Etang De Research Articles

Processes underlying the assembly of plant communities: The role of environmental filtering heterogeneity in a competition–dispersal experiment

AbstractQuestionInterspecific competition and seed dispersal are key mechanisms that may influence plant community assembly, but their relative importance remains difficult to disentangle as they can be affected by abiotic conditions (environmental filtering). We experimentally studied the balance between these processes in a Molinia wet meadow plant community in which abiotic constraints are mostly represented by flooding, while agricultural practices such as mowing prevent the dominance of a few competitive species. We hypothesized that (H1) mowing, by decreasing competitive exclusion and (H2) seed addition, by increasing immigration, both enhance plant species diversity, and that (H3) small variations in flooding intensity become secondary to these processes in determining species assembly.LocationFrench National Nature Reserve “Etang de Cousseau”, Nouvelle Aquitaine, France.MethodsIn a three‐year experiment, we added seeds of 17 species characteristic of Molinia wet meadows and managed above‐ground competition through mowing. We measured spatial variations in soil moisture as an indicator of the flooding regime. We recorded species relative cover, species richness and evenness annually, and measured light availability, linked with canopy openness, twice.ResultsFrom the beginning of the experiment, small‐scale variations in soil moisture mainly affected species richness, composition and evenness, and canopy openness. Mowing significantly increased light availability and evenness, and affected the relative cover of several species, but not species richness. The addition of seeds did not influence any of the variables monitored during the experiment.ConclusionOur study helps to disentangle processes underlying community assembly in wet meadows. It demonstrates significant and rapid effects of mowing on canopy opening and on community assembly, while seed addition had only a slight effect, possibly explained by an insufficient decrease in competitive interactions through mowing or unmeasured processes. It also shows that abiotic heterogeneity remains a primary driver of community assembly, even on a small scale. Finally, our results suggest that the respective weight of the different filters (dispersion, environment, competition) is subject to interannual variability or environmental stochasticity.

Using Bayesian networks for environmental health risk assessment.

The study investigated the potential relationships between air pollution, socio-economy, and proven pathologies (e.g., respiratory, cardiovascular) within an industrial area in Southern France (Etang de Berre), gathering steel industries, oil refineries, shipping, road traffic and experiencing a Mediterranean climate. A total of 178 variables were simultaneously integrated within a Bayesian model at intra-urban scale. Various unsupervised and supervised algorithms (maximum spanning tree, tree-augmented naive classifier) as well as sensitivity analyses were used to better understand the links between all variables, and highlighted correlations between population exposure to air pollutants and some pathologies. Adverse health effects (bronchus and lung cancers for 15-65 years old people) were observed for hydrofluoric acid at low background concentration (<0.003μgm-3) while exposure to particulate cadmium (0.210-0.250μgm-3) disrupts insulin metabolism for people over 65 years-old leading to diabetes. Bronchus and lung cancers for people over 65 years-old occurred at low background SO2 concentration (6μgm-3) below European limit values. When benzo[k]fluoranthene exceeded 0.672μgm-3, we observed a high number of hospital admissions for respiratory diseases for 15-65 years-old people. The study also revealed the important influence of socio-economy (e.g., single-parent family, people with no qualification at 15 years-old) on pathologies (e.g., cardiovascular diseases). Finally, a diffuse polychlorinated biphenyl (PCB) pollution was observed in the study area and can potentially cause lung cancers.

Wind-Induced Resuspension and Transport of Contaminated Sediment from the Rove Canal into the Etang De Berre, France

The present study concerns the erosion and transport of severely contaminated sediments in a Canal. It begins in the context of an engineering project aimed to re-introduce a forced convection at the entrance of this Canal by pumping marine water. The local wind is often strong enough to overpass the resuspension threshold; thus, there is a serious risk of downstream contamination of a Mediterranean lagoon. So, the goal is to evaluate this risk as a function of the pumping rate; this contamination is transported by the fine suspended particles. Different scenarios are investigated to determine the downstream transport of suspensions in terms of runoff. These scenarios (of 24 h) contains a succession of 3 periods: constant wind speed, wind slowdown and calm, for two opposite wind directions. Special attention is devoted to the modeling of complex mechanisms of erosion and resuspension during wind periods, deposition during windless periods and sediment consolidation. The main results concern the total flux of the suspended particles through the exit of the Canal at the confluence with the lagoon. It is shown that even for moderate runoff (&lt;6 m3/s) this total flux is large enough, not only during the wind period, but also after several hours of calm.

