Dam construction leads to both sediment discontinuities and the creation of internal phosphorus (P) loads in reservoirs capable of supporting eutrophication. Today, majority of large rivers are ...dammed and numerous of these infrastructures are constructed in cascade. However, few studies focus on the cumulative effect of the presence of dam on sediment P mobility and bioavailability in downstream reservoirs and rivers parts or throughout the continuum. The influence of three cascade dams has been studied herein on the sedimentary P distribution in surface bed sediments along a 17-km fluvial continuum of the Creuse River (Massif Central, France). The sediments (17 samples) were analyzed for their physical (grain size, specific surface area) and chemical (pH, contents of P, Fe, Al, Ca, Mn, organic matter (OM), and P fractionation) characteristics. Results indicated an amount of P 3 to 7 times higher in dam sediments (1.59 ± 0.51 mgP/g DW) than in free-flowing river sections (0.27 ± 0.11 mgP/g DW). Unexpectedly, sedimentary TP content did not decrease from the first to the third reservoir. The spatial variations of sediment characteristics between river and reservoirs were correlated with the retention of particles sized under 200 μm within the reservoirs. In reservoir sediment, P was mainly associated with the ascorbate fraction (P associated with the redox-sensitive Fe/Mn precipitates). Inside each dam reservoir, longitudinal variations of the sedimentary P distribution were mainly due to the increase of amorphous Fe precipitate content accumulated in fine sediments toward the dam, as characterized by a low Fe-Asc/P-Asc molar ratio. In the river sections, P distribution (mainly associated with HCl and ascorbate fractions) was not significantly influenced by cascade dams.
For more than half a century, chemical contamination has progressively spread to all the large river basins. Large river outlets integrate multiple anthropogenic pressures in watersheds, making them ...the largest source of sediment‐bound contaminants to continental shelf areas. However, comparing particulate micropollutant contaminations between the large river basins is a challenging task, especially due to the scarcity of long‐term river monitoring programs. Here we address this issue, with a focus on legacy particulate micropollutants (polychlorobiphenyls PCBi, polycyclic aromatic hydrocarbons PAHs and trace metal elements TME) yields. For this purpose, we employed a bottom‐up multiscale approach to chemical contamination in river basins that takes micropollutant yields measured in the Rhône River sub‐basins (France) as a benchmark of other large river basins. Data on the Rhône River basin came from a unique 10‐year‐long monitoring program within the Rhône Sediment Observatory (OSR), and were compared to data gathered on 18 major worldwide river outlets. The Rhône River basin is far cleaner now than a few decades ago, likely due to environmental regulations. At a wider spatial scale, our results depict an overall contamination gradient splitting the most heavily contaminated river basins, located in developing and industrializing low‐to‐middle‐income countries, from the least contaminated rivers located in developed high‐income countries. We argue that chemical contamination levels of large river basins depend on their stage of economic development.
For more than half a century, chemical contamination has progressively spread to all the large river basins. Comparing particulate micropollutant contaminations between the large river basins is a challenging task, as there is a lack of large‐scale monitoring for estimating chemical contamination at river outlets. Here we address this issue using yields of legacy micropollutants in a bottom‐up multiscale approach, from the well‐monitored Rhône River sub‐basins (as benchmark) up to the major large river basins. Results show an overall chemical contamination gradient that splits the most‐contaminated river basins, located in developing and industrializing low‐to‐middle‐income countries, from the least contaminated rivers located in developed high‐income countries. Data from the pluri‐decadal monitoring program on the Rhône River basin shows that since the 1980s, this river has transitioned from the more‐contaminated group to the less‐contaminated group.
•Assessment of microplastics (MPs) hotspots along a gravel-bed river.•Significant breakdown in MPs in the area of the main dams.•Major links between plastic factories, urban areas and MPs ...distribution.•Plastic assemblage greatly results from industrial heritage along the Ain River.
