Nutrients in the St. Lawrence River

Access PDF (871 kB)

Phosphorus and nitrogen are essential plant nutrients. When phosphorus or nitrogen levels in a river are too high or too low, however, these nutrients can have harmful effects on the food web. They are an important measure of the health of the river and its surrounding watersheds. This indicator provides the status of phosphorus and nitrogen levels along the St. Lawrence River.

Key results

Key results

  • During the 2015 to 2017 period:
    • phosphorus and nitrogen levels exceeded water quality guidelines at most monitoring stations (8 out of 9 stations)
    • only at Saint-Maurice did phosphorus and nitrogen level exceedances occur in less than 10% of samples
  • From 2008 to 2017:
    • of the 7 sites with sufficient data to estimate trends in phosphorus, Quebec City had increased levels while Saint-François and Yamaska had decreased levels
    • not enough data was available to estimate trends in nitrogen

Status of total phosphorus and total nitrogen levels for the 2015 to 2017 period and total phosphorus level trends in the St. Lawrence River, Canada, 2008 to 2017

Status of total phosphorus and total nitrogen levels for the 2015 to 2017 period and total phosphorus level trends in the St. Lawrence River, Canada, 2008 to 2017 (see data table below for the long description)
Data table for the long description
Status of total phosphorus and total nitrogen levels for the 2015 to 2017 period and total phosphorus level trends in the St. Lawrence River, Canada, 2008 to 2017
Monitoring station 2015 to 2017 total phosphorus guideline exceedance
(percentage)
Total phosphorus status 2015 to 2017 total nitrogen guideline exceedance
(percentage)
Total nitrogen status 2008 to 2017 total phosphorus trend
Carillon 24 Yellow 33 Yellow Phosphorous levels show no trend
Lavaltrie 94 Red 91 Red Insufficient data to test for trends
Richelieu 72 Red 56 Red Phosphorous levels show no trend
Yamaska 100 Red 96 Red Phosphorous levels are decreasing
Saint-François 33 Yellow 96 Red Phosphorous levels are decreasing
Nicolet 89 Red 95 Red Phosphorous levels show no trend
Saint-Maurice 8 Green 0 Green Insufficient data to test for trends
Bécancour 83 Red 72 Red Phosphorous levels show no trend
Quebec City 68 Red 63 Red Phosphorous levels are increasing

Download data file (Excel/CSV; 2.01 kB)

How this indicator was calculated

Note: Water quality at a monitoring station is considered Green when nutrient levels (phosphorus or nitrogen) exceed the guideline less than 10% of the time. A Yellow status is applied when the guideline is exceeded 10% to 50% of the time. A 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 a derived total nitrogen water quality guideline of 0.63 milligrams of nitrogen per litre (mg N/L). 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 (2018) Environment and Climate Change Canada.

More information

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. Farther downstream, tributary rivers draining agricultural regions transport higher concentrations of phosphorus and nitrogen which result from the chemical fertilizers and manure used to grow crops. Upstream of Quebec City, water from tributary rivers such as the Saint-Maurice which drain the north shore have lower phosphorus and nitrogen levels because they run through an area with more forest cover than that found on the south shore of the river. Past Quebec City, the St. Lawrence River flows into the Gulf of St. Lawrence, where the nitrogen and phosphorus levels contribute to harmful algal blooms.

During the 2015 to 2017 period, 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. There is sufficient data to estimate trends for phosphorus alone at 7 stations. One station (Quebec City) shows an increasing trend from 2008 to 2017 while 2 stations show a decrease. The other 4 stations show no trends.

For the St. Lawrence River, water quality at a monitoring station is considered to be minimally impacted by nutrients from human activities when fewer than 10% of samples exceed the water quality guidelines for total phosphorus or total nitrogen. The 10% cut-off limit allows for 1 sample per year to exceed the guideline. In rivers, total phosphorus and total nitrogen concentrations will often exceed the guidelines when water levels are high, a situation that is mainly observed when the snow melts in the spring.

When 10% to 50% of the samples exceed the guidelines, the watercourse is considered partially impaired by nutrient loading from human activity. In contrast, if more than 50% of the samples exceed the water quality guidelines, total phosphorus and nitrogen concentrations are more consistently above the guidelines and water quality is considered to be impaired by human activity.

Phosphorous

Phosphorus levels by water quality monitoring station

Key results

  • A trends analysis from 2008 to 2017 showed:
    • Quebec City had increased phosphorus levels
    • Saint-François and Yamaska had decreased phosphorus levels
    • Bécancour, Nicolet, Richelieu and Carillon had no detectable trends
  • There was insufficient data to test for trends at Saint-Maurice and Lavaltrie

Annual total phosphorus levels for 9 water quality monitoring stations along the St. Lawrence River

