Nutrients in Lake Winnipeg

Phosphorus and nitrogen levels in Lake Winnipeg

Key results

• In Lake Winnipeg, the highest levels of phosphorus and nitrogen in 2016 are found in the south basin near the inflow from the Red River. Levels decline as the water flows north
• In the 3 largest tributary rivers, for the 2014 to 2016 period
  • high phosphorus levels were detected frequently in the Red and Winnipeg rivers and intermittently in the Saskatchewan River
  • high nitrogen levels were detected frequently in the Red River and in the Winnipeg River, but rarely in the Saskatchewan River

Status of phosphorus and nitrogen levels in Lake Winnipeg, 2016, and its 3 largest tributary rivers, Canada, 2014 to 2016

How this indicator was calculated

Note: For Lake Winnipeg, an objective for total nitrogen of 0.75 milligrams per litre (mg N/L) and an objective for total phosphorus of 0.05 milligrams per litre (mg P/L) were used. For the Red, Winnipeg and Saskatchewan rivers, water quality is considered good when water quality measurements exceed the river's nutrient criteria or objective less than 10% of the time (see Data sources and methods). A fair status is applied when the nutrient criteria or objective is exceeded 10% to 50% of the time. Poor status is applied when measurements are above the nutrient criteria or objective in over 50% of samples.
Source: Manitoba Sustainable Development and Environment and Climate Change Canada.

Phosphorus levels by water quality monitoring site

Key Results

• Phosphorus levels are fluctuating but no trends between 1999 and 2016 can be detected at any of the sites

Annual total phosphorus concentrations in Lake Winnipeg and its 3 largest tributary rivers, Canada, 1999 to 2016

Note: The dotted line shows the objective or criteria value of 0.05 milligrams of phosphorus per litre (mg P/L) for Lake Winnipeg, 0.058 mg P/L (an average of the seasonal objectives) for the Saskatchewan River, 0.102 mg P/L for the Red River, and 0.012 mg P/L for the Winnipeg River. The solid (blue) line links the symbols to show the tendency in the average values. For the north basin and south basin and narrows, data are seasonally-weighted averages and vertical bars show annual minimum and maximum concentrations. For the Saskatchewan, Red and Winnipeg rivers, each boxplot summarizes annual phosphorus levels at a monitoring site and shows the range of values measured.
Source: Manitoba Sustainable Development and Environment and Climate Change Canada.

Nitrogen levels by water quality monitoring site

Key Results

• Nitrogen levels are not changing at any of the sites

Annual total nitrogen concentrations in Lake Winnipeg and its 3 largest tributary rivers, Canada, 1999 to 2016

Note: The dotted line shows the objective or criteria value of 0.75 milligrams of nitrogen per litre (mg N/L) for Lake Winnipeg, 0.80 mg N/L (an average of the seasonal objectives) for the Saskatchewan River, 1.4 mg N/L for the Red River, and 0.44 mg N/L for the Winnipeg River. The solid (blue) line links the symbols to show the tendency in the average values. For the north basin and south basin and narrows, data are seasonally-weighted averages and vertical bars show annual minimum and maximum concentrations. For the Saskatchewan, Red and Winnipeg rivers, each boxplot summarizes annual nitrogen levels at a monitoring site and shows the range of values measured.
Source: Manitoba Sustainable Development and Environment and Climate Change Canada.

About the indicator

What the indicator measures

The Phosphorus and nitrogen levels in Lake Winnipeg indicator reports on the status of total phosphorus and total nitrogen levels in Lake Winnipeg and its 3 largest tributaries: the Red, Saskatchewan and Winnipeg rivers.

The indicator assumes that water in the region would never be above phosphorus and nitrogen water quality criteria or objectives in the absence of human development. It provides information about how human activity contributes to phosphorus and nitrogen levels in lakes and rivers.

The phosphorus and nitrogen status in Lake Winnipeg is established by comparing phosphorus and nitrogen levels to water quality objectives. Failure to meet a water quality objective suggests a greater risk to the health of the lake ecosystem. In rivers, phosphorus and nitrogen status is determined by the frequency with which a water quality objective is exceeded. The more often the criteria or objective is exceeded, the greater the risk to the health of the river ecosystems.

Why the indicator is important

Clean freshwater is an essential resource. It protects the biodiversity of aquatic plants and animals. We use it for drinking, manufacturing, energy production, irrigation, swimming, boating and fishing. Degraded water quality damages the health of freshwater ecosystems and can disrupt economic activities, such as fisheries, tourism and agriculture. When phosphorus and nitrogen levels in water become too high, aquatic plant growth can become excessive and harmful. The decay of excess plant material can reduce the amount of oxygen available for fish and other aquatic animals. High nutrient levels can also lead to harmful algal blooms, which can kill animals that use the water and affect human health. Conversely, too little phosphorus or nitrogen can result in not enough plant growth to support a lake's food web, which can result in a collapse of the fishery.

The indicator is used to provide information about the state of the Lake Winnipeg Basin and Canadian environment. It is also used to assess progress towards the goals of the 2016–2019 Federal Sustainable Development Strategy.

Related indicators

The Phosphorus levels in the offshore waters of the Canadian Great Lakes and the Nutrients in the St. Lawrence River indicators report the status of total phosphorus and total nitrogen levels in those 2 ecosystems.

