Changes

Nutrient pollution has been noted as a critical environmental, public health, and economic concern in Canada, Great Lakes, Lake Winnipeg, Lac St. Charles, Lake Simcoe and other water bodies (CWN, 2017<ref name="example1">CWN (Canadian Water Network). (2017). Nutrient Management—Research Insights for Decision Makers. CWN Report, November, 26.</ref>). Nutrient pollution can cause environmental imbalance, pose a public health risk for drinking water (USEPA, 2009<ref>United States Environmental Protection Agency (USEPA), 2009. Managing Stormwater Runoff to Prevent Contamination of Drinking Water. Source Water Protection Practices Bulletin. United States Environmental Protection Agency, Office of Water, Washington, D.C.</ref>) and swimming, as inhalation of algae by swimmers or pet can cause hypoxic condition. It can also affect the economy by harming fisheries, tourism, recreation, and increase the treatment cost of drinking water. Historical algal bloom in the Lake Erie during 1960s caused a substantial decline of native aquatic species (CWN, 2017<ref name="example1" />). In 2015 more than 5,000 km² of Lake Erie was covered by algal blooms rendering the water unsuitable for drinking for residents of Pelee Island, Ontario and Toledo, Ohio (CWN, 2017<ref name="example1" />). In 2011 and 2014, severe nutrient pollution in this lake caused service interruption, equal to $71 million and $65 million USD (Bingham, Sinha, & Lupi, 2015<ref>Bingham, M., Sinha, S. K., & Lupi, F. (2015). Economic benefits of reducing harmful algal blooms in Lake Erie. Retrieved from International Joint Commission website: http://ijc.org/fi les/tinymce/uploaded/Publications/Economic-Benefits-Due-to-Reduction-in-HABs-October-2015.pdf</ref>). Reports of nutrient pollution are increasing across Canada causing more beach closures and decline in water quality and fisheries (CWN, 2017<ref name="example1" />).

Nutrient pollution has been noted as a critical environmental, public health, and economic concern in Canada, Great Lakes, Lake Winnipeg, Lac St. Charles, Lake Simcoe and other water bodies (CWN, 2017<ref name="example1">CWN (Canadian Water Network). (2017). Nutrient Management—Research Insights for Decision Makers. CWN Report, November, 26.</ref>). Nutrient pollution can cause environmental imbalance, pose a public health risk for drinking water (USEPA, 2009<ref>United States Environmental Protection Agency (USEPA), 2009. Managing Stormwater Runoff to Prevent Contamination of Drinking Water. Source Water Protection Practices Bulletin. United States Environmental Protection Agency, Office of Water, Washington, D.C.</ref>) and swimming, as inhalation of algae by swimmers or pet can cause hypoxic condition. It can also affect the economy by harming fisheries, tourism, recreation, and increase the treatment cost of drinking water. Historical algal bloom in the Lake Erie during 1960s caused a substantial decline of native aquatic species (CWN, 2017<ref name="example1" />). In 2015 more than 5,000 km² of Lake Erie was covered by algal blooms rendering the water unsuitable for drinking for residents of Pelee Island, Ontario and Toledo, Ohio (CWN, 2017<ref name="example1" />). In 2011 and 2014, severe nutrient pollution in this lake caused service interruption, equal to $71 million and $65 million USD (Bingham, Sinha, & Lupi, 2015<ref>Bingham, M., Sinha, S. K., & Lupi, F. (2015). Economic benefits of reducing harmful algal blooms in Lake Erie. Retrieved from International Joint Commission website: http://ijc.org/fi les/tinymce/uploaded/Publications/Economic-Benefits-Due-to-Reduction-in-HABs-October-2015.pdf</ref>). Reports of nutrient pollution are increasing across Canada causing more beach closures and decline in water quality and fisheries (CWN, 2017<ref name="example1" />).

