Identification of priority pollutants and priority areas in the Great Barrier Reef catchments

MTSRF Synthesis Report

Compiled by Jane Waterhouse¹ and Jon E. Brodie²

¹C2O Consultants, Townsville

²Australian Centre for Tropical Freshwater Research, James Cook University, Townsville

ISBN 978-1-921359-62-0
Published March 2011

MTSRF Theme 5 - Enhancing Delivery
MTSRF Program 7 - Halting and Reversing the Decline of Water Quality

Executive Summary

This report provides a synthesis of MTSRF-funded research relevant to defining priority pollutants for management of water quality in the GBR, and identifying areas for management intervention. The report contains an overview of the identification of priority pollutants, methods for calculating pollutant loads and current pollutant load estimates. Regional results of an assessment of the relative contribution of different sub-catchments and land uses to overall regional pollutant loads are presented. A relative risk assessment of regions and land uses from a water quality perspective is summarised, and the outcomes of a recent study on the exposure of plume waters in the GBR are included. Management implications, data limitations and future research directions are also described.

The priority pollutants derived from anthropogenic land uses considered most likely to pose a threat to the quality of runoff water entering the GBR ecosystem are suspended sediment, dissolved inorganic nitrogen (DIN) and photosystem II (PS-II) herbicides. The current pollutant load estimations do enable 'hot spots' of pollutant delivery to the GBR to be identified with a reasonable degree of certainty and, to date, management prioritisation is based on these estimates (see Brodie et al. 2009c). The assessment by Brodie and Waterhouse (2009), presented in this report, indicates that the Wet Tropics and Mackay Whitsunday regions have the highest priority ranking (High), the Burdekin and Fitzroy catchments a relatively high priority (Medium-high) and the Burnett Mary catchments a moderate priority in terms of the contribution and influence of land-based pollutants. The Cape York catchments were not included in the assessment but are expected to be relatively low priority.

The results of regional pollutant load assessments indicate that:

• The land uses and areas generating the highest pollutant loads are: DIN – sugarcane in the Burdekin and Wet Tropics regions; suspended sediments – grazing lands in the Burdekin and Fitzroy regions; and PS-II herbicides – sugarcane in the Wet Tropics and Mackay Whitsunday regions.
• A large proportion of the anthropogenic load of DIN (approximately 80%) is derived from sugarcane fertiliser losses (Wet Tropics 84%, lower Burdekin 80%, Mackay Whitsunday 88%), except in the Fitzroy region where almost all of the DIN load is from cereal grains and cotton.
• Hillslope erosion contributes the most suspended sediment to the overall load across the GBR catchments in comparison to bank and gully erosion.
• Diuron is the dominant herbicide found in the Wet Tropics, lower Burdekin and Mackay Whitsunday regions. It is generally associated with areas of sugarcane but is also found in other cropping areas.
• Tebuthiuron is the dominant herbicide in the Burdekin and Fitzroy regions associated with grazing lands. Atrazine is associated with other crops in the Fitzroy region.

In addition to these findings, the key achievements of MTSRF-funded research that have assisted in understanding priority pollutants and priority areas for management intervention in the GBR catchments are summarised below.

