Retro-observations of terrestrial and aquatic ecosystem degradation associated with agricultural intensification in South America using sedimentary archives

Since the mid-1980s, agriculture in South America has intensified and expanded significantly. For example, Brazilian census data show that cultivated land increased by 80% between 1996 and 2006, mainly in ecologically fragile areas (e.g., the Amazon, Cerrado, and Pampa). While agriculture plays a critical role in the socio-economic life of South America's agricultural regions, it also has negative environmental impacts, including land-use change, biodiversity loss, soil erosion and agrochemical contamination. To mitigate the negative effects of accelerated sediment transport, conservation practices such as no-tillage were adopted in the 2000s. Despite the advantage of not tilling the soil, the no-till system has a significant potential for soil and water degradation, both because of the high amount of inputs (pesticides and nutrients) added to the soil surface and because of the susceptibility to surface runoff formation and related processes.

Agricultural expansion and intensification are expected to continue in South America in the coming decades to meet growing food demand. However, the long-term (>40 years) responses of terrestrial and aquatic ecosystems to these anthropogenic pressures and conservation practices remain poorly documented due to a lack of multi-decadal monitoring stations or field measurements. Sedimentary archives collected in rivers and lakes draining South American regions affected by this agricultural expansion/intensification provide a unique opportunity to reconstruct the magnitude of these environmental impacts. In this study, we propose a synthesis of sedimentary archives published in Brazil, Uruguay, and Argentina, with a focus on the post-1950 period. These studies, which report on sediment dynamics and sediment characteristics (such as organic matter, phosphorus, accumulation rate), will be used to reconstruct the regional trajectory of terrestrial and aquatic ecological degradation related to these increasing human pressures. These trajectories will be compared with existing data on land use change, agricultural inputs, etc. to understand the response of the system to these perturbations and to better anticipate potential future degradation in line with expected trends in the coming years.