Phosphorus Indicator

The Phosphorus Indicator (official name: Indicator of the Risk of Water Contamination by Phosphorus) evaluates the relative risk of surface water contamination by phosphorus at the watershed scale across agricultural areas in Canada. This indicator has tracked phosphorus risk associated with Canadian agricultural activities from 1981 to 2011.

What are Agri-Environmental Indicators?

Agri-Environmental Indicators (AEIs) are measures of key environmental conditions, risks, and changes resulting from agriculture and of the management practices that producers use to mitigate these risks. They help explain:

  • how the agriculture sector is performing,
  • why it is performing as it is,
  • whether that performance is satisfactory, and
  • how it is likely to evolve in the future.

Agriculture and Agri-Food Canada (AAFC) has been compiling and analyzing data and reporting on AEIs since 1993, but uses data from as far back as 1981. The Phosphorus Indicator is one of several national indicators being tracked by AAFC.

Overall state and trend

Phosphorus risk has been increasing on agricultural lands in Canada, with the majority of agricultural land at moderate risk in 2011. From 1981 to 2011, the level of risk increased on 50% of agricultural land, primarily due to an increase in the area treated with fertilizers, an intensification of livestock production in some regions and unusually wet weather and high snowmelt runoff rates in the Prairies in 2011.

Use the interactive map below to zoom in and explore different regions.  Note that in the Prairies, risk is considered to be moderate, with pockets of low and very low risk in north and central regions as well as pockets of high and very high risk in southern Saskatchewan and Manitoba as well as in central Alberta. The pockets of higher risk can be attributed to a combination of phosphorus source—where phosphorus levels in the soil have been increasing as a result of mineral fertilizer use and manure from livestock production—and phosphorus transport to surface water bodies.  Risk of contamination is also high in the Lower Fraser Valley Region of British Columbia and is attributed to a higher concentration of livestock production in that area.  Risk is lower, but increasing steadily, in Eastern and Atlantic Canada.

In addition to exploring the 2011 values, click the play button to view changes over time. From 1981 to 2011 there has been an increase in risk in all agricultural regions of Canada. This has been especially evident in the Prairie Provinces, along with significant increases in parts of Eastern Canada, the Peace River Region of northern Alberta and the Lower Fraser Valley Region of British Columbia.

Figure 1: Risk of contamination of surface water by phosphorus in Canada in 2011

Legend: legend

You can also explore the change in the risk of contamination by phosphorus in the interactive map in Figure 2. This map uses a colour scheme to illustrate negative changes (reds and oranges) and positive changes (greens) between 1981 and 2011. The increase in risk is occurring across Canada, but is particularly evident in the Prairies.

Figure 2: Change in phosphorus risk, 1981 to 2011

Legend: legend

Phosphorus performance index

The state and trend of the Phosphorus Indicator can also be seen in the performance index below.

Figure 3: Risk of water contamination by phosphorus index
Description of this image follows.
Description - Figure 3
Year Index Value
1981 96
1986 85
1991 80
1996 77
2001 92
2006 77
2011 56

In 2011, the state of the environment, as it relates to phosphorus risk resulting from farming activities in Canada, was in the "Moderate" category. The index illustrates a deteriorating trend, representing increased risk to water quality. Phosphorus contamination occurs when there is both a source of phosphorus as well as means of transport, for example high snowmelt or rainfall runoff. The source component has increased somewhat due to the use of mineral fertilizers over the last 30 years and the intensification of livestock production in some regions. Abnormally high rates of spring runoff in several major watersheds, which increased phosphorus transport in 2011, played an even greater role in the decline in values observed between 2006 and 2011. The very high index value in 2001 is due to exceptionally low amounts of runoff in the Prairies that year, which reduced the risk of water contamination from phosphorus.

The index tends to aggregate and generalize trends and so should be viewed as a policy tool to give a general overview of state and trend over time.