Discovery of a Pelophylax saharicus (Anura, Ranidae) population in Southern France: a new potentially invasive species of water frogs in Europe

Abstract We report the discovery of a population of the exotic North African Water Frog Pelophylax saharicus around the Etang de Berre, on the Mediterranean coast of France, about 25 km north-west of Marseille. The animals had been originally identified as P. perezi or P. kl. grafi by a combination of acoustic and morphological characters and their true identity was not revealed until three samples from one locality were included in a large-scale genomic work dedicated to the genus Pelophylax. Mitochondrial barcoding of the samples from other areas around Etang de Berre did not detect any native P. perezi or P. kl. grafi and confirmed that P. saharicus has spread to several localities, does reproduce and has been present since 2011 at least. We suggest that dedicated field work is needed as soon as possible to (i) map the extant of P. saharicus’s distribution around the Etang de Berre, (ii) establish if populations of the native P. perezi – kl. grafi system still persist around the Etang de Berre or not and (iii) check if P. saharicus has spread to neighboring areas or not. Depending on the answers to these three questions, local conservationists will need to evaluate the feasibility and relevance of any action to control the spread of this new invasive species and attempt to eradicate it.

Natural and anthropogenic sources of copper to organic soils: a global, geochemical perspective

Copper (Cu) is essential for all organisms but is commonly deficient in organic soils or found locally in excess. Natural and anthropogenic inputs of Cu were examined using 32 peat cores from bogs in Europe, North America, New Zealand, Greenland, and Antarctica. The natural abundance of Cu in ombrotrophic (rainwater-fed) peat was studied using (1) samples from pre-industrial periods (representing background values), (2) bromine (Br) concentrations and the background Cu/Br ratio, and (3) cores from remote locations. Etang de la Gruère in Switzerland provides a record of 15 000 yr of peat accumulation. The lowest Cu concentrations (1.0 ± 0.20 mg·kg−1) are found in 18 peat layers dating from ca. 6000 to 9000 cal yr BP, when atmospheric deposition of soil-derived dust was at a minimum. Similar background values occur in peat bogs from other regions. Recent peat layers from bogs in developed areas reveal much greater concentrations. Using the Cu/Br ratio, “excess” Cu in peat profiles can be calculated and attributed either to anthropogenic inputs in recent peats or natural inputs from mineral–water interactions in deeper layers. Peat cores from remote regions of northern Alberta show little or no evidence of anthropogenic Cu.

Risk of wind-driven resuspension and transport of contaminated sediments in a narrow marine channel confluencing a wide lagoon

This work concerns the wind-driven resuspension in a narrow marine channel and the risk of transport of contaminated bottom sediments in a wide brackish lagoon in the context of a planned anthropogenic infrastructure (with forced convection, by pumping sea water). It is based on the modelling and 3D numerical simulation of salinity, current distributions and bottom shear stress (BSS). The goal is to demonstrate that, even for narrow channels of a few tens of meter of width, a wind of 10–20 m/s is sufficient to create intensive currents, to resuspend muddy bottom sediments and transport polluted sediments downstream. Several model scenarios are considered for such wind speeds in two dominant and opposite wind directions, for a channel whose bottom sediments are mainly constituted of fine particles, typically 85% of mud and 15% of fine sand. It is known that finer sediments usually play an important role to transport contaminants (due to larger surface area of smaller particles). Our main results concern the bottom shear stress along such a long and narrow channel; namely the Rove channel which confluences the Etang de Berre lagoon, and for which a project of forced current circulation is planned by pumping sea water. Our numerical results show that the mobility threshold can be easily overpassed for the muddy sediments in the Rove channel. For a bottom roughness of 5 μm (coarse silt) and a wind speed of 20 m/s, BSS can reach 0.18 N/m2 for the N-NW wind in the median part of the channel, and even 0.21 N/m2 in one enlargement for the S-SE wind, while BSScr is about 0.1 N/m2. We conclude that these local winds can permit floc erosion and even surface erosion of fine sediments in the Rove channel.Concerning the resuspension of muddy sediments, our results are consistent with the experimental study presented by Carlin et al. (2016) for a windy shallow lagoon. They are also consistent with the conclusion of Mengual et al. (2017), from erodimetry experiment for estuarine sediments, that the sediment behaves like a pure mud if the percentage of the mud fraction is more than 70%, and that the critical BSS for mobility of such bed sediments is of the order of 0.1 N/m2. Such a lower critical BSS when the mixture is muddier is opposite to trends most often published.

