Nutrients in the St. Lawrence River

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Phosphorus and nitrogen levels at the majority of water quality monitoring stations along the St. Lawrence River were above water quality guidelines more than 50% of the time during the 2012–2014 period. Higher phosphorus and nitrogen levels were found at stations next to agricultural areas along the south shore of the river between Richelieu and Bécancour.

Compared with the 2010–2012 period, two monitoring stations saw their status in terms of phosphorus levels change:

  • The status at Saint-François improved from > 50% of samples above the guideline to 10–50% above
  • The status at Carillon deteriorated from < 10% of samples above the guideline to 10–50% above

For nitrogen, a more precise guideline of 0.63 milligrams per litre was established specifically for the St. Lawrence River in 2016. As a result, the water quality at seven stations appears to have changed, even though there were no changes in nitrogen levels over the same period. The change in the guideline value did not impact the nitrogen status at the Saint-Maurice or Yamaska stations.

Only the stations at Carillon and Quebec City have data for phosphorus starting in 2005, which allows for an assessment of trends. Phosphorus levels in water entering the St. Lawrence River at Carillon decreased between 2005 and 2014 and showed no trend at Quebec City over the same period

Status of total phosphorus and total nitrogen levels in the St. Lawrence River, Canada, 2012 to 2014, and total phosphorus level trends at Carillon and Quebec City, 2005 to 2014

Map of St. Lawrence River - See long description below

Long description

The map shows the status of phosphorus and nitrogen levels at nine water quality monitoring stations along the St. Lawrence River. The total phosphorus status is green (less than 10% of samples above the guideline) at the Saint-Maurice station, yellow (between 10 and 50% of samples above the guideline) at the Carillon, Saint-François and Quebec City stations, and red (more than 50% of samples above the guideline) at the Lavaltrie, Richelieu, Yamaska, Nicolet and Bécancour stations.

The total nitrogen status is green (less than 10% of samples above the guideline) at the Saint-Maurice station, yellow (between 10 and 50% of samples above the guideline) at the Carillon station, and red (more than 50% of samples above the guideline) at the Lavaltrie, Yamaska, Richelieu, Saint-François, Nicolet, Bécancour and Quebec City stations.

The map shows that phosphorus levels decreased at Carillon and showed no trend at Quebec City between 2005 and 2014.

Data for this map
Status of total phosphorus and total nitrogen levels in the St. Lawrence River, Canada, 2012 to 2014, and total phosphorus level trends at Carillon and Quebec City, 2005 to 2014
Monitoring station2012–2014 Total phosphorus guideline exceedance
(percent)
Total phosphorus status2012–2014 Total nitrogen guideline exceedance
(percent)
Total nitrogen statusTrend
1995 to 2014
Carillon20Yellow22YellowPhosphorus levels are decreasing
Lavaltrie89Red89Redn/a
Richelieu65Red51Redn/a
Yamaska96Red96Redn/a
Saint-François44Yellow92Redn/a
Nicolet84Red71Redn/a
Saint-Maurice8Green3Greenn/a
Bécancour56Red65Redn/a
Quebec City36Yellow52RedPhosphorus levels show no trend

Note: n/a = not available.

Download data file (Excel/CSV; 1.82 KB)


How this indicator was calculated

Note: Water quality at a monitoring station is considered green when ambient water quality exceeds the guideline less than 10% of the time. A yellow status is applied when the guideline is exceeded 10–50% of the time. Red status is applied when exceedances occur in over 50% of samples. The status of total phosphorus and total nitrogen at water quality monitoring stations was determined by comparing water quality monitoring data to Quebec's total phosphorus water quality guideline of 0.03 milligrams of phosphorus per litre (mg P/L) Footnote [1] and total nitrogen water quality guideline of 0.63 milligrams of nitrogen per litre (mg N/L). The nitrogen guideline was changed from 1 mg N/L to 0.63 mg N/L for this update; for more details about the water quality guidelines, please refer to the Data Sources and Methods.
Source: St. Lawrence River Water Quality Monitoring and Surveillance Division (2015) Environment and Climate Change Canada.

