DENUDATION AND SEDIMENT FLUX TO THE GREAT BARRIER REEF

Project Summary

Fluvial sediments transported to the Great Barrier Reef (GBR) can have a negative impact on the health of the reef, stemming from associated pollutants and the smothering corals. Policies have been attempting to to manage and limit sediment export from the inland catchments to the ocean for the past few decades. However, in order to plan for an efficient and sustainable land management, spatial and temporal variables controlling the denudation rates and thus sediments flux must be examined.

Here we use preliminary results from both 10Be concentrations in river sediments and gauge measurements to infer time integrated sediment fluxes integrating over the last 60 ka and the last few years, respectively. This study includes 7 major catchments situated along the east coast of Australia, spanning most of the GBR region from the Wet Tropics (Daintree catchment, -16°S) to the Fitzroy catchment (-25°S), presenting variables climatic and geomorphic parameters. Samples collected for 10Be measurements from numerous sub-catchments, 44 in total, were used to determine 10Be-derived denudation rates ranging from 4.2 ± 0.2 mm.ka-1 (Suttor River) to 101.7 ± 10.3 mm.ka-1  (Carnarvon Gorge) with an overall mean of 18.3 ± 1.1 mm.ka-1 for the study area. 11 gauge stations have been selected near 10Be sampling points to act as spatial replicates with a shorter integrated measurement interval. The gauged derived denudation rates range from 0.9 ± 0.4 mm.ka-1 (Suttor River) to 66.7 ± 49.1 mm.ka-1 (South Johnstone River) with an overall mean of 23.4 ± 18.9 mm.ka-1.

We explore the differences between these two datasets in order to constrain the variables controlling denudation rates at a short time scale (gauge data) and at a longer time scale (10Be data). We find that 10Be denudation rates are mostly controlled by the average slope (R2: 0.65) of the catchment and the yearly rainfall (R2: 0.47). Conversely, the gauged derived denudation rates don't appear to be controlled by simple climatic or geomorphic parameters. The ratio of 10Be/gauged denudation rates is highly variable, from 0.3 to 4.7 and does not correlate with expected variables, such as land use or gully density. These results highlight the need for the management policies to operate on a case-by-case basis in each major catchment draining to the GBR.

Scientific Results

First results from this project were presented at AGU 2020.

The full study was published in 2021 in Marine Pollution Bulletin