Pédogenèse (géologie)

alt=mécanismes de la pédogenèse|vignette|redresse=1.7|Illustration simplifiée des mécanismes de base de la pédogenèse. La vitesse moyenne de formation d'un sol va de 0,017 à 0,036 mm/an (la formation d'une couche arable de prenant ainsi de à ). Des taux d'érosion deux fois plus élevé (voire quarante fois dans les pays développés actuels dont l'agriculture productiviste se traduit par un labour ou un travail du sol intensif) explique l'espérance de vie des grandes civilisations antiques qui a souvent suivi un même cycle d'expansion et de récession (en moyenne de 800 à , donnée compatible avec l'érosion complète des couches arables et fertiles par leur culture intensive reposant sur environ un mètre de terre végétale). La pédogenèse, (du grec pedon, sol, et de geneseôs, naissance) est l'ensemble des processus (physiques, chimiques et biologiques) qui, en interaction les uns avec les autres, aboutissent à la formation, la transformation ou la différenciation des sols. Cette formation

Etude du cycle biogéochimique du cuivre et du cadmium dans deux écosystèmes forestiers

Catherine Keller

The biogeochemical cycle of copper and cadmium has been studied in two forested ecosystems for two years. These two sites are: a) a Norway spruce forest (Picea abies) on an acid brown soil (FAQ: Dystric cambisol) and b) a mixed coniferous forest (Picea abies, Pinus cembra, Larix decidua and Abies alba) on a podzol. Both of them are located on low heavy metal polluted sites: the Swiss Plateau (850 m a.s.l.) for the first one and the oriental edge of the Mont-Blanc Massif (1650 m a.s.l.) for the second one. The Cu and Cd stocks in the vegetation and in the soil are evaluated. Heavy metal fluxes through the ecosystems are determined by analysis of concentrations and quantities of rain, throughfalls, stemflows, lysimetric soil solution and litterfall. In addition, the forms of Cu and Cd immobilization in soils are studied by means of sequential extraction, whereas immobilization forms in solution are studied by means of ion exchange chromatography and selective electrode. The results obtained allowed us to draw conclusions concerning the general pollution level in the experimental sites and the annual and/or detailed behaviour of Cu and Cd in the ecosystems. The conclusions are the following: As expected, the sites are not polluted since concentrations and fluxes are low. The chemical composition of solutions is modified during transition through the ecosystem, especially the copper concentrations. The acid brown soil humic layer is more efficient than the podzol humic layer in modifying this composition. There is no significant seasonal variation of concentrations and fluxes. However, the metal diffusion through the ecosystem is almost immediate. The soil plays an essential role in the immobilization of the heavy metals. The organic and organo-mineral layers are particularly active in this process. Exportations out of the ecosystems are limited. They are relatively more important for the podzol than for the acid brown soil and higher for Cd than for Cu. Transfer and stocking forms, and the ways of input to the soil depend on the metal considered: Copper input to the soil is mainly due to litterfall. In the soil, the metal has a preference to be associated with organic matter. In solution, it forms complexes with dissolved organic matter (mainly fulvic acid of MW < 1000 dalton). So, it is strongly retained within the soil and it cannot be easily drained out of the soil profile. At the opposite, cadmium is mostly transported by liquid means (throughfalls). In solution, it is present as free cadmium ions. In the soil, it is less strongly fixed than Cu since Cd is mostly associated with Fe and Mn oxides. For both of the metals, the free ion concentration in solution depends on pH and the saturation rate of organic matter. The latter has a heterogenous and polyfunctional character which explains a similar complexing capacity for all the samples studied. The differences observed in copper and cadmium behaviour can explain the variable diffusion of a polluting Cu and Cd flux through a given ecosystem and to the aquifer. The soil intervenes as a discriminating factor when the two experimental sites are compared.

EPFL1991

Spatial patterns of benthic biofilm diversity among streams draining proglacial floodplains

Tom Ian Battin, Massimo Bourquin, Jade Brandani, Susheel Bhanu Busi, Leïla Ezzat, Stylianos Fodelianakis, Tyler Joe Kohler, Grégoire Marie Octave Edouard Michoud, Hannes Markus Peter, Paraskevi Pramateftaki, Matteo Roncoroni

Glacier shrinkage opens new proglacial terrain with pronounced environmental gradients along longitudinal and lateral chronosequences. Despite the environmental harshness of the streams that drain glacier forelands, their benthic biofilms can harbor astonishing biodiversity spanning all domains of life. Here, we studied the spatial dynamics of prokaryotic and eukaryotic photoautotroph diversity within braided glacier-fed streams and tributaries draining lateral terraces predominantly fed by groundwater and snowmelt across three proglacial floodplains in the Swiss Alps. Along the lateral chronosequence, we found that benthic biofilms in tributaries develop higher biomass than those in glacier-fed streams, and that their respective diversity and community composition differed markedly. We also found spatial turnover of bacterial communities in the glacier-fed streams along the longitudinal chronosequence. These patterns along the two chronosequences seem unexpected given the close spatial proximity and connectivity of the various streams, suggesting environmental filtering as an underlying mechanism. Furthermore, our results suggest that photoautotrophic communities shape bacterial communities across the various streams, which is understandable given that algae are the major source of organic matter in proglacial streams. Overall, our findings shed new light on benthic biofilms in proglacial streams now changing at rapid pace owing to climate-induced glacier shrinkage.

2022

Etude du cycle biogéochimique du cuivre et du cadmium dans deux écosystèmes forestiers

Catherine Keller

EPFL1991

Etude du cycle biogéochimique du cuivre et du cadmium dans deux écosystèmes forestiers

Spatial patterns of benthic biofilm diversity among streams draining proglacial floodplains

Relevance of short-term dehydrogenase activity for assessing the impact of chemicals on soil microflora

Etude du cycle biogéochimique du cuivre et du cadmium dans deux écosystèmes forestiers

Spatial patterns of benthic biofilm diversity among streams draining proglacial floodplains

Relevance of short-term dehydrogenase activity for assessing the impact of chemicals on soil microflora