local industries. Spatial distribution and principal component analysis indicated that e-waste dismantling activities could be a vital source of local pollution. Besides, the confluence of tributaries seemed to determine the contaminant levels in the Xiaoqing River. Also, concentration ratios and Spearman’s correlation between metabolites and parent chemicals were analyzed. Low concentration ratios (3.6 ×10–4 to 0.16) indicated a low transformation degree, and Spearman’s correlation analysis suggested transformation products were partly stemming from commercial products. Considering the limited study of these transformation products, more studies on their sources, transform mechanism, and toxicity are required.

Modelling sediment (dis)connectivity across a river network to understand locational‐transmission‐filter sensitivity for identifying hotspots of potential geomorphic adjustment

AbstractRivers act as ‘jerky conveyor belts’ that transmit fluxes of flow and sediment downstream. This transmission of fluxes can be highly variable within a drainage basin resulting in either abrupt or gradational sediment (dis)connectivity patterns and processes. This study assesses sediment (dis)connectivity across a basin as a means to understand the locational, transmission and filter sensitivity properties of a fluvial system. Drawing upon the case study of Richmond River Catchment, New South Wales, Australia we use the concepts of effective catchment area and buffers, along with graph theory and an empirical sediment transport model CASCADE (Catchment Sediment Connectivity and Delivery), to assess (1) the degree to which modelled sediment cascades along the river network are connected or disconnected (2) how the position, pattern and configuration of (dis)connection facilitates or restricts geomorphic adjustment in different parts of a catchment, and (3) use the findings as a basis to explain the locational‐transmission‐filter sensitivity of the catchment. We use this analysis to segregate supply limited and transport limited reaches and identify various controls on sediment dynamics: in‐stream sediment storage units, junctions between different geomorphic river types, tributary confluences and sediment storage units within partly confined floodplain units. Such analysis lays the foundation for network scale identification of potential hotspots of geomorphic adjustment.

Effect of watershed disturbance and river-tributary confluences on watershed sedimentation dynamics in the Western Allegheny Plateau

Harmful algal blooms (HABs) have increased in the Ohio River Basin over the past decade. Fine sediment dynamics are now recognized to play an important role in the proliferation and toxicity of HABs. As a result, the fate of sediment at confluences of tributaries and regulated river systems may be important zones for sediment retention and burial. The objective of this study was to improve understanding of watershed sediment loading dynamics and backwater inundation impacts on sedimentation within confluence watersheds. The study site selected for this work was the Fourpole Creek watershed in the Western Allegheny Plateau ecoregion of Appalachia, which is a mixed-use watershed with predominantly forested and urban landcover with a backwater floodplain wetland at the confluence with the Ohio River. Approximately 16 months of high-frequency (15-minute) turbidity data was used as a surrogate for total suspended solids at upstream and downstream nodes of the backwater confluence feature. Continuous sediment yield estimates suggested an annual sediment yield of 82 t/km2 and was found to be higher than sediment yields reported elsewhere in Appalachian watersheds without mining disturbances. A modified sediment rating curve using both seasonal and annual regression approaches were found to underpredict sediment yield by 29% and 80%, respectively. A hysteresis-based source unmixing method and hysteresis index were used to quantify sediment source and flow pathways during events and suggested high variability in sediment source contributions both seasonally and within-seasons, suggesting three likely sediment sources in the watershed including in-channel/gully erosion, resuspension of recently deposited sediment in the fluvial network, and erosion of subsurface macropores from forested uplands. Upstream-downstream monitoring of the confluence floodplain suggested 34% of the annual sediment inputs were retained during the continuously monitored 2019 calendar year. Our results suggest that confluence floodplains play an important role in intercepting and storing sediment inputs. Efforts to limit downstream sediment loads should ensure the function of confluence floodplains is maintained or enhanced when considering watershed management strategies in these landscapes.