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[[File:Phosphorus Cycle copy.jpg|thumb|Phosphorus Cycle from Wikimedia Commons]]
[[File:Phosphorus Cycle copy.jpg|thumb|500px|Phosphorus Cycle from Wikimedia Commons]]
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==Phosphorus in stormwater==
Phosphorus in stormwater exists in both particulate and dissolved forms and is often explained in terms of total phosphorus (TP) and orthophosphate (–PO<sub>4</sub><sup>3-</sup>). Total phosphorus is the sum of particulate and dissolved phosphorus and contains both organic and inorganic forms. Particulate phosphorus is often associated with solids and sediments. Dissolved phosphorus consists of mainly inorganic orthophosphate and organic phosphorus. Orthophosphate meanwhile indicates the bioavailable phosphorus.
Phosphorus in stormwater is commonly considered to be primarily available in particulate form. While most studies reported majority of phosphorus (~55%) in particulate form (Maestre and Pitt 2005<ref name="example1">Maestre, A., and Pitt, R. (2005). “The National Stormwater Quality Database, Version 1.1 a compilation and analysis of NPDES stormwater monitoring information.” U.S. Environmental Protection Agency (EPA) Office of Water, Washington, DC.</ref>; Erickson et al, 2012<ref>Erickson, A. J., Gulliver, J. S., and Weiss, P. T. (2012). Capturing dissolved phosphorus with iron enhanced sand filtration. Water Res., 46(9), 3032–3042.</ref>) in some cases the dissolved form may explain up to 90% of the total phosphorus (Erickson et al. 2007<ref>Erickson, A., Gulliver, J. S., and Weiss, P. T. (2007). “Enhanced sand filtration for storm water phosphorus removal.” J. Environ. Eng., 10.1061/(ASCE)0733-9372(2007)133:5(485), 485–497.</ref>; Kayhanian et al. 2012<ref>Kayhanian, M., Fruchtman, B., Gulliver, J. S., Montanaro, C., Raniere, E., and Wuertz, S. (2012). “Review of highway runoff characteristics: Comparative analysis and universal implications.” Water Res., 46(20), 6609–6624.</ref>).
===Phosphorus levels in stormwater===
The total phosphorus concentrations in stormwater runoff depend on the type of land use and range in 0.16-0.46 mg/L (Maestre and Pitt 2005<ref name="example1" />). Stormwater features should reduce these nutrient concentrations before reaching receiving streams and lakes. Environment Canada (2004<ref name="example2">Environment Canada. (2004). Canadian guidance framework for the management of phosphorus in freshwater systems. Ecosystem Health: Science‐based solutions report no. 1–8. Cat. No. En1–34/8–2004E. </ref>) indicates a range of 0.001-2 mg/L (1-200 µg/L) for concentration of total phosphorus in natural waters, while the same range for uncontaminated freshwaters is within 0.01-0.05 mg/L (10-50 µg/L). Within lakes and rivers, trigger concentration ranges are identified and used internationally to explain trophic status of these waters. Based on these triggers, Environment Canada has identified the acceptable range of nutrients as 0.01-0.035 mg/L (10-35 µg/L). Given the flow of water within streams and capacity to flush out pollutants, rivers can maintain higher phosphorus loads than lakes without alterations of community composition and biomass (Environment Canada, 2004<ref name="example2" />). Stormwater features often drain into streams and therefore a similar outflow concentration ranges for total phosphorus is expected from those.
==Test methods to estimate the phosphorus concentrations in water and soil==
Phosphorus concentrations mentioned above relate to the phosphorus content in water. Depending on the LID type, phosphorus exists in the soil/media as well. Such LIDs include, [[bioretention]], [[enhanced swales|enhanced grass swales]], [[vegetated filter strips]], [[absorbent landscapes]], and [[green roofs]]. The methods used for phosphorus concentration estimation in both water and soil are summarized below.
Measuring the phosphorus concentrations in stormwater is important for performance evaluation/inspection and ensuring that outflow to the streams meets the mentioned concentration requirements. For performance evaluation, both inflow and outflow of a stormwater feature should be sampled. Sampling of just outflow reveals the concentrations entering streams and checks if they meet the requirements. There are several sampling methods, decision on the most appropriate method to use, depends on the sampling objectives and budget limitations.
#'''Grab sampling''' is the least expensive method and often does not yield accurate and representative results. Depending on the timing of the grab sample, concentrations may be too high or too low as they change quickly within a rain event.
#Automated samplers used to collect water from a rain event at given intervals (time or flow volume) are generally the most popular sampling method and involve compositing rain events to estimate an even mean concentration (EMC). For further information on sampling methods refer to the [https://sustainabletechnologies.ca/events/webinar-real-time-water-quality-monitoring-guide/ STEP Real-Time Water Quality Monitoring – How-To Guide]. The collected samples should be tested by a verified laboratory and handled based on laboratory instruction.
Measuring phosphorus concentration in soil or LID media, is important for assumption and/or verification inspections. An LID media contains some amount of phosphorus in support of plant growth; however, the amount of phosphorus should remain low to avoid substantial nutrient contribution to nearby receiving waters. The organic matter in the media, as well as deceased plants can decompose and release both organic and inorganic phosphorus. This can increase concentrations in outflow, rendering such LIDs an exporter of nutrients instead of a treatment feature (Bratieres et al. 2008<ref>Bratieres, K., Fletcher, T. D., Deletic, A., & Zinger, Y. A. R. O. N. (2008). Nutrient and sediment removal by stormwater biofilters: A large-scale design optimisation study. Water research, 42(14), 3930-3940</ref>). Therefore, it is important to measure the phosphorus content of LID media and/or bulk materials such as [[compost]], and [[topsoil]] and ensure that it is within appropriate design specification range. Extractable phosphorus is the portion of soil phosphorus that is easily available to organisms like plant and algae and is of immediate concern to water quality in large amounts.
==Limiting excess phosphorus==
==Limiting excess phosphorus==
To help ensure LID BMPs sustain healthy vegetation cover while not contributing substantially to nutrient loading of receiving waters, the quantity of extractable (i.e., available) P in the soil component needs to be measured and compared to design specifications or acceptance criteria.
To help ensure LID BMPs sustain healthy vegetation cover while not contributing substantially to nutrient loading of receiving waters, the quantity of extractable (i.e., available) P in the soil component needs to be measured and compared to design specifications or acceptance criteria.
{{:Phosphorus testing in media}}
{{:Phosphorus testing in media}}
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[[Category:Phosphorus]]
[[Category:Phosphorus]]
[[Category: Water quality]]
[[Category: Water quality]]