A review of acid sulfate soil impacts, actions and policies that impact on water quality in Great Barrier Reef catchments, including a case study on remediation at East Trinity.

An estimated 666,000 ha of acid sulfate soils (ASS) occur within the Great Barrier Reef (GBR) catchments of Queensland, Australia. Extensive areas have been drained causing acidification, metal contamination, deoxygenation and iron precipitation in reef receiving waters. The close proximity of ASS to reef waters makes them a substantial threat to water quality. Another important issue linked with ASS is their release of soluble iron, which is known to stimulate nuisance marine algal blooms, in particular Lyngbya majuscula. Known blooms of the cyanobacteria in reef waters have been confirmed at Shoalwater Bay, Corio Bay, the Whitsunday area and Hinchinbrook Channel. Acid sulfate soils are intimately related to coastal wetland landscapes. Where landscapes containing ASS have been disturbed (such as for agriculture, aquaculture, marinas, etc.) the biodiversity of adjacent wetlands can be adversely affected. However, there is no clear knowledge of the real extent of the so-called "hotspot" ASS areas that occur within the GBR catchments. Management of ASS in reef catchments has benefited from the implementation of the Queensland Acid Sulfate Soils Management Strategy through policy development, mapping, training programs, an advisory service, research and community participation. However, major gaps remain in mapping the extent and nature of ASS. Areas of significant acidification (i.e. hotspots) need to be identified and policies developed for their remediation. Research has a critical role to play in understanding ASS risk and finding solutions, to prevent the adverse impacts that may be caused by ASS disturbance. A case study is presented of the East Trinity site near Cairns, a failed sugar cane development that episodically discharges large amounts of acid into Trinity Inlet, resulting in periodic fish kills. Details are presented of scientific investigations, and a lime-assisted tidal exchange strategy that are being undertaken to remediate a serious ASS problem.