Philippe Bonté

Tracing sediment sources in a tropical highland catchment of central Mexico by using conventional and alternative fingerprinting methods

Land degradation is intense in tropical regions where it causes for instance a decline in soil fertility and reservoir siltation. Two fingerprinting approaches (i.e. the conventional approach based on radionuclide and geochemical concentrations and the alternative diffuse reflectance infrared Fourier transform spectroscopy method) were conducted independently to outline the sources delivering sediment to the river network draining into the Cointzio reservoir, in Mexican tropical highlands. This study was conducted between May and October in 2009 in subcatchments representative of the different environments supplying sediment to the river network. Overall, Cointzio catchment is characterized by very altered soils and the dominance of Andisols and Acrisols. Both fingerprinting methods provided very similar results regarding the origin of sediment in Huertitas subcatchment (dominated by Acrisols) where the bulk of sediment was supplied by gullies. In contrast, in La Cortina subcatchment dominated by Andisols, the bulk of sediment was supplied by cropland. Sediment originating from Potrerillos subcatchment characterized by a mix of Acrisols and Andisols was supplied in variable proportions by both gullies and rangeland/cropland. In this latter subcatchment, results provided by both fingerprinting methods were very variable. Our results outline the need to take the organic carbon content of soils into account and the difficulty to use geochemical properties to fingerprint sediment in very altered volcanic catchments. However, combining our fingerprinting results with sediment export data provided a way of prioritizing the implementation of erosion control measures to mitigate sediment supply to the Cointzio reservoir supplying drinking water to Morelia city. Copyright

Evolution of radioactive dose rates in fresh sediment deposits along coastal rivers draining Fukushima contamination plume

Measurement of radioactive dose rates in fine sediment that has recently deposited on channel bed-sand provides a solution to address the lack of continuous river monitoring in Fukushima Prefecture after Fukushima Dai-ichi nuclear power plant (FDNPP) accident. We show that coastal rivers of Eastern Fukushima Prefecture were rapidly supplied with sediment contaminated by radionuclides originating from inland mountain ranges, and that this contaminated material was partly exported by typhoons to the coastal plains as soon as by November 2011. This export was amplified during snowmelt and typhoons in 2012. In 2013, contamination levels measured in sediment found in the upper parts of the catchments were almost systematically lower than the ones measured in nearby soils, whereas their contamination was higher in the coastal plains. We thereby suggest that storage of contaminated sediment in reservoirs and in coastal sections of the river channels now represents the most crucial issue.

Tracing sediment sources in a tropical highland catchment of central Mexico by using conventional and alternative fingerprinting methodsTracing sediment sources in a tropical

Land degradation is intense in tropical regions where it causes for instance a decline in soil fertility and reservoir siltation. Two fingerprinting approaches (i.e. the conventional approach based on radionuclide and geochemical concentrations and the alternative diffuse reflectance infrared Fourier transform spectroscopy method) were conducted independently to outline the sources delivering sediment to the river network draining into the Cointzio reservoir, in Mexican tropical highlands. This study was conducted between May and October in 2009 in subcatchments representative of the different environments supplying sediment to the river network. Overall, Cointzio catchment is characterized by very altered soils and the dominance of Andisols and Acrisols. Both fingerprinting methods provided very similar results regarding the origin of sediment in Huertitas subcatchment (dominated by Acrisols) where the bulk of sediment was supplied by gullies. In contrast, in La Cortina subcatchment dominated by Andisols, the bulk of sediment was supplied by cropland. Sediment originating from Potrerillos subcatchment characterized by a mix of Acrisols and Andisols was supplied in variable proportions by both gullies and rangeland/cropland. In this latter subcatchment, results provided by both fingerprinting methods were very variable. Our results outline the need to take the organic carbon content of soils into account and the difficulty to use geochemical properties to fingerprint sediment in very altered volcanic catchments. However, combining our fingerprinting results with sediment export data provided a way of prioritizing the implementation of erosion control measures to mitigate sediment supply to the Cointzio reservoir supplying drinking water to Morelia city. Copyright

Sr/Ba in barite: a proxy of barite preservation in marine sediments?

Abstract The observation by Bertram and Cowen [J. Mar. Res. 55 (1997) 577–593] that the strontium content of marine barite decreased from the water column to the deep-sea floor suggested that the Sr/Ba ratio in barite was sensitive to barite dissolution. Following this observation, we have investigated the potential of using the Sr/Ba ratio in barite as a proxy of barite preservation by separating barite crystals from sediment cores collected at different water depths in the equatorial Pacific and in the Southern Ocean. Our investigations do not reveal significant downcore variations in the Sr/Ba ratios during the Holocene period in the two basins and up to a few hundred thousand years in the equatorial Pacific. However, a comparison of the mean Sr/Ba ratios in individual cores suggests that the Sr/Ba ratios in barite decrease with increasing water depth, a feature that could be related to dissolution of barite crystals during settling to the deep-sea floor and/or at the sediment–water interface. If confirmed, the Sr/Ba ratios in barite could be used to infer the intensity of barite dissolution and the state of preservation of barite crystals in sediments. Such information could be employed usefully in paleoproductivity reconstructions for the purpose of distinguishing between productivity and dissolution signals affecting barite distributions in marine sediments.

