Pesticides, and particularly herbicides from agricultural sources, have been detected in nearshore sites of the Great Barrier Reef (GBR) all year round. The actual impact from these concentrations of herbicides is under debate and information on cumulative impacts is required. To address this, a series of experiments will examine how plants and corals are affected by herbicides in the water in conjunction with other stressors such as temperature, low salinity and low light. An important source of herbicides in coastal waters is flood plumes from river runoff. By creating experimental conditions similar to GBR flood plumes we will determine how long herbicides persist and how they are transformed as they travel into coastal waters.
1. Quantify the chronic effects and toxic thresholds of herbicides detected in the GBR on seagrass and corals under current and future climate scenarios, using controlled laboratory experiments.
2. Determine the persistence (half lives) of herbicides (including diuron, atrazine, hexazinone and tebuthiuron) at multiple temperatures under light conditions relevant to tropical coastal and inshore waters in flood plumes and test the toxicity of their breakdown products using flask and outdoor tank experiments.
We lack fundamental knowledge about the fate and persistence of herbicides on the GBR. There are few data to explain the extent to which sensitive tropical organisms such as corals, and especially seagrass, are affected by chronic exposure to herbicides combined with increased sea temperature and/or declines in salinity and light.
Outputs from these experiments will provide managers, regulators, industry and NGOs with information to help develop improved environmental trigger values and spatial risk maps.