The memory of soils: role of historical land use on soil contamination by trace elements -examples from allotment gardens (Nantes, France)
La mémoire des sols : rôle des usages historiques sur la contamination par des éléments traces - exemples de jardins associatifs (Nantes, France)
Abstract
Urban gardening practices are exploding around the world, especially in industrialized countries. The question of soil contamination nevertheless arises, insofar as the soil memorizes the impacts linked to various successive human activities. Urban soils are therefore likely to have high concentrations of contaminants, particularly trace elements. Research on the link between contaminants distribution and different types of land use appears to be limited. In this context, this paper aims to illustrate how former land use influences the current spatial distribution of trace element in urban soils, based on the example of urban allotment gardens located in Nantes (France).
The 8 gardens studied are part of a large urban allotment garden (UAG) program in Nantes (France). Land use changes were determined using a historical analysis of the human activities for each site. Trace elements measurements in topsoils and soil profiles were carried out using a portable X-Ray fluorescence spectrometer, with additional laboratory analyses to calibrate the results. The origin of trace elements and their spatial distribution in soils were interpreted in light of land-use changes.
Successive human activities such as industry, backfilling, agricultural crops… appear as key factors of the distribution of trace element in soils. However, it is not always sufficient to understand the source of trace elements. Therefore, it is essential to characterize soil geochemistry in the context of soil management and urban redevelopment to ensure that soil quality is compatible with current and further land use.