Evidence of the radioactive fallout in France due to the Fukushima nuclear accident

Radioactive fallout due to the Fukushima reactor explosion in Japan was detected in environmental samples collected in France. The presence of (131)I in aerosols (200±6 μBq m(-3)) collected at the Pic du Midi observatory, located at 2877 m altitude in the French Pyrénées, indicated that the Japanese radioactive cloud reached France between 22 and 29 March, i.e. less than two weeks after the initial emissions, as suggested by a (137)Cs/(134)Cs ratio of 1.4. Cesium radioisotopes ((134)Cs and (137)Cs) were not detected in this sample but they were present in the aerosol sample collected the next week, i.e. between 29 March and 05 April (about 10 μBq m(-3)). We also report (131)I activities measured in grass (1.1-11 Bq kg(-1); fresh weight) and soil samples (0.4 Bq kg(-1)) collected in the Seine River basin between 30 March and 10 April. The (134)Cs from the damaged Fukushima power plant was also detected in grass collected in the Seine River basin between 31 March and 10 April (0.2-1.6 Bq kg(-1) fresh weight, with a (137)Cs/(134)Cs ratio close to 1, which is consistent with Fukushima radioactive release). Despite the installation of a network of nested stations to collect suspended matter in the upstream part of the Seine River basin, (131)I was only detected in suspended matter (4.5-60 Bq kg(-1)) collected at the most upstream stations between 30 March and 12 April. Neither (131)I nor (134)Cs has been detected in environmental samples since the end of April 2011, because of the rapid decay of (131)I and the very low activities of (134)Cs (about 400 times lower than after Chernobyl accident).

Spatio-temporal variability of solid, total dissolved and labile metal: passive vs. discrete sampling evaluation in river metal monitoring

In order to obtain representative dissolved and solid samples from the aquatic environment, a spectrum of sampling methods are available, each one with different advantages and drawbacks. This article evaluates the use of discrete sampling and time-integrated sampling in illustrating medium-term spatial and temporal variation. Discrete concentration index (CI) calculated as the ratio between dissolved and solid metal concentrations in grab samples are compared with time-integrated concentration index (CI) calculated from suspended particulate matter (SPM) collected in sediment traps and labile metals measured by the diffusive gel in thin films (DGT) method, collected once a month during one year at the Seine River, upstream and downstream of the Greater Paris Region. Discrete CI at Bougival was found to be significantly higher than at Triel for Co, Cu, Mn, Ni and Zn, while discrete metal partitioning at Marnay was found to be similar to Bougival and Triel. However, when using time-integrated CI, not only was Bougival CI significantly higher than Triel CI, CI at Marnay was also found to be significantly higher than CI at Triel which was not observed for discrete CI values. Since values are time-averaged, dramatic fluctuations were smoothed out and significant medium-term trends were enhanced. As a result, time-integrated concentration index (CI) was able to better illustrate urbanization impact between sites when compared to discrete CI. The impact of significant seasonal phenomenon such as winter flood, low flow and redox cycles was also, to a certain extent, visible in time-integrated CI values at the upstream site. The use of time-integrated concentration index may be useful for medium- to long-term metal studies in the aquatic environment.

Urbanization impact on metals mobility in riverine suspended sediment: Role of metal oxides

Spatial and temporal fractionation of trace metals and major elements in suspended particulate matter in the Seine River was investigated to study the impact of the increasing urbanization in the Greater Paris Region. Suspended sediments in the Seine River were collected between December 2008 to August 2009 upstream and downstream of Paris. They were subjected to total digestion and sequential extraction procedure certified by the Bureau Communautaire de Référence and trace metals along with major elements were analyzed with inductively coupled plasma mass spectroscopy. Metal enrichment factors increased up to eight folds after the Seine River downstream of the Greater Paris Region showing a significant contribution of urbanization. Enrichment of copper, lead and zinc downstream of Paris are followed by the increase of their reducible fraction of at least 10% implicating an increase in metals associated with iron oxides. The exchangeable fraction, which includes the carbonate-associated metals, is only significant for cadmium, nickel and zinc (more than 2 %) while the oxidisable fraction accounts for less than 20 % for the anthropogenic metals downstream except for copper. The metals can be divided to (a) “reducible” group including cadmium, lead, and zinc, associated with more than 60 % of the total Bureau Communautaire de Référence extractable metals to the reducible fraction containing mostly iron oxide phases for the downstream sites. (b) A “distributed” group including chromium, copper, and nickel that are associated to at least 3 different phase-groups: (1) oxides, (2) organic matter and sulphides and (3) mineral phases.

