Impact of construction of a hydroelectric project on the water quality of five lakes in Nova Scotia

Abstract

In February, 1975, a [Formula: see text] year study of five highland lakes (Big, Cheticamp, Gisborne, Long, and Surge Lakes) in the Wreck Cove area of Nova Scotia was initiated to determine the limnological effects of construction of a hydroelectric project. Almost 600 lake-water samples were used to monitor water-quality changes resulting from tunnelling, dam construction, reservoir clear-cutting, slashing, and burning, and establishment of access roads.The impact on Surge Lake was much more pronounced than on the other four lakes. Evidence strongly suggests that the significant water-quality changes in Surge Lake can be attributed to clear-cutting operations and construction activities (of longer duration and higher intensities in the vicinity of Surge Lake area in comparison with other areas) resulting in accelerated soil erosion, nitrification, and soil leaching. Also, the Surge Lake watershed had steeper slopes, and different vegetative cover.Nitrate, ammonia nitrogen, total and ortho phosphorus, calcium, magnesium, sodium, potassium, chloride sulfate, total solids, conductance, pH, suspended solids, and turbidity increased significantly in the lower-most lake (Surge) but only moderately in the remaining lakes. The relative rates and amounts of revegetation of exposed soils were also considered key factors in influencing the magnitude of changes in water quality of these highland (elevation 400 m) lakes.

Environmental effects of reservoirs

“…In small water supply reservoirs, it is sometimes worthwhile to remove the vegetation and topsoil completely before flooding, in order to obtain water of good quality as soon as possible (Campbell et al, 1975;. Activities associated with the construction of the dam, such as forest clearing and the construction of access roads, may lead to increased erosion and soil leaching within the watershed, contributing further to the deterioration of water quality (Kelly et at., 1980).…”

“…Even in the temperate zone, not all reservoirs follow this sequence. If impoundment also leads to an increase in turbidity (Kelly et at., 1980) which will decrease the light available for photosynthesis, or of dissolved humic material (Vogt, 1978;Ostrofsky & Duthie, 1975;Jackson & Hecky, 1981) which will decrease the light available and also bind nutrients and make them unavailable, the trophic upsurge may not occur or may be only of brief duration.…”