Wind effect on bottom shear stress, erosion and redeposition on Zostera noltei restoration in a coastal lagoon; part 2

This paper concerns wind effect on bottom shear stress (BSS), resuspension and redeposition of bottom sediments in the nearshore areas of the Etang de Berre (EB), a semi-enclosed lagoon, in the context of Zostera noltei (Z.n.) restoration. As in our previous paper, the first step is to compare BSS with its threshold, BSScr, for a wind speed of 21 m/s. But, here, a new simulation is performed for 16 wind directions regularly spaced. It permits to analyze the combined effect, over one year, of these winds on the erosion risk. For that, a mean value of |BSS|, i.e., a weighted average based on the frequency of each wind directions, has been determined and compared to BSScr for a class of roughness parameters. A similar averaging of BSS→ has been also evaluated to obtain the direction of an average bottom current.Then, the most important contribution of the present paper concerns the modelling of the wind-induced sediment erosion, transport and redeposition. The specific module SEDIM/MARS3D is used to determine how the thickness of a given mud-sand sedimentary layer can be changed by the wind-induced current during typical periods of 3 days of constant wind. This numerical study is performed for three wind speeds in the two main wind directions: N-NW and S-SE. The time evolution of this initial sedimentary layer permits to determine where and when the erosion would be large enough to be a stressor for the Z.n. restoration.For an extreme erosion rate of 10−3 kg/m2/s, for a strong wind speed of 21 m/s and an initial sedimentary layer of 15 cm, all this layer would be eroded in several nearshore areas after 3 days. The erosion risk is maximum along the eastern shore, where an additive effect of the two opposite winds can be expected. Indeed, S-SE and N-NW winds create coastal jets of opposite direction and of about the same intensity exerting alongshore erosion and deposition at about the same places.The present results concerning the time evolution of erosion depth induced by the wind improve our knowledge of the erosion risk on the Z.n. restoration in EB. They will be useful to appropriately orient the action of politics and managers for a future restoration program.

Contribution to remediation of brackish lagoon: 3D simulation of salinity, bottom currents and resuspension of bottom sediments by strong winds

This work concerns the modelling and numerical simulation of the 3D salinity and current distribution in a very shallow Mediterranean lagoon subject to strong winds which create intensive resuspension of polluted bottom sediments. We consider wind speeds of 10 m/s and 20 m/s in the two dominant wind directions (N-NW and S-SE). This study is made for different scenarios of flow exchanges with the surrounding hydrosystems: a brackish lagoon on the North (the Etang de Berre), the Cadiere River on the East, and a brackish channel on the South (the Rove channel). The bottom shear stress (BSS) are compared to the BBS threshold given in the literature in terms of the bottom roughness. It permits to determine which kind of bottom sediments (muds and sands) will be resuspended by each wind. The bottom currents permit to predict in which direction the suspended sediments will be moved and where are the sedimentary deposit zones. It provides a guide for the specialists of remediation of the lagoon for a mechanical extraction of sediments in such zones.In addition, numerical experiments have been performed to understand how the salinity distribution depends on the flow exchanges with the two brackish surrounding hydrosystems. This new knowledge will permit the owner of this lagoon to know how to maintain efficiently the level of salinity in the suitable range.

Mapping for the management of diffuse pollution risks related to agricultural plant protection practices: case of the Etang de l'Or catchment area in France.

Faced with health, environmental, and socio-economic issues related to the heavy use of pesticides, diffuse phytosanitary pollution becomes a major concern shared by all the field actors. These actors, namely the farmers and territorial managers, have expressed the need to implement decision support tools for the territorial management of diffuse pollution resulting from the plant protection practices and their impacts. To meet these steadily increasing requests, a cartographic analysis approach was implemented based on GIS which allows the spatialization of the diffuse pollution impacts related to plant protection practices on the Etang de l'Or catchment area in the South of France. Risk mapping represents a support-decision tool that enables the different field actors to identify and locate vulnerable areas, so as to determine action plans and agri-environmental measures depending on the context of the natural environment. This work shows that mapping is helpful for managing risks related to the use of pesticides in agriculture by employing indicators of pressure (TFI) and risk on the applicator's health (IRSA) and on the environment (IRTE). These indicators were designed to assess the impact of plant protection practices at various spatial scales (field, farm, etc.). The cartographic analysis of risks related to plant protection practices shows that diffuse pollution is unequally located in the North (known for its abundant garrigues and vineyards) and in the South of the Etang de l'Or catchment area (the Mauguio-Lunel agricultural plain known for its diversified cropping systems). This spatial inequity is essentially related to land use and agricultural production system. Indeed, the agricultural lands cover about 60% of the total catchment area. Consequently, this cartographic analysis helps the territorial actors with the implementation of strategies for managing risks of diffuse pollution related to pesticides use in agriculture, based on environmental and socio-economic issues and the characteristics of the natural environment.

