Olivier Radakovitch

Institut de Radioprotection et de Sûreté Nucléaire (IRSN) | IRSN · LRTA - research Laboratory for Radionuclides Transfer in Aquatic ecosystems

Estuaries at the river-sea interface are capable of modulating the export of water and pollutants to the sea through their circulation and reactivity leading to large uncertainties. As a result, coupling large scale models of pollutant transfer in aquatic ecosystems (river and sea) requires an interfacing, even minimal, between them. We propose to...

Particle-size classes (7 fractions from 0.8 to 2000 μm) were collected in the deep chlorophyll maximum along a Mediterranean transect including the northern coastal zone (bays of Toulon and Marseilles, France), the offshore zone (near the North Balearic Thermal Front), and the southern coastal zone (Gulf of Gabès, Tunisia). Concentrations of biotic...

This study aimed to describe the interannual variability of dense shelf water cascading and open ocean convection in the Gulf of Lions (NW Mediterranean) based on long-term temperature and current records and its impact on particle fluxes and associated metals. These observations highlight the predominant role of the rare intense events of dense sh...

In the marine coastal environment, freshwater and seawater coalescing communities are facing a complex set of abiotic and biotic cross-influences. This study aimed at evaluating the respective influences of blending and prokaryotic dynamics on community structure. For that, the surface salinity gradient of a nutrient-rich estuary (Arno River, Medit...

This paper looks at experiential feedback and the technical and scientific challenges tied to the MERITE-HIPPOCAMPE cruise that took place in the Mediterranean Sea in spring 2019. This cruise proposes an innovative approach to investigate the accumulation and transfer of inorganic and organic contaminants within the planktonic food webs. We present...

Sediment cores from the central Algerian coast were collected to investigate the distribution, sources and risk of trace metals. The local geochemical background of metals was defined from the core S collected in an uncontaminated area of the coast. The anthropogenic inputs in Algiers Bay elevated Ag, Cd, Pb and Zn concentrations as their maximum w...

Metal pollution in rivers should not be overlooked before their entry into the sea. However, there are few studies for estimating such contamination in rivers entering the Algerian coastal waters. Semimonthly quantification of dissolved and particulate metals, near the mouths of two industrial-tainted rivers, El Harrach and Mazafran rivers, was car...

Purpose Radiocarbon and tritium are the dominant radionuclides released by nuclear industries over the world. Close interactions of these elements with particulate organic matter (POM) in soils and rivers are widely reported in the literature but only few studies focus on their relationships with POM within nuclearized rivers. Here, we focus on the...

Industrial and urban waste is drained and dumped directly into Algiers Bay without any prior treatment. Increasingly. this waste has damaged the marine environment. The main objective was to evaluate the degree of contamination by trace metals in the continuous monitoring of the marine environment. The study was carried out in two different phases...

The Rhône River is among the main rivers of western Europe and the biggest by freshwater discharge and sediment delivery to the Mediterranean Sea. Its catchment is characterized by distinct hydrological regimes that may produce annual sediment deliveries ranging from 1.4 to 18.0 Mt yr−1. Its course meets numerous dams, hydro and nuclear power plant...

We report lead (Pb) analyses in juvenile (n = 37; mean length = 24.7 ± 2.3 cm) and adult (n = 16; mean length = 52.3 ± 9.3 cm) Centroscymnus coelolepis Mediterranean deep-sea sharks that are compared to Pb content in bathy-demersal, pelagic and shallow coastal sharks. Median Pb concentrations of C. coelolepis muscle (0.009–0.056 wet ppm) and liver...

The Rhône River is amongst the main rivers of Western Europe and the biggest by freshwater discharge and sediment delivery to the Mediterranean Sea. Its catchment is characterized by distinct hydrological regimes that may produce annual sediment deliveries ranging from 1.4 to 18.0 Mt y−1. Furthermore, the course of the Rhône River meets numerous da...

Un des objectifs de l'Observatoire des sédiments du Rhône (OSR) mis en place depuis 2009 est de combler le manque de connaissances sur les flux particulaires de micropolluants rejetés dans la mer Méditerranée. Le réseau de mesure des flux de l’OSR comprend douze stations de mesure en continu, dont trois stations situées sur le Rhône lui-même, et ne...

