FAQs

Water quality within the Townsville region is impacted by nutrients and sediments. Within Townsville, the main sources of nutrients and sediments are from point source pollutants and non-point source pollutants. A point source is a single localised point (such as a drain) where pollutants are discharged. Non-point sources (or diffuse sourced), refer to numerous sources of pollutants that have no specific point of discharge. This can include excess fertilizers from gardens or oils from roads being washed into our waterways.

Within Townsville, the major point sources are the Sewage Treatment Plants, which discharge into the Bohle River, Snaggy Creek, Louisa Creek Estuary and Cleveland Bay, and industrial discharges, which can include heavy metals and other contaminants. The non-point source pollutants are mainly from the urban environment, including fertilisers, pesticides, lawn clippings, litter and soil erosion.

Agricultural landscapes and grazing lands also contribute to non-point source pollutants. Grazing can cause erosion of gullies, hillslopes and/or streambanks, resulting in fine sediments being washed into waterways and out into the Reef. Horticulture and intensive agriculture can contribute to high concentrations of nutrients being washed into watercourses, especially after heavy rains.

Nutrients are natural chemical elements and compounds that plants and animals need to grow. Carbon, hydrogen and oxygen are abundant nutrients in nature, but nitrogen and phosphorus are not always so freely available.

Nitrogen and phosphorus are transported in run-off as tiny particles (particulates) often attached to sediment and dissolved in water. The dissolved fraction can be organic (a compound including carbon) or inorganic (a compound without carbon). The dissolved nutrients are immediately available for biological uptake. Particulate nutrients are mostly deposited close to river mouths. Once they settle, they can be broken down by bacteria into dissolved inorganic nutrients; nitrogen can also become a gas.

During the wet season, dissolved nutrients may travel into the Great Barrier Reef lagoon where they are ingested by phytoplankton, algae and bacteria. Transport of the nutrients may also occur outside of the wet season. Also, they can be released from the sediments some years after they are deposited.

Under normal circumstances, nutrients are a necessary component of life, however, in excess, nutrient levels can be problematic.

For more information see Australia and Queensland Government, 2020.

Excess nutrients can upset the natural balance of reef ecosystems. There is strong evidence that nutrients impact upon Great Barrier Reef ecosystems.

These impacts include:

• increasing macroalgae abundance resulting in lower coral diversity,
• increasing the susceptibility of coral to bleaching,
• increasing bioerosion and certain coral diseases,
• increasing crown-of-thorns starfish outbreaks,
• reducing benthic light due to algal blooms, and
• increased macroalgae and epiphytes on seagrass.

While most effects occur in the wet season during river discharge conditions, some effects are longer-lasting and continue for many years, such as crown-of-thorns starfish outbreaks. Most of the land-based nitrogen and phosphorus discharged into the Great Barrier Reef is in particulate form, but this varies greatly between catchments. However, dissolved inorganic nitrogen and phosphorus are of greatest concern because they are immediately and completely available for uptake by marine plants.

For more information see Australia and Queensland Government, 2020.