Numerical simulation of the wind influence on bottom shear stress and salinity fields in areas of Zostera noltei replanting in a Mediterranean coastal lagoon

The paper concerns the numerical simulation of the wind influence on bottom shear stress and salinity fields in a semi-enclosed coastal lagoon (Etang de Berre) which is connected to the Mediterranean through a long and narrow channel (called Caronte). Two different scenarios are considered. The first scenario (scen.#1), starting with a homogeneous salinity of S=20 PSU and without wind forcing, studies a stratification process under the influence of a periodic seawater inflow and a strong freshwater inflow from a hydropower plant (250m3/s). Then, in the second scenario (scen.#2), we study how a strong wind of 80km/h can destroy the haline stratification obtained at the end of scen.#1. The MARS3D numerical model is used to analyze the 3D current and salinity distribution induced by these three meteorological, oceanic and anthropogenic forcings in this lagoon and in the Caronte channel.The main goal is to determine the bottom shear stress (BSS) in the nearshore areas of Zostera noltei replanting, and to compare it with the threshold for erosion of the bottom sediments for different bottom roughness parameters.The most interesting results concern the four nearshore replanting areas; two are situated on the eastern side of EB and two on the western side. The results of scen.#2 show that all these areas are subject to a downwind coastal jet. The destratification process is very beneficial; salinity always remains greater than 12 PSU for a N-NW wind of 80km/h and a hydropower runoff of 250m3/s. Concerning BSS, it presents a maximum near the shoreline and decreases along transects perpendicular to the shoreline. There exists a zone, parallel to the shoreline, where BSS presents a minimum (where BSS=0). When comparing the BSS value at the four control points with the critical value, BSScr, at which the sediment mobility would occur, we see that for the smaller bottom roughness values (ranging from z0=3.5×10−4mm, to 3.5×10−2mm) BSS largely surpasses this critical value. For a N-NW wind speed of 40km/h (which is blowing for around 100days per year), BSS still largely surpasses BSScr - at least for the silt sediments (ranging from z0=3.5×10−4mm, to 3.5×10−3mm). This confirms the possibility that the coastal jet could be a stressor for SAV replanting.

The effect of wind induced bottom shear stress and salinity on Zostera noltii replanting in a Mediterranean coastal lagoon

The paper concerns the wind influence on bottom shear stress and salinity levels in a Mediterranean semi-enclosed coastal lagoon (Etang de Berre), with respect to a replanting program of Zostera noltii. The MARS3D numerical model is used to analyze the 3D current, salinity and temperature distribution induced by three meteorological, oceanic and anthropogenic forcings in this lagoon. The numerical model has been carefully validated by comparison with daily observations of the vertical salinity and temperature profiles at three mooring stations, for one year. Then, two modelling scenarios are considered. The first scenario (scen.#1), starting with a homogeneous salinity of S = 20 PSU and without wind forcing, studies a stratification process under the influence of a periodic seawater inflow and a strong freshwater inflow from a hydropower plant (250 m3/s). Then, in the second scenario (scen.#2), we study how a strong wind of 80 km/h can mix the haline stratification obtained at the end of scen.#1. The most interesting results concern four nearshore replanting areas; two are situated on the eastern side of EB and two on the western side. The results of scen.#2 show that all these areas are subject to a downwind coastal jet. Concerning bottom salinity, the destratification process is very beneficial; it always remains greater than 12 PSU for a N-NW wind of 80 km/h and an hydropower runoff of 250 m3/s.Special attention is devoted to the bottom shear stress (BSS) for different values of the bottom roughness parameter (for gravels, sands and silts), and to the bottom salinity. Concerning BSS, it presents a maximum near the shoreline and decreases along transects perpendicular to the shoreline. There exists a zone, parallel to the shoreline, where BSS presents a minimum (close to zero). When comparing the BSS value at the four replanting areas with the critical value, BSScr, at which the sediment mobility would occur, we see that for the smaller roughness values (ranging from z0 = 3.5 × 10−4 mm, to 3.5 × 10−2 mm) BSS largely surpasses this critical value. For a N-NW wind speed of 40 km/h (which is blowing for around 100 days per year), BSS still largely surpasses BSScr - at least for the silt sediments (ranging from z0 = 3.5 × 10−4 mm, to 3.5 × 10−3 mm). This confirms the possibility that the coastal jet could generate sediment mobility which could have a negative impact for SAV replanting.