How performance indices are calculated

Specific trends

This section highlights a few other trends of interest. In some cases, these are occurring in certain regions and in others they are affecting certain sectors, such as the beef or dairy industries. This is not an exhaustive list; additional findings can be found in the full publication: Environmental Sustainability of Canadian Agriculture, Agri-Environmental Indicator Report Series - Report #4 .

Trend 1 - Phosphorus build-up in soils across Canada

Phosphorus is bound tightly to soil particles, so only a fraction of phosphorus applied as fertilizer or manure is available to the crop in the year that it is applied. Additionally, manure applied to meet the nitrogen requirements of crops will supply more phosphorus than those crops require. As a result, the application rates often exceed the amount removed with the crop when it is harvested. In other words, phosphorus accumulates in the soil over time, creating a positive phosphorus balance. In addition to being removed with the crop, this built-up phosphorus can be removed via runoff of rainfall or snowmelt. If there is enough runoff, the soils can be ‘flushed’ and large quantities of phosphorus can be released at a time, creating a risk to nearby water bodies. Some provinces carry quite large phosphorus balances as phosphorus continues to accumulate in soils over time.

Figure 4 (below) shows the annual phosphorus balance by province (combined for the Atlantic Provinces) from 1981 to 2011.  The highest phosphorus balance values have been recorded in the Atlantic Provinces (intensive livestock and potato production), followed by Quebec (intensive livestock production), British Columbia (intensive livestock and horticultural production) and Ontario. The trend in Eastern Canada has been towards a declining phosphorus balance, but the balance is still slightly positive in Ontario. Even though Ontario is the province that is closest to balancing phosphorus inputs and outputs, a small accumulation of phosphorus in the soil still occurs each year. In contrast, the Prairie Provinces had zero or negative phosphorus balances for the first few Census years, but this trend has been reversed with the intensification of production and increases in fertilizer use. The greatest increase has been recorded in Manitoba.

Figure 4: Phosphorus balance (in kilograms per hectare - kg ha-1) by province, between 1981 and 2011
Description of this image follows.
Description - Figure 4
Phosphorus balance, in kilograms per hectare, by province, between 1981 and 2011
1981 1986 1991 1996 2001 2006 2011
British Columbia 4.53 5.04 4.69 5.90 5.76 4.77 2.11
Alberta -1.18 0.12 1.80 2.25 4.98 5.13 2.39
Saskatchewan -0.85 -0.46 -0.69 -0.32 2.32 2.32 1.55
Manitoba 0.28 1.69 2.68 2.51 4.41 4.31 5.77
Ontario 5.45 5.05 3.59 2.21 3.94 0.96 1.73
Quebec 13.63 14.58 15.05 11.47 8.56 5.50 8.98
Atlantic Provinces 17.60 20.43 19.93 17.74 19.93 17.30 16.18

*Atlantic provinces include New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland and Labrador.

Trend 2 – Wet weather increases risk of contamination

In addition to the accumulation of phosphorus in the soils, the second main factor affecting the risk of contamination is transportation—that is, how the phosphorus can be moved from the soils to surface water. The primary means of transportation is water, through snowmelt runoff or rainfall, particularly storm events. In 2011, areas in the southern Prairies that showed high risk values actually had quite low phosphorus source ratings, but very high phosphorus transport risk because of the extreme weather conditions that year. Figure 5 shows the flows in the Assiniboine River at Headingley, Manitoba, illustrating the unusually wet conditions in the spring and summer of 2011. In that year the amount of snowmelt in the Prairie Provinces was much greater than in 2006 and approximately double that of 2001, when the overall risk values were much lower. The record snowmelt coincided with above-average spring rainfall, leading to record runoff levels and significant flooding throughout the southern Prairies. This wet weather dramatically increased the phosphorus risk values for the Prairies that year and affected the national trend for this indicator. Conversely, the very low risk values in 2001 can be attributed to the exceptionally low amounts of runoff from both snowmelt and rainfall in the Prairies that year, which reduced the risk of water contamination from phosphorus. Conditions in Eastern Canada were stable from 2006 to 2011.

