Effects of Emission Reductions on Lake Water Quality in Western Québec  (1999)

As shown by many studies, surface waters in Québec are highly vulnerable to acidification due to a combination of factors such as high acidic deposition and high sensitivity of soils and bedrock. Soil sensitivity is a natural characteristic of the ecosystems that cannot be changed. Acidic nitrate and sulphate deposition come mostly from the chemical transformation of nitrogen and sulphur oxides emitted by the industries, thermal plants and combustion of fossil fuels on which changes can be effected.

The most important point source of SO₂ emissions in Québec is Noranda Mines' Horne facility, which is located in Rouyn-Noranda. It was responsible for a large portion of the total 1,098,000 metric tons of SO₂ emitted in 1980. Phase I of the lake survey conducted in 1982 in the Rouyn-Noranda area was carried out to assess the direct effects of this pollution source on the acidity of neighbouring lakes. In fact, this first survey revealed that the Noranda Mines smelter had an impact on surrounding lakes up to a distance of 125 km. In compliance with Québec's legislation on acid precipitation, Noranda Mines finally built a sulfuric acid production plant, which has since led to a 70% cut in its emissions of SO₂ with reference to 1980. This percentage of reduction is expected to reach 90% around the year 2000, and, in combination with the reduction achieved in Ontario (60%), should bring forth a possible improvement in water quality for surrounding lakes.

In order to verify if the reductions were beneficial to the environment, the 64 lakes surveyed in 1982 were visited again in 1991 and in 1996 to detect a change in lake water quality.  This document provides results from this study. Information was structured as follows:  

• Material and methods
• State of water quality in 1996
• Indication of a change in water quality between 1982 and 1996
• Is lake acidification receding?
• The nitrate effect
• Conclusion 

People interested in obtaining more details from the study

Dupont, J. 1996. Effets des réductions des émissions de SO2 sur la qualité de l’eau des lacs de l'ouest québécois, Ministère de l’Environnement et de la faune du Québec, Direction des écosystèmes aquatiques, Envirodoq no EN980066, rapport no PA-53/1, 31 pages.

may download the French version. This compressed file (1 Mo) contains the document in Microsoft Word 6 format, along with an appendix in Microsoft Excel 5 format.

Material and methods

In 1982, 65 lakes surrounding Rouyn-Noranda were selected at various points and distances from the source of emission.

Location of the study area

Sixty four lakes were sampled with success in 1982, 60 in 1991, and 62 in 1996. The three lake surveys were conducted in March of 1982, 1991 and 1996 under ice cover conditions. An integrated 0-5 meters sample was taken at lake center where lake depth was estimated highest. More than 20 variables were analyzed (pH, pH at equilibrium with atmospheric CO₂ pressure, SO₄, NO_x, NH₄, total N, total P, tanin, turbidity, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), Cl, conductivity, F, Si, Ca, Mg, Na, K, Fe, Mn, filtrated Al, and inorganic Al). Details of the sampling protocol and laboratory analyses are presented in the following technical report :

Dupont, J. 1992. Effects of the reduction of SO₂ emissions on the water quality of lakes in the Rouyn-Noranda region , Ministère de l’Environnement du Québec, Direction de la qualité des cours d'eau, Envirodoq n^o EN920422, report n^o QEN/PA-43a/1, 72 pages.

State of water quality in 1996

The quality of surface water in western Québec is highly affected by the physical properties of the underlying soil and bedrock. A majority of lakes located to the south and east of Rouyn-Noranda (Laurentian Highlands) show great depths along with clear waters. These lake waters are very diluted however, which makes them very sensitive to acidification. Lakes from the Abitibi Lowlands, on the other hand, are very shallow and very rich in organic matter. Their waters are often coloured and turbid. These lakes, which are generally located under an altitude of 300 meters, are rarely acidic. They can be found near Rouyn-Noranda or north of this city.

The spatial variability of surface water quality depends on physical characteristics of the land and the inputs of airborne pollutants. Thus, lakes from the Laurentian Highlands show pHs ranging from 5.5 to 7.0 units, along with low alkalinity, basic cations and conductivity levels. Lakes from the Lowlands show a greater level of water mineralization. pH is higher (>7.0), and values of alkalinity, basic cations, conductivity, colour and dissolved organic carbon can also be important. Acidic precipitation has a marked effect on the spatial distribution of sulphate in lakes. These lake sulphate concentrations, as for those in wet deposition, show a southwest-northeast gradient where the highest concentrations are observed near Rouyn-Noranda and south of the study area. However, this gradient has decreased however since 1982, following the implementation of the emission reduction programs. Most of the other water quality variables have not shown any particular trend.

Among the 64 lakes studied as part of the Noranda Project, the most acidic lakes (4.3) are located less than 125 km from Rouyn-Noranda. Their acidity comes mostly from deposition of acidifying substances received in the last century, even though the acidity of several of these lakes was in some way affected by a natural component related to organic matter. The Noranda Project also enabled us to analyze the data from ten walleye lakes located in the Belleterre sector, which is 125 to 150 km south of Rouyn-Noranda. This sector is known to be highly affected by chronic acidification problems.