Changes

The levels of phosphorus in media can also be evaluated and discussed as Phosphorus Saturation Index (PSI). PSI is the proportion of extractable phosphorus to extractable aluminum and iron in the soil sample.

The levels of phosphorus in media can also be evaluated and discussed as Phosphorus Saturation Index (PSI). PSI is the proportion of extractable phosphorus to extractable aluminum and iron in the soil sample.

==Design and Maintenance considerations==

==Design and maintenance considerations==

The mechanisms for phosphorus removal are sedimentation, filtration, adsorption, [[Understanding rainfall statistics|precipitation]], and [[Plants#Plant Characteristics|plant uptake]]. Particulate phosphorus can be removed through sedimentation and filtration and is often trapped among other solids within a shallow depth at the media surface (Hsieh et al. 2007<ref name="example3">Hsieh, C.-H., Davis, A. P., and Needelman, B. A. (2007).“Bioretentioncolumn studies of phosphorus removal from urban stormwater runoff.” Water Environ. Res., 79(2), 177–184.</ref>). Dissolved phosphorus is removed deeper in the media as it requires higher retention time (Hsieh et al. 2007<ref name="example3" />). Hunt et al. (2006)<ref name="example4">Hunt, W. F., Jarrett, A. R., Smith, J. T., and Sharkey, L. J. (2006).“Evalu-ating bioretention hydrology and nutrient removal at three field sites in North Carolina.” J. Irrig. Drain. Eng., 132(6), 600–608.</ref>, suggested a minimum depth of 0.6m and recommends 0.9m and infiltration rate of 0.007- 0.028 mm/s (1-4 in/h) for targeted removal of dissolved phosphorus. Removal of dissolved phosphorus relies heavily on the specifications of the LID media, it’s phosphorus content, type and percentage of organic matter, its potential hydrogen (pH), and temperature.

The mechanisms for phosphorus removal are sedimentation, filtration, adsorption, [[Understanding rainfall statistics|precipitation]], and [[Plants#Plant Characteristics|plant uptake]]. Particulate phosphorus can be removed through sedimentation and filtration and is often trapped among other solids within a shallow depth at the media surface (Hsieh et al. 2007<ref name="example3">Hsieh, C.-H., Davis, A. P., and Needelman, B. A. (2007).“Bioretentioncolumn studies of phosphorus removal from urban stormwater runoff.” Water Environ. Res., 79(2), 177–184.</ref>). Dissolved phosphorus is removed deeper in the media as it requires higher retention time (Hsieh et al. 2007<ref name="example3" />). Hunt et al. (2006)<ref name="example4">Hunt, W. F., Jarrett, A. R., Smith, J. T., and Sharkey, L. J. (2006).“Evalu-ating bioretention hydrology and nutrient removal at three field sites in North Carolina.” J. Irrig. Drain. Eng., 132(6), 600–608.</ref>, suggested a minimum depth of 0.6m and recommends 0.9m and infiltration rate of 0.007- 0.028 mm/s (1-4 in/h) for targeted removal of dissolved phosphorus. Removal of dissolved phosphorus relies heavily on the specifications of the LID media, it’s phosphorus content, type and percentage of organic matter, its potential hydrogen (pH), and temperature.

Media with high phosphorus content provides additional support for plant growth, however it will harm the phosphorus removal capability of the feature (Hunt et al. 2006)<ref name="example4" />). Similarly high percentage of organic matter in the media can increase the phosphorus content after degradation and lead to leaching of phosphorus (Clark and Pitt 2009<ref>Clark, S. E., and Pitt, R. (2009).“Storm-water filter media pollutantretention under aerobic versus anaerobic conditions.” J. Environ.Eng., 135(5), 367–371.</ref>). Different types of organic matter have various degrees of phosphorus leaching. To ensure that an LID can provide phosphorus removal, the phosphorus content and percentage of organic matter must be carefully selected and implemented during construction. For proper ranges of these values refer to the [[Bioretention: Filter media|bioretention media page]]. The suggested ranges should be met during the design phase and inspected before assumption of the feature.

Media with high phosphorus content provides additional support for plant growth, however it will harm the phosphorus removal capability of the feature (Hunt et al. 2006)<ref name="example4" />). Similarly high percentage of organic matter in the media can increase the phosphorus content after degradation and lead to leaching of phosphorus (Clark and Pitt 2009<ref>Clark, S. E., and Pitt, R. (2009).“Storm-water filter media pollutantretention under aerobic versus anaerobic conditions.” J. Environ.Eng., 135(5), 367–371.</ref>). Different types of organic matter have various degrees of phosphorus leaching. To ensure that an LID can provide phosphorus removal, the phosphorus content and percentage of organic matter must be carefully selected and implemented during construction. For proper ranges of these values refer to the [[Bioretention: Filter media|bioretention media page]]. The suggested ranges should be met during the design phase and inspected before assumption of the feature.

A maintenance strategy common to all types of LID practices to avoid nutrient leaching is annual removal of accumulated sediment and debris from inlets.  For bioretention cells, bioswales and stormwater tree trenches featuring surface inlets and soil media, periodic removal of the top 2 to 5 centimetres of media in areas adjacent to inlets, and replacement with material that meets design specifications (e.g., every two years) has also been recommended.<ref> Johnson, J.P., Hunt, W.F. 2016. Evaluating the spatial distribution of pollutants and associated maintenance requirements in an 11 year-old bioretention cell in urban Charlotte, NC. Journal of Environmental Management. 184 (2016):363-370. https://www.sciencedirect.com/science/article/pii/S0301479716307812 </ref> <ref>Jones, P.S., Davis, A.P. 2013. Spatial Accumulation and Strength of Affiliation of Heavy Metals in Bioretention Media. Journal of Environmental Engineering. 139(4): 479-487. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EE.1943-7870.0000624 </ref>

A maintenance strategy common to all types of LID practices to avoid nutrient leaching is annual removal of accumulated sediment and debris from inlets.  For bioretention cells, bioswales and stormwater tree trenches featuring surface inlets and soil media, periodic removal of the top 2 to 5 centimetres of media in areas adjacent to inlets, and replacement with material that meets design specifications has also been recommended.<ref> Johnson, J.P., Hunt, W.F. 2016. Evaluating the spatial distribution of pollutants and associated maintenance requirements in an 11 year-old bioretention cell in urban Charlotte, NC. Journal of Environmental Management. 184 (2016):363-370. https://www.sciencedirect.com/science/article/pii/S0301479716307812 </ref> <ref>Jones, P.S., Davis, A.P. 2013. Spatial Accumulation and Strength of Affiliation of Heavy Metals in Bioretention Media. Journal of Environmental Engineering. 139(4): 479-487. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EE.1943-7870.0000624 </ref>

==Additives for Enhanced Phosphorous Removal==

==Additives for Enhanced Phosphorous Removal==