As part of the long-term strategy for addressing issues related to municipal wastewater effluents (MWWE), Environment Canada is developing environmental quality objectives (EQOs) for the aquatic receiving environment. Recommended biological monitoring components of the aquatic ecosystem include fish communities, benthic macroinvertebrate communities, sentinel fish species and primary producers (macrophytes, attached algae, phytoplankton). A set of criteria was developed for measurable attributes (indicators) of each of those components. Recommended numeric and narrative criteria could be used to determine when MWWE should be managed. Warning-level criteria for indices of benthic community composition are considered effects on indices of composition that deviate from the mean reference response by more than ±2 standard deviations. For sentinel fish population parameters, warning-level effects are considered >25% differences from reference in gonad or liver size, growth, or age, or a >10% change in condition factor. For primary producers, warning-level effects are considered those that coincide with anticipated changes in fish communities based on existing models. Where warning-level criteria are exceeded, it is recommended that monitoring be repeated at two- to three-year intervals. Where continued monitoring demonstrates an increase in the extent or magnitude of effects on indices of benthic community composition, or sentinel fish population parameters, it is recommended that effects be considered unacceptable and that the cause of effects be identified and managed. Losses of non-rare species or shifts in dominance are considered severe fish-community effects that should trigger management (i.e., identification and elimination of causative agents). Domination of the benthic community by one or a few tolerant taxa normally coincides with effects on fish communities, and should also be considered a severe effect that triggers management.

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