Nature and Evolution of the Lithospheric Mantle beneath the Hoggar Swell (Algeria): a Record from Mantle Xenoliths

Peridotite xenoliths exhumed by Quaternary alkaline magmatism in the Tahalgha district, southern Hoggar, represent fragments of the subcontinental lithospheric mantle beneath the boundary between the two major structural domains of the Tuareg Shield: the ‘Polycyclic Central Hoggar’ to the east and the ‘Western Hoggar’, or ‘Pharusian Belt’, to the west. Samples were collected from volcanic centres located on both sides of a major lithospheric shear zone at 4°35' separating these two domains. Although showing substantial variations in their deformation microstructures, equilibrium temperatures and modal and chemical compositions, the studied samples do not display any systematic changes of these features across the 4°35' fault. The observed variations rather record small-scale heterogeneities distributed throughout the study area and reflecting the widespread occurrence of vein conduits and metasomatized wall-rocks related to trans-lithospheric melt circulation during the Cenozoic. These features include partial annealing of pre-existing deformation microstructures, post-deformation metasomatic reactions, and trace-element enrichment, coupled with heating from 750–900°C (low-temperature lherzolites) to 900–1150°C (intermediate-T lherzolites and high-T harzburgites and wehrlites). Trace-element modelling confirms that the range of rare earth element (REE) variations observed in the Tahalgha clinopyroxenes may be accounted for by reactive porous flow involving a single stage of basaltic melt infiltration into a light REE (LREE)-depleted protolith. Whole-rock compositions record the final entrapment of disequilibrium metasomatic melts upon thermal relaxation of the veins–wall-rock system. The striking correlations between equilibrium temperatures and trace-element enrichment favor a scenario in which the high-temperature peridotites record advective heat transport along melt conduits, whereas the intermediate- and low-temperature lherzolites reflect conductive heating of the host Mechanical Boundary Layer. This indicates that the lithosphere did not reach thermal equilibrium, suggesting that the inferred heating event was transient and was rapidly erased by thermal relaxation down to the relatively low-temperature present-day geotherm. The low-T (<900°C) deformed lherzolites (porphyroclastic to equigranular) are characterized by only incipient annealing and LREE-depleted clinopyroxene compositions. They were only weakly affected by the Cenozoic events and could represent relatively well-preserved samples from rejuvenated Pan-African lithosphere. Extensive lithospheric rejuvenation occurred either regionally during the Pan-African orogeny, as a result of lithospheric delamination or thermomechanical erosion after thickening, or more locally along the meridional shear zones. The low-T Tahalgha lherzolites are comparable with lherzolites from Etang de Lherz, southern France, interpreted as lithospheric mantle rejuvenated by melt-induced refertilization during a late stage of the Variscan orogeny.

Environmental imprints of climate changes and anthropogenic activities in the Ore Mountains of Bohemia (Central Europe) since 13 cal. kyr BP

