Toxic levels of metals in Ferralsols under natural vegetation and crops in New Caledonia

The chemistry of soil solutions and the potential toxicity of trace metals (Co, Cr, Cu, Ni and Mn) were investigated on soils formed on ultramafic rocks. Soil solutions were collected along a soil toposequence under natural vegetation and under a cropped field. In the latter, metal speciation and species activity were computed with the WHAM 6 model. Total element concentrations varied with the soil topographic position. Upslope, in well-drained soils, they were relatively small with mean concentrations of < 0.2 mu mol l(-1) for Co and Cr and < 2 mu mol l(-1) for Ni and Mn. Downslope, in temporarily waterlogged soils, concentrations reached 37 (Mn), 5.6 (Ni), 1.9 (Co) and 0.1 (Cr) mu mol l(-1). Under crops, Ni, Mn and Co concentrations were similar to those under natural vegetation, but Cr concentration averaged 5 mu mol l(-1). Cu concentration was close to 1 mu mol l(-1). Free-ion species amounted to 53-71% of all species for Co, Ni and Mn but only 5% for Cu. Cr was almost entirely in the Cr(VI) form (CrO42-, HCrO4-). The free-metal-ion activities were in the range 26-81% of the corresponding free-metal-ion concentration. Comparing our data with levels that are toxic to crops, Ni and Cr are potentially toxic in the well-drained and the poorly-drained soils. In the latter, Co and Mn are also potentially toxic. Both the large concentration of metals and the chemical species in which they occur in solution could limit the use of the land for agricultural purpose

Aluminium toxicity in declining forests : a general overview with a seasonal assessment in a silver fir forest in the Vosges mountains (France)

International audienc

Influence of mature Douglas fir roots on the solid soil phase of the rhizosphere and its solution chemistry

International audienc

Influence of granite mineralogy, rainfall, vegetation and relief on stream water chemistry (Vosges Mountains, north-eastern France)

International audienceThe influence of rock mineralogy, climate, vegetation and relief on stream water composition and export as a result of weathering is a major scientific concern both at the local scale, because of the link between stream chemistry and biodiversity, and at the global scale, in relation to global climate changes. Environmental factors influencing stream chemistry at baseflow were studied for 95 forested catchments located in the granite part of the Vosges Mountains (NE France). Mean annual rainfall, slope, altitude, catchment area, forest cover and granite composition were attributed to each catchment using a geographic information system (GIS) and spatially distributed databases. These variables were then used to model stream water concentrations in SO4, Ca, Mg, K, Na, Si, ANC (Acid Neutralizing Capacity) and pH via linear regression analyses. Sulfate concentration is mainly negatively correlated to the mean altitude of the catchment. Silica and Na concentrations are strongly correlated and negatively related to the mean annual rainfall and not to altitude. pH is positively related to the sum of Ca, Mg and K, but not to SO4. For any type of granite, Ca, Mg and pH are generally negatively related to the mean annual rainfall, and positively related to the catchment area. Calcium is best explained by the rock content in hornblende, Mg by the rock contents of biotite and hornblende, K by the content in K-feldspar. Nevertheless models differ for each granite type, in relation to the availability of weatherable minerals and, probably, to water pathways. This study shows the interest of spatial analysis methods for understanding stream water concentrations at the mountain range scale in combination with local process studies and modelling at the catchment scale