ANALYSIS OF 10BE-BASED EROSION AND DENUDATION RATES IN THE GEORGE RIVER BASIN, TASMANIA, AUSTRALIA

A lack of local geomorphological data from Tasmania’s fluvial landscapes has limited efforts to improve water quality of Tasmanian rivers and coastal environments with regards to increased sediment delivery following land-use change. In this study, we present and analyze cosmogenic nuclide-based erosion and denudation rates for the main branch and tributaries of the George River (n = 9) derived using the in-situ and meteoric 10-beryllium (¹⁰Be_i and ¹⁰Be_m, respectively). Measuring both ¹⁰Be_i erosion rates and ¹⁰Be_m denudation rates in a small catchment with relatively uniform lithology provides us with the opportunity to test how well denudation rates derived by normalizing ¹⁰Be_m concentrations to concentrations of native ⁹Be found in the reactive phase (⁹Be_reac) using recently-developed techniques replicate more widely-used ¹⁰Be_i erosion rates. We find that the average ¹⁰Be_i erosion rate (~43 ± 21 Mg km^-2 yr^-1) and the average ¹⁰Be_m/⁹Be_reac denudation rate (~34 ± 12 Mg km^-2 yr^-1) reproduce within uncertainty. ¹⁰Be_i erosion rates are strongly correlated to mean annual precipitation (R² = 0.81) but not to mean basin slope (R² = 0.13), which supports previous work suggesting that in low-elevation, low-slope landscapes, precipitation and vegetation primarily control landscape erosion rates. We find that the ¹⁰Be_i erosion rates and ¹⁰Be_m/⁹Be_reac denudation rates for five out of eight tributaries plot near a 1:1 line, which suggests that ¹⁰Be_m/⁹Be_reac denudation rates replicate ¹⁰Be_i erosion rates for small river basins in Tasmania with uniform bedrock geology. This finding supports the use of ¹⁰Be_m/⁹Be_reac denudation rates for quantifying landscape evolution in quartz-poor regions where ¹⁰Be_i erosion rates cannot be derived. ¹⁰Be_m/⁹Be_reac denudation rates and ¹⁰Be_i erosion rates for the remaining three tributaries plot below the 1:1 line and may have been affected by land-use changes and forestry operations in the past. The ¹⁰Be_i erosion rates and the ¹⁰Be_m/⁹Be_reac denudation rates presented here are the first from Tasmanian rivers and will be useful for contextualizing the impact of modern sediment loads on water quality in the George River, relative to pre-disturbance levels.