Estimates of late Holocene soil production and erosion in the Snowy Mountains, Australia

• Soil development rates comparable to previous alpine measurements (20–220 t/km2/yr)
• Erosion rates were low (60 t/km2/yr) compared to non-alpine Australian hillslopes.
• Soil development on balance exceeded erosion over mid-late Holocene.
• Contemporary erosion rates > order of magnitude lower than grazing era
• High soil development and low erosion rates attributed to alpine vegetation

Soil production in actively uplifting or high precipitation alpine landscapes is potentially rapid. However, these same landscapes are also susceptible to erosion and can be sensitive to changes in climate and anthropogenic activity which can upset the balance between soil production and erosion. The Snowy Mountains, southeastern Australia, are a tectonically stable, low relief, moderate precipitation mountain environment. The alpine area is extensively blanketed by soil that has been subjected to more intensive episodes of erosion during past periods of anthropogenic disturbance and under cold climate conditions of the late Quaternary. In this study, rates of soil development and hillslope erosion were investigated using radiocarbon dating, fallout radionuclides and sediment cores collected from lakes and reservoirs. Estimated Holocene soil development rates were 20–220 t/km2/y. Erosion rates determined from the radionuclides 137Cs and 210Pb were equivocal, due to the inherent spatial variability of radionuclide inventories relative to apparent erosion rates. Estimated average erosion rates over the past 100 years, determined from 210Pbex inventories, were 60 t/km2/y (95% CI: 10, 90). Inventories of 137Cs observed at the same site implied that more recent erosion rates (over the past 60 years) was below the detection limits of the sampling method applied here (i.e. < 70 t/km2/y). The upper estimate of 90 t/km2/y is comparable to the mean erosion rate estimated using the radionuclide method for uncultivated sites in Australia and is significantly lower than that measured at sites were vegetation cover was disturbed by livestock grazing prior to its exclusion from the alpine area in the 1940s CE. Low erosion and high soil production rates relative to the lowland soils are likely related to extensive vegetation cover, which, in this context, protects soils against erosion and contributes to the formation of organic alpine soils, that rapidly accumulate organic matter by comparison to other soil types.