Annual total phosphorus levels for 9 water quality monitoring stations along the St. Lawrence River (see data table below for the long description)
Data table for the long description
Annual total phosphorus levels for 9 water quality monitoring stations along the St. Lawrence River
Monitoring station Year Median 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
Carillon 2005 0.028 0.018 0.150 23
Carillon 2006 0.024
0.016 0.051 20
Carillon 2007 0.021 0.010 0.044 20
Carillon 2008 0.021 0.015 0.065 14
Carillon 2009 0.020 0.016 0.058 17
Carillon 2010 0.019 0.009 0.030 14
Carillon 2011 0.012 0.008 0.021 14
Carillon 2012 0.019 0.008 0.025 14
Carillon 2013 0.024 0.014 0.046 13
Carillon 2014 0.022 0.015
0.034 14
Carillon 2015 0.020 0.014 0.092 14
Carillon 2016 0.022 0.014 0.077 14
Carillon 2017 0.021 0.017 0.083 14
Lavaltrie 2009 0.060 0.030 0.058 9
Lavaltrie 2010 0.050 0.032 0.030 12
Lavaltrie 2011 0.055 0.016 0.021 12
Lavaltrie 2012 0.040 0.023 0.025 12
Lavaltrie 2013 0.046 0.032 0.046 13
Lavaltrie 2014 0.040 0.030 0.034 12
Lavaltrie 2015 0.046 0.031 0.092 12
Lavaltrie 2016 0.046 0.027 0.077 12
Lavaltrie 2017 0.043 0.033 0.083 12
Richelieu 2008 0.030 0.016 0.118 12
Richelieu 2009 0.030 0.018 0.118 10
Richelieu 2010 0.039 0.019 0.072 12
Richelieu 2011 0.043 0.020 0.066 12
Richelieu 2012 0.044 0.017 0.123 12
Richelieu 2013 0.041 0.019 0.192 13
Richelieu 2014 0.030 0.019 0.110 12
Richelieu 2015 0.039 0.018 0.133 12
Richelieu 2016 0.045 0.026 0.111 12
Richelieu 2017 0.033 0.020 0.253 12
Yamaska 2008 0.106 0.044 0.143 19
Yamaska 2009 0.113 0.066 0.520 17
Yamaska 2010 0.090 0.015 0.164 18
Yamaska 2011 0.122 0.060 0.175 14
Yamaska 2012 0.140 0.093 0.195 7
Yamaska 2013 0.131 0.084 0.156 9
Yamaska 2014 0.108 0.015 0.136 9
Yamaska 2015 0.099 0.040 0.197 12
Yamaska 2016 0.113 0.041 0.186 16
Yamaska 2017 0.087 0.035 0.125 17
Saint-François
2008 0.035 0.021 0.108 15
Saint-François 2009 0.033 0.021 0.105 15
Saint-François 2010 0.027 0.021 0.055 15
Saint-François 2011 0.031 0.021 0.172 14
Saint-François 2012 0.030 0.027 0.035 7
Saint-François 2013 0.031 0.025 0.064 9
Saint-François 2014 0.023 0.019 0.028 9
Saint-François 2015 0.029 0.018 0.045 12
Saint-François 2016 0.028 0.020 0.040 16
Saint-François 2017 0.023 0.017 0.048 17
Nicolet 2008 0.046 0.025 0.102 15
Nicolet 2009 0.053 0.036 0.126 15
Nicolet 2010 0.053 0.042 0.116 15
Nicolet 2011 0.050 0.010 0.073 14
Nicolet 2012 0.071 0.047 0.085 7
Nicolet 2013 0.046 0.035 0.053 9
Nicolet 2014 0.031 0.029 0.039 9
Nicolet 2015 0.040 0.023 0.149 12
Nicolet 2016 0.052 0.026 0.144 16
Nicolet 2017 0.042 0.027 0.094 17
Bécancour 2008 0.037 0.013 0.293 12
Bécancour 2009 0.038 0.024 0.062 12
Bécancour 2010 0.038 0.020 0.172 12
Bécancour 2011 0.041 0.024 0.103 12
Bécancour 2012 0.030 0.013 0.087 12
Bécancour 2013 0.043 0.022 0.136 12
Bécancour 2014 0.031 0.007 0.067 12
Bécancour 2015 0.045 0.020 0.091 12
Bécancour 2016 0.050 0.027 0.293 12
Bécancour 2017 0.043 0.024 0.240 12
Saint-Maurice
2009 0.015 0.010 0.048 10
Saint-Maurice 2010 0.015 0.009 0.184 12
Saint-Maurice 2011 0.008 0.005 0.015 13
Saint-Maurice 2012 0.014 0.010 0.024 12
Saint-Maurice 2013 0.015 0.012 0.250 13
Saint-Maurice 2014 0.015 0.008 0.147 12
Saint-Maurice 2015 0.013 0.009 0.019 12
Saint-Maurice 2016 0.014 0.010 0.018 12
Saint-Maurice 2017 0.015 0.011 0.040 12
Quebec City 2005 0.033 0.019 0.135 16
Quebec City 2006 0.034 0.019 0.135 16
Quebec City 2007 0.026 0.013 0.072 18
Quebec City 2008 0.029 0.020 0.080 18
Quebec City 2009 0.025 0.008 0.070 17
Quebec City 2010 0.025 0.013 0.062 17
Quebec City 2011 0.030 0.015 0.104 17
Quebec City 2012 0.030 0.013 0.049 20
Quebec City 2013 0.036 0.015 0.075 15
Quebec City 2014 0.033 0.013 0.058 15
Quebec City 2015 0.034 0.016 0.137 17
Quebec City 2016 0.042 0.019 0.114 17
Quebec City 2017 0.032 0.022 0.142 17

Note: Samples from the mouths of the Yamaska, Saint-François and Nicolet rivers are collected from May to September only.

