A modelling framework is developed for the Wet Tropics region of the Great Barrier Reef that links a quantitative river discharge parameter (viz. dissolved inorganic nitrogen concentration, DIN) with an eutrophication indicator within the marine environment (viz. chlorophyll-a concentration, chl-a). The model predicts catchment-specific levels of reduction (%) in end-of-river DIN concentrations (as a proxy for total potentially reactive nitrogen, PRN) needed to ensure compliance with chl-a 'trigger' guidelines for the ecologically distinct, but PRN-related issues of crown-of-thorns starfish (COTS) outbreaks, reef biodiversity loss, and thermal bleaching sensitivity. The results indicate that even for river basins dominated by agricultural land uses, quite modest reductions in end-of-river PRN concentrations (∼20-40%) may assist in mitigating the risk of primary COTS outbreaks from the mid-shelf reefs of the Wet Tropics. However, more significant reductions (∼60-80%) are required to halt and reverse declines in reef biodiversity, and loss of thermal bleaching resistance.
Keywords: Coral bleaching; Coral health; Crown-of-thorns starfish; Nutrient enrichment; Resilience; Water quality.
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