Mr. Chair and members of the committee, thank you for your invitation.
Today, I'd like to share a few scientific principles on how freshwater ecosystems work and, in particular, why it's important to adopt a watershed-based approach.
Freshwaters are by nature connected ecosystems with directionality in their fluxes and flows. The watershed of a waterbody is more simply defined as the entire land area drained by a body of water, including groundwater aquifers.
All activity within a watershed that can influence the quality of water that flows as precipitation, irrigation or groundwater will influence the associated waterbodies.
While we still have a lot to learn scientifically about all the significant connections, we know with certainty that human activity in watersheds influences their aquatic ecosystems, and that there is directionality of flows through watersheds. Thus, disturbances can influence aquatic ecosystems even if the effects occur far away, although attention is often focused on uses near waterbodies.
Unfortunately, watershed boundaries, defined by the landscape's topography, rarely overlap with political boundaries. Our cities and farming, mining and forestry activities often overlap more than one watershed, or unduly occupy a large proportion of a given watershed.
Recent work we have conducted as part of the NSERC Lake Pulse Network, which sampled over 650 lakes across Canada, has shown that even urbanization levels of less than 5% in a watershed can lead to changes in the organisms present in a lake, potentially influencing ecosystem functioning. Thus, aquatic ecosystem structure and function are partially driven by what happens in the watershed, and not only by internal functioning within the waterbody itself. We call these “allochthonous influences” on a waterbody; these will complement, and in some cases even overwhelm, the internal “autochthonous” interactions within a waterbody.
Given the effects of climate change, such as the forest fires and increasingly intense storm events we witnessed in Canada this past summer, the influence of allochthonous inputs from the terrestrial portions of watersheds will increase, potentially overwhelming the internal functioning of many of our aquatic ecosystems.
The first message to take away is that activity in the terrestrial part of a watershed influences the structure and functioning of its waterbodies. The second message is that political boundaries and watershed boundaries do not necessarily overlap.
I would now like to turn to why it's so important to consider the natural boundaries of watersheds in conservation.
I've mentioned the flows from terrestrial to aquatic ecosystems, but there is also the fact that there is a connectivity between the waterbodies that make up watersheds. It is critical to consider connectivity for several reasons.
Firstly, these aquatic connections serve as migratory corridors for many organisms. In addition, with climate change and the warming of Canada's waters, aquatic organisms will need corridors within watersheds to move northward to cooler waters.
These migratory pathways also aid exotic species invasions that are challenging many ecosystems across Canada. In managing the effects of these species, we will also need to adopt a watershed-based approach and not focus solely on a single invaded river or lake, for example.
Water contamination by pesticides, other toxins, microplastics and nutrients must also be managed, in a watershed context, because of their connectivity.
Furthermore, damming flowing waters is an obvious barrier to natural connectivity, as are bridge and culvert installations. Such activities are related to human needs, such as transportation, water level management for agriculture and drinking water, and hydroelectricity generation. So, politically speaking, several departments at all levels of government are involved in watershed disturbances, and therefore in their mitigation.
For all these reasons, my third message is that internal flows within watersheds need to be considered when managing contamination, invasive species, migration and climate change mitigation for aquatic life.
Finally, many different types of human activity can influence watershed connectivity and, politically, different agencies need to be involved in their protection and management.
Overall, based on scientific limnological knowledge, the committee is advised to support structuring, collaborative and scientific initiatives at the watershed level for their better protection and conservation.
Thank you for your attention. I'd also like to thank you for giving me the opportunity to speak to you today.