Download data file (Excel/CSV; 4.09 kB)

How this indicator was calculated

Note: Each boxplot summarizes annual phosphorus levels at a monitoring station and shows the range of values measured. The dotted line shows Quebec's total phosphorus water quality guideline value of 0.03 mg P/L. The solid line is drawn through the median to give a sense of the changes in concentrations over time. A Seasonal Kendall trend analysis for phosphorus was calculated at the 7 stations that had data from at least 2008 to 2017.
Source: St. Lawrence River Water Quality Monitoring and Surveillance Division (2018) Environment and Climate Change Canada.

Plotting phosphorus data for each station by year provides a general view of how phosphorus levels are changing along the St. Lawrence River. The worsening trend near Quebec City may be driven by a urban population growth and agriculture expansion upstream of the station.

Nitrogen

Nitrogen levels by water quality monitoring station

Key results

  • Annual nitrogen levels at Saint-Maurice and Carillon were consistently below the water quality guideline
  • There was insufficient data to test for trends at any of the 9 monitoring stations

Annual total nitrogen levels for 9 water quality monitoring stations along the St. Lawrence River

Annual total nitrogen levels for 9 water quality monitoring stations along the St. Lawrence River (see the data table below for the long description)
Data table for the long description
Annual total nitrogenlevels for 9 water quality monitoring stations along the St. Lawrence River
Monitoring station Year Median 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
Carillon 2009 0.492 0.426 0.713 11
Carillon 2010 0.543 0.450 0.897 14
Carillon 2011 0.540 0.440 0.870 14
Carillon 2012 0.530 0.440 0.690 13
Carillon 2013 0.570 0.480 1.060
13
Carillon 2014 0.515 0.400 1.070
14
Carillon 2015 0.520 0.340 1.130
14
Carillon 2016 0.545 0.380 0.780 14
Carillon 2017 0.605 0.440 1.050
14
Lavaltrie 2009 0.900 0.580 1.400
9
Lavaltrie 2010 0.875 0.670 1.440
12
Lavaltrie 2011 0.920 0.580 1.350 12
Lavaltrie 2012 0.910 0.610 1.770 12
Lavaltrie 2013 0.705 0.730 1.860
12
Lavaltrie 2014 0.600 0.540 1.250
12
Lavaltrie 2015 0.610 0.390 1.520
11
Lavaltrie 2016 0.850
0.540 2.220
12
Lavaltrie 2017 0.665 0.740 1.560
12
Richelieu 2010 0.780
0.520 1.020
9
Richelieu 2011 0.650
0.430 1.030
12
Richelieu 2012 0.645
0.400 2.030
12
Richelieu 2013 0.705
0.400 2.520
12
Richelieu 2014 0.600
0.410 1.160
12
Richelieu 2015 0.610
0.500 2.440
12
Richelieu 2016 0.850
0.390 3.720
12
Richelieu 2017 0.665
0.390 1.590
12
Yamaska 2009 3.580
1.460
2.480
15
Yamaska 2010 2.270
1.250
3.910
15
Yamaska 2011 1.920
1.170
5.700
14
Yamaska 2012 0.750
0.660
1.370
7
Yamaska 2013 1.870
1.070
4.120
9
Yamaska 2014 1.170
0.570
2.600
9
Yamaska 2015 3.060
0.560
5.090
12
Yamaska 2016 1.750
0.580
7.300
16
Yamaska 2017 1.840
1.200
4.970
17
Saint-François 2009 0.770
0.650
1.120
15
Saint-François 2010 0.800 0.460 1.070
15
Saint-François 2011 0.830 0.590 2.420
14
Saint-François 2012 0.810 0.710 1.040
7
Saint-François 2013 0.760 0.610 1.110
9
Saint-François 2014 0.740 0.600 0.870
9
Saint-François 2015 0.770 0.410 0.969 12
Saint-François 2016 0.920 0.650 1.240
16
Saint-François 2017 0.830 0.580 3.040
17
Nicolet 2009 1.560
0.730 2.570
15
Nicolet 2010 0.940 0.550 1.810
15
Nicolet 2011 0.990 0.570 2.900
14
Nicolet 2012 0.680 0.400 2.030
16
Nicolet 2013 1.280
0.710 1.940
9
Nicolet 2014 0.670 0.340 1.220
9
Nicolet 2015 1.390
0.170 3.070
12
Nicolet 2016 1.240
0.640 3.070
15
Nicolet 2017 1.340
0.620 2.540
17
Bécancour 2009 0.855 0.370 1.210
9
Bécancour 2010 0.925 0.470 1.470
12
Bécancour 2011 0.915 0.470 1.420
12
Bécancour 2012 0.665 0.420 1.290
12
Bécancour 2013 0.935 0.490 1.290
12
Bécancour 2014 0.765 0.440 1.390
12
Bécancour 2015 0.825 0.440 1.910
12
Bécancour 2016 0.850 0.310 1.800
12
Bécancour 2017 0.950 0.440 1.490
12
Saint-Maurice 2009 0.360 0.270 0.380
9
Saint-Maurice 2010 0.315 0.243 0.630
12
Saint-Maurice 2011 0.340 0.290 0.417 13
Saint-Maurice 2012 0.330 0.270 0.400 12
Saint-Maurice 2013 0.330 0.270 0.760 13
Saint-Maurice 2014 0.340 0.280 0.560 12
Saint-Maurice 2015 0.320 0.210 0.490 12
Saint-Maurice 2016 0.320 0.190 0.360 12
Saint-Maurice 2017 0.320 0.260 0.380 12
Quebec City 2009 0.595 0.420 0.900 14
Quebec City 2010 0.630 0.400 0.960 17
Quebec City 2011 0.620 0.430 0.970 17
Quebec City 2012 0.605 0.330 1.020
20
Quebec City 2013 0.715 0.450 0.940 14
Quebec City 2014 0.645 0.480 0.890 14
Quebec City 2015 0.670 0.270 1.180 17
Quebec City 2016 0.700 0.370 0.960 17
Quebec City 2017 0.650 0.440 1.170
17