The behavior and impact of trace metals discharged into rivers depend on their solid/liquid fractionation and the fate of these two phases according to hydro-sedimentary processes. The solid/liquid fractionation depends on many environmental factors which imply uncertainties of several orders of magnitude in the evaluation of the partition coeffici...

Ferralsols upon ultramafic rocks are among the most Cr-enriched soils at the Earth surface. Weathering and erosion of these soils represents a major source of Cr for coastal sediments downstream of ultramafic settings. Although Cr mainly occurs as Cr(III)-bearing chromite and Fe-(hydr) oxides in Ferralsols upon ultramafic rocks, several evidences o...

Temporal reconstruction of Hg deposition from sediment archives is relatively straightforward in organic-rich or high sedimentation rate environments, such as lakes and ocean margins. To retrieve long-term records at regional or global scales, deep-sea sediments are more appropriate, but such records are scarce and their reliability has been questi...

Chronic hypoxia and anoxia have strong impacts on coastal ecosystems worldwide. In shallow coastal ecosystems, such situations are essentially driven by high benthic oxygen (O2) demand resulting from organic matter mineralization in surface sediment and amplified by a low mixing of the water column. However, the benthic O2 demand may greatly vary a...

The determination of copper (Cu) speciation and its bioavailability in natural waters is an important issue due to its specific role as an essential micronutrient but also a toxic element at elevated concentrations. Here, we report an improved anodic stripping voltammetry (ASV) method for organic Cu speciation, intended to eliminate the important p...

Assessing and modelling the coastal plume dispersion of nuclearized rivers is strategic in case of accidental releases, but taking into account the variation of main hydrodynamic forcings is challenging. This study uses fuzzy c-mean clustering of a 10 years series of discharge and wind speed at the Rhone River estuary (France) in order to explain t...

La contamination chimique marine en Méditerranée s’inscrit dans un contexte de dégradation généralisée des écosystèmes marins et d’un besoin d’amélioration des bases scientifiques pour décrire le bon état écologique et pour fournir de meilleurs indicateurs l’évolution de cette pression anthropique sur l’environnement. La Méditerranée y est particul...

Understanding the processes governing the behavior of radiocesium in the sea is still essential to make accurate assessments of its potential impacts on marine ecosystems. One of the most important of this process is the desorption that may occur at the river-sea interface due to changes in physico-chemical conditions, including ionic strength and...

Land-based micropollutants are the largest pollution source of the marine environment acting as the major large-scale chemical sink. Despite this, there are few comprehensive datasets for estimating micropollutant fluxes released to the sea from river mouths. Hence, their dynamics and drivers remain poorly understood. Here, we address this issue by...

Location of river-groundwater exchange zones and biodiversity hotspot is essential for a river management plan, especially for Mediterranean karstic rivers. This location is often difficult and time-consuming when long river sectors are considered. We studied a 13 km-long sector of the Cèze River (Southern France) located in a karstic canyon. We co...

Determination of submarine groundwater discharge (SGD) from karstic coastal aquifers is important to constrain hydrological and biogeochemical cycles. However, SGD quantification using commonly employed geochemical methods can be difficult to constrain under the presence of large riverine inputs, and is further complicated by the determination of t...

The Rhone River (France) has been used for energy production for decades and 21 dams have been built. To avoid problems due to sediment storage, dam flushing operations are periodically organized. The impacts of such operations on suspended particulate matter (SPM) dynamics (resuspension and fluxes) and quality (physico-chemical characteristics and...

Microplastics have become widely dispersed throughout the marine environment in and around Japan since the 1960s, which corresponds to the onset of mass plastic production and use in this country. Our study documents a possible abrupt microplastic depositional event in continental shelf and deep-sea environments triggered by a tsunami. The sediment...

