Factors influencing the Region’s values
have been absent from the Region’s environment prior to European settlement.237 It is estimated from 2013 modelling that at least 12,114 kilograms of herbicides are now introduced into the Region each year from diffuse source agricultural run-off.217 Systematic monitoring of pesticide residues238 has shown widespread contamination by a range of pesticides in rivers, streams and estuaries that drain to the Region237, with the highest exposure around Mackay. This includes frequent exceedances of the Australian and New Zealand Water Quality Guidelines for fresh waters239 (often 10 to 50 times), for example atrazine and diuron, in some rivers. 240 However, a 2013 risk assessment undertaken as part of the review of Reef Plan has shown that in the Region the highest pesticide risks are confined to only a couple of locations (Mackay region and the lower Burdekin area). 202 Concentrations of pesticides in waters around reefs remains generally very low. 241 Elevated herbicide concentrations in the Region (Figure 6.16) have been particularly linked with sugarcane cultivation in the adjacent catchment. 242,243,244 Irrigation shortly after herbicide application is a major contributor to herbicide loss from farms. 245 The sugarcane industry has taken initiatives, many funded through the Australian Government Reef Programme, to reduce herbicides in run-off 246; resulting in good progress in reducing pesticide losses to the environment. There has been a 28 per cent pesticide load reduction across the Region and a 42 per cent reduction in the Mackay region, the highest risk area.199
Figure 6.16 Modelled exposure of additive PSII herbicide residues, 2010–11
The map shows risk areas for photosystem II inhibiting (PSII) herbicide residue based on modelling. The model calculated additive PSII herbicide concentrations using end-of-river monitoring data. The established relationship between concentration of dissolved organic matter and salinity was applied to corresponding satellite images of flood plumes to predict the additive PSII concentrations. Conservative mixing processes in the Great Barrier Reef lagoon were assumed. Exposure categories were based on known toxicity thresholds for coral and seagrass species. Source: Lewis et al. 2013247
Other pollutants In addition to nutrients, sediments and pesticides, a number of additional pollutants generally associated with human development are currently, or likely to be, found in Great Barrier Reef waters. Examples include marine debris (including microplastics), pharmaceuticals and personal care products and trace metals.185 As human populations along the coast grow, input levels may increase. There is little information or marine monitoring for most of these pollutants, other than marine debris.
Communities are working to reduce stormwater contributions to marine debris.
Common items of marine debris found within the Region are plastic bags, discarded fishing gear, plastic and glass bottles, rubber thongs, aerosols and drink cans.248 Plastic is the most prevalent type of marine debris found on beaches worldwide, comprising between 50 to 90 per cent by number of all debris items recorded.249,250,251,252 Between 2008 and March 2014, about 683,000 individual items of marine debris, weighing over 42 tonnes, were collected from the Region’s beaches by volunteers in the Australian Marine Debris Initiative.249 Marine debris from the catchment appears to accumulate and remain confined within the lagoon system of the Reef but with a northward movement.248 At the southern end of the Reef, debris appears to be more ocean-sourced.248 Stormwater run-off receives no treatment (other than gross pollutant traps for some drains) Townsville City Council, a Reef Guardian council, has stencilled entries to stormwater drains