Pollutant Pb burden in Mediterranean Centroscymnus coelolepis deep-sea sharks

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 (0.023-0.061 wet ppm) are among the lowest encountered in shark records. Stable Pb isotope imprints in adult C. coelolepis muscles highlight that most of Pb in C. coelolepis is from human origin. Lead isotopes reveal the persistence of gasoline Pb emitted in the 1970s in low-turnover adult shark's muscle while associated liver imprints are in equilibrium with recent pollutant Pb signatures suggesting an efficient pollutant Pb turnover metabolism. The comparison of Pb distribution between adult and juvenile cohorts suggests the role of dietary exposure and possible maternal offloading of Pb during gestation, likely associated to vitellogenesis in this aplacental viviparous deep-sea shark.

Are surface water characteristics efficient to locate hyporheic biodiversity hotspots?

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 compared five indicators of river-groundwater exchanges: longitudinal profiles of temperature, electrical conductivity and ²²²Rn concentrations in the surface water of the river, chemical characteristics of the hyporheic water and hyporheic biodiversity. Upwelling zones occurred downstream of geomorphological heterogeneities (here at the tail of gravel bars). Surface water chemistry, especially electrical conductivity and ²²²Rn concentrations, clearly traces large scale gaining sections, which were not associated to valley narrowing but with lateral springs, suggesting a crucial role of the geological structuration of the karstic plateau of Méjanne-le-Clap. Hyporheic water chemistry fits with the large-scale hydrological pattern, but with a high variability corresponding to local heterogeneities. The stygobite fauna (obligate groundwater organisms) and benthic EPTC (Ephemeroptera, Plecoptera, Trichoptera and Coleoptera) occurred preferentially in the gaining sections fed by groundwater, likely because of oligotrophic water and cooler temperature. The spatial distribution of river-groundwater exchange zone and hyporheic biodiversity may be thus predicted using changes in surface water chemistry, especially for electrical conductivity and ²²²Rn concentrations.

A review on cesium desorption at the freshwater-seawater interface

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 solution composition. It has been the subject of many studies using field measurements or laboratory experiments, but there was no global interpretation of these works and their results. The present review summarizes relevant laboratory experiments studying desorption of Cs (stable or radioactive) from particles in sea or brackish waters. To date, 32 experimental studies have been carried out on 68 Cs-bearing samples since 1964. A wide range of desorbed fraction (0-86%) was observed, partly depending on the experimental design. For particles containing radiocesium issued from a contamination in the environment, the desorption ranges from 0 to 64% of the particulate activity, with a median at only 3%. Particles contaminated in laboratory show a range between 6 and 86% with a multimodal distribution. The desorption initiates at low salinity (3-4) and rapidly reaches a threshold around 10-15. Laboratory experiments show that two first-order reactions govern the kinetics of the process, with half-life reaction times of 1 h and a few days. These two reactions are probably linked to the adsorption of Cs onto different particles sites. Also, the dynamic of Cs desorption depends on its initial distribution on these different sites, in relation with the history of its contamination and an aging effect.

Suspended sediment flux at the Rhone River mouth (France) based on ADCP measurements during flood events

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 obtained from suspended sediment measurements based on surface sampling at an automated station located 35 km upstream. Suspended sediment concentrations (SSC) and GSDs showed little variation along the channel cross-section, except for a graduate suspension that appeared at the maximum of discharge, corresponding to velocities lower than 1 m s^-1 near the bottom. However, without post processing to account for the GSD, an under-estimation of 10% was observed during the two flood periods. The two flood events (12 November 2012 and 29 November 2012), separated by only 2 weeks, had clear differences in suspended sediment fluxes (SSF) and SSC during the peak of the river discharge, with twice more flux during the first, respectively, 925,226 and 430,879 tons of SSF.

Estimation of air-water gas exchange coefficient in a shallow lagoon based on 222Rn mass balance

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 6m and surface area of 1.55*10(8) m(2)) 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.

Reconstructing historical trends of Berre lagoon contamination from surface sediment datasets: influences of industrial regulations and anthropogenic silt inputs

These last decades, the Berre lagoon (in southeastern France) has been deeply affected since the 1930s by strong inputs of contaminants associated with industrial development and since 1966 by huge inputs of freshwater and silts due to the installation of a hydroelectric power plant. Surveys of the surface sediment contamination have been sparsely performed since 1964 for management and research purposes. These surveys were performed by various laboratories that investigated different chemicals and sampling areas using different analysis protocols. Therefore, the available data are disconnected in time and space and differ in quality. In order to reconstruct coherent time series of sediment contamination from this heterogeneous datasets and to discuss the influences of industrial and hydroelectric discharges we used a statistical approach. This approach is based on Principal Component Analysis (PCA) and Fuzzy clustering analysis on data from one extensive survey realized on surface sediments in 1976. The PCA allowed identifying two geochemical indexes describing the main surface sediment geochemical characteristics. The fuzzy clustering analysis on these indexes allowed identifying sub-areas under the specific influence of industrial or hydroelectric discharges. This allowed us to reconstruct, for each sub-area, a coherent and interpretable long-term time series of sediment contamination from the available database. Reconstructed temporal trends allowed us to estimate: (i) the overall decrease of sediment contamination since the mid-1970 attributed to industrial discharge regulations enacted at this period and (ii) the dilution of the concentrations of sediment bound contaminants induced by the hydroelectric power plant and its associated particulate matter inputs.

Anthropogenic metal contamination and sapropel imprints in deep Mediterranean sediments

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 Mediterranean. 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.

The effect of fire frequency on local cembra pine populations

It has been predicted that global climate change will lead to increasing drought in the Alps during the 21st century, as well as an increased fire risk, fires being currently rare in these mountains. Herein we describe fire frequency reconstruction using high-resolution analyses of macroscopic sedimentary charcoal, pollen, and plant macrofossils. Sediments were sampled from a subalpine pond within the dry western French Alps. Results show that the early-Holocene expansion of Pinus cembra (7200 calibrated years BP) occurred in Acer/Alnus incana/Betula woodlands, which were affected by fires with moderate mean fire-free intervals (MFFI = 173 +/- 61 yr [mean +/- SE]). Superposed Epoch Analyses show that the abundance of P. cembra macroremains decreased significantly after burning, although they never disappeared entirely. Statistics suggest that fires spread through cembra pine communities; they were not stand-replacing fires but mainly surface fires, probably killing nonreproductive pines. An increase in fire frequency occurred 6740 years ago, when four fires appear to have occurred within 140 years. These fires may have been associated with a regional drought and could have affected the composition of the subalpine forest by depleting the local P. cembra population in the short-term. The predicted increase in drought in the future could, therefore, affect the cembra pine ecosystem in the Alps if fire frequency is reduced to intervals of less than 80 years.

Atmospheric lead fallout over the last century recorded in Gulf of Lions sediments (Mediterranean Sea)

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 microg g(-1) and the mean sediment anthropogenic inventory is 110+/-7 microg 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.

Multitracer study of anthropogenic contamination records in the Camargue, Southern France

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 ((137)Cs, (210)Pb, (239)Pu and (240)Pu) and stable lead isotope ((206)Pb, (207)Pb) profiles were investigated in two cores collected in wetlands of the Rhône 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 Rhône 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 (210)Pb inventory of 4240 Bq m(-2) is approximately 30% higher than atmospheric deposit estimation. The pollutant lead inventory is 139 microg cm(-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.