We have measured pollen, aluminum, and lead abundances in a Czech peat bog at Bozi Dar in order to investigate the environmental impact of Holocene climate changes and mining activities in Central Europe. The pollen record shows a continuous vegetal cover since 13 kyr BP. Aluminum and pollen deposition characterize the Younger Dryas (YD) cold event at 12.3–11.0 kyr BP, within its expected time frame in Northern Europe. Aluminum fluxes reveal four other significant dust events with significant Asian and Saharan sources, as shown with variations in stable 204Pb, 206Pb, and 207Pb isotopes. Recurrent Asian incursions are seen at Bozi Dar during the YD and Mid-Holocene dust events (at 7.1, 6.5, and 5.9 kyr BP). These Asian imprints are also observed by Le Roux and colleagues during the YD in the nearest Holocene-long geochemical peat record from Switzerland (Etang de la Gruère). We do not see at Bozi Dar the distinct western European volcanic inputs identified in the Swiss peat by Shotyk and colleagues. However, isotopic ratios characteristics of Mediterranean airflows are evident at both locations during the Mid- and Late Holocene. The occurrence of these various air mass sources in Switzerland and the Czech Republic substantiates Holocene atmospheric circulation models in Central Europe with dominating zonal airflows during the Early Holocene, followed by a governing meridian dispersion during the Mid- and Late Holocene. Lead inputs at 5.1–4.3 and 1.9 kyr BP cannot be explained by increased dust deposition only. The 1.9 kyr event fits local Bohemian ore isotopic imprints of which isotopic signatures are seen as early as 2.2 kyr BP in our core, hence revealing the oldest ever environmental record of mining-related activities in the Czech Republic. Relatively elevated Pb deposition at 5.1 and 4.3 kyr BP are tentatively attributed to contamination that may be from local sources and/or long-range transport.

Comment on: “Exhumation of subcontinental mantle rocks: evidence from ultramafic-bearing clastic deposits nearby the Lherz peridotite body, French Pyrenees” by C. Clerc et al. (Bull. Soc. géol. Fr., 2012, 183, 5, 443–459)

In their recently published paper, C. Clerc et al . [2012] describe the geological setting of the Etang de Lherz peridotite body and give a short review of the associated clastic deposits, proposing a detailed analysis of the breccias cropping out in a limited area east of the lherzolite massif. The cartographic, sedimentological and metamorphic evidence leads the authors to regard these breccias as a shallow marine to lacustrine equivalent of the Albo-Cenomanian “Flysch noir” of the Pyrenees. This interpretation backs up their previous attribution of the breccias to a thick submarine clastic formation, of Albo-Cenomanian age, which incorporates olistoliths derived from the famous Etang de Lherz lherzolite and its neighbouring bodies. Clerc et al. firstly present a somewhat theoretical discussion concerning a 3D reconstruction of the depositional environment of the Lherz breccias, along with a possible scenario for their origin and structural history, which then leads onto three possible scenarios for North-Pyrenean rifting. The authors use this approach to support their previous conclusions, i.e.: the heterometric peridotite fragments contained in the Lherz breccias (from sand-sized debris up to olistoliths) provide clear evidence for an Albo-Cenomanian subaqueous exhumation of the subcontinental mantle at the borders or on the floor of the North-Pyrenean Aulus basin. Our comment focuses on a number of geological details concerning the Lherz breccias and their local or regional context, which the authors fail to take into account, either in their present paper or in earlier studies. Indeed, these details are of crucial interest since they call into question the assumption of a sedimentary origin for the Lherz breccias and, consequently, the exhumation of mantle in the Aulus basin. This map covers an area of 100×200 m located on the western side of the middle part of the so called “Ravin de Paumeres” [or “Ravin de l’Homme-mort” …

Comparative evaluation of the mineralogical composition of Sphagnum peat and their corresponding humic acids, and implications for understanding past dust depositions

With 6.5 m of peat accumulated during the past ca. 15,000 years, Etang de la Gruère (EGr) represents the longest continuous record of atmospheric dust deposition in northern hemisphere. This paper presents a comparative study of the mineralogical composition of Sphagnum peat samples and their corresponding humic acids (HA) from a peat core collected at EGr bog. The purpose of this study was to better understand the dominant process responsible for the amount and distribution of mineral matter in ombrotrophic (i.e., rain-fed) peat. Specifically, the goal was to separate the relative importance of the changing rates of atmospheric mineral dust deposition (during the past two millennia) from the mineralization of organic matter (OM), for the distribution of the ash fraction of the peat profile.The results suggest that variations in ash content at EGr are mainly the result of an increase in the rate of supply of dust particles and cannot be attributed simply, or exclusively, to differences in the degree of OM decay: evidence is provided by both acid insoluble ash (AIA) profiles and the correlations among lithogenic elements (Al, Si, Ti, Y, and Zr), total ash content and AIA. Moreover, our findings suggest that part of the AIA occurring in peat extremely is stable, and is unaffected by the extreme chemical conditions used to extract the HA fraction: this may be partly due to the inherent stability of quartz and “heavy minerals” such as zircon and rutile, but organic coatings developed on mineral surfaces during peat diagenesis, or the formation of some other kind of organo-mineral complex, might also play a role. Consequently, testimonies of past dust depositions can be observed also into the recalcitrant HA fraction of the peat.

