4.0 Aquatic Effects Assessment
Fisheries and Oceans Canada (DFO) developed the Pathways of Effect (PoE) as a framework for assessing the potential impacts of a project on fish and fish habitat. In the Guide to the Risk Management Framework for DFO Habitat Management Staff Practitioners Version 1.0 (Fisheries and Oceans Canada 2006), hereafter referred to as the RMF Guide, PoE are used to describe projects in terms of the activities that are involved (e.g., vegetation clearing, flow management) and the mechanisms by which stressors ultimately lead to effects on the aquatic environment. The aquatic effects assessment described in the following sections was guided by this PoE framework.
The PoE are pathways that are also linked to mitigation, in that the effect pathway can be ‘broken’ by applying mitigation measures to avoid or minimize the effect. This PoE approach is useful to determine possible cause-and-effect relationships between in-water or near water activities and the aquatic environment. At the beginning stages of project design, all activities that have the potential to affect fish habitat in a negative way are identified.
4.1 Proposed Works and Potential Impacts
Standard activities associated with construction projects of this type and scale can often be linked to fish and fish habitat impacts. These more general activities and associated impacts include the following:
- Land-based activities such as vegetation clearing, grading, and excavation. These activities, although not directly affecting fish and fish habitat, can produce stressors such as the addition or removal of instream organic structure, reduced bank stability and sediment deposition from erosion of exposed soils when adequate mitigation is not sufficiently employed.
- Placement of material or structures in water, excavation/dredging, and water extraction. Aside from direct displacement of fish and fish habitat, these activities can directly affect fish habitat by resulting in debris deposition, bank or bed alteration, removal of aquatic macrophtyte, substrate and instream cover, alteration to fish passage and sedimentation of the water column when conducted in the absence of appropriate mitigation. Similarly, the direct alteration of a channel during realignment projects can cause changes in