Kejimkujik National Park and National Historic Site of Canada

Natural Heritage: Research

Acid Precipitation Monitoring Network

Environment Canada selected a network of lakes in eastern Canada to monitor lake water to determine potential changes to ecosystems. This program was initiated in Kejimkujik National Park in 1983 when 27 lakes were selected to become part of the network.

National Parks were selected as sites for these networks as they protect environmentally sensitive areas susceptible to changes in atmospheric pollution. The Kejimkujik landscape is especially sensitive since it features granite and metamorphic bedrock covered by glacially derived deposits and thin soils. This environment contains limited calcium and magnesium, which can neutralize acids.

Researchers collect water samples each spring and fall to track long-term acidity trends as well as runoff conditions. Data collected in Kejimkujik from 1983 to 1994 suggest that although acid deposition is decreasing, the acidity of the lakes is not improving.
Lakes and their drainage basins that continue to receive more than their critical load of acidic deposition will likely remain acidified. Critical load is the maximum amount of deposition an ecosystem is able to tolerate without any significant damage. Kejimkujik has a very low critical load of less than six kilograms of sulphate deposition per hectare per year.

Despite reductions in acid deposition, few lakes show improved water chemistry, perhaps because it is too soon to see the results of the reductions. Also, since wetlands can store atmospherically deposited sulphur and nitrogen for years, these stored compounds are slowly released and may delay a lake's response to reduced deposition.

In eastern Canada, the pH of lake water functions as a reliable indicator of species diversity. This diversity is highest for all forms of life in water with a pH of approximately 6.0.

Environment Canada recorded the average pH values for the following Kejimkujik lakes between 1987 and 1997. The results varied from a low of pH 4.3 in Big Red Lake to a high of pH 5.9 for the eastern part of Big Dam Lake.

A multitude of factors cause the natural variations in pH between the different lakes within Kejimkujik. The specific bedrock and soils, within the drainage basin of each lake, determine the chemistry of that lake. Soils with more calcium help to neutralize acidity whereas the organic soils present in bogs contribute to the acidity.

The slope of the landscape also affects pH. In flat areas, such as that surrounding Pebbleloggitch Lake, waters accumulate and bogs form. Those boggy wetlands are carpeted with sphagnum moss, which contributes organic acids that naturally acidify waters. The Kejimkujik landscape is so flat that any water which has flowed a distance will pass through some of the numerous bogs and become darkly coloured and acidic.

In areas where uplands slope into a headwater lake, such as Beaverskin Lake, the water has few chemicals, is clear in colour and can have a higher pH.

Park visitors may be more familiar with Kejimkujik Lake as it is popular with both swimmers and canoeists. The largest lake in the Park, it has a huge drainage basin and receives water from many rivers and lakes. Although it is fed by both dark-coloured and clear waters, Kejimkujik Lake's brown waters suggest that it is more strongly influenced by the acidic waters of the darkly coloured lakes.

Climatic variation will also cause lake pH to fluctuate. The amount of precipitation an area receives in each season affects the volume of water passing through the drainage basin. High amounts of precipitation dilute the concentration of chemicals in the waters.

The following graphs illustrate seasonal fluctuations in the pH of Beaverskin Lake and Pebbleloggitch Lake.

References:

Clair, T.A., J. Pomeroy, A. Bouchard, A. Ouellet, R. Cook, C. McCarthy, and K. Robinson. 1997. Trends of Acid Precipitation Chemistry Variables in some Atlantic Canada National Park lakes. Environment Canada - Atlantic Region, Occasional Report no. 10, Environment Canada, Sackville, New Brunswick, 56 pp.

Jeffries, D.S. 1997. 1997 Canadian acid rain assessment: The effects on Canada's lakes, rivers and wetlands (vol. 3). Environment Canada.

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