Eric Lucot

Spatial distribution of heavy metal concentrations in urban, suburban and agricultural soils in a Mediterranean city of Algeria.

As part of a larger program aiming at assessing transfer and effects of metals in food webs, this work studied the spatial distribution of Cd, Cr, Cu, Pb, and Zn in 101 sub-surface soils, systematically sampled (1 x 1 km regular grid) over a large area around Annaba, the fourth most-populated city of Algeria. Cd and Cr exhibited only one abnormally high value, with all other concentrations being close to pedogeological background. Some places in the centre of the city were polluted by Pb (up to 823 mg kg(-1)), probably due to aerial deposition from gasoline exhausts. Zn never exceeded regulatory limits over the whole sampling area. Cu was the only element for which a spatial autocorrelation occurred. A spatial interpolation by cokriging allowed the identification of agricultural activities as the main Cu pollution source. Our approach revealed various anthropogenic pollution sources, more efficiently for large-scale patterns than for local abnormalities.

Transfer of rare earth elements (REE) from natural soil to plant systems: implications for the environmental availability of anthropogenic REE

Background and aimsRare Earth Elements (REE) are widely used to trace natural geochemical processes. They are also increasingly used by man (electronics industry, medicine, agriculture) and therefore considered as emerging pollutants. The present study documents REE mobility in non-polluted natural soil-plant systems in order to characterize their environmental availability for future anthropogenic pollution.MethodsThe study is based on a field approach in non-polluted natural sites with contrasting geological environments (limestone, granite, and carbonatite) and highly variable REE contents.ResultsREE concentrations in soils do not directly reflect bedrock concentrations, but depend largely on pedogenetic processes and on the mineralogy of bedrock and soil. The soils of all sites are with respect to bedrock enriched in heavy REE. The REE uptake by plants is not primarily controlled by the plant itself, but depends on the concentration and the speciation in the soil and the adsorbed soil water pool.ConclusionsREE uptake by plant roots are linked with those of Fe. Roots absorb preferentially the light REE. Before translocation, REE are retained by the Casparian strip leading to much lower concentrations in the aerial parts. The transport of the REE within the xylem is associated with the general nutrient flux.

Douglas-fir root biomass and rooting profile in relation to soils in a mid-elevation area (Beaujolais Mounts, France)

Douglas-fir is the main reforestation species in the French Massif Central area (14 000 ha), but little is known about its rooting strategy in different soil conditions. This information has important implications for the choice of better soils for settling Douglas-fir, and consequently limiting risks of failure, pests or diseases. As a result, the influence of edaphic conditions on rooting patterns of dominant Douglas-fir was studied over a large range of ecological conditions in a mid-elevation area of the French Massif Central (Beaujolais Mounts). Root systems were studied extensively using the trench profile wall technique and the sector method in 74 pure and evenly aged Douglas-fir stands. The stands were chosen as being representative of soil conditions among 165 stands in an auto-ecological study. The rooting patterns were related to seven typical soil profiles, and to root profile groups. Results stressed that edaphic constraints due to substratum and soil structures have a strong influence on root system morphology. Important variations in root biomass and vertical distribution were highlighted among soils. Small fine root biomass is maximal for soils with no major edaphic constraints. The vertical distribution of fine root biomass is positively correlated for some soil types with organic C, total N, and most cations. For some types it was negatively correlated with the amount of exchangeable aluminum and coarse fragments, and with constraining rock facies. Harsher soils however, showed no correlation between soil chemical variables and fine-root biomass. A practical implication is that Douglas-fir seems to be a pliable and adaptive species: variation in habit and root system biomass are considerable within a study area which was presumed uniform.

Middle Term Evolution of Water Chemistry in a Karst River: Example from the Loue River (Jura Mountains, Eastern France)

Plotting multiyear chemographs in a karst river may display evolutional trends in water quality. In recent decades, different factors could explain for instance phosphate decrease and nitrate increase. In the Jura karst area, different springs and rivers not only exhibit variation of anthropogenic molecule concentrations, but also evolution of major element concentrations, that results in a change in electrical conductivity. Over a 30-year period, average electrical conductivity of the Loue River, which is totally supplied by karst springs, has increased from 260 to 470 µS/cm. Such an 81 % variation is only explainable by increases in major components, i.e. calcium and hydrogenocarbonate ions, which are the almost exclusive by-products of karstification processes in the Jurassic limestones of the Jura Mountains. Indeed, no direct anthropogenic cause may be invoked for such an evolution. An increase of dissolution throughout the system is necessarily correlated to an increase in the carbon dioxide transfer, resulting from an increase in dissolution and/or production rate.