High-Resolution Mapping of Anthropogenic Impacts on Sediment Flux in the Northern Andes

Human activities, including deforestation, agriculture, mining, and dam construction, significantly influence erosion and river sediment flux. However, few data exist that constrain how river sediment flux have changed compared to natural conditions. Here we compare natural erosion estimates from millennial time-scale cosmogenic nuclide measurements with sediment yields from sediment gauging and river bedload modelling to study the magnitude and driving factors of anthropogenic erosion change in the Northern Andes of Colombia.

We calculated suspended sediment yields for 139 small to medium sized rivers (10-10’000 km²) in the Northern Andes by fitting rating curves to sediment concentration and discharge measurements. Additionally, we use an empirically calibrated model to account for bedload sediment flux in these mountainous catchments and calculate the total sediment flux for time periods of 1980 to 2000 and 2000 to 2022. We convert our sediment flux to erosion rates under anthropogenic conditions and compare them to millennial time-scale natural erosion rates estimated from cosmogenic nuclide data.

Our findings reveal that river sediment flux was, on average, 78% higher than natural conditions from 1980 to 2000, and increased to 111% above baseline between 2000 and 2022, primarily due to increases in the Central Cordillera. Factors such as agriculture, rainfall erosivity, mining, and deforestation are correlated with increased erosion and sediment flux. Interestingly, the variance in sediment yield also increases with the percentage of agricultural land and rainfall erosivity. On average current river sediment yields match RUSLE soil erosion estimates, suggesting high sediment connectivity and negligible storage of eroded soils in the mountainous catchments. Our data document a doubling of sediment flux in the Northern Andes due to the joint effects of agriculture, mining, and deforestation, however, the erosional response to land use change varies with environmental conditions such as rainfall erosivity.