6.5 Land-based runoff

Land-based runoff refers to freshwater flow (Section 3.2.3) from the terrestrial environment and what is carried with it into receiving waterbodies, such as rivers, creeks, wetlands, and nearshore marine waters. Land-based runoff is often associated with increased supply into the Reef lagoon of pollutants, such as suspended sediments, particulate and dissolved forms of nitrogen and phosphorus, and pesticides.1816 Activities, such as the application of fertilisers, deforestation, coastal development (Section 6.4), livestock management, pest control, stormwater and sewage management, aquaculture, mining and fracking and earthworks, can all influence land-based runoff and negatively affect downstream water quality. 

Land-based runoff remains the greatest contributor to reduced water quality, resulting in the declining state of many inshore marine ecosystems in some areas of the Reef.1817 The main contemporary source of the primary pollutants (nutrients, sediments, and pesticides including herbicides, insecticides and fungicides) from the Catchment is diffuse source pollution from agriculture.40,1818,1819  Groundwater also has a potential role in nutrient and pesticide transport into the marine environment.1820,1821,1822,1823 The impact of pollutants found in riverine plumes is evident up to 20 to 30 kilometres offshore during large flood events, and will depend on the size and duration of the event.1824

The Reef 2050 Water Quality Improvement Plan 2017–2022 1825 (Reef 2050 WQIP) seeks to improve the quality of water flowing from the catchments adjacent to the Reef and support the resilience of the Reef’s ecosystems. The whole-of-Reef water quality targets in the Reef 2050 WQIP to be achieved by 2025 include a:

  • 60 per cent reduction in anthropogenic end-of-catchment dissolved inorganic nitrogen loads
  • 20 per cent reduction in anthropogenic end-of-catchment particulate nutrient loads
  • 25 per cent reduction in anthropogenic end-of-catchment fine sediment loads
  • Pesticide target: to protect at least 99 per cent of aquatic species at the end-of-catchments. 
     
Aerial image showing a river with trees and agricultural landscape, with sea in the background.
Aerial view of Coolbie. © Nick O'Carroll 2024
  • 40. McCloskey, G.L., Baheerathan, R., Dougall, C., Ellis, R., Bennett, F.R., et al. 2021, Modelled estimates of fine sediment and particulate nutrients delivered from the Great Barrier Reef catchments, Marine Pollution Bulletin 165: 112163.
  • 1816. Furnas, M. 2003, Catchments and corals: Terrestrial runoff to the Great Barrier Reef, Australian Institute of Marine Science, Townsville.
  • 1817. Great Barrier Reef Marine Park Authority 2020, Position Statement: Water Quality (Document no. 100516), Great Barrier Reef Marine Park Authority, Townsville.
  • 1818. Schaffelke, B., Collier, C., Kroon, F., Lough, J., McKenzie, L., et al. 2017, Scientific Consensus Statement 2017: A synthesis of the science of land-based water quality impacts on the Great Barrier Reef, Chapter 1: The condition of coastal and marine ecosystems of the Great Barrier Reef and their responses to water quality and disturbances, State of Queensland, Brisbane.
  • 1819. Prosser, I.P. and Wilkinson, S.N. 2024, 2022 Scientific Consensus Statement: Summary | Evidence Statement for Question 3.3: How much anthropogenic sediment and particulate nutrients are exported from GBR catchments? in 2022 Scientific Consensus Statement on land-based impacts on Great Barrier Reef water quality and ecosystem condition, eds J. Waterhouse, M. Pineda and K. Sambrook, Commonwealth of Australia and Queensland Government.
  • 1820. Tait, D.R., Santos, I.R., Lamontagne, S., Sippo, J.Z., McMahon, A., et al. 2023, Submarine Groundwater Discharge Exceeds River Inputs as a Source of Nutrients to the Great Barrier Reef, Environmental Science & Technology 57(41): 15627-15634.
  • 1821. Nahar, K., Baillie, J., Zulkarnain, N.A. 2023, Herbicide Fate and Transport in the Great Barrier Reef: A Review of Critical Parameters, Water 15(2): 237.
  • 1822. Tait, D.R., Santos, I.R., Lamontagne, S., Sippo, J.Z., McMahon, A., et al. 2024, Rebuttal to correspondence on "Submarine groundwater discharge exceed river inputs as a source of nutrients to the Great Barrier Reef", Environmental Science & Technology.
  • 1823. Lewis, S.E., Baird, M.E., Bainbridge, A. and Davis, A.M. 2024, Correspondence on "Submarine groundwater discharge exceeds river inputs as a source of nutrients to the Great Barrier Reef", Environmental Science & Technology.
  • 1824. Wooldridge, S., Brodie, J. and Furnas, M. 2006, Exposure of inner-shelf reefs to nutrient enriched runoff entering the Great Barrier Reef Lagoon: post-European changes and the design of water quality targets, Marine Pollution Bulletin 52(11): 1467-1479.
  • 1825. Commonwealth of Australia and State of Queensland 2018, Reef 2050 Water Quality Improvement Plan 2017-2022, Reef Water Quality Protection Plan Secretariat, Brisbane.