Note: Samples from the mouths of the Yamaska, Saint-François and Nicolet rivers are collected from May to September only.

Download data file (Excel/CSV; 3.37 kB)

How this indicator is calculated

Note: Each boxplot summarizes annual nitrogen levels for a monitoring station and shows the range of values measured. The dotted line shows the guideline value of 0.63 mg N/L. The solid line is drawn through the median to give a sense of trends in concentration. None of the stations had enough data to perform a Seasonal Kendall trend analysis.
Source: St. Lawrence River Water Quality Monitoring and Surveillance Division (2018) Environment and Climate Change Canada.

Plotting nitrogen data for each station by year provides a general view of how nitrogen levels are changing over time along the St. Lawrence River. Nitrogen levels tend to be below water quality guidelines at stations situated near forested areas with smaller urban populations, such as Carillon and Saint-Maurice.

About the indicator

About the indicator

What the indicator measures

The indicator reports on the status of total phosphorus and total nitrogen levels along the St. Lawrence River. It ranks the status based on how often total phosphorus and total nitrogen levels exceed their respective water quality guidelines.

This indicator assumes that water in the St. Lawrence River would rarely exceed water quality guidelines for phosphorus and nitrogen in the absence of human development. It provides information about how human activity contributes to phosphorus and nitrogen levels in the river. The more often the water quality guidelines are exceeded, the greater the risk to the health of the St. Lawrence River. The phosphorus trend analysis provides information about how concentrations are changing over time.

Why this 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 are too high or too low, they can cause harmful effects on the river.

Phosphorus and nitrogen used in chemical fertilizers reach the river through erosion and leaching from urban areas, farmland runoff, municipal and industrial wastewater discharges, and air pollution. Over time, excess phosphorus and nitrogen levels in the river can alter its food web.

This indicator is used to provide information about the state of the St. Lawrence River. Ongoing tracking of phosphorus and nitrogen levels allows governments and citizens to remain aware of an important aspect of the environmental condition of the river. This indicator also contributes to the measurement of progress towards 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 Lake Winnipeg indicators report on the status of total phosphorus and total nitrogen levels in those 2 ecosystems.

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

Pristine lakes and rivers

This 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 and methods

Data sources

Total phosphorus and total nitrogen data were provided by Environment and Climate Change Canada's Fresh Water Quality Monitoring and Surveillance program. The data can be found on the Freshwater quality monitoring: online data web page.

More information

Sampling

The status of total phosphorus and total nitrogen levels are based on measurements recorded between January 2015 and December 2017. The trend analysis uses total phosphorus data from 2008 to 2017 recorded at 7 monitoring stations (Carillon, Richelieu, Yamaska, Saint-François, Nicolet, Bécancour and Quebec City).

The sampling frequency at the water quality monitoring stations included in this indicator is not uniform. Sampling at the Carillon, Lavaltrie, Richelieu, Bécancour, Saint-Maurice and Quebec City stations is conducted on a monthly basis. At monitoring stations at the mouths of the Nicolet, Saint-François and Yamaska rivers, samples are typically collected on a weekly basis from June until the end of August. Gaps exist in the data due to program changes, weather and mechanical issues with the equipment used to collect the data.

Water quality monitoring station locations

Data were obtained from 9 monitoring stations along the St. Lawrence River from the Quebec‑Ontario border in the west to Quebec City in the east (Table 1). The stations are sited so as to monitor the principal water sources entering the St. Lawrence River and are sometimes installed at the mouths of tributary rivers.