Environmental impacts of hydroelectric power and other anthropogenic developments on the hydromorphology and ecology of the Durance channel and the Etang de Berre, southeast France

The generation of electricity through hydropower can, along with other anthropogenic activities, degrade river hydromorphology and ecosystems. In this case, water for power generation is diverted from the River Durance to a canal, which services a chain of 17 power stations, with the lower three being in the catchment of the Etang de Berre. This means that excess water and sediments are discharged into the salt-water lagoon with enormous consequences for ecosystems there. This paper summarizes the impacts of HEP and other human activities on both the river and lagoonal systems. It also considers agency and government attempts to understand and counter the degradation of these systems, both to date and in the future, with the latter catering for the potential impacts of future human development and global warming.

Response to Interpreting the ash trend within ombrotrophic bog profiles: atmospheric dust depositions vs. mineralization processes. The Etang de la Gruère case study

In ‘Interpreting the ash trend within ombrotrophic bog profiles: atmospheric dust depositions vs. mineralization processes. The Etang de la Gruere case study’, Zaccone et al. (2011a) question our interpretation of enhanced ash contents in depth profiles of ombrotrophic bogs. We see them as an indication for C-loss through peat decay (Leifeld et al. 2011). We highly appreciate the work by Claudio Zaccone, William Shotyk and co-authors on peatlands, including their discussion of methods and their limitations. The approach described in Leifeld et al. (2011) has the potential to overcome some limitations of other methods to estimate C-loss from disturbed peatlands but needs to be carefully evaluated. The criticism of Zaccone et al. (2011a) relates to one (EGr) of the four different bogs discussed in our study. EGr is a rather small bog (5 ha). Therefore, the concerns raised in this single case may not be generalized. In our study, EGr served as a reference site and its ash peak has been attributed mainly to human disturbance but less to changing patterns in atmospheric deposition or drainage. Zaccone et al. (2011a) challenge this assumption and raise three points of concern, (1) sampling methodology, (2) normalization of ash peaks to depth, and (3) discussion and interpretation of ash peaks. We reply to each of them.

Interpreting the ash trend within ombrotrophic bog profiles: atmospheric dust depositions vs. mineralization processes. The Etang de la Gruère case study

Introduction Ash peaks along ombrotrophic bog profiles may arise from several different processes. In a recent paper, Leifeld and co-authors (Plant Soil 341:349–361, 2011) argued that ash peaks along the Etang de la Gruere (EGr) peat bog profiles are signs of previous periods of higher peat decomposition rather that an indication of periods of elevated dust inputs.

Ring-hydroxylating dioxygenase (RHD) expression in a microbial community during the early response to oil pollution

The early functional response of a bacterial community from the sediments of a chronically oil-polluted retention basin located at the Etang de Berre (France) was investigated just after petroleum addition. After removing hydrocarbon compounds by natural abiotic and biotic processes, the sediments were maintained in microcosms and Vic Bilh petroleum was added. The diversity and the expression of genes encoding ring-hydroxylating dioxygenases (RHD) were examined just after the petroleum addition until 14days focussing on the first hours following the contamination. RHD gene copy numbers and diversity were maintained throughout all the incubation period; however, transcripts were detected only during the first 2days. One dominant RHD gene, immediately and specifically expressed in response to petroleum contamination, was related to RHD gene carried by a plasmid found in Pseudomonas spp. The expression of the RHD genes was correlated with high biodegradation levels observed for low molecular weight PAHs at 7days of incubation. The study shows that the bacterial metabolism induced just after the oil input is a key stage that could determine the bacterial community structure changes. Monitoring the expression of RHD genes, key genes involved in hydrocarbon degradation, may provide useful information for managing bioremediation processes.

Numerical realization of the three-dimensional model of hydrodynamics for shallow water basins on a high-performance system

The paper is dedicated to the development and application of the 3D shallow water hydrodynamics model. Parallel realization of the deepest descent the symmetric successive over relaxation (SSOR) algorithm is presented for solving finite-difference equations obtained after discretization of the initial problem. Estimates for speeding up and increasing the efficiency of the parallel algorithm are given, and the flow velocity distribution for the Azov Sea (South of Russia) and the Lagoon Etang de Berre (South of France) are presented.