GREAT BARRIER REEF
// Outlook Report 2014
and therefore any chemicals or rubbish it contains can flow into creeks or rivers and into the marine environment. To improve the quality of stormwater and reduce marine debris, local councils are working with their communities and Queensland government agencies to better manage water flow, rubbish disposal and the use of chemicals. Industrial discharge is subject to national, state and Great Barrier Reef-specific water quality guidelines that identify trigger levels on the discharge of chemicals such as metals, metalloids and non-metallic inorganics in wastewater.110 However, many facilities were built decades ago, with long-term permits containing a variety of conditions. Marine pollutant benchmarking work in 2004 did not identify any significant toxic trace (‘heavy’) metal concentrations in the inshore waters of the Great Barrier Reef, especially when compared to levels in other Australian locations. Within the Region elevated levels of toxic trace metals have been reported at some sites around harbours and ports, but these are not necessarily above guideline levels.236 Trace metals often accumulate in the food chain; testing of tissues from deceased dugongs within the Region has generally found low levels by world standards.253 In mid-2012, following consecutive years of above average freshwater flow in the Burdekin region, 102 marine turtles stranded in a short period of time in Upstart Bay. Of these, 82 were already dead. Severe neurological symptoms were common in the turtles found alive. Exploratory testing of blood and tissue samples254 revealed cobalt levels potentially high enough to cause acute effects based on case studies in mammals255,256,257; comparative information for reptiles is limited258. The source of the cobalt and the circumstances under which the exposure occurred are not yet known. Some pollutants from historical mining activity in the catchment have reached the marine environment through land-based run-off, especially after periods of heavy rainfall. Sediment cores from inshore areas near Townsville have shown a spike in mercury of 25 times the background levels (before European settlement) that coincides with a period of intense gold mining in the adjacent catchment area (between 1870 and the early 1900s) when mercury was used in gold processing.259 Some small-scale extractive mining operations have previously released toxicants that have had severe effects, at least locally, in streams and creeks, for example arsenic associated with tin mining near Herberton.260 An emerging issue is the volume of water requiring disposal at mines and refineries after high rainfall events. A pilot program of allowing coal mine wastewater releases during flood conditions was implemented in the 2012–13 wet season for four coal mines in the catchment. This has subsequently been expanded to all coal mines within the Fitzroy basin.261 It is anticipated that the results of monitoring associated with these releases262 will improve understanding of the extent of any effects on water quality in the Region. Freshwater flows La Niña conditions increased average annual rainfall and flood events between 2008 and 2012 (see Figure 3.3)35, resulting in inshore areas of the Region being exposed to freshwater. Heavy rainfall events could become more frequent in future as the climate changes (Section 6.3.1)37. Modifications to terrestrial habitats within the catchment (see Section 3.5) have affected the magnitude and timing of freshwater flows to the Region. For example natural flow has been altered and the velocity of discharges increased by infilling of wetlands, clearing of forests and woodlands, and constructing dams, levee banks, roads and stormwater drains. Both the intensity and amount of rainfall and the velocity of freshwater flow affect how much sediment, nutrient, pesticide, plastic and other debris enters the Region from the land.
Inshore areas have recently been exposed to significant freshwater flow events.