Table 1. Water quality monitoring stations used for the indicator
Monitoring station Station code Station name Longitude Latitude
Carillon QU02LB9001 Rivière des Outaouais, en aval du barrage de Carillon -74.379870 45.567570
Lavaltrie QU02OB9004 Fleuve Saint-Laurent, prise d'eau de l'usine de filtration de Lavaltrie -73.280645 45.874418
Richelieu
QU02OJ0052 Rivière Richelieu, prise d'eau de l'usine de filtration de Sorel -73.117582 46.033974
Yamaska
QU02OG3007 Rivière Yamaska, pont de la route 132 -72.910075 46.005059
Saint-François QU02OF3004 Rivière Saint-François à Pierreville -72.812180 46.066375
Nicolet QU02OD3004 Rivière Nicolet à Nicolet -72.651229 46.245373
Bécancour QU02OD9009 Fleuve Saint-Laurent, prise d'eau de l'usine de filtration de Bécancour -72.546012 46.311578
Saint-Maurice QU02NG3013 Rivière Saint-Maurice, prise d'eau de l'usine de filtration de Trois-Rivières -72.610500 46.382000
Quebec City QU02PH9024 Fleuve Saint-Laurent, prise d'eau de l'usine de filtration de Lévis -71.190009 46.807123

Methods

The status of phosphorus and nitrogen levels at each monitoring station was ranked on the basis of how often levels were above their water quality guidelines.

A Seasonal Kendall test with Seasonal Kendall slope was used to test for the presence of a statistically significant increasing or decreasing trend in total phosphorus at stations with 10 years of data.Footnote 2 

More information

Water quality guidelines

Total phosphorus

Quebec's total phosphorus water quality guideline for the protection of aquatic life, specifically 0.03 milligrams of phosphorus per litre (mg P/L) was used.Footnote 1

Total nitrogen

Neither Quebec nor the Canadian Council of Ministers of the Environment (CCME) has a water quality guideline for total nitrogen. Accordingly, a total nitrogen guideline for the St. Lawrence River was derived in keeping with the CCME's lines-of-evidence approach (PDF; 1.95 MB). A total nitrogen guideline of 0.63 milligrams of nitrogen per litre (mg N/L) was selected for calculation of the Nutrients in the St. Lawrence River indicator. This coincides with the ideal performance standardFootnote 3 of 0.63 mg N/L for large rivers in the Mixedwood Plains Ecozone as recommended during Environment and Climate Change Canada's National Agri‑Environmental Standards Initiative.Footnote 4

See Annex A for more detail about how the total nitrogen guideline was derived.

Calculation of phosphorus and nitrogen status for the St. Lawrence River

The phosphorus status at each of the 9 water quality monitoring stations was computed by comparing total phosphorus concentrations at each station with Quebec's total phosphorus water quality guideline for the protection of aquatic life of 0.03 mg P/L.Footnote 5 Similarly, the nitrogen status at each water quality monitoring station was determined by comparing the total nitrogen concentrations at each station to the St. Lawrence-specific total nitrogen water quality guideline for the protection of aquatic life of 0.63 mg N/L (see Annex A).

The number of times total phosphorus and total nitrogen concentrations exceeded the guidelines were summed from 2015 to 2017, and the results were divided by the total number of samples collected over the same time period. The status of each station was determined by calculating the percentage of samples exceeding the guidelines. Stations with fewer than 10% of samples exceeding the guidelines were given a Green water quality status. Stations with 10% to 50% exceedances were given a Yellow water quality status. Stations with more than 50% of samples exceeding the guidelines were given a Red water quality status.

Trend Analysis

Stations sampled monthly

Within the dataset, each sample was assigned to a month. One sample per month (approximate 30-day interval) was used for the analysis. This was done in order to correct sampling frequency variation in the data and to minimize analytical issues associated with serial correlation in the data. The analysis was run using the Kendall package within the R software environment.

Stations sampled weekly

Within the dataset, each sample was assigned to 1 of 22 weeks from May 1 to October 1. To correct sampling frequency variation in the data, and to minimize analytical issues associated with serial correlation in the data, a single sample taken approximately every 7 days was selected for the analysis. Only weeks 9 through 17 (June 26 to August 27) had enough samples over the 10-year period to be used for the trend analysis. The analysis was run using the Kendall package within the R software environment.

Data requirements

With environmental trend analysis, the more data available, the more statistical power the test has. For a station to be included in trend analysis reporting, at least 10 years of data were required. Total phosphorus concentrations are strongly correlated with the river's flows because high flows transport more suspended sediment with bound phosphorus.

These data requirements were met by 7 stations (Table 2).

Table 2. Seasonal Kendall analysis output for total phosphorus, 2008 to 2017
Monitoring station Parameter Tau Score 2-sided p value Seasonal Kendall slope
Carillon Total phosphorous 0.1345029 69 0.06694428 0.0003
Richelieu Total phosphorous 0.005747126 3 0.9576477 0
Yamaska Total phosphorous -0.1717452 -62 0.04937288 -0.002
Saint-François Total phosphorous -0.2777778 -105 0.001080528 -0.001
Nicolet
Total phosphorous -0.1428571 54 0.09701621 -0.001
Bécanour Total phosphorous 0.1055556 57 0.1460782 0.0006666667
Quebec City Total phosphorous 0.2042802 105 0.005416289 0.00125

Recent changes

Total phosphorus trends are reported for all monitoring stations that met the trend data requirements. Refer to the Methods for more information on the trend analysis.

A correction was made to the data for phosphorus level status at Quebec City for the 2012 to 2014 period. The status was changed from Yellow (10% to 50% of phosphorus samples were above the guideline) to Red (over 50% of phosphorus samples were above the guideline).

Caveats and limitations

The indicator reflects the state of water quality in the St. Lawrence River based on total phosphorus and total nitrogen concentrations. These concentrations do not reflect the effect of spills or other transient events unless they are frequent or long-lasting.