The St. Lawrence River links the Great Lakes with the Atlantic Ocean and is among the world's most important commercial waterways. It is a complex ecosystem that includes freshwater lakes and river reaches, a long estuary, and a salt-water gulf. Its many different habitats are home to a diverse range of plants, fish and animals.

Phosphorus and nitrogen levels in the St. Lawrence River are affected by a variety of human activities along the river. Just downstream of Montreal, at Lavaltrie, phosphorus and nitrogen levels exceeded the water quality guidelines because of the release of municipal wastewater into the river. Further along, tributary rivers draining agricultural regions bring more phosphorus and nitrogen with them from the chemical fertilizers and manure used to grow crops. Just upstream of Quebec City, water from tributary rivers draining the north shore have lower phosphorus and nitrogen levels because they run through a more forested area than the land on the south shore of the river. The cleaner water allows phosphorus and nitrogen levels in the water to decline to levels closer to the guidelines. Past Quebec City, the St. Lawrence River flows into the Gulf of the St. Lawrence, where the nitrogen and phosphorus levels contribute to harmful algal blooms.

Phosphorus and nitrogen are key nutrients for plant growth in lakes and rivers. They are both naturally occurring and manufactured by human activity. Natural sources of phosphorus include weathering of rocks and decomposition of plants and animals. Nitrogen is added to the environment by bacteria that convert nitrogen gas in the air into forms plants can use for growth. Phosphorus and nitrogen from human activity enters the St. Lawrence River through municipal and industrial wastewaters, agricultural runoff, and air pollution. Problems arise when too much, or too little, nitrogen and phosphorus enters the environment. When phosphorus and nitrogen levels in water become too high, aquatic plant growth thrives and can cause excessive blooms. The decay of excess plant material can reduce the amount of oxygen available for fish and other aquatic animals. Further, high nutrient levels can also lead to harmful algal blooms, which can kill animals that use the water and affect human health.

Phosphorus levels by water quality monitoring stations

Plotting phosphorus data for each station for each year provides a general view of how phosphorus levels are changing along the St. Lawrence River. Each boxplot summarizes annual phosphorus levels at a monitoring station and shows the range of values measured. The boxes are joined by a solid line (red) to give a sense of the direction of change in phosphorus levels over time.

Trend analysis can be performed for Carillon and Quebec City, where data are available from 2005. The analysis indicates a decreasing trend at Carillon, and no change at Quebec City. While this analysis cannot be performed for other stations, the available data suggest that phosphorus levels are slowly falling at the Saint-François station and are not changing at any of the other stations along the river.

Annual total phosphorus boxplots for nine water quality monitoring stations along the St. Lawrence River

Annual phosphorus boxplots - see long description below

Long description

The graphic presents annual phosphorus boxplots from 2008 to 2014 for six water quality monitoring stations along the St. Lawrence River (Richelieu, Yamaska, Saint-François, Nicolet, Bécancour and Saint-Maurice), from 2009 to 2014 for the Lavaltrie monitoring station, and from 2005 to 2014 for the Carillon and Quebec City monitoring stations. The boxes are joined by a solid line (red) to give a sense of the direction of change in phosphorus levels over time. A dotted line is also provided in each boxplot representing Quebec's water quality guideline for phosphorus of 0.03 milligrams of phosphorus per litre.