• Collaborative projects were undertaken between the ACTFR and regional NRM groups to establish pollutant load targets for the regional water quality plans. These target setting processes require definition of priority pollutants and priority areas for pollutant generation. Examples of this work in the Burdekin catchment include Bainbridge et al. (2006a, 2006b, 2007a, 2008) and in the Tully catchment, Bainbridge et al. (2009a, 2009b) and Mitchell et al. (2009). Brodie et al. (2009a) also described the target setting approach applied in the Burdekin and Tully catchments. These are all projects that were partly supported through the MTSRF. MTSRF researchers also participated in similar projects in other regions including the Mackay Whitsunday region (e.g. Rhode et al. 2008).
• Brodie and others at the ACTFR completed a project funded by the Australian Government and supported by the MTSRF to establish the best estimates of current pollutant loads for all of the GBR catchments. These estimates were entered into the Reef Rescue Multi Criteria Analysis for determining investment priorities across the GBR (Brodie et al. 2009b).
• The best estimates of pollutant loads for the GBR referred to above were then used as the basis for two reports funded by the Queensland Government, firstly to undertake a relative risk assessment of contaminant loads between the GBR catchment NRM regions (Brodie and Waterhouse, 2009) and, subsequently, to develop load estimations at a basin and sub-basin scale for the Wet Tropics, Burdekin, Mackay Whitsunday and Fitzroy regions (Brodie et al. 2009c). These projects were also supported by the MTSRF.
• Techniques for calculating pollutant loads have been improved through the MTSRF with considerable effort put towards quantifying uncertainty in load estimations. For example, Kuhnert and others have developed the Loads Regression Estimator (LRE) package (Kuhnert et al. 2009; Kuhnert and Henderson, 2010) to estimate suspended sediment loads from the Burdekin catchment. This approach deals with the uncertainty inherent in the large episodic flow events that are typical of the Burdekin catchment. In addition, statistical and modelling work has shown the importance of including variability of the system in the calculation of pollutant load estimates (e.g. Kuhnert et al. 2007, 2008, 2009, 2010; Kuhnert and Henderson, 2010).
• Priority management practices for reducing sediment, nutrient and pesticide runoff from agricultural areas and the cost effectiveness of these practices have also been established through MTSRF-funded research by van Grieken and others (e.g. van Grieken et al. 2010a, 2010b; Roebeling et al. 2007a, 2007b). Results of their analyses of the cost effectiveness of various management practices have already been used directly as part of the Reef Plan Paddock to Reef Integrated Monitoring, Modelling and Reporting Program (Queensland Department of the Premier and Cabinet, 2010).
• In parallel to the efforts identified above, a number of MTSRF-funded research projects focused on understanding pollutant transport and trapping (e.g. Lewis et al. 2009a; Wallace et al. 2010a, 2010b; Wolanski et al. 2008; Bainbridge et al. 2009a, 2010), water quality impacts on freshwater ecosystems (e.g. Pearson et al. 2010a), estuarine ecosystems (e.g. Sheaves et al. 2010) and marine ecosystems (e.g. Fabricius, 2011a, 2011b; Cooper et al. 2009; Negri et al. 2009). The outcomes of these studies and the ways in which they fit together to improve capacity to manage water quality issues in the GBR region are described in the companion MTSRF synthesis reports 'Catchment to Reef Connections' (Devlin and Waterhouse, 2010) and 'Water Quality Monitoring and Evaluation in the GBR'  (Waterhouse, 2010a).
• While the study of the relative risk assessment of priority pollutants within and between regions (Brodie and Waterhouse, 2009) provides useful information for managers to determine investment priorities for land management in the GBR catchments, it was not intended to provide a water quality risk assessment for the GBR. An example of a recent project that does attempt to identify exposure and risk of GBR ecosystems to priority pollutants is a collaborative project between the GBRMPA and the ACTFR that aimed to identify areas of high frequency exposure to plume waters in the GBR, and the probability of water quality parameters exceeding the Water Quality Guidelines for the Great Barrier Reef Marine Park (Devlin et al. 2010). The input data for this project were largely derived from MTSRF-funded research and the Reef Rescue Marine Monitoring Program.

Many of these findings have already been used by managers making decisions directing effort and guiding investment priorities in the GBR. For example, and of considerable significance, the management responses presently being assisted through Reef Rescue initiatives and the Great Barrier Reef Protection Amendment Act 2009 ('Reef Protection Package') are focused on the prioritised areas and industries identified in the overall risk assessment of priority pollutants and priority areas presented in this report. However, it is recognised that uncertainties do exist in this information and a number of future research priorities are identified to continue the delivery of applied research outcomes equivalent to those generated through the MTSRF. A number of these are presented in this report.