Cumulative Effects Management


There are multiple definitions for cumulative effects. Two examples include:

“Changes to the environment caused by a variety of activities over time”[i]

“Change in the environment caused by multiple interactions among human activities and natural processes that accumulate across space and time”[ii]

Simply put, cumulative effects consider all of the ‘things’ that cause change in the environment. These ‘things’ could be industry, hunting, harvesting, hiking, road systems, pollution, etc.

Let’s use the infamous salmon as an example! If we want to explore salmon health in a specific river system, we would need to understand all of the ‘things’ that influence their health. Perhaps there is agricultural land bordering the river that impacts the quality of runoff. Or maybe there is a recreational fishery that captures salmon as bycatch. There could even be some kind of barrier, such as a dam, that prevents salmon from migrating upriver to spawn. Rather than looking at these activities individually, cumulative effects takes all the activities into account.

And there’s more to it than just that

Not only do cumulative effects look at changes to the environment in the present time, they also consider things that have happened in the past and things that are predicted to happen in the future.

Going back to the salmon example, there could be a historic gold mine in the area that contributes arsenic and mercury to the river system. Or there may be a proposed mill that, should it be approved, will release its effluent into the water.

Essentially, cumulative effects are effects that occur from multiple ‘things’, which may have taken place in the past, are currently happening in the present, or could/will happen in the future.

The benefits of looking at impacts cumulatively is that it provides a more realistic view of what is occurring in the environment and the interactions that take place. Looking at the system as a whole can also identify potential compounding effects from activities.

For example, Chemical A in the effluent may be fine on its own; however, when it interacts with Compound B from the agricultural runoff, it becomes toxic.


Let’s say that a group of people want to understand how ‘things’ are impacting their community. Where do you start? Do you monitor the air, water, and soil? What specifically would you monitor? The amount of carbon dioxide in the atmosphere? The concentration of nitrates in the water? The pH of the soil? What about species? Should you monitor deer? Should you monitor species important to your community? Should you monitor invasive species or species at risk? As you can see, the number of items to monitor builds up very quickly. Unfortunately, monitoring everything is unrealistic, which means that when you study cumulative effects, you need to choose the most important features to monitor. These features are called Valuable Ecosystem Components (VECs) and they are “identified as having scientific, ecological, social, cultural, economic, historical, archaeological or aesthetic importance”[i].

For some people, VECs are used as indicators of larger values that address culture, socio-economic conditions, environment, language, etc.


People define effects and impacts differently.

For example, the image below illustrates the cascading quality of effects and impacts where “an effect represents a change in the environment and an impact represents the consequences of such change”, which could “range from social and environmental factors capable of influencing health and well-being.


Ethics and Protocols:

Mi’kmaw Ecological Knowledge Protocol Assessment (MEK) 

Ethics in First Nations Research- Assembly of First Nations


Two Eyed Seeing:

Bartlett_Marshall_2009- Two Eyed Seeing in the Classroom Environment: Concepts, Approaches and Challenges 

Bartlett_Marshall _2012-Two eyed seeing and other lessons learned within a co-learning journey of bringing together indigenous and mainstream knowledges and ways of knowing


General Resources: 

Cumulative Effects of Marine Shipping

Assessing Cumulative Effects under the Canadian Environmental Assessment Act, 2012 

Assessing Cumulative Effects under the Canadian Environmental Assessment Act, 2012 – Interim Technical Guidance 

Open Science and Data Platform (OSDP)


Frequently Asked Questions: 

Cumulative Effects Frequently Asked Questions 

How Law Shapes Cumulative Effects Assessment in Environmental Assessments in Nova Scotia



[1] Government of Canada. 2018. Cumulative effects. Retrieved from

[1] Noble, B.F. 2015. Introduction to environmental impact assessment: A guide to principles and practice (Ed. 3). Don Mills, Ontario: Oxford University Press Canada.

[1] Stillwater Canada Inc. 2012. Section 2.0: Project scoping. Environmental Impact Statement: Main Report. Retrieved from

[1] Gillingham, M.P., Halseth, G.R., Johnson, C.J., Parkes, M.W. 2016. The integration imperative: Cumulative environmental, community and health effects of multiple natural resource developments. Springer International Publishing Switzerland. P. 142



Agricultural runoff: U.S. Department of Agriculture. 2013. Water quality index for agricultural runoff, streamlined and accessible. Retrieved from

Dam: Pratisruti Plus. 2018. World bank aid for rehabilitation of dams. Retrieved from

Gold Mine: The Elements Unearthed. 2013. Post tagged ‘mine dump’. Retrieved from

Effluent: Wiki. 2019. Effluent. Retrieved from

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