Excessive algal growth requires both phosphorus and nitrogen. While in some environments nitrogen is considered to be the limiting nutrient that controls such growth, phosphorus has been considered as the main limiting factor in most freshwaters (Howarth & Marino, 2006<ref>Howarth, R. W., & Marino, R. (2006). Nitrogen as the limiting nutrient for eutrophication in coastal marine ecosystems: Evolving views over three decades. Limnology and Oceanography, 51, 364-376. doi:10.4319/lo.2006.51.1_part_2.0364</ref>; Schindler et al., 2016<ref>Schindler, D. W., Carpenter, S. R., Chapra, S. C., Hecky, R. E., & Orihel, D. M. (2016). Reducing phosphorus to curb lake eutrophication is a success. Environmental Science & Technology, 50, 8923-8929. doi: 10.1021/acs.est.6b02204.</ref>). Therefore, controlling the load of phosphorous leaving a sub-watershed can reduce the chances of nutrient pollution in receiving surface waters. Formation of policies such as Lake Simcoe Phosphorous Offsetting Policy (LSPOP) are examples of such an approach. LSPOP requires a Zero Export Target where all new developments should control 100% of phosphorus from leaving the property (LSRCA, 2021<ref>LSRCA (Lake Simcoe Region Conservation Authority). (2021). Phosphorus Offsetting Policy. July). Available at: https://www.lsrca.on.ca/Shared%20Documents/Phosphorus_Offsetting_Policy.pdf.</ref>).   

Excessive algal growth requires both [[Phosphorus| phosphorus]] and nitrogen. While in some environments nitrogen is considered to be the limiting nutrient that controls such growth, phosphorus has been considered as the main limiting factor in most freshwaters (Howarth & Marino, 2006<ref>Howarth, R. W., & Marino, R. (2006). Nitrogen as the limiting nutrient for eutrophication in coastal marine ecosystems: Evolving views over three decades. Limnology and Oceanography, 51, 364-376. doi:10.4319/lo.2006.51.1_part_2.0364</ref>; Schindler et al., 2016<ref>Schindler, D. W., Carpenter, S. R., Chapra, S. C., Hecky, R. E., & Orihel, D. M. (2016). Reducing phosphorus to curb lake eutrophication is a success. Environmental Science & Technology, 50, 8923-8929. doi: 10.1021/acs.est.6b02204.</ref>). Therefore, controlling the load of phosphorous leaving a sub-watershed can reduce the chances of nutrient pollution in receiving surface waters. Formation of policies such as Lake Simcoe Phosphorous Offsetting Policy (LSPOP) are examples of such an approach. LSPOP requires a Zero Export Target where all new developments should control 100% of phosphorus from leaving the property (LSRCA, 2021<ref>LSRCA (Lake Simcoe Region Conservation Authority). (2021). Phosphorus Offsetting Policy. July). Available at: https://www.lsrca.on.ca/Shared%20Documents/Phosphorus_Offsetting_Policy.pdf.</ref>).   

In addition to contaminating surface waters, abundance of nutrients can also contaminate the ground waters. Contrary to surface waters, nitrogen is the primary nutrient of concern  regarding groundwater quality. Hobbie, et al. (2017<ref name="example2">Hobbie, S.E., Finlay, J.C., Janke, B.D., Nidzgorski, D.A., Millet, D.B., Baker, L.A., 2017. Contrasting nitrogen and phosphorus budgets in urban watersheds and implications for managing urban water pollution. Proc. Natl. Acad. Sci. U. S. A. 114 (16), 4177–4182.</ref>) reported that only 22 % of phosphorous is retained within its watershed, while the same estimated for nitrogen is 80%. Therefore, most of the nitrogen is leached in the groundwater or transformed through denitrification. Phosphorus retained in the watershed is often in particle form. Therefore, it tends to be bound to soil particles and retained in the vadose zone (area between ground surface and the groundwater table). However, nitrogen is often available in dissolved form which is more mobile and bioavailable. Thus, it can travel through the vadose zone and contaminate the groundwater.

