Papers by Olivier Radakovitch
Dissolved and particulate major and trace element concentrations and suspended particulate conten... more Dissolved and particulate major and trace element concentrations and suspended particulate contents were determined during three years on the lower Rhône River (France) from subsurface water samples collected about twice a month and more regularly during flood events. Dissolved elements can be grouped into two sets showing similar relationship between concentration and water discharge related to dilution process and to local and diffuse inputs of dissolved elements in the Rhône basin. The variation of NO 3 /Na and Cl/Na ratios and the absence of correlation between NO 3 and the enrichment in Cl show that Rhône River is not highly affected by fertilizer applications compared to other large French rivers (Seine and Loire rivers). In particulate phase, Ca, Sr, U, Pb, Bi, Cd, Sb and Zn displayed high enrichment factors over shale composition. Lead, Bi, Cd and Zn enrichment could be related to the anthropogenic inputs, while Ca, Sr and U enrichment was explained by lithological composition of the Rhône basin dominated by carbonate rocks. Distribution coefficients of elements (Kd) are relatively stable with however some variations with increasing SPM concentrations. These variations were attributed to local and diffuse inputs and to a higher contribution of carbonate bedrock in the Rhône basin during flood events. Dissolved and particulate major and trace elements, and suspended particulate matter (SPM) fluxes of the Rhône River to the Mediterranean Sea were estimated for the period 2001–2003. SPM and particulate element fluxes were highly dependent on flood events: 69 to 91% of the annual fluxes were exported in less than 12% of the time. Rhône River inputs were the principal source of particulate elements (except for Cd and Zn) in the northwestern Mediterranean Sea, while the major part of dissolved elements were carried out by atmospheric inputs except dissolved As, for which Rhône River contributed to more than 50% of the input to the marine system.
Estuarine, Coastal and Shelf Science, 2008
Fluxes of the heavy metals chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), lead (Pb), cadmi... more Fluxes of the heavy metals chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), lead (Pb), cadmium (Cd) and zinc (Zn) delivered by rivers to the Gulf of Lion (NW Mediterranean Sea) were estimated over a three year study of the River Rhone and its smaller tributaries. Most of the particulate metal fluxes (80e90%) delivered by these rivers occurred within a very short period of time (less than 12%), a typical trend for the Mediterranean environment, where highly contrasting hydrological regimes were observed over the year. Temporal and spatial variations in the fluxes of these particulate metals were driven by the fluxes in both water discharge and suspended particulate matter load. On the shelf, these particulate metal fluxes, largely arising from the Rhone watershed, were two to ten times more important than those resulting from atmospheric deposition. Co, Cr and Ni in the rivers and on the shelf surface sediments were mainly natural and associated with the finest particles. Cd and Phosphorus appeared to be associated with the silt fraction and to be enriched in the prodelta areas. Pb, Zn and Cu were more closely associated with the organic matter content and also showed enrichment in the organic rich prodeltaic sediments. Anthropogenic influences diminished offshore, except for Pb and Zn which could be supplied from the atmosphere by man-made aerosols. Although most of the metals tended to be enriched in the prodelta areas, these did not constitute a permanent sink due to resuspension processes affecting these shallow depths. A resuspension experiment conducted on sediment cores from the Rhone prodelta demonstrated that metal deposited on the surface layer, especially those associated with the organic matter, may be resuspended; this should be taken into account for a complete understanding of the biogeochemical cycle of these metals.
