The hidden consequences of agricultural development: Soil degradation and pesticide contamination in the South American Pampa

Agricultural expansion has led to an acceleration of soil erosion and sediment dynamics in South America in general and in the Pampa biome in particular. This region is a hotspot of land-use and land-cover changes and was marked by important and rapid shifts in farming practices. However, the environmental consequences of these changes remain under-documented. To address this lack, the current research uniquely reconstructed sediment fluxes since the 1950s in the Pampa region in Uruguay from a sediment archive collected in a dam reservoir inaugurated in 1945. This core was analysed following a multi-proxy approach and fluxes of key pesticides were reconstructed since the 1950s. Results revealed that while early agricultural phases included widespread pesticide use, their impact remained limited due to the limited size of cultivated areas. A transitional period to no-tillage farming and pasture rotation first reduced sediment delivery. Nevertheless, afterwards, large-scale land conversion, combined with intensive pesticide application, has led to another episode of acceleration in soil erosion and an increase in sediment fluxes, largely decoupled from the precipitation variability alone. Notably, a resurgence of the banned DDT pesticide was observed suggesting the possible remobilisation of DDT originating from past applications. These findings provide long-term insights into the environmental consequences of the changes in land-use, land-cover and farming practices since the mid-twentieth century in a relatively understudied region and highlight the need for continued monitoring and for the implementation of measures to mitigate soil erosion and pesticide contamination in the Pampa region.