SOIL EROSION RATES IN SOUTH AFRICA COMPARED WITH COSMOGENIC 3HE-BASED RATES OF SOIL PRODUCTION

Soil erosion has been considered a major problem in South Africa since the early 20th Century, yet the degree to which rates of soil erosion may exceed rates of soil production has not been well constrained by previous studies. Here we present 22 cosmogenic 3He-based maximum denudation rates of Karoo dolerite bedrock surfaces, and interpret these values as local rates of soil production. These generally low soil production rates (<4 m/Myr measured over a 105 yr timescale) are in all instances lower than various literature estimates for the corresponding rates of soil erosion in the same catchments, by up to two orders of magnitude. This significant contrast between long term rates of soil production and short term rates of soil erosion suggests that current agricultural practices are unsustainable under prevailing geological conditions.