Attached algal species composition and specific conductivity were monitored above and below two sulphite pulp and paper mills near Ottawa. Continuous monitoring of the river's specific conductivity below the upstream mill revealed sharp peaks at irregular intervals over the summer. These peaks were interpreted as indications of large scale effluent release by the company as they did not occur on the upstream conductivity monitors. Continuous monitoring of specific conductivity above and below a second (larger) sulphite mill revealed a steady release of effluent without large sporadic releases.

The reduction in the total number of periphyton species below each of these pulp mills was similar even though the upstream mill released nearly ten times less effluent than the downstream mill. Furthermore, periphyton species composition and density below the two mills was surprisingly similar even though the larger mill was continuously releasing its effluent. It was concluded that sporadic dumping of concentrated wastes is as harmful to most algal species as continuous release of these same wastes over an extended period of time. Environmental agencies invested with the responsibility of ensuring acceptable water quality conditions should therefore develop a comprehensive network of continuous monitors immediately below major industries which discharge into our lakes, rivers and oceans to discourage industries from shock loading.

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