Journal of Geochemical Exploration, 2006
Dissolved major and trace element concentrations were determined from November 2000 to December 2... more Dissolved major and trace element concentrations were determined from November 2000 to December 2003 in the lower Rhône River (France). Subsurface water samples were collected about twice a month and more regularly during flood events. An unusual trend was observed for As, Sb, Ni and Ba concentrations which increased with river discharge at the beginning of the floods, in contrast with other elements. Variations of Sb/Na and As/Na molar ratios show that it is related to higher contributions of waters from western tributaries of the Rhône River enriched in As, Sb, Ni and Ba due to ancient mining activities. These unusual variations of dissolved element concentrations are thus interpreted as mark of a water mass origin within the watershed. D
Marine Chemistry, 2008
Submarine groundwater discharge (SGD) is now recognized as an important pathway for water and che... more Submarine groundwater discharge (SGD) is now recognized as an important pathway for water and chemical species fluxes to the coastal ocean. In order to determinate SGD to the Gulf of Lion (France), we measured the activities of 226 Ra and 228 Ra by thermal ionization mass spectrometry (TIMS) in coastal waters and in the deep aquifer waters of the Rhone deltaic plain after preconcentration of radium by MnO 2 . Compared to conventional counting techniques, TIMS requires lower quantities of water for the analyses, and leads to higher analytical precision. Radium isotopes were thus measured on 0.25-2 L water samples containing as little as 20 fg of 226 Ra and 0.2-0.4 fg of 228 Ra with precision equal to 2%. We demonstrate that coastal surface waters samples are enriched in 226 Ra and 228 Ra compared to the samples further offshore. The high precision radium measurements display a small but significant 226 Ra and 228 Ra enrichment within a strip of circa 30 km from the coast. Radium activities decrease beyond this region, entrained in the northern current along the shelf break or controlled by eddy diffusion. The radium excess in the first 30 km cannot be accounted for by the river nor by the early diagenesis. The primary source of the radium enrichment must therefore be ascribed to the discharge of submarine groundwater. Using a mass-balance model, we estimated the advective fluxes of 226 Ra and 228 Ra through SGD to be 5.2 × 10 10 and 21 × 10 10 dpm/d respectively. The 226 Ra activities measured in the groundwater from the Rhone deltaic plain aquifer are comparable to those from other coastal groundwater studies throughout the world. By contrast, 228 Ra activities are higher by up to one order of magnitude. Taking those groundwater radium activities as typical of the submarine groundwater end-member, a minimum volume of 0.24-4.5 × 10 10 l/d is required to support the excess radium isotopes on the inner shelf. This has to be compared with the average rivers water runoff of 15.4 × 10 10 l/d during the study period (1.6 to 29% of the river flow).
Geochimica et Cosmochimica Acta, 2010
Numerous studies of weathering fluxes have been carried out on major world rivers during the last... more Numerous studies of weathering fluxes have been carried out on major world rivers during the last decade, to estimate CO 2 consumption rates, landscape evolution and global erosion rates. For obvious logistical reasons, most of these studies were based on large scale investigations carried out on short timescales. By comparison, much less effort has been devoted to long term monitoring, as a means to verify the temporal variability of the average characteristics, their trends, and the representativeness of short-term investigations. Here we report the results of a three-year survey (November 2000 to December 2003 of the major and trace element composition of dissolved and suspended matter in the lower Rhone River (France), the largest river of the Mediterranean area. Subsurface water samples were collected in Arles, about 48 km upstream of the estuary, twice a month routinely, and at higher frequency during flood events.
Major and trace element partition and fluxes in the Rhône River
Chemical Geology, 2011
Dissolved and particulate major and trace element concentrations and suspended particulate conten... more Dissolved and particulate major and trace element concentrations and suspended particulate contents were determined during three years on the lower Rhône River (France) from subsurface water samples collected about twice a month and more regularly during flood events.Dissolved elements can be grouped into two sets showing similar relationship between concentration and water discharge related to dilution process and to local
Autoxidation is a complex abiotic degradation process, and while it has long been known and well ... more 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 critical to better understand how and why this degradative process takes place. At the riverine/marine interface, recent findings evidenced a spike in autoxidation rates upon the arrival of suspended particulate matter in seawater. In this study, we aimed at identifying autoxidation-favoring factors in vitro by analyzing suspended particulate matter incubated under different conditions. If metal ions have long been known to induce autoxidation in biological systems, we show that they indeed induce autoxidation in particulate matter incubated in water, but also that the content in photochemically-produced hydroperoxides in suspended particulate matter is crucial to the induction of its autoxidation in water.