Caution must be exercised when comparing this indicator with similar indicators for lakes. In rivers, total phosphorus concentrations are influenced by suspended particles in the water that increase during high-flow events. Elevated total nitrogen concentrations result from high runoff associated with precipitation, which washes nitrogen out of soils. This situation differs in lake ecosystems, as suspended particles generally settle out. However, it is still reasonable to compare lake and river systems as long as the methods used to determine the water quality classifications are clear.

Resources

Resources

References

Canadian Council of Ministers of the Environment (2016) Guidance manual for developing nutrient guidelines for rivers and streams (PDF; 1.95 MB). Retrieved on July 30, 2018.

Chambers PA, Guy M, Dixit SS, Benoy GA, Brua RB, Culp JM, McGoldrick D, Upsdell BL, Vis C (2009) Nitrogen and Phosphorus Standards to Protect the Ecological Condition of Canadian Streams, Rivers and Coastal Waters. National Agri-Environmental Standards Initiative Synthesis Report No. 11. Environment Canada. Gatineau, Quebec. 79 p.

Ministère du Développement durable, de l'Environnement et de la Lutte contre les changements climatiques (2009) Critères de qualité de l'eau de surface : phosphore total (en P) (in French only). Retrieved on July 30, 2018.

United States Environmental Protection Agency (2000a) Nutrient Criteria Technical Guidance Manual: Rivers and Streams. Report No. EPA-822-B-00-002. Retrieved on July 30, 2018.

United States Environmental Protection Agency (2000b) Ecoregional Nutrient Criteria Documents for Rivers and Streams in Nutrient Ecoregion VII: Mostly Glaciated Dairy Region (PDF; 331 kB). Report No. EPA-822-B-00-018. Retrieved on July 30, 2018.

United States Environmental Protection Agency (2001) Ecoregional Nutrient Criteria Documents for Rivers and Streams in Nutrient Ecoregion VIII: Nutrient-Poor, Largely Glaciated Upper Midwest and Northeast (PDF; 2.53 MB). Report No. EPA-822-B-01-015. Retrieved on July 30, 2018.

Related information

Environment and Climate Change Canada (2015) Phosphorus in aquatic ecosystems. Retrieved on July 30, 2018.

Governments of Canada and Quebec (2015) St. Lawrence Action Plan 2011-2026. Retrieved on July 30, 2018.

Environment and Climate Change Canada (2017) St. Lawrence River: phosphorus at the mouths of Lake Saint-Pierre tributaries. Retrieved on July 30, 2018.

Annex

Annex A. A total nitrogen guideline to protect the ecological condition of the St. Lawrence

Neither the Quebec government nor the Canadian Council of Ministers of the Environment (the council) has a water quality guideline for total nitrogen. In order to develop a guideline for the indicator, research and analysis was performed following the lines-of-evidence approach outlined in the council's Guidance manual for developing nutrient guidelines for rivers and streams (PDF; 1.95 MB). This approach recommends a number of consecutive steps to formulate a final guideline. A summary of the key steps followed to develop the guideline of 0.63 mg N/L for the calculation of the Nutrients in the St. Lawrence River indicator are set-out below.

It is important to note that this guideline has been designed for use in this indicator and may not include all possible data. Should an official total nitrogen guideline be developed for the St. Lawrence River, it will replace the guideline derived here.

Step 1. Definition of the area of interest

For the purpose of the indicator and the analysis performed, the St. Lawrence River is defined as extending from the Ontario‑Quebec border in the west to Quebec City in the east.

Site Description

The St. Lawrence River is a very large river with a catchment area of 1 610 000 km2. It is situated in the St. Lawrence Lowlands ecoregion of the Mixedwood Plains Ecozone. About 60% of the region is intensively cultivated farmland, with dairy and mixed farming systems prevailing. Urban development is extensive. Intensive land use is increasing, with a trend toward rising nutrient loads to streams and rivers. The St. Lawrence Lowlands ecoregion has a humid, continental climate with very cold winters and very hot summers. Rivers in humid regions tend to have more water throughout the year.

The river was formed around the end of the last ice age when faulting led to the sinking of the area around the river (a rift valley), which was then flooded with water from the Atlantic Ocean. It forms much of the southwestern outline of the Canadian Shield in Quebec.

Step 2. Establishment of the desired outcomes and selection of the guideline variables

The desired outcome of this nitrogen guideline is to prevent eutrophication in the St. Lawrence River and the Gulf of St. Lawrence caused by total nitrogen.

Step 3. Classification of streams

The St. Lawrence River is a very large river ecosystem. In such systems, the relationships between aquatic communities and nutrients may be confounded by physical factors that exert their influence temporally and spatially at the local scale, as well as along a continuum of river size from small streams to large rivers. Water quality in streams is more subject to sudden changes in hydrology than is the case for rivers, and plant and animal community abundance and composition varies with river size. For these reasons, separate standards to protect the ecological condition of different rivers are necessary.

The river was not subdivided into separate subregions for this guideline derivation because of the need for a single value that would apply along the whole river to allow comparability among stations.

Step 4. Collection and analysis of data

Total phosphorus and total nitrogen data were provided by Environment and Climate Change Canada's Freshwater Quality Monitoring and Surveillance program. The data can be found on the Freshwater quality monitoring: online data web page.