Data for Carillon
Data for Carillon
Monitoring stationYearMedian phosphorus level
(milligrams of phosphorus per litre)
Minimum phosphorus level
(milligrams of phosphorus per litre)
Maximum phosphorus level
(milligrams of phosphorus per litre)
Number of samples
Carillon20050.0280.0180.15023
Carillon20060.0240.0160.05120
Carillon20070.0210.0100.04420
Carillon20080.0210.0150.06514
Carillon20090.0200.0160.05817
Carillon20100.0190.0090.03014
Carillon20110.0120.0080.02114
Carillon20120.0190.0080.02514
Carillon20130.0240.0140.04613
Carillon20140.0220.0150.03414
Data for Lavaltrie
Data for Lavaltrie
Monitoring stationYearMedian phosphorus level
(milligrams of phosphorus per litre)
Minimum phosphorus level
(milligrams of phosphorus per litre)
Maximum phosphorus level
(milligrams of phosphorus per litre)
Number of samples
Lavaltrie20090.0600.0300.0759
Lavaltrie20100.0500.0320.07412
Lavaltrie20110.0550.0160.18312
Lavaltrie20120.0400.0230.08812
Lavaltrie20130.0460.0320.11213
Lavaltrie20140.0400.0300.05812
Data for Richelieu
Data for Richelieu
Monitoring stationYearMedian phosphorus level
(milligrams of phosphorus per litre)
Minimum phosphorus level
(milligrams of phosphorus per litre)
Maximum phosphorus level
(milligrams of phosphorus per litre)
Number of samples
Richelieu20080.0300.0160.11812
Richelieu20090.0300.0180.11810
Richelieu20100.0390.0190.07212
Richelieu20110.0430.0200.06612
Richelieu20120.0440.0170.12312
Richelieu20130.0370.0190.19213
Richelieu20140.0300.0190.11012
Data for Yamaska
Data for Yamaska
Monitoring stationYearMedian phosphorus level
(milligrams of phosphorus per litre)
Minimum phosphorus level
(milligrams of phosphorus per litre)
Maximum phosphorus level
(milligrams of phosphorus per litre)
Number of samples
Yamaska20080.1060.0440.14319
Yamaska20090.1130.0660.52017
Yamaska20100.0900.0150.16418
Yamaska20110.1220.0600.17514
Yamaska20120.1400.0930.1957
Yamaska20130.1310.0840.1569
Yamaska20140.1080.0150.1369

Note: Samples from the mouth of the Yamaska River are collected from May until the end of September only.

Data for Saint-François
Data for Saint-François
Monitoring stationYearMedian phosphorus level
(milligrams of phosphorus per litre)
Minimum phosphorus level
(milligrams of phosphorus per litre)
Maximum phosphorus level
(milligrams of phosphorus per litre)
Number of samples
Saint-François20080.0350.0210.10815
Saint-François20090.0330.0210.10515
Saint-François20100.0270.0210.05515
Saint-François20110.0310.0210.17214
Saint-François20120.0300.0270.0357
Saint-François20130.0310.0250.0649
Saint-François20140.0230.0190.0289

Note: Samples from the mouth of the Saint-François River are collected from May until the end of September only.

Data for Nicolet
Data for Nicolet
Monitoring stationYearMedian phosphorus level
(milligrams of phosphorus per litre)
Minimum phosphorus level
(milligrams of phosphorus per litre)
Maximum phosphorus level
(milligrams of phosphorus per litre)
Number of samples
Nicolet20080.0460.0250.10215
Nicolet20090.0530.0360.12615
Nicolet20100.0530.0420.11615
Nicolet20110.0500.0100.07314
Nicolet20120.0710.0470.0857
Nicolet20130.0460.0350.0539
Nicolet20140.0310.0290.0399

Note: Samples from the mouth of the Nicolet River are collected from May until the end of September only.

Data for Bécancour
Data for Bécancour
Monitoring stationYearMedian phosphorus level
(milligrams of phosphorus per litre)
Minimum phosphorus level
(milligrams of phosphorus per litre)
Maximum phosphorus level
(milligrams of phosphorus per litre)
Number of samples
Bécancour20080.0370.0130.29312
Bécancour20090.0380.0240.06212
Bécancour20100.0380.0200.17212
Bécancour20110.0410.0240.10312
Bécancour20120.0300.0130.08712
Bécancour20130.0430.0220.13612
Bécancour20140.0310.0070.06712
Data for Saint-Maurice
Data for Saint-Maurice
Monitoring stationYearMedian phosphorus level
(milligrams of phosphorus per litre)
Minimum phosphorus level
(milligrams of phosphorus per litre)
Maximum phosphorus level
(milligrams of phosphorus per litre)
Number of samples
Saint-Maurice20090.0150.0100.04810
Saint-Maurice20100.0150.0090.18412
Saint-Maurice20110.0080.0050.01513
Saint-Maurice20120.0140.0100.02412
Saint-Maurice20130.0150.0120.25013
Saint-Maurice20140.0150.0080.14712
Data for Quebec City
Data for Quebec City
Monitoring stationYearMedian phosphorus level
(milligrams of phosphorus per litre)
Minimum phosphorus level
(milligrams of phosphorus per litre)
Maximum phosphorus level
(milligrams of phosphorus per litre)
Number of samples
Quebec City20050.0330.0190.13516
Quebec City20060.0340.0190.13516
Quebec City20070.0260.0130.07218
Quebec City20080.0290.0200.08018
Quebec City20090.0250.0080.07017
Quebec City20100.0250.0130.06217
Quebec City20110.0300.0150.10417
Quebec City20120.0300.0130.04920
Quebec City20130.0360.0150.07515
Quebec City20140.0330.0130.05815