Understanding microplastic particles (MPs) accumulation and transport along rivers represents a major task due to the complexity and heterogeneity of rivers, and their interactions with their wider corridor. The identification of MPs hotspots and their potential sources is especially challenging in coarse-bed rivers transporting a wide range of particle sizes with a high degree of variability in time and space. This research focuses on the gravel-bed Ain River (Rhône River tributary, France) which is managed by means of various dams and also hosts one of the major plastic production centres in Europe (Oyonnax and Bienne Plastic Valleys). In this research, (i) Geographical Information Systems (GIS) were used to locate plastic factories and to characterise the land use of the Ain River watershed. (ii) On the field, sediment samples were extracted from the hyporheic zone (HZ) of mobile gravel bar heads, while hydro-sedimentary settings were measured in order to describe site conditions. Sampling sites were especially established in downwelling areas (i.e. where the surface water entered the hyporheic zone), upstream and downstream of dams and plastic factories. (iii) After density separation and organic matter digestion of sediment, MPs were characterised with a µFTIR device followed by data processing via the siMPle software. This work highlighted the trapping efficiency of alluvial bars for MPs. The highest MPs concentrations were found along the Plastic Valleys (up to 4400 MPs/kg), while the lower river was less contaminated by MPs. After grain-size correction, a significant breakpoint was identified in the area of the main dams, revealing their major influence on MPs distribution. The variability in MPs concentrations and types suggested a local origin for most of MPs. A particular feature was the dominance of polypropylene (PP) which appears as a critical industrial heritage as the studied region is specialised in the manufacturing of hard plastics. Indeed, multivariate analyses also revealed that MPs concentrations and types were mostly driven by the vicinity of plastic factories and urban areas. This relationship between the land use, the presence of dams and MPs characteristics provides key results for the MPs assessment and the improvement of management issues along coarse-bed rivers.
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•Joint analysis of dated cores and subsurface sediments to reconstruct pollution trends.•Local geochemical backgrounds established from pre-industrial palaeochannel cores.•Metal trajectories ...influenced by local hotspots and diffuse pollution until the 1990s.•Sediment quality recovery varied from a metal to another and according to the location.•High influence of some metals (e.g. Cu) in the risk of pollutant mixture.
In European rivers, research and monitoring programmes have targeted metal pollution from bed and floodplain sediments since the mid-20th century by using various sampling and analysis protocols. We propose to characterise metal contamination trajectories since the 1960s based on the joint use of a large amount of data from dated cores and subsurface sediments along the Rhône River (ca. 512 km, Switzerland–France). For the reconstruction of spatio-temporal trends, enrichment factors (EF) and geo-accumulation (Igeo) approaches were compared. The latter index was preferred due to the recurrent lack of grain-size and lithogenic elements in the dataset. Local geochemical backgrounds were established near (1) the Subalps and (2) the Massif Central to consider the geological variability of the watershed. A high contamination (Igeo = 3–5) was found for Cd, Cu and Zn from upstream to downstream over the period 1980–2000. This pattern is consistent with long-term emissions from major cities and the nearby industrial areas of the Upper Rhône (Geneva, Arve Valley), and Middle Rhône (Lyon, Chemical Corridor, Gier Valley). Hotspots due to Cu and Zn leaching from vineyards, mining, and highway runoff were also identified, while Pb was especially driven by industrial sources. The recovery time of pollution in sediment varied according to the metals and was shorter upstream of Lyon (15–20 years) than downstream (30–40 years). More widely, it was faster on the Rhône than along other European rivers (e.g. Seine and Rhine). Finally, the ecotoxicological mixture risk of metal with Persistent Organic Pollutants (POPs) for sediment-dwelling organisms showed a medium “cocktail risk” dominated by metals upstream of Lyon, although it is enhanced due to POPs downstream, and southward to the delta and the Mediterranean Sea. Overall, this study demonstrates the heterogeneity of the contamination trends along large fluvial corridors such as the Rhône River.
