The Coastal Range in the Mediterranean segment of Chile is a soil mantled landscape with potential to store valuable supplies of fresh water and support a biodiverse native forest. Nevertheless, human intervention has been increasing soil erosion for ~ 200 yr, with  intensive management of exotic tree plantations during the last ~ 45 yr. At the same time, this landscape has been affected by a prolonged megadrought, and is not yet well understood how the combined effect of anthropogenic disturbances and hydrometeorologic trends affect sediment transport at the catchment scale.

In this study we calculate a decadal-scale catchment erosion rate from suspended sediment loads and compare it with a 10⁴-year-scale catchment denudation rate estimated from detritic ¹⁰Be. We then contrast these rates against the effects of discrete anthropogenic disturbances and hydroclimatic trends. Erosion/denudation rates are similar on both time scales, i.e. 0.018 ± 0.005 mm/yr and 0.024 ± 0.004 mm/yr, respectively. Recent human-made disturbances include logging operations during each season and a dense network of forestry roads, which increase structural sediment connectivity. Other disturbances include two widespread wildfires (2015 and 2017) and one Mw 8.8 earthquake (2010).

We observe a decrease in suspended sediment load during the wet seasons for the period 1986-2018 coinciding with declines in streamflow, baseflow and rainfall. The low 10⁴-year denudation rate agrees with a landscape dominated by slow diffusive soil creep. However, the low 10-year-scale erosion rate and the decrease in suspended sediments are not in agreement with the expected effect of intensive anthropogenic disturbances and increased structural (sediment) connectivity. These paradox suggest that, either suspended sediment loads and, thus, catchment erosion, are underestimated, and/or that decennial sediment detachment and transport were smeared by decreasing rainfall and streamflow. Our findings indicate that human-made disturbances and hydrometeorologic trends may result in opposite, partially offsetting effects on recent erosion, but both contribute to the landscape degradation.