Quantification of soil erosion using ⁷Be in a steep watershed used for natural grazing in Brazil

Cosmogenic ⁷Be was used to evaluate soil loss in a mountainous micro-watershed near Belo Horizonte, Southwest Brazil. Two nearby sites were selected, a reference site in a flat area and an eroded site in a hill slope. At the reference site, soil samples were collected monthly throughout the year in order to evaluate seasonal variations of ⁷Be inventory in soil and its relation with the precipitation regime. Additionally, rainwater was collected and the expected ⁷Be soil content was predicted. At the reference site, the ⁷Be inventory shows seasonal variations, in accordance with the rainy season, and its distribution in the soil profile shows an exponential decrease in depth (h₀ = 6.9 ± 0.6 kg m^-2; r² = 0.97). At the eroded site, two soil sampling campaigns were performed in order to measure soil erosion in the watershed. The estimated net erosion was 42.2 ± 3.7 t ha^-1, indicating the loss of upper 5mm of soil per year. This corresponds to soil losses in the area in the range from moderate to severe erosion.