Since the Second World War, agricultural expansion in South America has had a lasting impact on ecosystems, but there is still very little data available to measure the consequences of this expansion. An international study led by LSCE, based on the analysis of Uruguayan sediments, highlights the impact of intensive agriculture on these areas.
This lack of available data is particularly marked in South America, a region where agriculture has rapidly developed at the expense of natural biomes. While the deforestation of the Amazon often makes the headlines, other biomes, rich in carbon and biodiversity, remain largely unknown, such as the Pampa, which covers vast stretches of natural grassland across the far south of Brazil, north-east Argentina and Uruguay. These grasslands, traditionally used for extensive livestock farming, are gradually being replaced by pine, eucalyptus and soybean plantations.
For the first time, a study led by the LSCE in collaboration with its partners in South America (Instituto de Ecologia y ciencas ambientales and Laboratorio de Radioquimica, in Montevideo,Uruguay), France (Edytem laboratory and BRGM) and Switzerland (Environmental Geosciences, Basel and Nuclear Chemistry Division, Spiez), has made it possible to reconstruct the impact of these changes on soil degradation. This research is part of the CNRS CELESTE Lab international project (IRP) and the AVATAR Franco-Swiss ANR project.
The multi-proxy analysis of a sediment core taken from the reservoir of the Rincón del Bonete dam in Uruguay, inaugurated in 1945 and considered to be one of the oldest dams on the continent, has made it possible to reconstruct the evolution of sediment fluxes and pesticide transfers in the region. This approach highlights the clear imprint of agricultural transformations and reveals a succession of distinct phases, including two key stages:
– a period of minimal erosion thanks to the implementation of direct seeding and rotational grazing (1991-2007),
– a phase of unprecedented erosion acceleration (2007-2023), linked to major land conversion and intensified pesticide use.
This latter trend reflects the strong international demand for commodities such as soybean and wood, which is increasing pressure on natural areas, converting them into farmland and plantations, and thus accentuating soil erosion.
In addition, the recent detection of the remobilisation of DDT – an insecticide that has been banned for several decades due to its toxicity – also highlights the persistence in soils of pollutants inherited from past activities, which are likely to be remobilised in the event of a change in land use.
Taken together, these results highlight the lasting impact of intensive agriculture on South American landscapes, and warn of the threats to soil and water resources posed by the current intensification of agricultural practices.
Reference : Bardelle, A., Gastineau, R., Guillevic, F., Foucher, A., Chaboche, P. A., Corcho-Alvarado, J. A., … & Evrard, O. (2025). The hidden consequences of agricultural development: Soil degradation and pesticide contamination in the South American Pampa. Science of The Total Environment, 1002, 180584. https://doi.org/10.1016/j.scitotenv.2025.180584