Pathways of Effects - National Guidelines
Illustrating the links between human activity and its potential impact on aquatic ecosystems

Table of Contents


A step-wise process is proposed for the development of any PoE. However, depending on the particular PoE model under development, different partners and affected parties will be involved according to their expertise, authority and management responsibilities. Models can be developed during workshops, by a smaller group of experts or by a consultant. If a holistic model is developed in a workshop, a broad range of participants with different backgrounds, skills and interests will usually be involved. For an endpoint model, more specialized expertise is required. The type of participants involved in developing PoEs will also depend on the geographic unit, the type of drivers, pressures and selected endpoints. The participants may be involved at all or any stages, including the selection of ecological components, the identification of potential pressures and impacts generated by human activities, the provision of advice, and during scientific validation. Involving experts from various regulatory agencies and industry from the beginning fosters acceptance of the resulting model and builds support for the entire planning process.

5.1 PoE components

5.1.1 Identification of measurable endpoints


The first step involves identification of the PoE components described in Section 3, starting with identification of specific, measurable endpoint(s) that will structure the rest of the PoE development process. The endpoints are equivalent to environmental/state indicators since both are used to measure and track changes over time with respect to the objective. Measurable endpoints will also help to ‘operationalize’ the objectives.

Measurable endpoints have to be practical and well-defined. They should be easily understood both by the public and decision-makers, yet meaningful to environmental, social, cultural and economic scientists. Measurable endpoints include both an ecological entity (e.g., eelgrass) and a measurable attribute (e.g., distribution). They provide direction for the assessment and are the basis for the development of questions, predictions, models and analyses. Measurable endpoints are selected based on their relevance to the management objectives, their importance in the ecosystem and their susceptibility to pressures (EPA, 1998).

The identification of measurable endpoints can be challenging. It requires the translation of abstract environmental, social, cultural and economic management objectives into specific well-defined attributes of the system. The rationale behind this linkage should be documented.

Examples of ecological measurable endpoints:

For species:

  • Estuarine eelgrass habitat abundance and distribution;
  • Fry survival;
  • Area of spawning ground; and
  • Benthic invertebrate diversity.

For ecosystems:

  • Biodiversity/physical structure;
  • Ecosystem structure maintained; and
  • Carrying or adaptive capacity.

5.1.2 Identification of human activities and sub-activities


The next step of the process is the identification of the various human activities and sub-activities within the spatial unit that could potentially generate pressures and impacts on the selected endpoint(s).

Human activities (e.g., agriculture) and sub-activities (e.g., applying fertilizer) are entities or actions that are released or impose pressures on the environment. The sources of the pressures are the focus of management options. When multiple sources are identified, it may be beneficial to focus on those important sources that management measures can control.

5.1.3 Identification of pressures


The third step is the identification of one or more specific pressures that can potentially impact or have an environmental effect on the selected endpoint(s) within the study area (e.g., change in nutrient regime). Pressures are defined as any chemical, physical or biological entity that can cause an adverse effect on a measurable endpoint(s).

5.1.4 Identification of impacts/ environmental effects


The final step is identification of the potential impacts or environmental effects on the selected endpoint(s). An impact is a measurable change to an ecosystem component/function (e.g., loss of spawning habitat) as a result of human-induced pressures. An impact can be positive or negative.

The Canadian Environmental Assessment Act (2009) defines environmental effect (i.e., impact) as “any change that the project may cause in the environment (e.g., nutrient regime alteration)…”.

5.2 PoE validation

Once a PoE is developed, scientific review and validation of the model is needed to confirm what is known and what is not known about the relationships within the PoE. Validation may occur through formal or informal processes such as those outlined below.

5.2.1 Canadian Science Advisory Secretariat (CSAS) review process

CSAS processes provide quality control for information and advice on the pressure-impact linkages identified in PoEs, and identify knowledge gaps or areas of uncertainty. Scientific validation of PoE diagrams involves the review and documentation of existing data and research that confirm (or contradict) the linkages in the pathways.

5.2.2 Social, cultural and economic PoE models review process

In the absence of a formal process to assess social, cultural and economic PoEs, it is helpful to consult with academic experts (e.g., in the domains of economics, sociology, anthropology), depending on the subject matter.

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