Combining radon, short-lived radium isotopes and hydrodynamic modeling to assess submarine ground... more Combining radon, short-lived radium isotopes and hydrodynamic modeling to assess submarine groundwater discharge from an anthropized semiarid watershed to a
The radon-222 mass balance is now commonly used to quantify water fluxes due to Submarine Groundw... more The radon-222 mass balance is now commonly used to quantify water fluxes due to Submarine Groundwater Discharge (SGD) in coastal areas. One of the main loss terms of this mass balance, the radon evasion to the atmosphere, is based on empirical equations. This term is generally estimated using one among the many empirical equations describing the gas transfer velocity as a function of wind speed that have been proposed in the literature. These equations were, however, mainly obtained from areas of deep water and may be less appropriate for shallow areas. Here, we calculate the radon mass balance for a windy shallow coastal lagoon (mean depth of 6 m and surface area of 1.55*10 8 m2) and use these data to estimate the radon loss to the atmosphere and the corresponding gas transfer velocity. We present new equations, adapted to our shallow water body, to express the gas transfer velocity as a function of wind speed at 10 m height (wind range from 2 to 12.5 m/s). When compared with those from the literature, these equations fit particularly well with the one of Kremer et al. (2003). Finally, we emphasize that some gas transfer exchange may always occur, even for conditions without wind.
Rationale for precise and accurate 210 Po and 210Pb assay in the ocean The 210Pb (t 1/2 = 22.3 y)... more Rationale for precise and accurate 210 Po and 210Pb assay in the ocean The 210Pb (t 1/2 = 22.3 y) and 210Po (t 1/2 = 138 d) parent and granddaughter radionuclide pair has proven to be effective tracers of oceanographic processes. Studies of particulate and dissolved 210Po and 210Pb in the marine environment have been used for quantifying the scavenging and removal of par
An exceptional flood event, accompanying a marine storm, was investigated simultaneously at the e... more An exceptional flood event, accompanying a marine storm, was investigated simultaneously at the entrance and the exit of the Gulf of Lion's hydrosystem (NW Mediterranean) in December 2003. Cs, Cr, Co, Ni, Cu, Zn, Cd and Pb signatures of both riverine and shelf-exported particles indicate that continental inputs and resuspended prodeltaic sediments were intensively mixed with resuspended sediments from middle/outer shelf areas during advective transport. As a result, particles leaving the Gulf of Lion inherited the mean signature of shelf bottom sediments, exporting anthropogenic Pb and Zn out into the open sea. When assessing the particulate metal budget in relation with the event, it appears that the output fluxes accounted for between 15% and 60% of the input fluxes, depending on the element and the period of reference. This trend is also observed for annual budgets, which were drawn up by compiling the data from this study and the literature. Results evidenced that, except some element fluxes during extreme output scenario, outputs never counterbalance the inputs. In its current functioning, the Gulf of Lion's shelf seems to act as a retention/sink zone for particulate metals. Regarding anthropogenic fluxes, the contribution of the oceanic flood of December 2003 to the mean annual scenario is considerable. Environmental impacts onto coastal and deep-sea ecosystems should therefore tightly depend on both the intensity and the frequency of event-dominated sediment transport.
Six marine sediment cores from the Gulf of Lions continental slope (700–1700 m water depth) were ... more Six marine sediment cores from the Gulf of Lions continental slope (700–1700 m water depth) were analyzed for stable lead isotopes and 210/Pb geochronology in order to reconstruct lead atmospheric fallout pattern during the last century. The detrital lead contribution is 25 µg.g -1 and the mean sediment anthropogenic inventory is 110 ± 7 g cm-2 , a little bit higher than atmospheric deposition estimate. Anthropogenic lead accumulation in sediments peaked in early 1970s (1973 ± 2) in agreement with lead emissions features. For the period 1986–1997, the sediment signal also reflect the decrease of atmospheric lead described by independent atmospheric fallout investigations. The anthropogenic Pb deposition in the late 1990s was similar to the 1950s deposition, attesting thus of the output of European environmental policies.