Figure 5: Comparison of flow rates at the Headingley, Manitoba gauge station on the Assiniboine River in 2001 and 2011 (Environment Canada Water Office, 2015)
Description of this image follows.
Description - Figure 5
Average daily discharge in cubic metres by month, 2001
January 41 cubic metres
February 40 cubic metres
March 30 cubic metres
April 131 cubic metres
May 287 cubic metres
June 112 cubic metres
July 90 cubic metres
August 44 cubic metres
September 26 cubic metres
October 22 cubic metres
November 24 cubic metres
December 55 cubic metres
Average daily discharge in cubic metres by month, 2011
January 87 cubic metres
February 78 cubic metres
March 64 cubic metres
April 210 cubic metres
May 507 cubic metres
June 512 cubic metres
July 470 cubic metres
August 349 cubic metres
September 175 cubic metres
October 108 cubic metres
November 64 cubic metres
December 62 cubic metres

Why this indicator matters

Phosphorus is an essential nutrient for all plants and animals. It is applied to soils in the form of fertilizers, manures and biosolids in order to maintain crop yields. Since the early 1950s, intensified cropping and animal production have increased soil nutrients in some regions to levels exceeding crop needs. These surpluses have enriched the soil and increased the risk of transport from agricultural fields to surface water bodies. Excessive inputs of phosphorus can contribute to eutrophication of freshwater and development of algal blooms, which can lead to the deterioration of water quality and to restrictions on the use of water bodies for drinking water and recreational activities, such as swimming. The loss of soil phosphorus is not only an environmental concern; it represents an economic loss to producers since this valuable nutrient is not available for crop production.

Agriculture has the potential to mitigate risk from phosphorus by implementing beneficial management practices (BMPs) that reduce application rates or that prevent phosphorus from reaching water bodies.

Beneficial Management Practices

Strategies for reducing the risk of water contamination by phosphorus include better matching the amount of phosphorus applied with the needs of crops and reducing the risk of transport to surface water.

Soil testing is an essential step for measuring how much phosphorus is in the soil prior to the application of fertilizer or manure, which can then be adjusted accordingly. The addition of forages or other crops that have a high phosphorus uptake into crop rotations can help remove excess phosphorus and reduce the soil's phosphorus balance. Livestock producers can reduce the phosphorus content of manure by switching to feed containing the enzyme phytase, which helps animals digest phytate, the principle storage form for phosphorus in plant material. Because surface runoff is such an important transport mechanism, it is critical that fertilizers and manures only be applied in suitable weather conditions and with the recommended application techniques. Buffer strips established around surface water bodies can help to trap and filter particulate phosphorus from surface runoff, and the use of plant species that have an economic value can help offset the cost of implementing and maintaining these structures.

How performance indices are calculated

The agri-environmental performance index shows environmental performance state and trends over time, based on weighting the percentage of agricultural land in each indicator class, such that the index ranges from 0 (all land in the most undesirable category) to 100 (all land in the most desirable category). The equation is simply "(% in poor class multiplied by .25) plus (% in moderate class multiplied by .5) plus (% in good class multiplied by .75) plus (% in desired class)." As the percentage of land in the "at risk" class is multiplied by zero, it is not included in the algorithm.

The table below shows the index classes. The index uses the same five-colour scheme as the indicator maps whereby dark green represents a desirable or healthy state and red represents least desirable or least healthy.

The index classes
Scale Colour scheme Class
80-100 Dark green Desired
60-79 Light green Good
40-59 Yellow Moderate
20-39 Orange Poor
0-19 Red At risk

The index tends to aggregate and generalize trends and so should be viewed as a policy tool to give a general overview of state and trend over time.

Related indicators

Additional resources and downloads

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