A wide range of persistent organic chemicals, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), some insecticides, as well as polybrominated diphenyl ethers (PBDEs) ...and some perfluoroalkyl substances (PFASs) were analyzed in 17 bed sediments collected along the Saigon River and at adjacent canal mouths from upstream to downstream in Ho Chi Minh City (Vietnam). Concentrations were rather low for PAHs, as well as for legacy PCBs and dichloro-diphenyl-trichlorethane and metabolites (DDTs), or below detection limits for several PFASs and all PBDEs measured. Several insecticides (chlorpyrifos-ethyl, and the pyrethroids cypermethrin and λ-cyhalothrin) displayed rather high concentrations at a few sites within the city. There was no distinct upstream – downstream trend for PAHs, (DDTs) or PCBs. Although adjacent canal sediments tended to be more contaminated than Saigon River sediments, the differences were not significant. Emissions are almost certainly substantial for PAHs, and probably also for other contaminants such as PBDEs and some PFASs. During the dry season, contaminants are presumably stored in the city, either in canals or on urban surfaces. Heavy rainfall during the monsoon period carries away contaminated particle flows into the canals and then the Saigon River. The strong tidal influence in the river channel hinders the accumulation of contaminated particles. Contaminated deposits should accordingly be investigated further downstream in depositional environments, such as the mangrove.
•Saigon River sediments displayed low concentrations of persistent organic contaminants.•For PAHs, emissions appear similar to those of other cities in South-East Asia.•Tidal influence in Saigon River, water management and monsoon control PAH fate.•Similar patterns are applicable to other contaminants such as PBDEs or PFASs.•Ecotoxicological impacts might be expected in the mangrove where sediment deposit.
Abstract 137 Cs is a long-lived man-made radionuclide introduced in the environment worldwide at the early beginning of the nuclear Era during atmospheric nuclear testing’s followed by the civil use ...of nuclear energy. Atmospheric fallout deposition of this major artificial radionuclide was reconstructed at the scale of French large river basins since 1945, and trajectories in French nuclearized rivers were established using sediment coring. Our results show that 137 Cs contents in sediments of the studied rivers display a large spatial and temporal variability in response to the various anthropogenic pressures exerted on their catchment. The Loire, Rhone, and Rhine rivers were the most affected by atmospheric fallout from the global deposition from nuclear tests. Rhine and Rhone also received significant fallout from the Chernobyl accident in 1986 and recorded significant 137 Cs concentrations in their sediments over the 1970–1985 period due to the regulatory releases from the nuclear industries. The Meuse River was notably impacted in the early 1970s by industrial releases. In contrast, the Seine River display the lowest 137 Cs concentrations regardless of the period. All the rivers responded similarly over time to atmospheric fallout on their catchment, underlying a rather homogeneous resilience capacity of these river systems to this source of contamination.
Purpose
River infrastructures such as dikes, groynes, and dams are ubiquitous on most large rivers, and although their consequences on the riverbed morphology have often been studied, the effect they ...might have on the river floodplain and margins remains largely unknown. By investigating the structure and composition of floodplain sediments in three areas along the Rhône River that were extensively engineered during the last 150 years, this paper aims to understand whether river infrastructures might systematically induce a change in sedimentation patterns in the river margins.
Materials and methods
A total of fifteen sediment cores were sampled in three distinct reaches of the Rhône valley downstream of Lyon. They were thoroughly analyzed in terms of grain size, using heatmap representations and end-member analysis. Six metallic elements (Zn, Cr, Pb, Cu, Ni, Cd) were systematically quantified. In six out of the fifteen cores, total organic carbon (TOC), organic contaminants (PCBs) concentrations, and
137
Cs activity were also assessed.
Results and discussion
A sharp change in grain size distribution is consistently identified in the sediment cores of all three study reaches. The sediments above this change are fine (D
50
< 100 μm), poorly classified and homogenous. They also show a relative increase in contamination when compared with deeper sediments. We interpret this change in sediment characteristics as the consequence of an abrupt decrease in connectivity between the floodplain and the river channel, likely due to the implementation of navigation infrastructures in the channel in the second half of the nineteenth century. In one case, the dating of the sediment cores allows linking the grain size change to the implementation of navigation infrastructures in the channel. In the other study areas, the effect of engineering seems delayed in time due to local variability.