Contaminants are supplied to the coastal zone by the atmosphere, rivers and point sources like wa... more Contaminants are supplied to the coastal zone by the atmosphere, rivers and point sources like wastewaters or industrial area. Wetlands retain many of these contaminants and can be used to reconstruct sources and magnitudes of contaminant inputs. Radionuclides (137Cs, 210Pb, 239Pu and 240Pu) and stable lead isotope (206Pb, 207Pb) profiles were investigated in two cores collected in wetlands of the Rhone River delta, south of France (Camargue), to estimate the recent sediment accumulation rates and reconstruct the deposition of pollutants during the last century. One site was affected by storm or flood deposition from the Rhone river and showed the influence of Marcoule reprocessing plant releases on the plutonium isotopic ratios. The other site appears suitable for the reconstruction, even if mixing is evidenced at the surface by the radionuclides profiles. Plutonium isotopic ratios are characteristic of global fallout and the Pb inventory of 4240 Bq m-2 is approximately 30% higher than atmospheric deposit 210Pb estimation. The pollutant lead inventory is 139 mg cm-1 y-2 , slightly higher than previous estimation from direct fallout. This difference can be partly due to an over-collection at this site (due to canopy cover) but also to variations with time in the deposition.
Lake Abiyata is a small, closed, saline/alkaline lake located in the central part of the Ethiopia... more Lake Abiyata is a small, closed, saline/alkaline lake located in the central part of the Ethiopian Rift Valley, East Africa. A multi-proxy study of a sediment core, 116 cm long and with undisturbed mud^water interface, was performed to test the sensitivity of the lake system and of different proxies to the changes in climate and human activities that occurred in the catchment during the past few centuries. The 210Pb analyses suggest that the upper 80 cm of the core represent the past 200 years. This study complements millennial-scale environmental records available in the region. The main freshwater-climatic and biological features of the modern lake system and their variations over the past decades, as known from observations, are first summarised. Results derived from individual proxies analysed along the core are then presented (successively, major physical and chemical properties of bulk sediments, diatoms and pollen). Uncertainties on the chronological framework are discussed. Major limnological stages are finally identified based on the multi-proxy interpretation of our record. Our record shows large variations in the lake water and salt balances, in the sediment sources, and in the vegetation distribution in the basin. Using our 210 Pb chronology, major changes observed in the core are tentatively compared with environmental events known from instrumental and historical records. The upper 41 cm of the core (210 Pb age: 1940-1998 AD) reveal several fluctuations in diatom-inferred water depth and salinity which seem to be consistent with known changes in water level. Human impact on vegetation clearly appears since about 30 years. The interval 85^41 cm suggests a period of overall water deficit. Lake Abiyata experienced episodes shallower and more saline than over the past decades, especially around 68-66 cm, 210 Pb dated at ca. 1890 AD. This level may coincide with one of the worst droughts known in the Ethiopian history during 1888-1892. The lower part of the core includes a stage (108-85 cm) of lake level much higher than today and which ended before 1800 AD. Although its base is undated so far, this stage suggests that conditions much wetter than today have prevailed in the region during at least part of the 18th century. Lake Abiyata appears to be a suitable site for a detailed environmental reconstruction over the recent past, although further work is needed to reduce the uncertainties on our record, as discussed in the conclusions.
Sediment cores from the deep Balearic basin and the Cretan Sea provide evidence for the accumulat... more Sediment cores from the deep Balearic basin and the Cretan Sea provide evidence for the accumulation of Cd, Pd and Zn in the top few centimeters of the abyssal Mediterranean sea-bottom. In both cores, 206Pb/ 207Pb profiles confirm this anthropogenic impact with less radiogenic imprints toward surface sediments. The similarity between excess 210Pb accumulated in the top core and the 210Pb flux suggests that top core metal inventories reasonably reflect long-term atmospheric deposition to the open Mediterra-nean. Pb inventory in the western core for the past 100 years represents 20–30% of sediment coastal inventories, suggesting that long-term atmospheric deposition determined from coastal areas has to be used cautiously for mass balance calculations in the open Mediterranean. In the deeper section of both cores, Al normalized trace metal profiles suggest diagenetic remobilization of Fe, Mn, Cu and, to a lesser extent, Pb that likely corresponds to sapropel event S1.
