Combining contemporary and long-term erosion rates to target erosion hot-spots in the Great Barrier Reef, Australia

Abstract

Highlights This paper presents the first non-modelled estimates of contemporary measured erosion rates against background long term erosion rates in the Great Barrier Reef (GBR) catchments. Using an accelerated erosion factor (AEF), this study has highlighted that there are very specific 'hot-spot' areas that warrant priority treatment in terms of catchment remediation (Bowen sub-catchment, Upper Burdekin sub-catchment and low cover grazing areas). Due to the large intra-catchment variability of erosion in space and time, this study highlights that having a single end of catchment water quality target is inappropriate. Sub-catchment monitoring and evaluation is more suitable. The erosion rates presented in this paper represent a more robust way to 'bench-mark' current erosion rates compared with the current water quality 'targets'. AbstractMethods for prioritising catchment remediation are based on understanding the source of sediment over the short-medium timescales (10-10 2 years) using techniques such as sediment finger-printing, sediment flux monitoring, and catchment modelling. Because such approaches do not necessarily quantify the natural variation in sediment flux over the longer timescale, they often represent background or pre-agricultural erosion rates poorly. This study compares long-term (~100 to >10,000 years) erosion rates derived from terrestrial cosmogenic nuclides ( 10 Be) with contemporary erosion rates obtained by monitoring sediment fluxes over ~5-10 years. The ratio of these two data sets provides a measure of the accelerated erosion factor (AEF), which can be used to identify erosion hot-spots at the sub-catchment scale. The study area is the Burdekin catchment, the largest source of contemporary sediment to the Great Barrier Reef lagoon. Long-term erosion rates vary from <0.0077 mm yr -1 in the Suttor and Belyando subcatchments to 0.0296 mm yr -1 in the Bowen. The contemporary erosion rates are highest on small hillslopes with patchy ground cover (0.2726 mm yr -1 ) and in the Bowen sub-catchment (0.2207 mm yr -1 ), and lowest in the Belyando sub-catchment (0.0019 mm yr -1 ). All but two of the sub-catchment sites have an AEF > 1.0, indicating higher contemporary erosion rates than estimated long-term averages. Results confirm that the contemporary or agriculturally-induced erosion rates at these sites have increased considerably. Within the context of the Reef Water Quality Protection Plan, these results provide justification for water quality targets to be set at the sub-catchment scale, particularly for large and geomorphically diverse catchments.

Grazing impacts on gully dynamics indicate approaches for gully erosion control in northeast Australia

“…The predominant soil classification is Red Chromosol, known locally as red goldfields soil, which is a duplex textured sandy clay loam. These soils occur predominantly on the northeast side of the river basin, which is the area making the highest per hectare contributions of fine sediment to the GBR (McKergow et al ; Bartley et al ; Furuichi et al ). Gully erosion is more prevalent in Chromosols than in other soil orders in the Burdekin basin; while they cover 12% of the Burdekin basin, 25% of the area mapped as having medium or high gully density has Chromosol soils (Gilad et al ).…”

Denudation variability of the Sila Massif upland (Italy) from decades to millennia using 10Be and 239+240Pu

“…These studies, however, often used catchment‐wide approaches (e.g., Bartley, Croke, Brainbridge, Austin, & Kuhnert, ; Ibbeken & Schleyer, ) and, thus, cannot distinguish soil erosion from denudation as a general degradation process, which is a combination of (soil and rock) erosion, weathering, and mass wasting. Qualitative or quantitative estimates of erosion rates over different timescales have been reported for river sediment yields (Bartley et al, ; Kirchner et al, ), for lake and marine sedimentation (Mourier, Poulenard, Carcaillet, & Williamson, ), and for speleothem growth rates (Clift, Wan, & Blusztajn, ). Under specific conditions, the quantification of soil erosion over a few millennia has been possible to high precision through the use of lake sediment records (Bajard et al, ).…”

“…Several recent studies attempt to compare erosion rates over various time periods in order to estimate rates of various geomorphic processes (e.g., Kirchner et al, 2001). These studies, however, often used catchment-wide approaches (e.g., Bartley, Croke, Brainbridge, Austin, & Kuhnert, 2015;Ibbeken & Schleyer, 1991) and, thus, cannot distinguish soil erosion from denudation as a general degradation process, which is a combination of (soil and rock) erosion, weathering, and mass wasting.…”

Characterisation of Hydrological Response to Rainfall at Multi Spatio-Temporal Scales in Savannas of Semi-Arid Australia

“…We chose the Upper Burdekin catchment because it has some of the highest runoff and sediment yields of any basin draining to the GBR [34,35]. The Upper Burdekin catchment drains above Sellheim Gauging station covering 36,260 km 2 ( Figure 1).…”