Water quality objectives and targets in the Mackay Whitsunday region to protect water quality to the Great Barrier Reef

This paper presents an overview of the development of water quality objectives (water quality guidelines for local waterways), and water quality targets to protect waterways draining to the Great Barrier Reef (GBR). The Great Barrier Reef World Heritage Area is the world’s largest World Heritage Area, and contains the largest single collection of coral reefs in the world, supporting many diverse ecosystems of immense conservation value. The Mackay Whitsunday region occupies only about 2% of the total area of the GBR’s catchments but is one of the most intensively farmed sugarcane areas, producing about one third of Australia’s annual sugar production. Research indicates that nutrient, sediment and herbicide inputs to the GBR have detrimental effects on water quality and organisms in the GBR lagoon. An overview of the environmental values (human and ecosystem uses) for protection, ambient and eventbased water quality objectives, and water quality targets for 33 subcatchments for the Mackay Whitsunday region is presented. Current water quality for both ambient and events were also evaluated in the subcatchments. Water quality objectives were developed as part of the Water Quality Improvement Plan (WQIP) in the region. Emphasis was placed on long-term event-based loads and event mean concentrations, evaluations of current condition of water quality using SedNet and ANNEX modelling data in conjunction with local knowledge, community engagement and water quality monitoring from up to 13 ambient and event water quality monitoring sites. Catchment modelling and water quality data were used to evaluate loads across the region. The predominant diffuse source of nutrient and herbicide pollutants is cane farming followed by grazing and conservation areas. Cane farming is the dominant intensive agricultural land use (19% of land area in the region) and produces about half of the regional load of particulate nitrogen and phosphorus. Cane farming produces about 77% of the regional dissolved inorganic nitrogen load. Cane farming produces the majority of filterable reactive phosphorus, and the herbicides atrazine, diuron, hexazinone, and ametryn. Community engagement was an important component in the development of the water quality objectives and targets, particularly practical targets for achieving load reductions. Other components included economic modelling to assess profitability of improved management practices on cane farms in the region, and development of a strategy to achieve accelerated adoption of improved soil, nutrient and herbicide management practices to meet water quality targets.