Juliette Asta

Correlation between the nitrogen concentration of two epiphytic lichens and the traffic density in an urban area

A field experiment was carried out in the urban environment of the Grenoble area using two epiphytic lichens: the nitrophytic Physcia adscendens and the acidiphytic Hypogymnia physodes. Two complementary studies characterized this experiment. Firstly, a sampling of the two lichens in 48 sites randomly located throughout the Grenoble area indicated that roads (size and proximity to sampling sites) influenced the nitrogen concentrations of P. adscendens, but not those of H. physodes. Secondly, to study more accurately the influence of roads, a traffic index was calculated and applied along two transects located perpendicularly to urban motorways. Significant positive correlations were found between this traffic index and the total nitrogen concentration of P. adscendens.

The inclusion of atmospheric particles into the bark suber of ash trees

A slow deposition of atmospheric components occurs on tree barks. One part of them can be incorporated into bark tissues. This work demonstrates that mineral particles are present inside the suber tissue in four-year-old ash tree stems. Most of these particles are smaller than 2 microm. Scanning electronic microscope studies - using energy dispersive X-ray spectroscopy (SEM-EDX) - on stem cuttings show that they are located either inside the dead suber cells or between these cells. Numerous particles are composed of clay, quartz, feldspar or mica. Others, clearly of anthropogenic origin, are metallic fragments composed of Fe, Ni, Cr, Pb, etc. Spherical fly ashes were found, composed of Si, Al or Fe, and demonstrating an anthropogenic formation. Such particles were isolated and purified from suber ashes obtained at 550 degrees C, after aqueous and acidic treatments, and their composition was established through SEM-EDX. These results reinforce the idea that the suber of tree barks alone can be considered as archives for atmospheric deposition.

A PIXE and ICP-MS Analysis of Metallic Atmospheric Contaminants in Tree Bark Tissues, A Basis for Biomonitoring Uses∗

The qualitative and quantitative metallic content of tree barks of Argania spinosa (L.) Skeels were studied. Argania spinosa is an endemic species in Morocco. This tree is adapted to semi-arid climates and exposed to specific conditions of relative humidity, temperature, wind, and particle transport. Three sites were sampled in Morocco: the large town of Rabat, the harbor of Agadir, and Aït Baha, a countryside location exposed to continuous desert wind. The methodologies included (1) in situ microanalysis with proton-induced X-ray emission (PIXE) and (2) trace element determinations by mass spectrometry with inductively coupled plasma (ICP-MS) associated with extraction procedures. Both methods allowed detection of elements coming from different bark compartments. The profile of airborne contaminants in the barks was typical of the sampling sites. The level of lead in barks sampled in Rabat reached 100 ng cm−2, or higher, while it varied between 3 and 35 ng cm−2 in Aït Baha. The in situ study of the microscopic structure of the bark provided the location of major and minor elements at various depths inside the bark. A differential between free deposit on the bark surface and penetrated content was found for the major and trace elements. The free deposit on the bark surface was suspected to be mostly the result of recent contamination. Part of the contaminants spread out on the surface penetrated the superficial suber. This long-term accumulation affected mostly Pb. In deeper levels, airborne elements at low concentrations and elements resulting from root uptake were concurrently present and resulted in a complex situation, as noted for zinc.

A comparative study of atmospheric deposits and lichen populations in a protected alpine area in the Grenoble region (France)

The atmospheric mixture deposited on ash tree stems was studied in Les Seiglieres, an alpine station located at an altitude of 1100 m in the Belledonne Mountains and in the town of Grenoble (300,000 inhabitants, altitude 200 m). The composition of the mixture of elements was fairly similar in the two stations, although the soil particles deposited on the stems had not the same geological origin. The deposit on the Seiglieres trees had a weight per area unit twice lower and a concentration of anthropic elements in this deposit three times lower than in Grenoble. Concurrently, the lichen flora of Seiglieres was studied from 1970 to 2007, showing a high biodiversity as well as important changes occurring in its composition, with a marked increase in the nitrophilous species, possibly due to higher amounts of NOx, P, Mg and S wafted over in the atmosphere.

Atmospheric elements deposition and evaluation of the anthropogenic part; the AAEF concept

The atmospheric deposition on tree trunks is commonly used for evaluating air contamination on a large time scale. However, the deposits are mostly composed of organic matter (generally more than 80 %) and of minerals of geogenic origin. From the elemental composition of the whole deposit, measured by ICP-MS, a calculation was conceived which allows to separate the amounts of elements corresponding to organic matter, to geogenic compounds and, finally, to anthropogenic minerals. For this purpose, the weight of organic matter was obtained through incineration at 550°C. The elements composition of organic matter was deduced from plant composition. The weight of geogenic compounds was evaluated from the Si, Al content. The formula of geogenic elemental composition took into account the composition of the local soil. This calculation was carried out on four different situations showing the contribution of the main anthropic atmospheric contaminants (Sb, Cd, Sn, Pb, Cu, V, Zn, W, Cr, Ni, Co, As).