Changes

Another group of studies of bioretention facilities examines nutrient removal of these LID installation, with mixed results. Some facilities have been observed to increase total phosphorus in infiltrated water (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>; Hunt ''et al''., 2006<ref>Hunt, W.F. and W.G. Lord. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC</ref> ; TRCA, 2008<ref>. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario. </ref>). These findings have been attributed to leaching from filter media soil mixtures which contained high phosphorus content. To avoid phosphorus export, the phosphorus content (i.e., Phosphorus Index) of the filter media soil mixture should be examined prior to installation and kept between 10 to 30 ppm (Hunt and Lord, 2006<ref>Hunt, W.F. and W.G. Lord. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC</ref>). While moderate reductions in total nitrogen and ammonia nitrogen have been observed in laboratory studies (Davis ''et al''., 2001<ref>Davis, A., M. Shokouhian, H. Sharma and C. Minami. 2001. Laboratory Study of Biological Retention for Urban Stormwater Management. Water Environment Research. 73(5): 5-14.</ref>) and field studies (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>), nitrate nitrogen has consistently been observed to be low. Little data exists on the ability of bioretention to reduce bacteria concentrations, but preliminary laboratory and field study results report good removal rates for fecal coliform bacteria (Rusciano and Obropta, 2005; Hunt ''et al''., 2006<ref>Hunt, W.F., A.R. Jarrett, J.T. Smith, and L.J. Sharkey. 2006. Evaluating Bioretention Hydrology and Nutrient Removal at Three Field Sites in North Carolina. ASCE Journal of Irrigation and Drainage Engineering. 132(6): 600-608.</ref>; TRCA, 2008<ref>. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario.</ref>).

Another group of studies of bioretention facilities examines nutrient removal of these LID installation, with mixed results. Some facilities have been observed to increase total phosphorus in infiltrated water (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>; Hunt ''et al''., 2006<ref>Hunt, W.F. and W.G. Lord. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC</ref> ; TRCA, 2008<ref>. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario. </ref>). These findings have been attributed to leaching from filter media soil mixtures which contained high phosphorus content. To avoid phosphorus export, the phosphorus content (i.e., Phosphorus Index) of the filter media soil mixture should be examined prior to installation and kept between 10 to 30 ppm (Hunt and Lord, 2006<ref>Hunt, W.F. and W.G. Lord. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC</ref>). While moderate reductions in total nitrogen and ammonia nitrogen have been observed in laboratory studies (Davis ''et al''., 2001<ref>Davis, A., M. Shokouhian, H. Sharma and C. Minami. 2001. Laboratory Study of Biological Retention for Urban Stormwater Management. Water Environment Research. 73(5): 5-14.</ref>) and field studies (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>), nitrate nitrogen has consistently been observed to be low. Little data exists on the ability of bioretention to reduce bacteria concentrations, but preliminary laboratory and field study results report good removal rates for fecal coliform bacteria (Rusciano and Obropta, 2005; Hunt ''et al''., 2006<ref>Hunt, W.F., A.R. Jarrett, J.T. Smith, and L.J. Sharkey. 2006. Evaluating Bioretention Hydrology and Nutrient Removal at Three Field Sites in North Carolina. ASCE Journal of Irrigation and Drainage Engineering. 132(6): 600-608.</ref>; TRCA, 2008<ref>. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario.</ref>).

Research into the role of plants in bioretention confirms they play an important roles in hydraulic and nitrogen removal performance. In a recent review of scientific literature, Dagenais ''et al.'' (2018) found that planted facilities are more effective than unplanted ones, as the presence of plants increases filter bed permeability and nitrogen removal. Plant species selection can considerably affect hydraulic and nitrogen removal performance, with root traits (e.g., thickness and depth) identified as playing important roles. They identified further research needed to test the hypothesis that native or diversely-planted facilities perform better than ones planted with exotic or fewer species.<ref>Dagenais, D., Brisson, J. and Fletcher, T.D. 2018. The role of plants in bioretention systems; does the science underpin current guidance?. Ecological Engineering, 120, pp.532-545. http://www.phytotechno.com/wp-content/uploads/2018/10/Dagenais-2018-Bioretention.pdf</ref>

Recent research into the role of plants in bioretention confirms they play an important roles in hydraulic and nitrogen removal performance. In a recent review of scientific literature, Dagenais ''et al.'' (2018) found that planted facilities are more effective than unplanted ones, as the presence of plants increases filter bed permeability and nitrogen removal. Plant species selection can considerably affect hydraulic and nitrogen removal performance, with root traits (e.g., thickness and depth) identified as playing important roles. They identified further research needed to test the hypothesis that native or diversely-planted facilities perform better than ones planted with exotic or fewer species.<ref>Dagenais, D., Brisson, J. and Fletcher, T.D. 2018. The role of plants in bioretention systems; does the science underpin current guidance?. Ecological Engineering, 120, pp.532-545. http://www.phytotechno.com/wp-content/uploads/2018/10/Dagenais-2018-Bioretention.pdf</ref>

===Stream Channel Erosion===

===Stream Channel Erosion===