3.21 St. Lawrence drainage region
Profile highlights
- The St. Lawrence drainage region includes areas surrounding and draining into the St. Lawrence River, including the cities of Brockville, Montréal and Québec. Its 5,971 km2 of built-up area, accounting for 5.0% of the total area, was the second highest in the country in 2011. Natural and semi-natural area accounted for 81.3% of the area, followed by arable land (12.8%) and smaller amounts of natural land for pasture (0.8%).
- This drainage region had the highest density of linear infrastructure including roads, rail lines and transmission lines at 1,093.9 m/km2 in 2011.
- The population was 6,583,552 in 2011, with a population density of 59.9 persons/km2, the highest in the country. Population was up 33% compared to 4,941,807 in 1971.
- Surface freshwater intake from drinking water plants, manufacturing, mining, irrigation and thermal-electric production was 2,045.2 million m3 in 2013, the second highest in the country.
- The average annual water yield was 72.3 km3 over the period 1971 to 2013. The water yield per unit area was 0.61 m3/m2, compared to 0.35 m3/m2 at the Canada level. Monthly water flows peak in April.
- Sources of nitrogen and phosphorus residuals in the environment include fertilizer application, livestock and poultry production and industrial emissions. On average residual soil nitrogen on agricultural land was 51.8 kg/ha in 2011 compared to 23.2 kg/ha at the Canada level. The risk of phosphorus release from agricultural soils was high, with 3.5 mg/kg of water extractable phosphorus potentially released in 2011.
- Turbidity levels of source water for drinking water plants were among the highest in the country at 9.8 nephelometric turbidity units (NTU) in 2013.
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