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Regional scale treatment

The final component of a treatment train to improve water quality in agricultural production landscapes is regional scale treatment. Treatment systems for agricultural water quality improvement can be used to undertake a ‘final polish’ of runoff from multiple properties. It can be more cost effective to locate a large treatment system regionally, than on an individual farm, to share the costs of construction, operation and foregone production area among multiple entities. These regional treatment systems often replicate natural wetlands and their associated physical, biological and chemical treatment processes. These systems have the potential to provide multiple services such as habitat, flood mitigation, amenity and recreation.

Treatment wetland Photo by EDAW Australia

Quick facts

of dissolved inorganic nitrogen are considerably higher in downstream aquatic areas, compared to upland streams in coastal catchments adjoining the Great Barrier Reef[1].
Which treatment
systems can I use?



Wetlands have naturally occurring processes that remove, transform, sequester and adsorb/absorb nutrients, chemicals, sediments and other pollutants. Many wetlands have been lost or degraded in agricultural production landscapes, thereby reducing the capacity of wetlands and floodplains to slow and filter runoff. Regional scale treatment systems that replicate natural wetlands are an option to help restore natural wetland treatment processes in agricultural landscapes. Use these treatment systems in existing water storage areas, drains, poorly performing agricultural land or degraded wetlands. Any treatment systems in natural wetlands need to be designed and installed so that they enhance the other services provided by the wetland such as habitat, amenity and recreation.

Regional scale treatment systems use one or more of the following treatment processes[5][4][6].

  • Physical: sedimentation and adsorption
    • Sedimentation can be filtered through the use of vegetation to slow water velocity.
    • Vegetation also provides a surface for biofilms facilitating adsorption of fine particles and any attached nutrients and chemicals.
  • Biological: uptake (or absorption) and denitrification.
    • Nutrients, heavy metals and some chemicals are removed through uptake by plants, algae, microbes or filter feeders, enhanced through the use of vegetation or shellfish such as oysters, with individual oysters able to filter up to 100L of water a day[3]. When plants uptake nutrients, the nutrients can be returned to the system when the plant or leaves die. Systematic harvesting of plant material can help permanently remove the nutrients from the waterbody.
    • Denitrification is the dominant and most sustainable nitrogen removal process[2], converting nitrates to inert nitrogen gas (N2). It is performed by microbes and requires a carbon source (e.g. vegetation) and anoxic conditions.
  • Chemical: transformation, adsorption, chemical precipitation and volatilisation.
    • Transformation of nutrients and chemicals occurs through processes such as photolysis and hydrolysis.
    • Attachment of a pollutant to the surface of a media (adsorption)
    • Chemical precipitation occurs when two inorganic dissolved pollutants join and precipitate out of the water column.
    • Some pollutants may volatilise to gas forms and be released to the atmosphere.

Table 1 lists the types of treatment systems that may be suitable for regional scale treatment.

Table 1: Suitability and complexity of different treatment systems for regional scale treatment.
Treatment system Suitability for regional scale treatment Relative complexity (design, construction and operation)
Floating wetland yes H
Treatment wetland yes H
Algae treatment yes H
Recycle pit yes M
Vegetated buffers and swales Not suitable  
Sediment basin Not suitable  
High efficiency sediment basin Not suitable  
Bioreactor Not suitable  

Additional information

WATERSHEDSS: Water, Soil and Hydro-Environmental Decision Support System

Water Environment Research Foundation—Critical assessment of stormwater treatment and control selection treatment

The use of constructed wetlands for removal of pesticides from agricultural runoff and drainage: a review. Environment International

Ponds Vs Wetlands – Performance considerations in stormwater quality management. Proceedings of the 1st South Pacific Conference on Comprehensive Stormwater and Aquatic Ecosystem Management


In addition to the standard disclaimer located at the bottom of the page, please note the content presented is based on published knowledge of treatment systems. Many of the treatment systems described have not been trialled in different regions or land uses in Queensland. The information will be updated as new trials are conducted and monitored. If you have any additional information on treatment systems or suggestions for additional technologies please contact us using the feedback link at the bottom of this page.


  1. ^ Connolly, NM, Pearson, BA, Loong, D, Maughan, M & Pearson, RG (2007), 'Hydrology, geomorphology and water quality of four Wet Tropics streams with contrasting land-use management.', in A H Arthington & R G Pearson (eds), Biological indicators of ecosystem health in Wet Tropics streams. Final Report to the Catchment to Reef Re- search Program, CRC for Rainforest Ecology and Management and CRC for the Great Barrier Reef., James Cook University, Townsville, Australia, pp. 14-14-78.
  2. ^ Kadlec, RH, Knight, RL, Vymazal, J, Brix, H, Cooper, P & Haberl, R (2000), Constructed wetlands for pollution control: processes, performance, design and operation, IWA Publishing, London.
  3. ^ McAfee, D, McLeod, I, Vozzo, M & Cumbo, V (2018), The surprising benefits of oysters.. [online], The Conversation Group Media Ltd. Available at: [Accessed 27 February 2018].
  4. ^ Melbourne Water (28 September 2017), Constructed wetlands. [online], Melbourne Water. Available at: [Accessed 27 February 2018].
  5. ^ Minnesota Pollution Control Agency (14 July 2017), Processes for removing pollutants from stormwater runoff. [online], Minnesota Pollution Control Agency. Available at: [Accessed 29 July 2018].
  6. ^ Wong, T, Fletcher, T, Duncan, H, Coleman, J & Jenkins, G (2002), 'A model for urban stormwater improvement conceptualization', Global Solutions for Urban Drainage, pp. 8-13.

Last updated: 3 October 2018

This page should be cited as:

Department of Environment and Science, Queensland (2018) Regional scale treatment, WetlandInfo website, accessed 13 May 2021. Available at:

Queensland Government
WetlandInfo   —   Department of Environment and Science