Changes

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" />).

* '''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==