1 Citation: Bartley, R., Waters, D., Turner, R., Kroon, F., Wilkinson, S., Garzon-Garcia, A., Kuhnert, P., Lewis, S., Smith, R., Bainbridge, Z., Olley, J., Brooks, A., Burton, J., Brodie, J., Waterhouse, J., 2017. Scientific Consensus Statement 2017: A synthesis of the science of land-based water quality impacts on the Great Barrier Reef, Chapter 2: Sources of sediment, nutrients, pesticides and other pollutants to the Great Barrier Reef. State of Queensland, 2017. © State of Queensland, 2017 The Queensland Government supports and encourages the dissemination and exchange of its information. The copyright in this publication is licensed under a Creative Commons Attribution 3.0 Australia (CC BY) licence. Under this licence you are free, without having to seek our permission, to use this publication in accordance with the licence terms. You must keep intact the copyright notice and attribute the State of Queensland as the source of this publication. For more information on this licence, visit creativecommons.org/licenses/by/3.0/au/deed.en. This document was prepared by a panel of scientists with expertise in Great Barrier Reef water quality. This document does not represent government policy. Scientific Consensus Statement 2017—Chapter 2 Contents Acronyms, units and definitions ...................................................................................................................... ii Acknowledgements ........................................................................................................................................ iii Executive summary ......................................................................................................................................... 1 1. Introduction ............................................................................................................................................... 5 Synthesis process ................................................................................................................................... 5 The questions this chapter addresses ................................................................................................... 7 Definitions and clarifications ............................................................................................................... 10 2. Sources of pollutants—an update of research from 2013 to 2016 ........................................................... 14 Sediments ............................................................................................................................................ 14 Where are the sediments coming from? ........................................................................................ 14 How does the source of sediments vary over time and space? ...................................................... 23 What processes are responsible for the excess sediment? ............................................................ 26 What are the drivers and land uses delivering the anthropogenic sediment loss? ........................ 29 Nutrients .............................................................................................................................................. 34 Where are the nutrients coming from? .......................................................................................... 34 What are the drivers and land uses delivering the anthropogenic nutrient loss? .......................... 49 How does the source of nutrients vary over time and space? ........................................................ 53 What processes are responsible for the excess nutrients? ............................................................. 55 Pesticides and other pollutants ........................................................................................................... 56 Where are the pesticides coming from? ......................................................................................... 56 What are the drivers and land uses delivering the pesticide loss? ................................................. 61 Other pollutants .............................................................................................................................. 63 New approaches to estimating catchment loads and water quality trends ........................................ 66 Validating modelled load estimates ................................................................................................ 66 Data assimilation and estimating confidence ................................................................................. 66 3. Synthesis of key findings .......................................................................................................................... 67 4. Research gaps and areas of further research ........................................................................................... 76 5. Reference list ........................................................................................................................................... 78 Appendix ....................................................................................................................................................... 94 Sources of pollutants to the Great Barrier Reef i Scientific Consensus Statement 2017—Chapter 2 Acronyms, units and definitions Acronyms DIN = dissolved inorganic nitrogen DIP = dissolved inorganic phosphorus DON = dissolved organic nitrogen GBR = Great Barrier Reef NPI = National Pollutant Inventory NRM = natural resource management PN = particulate nitrogen PP = particulate phosphorus PSII = Photosystem II TN = total nitrogen TP = total phosphorus TSS = total suspended sediment Units d-eq. kg = diuron-equivalent in kilograms kg = kilograms km = kilometres kt/yr = kilotonnes per year mg/L = milligrams per litre t = tonnes t/ha = tonnes per hectare t/km2/yr = tonnes per square kilometre per year t/km2 = tonnes per square kilometre t/yr = tonnes per year µm = micrometres (microns) Sources of pollutants to the Great Barrier Reef ii Scientific Consensus Statement 2017—Chapter 2 Definitions Basin: There are 35 basins that drain into the Great Barrier Reef. A basin can be made up of a single or multiple rivers (e.g. North and South Johnstone is one basin). Basins are primarily used here when discussing the relative delivery of a pollutant to the marine system. Catchment: The natural drainage area upstream of a point that is generally on the coast. It generally refers to the ‘hydrological’ boundary and is the term used when referring to modelling in this document. There may be multiple catchments in a basin. Management unit: There are 47 management units in the Great Barrier Reef catchment, which incorporate the 35 basins that drain directly to the Great Barrier Reef including additional internal catchments or management units within the Burdekin (7 management units) and Fitzroy (7 management units) basins. Pollutants: Pollution means the introduction by humans, directly or indirectly, of substances or energy into the environment resulting in such deleterious effects as harm to living resources, hazards to human health, hindrance to aquatic activities including fishing, impairment of quality for use of water and reduction of amenities (GESAMP, 2001). This document refers to suspended (fine) sediments, nutrients (nitrogen, phosphorus) and pesticides as ‘pollutants’. Within this chapter we explicitly mean enhanced concentrations of or exposures to these pollutants, which are derived from (directly or indirectly) human activities in the Great Barrier Reef ecosystem or adjoining systems (e.g. river catchments). Suspended sediments and nutrients naturally occur in the environment; all living things in ecosystems of the Great Barrier Reef require nutrients, and many have evolved to live in or on sediment. Region: There are six natural resource management (NRM) regions covering the Great Barrier Reef catchments. Each region groups and represents catchments with similar climate and bioregional setting. The regions include Cape York, Wet Tropics, Burdekin, Mackay Whitsunday and Burnett Mary. Sub-catchment: An internal drainage area within a catchment. Acknowledgements This chapter was led by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) with contributions from several representatives from the Department of Natural Resources and Mines (DNRM) (Queensland), Department of Science, Information Technology and Innovation (Queensland) (DSITI), Australian Institute of Marine Science (AIMS), James Cook University (JCU) and Griffith University (GU). We would like to thank Dr Andrew Ash (CSIRO), for his contribution to Section 2.1.4, and Dr Christian Roth and Dr David Post (CSIRO), for formal reviews on earlier versions of this document. We would also like to thank Reiner Mann and Rohan Wallace (DSITI), John Bennett and Nyssa Henry (OGBR) and several of the catchment modelling team (Rob Ellis) for comments on previous versions. Finally, we thank ISP members Dr Bronwyn Harch (QUT), Dr Jenny Stauber (CSIRO), Dr Graham Bonnet (CSIRO) and Dr Roger Shaw (ISP Independent Chair) for constructive comments on earlier versions. The chapter was prepared with the support of funding from the Office of the Great Barrier Reef within the Queensland Department of Environment and Heritage Protection and from the Department of the Environment and Energy and in-kind support from the organisations of the authors. Thank you to Jane Mellors (TropWATER JCU) for final editing. Sources