Quantification de l’érosion par le 137Cs et le 210Pb : Cas de deux bassins versants au Nord-Ouest du Maroc (Région de Tanger-Tétouan)/QUANTIFYING EROSION USING 137Cs AND 210Pb IN CULTIVATED SOILS IN TWO DRAINAGE BASINS IN NORTH WEST MOROCCO (Tanger-Tétouan region)
Measurements of soil erosion on the Moroccan landscape using classical erosion methods have been ... more Measurements of soil erosion on the Moroccan landscape using classical erosion methods have been the main objective of several research studies. These classical methods are very difficult, time consuming and very expensive. The quantitative estimation of soil loss remains insufficient particularly in the North of Morocco. In this study, we present results showing the quantification of the soil erosion using 137Cs and 212Pb in two dam catchments: Raouz and Nakhla. In the Raouz catchment, the inventories of 137Cs vary between 574 Bq/m2 and 3422 Bq/m2 and of 210Pbexc vary between 274 Bq/m² and 2704 Bq/m². In the second study area situated in the drainage basin of the Nakhla dam the mean inventories of 137Cs consist between 426 and 777 Bq/m2, while the mean inventories of 210Pbexc vary between 580 and 891 Bq/m². The conversion of the inventories in terms of erosion rate and/or accumulation has been done using a mass balance model (1 and 2) and the 210Pbexc model. The mean erosion rates ...
As part of the ECOFER experiment (ECOMARGE program, JGOFS-France), concentrations of the natural ... more As part of the ECOFER experiment (ECOMARGE program, JGOFS-France), concentrations of the natural radionuclide 210Pb were measured in particulate matter collected by sediment traps deployed for a 14-month period (June 1990}August 1991) on two mooring lines within the Cap-Ferret Canyon, on the French continental slope of the Bay of Biscay (northeastern Atlantic). 210Pb concentrations (range 63}218 dpm g\) and fluxes (range 0.1}11.2 dpm cm\ yr\) displayed typical gradients, increasing with depth at both mooring sites. Also, at equivalent trap depths, 210Pb activities were systematically higher on the deep slope mooring (3000 m) compared to the shallow one (2300 m). Fluxes of 210Pb generally decreased seaward and exhibited temporal variations, but with no marked seasonal trend, essentially matching variations in total mass flux. Various correlations between 210Pb activities and major constituents of trapped particles were examined. Pb activities were independent of the particle composition, indicating that in this area scavenging of this nuclide from the water column was not directly tied to the quality of settling particles. The 210Pb budget, as determined by the balance of local supply flux and fluxes to sediment traps and sediments, implies important lateral inputs to both mooring sites (65}89% of the flux measured by traps), a feature typical of continental margin environments. On the basis of annual mean Pb activity in traps of the two mooring sites, two particle sources are hypothesized. The first source, located in shallow waters of the shelf and upper slope, supplies the entire slope region. The second source, probably composed of resuspended particles from upper slope sediments, feeds essentially the upper and intermediate slope region. Maximum sedimentation rates, determined on seven box-cores, decreased with bottom depth, from 0.3 to 0.4 cm yr\ at the canyon heads down to 0.06 cm yr\ at 3000 m. A good agreement was observed, at both mooring sites, between 210Pb
Various anthropogenic radionuclides and 210Pb were analyzed in a 4.3-m-long core, sampled near th... more Various anthropogenic radionuclides and 210Pb were analyzed in a 4.3-m-long core, sampled near the Rhone River mouth in March 1991, to evaluate the extent of industrial releases that accumulate in this area. The whole core was significantly marked by radionuclide inputs from the nuclear facilities located along the river (l1337Cs, 134Cs, 60Co). Irregular profiles in natural and artificial radionuclides should be related to variations in their respective inputs from the Rhone River to the Mediterranean Sea. Minimum concentrations were found during high flow periods. Using both the 137Cs/134Cs profile in the core and the range of this ratio in Rhone waters, mean apparent accumulation rates were estimated to range between 37 cm yr-1 and 48 cm yr ~. This core would then represent a sedimentary record over a 7-10 year period. However, the presence of a signal from the Chernobyl accident, which occurred on April 26, 1986, was not clearly observed in the core. Inventories of both artificial and natural radionuclides were greater than expected from atmospheric inputs. The increased sedimentation occurring in close vicinity to the mouth of the Rhbne River is thus responsible for trapping of elements transported by the fiver to the Mediterranean Sea. In this area, inventories of artificial radionuclides are well in excess of aerial deposition from Chernobyl and atmospheric weapons tests and are linked primarily to industrial releases.