Download data file (Excel/CSV; 3.16 KB)
How this indicator was calculated

Note: The dotted line shows the guideline value of 0.03 mg P/L. The solid (red) line is drawn through the median to give a sense of the changes in concentrations over time. Only the Carillon and Quebec City stations have enough data for a seasonal Mann-Kendall trend analysis for phosphorus.
Source: St. Lawrence River Water Quality Monitoring and Surveillance Division (2015) Environment and Climate Change Canada.

Nitrogen levels by water quality monitoring stations

Plotting nitrogen data for each station for each year provides a general view of how nitrogen levels are changing over time along the St. Lawrence River. Each boxplot below summarizes annual nitrogen levels for a monitoring station and shows the range of values measured. The boxes are joined by a solid line (red) to give a sense of the direction of change in nitrogen levels over time.

None of the stations have enough data to perform a trend analysis. However, the information available suggest nitrogen levels have declined at the Richelieu, Yamaska and Nicolet stations and are not changing at any of the other stations along the river.

Annual total nitrogen boxplots for nine water quality monitoring stations along the St. Lawrence River

Annual nitrogen boxplots - see long description below

Long description

The graphic presents annual nitrogen levels from 2009 to 2014 for eight water quality monitoring stations along the St. Lawrence River (Carillon, Lavaltrie, Yamaska, Saint-François, Nicolet, Bécancour, Saint-Maurice and Quebec City) and from 2010 to 2014 for the Richelieu monitoring station. The boxes are joined by a solid line (red) to give a sense of the direction of change in nitrogen levels over time. A dotted line is also provided in each boxplot representing the water quality guideline for nitrogen of 0.63 milligrams of nitrogen per litre derived for the St. Lawrence River.

Data for Carillon
Data for Carillon
Monitoring stationYearMedian nitrogen level
(milligrams of nitrogen per litre)
Minimum nitrogen level
(milligrams of nitrogen per litre)
Maximum nitrogen level
(milligrams of nitrogen per litre)
Number of samples
Carillon20090.4920.4260.71311
Carillon20100.5430.4500.89714
Carillon20110.5400.4400.87014
Carillon20120.5300.4400.69013
Carillon20130.5700.4801.0613
Carillon20140.5150.4001.0714
Data for Lavaltrie
Data for Lavaltrie
Monitoring stationYearMedian nitrogen level
(milligrams of nitrogen per litre)
Minimum nitrogen level
(milligrams of nitrogen per litre)
Maximum nitrogen level
(milligrams of nitrogen per litre)
Number of samples
Lavaltrie20090.9000.5801.409
Lavaltrie20100.8750.6701.4412
Lavaltrie20110.9200.5801.3512
Lavaltrie20120.9100.6101.7712
Lavaltrie20130.9500.7301.8612
Lavaltrie20140.8900.5401.2512
Data for Richelieu
Data for Richelieu
Monitoring stationYearMedian nitrogen level
(milligrams of nitrogen per litre)
Minimum nitrogen level
(milligrams of nitrogen per litre)
Maximum nitrogen level
(milligrams of nitrogen per litre)
Number of samples
Richelieu20100.7800.5201.029
Richelieu20110.6500.4301.0312
Richelieu20120.6450.4002.0312
Richelieu20130.7050.4002.5212
Richelieu20140.6000.4101.1612
Data for Yamaska
Data for Yamaska
Monitoring stationYearMedian nitrogen level
(milligrams of nitrogen per litre)
Minimum nitrogen level
(milligrams of nitrogen per litre)
Maximum nitrogen level
(milligrams of nitrogen per litre)
Number of samples
Yamaska20093.581.466.4815
Yamaska20102.271.253.9115
Yamaska20111.921.175.7014
Yamaska20120.750.6601.377
Yamaska20131.871.074.129
Yamaska20141.170.5702.609

Note: Samples from the mouth of the Yamaska River are collected from May until the end of September only.

