A. Bruand

Textural porosity analysis of a silty clay soil using pore volume balance estimation, mercury porosimetry and quantified backscattered electron scanning image (BESI).

Textural porosity, which is due to the packing of soil elementary particles, can be divided into clay pores of the clay fabric and lacunar pores resulting from the packing of skeleton particles with clay particles. First established for artificial mixtures, the validity of this pore space division was tested on aggregates from a silty soil. Porosity was determined by three independent methods: (1) pore volume balance estimation; (2) mercury porosimetry; and (3) SEM observations and image analysis. Consistent values of lacunar pore volume were found, showing the proposed textural porosity division to be valid for the studied soil. The suggestion is made that such a division for the studied soil material might apply to the top layer of natural soils.

Experimental study of 'fragipans' formation in soils. Role of both clay dispersion and wetting-drying cycles

Abstract There is considerable literature about fragipans but their origin is still under discussion. In the laboratory, we investigated silt-clay fabrics which were obtained by mixing a silt fraction with either air-dried clay forming clayey aggregates or wet clay as a paste. The results from scanning electron microscopy and porosity analysis were used to study the formation of fragipans. Our results suggest that fragipans originate from successive wetting and drying cycles. Each wetting period would favour the dispersion of clay particles within the soil matrix and each drying period would favour its reorganization into coatings over the skeleton grains and wall-shaped bridges between these grains. The prevalence of these processes makes possible the formation of fragipans under varied climatic conditions.

Analysis of porosity in a tilled crusting soil' in Zimbabwe

Abstract Samples were collected in a tilled “crusting soil” from zones with different structures and their porosity was analysed with mercury porosimetry. The results showed three types of elementary pore volumes that differ in both the size and origin of the pores. The first type of elementary pore volume results from the packing of clay particles, and the second one mainly arises from the packing of silt and sand particles with the porous clay fraction. Their variations are mainly related to the clay content. The third elementary pore volume is related to tillage and biological activity, but there is no close relationship between its variation and the type of structure. These results obtained with mercury porosimetry are consistent with observations on thin-section images, using scanning-electron microscopy with backscattered electrons.

Stratification hydrogéochimique et écoulements verticaux dans l'aquifère des calcaires de Beauce (France) : un système anthropisé à forte variabilité spatiale et temporelle

Abstract Vertical profiles of temperatures and flow velocities, as well as water samples taken at different depths, reveal a hydrogeochemical stratification of the Beauce calcareous aquifer. This stratification, which is particularly well marked for the NO 3 − and Cl − profiles, is related to the development of intensive agriculture. It presents a strong variability: (i) in space because of the aquifers multi-layered structure and the presence of reducing levels, (ii) and in time due to the existence in the boreholes of a vertical flow, the direction of which depends on the periodic exploitation of the aquifer.