Observed spatial patterns in the data (Figure A.1; Table A.3):

  • total nitrogen concentrations in the river tend to be lowest in summer and highest in winter
  • total nitrogen concentrations increase from Carillon to Lavaltrie and then decrease to Bécancour and Quebec City
    • total nitrogen concentrations at Lavaltrie are influenced by the region of Montreal's sewage outfall
    • at Bécancour, the influence of nitrogen inflow from tributaries draining the agricultural regions on the south shore of Lake Saint-Pierre can be seen

Figure A.1. Total nitrogen data for 4 water quality monitoring stations on the St. Lawrence River (stations are presented in order from Carillon in the west to Quebec City in the east)

Total nitrogen data for 4 water quality monitoring stations on the St. Lawrence River (stations are presented in order from Carillon in the west to Quebec City in the east) (see the data table below for the long description)
Long description

The line charts show the total nitrogen concentrations measured at 4 water quality monitoring stations (Carillon, Lavaltrie, Bécancour and Quebec City) on the St. Lawrence River between January 1, 2009 and January 1, 2015. All samples collected were measured in milligrams of nitrogen per litre.

Step 5. Literature review

Existing suggested guidelines for the St. Lawrence River were found in the primary and grey literature. The examples below were the most applicable.

Chambers et al. 2009

Ideal performance standards for medium and large rivers draining agricultural regions in Canada were developed following 2 lines of data analysis. The first method involved approximating background nutrient concentrations by calculating 25th percentiles for total phosphorus and total nitrogen following the U.S. EPA's nutrient criteria methodology (U.S. EPA 2000a). The second method involved exploring relationships between total nitrogen and total phosphorus and either benthic or sestonic algal biomass expressed as chlorophyll a using stepwise multiple linear regression on log10-transformed data.

The results of the analysis produced a suggested total nitrogen guideline of 0.63 mg N/L for large rivers in the Mixedwood Plains. Chambers et al. also recommended an ideal performance standard of 0.100 mg N/L for total nitrogen for Prince Edward Island coastal waters. This value is 6 times lower than the concentrations currently seen at Quebec City.

Caveats

Rivers with drainage basins larger than 10 000 km2 were considered too large to be included in the analysis.

The methods deviated from the U.S. EPA approach by only using 25th percentiles for 2 reasons. First, given the amount of data in the freshwater database and the number of disparate sources of data, it was not possible to determine whether a site could be considered reference or low-impact. Second, the data came from rivers draining agricultural areas, signifying that they are impacted. The methods also deviated from the U.S. EPA method by analyzing data for large rivers collected for a 20‑year period between 1985 and 2005 rather than the recommended 10‑year period.

United States Environmental Protection Agency 2000b

The U.S. EPA's ecoregional nutrient criteria are intended to address cultural eutrophication. The criteria, or guidelines, are empirically derived to represent surface water conditions that are minimally impacted by human activities and protective of aquatic life and recreational uses.

This document sets out the U.S. EPA's recommended criteria for total nitrogen for rivers and streams in Nutrient Ecoregion VII (Mostly Glaciated Dairy Region) derived following procedures described in U.S. EPA 2000a. Reference condition criteria are based on the 25th percentiles of all nutrient data including a comparison of reference conditions for the aggregate ecoregion and the sub-ecoregions.

The analysis resulted in suggested total nitrogen guidelines for the whole ecoregion, as well as the sub-ecoregions closest to the St. Lawrence River (Table A.1).

Table A.1. Suggested total nitrogen guidelines for the United States Nutrient Ecoregion VII: Mostly Glaciated Dairy Region
Name Suggested total nitrogen guideline
(milligrams of nitrogen per litre)
Aggregate ecoregion VII 0.54 (reported)
Aggregate ecoregion VII 0.54 (calculated)
Sub-ecoregion 83 - Eastern Great Lakes and Hudson Lowlands 0.48 (reported)
Sub-ecoregion 83 - Eastern Great Lakes and Hudson Lowlands 0.50 (calculated)
Caveats

Nutrient criteria are derived for wadeable streams in the U.S. only, which generally have basins much smaller than 10 000 km2.

United States Environmental Protection Agency 2001

The analysis in U.S. EPA 2001 is the same as that in U.S. EPA 2000b, except that it encompasses Nutrient Ecoregion VIII (Nutrient-Poor Largely Glaciated Upper Midwest and Northeast) (Table A.2).

Table A.2. Suggested total nitrogen guidelines for the United States Nutrient Ecoregion VIII
(Nutrient-Poor Largely Glaciated Upper Midwest and Northeast)
Name Suggested total nitrogen guideline
(milligrams of nitrogen per litre)
Aggregate ecoregion VIII 0.38 (reported)
Sub-ecoregion 58 - Northeastern Highlands 0.42 (reported)
Sub-ecoregion 58 - Northeastern Highlands 0.26 (calculated)

Step 6. Collection and analysis of data

The following guideline calculation techniques were applied to the data for the 4 St. Lawrence River water quality monitoring stations. The U.S. EPA recommends the use of 10 years of data for its analysis; however, there were only 6 years of data available for the St. Lawrence River at the time of calculation.