The Reductions in phosphorus loads to Lake Winnipeg indicator shows the extent to which projects funded by the Lake Winnipeg Basin Stewardship Fund (April 2010 to March 2017) and the Lake Winnipeg Basin Program (since March 2017) have reduced the amount of phosphorus reaching the lake from its watershed.

The Water quality in Canadian rivers indicator ranks water quality at monitoring sites across Canada where human activity is likely to harm a river's ecosystem.

The Household use of chemical pesticides and fertilizers indicator reports on how many people in Canada use pesticides and fertilizers on their lawns and gardens.

Pristine lakes and rivers

The indicator supports the measurement of progress towards the following 2016–2019 Federal Sustainable Development Strategy long-term goal: Clean and healthy lakes and rivers support economic prosperity and the well-being of Canadians.

Data sources and methods

Data sources

Manitoba Sustainable Development's Water Quality Management Section collects and provides the average phosphorus and nitrogen concentration data for Lake Winnipeg.

Data for the Red, Winnipeg and Saskatchewan rivers are collected by the Freshwater Quality Monitoring and Surveillance Division of Environment and Climate Change Canada. The indicator is calculated using the most recent data available for the lake and each of the 3 rivers.

Methods

For the status of phosphorus and nitrogen levels in Lake Winnipeg, seasonally-weighted, average phosphorus and nitrogen concentrations for 2016 were compared to water quality objectives. The status of phosphorus and nitrogen levels was categorized as good (at or near the guideline) or poor (above the guideline).

For the status in the Red, Saskatchewan and Winnipeg rivers, the number of times total phosphorus and total nitrogen samples are above water quality guidelines is counted and divided by the total number of samples taken between 2014 and 2016. The status of phosphorus and nitrogen levels was categorized on the basis of how frequently levels are above their guidelines.

Recent changes

The Phosphorus and nitrogen levels in Lake Winnipeg indicator now includes data for 2014, 2015 and 2016.

The water quality guideline for total nitrogen at all sites was changed from 1 milligram of nitrogen per litre (mg N/L) to a more appropriate site-specific target for each site.

Phosphorus guidelines were changed for the rivers to match the nitrogen guidelines:

• for Lake Winnipeg, a total nitrogen objective of 0.75 mg N/L was used for the north basin and south basin and narrows
• for the Red River, the United States Environmental Protection Agency's nutrient criteria for nutrient ecoregion 46 of 0.102 mg P/L and 1.4 mg N/L were used
• for the Saskatchewan River, the Prairie Provinces Water Board's 2015 interprovincial nutrient objectives of 0.088 mg P/L and 0.838 mg N/L for open-water periods and 0.028 mg P/L and 0.761 mg N/L for ice-covered months were used
• for the Winnipeg River, the United States Environmental Protection Agency's nutrient criteria for nutrient ecoregion 50 of 0.012 mg P/L and 0.44 mg N/L were used

These changes had affected nitrogen level status for all sites. The changes in status do not reflect a change in water quality at these sites due to increased nitrogen pollution; it reflects the changes in the guidelines.

Caveats and limitations

The Phosphorus and nitrogen levels in Lake Winnipeg indicator reflects the overall state of phosphorus and nitrogen levels in the Lake Winnipeg basin. It does not show the effect of spills or other transient events, unless these are frequent or long-lasting.

Even where the average levels are generally below the guideline, the maximum recorded values may still be above.

The calculation used for the indicator for the tributaries is different from that used for the lake. This difference exists because total phosphorus concentrations in rivers are influenced by suspended particles in the water, which may increase during high-flow events. Allowing for some natural exceedances associated with high-flow events is important. The ratings for Lake Winnipeg and its tributaries are, however, comparable, with the poor status showing the highest level of impairment by phosphorus or nitrogen in both cases.

Resources

References

Bunting L, PR Leavitt, B Wissel, KR Laird, BF Cumming, A St. Amand, BJ Hann and DR Engstrom (2011) Sudden ecosystem state change in Lake Winnipeg, Canada, caused by eutrophication arising from crop and livestock production during the 20th century. 132 p.

Prairie Provinces Water Board (2015) 2015 Interprovincial Water Quality Objectives (PDF; 422 kB). Retrieved on August 22, 2017.

United States Environmental Protection Agency (2000) Ambient Water Quality Criteria Recommendations Information Supporting the Development of State and Tribal Nutrient Criteria for Rivers and Streams in Nutrient Ecoregion VI: Corn Belt and Northern Great Plains. Report No. EPA-822-B-00-017. United States Environmental Protection Agency. Washington, D.C. (PDF; 326 kB). Retrieved on August 22, 2017.

United States Environmental Protection Agency (2001) Ambient Water Quality Criteria Recommendations Information Supporting the Development of State and Tribal Nutrient Criteria for Rivers and Streams in Nutrient Ecoregion VIII: Nutrient-Poor, Largely Glaciated Upper Midwest and Northeast. Report No. EPA-822-B-01-015. United States Environmental Protection Agency. Washington, D.C. (PDF; 2.53 MB). Retrieved on August 22, 2017.

Related information

• Manitoba Sustainable Development – Lake Winnipeg
• Manitoba Sustainable Development – State of Lake Winnipeg Report