Abstract. Long-term erosion rates in Tasmania, at the southern end of Australia's Great Dividing Range, are poorly known; yet, this knowledge is critical for making informed land-use decisions and improving the ecological health of coastal ecosystems. Here, we present quantitative, geologically relevant estimates of erosion rates for the George River basin, in northeast Tasmania, based on in situ-produced 10Be (10Bei) measured from stream sand at two trunk channel sites and seven tributaries (mean: 24.1±1.4 Mgkm-2yr-1; 1σ). These new
10Bei-based erosion rates are strongly related to elevation, which appears to control mean annual precipitation and temperature,
suggesting that elevation-dependent surface processes influence rates of erosion in northeast Tasmania. Erosion rates are not correlated with slope
in contrast to erosion rates along the mainland portions of Australia's Great Dividing Range. We also extracted and measured meteoric 10Be
(10Bem) from grain coatings of sand-sized stream sediment at each site, which we normalize to measured concentrations of reactive 9Be
and use to estimate 10Bem-based denudation rates for the George River. 10Bem/9Bereac denudation rates
replicate 10Bei erosion rates within a factor of 3 but are highly sensitive to the value of 9Be that is found in bedrock
(9Beparent), which was unmeasured in this study. 10Bem/9Bereac denudation rates seem sensitive to recent
mining, forestry, and agricultural land use, all of which resulted in widespread topsoil disturbance. Our findings suggest that
10Bem/9Bereac denudation metrics will be most useful in drainage basins that are geologically homogeneous, where recent
disturbances to topsoil profiles are minimal, and where 9Beparent is well constrained.
Abstract. Long-term erosion rates in Tasmania, at the southern end of Australia’s Great Dividing Range, are poorly known, yet such knowledge is critical for making informed land-use decisions and improving ecological health of coastal ecosystems. Here, we present the first quantitative, geologically-relevant estimates of erosion rates for the George River basin, in northeast Tasmania, based on in-situ produced 10Be (10Bei) measured from stream sand at two trunk channel sites and seven tributaries (average 10.5 mm kyr−1). These new 10Bei-based erosion rates are strongly related to mean annual precipitation rates and elevation, and we suggest that the current East-West precipitation gradient across George River greatly influences erosion in northeast Tasmania. This stands in contrast to erosion rates along the mainland portions of Australia’s Great Dividing Range, which are more strongly related to basin slope. We also extract and measure meteoric 10Be (10Bem) from sediment grain coatings of the stream sand at each site, which we use to estimate 10Bem-based erosion and denudation rates for George River. 10Bem based erosion and denudation metrics, particularly those from the central and eastern tributaries, are also closely related to elevation and precipitation in the same manner as 10Bei erosion rates. Although 10Bem-based denudation rates replicate 10Bei erosion rates within a factor of two, 10Bem-based erosion rates are systematically 5–6x higher than 10Bei erosion rates. 10Bem erosion and denudation metrics for the westernmost headwater catchments are significantly lower than expected and have likely been affected by intensive and widespread topsoil erosion related to forestry, which delivers large volumes of sediment rich in 10Bem to tributary streams. The 10Bei erosion rates presented in this study may be useful for land managers seeking to restore ecological health of Tasmania’s estuaries by reducing sediment input to levels prior to landscape disturbance.
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