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Treat fine sediments, nutrients and other toxicants

Fine sediments, nutrients bound to particles (particulate nutrients), dissolved nutrients (especially nitrogen) and toxicants (including pesticides, herbicides, heavy metals) can be exported from agricultural areas through surface runoff or leaching/deep drainage into groundwater. They can be transported long distances and can cause eutrophication and algal blooms, alter primary productivity and food webs and kill sensitive plants and animals in waterways, coastal wetlands and marine environments, including the Great Barrier Reef[8]. Treatment systems can remove these pollutants from surface run-off or groundwater through a range of physical, chemical and biological processes and need to be specifically designed to maximise the treatment processes for the target pollutant. Dissolved inorganic nitrogen (DIN) is the main nutrient of concern for intensive agriculture but it can be removed by denitrification and other processes in treatment systems  and natural vegetated wetlands[1][3]. These processes are explained on the nitrogen conceptual model pages.

Dense vegetation provides suitable conditions for denitrification. Photo by Queensland Government

Quick facts

is the dominant nitrogen removal process in wetlands[2]. For more see here.
Which treatment systems can I use?

Treatment systems for agriculture – Treat fine sediments, nutrients and other toxicants

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Numerous physical, biological and chemical processes act to remove, transform, sequester and adsorb/absorb fine sediments, nutrients and other toxicants (Table 1). Individual treatment systems are designed to enhance natural physical, biological and chemical treatment processes, targeted at specific types of pollutants (Table 2) and use the specific components and processes of these systems to do so. Understanding the treatment processes and the nature of the pollutant helps to identify what features (components and processes) are needed in the treatment system to effectively remove the target pollutant/s. For example, in the case of herbicides the physiochemical properties (e.g. the soil adsorption coefficient Koc) and half-life of each chemical will determine the most appropriate treatment processes[7].

Table 1: Treatment processes to remove different types of pollutants[4][5][6][9]
Target pollutant Treatment processes Features and function of the treatment system
Fine sediments and particulate nutrients (nitrogen, phosphorous) Sedimentation and enhanced sedimentation (physical)

Vegetation to slow water velocity and intercept particles and also reduce the risk of re-suspension. Detention time sufficient to enable particles to settle out of the water column or dosing with flocculants or coagulants to facilitate enhanced sedimentation.

Adsorption (physical) Vegetation provides a surface for biofilms facilitating adsorption of fine sediments and particulate nutrients.
Filtration (physical) Fine filter media to filter out small particles.
Decomposition (biological) Surface for microbes to grow and break down organic compounds.
Dissolved nutrients (nitrogen, phosphorous) Nitrification and denitrification (biological) Vegetation or alternative carbon source and anoxic conditions to enhance denitrification. Oxygen is required for nitrification.
Uptake/absorption (biological) Vegetation, algae or diatoms to take up nutrients. To avoid the nutrients being released back into the system when the vegetation or algae dies, the vegetation or algae will need to be removed from the system.
Adsorption (chemical) Phosphorous adsorption by aluminium and iron oxides and hydroxides. Maximised by the presence of clay containing aluminium and iron.
Precipitation (chemical) Phosphorous precipitated in conjunction with aluminium, iron or calcium in the presence of oxygen. Regular wetting and drying of wetland soils can prevent releases of phosphorous in the sediment.
Chemicals (herbicides, pesticides) Sedimentation and adsorption (physical) Some chemicals attach to sediments or organic matter and can be removed through sedimentation. Need to have sufficient detention time and vegetation/filter media to slow water.
Uptake/absorption (biological)

Vegetation can take upsome chemicals and provide a substrate for microbes/biofilm to grow and take upchemicals.

Transformation and volatilisation (chemical) Exposure of water to sunlight to enhance photolysis/UV degradation. Presence of water for hydrolysis. Detention time needs to be sufficient.
Microbial degradation (biological) Substrate for microbes to grow and degrade chemicals.



Table 2: Relative suitability and complexity of different treatment systems for removing particulate matter, dissolved nutrients and pesticides.
Treatment system Fine sediment and particulate nutrient removal capacity Dissolved nutrient removal capacity Pesticide removal capacity* Relative complexity (design, construction and operation)
High efficiency sediment basin Med-High Low Low Low-Med
Recycle pit High High High Low-Med
Treatment wetland Med-High Med-High Med Med
Bioreactor Med High Med Med
Algae treatment Med-High High Low-Med High
Floating wetland Med Med Low-Med High
Vegetated buffers and swales Low Low Low Low
Vegetated drains Med Med Low Low
Sediment basin Low-Med Low Low Low

NB: pesticide removal is highly variable depending on the type of pesticide and the system design.

Table 1 on the main treatment system page provides more details on main treatment processes, type of flow treated and land uses treatment systems have been primarily used in.


  1. ^ Adame, Franklin, H, Waltham, NJ, Rodriguez, S, Kavehei, E, Turschwell, MP, Balcombe, SR, Kaniewska, P, Burford, MA & Ronan, M (2019), 'Nitrogen removal by tropical floodplain wetlands through denitrification', Marine and Freshwater Research, vol., no. September.
  2. ^ Bachand, PAM & Horne, AJ (2000), 'Denitrification in constructed free-water surface wetlands: II. Effects of vegetation and temperature', Ecological Engineering, vol. 14, pp. 17-32.
  3. ^ Kavehei, E, Hasan, S, Wegscheidl, C, Griffiths, M, Smart, JCR, Bueno, C, Owen, L, Akrami, K, Shepherd, M, Lowe, S & Adame, MF (22 November 2021), 'Cost-Effectiveness of Treatment Wetlands for Nitrogen Removal in Tropical and Subtropical Australia', Water. [online], vol. 13, no. 22, p. 3309. Available at: [Accessed 21 December 2021].
  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. ^ Osmond, DL, Line, DE, Gale, JA, Gannon, RW, Knott, CB, Bartenhagen, KA, Turner, MH, Coffey, SW, Spooner, J, Wells, J, Walker, JC, Hargrove, LL, Foster, MA, Robillard, PD & Lehning, DW (1997), 'WATERSHEDSS: Water, Soil and Hydro-Environmental Decision Support System', Journal of the American Water Resources Association. [online], vol. 33, no. 2, pp. 327-341. Available at:
  7. ^ Vymazal, J & Brezinova, T (2015), 'The use of constructed wetlands for removal of pesticides from agricultural runoff and drainage: a review', Environment International, vol. 75, pp. 11-20.
  8. ^ Waterhouse, J, Schaffeike, B, Bartley, R, Eberhard, R, Brodie, J, Star, M, Thorborn, P, Rolfe, J, Ronan, M, Taylor, B & Kroon, F (2017), Scientific Consensus Statement. [online], The State of Queensland, Brisbane. Available at:
  9. ^ 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: 28 June 2022

This page should be cited as:

Department of Environment and Science, Queensland (2022) Treatment systems for agriculture – Treat fine sediments, nutrients and other toxicants , WetlandInfo website, accessed 1 July 2022. Available at:

Queensland Government
WetlandInfo   —   Department of Environment and Science