Dissolved Inorganic Nitrogen (DIN)
The anthropogenic DIN load from the Fitzroy River is estimated to be only 80 tonnes though there is still considerable uncertainty about this number. This modelled estimate assumes no anthropogenic DIN is generated from grazing lands and that virtually all anthropogenic DIN from the Fitzroy Region originates from grains and cotton cropping activities.
DIN that is discharged into the Great Barrier Reef is known to drive negative ecological effects, including increased algae production and crown-of-thorns starfish outbreaks. Dissolved inorganic forms of nitrogen and phosphorus are considered to be of greater concern than dissolved organic and particulate forms as they are immediately bioavailable for supporting algal growth. Reducing the amount of DIN is integral to improving coral cover within the Reef, as approximately 40% of coral cover loss since 1987 has been directly attributed to crown-of-thorns starfish predation.
In addition to the above effects, coral reefs are also known to be more susceptible to pesticide impacts during times when dissolved inorganic nitrogen concentrations are elevated. Furthermore, the impacts of DIN contributes to the cumulative impacts of other stressors (e.g. freshwater flood plumes, elevated nutrients, impacts from cyclones, increasing sea surface temperatures) to increase the overall impact on organisms of the Reef.