An independent compilation of knowledge about the effects of dredging and sediment disposal on the Great Barrier Reef World Heritage Area has found the impacts will differ, depending on the location, timing, size and type of dredging and disposal activity.
The Dredge Synthesis Report was produced by a 19-member panel of experts, brought together through a joint initiative of the Great Barrier Reef Marine Park Authority (GBRMPA) and the Australian Institute of Marine Science (AIMS).
The technical and scientific experts, with a range of skills from oceanographic modelling to coral ecology, were asked to review and synthesise existing studies and data on the biophysical effects of dredging and disposal, while also identifying key knowledge gaps.
The outcome is an overview of the potential impacts of dredging and disposal on habitats such as coral reefs and seagrass meadows, and on fish and species of conservation concern such as dugong or marine turtles.
Among its key findings, the panel concluded:
– In terms of direct effects, dredging and burial of seafloor habitats during disposal can have substantial impacts at a local level, but have only a small impact on the broader Great Barrier Reef and its biodiversity as a whole;
– In terms of indirect effects, sediments released by dredging and disposal have the potential to stay suspended in the water and move. This may be contributing significantly to the long-term chronic increase in fine suspended sediments in inshore areas, however there wasn’t consensus among the panelists on the extent to which this happens and its impact on biodiversity;
– Dredging and disposal may be a significant source of fine sediments in the World Heritage Area, in addition to other sources, such as land run-off. A general comparison shows past large dredging projects produced amounts of fine sediment similar in magnitude to natural loads coming from land run-off in the same region;
– The recent policy commitments to ban disposal of capital dredge material in marine environments will mean future disposal, which will be limited to maintenance dredging, will contribute much less fine sediment. This reduced amount will still need to be considered in the context of other cumulative impacts on the Great Barrier Reef.
The publication is part of ongoing efforts by GBRMPA and the Australian Institute of Marine Science to improve understanding of the effects of dredging and dredge disposal, enabling better management of the risks associated with these activities.