Land-based human activities are known to be the largest sources of marine pollution. Once released into the hydrographic networks, metals and hydrophobic organic micropollutants reach coastal ecosystems mainly through suspended particulate matter (SPM). As a result, the accurate assessment of micropollutant fluxes discharged by rivers is critical t...

In order to assess the release of UV filters from the sunscreen used by beachgoers into seawater within the bathing zone, a field campaign was carried out during the summer of 2017 at three beaches in Marseille, along the French Mediterranean coast. A social survey analyzed beachgoer attendance, the quantities and types of suncare products used and...

Trace metal contamination in the European sardine and anchovy food web was investigated in the Gulf of Lions, NW Mediterranean Sea, including seawater and size fractions of plankton. The results highlighted: i) higher and more variable concentrations in the smaller plankton size classes for all metals except cadmium; ii) higher concentrations in an...

Submarine Groundwater Discharge (SGD) has received increased attention in recent years since it was recognized that it may be both volumetrically and chemically important. Around the Mediterranean Sea, 60% of the coastline is composed of karstic aquifers, and to properly estimate the hydrological budget of the Mediterranean Sea it is therefore nece...

Suspended sediment distribution and fluxes were estimated within the dominant channel at the mouth of the Rhone River for two annual flood events. The estimates were based on ADCP acoustic backscatter intensity and using calibration and post-processing methods to account for the grain-size distribution (GSDs). The fluxes were very similar to those...

The Rhône River plays a major role in the Mediterranean Sea, being both its main freshwater source and its major particulate matter provider. This survey of the fate of terrestrial particulate organic matter (POM) was conducted along the salinity gradient of the Rhône River plume, between 2012 and 2014. It revealed that autoxidation acts rapidly an...

The contamination of freshwater systems by metals is a worldwide problem due to their toxicity, abundance and persistence in the environment. One of the main processes affecting their residence time in freshwater systems is their solid-liquid fractionation, often modeled by the Kd approach defined as the concentration ratio between the particulate...

The objective of this paper is to present a model simulating and predicting the exchange kinetics of lead (Pb) between contaminated sediments and water during resuspension events potentially occurring in reservoirs. We developed an innovative model that combines thermodynamic speciation of particulate surfaces (oxides and Particulate Organic Carbon...

The bioavailability of trace elements (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Zn) in lowly to moderately contaminated coastal sediments from the Berre lagoon, France, was assessed by comparing their potentially bioavailable concentrations and bioaccumulated concentrations in the polychaete Alitta succinea. No linear correlations were observed contrarily t...

During the 1980s-90s, the contamination of the Mediterranean Sea by radionuclides was widely studied following the Chernobyl accident and the recognition of the influence of Rhône discharges. At this time, numerous in situ or laboratory studies were conducted to evaluate the behavior of radionuclides in trophic chains and in the water column. For v...

RESUME. L’Observatoire Hommes-Milieux (OHM) Vallée du Rhône appréhende les dynamiques de l’hydrosystème et des sociétés riveraines sur l’ensemble du Rhône français. Depuis sa création en 2010, la mutualisation et la valorisation des données produites ont été structurées dans une Infrastructure de Données Spatio-temporelles (IDS), ce qui a renforcé...

RESUME. L’Observatoire Hommes-Milieux (OHM) Vallée du Rhône appréhende les dynamiques de l’hydrosystème et des sociétés riveraines sur l’ensemble du Rhône français. Depuis sa création en 2010, la mutualisation et la valorisation des données produites ont été structurées dans une Infrastructure de Données Spatio-temporelles (IDS), ce qui a renforcé...

Evaluating the sources of nutrient inputs to coastal lagoons is required to understand the functioning of these ecosystems and their vulnerability to eutrophication. Whereas terrestrial groundwater processes are increasingly recognized as relevant sources of nutrients to coastal lagoons, there are still limited studies evaluating separately nutrien...

The level and the ecological risk assessment of heavy metals (Zn, Cu, Mn, Fe, Ni, Cr, V, As, Pb, Cd and Co) were evaluated in surface sediments from fifty-one stations along the Algerian coast. The main objective was to evaluate the risk that such metals may cause to the ecosystem, and thus the stations were choose in relation with the fishing traw...

