Nutrients in the St. Lawrence River .: En4-144/47-2016E-PDF

“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”—p. 5.

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publications.gc.ca/pub?id=9.822331&sl=0

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