Total suspended solids, nutrient and pesticide loads (2015–2016) for rivers that discharge to the Great Barrier Reef – Great Barrier Reef Catchment Loads Monitoring Program.

Executive summary
Poor water quality within the Great Barrier Reef lagoon, which occurs as a consequence of the export of diffuse pollutants from catchments, is a significant threat to the health and resilience of the Reef. Sediment, nutrients and pesticides leaving agricultural land have been identified as the most significant cause of poor water quality within the Reef lagoon (Brodie et al. 2013a). The Reef Water Quality Protection Plan 2013 (Reef Plan 2013), has the long-term goal of ‘ensuring that by 2020 the quality of water entering the Reef from broad scale land use has no detrimental effect on the health and resilience of the Great Barrier Reef’ (DPC 2013a).
Reef Plan 2013 established new land and catchment management targets and water quality targets that are measured against baseline conditions outlined in the preceding Reef Water Quality Protection Plan 2009. These reduction targets, to be achieved in 2018, are: at least a 20 per cent reduction in anthropogenic end-of- catchment loads of sediment and particulate nutrients; at least a 50 per cent reduction in anthropogenic end-of-catchment dissolved inorganic nitrogen loads; and at least a 60 per cent reduction in end-ofcatchment pesticide loads.
Progress towards the Reef Plan 2013 water quality targets is measured based on modelled values (Waters et al. 2014) through the Paddock to Reef Integrated Monitoring, Modelling and Reporting Program (Paddock to Reef Program) and reported via annual Report Cards (SoQ 2016b). The Paddock to Reef Program
also includes catchment scale water quality monitoring of pollutant loads entering the Great Barrier Reef lagoon. This monitoring program is implemented through the Great Barrier Reef Catchment Loads Monitoring Program. Under Reef Plan 2013, pollutant loads are calculated annually by the Great Barrier Reef Catchment Loads Monitoring Program in the following natural resource management regions and priority basins:
• Cape York region – Normanby Basin
• Wet Tropics region – Barron, Mulgrave-Russell, Johnstone, Tully and Herbert basins
• Burdekin region – Burdekin and Haughton basins
• Mackay Whitsunday region – O’Connell, Pioneer and Plane basins
• Fitzroy region – Fitzroy Basin
• Burnett Mary region – Burnett and Mary basins.
This report presents annual loads calculated using monitoring data (monitored annual loads) collected during the 2015–2016 monitoring year (i.e. 1 July 2015 to 30 June 2016). The data made available through the Great Barrier Reef Catchment Loads Monitoring Program provides a foundation to validate the
catchment models used to monitor progress against Reef Plan 2013 water quality targets, and thus assist in the effective management of Queensland and Australian natural resources. Reef Plan 2013 targets are based on reductions in anthropogenic loads, monitored annual loads do not define the anthropogenic or natural components of the loads. During the 2015–2016 monitoring year, 17 end-of-catchment sites and nine sub-catchment sites across the
14 basins, were monitored for total suspended solids and nutrients. Pesticides were monitored at a sub-set of 15 end-of-catchment sites and two sub-catchment sites across 12 basins (pesticides were not monitored in the Normanby and Barron basins).
Total annual rainfall was average in the monitored catchments of the Cape York and Mackay Whitsunday natural resource management regions. The monitored catchments of the Wet Tropics received below average to very much below average rainfall. Total annual rainfall was below average in much of the
Burdekin region, but average in southern areas of the Burdekin catchment. The Fitzroy and Burnett Mary regions generally received average to below average rainfall.
During the 2015–2016 monitoring year, all monitored reef catchments recorded annual discharges that were below the long-term mean. The annual discharges in the Barron, Mary, Barratta Creek and Tinana Creek catchments as well as sub-catchment sites in the Tully, Fitzroy (with the exception of the Dawson River) and
Burnett catchments were the lowest recorded since water quality monitoring in these catchments commenced under the Great Barrier Reef Catchment Loads Program in 2009.
