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Freshwater fish assemblage patterns and risks posed by acidic deposition in northeastern British Columbia Murray, Sonia Bennett.

Abstract

In order to manage and protect natural resources it is important to understand local ecological processes and to assess potential risks. I studied the effects of environment on fish assemblage structure and assessed the potential risk of acidic deposition from oil and gas development in northeastern British Columbia (BC) in order to inform future management decisions. This project was part of a cumulative impact assessment project initiated by Treaty #8 First Nations in northeastern BC. They are concerned that recent rapid development in the area may be degrading the environment and infringing upon their rights. I used canonical correspondence analysis to relate environmental variables to patterns in fish assemblage structure at local and regional scales. At the local scale I compared low and high gradient watershed groups in the northern and southern portion of the study area and found that a unique set of variables related to local habitat features in each watershed group best accounted for variation in fish assemblage structure. At the regional scale two gradients best explained patterns in species distribution and abundance. The strongest gradient was correlated with temperature and the second gradient was correlated with stream width, boulder cover and in-stream vegetation cover. These patterns correspond with patterns found in other studies on fish assemblage structure, showing that scale is an important factor in determining the effect of environmental variables on fish and that temperature plays an important role in determining regional species distribution. I used soil maps to predict the potential sensitivity of different areas to acidic deposition, supported by water sampling and fish surveys in the field. In most areas of northeastern BC fish are not at risk from acidification because the ground water is generally quite alkaline and able to buffer incoming acidity. An area north of Fort St. John with organic soils, however, has quite acidic streams (pH 5-6.5) and may be sensitive to acidic deposition. The sensitivity of this area had not been recognized in previous studies of acidic deposition in BC. Further study will be necessary to better delineate the area and the level of sensitivity.

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