In addition to contaminating surface waters, abundance of nutrients can also contaminate the ground waters. Contrary to surface waters, nitrogen is the primary nutrient of concern  regarding groundwater quality. Hobbie, et al. (2017<ref name="example2">Hobbie, S.E., Finlay, J.C., Janke, B.D., Nidzgorski, D.A., Millet, D.B., Baker, L.A., 2017. Contrasting nitrogen and phosphorus budgets in urban watersheds and implications for managing urban water pollution. Proc. Natl. Acad. Sci. U. S. A. 114 (16), 4177–4182.</ref>) reported that only 22 % of phosphorous is retained within its watershed, while the same estimated for nitrogen is 80%. Therefore, most of the nitrogen is leached in the groundwater or transformed through denitrification. Phosphorus retained in the watershed is often in particle form. Therefore, it tends to be bound to soil particles and retained in the vadose zone (area between ground surface and the groundwater table). However, nitrogen is often available in dissolved form which is more mobile and bioavailable. Thus, it can travel through the vadose zone and contaminate the groundwater.

==Nutrient Management==

==Nutrient management==

Due to their differing stoichiometry, managing nitrogen pollution is different from that of phosphorous. To reduce the nitrogen pollution, the watershed inputs should be reduced in general, while reducing phosphorus pollution would require reducing the movement of phosphorus from the contributing areas in the watershed (Hobbie et al., 2017<ref name="example2" />).

Due to their differing stoichiometry, managing nitrogen pollution is different from that of phosphorous. To reduce the nitrogen pollution, the watershed inputs should be reduced in general, while reducing phosphorus pollution would require reducing the movement of phosphorus from the contributing areas in the watershed (Hobbie et al., 2017<ref name="example2" />).

The key method for nutrient management is source control, or prevention of pollutants from entering stormwater, at the source. Low Impact Development (LID) features are source control measures in this way. Source control policies are cost effective tools for nutrient management (Marsalek and Viklander, 2011<ref>Marsalek, J., Viklander, M., 2011. Controlling contaminants in urban stormwater: Linking environmental science and policy. In: Lundqvist, J. (Ed.), On the Water Front: Selections from the 2010 World Water Week in Stockholm. vol. 101. Stockholm International Water Institute (SIWI), Stockholm.</ref>) that support and encourage the implementation of LIDs. Examples of such policies are adapted by Lake Simcoe Region Conservation Authority, South Nation Conservation (SNC), Nottawasaga Valley Conservation Authority (NVCA), and Halton Region in Ontario, as well as Chesapeake Bay and Mississippi River Basin (Region of Waterloo, 2017<ref>Region of Waterloo. (2017). Phosphorus Offsetting: Review of Existing Ontario Programs and Opportunities. Available at: https://www.regionofwaterloo.ca/en/living-here/resources/Documents/water/projects/wastewater/plan/WS2018V5-Tech_Memo_9A_WWTMP-Phosphorus_Offsetting_2017.PDF</ref>), municipalities as nutrient management by-laws, provinces like Ontario Nutrient Management Act and the Great Lakes Protection Act, and countries like Great Lakes Agreement between Canada and the US (CWN, 2017<ref name="example1" />). Additionally, design guidelines such as this one, provide tools for design and implementation of LIDs. While historically these guidelines indicated percent removal rates, the recent approaches are guiding to meet specific numeric objectives such as concentration (Clark and Pitt, 2012<ref>Clark, S. E., and Pitt, R. (2012). Targeting treatment technologies to address specific stormwater pollutants and numeric discharge limits. Water Res., 46(20), 6715–6730.</ref>).