Across the six natural resource management regions, monitored catchments generated approximately 1.8 million tonnes of total suspended solids, 11,000 tonnes of total nitrogen and 2300 tonnes of total phosphorus. The Burdekin catchment generated the largest proportion of total suspended solids, with
similarly high loads generated by the Fitzroy catchment (38 per cent and 37 per cent of the total monitored load respectively). The Fitzroy catchment also contributed the largest proportion to the combined loads of total nitrogen (29 per cent) and total phosphorus (40 per cent) followed by the Burdekin catchment (14 per cent and 20 per cent respectively). Substantial contributions of total nitrogen were also made by the Tully (10 per cent) and Normanby (8.3 per cent) catchments. The largest contributions to the combined total loads of particulate nitrogen and particulate phosphorus were made by the Fitzroy (36 percent and 42 per cent, respectively) and Burdekin (19 per cent and 23 per cent, respectively) catchments followed by the Johnstone (6.7 per cent and 7.2 per cent, respectively) catchment. Over half the combined load of dissolved inorganic nitrogen was derived from the Wet Tropics (51 per cent) region; substantial contributions were made by the Tully (18 per cent) and Russell (11 per cent) catchments. Generally, the Tinana Creek catchment in the Mary
basin generated the smallest loads of all monitored analytes.
Catchment yields (the load divided by the monitored surface area of the catchment) provide a measure of the supply of pollutants from monitored catchments. This metric allows a comparison of the rate of pollutant
delivery between catchments standardised by area. Of the monitored end-of-catchment sites, the highest monitored yield of total suspended solids occurred in the Russell catchment within the Mulgrave-Russell Basin. The Russell catchment also produced the highest monitored yields of all forms of nitrogen and phosphorus, with the exception of dissolved inorganic phosphorus in which the Sandy Creek catchment produced the highest yield. The Tully catchment also produced high yields of total nitrogen, dissolved inorganic nitrogen and dissolved organic nitrogen and the Johnstone catchment of total phosphorus and
dissolved organic phosphorus.
The total monitored annual loads of photosystem II inhibiting herbicides1 were (from largest to smallest): 1000 kg of tebuthiuron; 780 kg of total atrazine; 660 kg of total diuron; 260 kg of hexazinone; and 4.5 kg of ametryn. The combined toxicity-based load (toxic pesticide load2) of all monitored catchments was 750 kg TEqdiuron, with total diuron accounting for 87 per cent or 650 kg TEqdiuron. The Pioneer (180 kg TEqdiuron) and Tully (150 kg TEqdiuron) catchments produced the largest toxic pesticide load accounting for 44 per cent of the
combined monitored toxic pesticide load.
The highest land use yields (the load divided by the total surface area of land uses where the pesticide is registered for use) of ametryn were in the Mulgrave and Tinana Creek catchments. Consistent with the previous monitoring year, the Barratta Creek catchment produced the highest yield of total atrazine, which
was double the yield monitored in all other catchments. The highest land use yields of total diuron occurred in the Russell catchment which was also the case during the 2014–2015 monitoring year, although the yield was less than half of that recorded in 2014–2015. The highest monitored land use yields of hexazinone were in the Tully and Russell catchments. The highest land use yield of tebuthiuron was in the Fitzroy catchment, which also produced the largest monitored annual load of tebuthiuron.
This is the seventh technical report to be released by the Great Barrier Reef Catchment Loads Monitoring Program and the third under Reef Plan 2013. Access to water quality data associated with the Great Barrier Reef Catchment Loads Monitoring Program can be requested by completing the scientific data supply form available on the Queensland Government website (https://www.qld.gov.au/dsiti/scienceinnovation/
science/services/sci-reefsds-form) (SoQ 2017).
In order to maintain consistency in the reported data, the underlying methods of the Great Barrier Reef Catchment Loads Monitoring Program have not changed substantially over the years. Improvements to the Program are ongoing and during the 2015–2016 monitoring year this included the commissioning of a new monitoring site in the lower Johnstone catchment. The capital cost of this site was co-funded by Terrain NRM and the Department of Environment and Science.