210Pb, 137Cs and 134Cs profiles were determined on 13 box-cores from the Rhone submarine delta (n... more 210Pb, 137Cs and 134Cs profiles were determined on 13 box-cores from the Rhone submarine delta (northwestern Mediterranean Sea). Maximum accumulation rates were estimated using the 210 Pb dating method or the evolution of the 137Cs/ 134Cs activity ratio with depth in the sediment. Rates ranged from more than 20 cm year 1 near the river mouth to 0·2 cm year 1 on the shelf, decreasing rapidly seawards with a preferential S-SW direction from the mouth in relation to the spreading of surface and bottom nepheloid layers in this area. Mixing and diffusion processes were evidenced by 137 Cs that penetrated to greater depths than expected from the 210 Pb derived accumulation rates. The delta area is an important sink for the riverine inputs. The 137 Cs inventory over the studied area (480 km 2) was estimated to be 19·6 TBq in 1990, of which more than 40% was found in the prodelta (30 km 2), in the vicinity of the river mouth. This inventory appears to be well in excess (50%) of both direct and indirect 137 Cs inputs arising from Chernobyl and weapons test fallout in this region. If it is assumed that this excess is due only to liquid discharges by nuclear installations on the Rhône river, it represents 20% of the 137 Cs cumulative discharges by the various nuclear power plants and the Marcoule reprocessing plant released between 1961 to 1990. The 210 Pb budget shows that the sediments are also efficient to scavenge elements transported by advection or diffusion on the shelf. The Rhone delta, and more particularly the prodelta area, is thus an effective sink for particle-reactive elements and pollutants. 1999 Academic Press
210Pb and 210Po were measured in particulate matter collected by five sediment traps deployed in ... more 210Pb and 210Po were measured in particulate matter collected by five sediment traps deployed in the Grand-Rhone canyon (Gulf of Lion, Mediterranean Sea) and on its adjacent open slope. The experiment, part of the JGOFS-France ECOMARGE program, lasted one year, from January 1988 to January 1989. Correlations of 210Pb or 210Po concentrations with major constituents of the flux were weak to nonexistent. The Pb budget was evaluated for each sediment trap. The calculations indicated that there is a net lateral export of 210Pb from the surface water layers of the canyon (80}200 m depth) and from the open slope (900 m depth). In the lower layers of the canyon (600}900 m depth), a net lateral input of 210Pb is required. The two nuclides (and especially the ratio 210Po/210Pb) were useful in identifying the origin of the particles. A biological signature was seen clearly in the upper layers and on the open slope, where the 210Po/210Pb ratios were greater than unity. On the other hand, 210Po/210Pb ratios close to one at 900 m depth and (sometimes) at 600 m depth in the canyon denoted particles that originated from resuspension mainly on the open slope. A scenario of particle transfer process in this continental margin is proposed on the basis of these radionuclide data, the temporal variability of the particulate fluxes and the dynamical processes involved in shelf-slope exchanges.
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Papers by Olivier Radakovitch