The key method for nutrient management is source control, or prevention of pollutants from entering stormwater, at the source. Low Impact Development (LID) features are source control measures in this way. Source control policies are cost effective tools for nutrient management (Marsalek and Viklander, 2011<ref>Marsalek, J., Viklander, M., 2011. Controlling contaminants in urban stormwater: Linking environmental science and policy. In: Lundqvist, J. (Ed.), On the Water Front: Selections from the 2010 World Water Week in Stockholm. vol. 101. Stockholm International Water Institute (SIWI), Stockholm.</ref>) that support and encourage the implementation of LIDs. Examples of such policies are adapted by Lake Simcoe Region Conservation Authority, South Nation Conservation (SNC), Nottawasaga Valley Conservation Authority (NVCA), and Halton Region in Ontario, as well as Chesapeake Bay and Mississippi River Basin (Region of Waterloo, 2017<ref>Region of Waterloo. (2017). Phosphorus Offsetting: Review of Existing Ontario Programs and Opportunities. Available at: https://www.regionofwaterloo.ca/en/living-here/resources/Documents/water/projects/wastewater/plan/WS2018V5-Tech_Memo_9A_WWTMP-Phosphorus_Offsetting_2017.PDF</ref>), municipalities as nutrient management by-laws, provinces like Ontario Nutrient Management Act and the Great Lakes Protection Act, and countries like Great Lakes Agreement between Canada and the US (CWN, 2017<ref name="example1" />). Additionally, design guidelines such as this one, provide tools for design and implementation of LIDs. While historically these guidelines indicated percent removal rates, the recent approaches are guiding to meet specific numeric objectives such as concentration (Clark and Pitt, 2012<ref>Clark, S. E., and Pitt, R. (2012). Targeting treatment technologies to address specific stormwater pollutants and numeric discharge limits. Water Res., 46(20), 6715–6730.</ref>).

Selection of the LID type and its implementation for proper nutrient management, requires a good understanding of site limitations, sources of nutrients, their forms (particulate/soluble), and nutrient removal mechanisms associated with each LID type. The sources of nutrients and removal mechanisms are reviewed in this page, for additional details on [[phosphorus]] and [[nitrogen]], refer to their relative pages.

Selection of the LID type and its implementation for proper nutrient management, requires a good understanding of site limitations, sources of nutrients, their forms (particulate/soluble), and nutrient removal mechanisms associated with each LID type. The sources of nutrients and removal mechanisms are reviewed in this page. See [[Phosphorus]] page for additional information on managing phosphorus.

==Nutrient sources==

==Nutrient sources==

* '''Nitrification/denitrification''' – This is a microbial process where ammonia is converted to nitrite and then to nitrate by nitrifying bacteria. Through the denitrification process, the nitrate is further converted into gaseous nitrogen. This process is carried by denitrifying bacteria and requires anaerobic conditions. Anaerobic condition, can occur in lower depths of an LID, given the saturated conditions last long enough to minimize oxygen concentrations. Both processes require presence of organic matter as a source of energy.   

* '''Nitrification/denitrification''' – This is a microbial process where ammonia is converted to nitrite and then to nitrate by nitrifying bacteria. Through the denitrification process, the nitrate is further converted into gaseous nitrogen. This process is carried by denitrifying bacteria and requires anaerobic conditions. Anaerobic condition, can occur in lower depths of an LID, given the saturated conditions last long enough to minimize oxygen concentrations. Both processes require presence of organic matter as a source of energy.   

Each LID practice has the potential to offer one or all the mentioned removal mechanisms. In practice, the chemical and biological removal mechanisms each require favorable environments for activation. These environmental factors include oxygen availability, percentage of available organic matter, potential hydrogen (pH), salinity, and temperature. Please refer to the [[phosphorus]] and [[nitrogen]] pages for further details. Additionally, proper maintenance of the LID practice in question is the key to maintain the removal capacity of the feature and ensure that it does not become an exporter of nutrients itself.  

Each LID practice has the potential to offer one or all the mentioned removal mechanisms. In practice, the chemical and biological removal mechanisms each require favorable environments for activation. These environmental factors include oxygen availability, percentage of available organic matter, potential hydrogen (pH), salinity, and temperature. Please refer to the [[phosphorus]] and nitrogen pages for further details.  

 

Additionally, adequate maintenance of LID practices is needed to maintain the nutrient removal capacity of the facility and ensure that it does not become an exporter of nutrients itself. A 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> 

 

 

==References==

==References==