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  Biological removal of contaminants or nutrients as fluid passes through a media or a biological system.

This can result in bioaccumulation within an organism and compounded at higher trophic levels of a food web. Alternatively, metabolism and catabolism transform the substance into other stuff.

In water treatment, and stormwater management, bioretention by microbes growing within soil or filter media enhance retention and degradation of contaminants from the water. Root surfaces also provide surfaces for biofilm growth from which plants extract nutrients, thus removing them from the filter media. Bioretention cells often refer to chambers where plants grow in the filter media that water flows through. Bioretention areas refer to vegetated areas where soil serves as the filter media. The word retention implies that the substance of concern does not flow out of the soil plant system, regardless of whether surface water flows among plant shoots in a treatment wetland, or infiltrated water is itself detained in rain garden soil from which evapotranspiration may greatly reduce groundwater outflow rates --hence extending contaminant retention times.

Retention within filtration systems need not be absolute to achieve treatment. The capacity to detain contaminants can buffer sudden concentration spikes from occurring in the outflow.

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Bioretention". A list of authors is available in Wikipedia.
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