Conclusions
The implementation of river infrastructures resulted in a loss of connectivity between the floodplain and the channel. This was reflected as the homogenization of the floodplain sedimentary environment of the Rhône River all along its course from Lyon to the sea. A similar phenomenon might be present in most engineered rivers across Europe.
Despite increasingly strict control of polychlorinated biphenyl (PCB) releases in France since the mid-1970s, PCB contamination of fish recently has emerged as a major concern in the lower Rhône ...River basin. We measured PCB concentrations in Rhône sediment to evaluate the effects of PCB releases from major urban and industrial areas, sediment redistribution by large floods, and regulatory controls on PCB trends from 1970 to present. Profiles of PCBs (the sum of seven indicator PCB congeners) were reconstructed from sediment cores collected from an off-river rural reference site and from three depositional areas along the Rhône upstream and downstream from the city of Lyon, France. Core chronology was determined from radionuclide profiles and flood deposits. PCB concentrations increased progressively in the downstream direction, and reached a maximum concentration in 1991 of 281μg/kg at the most downstream site. At the rural reference site and at the upstream Rhône site, PCB concentrations peaked in the 1970s (maximum concentration of 13 and 78μg/kg, respectively) and have decreased exponentially since then. PCB concentrations in the middle and downstream cores were elevated into the early 1990s, decreased very rapidly until 2000, and since then have remained relatively stable. Congener profiles for three time windows (1965–80, 1986–93, and 2000–08) were similar in the three sediment cores from the Rhône and different from those at the rural reference site. The results indicate that permitted discharges from a hazardous-waste treatment facility upstream from Lyon might have contributed to high concentrations into the 1980-90s, but that industrial discharges from the greater Lyon area and tributaries to the Rhône near Lyon have had a greater contribution since the 1990s. There is little indication that PCB concentration in sediments downstream from Lyon will decrease over at least the short term.
►We reconstructed trends in PCBs in the Rhône River, France, using sediment cores. ►PCB concentrations in sediments of the Rhône increase in a downstream direction. ►Concentrations of PCBs at the downstream sites remained elevated into the 1990s. ►PCBs in sediment downstream from Lyon are unlikely to decrease over the short term.
Environmental pollution by polychlorinated biphenyls (PCBs) is a key cause for concern
about river quality because of their low degradation rates leading to their
accumulation in sediments and living ...organisms. An original
interdisciplinary work was conducted along the four main French rivers
(Seine, Rhône, Loire and Garonne rivers), which flow into major European
seas. We completed a dataset based on sediment analyses provided by
monitoring agencies, port authorities and research teams on different solid
matrices (sediment cores, bed and flood deposits, suspended particulate
matter and dredged sediments). This dataset focused on the seven indicator
PCBs and their sum (ΣPCBi) from 1945 to 2018 (nΣPCBi
=1416). Special effort was put into the quality control to provide robust
spatio-temporal information. Taking into account hydrological and human
drivers, we outlined two main pollution trends: (1) from 1945 to 1975, a
quick increase in ΣPCBi (up to 4 mg kg−1 dry weight, dw) and a
sharp decrease in the 1980s on the Seine and Loire rivers and (2) increasing
but moderate ΣPCBi levels (50 to 150 µg kg−1 dw)
followed by a decline after the 1990s on the Rhône and Garonne rivers.
In addition to these patterns, PCB emissions from urban and industrial areas
or accidental events were significant in each river. Finally, when
calculating specific flux, the Rhône exhibited the uppermost
ΣPCBi load (up to 12 µgm-2yr-1 in 1977–1987),
at least 25 % higher than those of the Seine and Loire rivers, while the
Garonne showed a very low flux. In western Europe, we confirmed that
the Rhône, Seine and Loire rivers contribute significantly to the PCB
contamination of the seas, while French specific ΣPCBi fluxes are
2 orders of magnitude lower than those found in American or Asian rivers.
The dataset is available at https://doi.org/10.1594/PANGAEA.904277 (Dendievel et al., 2019).
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