Written by Nicolas St-Gelais, PhD | 2020
We often tend to forget that the idea of “good” water is a matter of perspective. Lakes and rivers are used for a variety of functions such as drinking water, swimming, irrigation and therefore each person’s perspective of “good” water quality comes from how they use it. For example, for a beach operator, water is considered to be of high quality when it has low concentration of fecal coliforms meaning that the water is safe for aquatic activities, whereas for an angler it will be water that is rich in fish.
When assessing the health of a waterway, we need to be able to evaluate these different perspectives as a whole, but not much is known about how these perspectives overlap in terms of safety standards. How are these various perspectives aligned in Canadian lakes and rivers? Is water that is safe to swim in also safe to drink? Is this same water also safe for aquatic wildlife and field irrigation?
In ecology, the trophic status is widely used to determine the health of a waterway such as a river or lake. It is commonly based on nutrient concentrations, because any excess will promote high algal productivity, which can lead to blooms. For this reason, strategies to protect aquatic ecosystems often involve reducing nutrient inputs to rivers, much of which comes from agriculture. But if the nutrient concentrations are lower, can the water quality be considered good enough for recreational activities, irrigation or to protect aquatic wildlife?
As part of my postdoctoral work at the Université de Montréal, I studied the performance of trophic status as an indicator of the possible uses of river water and the results were published a few weeks ago in the scientific journal BioScience.
To achieve this, more than 60,000 open water quality data sources in Canadian rivers have been used to assess water quality for a variety of aquatic activities, as per the Canadian Council of Ministers of the Environment (CCME) standards. This allowed us to develop a profile of each river’s safe uses and determine the adequacy of trophic status as an indicator of whether or not these rivers can be used for their intended purposes in a safe manner.
For a majority of rivers, it was observed that the water was safe for swimming. However, according to Canadian standards, less than 50% of the rivers were considered safe for aquatic wildlife.
On the question of trophic status as an indicator of the safety of a waterway for recreational activities or drinking capability, it was observed that for activities that are severely limited by fecal contamination, such as swimming and irrigation, trophic status was a good indicator of water quality in the majority of cases. However, it was a much weaker indicator for activities limited by the presence of heavy metals, such as the protection of aquatic wildlife.
Trophic status is a valid barometer for assessing the general health of a waterway in many aspects, but since the bacteriological water quality of a waterway can vary very rapidly, trophic status cannot be used as an indicator of the safety of a waterway for recreational activities or drinking capability. For this reason, it is important to consider the impact of our activities on the different perspectives of water quality and to identify presently safe uses of these water bodies that may be lost in the future in order to develop the necessary preservation strategies.