Remanence of lead pollution in an urban river system: a multi-scale temporal and spatial study in the Seine River basin, France

Total lead (Pb) concentration and Pb isotopic ratio (206Pb/207Pb) were determined in 140 samples from the Seine River basin (France), covering a period of time from 1945 to 2011 and including bed sediments (bulk and size fractionated samples), suspended particulate matter (SPM), sediment cores, and combined sewer overflow (CSO) particulate matter to constrain the spatial and temporal variability of the lead sources at the scale of the contaminated Seine River basin. A focus on the Orge River subcatchment, which exhibits a contrasted land-use pattern, allows documenting the relation between hydrodynamics, urbanization, and contamination sources. The study reveals that the Pb contamination due to leaded gasoline that peaked in the 1980s has a very limited impact in the river nowadays. In the upstream Seine River, the isotopic ratio analysis suggests a pervasive contamination which origin (coal combustion and/or gasoline lead) should be clarified. The current SPM contamination trend follows the urbanization/industrialization spatial trend. Downstream of Paris, the lead from historical use originating from the Rio Tinto mine, Spain (206Pb/207Pb = 1.1634 ± 0.0001) is the major Pb source. The analysis of the bed sediments (bulk and grain size fractionated) highlights the diversity of the anthropogenic lead sources in relation with the diversity of the human activities that occurred in this basin over the years. The “urban” source, defined by waste waters including the CSO samples (206Pb/207Pb = 1.157 ± 0.003), results of a thorough mixing of leaded gasoline with “historical” lead over the years. Finally, a contamination mixing scheme related to hydrodynamics is proposed.

Novel Insights into Fukushima Nuclear Accident from Isotopic Evidence of Plutonium Spread along Coastal Rivers

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident led to important releases of radionuclides into the environment, and trace levels of plutonium (Pu) were detected in northeastern Japan. However, measurements of Pu isotopic atom and activity ratios are required to differentiate between the contributions of global nuclear test fallout and FDNPP emissions. In this study, we used a double-focusing sector field ICP-MS to measure Pu atom and activity ratios in recently deposited sediment along rivers draining the most contaminated part of the inland radioactive plume. Results showed that plutonium isotopes (i.e., (239)Pu, (240)Pu, (241)Pu, and (242)Pu) were detected in all samples, although in extremely low concentrations. The (241)Pu/(239)Pu atom ratios measured in sediment deposits (0.0017-0.0884) were significantly higher than the corresponding values attributed to the global fallout (0.00113 ± 0.00008 on average for the Northern Hemisphere between 31°-71° N: Kelley, J. M.; Bond, L. A.; Beasley, T. M. Global distribution of Pu isotopes and (237)Np. Sci. Total. Env. 1999, 237/238, 483-500). The results indicated the presence of Pu from FDNPP, in slight excess compared to the Pu background from global fallout that represented up to ca. 60% of Pu in the analyzed samples. These results demonstrate that this radionuclide has been transported relatively long distances (∼45 km) from FDNPP and been deposited in rivers representing a potential source of Pu to the ocean. In future, the high (241)Pu/(239)Pu atom ratio of the Fukushima accident sourced-Pu should be measured to quantify the supply of continental-originating material from Fukushima Prefecture to the Pacific Ocean.

Environmental mobility of 110mAg: lessons learnt from Fukushima accident (Japan) and potential use for tracking the dispersion of contamination within coastal catchments

Silver-110 metastable ((110m)Ag) has been far less investigated than other anthropogenic radionuclides, although it has the potential to accumulate in plants and animal tissues. It is continuously produced by nuclear power plants in normal conditions, but emitted in much larger quantities in accidental conditions facilitating its detection, which allows the investigation of its behaviour in the environment. We analysed (110m)Ag in soil and river drape sediment (i.e., mud drapes deposited on channel-bed sand) collected within coastal catchments contaminated in Fukushima Prefecture (Japan) after the Fukushima Dai-ichi Nuclear Power Plant accident that occurred on 11 March 2011. Several field experiments were conducted to document radiosilver behaviour in the terrestrial environment, with a systematic comparison to the more documented radiocesium behaviour. Results show a similar and low mobility for both elements in soils and a strong affinity with the clay fraction. Measurements conducted on sediment sequences accumulated in reservoirs tend to confirm a comparable deposition of those radionuclides even after their redistribution due to erosion and deposition processes. Therefore, as the (110m)Ag:(137)Cs initial activity ratio varied in soils across the area, we justified the relevance of using this tool to track the dispersion of contaminated sediment from the main inland radioactive pollution plume generated by FDNPP accident.