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Treat fine sediments, nutrients and other toxicants

Fine sediments, nutrients bound to particles (particulate nutrients), dissolved nutrients and toxicants (including pesticides, herbicides, heavy metals) can be exported from modified systems through surface runoff or leaching/deep drainage into groundwater. These pollutants can cause eutrophication, alter primary productivity and food webs and kill sensitive plants and animals in waterways, wetlands and marine environments. Fine sediments, nutrients and toxicants can be transported long distances affecting aquatic and marine environments far from the source of the pollutant. Treatment systems for agricultural water quality improvement can remove these pollutants from surface or groundwater runoff through a range of physical, chemical and biological processes. Treatment systems need to be specifically designed to maximise the treatment processes for the target pollutant.

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

Quick facts

is the dominant nitrogen removal process in wetlands[1].
Which treatment systems can I use?

Conceptual model that illustrates the effect of nutrient load on bodies of water. Click the diagram to navigate to the 'Pressures' page for additional information.


Fine sediments, nutrients and other toxicants from agricultural production systems can affect the health and resilience of wetlands, inshore and marine environments, such as the Great Barrier Reef[6]. Fine sediments, nutrients (particulate or dissolved) and other toxicants (e.g. herbicides, pesticides and heavy metals) alter primary production and food webs, cause eutrophication, harmful algae blooms and kill sensitive plants and animals, leading to significant changes in aquatic communities.

Numerous physical, biological and chemical processes act to remove, transform, sequester and adsorb/absorb fine sediments, nutrients and other toxicants (Table 1). Different treatment systems for agricultural water quality improvement can be selected or tailored to the pollutant/s being generated in the agricultural production landscape (Table 2). Individual treatment systems are designed to enhance natural physical, biological and chemical treatment processes, targeted at specific types of pollutants 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[5].

Table 1: Treatment processes to remove different types of pollutants[2][3][4][7]
Target pollutant Treatment processes Features and function of the treatment system
Fine sediments and particulate nutrients Sedimentation (physical)

Vegetation to slow water velocity and intercept particles and reduces 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 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 can be used 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 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 uptake some chemicals. Substrate for microbes/biofilm to grow and uptake chemicals.

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: 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 M
Recycle pit High High High M
Treatment wetland Med-high Med-high Low-Med H
Bioreactor Not suitable High Low M
Algae treatment Med-High High Low-Med H
Floating wetland Med Med Low H
Vegetated buffers and swales Low Low Low L
Sediment basin Low Low Low M


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. ^ Bachand, PAM & Horne, AJ (2000), 'Denitrification in constructed free-water surface wetlands: II. Effects of vegetation and temperature.', Ecological Engineering. [online], vol. 14, pp. 17-17-32. Available at:
  2. ^ Melbourne Water (28 September 2017), Constructed wetlands. [online], Melbourne Water. Available at: [Accessed 27 February 2018].
  3. ^ 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].
  4. ^ 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:
  5. ^ 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.
  6. ^ 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, The State of Queensland, Brisbane.
  7. ^ Wong, T, Fletcher, T, Duncan, H, Coleman, J & Jenkins, G (2002), 'A model for urban stormwater improvement conceptualization', Global Solutions for Urban Drainage, vol. 8, no. 13.

Last updated: 10 October 2018

This page should be cited as:

Department of Environment and Science, Queensland (2018) Treat fine sediments, nutrients and other toxicants , WetlandInfo website, accessed 24 September 2020. Available at:

Queensland Government
WetlandInfo   —   Department of Environment and Science