United States Environmental Protection Agency 2000a

To derive nutrient criteria, the U.S. EPA recommends using the 75th percentile of 10 years of monitoring data from reference or low-impact sites. In the absence of adequate reference data, the 25th percentile of all monitoring sites can be used (Table A.3).

For the 25th percentile analysis for the St. Lawrence River, all total nitrogen data for each station were combined into a single median value for each season. The 25th percentile of all station medians was then calculated for each season (Table A.3). The median value from the 4 seasonal 25th percentile values is considered the standard. This analysis generated a guideline of 0.65 mg N/L (Table A.4).

Table A.3. Total nitrogen data summary for the St. Lawrence River
Monitoring station Season Number of records for total nitrogen Minimum
(milligrams of nitrogen per litre)
25th percentile
(milligrams of nitrogen per litre)
Median
(milligrams of nitrogen per litre)
75th percentile
(milligrams of nitrogen per litre)
Maximum
(milligrams of nitrogen per litre)
Carillon Whole year 79 0.400 0.490 0.530 0.600 1.070
Carillon Spring 31 0.440 0.499 0.550 0.625 1.070
Carillon Summer 17
0.400 0.470 0.490 0.510 0.670
Carillon Fall 16 0.434 0.494 0.510 0.607 0.770
Carillon Winter 15
0.470 0.533 0.560 0.624 0.897
Lavaltrie Whole year 69 0.540 0.780 0.900 1.070 1.860
Lavaltrie Spring 19 0.650 0.795 0.890 1.240 1.860
Lavaltrie Summer 15 0.540 0.615 0.750 0.825 0.900
Lavaltrie Fall 21
0.690 0.790 0.940 1.040 1.660
Lavaltrie Winter 14 0.930 0.973 1.045 1.158 1.440
Bécancour Whole year 69 0.370 0.610 0.780 1.060 1.470
Bécancour Spring 18 0.600 0.705 0.780 1.033
1.320
Bécancour Summer 17 0.420 0.490 0.610 0.720
1.420
Bécancour Fall 19 0.370 0.580 0.700 1.060
1.470
Bécancour Winter 15 0.750 0.840 1.010 1.125
1.390
Quebec City Whole year 96 0.330 0.540 0.630 0.735
1.020
Quebec City Spring 29 0.540 0.620 0.680 0.840
1.020
Quebec City Summer 30 0.400 0.480 0.520 0.660 0.890
Quebec City Fall 23
0.330 0.515 0.570 0.660 0.930
Quebec City Winter 14 0.610 0.653 0.720 0.780 0.960
Whole river Whole year 313 0.330 0.540 0.670 0.890 1.860
Whole river Spring 97 0.440 0.590 0.690 0.890 1.860
Whole river Summer 79 0.400 0.480 0.540 0.695 1.420
Whole river Fall 79 0.330 0.550 0.680 0.915 1.660
Whole river Winter 58 0.470 0.653 0.810 0.018
1.440
Table A.4. Twenty-fifth percentiles of seasonal means for each station along the St. Lawrence River as well as the all stations combined (whole river)
Monitoring station 25th percentile of seasonal medians
(milligrams of nitrogen per litre)
Carillon 0.505
Lavaltrie 0.855
Bécancour 0.678
Quebec City 0.558
Whole river 0.645

The U.S. EPA also suggests using reference reaches to establish criteria. For this approach, it recommends using the 75th percentile of the nutrient frequency distribution for reference sites. As Carillon is the most upstream station, it can be considered the reference site for the dataset, even though technically its water quality is not degraded, as it is situated at the mouth of the Ottawa River. Total nitrogen is at its lowest here until the water reaches Quebec City. The 75th percentile of Carillon's total nitrogen concentrations is 0.60 mg N/L (Table A.3).

Step 7. Establishment of guidelines

In the absence of more detailed analyses to assess the relationship between nitrogen and aquatic plant growth in the St. Lawrence River, the analysis presented here helps point toward a total nitrogen guideline. Based on the recommended total nitrogen guideline values summarized in the table below, the values calculated using Canadian data for the area result in a total nitrogen guideline in the 0.60 to 0.65 mg N/L range (Table A.5). The mid-point of the range, 0.63 mg N/L, is the value used to calculate of the Nutrients in the St. Lawrence River indicator.

Table A.5. Comparison of possible total nitrogen standards
Value type Guideline analysis reference Recommended total nitrogen guideline
(milligrams of nitrogen per litre)
Notes or comments
Calculated value U.S. EPA 2000a 0.65 25th percentile of seasonal medians for all sites in an ecoregion
Calculated value U.S. EPA 2000a 0.60 75th percentile of reference site (Carillon)
Literature value Chambers et al. 2009 0.63 For large rivers in the Mixedwood Plains Ecozone
Literature value U.S. EPA 2000b 0.54 Streams in Aggregate ecoregion VII – Mostly Glaciated Dairy Region
Literature value U.S. EPA 2001 0.38 Streams in Aggregate ecoregion VIII – Nutrient Poor Largely Glaciated Upper Midwest and Northeast
Report a problem or mistake on this page
Please select all that apply:

Thank you for your help!

You will not receive a reply. For enquiries, contact us.

Date modified: