The scientific goal is to define representative Technosols and technogenic material models, which may be used as a basis to answer questions relating to their pedogenetic evolution, such as: what are the dominant pedogenetic processes in the Technosols, what is the influence of technogenic materials in the construction and evolution of aggregates, what the influence of aggregation is on the availability of pollutants and nutritive elements in the long term? Modelisation is thus envisaged in order to predict the impact of pedogenetic processes on Technosol’s capacity to support plant cover and thereby to ensure its food function.
Theme I is divided into two Sub-themes.
The typology of Technosols
The part of the pedological cover constituted by Technosols is significant and growing with urban and industrial activities, which fundamentally modify soil functions. Despite the high agronomic and environmental stakes that they represent, very little is known about them and they have yet to be integrated to any significant extent, into the various existing classifications.
Technosols represent a very diverse range of solutions depending on the composition of their parent material and on their organisation. Whilst the majority of classifications mention them, they are not on the whole, consistent enough to define anthropized soils and are developed in the higher hierarchical levels.
As a response to the limited nature of this knowledge, we have been progressively developing, since 1993, a study methodology for strongly anthropised soils, by proposing an adaptation to standard pedological approaches. This undertaking has allowed a database to be built up of contrasted anthroposoils and has enabled us to put forward an initial typology of strongly anthropised soils, including Technosols. It is firstly a question of contributing to the establishment of a Technosol typology, based on the nature of the constituent materials, the major pedogenetic processes which affect them as well as the long term evolution of persistent pollutants.
This prior undertaking is indispensable in defining the model soil profiles and materials, which are studied in an in depth and generic manner dependent on the way they function and on their pedogenetic evolution.
Pedogenetic process and Technosol evolution
The evolution of technogenic materials which make up Technosols is studied by sticking closely to a hierarchical organisation and by modelling the early pedogenitic processes with the perspective of predictive pedology. The study of the pedogenetic evolution of Technosols involves:
- knowledge of alteration mechanisms, obtained by using model systems (reactive transport) which allows a characterization to be obtained of the reactions and products occurring within an accelerated pedogenisis,
- understanding of the structural organisation of the soil and the aggregation processes in order to (i) characterize the modes of pedogenisis and Technosol typology, (ii) understand organic matter dynamics and organo-mineral associations, by defining the formation, evolution and functionality of their aggregates, (iii) grasp the availability of the pollutants and nutritive elements present, by characterizing their association within aggregates ,
- hierarchical organization of factors (flora, fauna, organo-mineral soil constituents, technological material, pollutants) which have preponderant effects on the functioning and particularly the structural organisation of Technosols and on element availibility.
These approaches, completed by trials on real scale field trials and by analogous natural studies, should allow scenarios to be developed concerning the evolution of Technosol profiles.
The characteristics common to the various approaches used are (i) the possibility of carrying them out in situ and/or in the laboratory and (ii) the link established between the measures used on different scales (field, pedon, aggregate, ultra-structure). The comparison and/or the monitoring over a period of time of these diverse analyses enable us to ascertain which factors should be taken into account in modifications to the way in which Technosols function. The principle methods used are the :
- inventory and cartography of strongly anthropised soils on a model territory
- establishment and building-up of a database, gathering together the morphological, biological and physico-chemical characteristics of Technosols and the constituent materials
- definition of model profiles, diagnostic horizons and model materials, chosen for the frequency of their appearance within a given territory
- acceleration of pedogenetic processes through reactive transport column trials on technological material
- analyses of the macrostructure (observation and description of profiles, micromorphology, analysis of images on different observation and resolution scales)
- characterizations of the microstructures (morphological and analytical characterizations of organo-mineral associations by observation in situ or after granulodensimetric fractioning of the soil under electronic transmission microscopy associated with EELS and EDXS analyses.
- studies of the fragmentation and the structural stability of the aggregates
- study of natural analogues of the Technosols
- study of biological and functional diversity of Technosols