Data for Saint-François
Data for Saint-François
Monitoring stationYearMedian nitrogen level
(milligrams of nitrogen per litre)
Minimum nitrogen level
(milligrams of nitrogen per litre)
Maximum nitrogen level
(milligrams of nitrogen per litre)
Number of samples
Saint-François20090.7700.6501.1215
Saint-François20100.8000.4601.0715
Saint-François20110.8300.5902.4214
Saint-François20120.8100.7101.047
Saint-François20130.7600.6101.119
Saint-François20140.7400.6000.8709

Note: Samples from the mouth of the Saint-François River are collected from May until the end of September only.

Data for Nicolet
Data for Nicolet
Monitoring stationYearMedian nitrogen level
(milligrams of nitrogen per litre)
Minimum nitrogen level
(milligrams of nitrogen per litre)
Maximum nitrogen level
(milligrams of nitrogen per litre)
Number of samples
Nicolet20091.560.7302.5715
Nicolet20100.9400.5501.8115
Nicolet20110.9900.5702.9014
Nicolet20120.6800.4002.0316
Nicolet20131.280.7101.949
Nicolet20140.6700.3401.229

Note: Samples from the mouth of the Nicolet River are collected from May until the end of September only.

Data for Bécancour
Data for Bécancour
Monitoring stationYearMedian nitrogen level
(milligrams of nitrogen per litre)
Minimum nitrogen level
(milligrams of nitrogen per litre)
Maximum nitrogen level
(milligrams of nitrogen per litre)
Number of samples
Bécancour20090.8550.3701.2110
Bécancour20100.9250.4701.4712
Bécancour20110.9150.4701.4212
Bécancour20120.6650.4201.2912
Bécancour20130.9350.4901.2912
Bécancour20140.7650.4401.3912
Data for Saint-Maurice
Data for Saint-Maurice
Monitoring stationYearMedian nitrogen level
(milligrams of nitrogen per litre)
Minimum nitrogen level
(milligrams of nitrogen per litre)
Maximum nitrogen level
(milligrams of nitrogen per litre)
Number of samples
Saint-Maurice20090.3600.2700.3809
Saint-Maurice20100.3150.2430.63012
Saint-Maurice20110.3400.2900.41713
Saint-Maurice20120.3300.2700.40012
Saint-Maurice20130.3300.2700.76013
Saint-Maurice20140.3400.2800.56012
Data for Quebec City
Data for Quebec City
Monitoring stationYearMedian nitrogen level
(milligrams of nitrogen per litre)
Minimum nitrogen level
milligrams of nitrogen per litre)
Maximum nitrogen level
(milligrams of nitrogen per litre)
Number of samples
Quebec City20090.5950.4200.90014
Quebec City20100.6300.4000.96017
Quebec City20110.6200.4300.97017
Quebec City20120.6050.3301.0220
Quebec City20130.7150.4500.94014
Quebec City20140.6450.4800.89014

Download data file (Excel/CSV; 2.51 KB)
How this indicator was calculated

Note: The dotted line shows the guideline value of 0.63 mg N/L. The solid line (red) is drawn through the median to give a sense of trends in concentration.
Source: St. Lawrence River Water Quality Monitoring and Surveillance Division (2015) Environment and Climate Change Canada.

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This indicator is used to measure progress towards Target 3.5: St. Lawrence River – Take federal actions to reduce pollutants in order to improve water quality, conserve biodiversity and ensure beneficial uses in the St. Lawrence River by 2016 of the Federal Sustainable Development Strategy 2013–2016.

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