The level and the ecological risk assessment of heavy metals (Zn, Cu, Mn, Fe, Ni, Cr, V, As, Pb, Cd and Co) were evaluated in surface sediments from fifty-one stations along the Algerian coast. The main objective was to evaluate the risk that such metals may cause to the ecosystem, and thus the stations were choose in relation with the fishing traw...

This study presents a specifically designed Mercury module in a coupled benthic-pelagic reactive-transport model - Bottom RedOx Model (BROM) that allows to study mercury (Hg) biogeochemistry under different conditions. This module considers the transformation of elemental mercury (Hg(0)), divalent mercury (Hg(II)) and methylmercury (MeHg). The beha...

Purpose Dam reservoirs sometimes need to be fully drawn down, an operation that induces sediment resuspension. In the case of contaminated sediments, such resuspension may promote the remobilization of trace metals from the solid to the dissolved phase, threatening the water quality. The objective of this study is to evaluate the kinetic release an...

The database for hydrological observatories (BDOH) is an efficient tool for storage which allows the combination of water discharge data, suspended particulate matter (SPM) and particulate contaminants concentrations, produced thought a same observatory network, to calculate time series fluxes. This application is used in the Rhône Sediment Observa...

Determining the riverine carbon fluxes to oceans is critical for an improved understanding of C budgets and biogeochemical cycles (C, O) over a broad range of spatial and time scales. Among the particulate organic carbon (POC) involved in these fluxes, those yielded by sedimentary rocks (petrogenic POC: pPOC) remain somewhat uncertain as to their s...

The increasing need on energy and fluvial transport due to industrialization during the last century resulted in the construction of infrastructures along rivers, as dams or sluices. Thus, 21 hydro-electrical dams were built along the Rhône River since 1950. To improve the production of electricity and avoid problems due to sediment storage within...

There exists a substantial amount of research on abiotic (e.g. photochemical) degradation pertaining to organic matter (OM) in the marine realm. While recent research has shown its importance in the degradation of terrestrial particulate OM (TPOM), the mechanisms involved in the induction of autoxidation in estuaries remain unclear. In this study,...

The supply of irrigation water often overcomes crop evapotranspiration, and the resulting return flow may infiltrate and significantly contribute to an aquifer water budget. Despite its crucial importance for water resource management, the proportion of irrigation water that contributes to groundwater recharge, namely the return flow coefficient, o...

There exists a substantial amount of research on abiotic (e.g. photochemical) degradation pertaining to organic matter (OM) in the marine realm. While recent research has shown its importance in the degradation of terrestrial particulate OM (TPOM), the mechanisms involved in the induction of autoxidation in estuaries remain unclear. In this study,...

The Rhône River plays a major role in the Mediterranean Sea, being both its main freshwater source and its major particulate matter provider. This survey of the fate of terrestrial particulate organic matter (POM) was conducted along the salinity gradient of the Rhône River plume, between 2012 and 2014. It revealed that autoxidation acts rapidly an...

Presentation of the Rhone Sediment Observatory. The program is described and some main results are briefly presented, as well as the tools produced for their dissemination.

Autoxidation is a complex abiotic degradation process, and while it has long been known and well studied in biological compounds, it has been widely overlooked in environmental samples and as a part of environmental processes. With recent observations showing the magnitude of the involvement of autoxidation in coastal environments, it has become cr...

rophic transfer of metallic trace elements within a phytoplankton-zooplankton-anchovy/sardine food web.

Trace metal (TM) concentrations in water samples collected in the Arno River, its main tributaries and estuarine transect were measured in order to evaluate anthropogenic influence, TM dynamics and a potential impact on the coastal sea. A downstream increase of concentration for most of TM was observed in the river, whereas a (near)conservative beh...

Organic matter concentration and the optical properties of its chromophoric fraction (CDOM) were measured along the Arno River and in its estuary, in September 2015. Organic matter concentration strongly increased along the river, while in the estuary it was mainly affected by conservative mixing.

Assessing the heteroaggregration of manufactured particles with naturally occuring colloids in a typical surface waters