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Agricultural pollution of waterways: why should we be concerned?

Bétail près d'un cours d'eau

In Quebec, there are nearly 30,000 agricultural operations. What's more, more than 40,000 people work in this sector. This therefore means that agriculture occupies a preponderant place in our economy. Unfortunately, it also occupies an important place in the list of sources of contamination of our waterways. But how exactly does agriculture have a damaging effect on lakes and rivers? 

Water samples

Many agricultural lands in Quebec have direct access to watercourses. While consulting the regional profile of the biofood industry in Quebec, we notice that several are close to the St. Lawrence River or Lac-Saint-Jean, for example. This phenomenon can be explained by historical reasons and by the fact that agriculture requires large quantities of water.

Répartition des exploitations agricoles dans les régions du Saguenay-Lac-Saint-Jean (à gauche) et de la Mauricie (à droite)
Distribution of agricultural operations in the Saguenay-Lac-Saint-Jean (left) and Mauricie (right) regions. Source : Regional profile of the biofood industry in Quebec for the year 2019

In fact, agriculture requires more water than any industry: globally, water for agricultural irrigation purposes monopolizes 70 % to 80 % of all the fresh water consumed on the planet. The animal products sectors are the most voracious. Quebec is also fertile ground for the pork industry: it provides 6 % of all pork consumed in the world. In 2019, this represented a production of 7.1 million animals! Watering the cereals used to feed the animal, hydration, cleaning of facilities: when we consider all of Quebec's animal production, we understand why water consumption is increasing so quickly.

Where does the water taken come from? 

This water, just like drinking water, is drawn from groundwater or simply surface water (in lakes and rivers). It even happens that water is drawn from certain wetlands. 

Some farmers manage to make do with rainwater collected in a well to irrigate their land; their actions are therefore not taken into consideration in the calculation of the levy. On the other hand, with climate change and periods of drought and flooding, these farmers risk turning to sources other than rainfed and inflating the current figures. 

Credit: Lise1011/Flickr

Consequences of water withdrawals 

When a significant quantity of water is withdrawn, this risks creating low water (the lowest water level) and modifying the natural flow of the watercourse. In the event of a weakened flow, the contaminants are therefore less well diluted. During low water periods, nautical and swimming activities are affected.

The most worrying thing is that drinking water and agricultural water are, in a way, in competition : we will have to make a choice considering that we plan to reach a population of 9.6 billion humans in 2050, that global food demand will double, that climate change will alter the quantity of available water by generating droughts and floods, and that certain regions already have drinking water shortage issues.

Contaminants: phosphorus, nitrogen and fecal coliforms

Agricultural production has several other impacts on waterways. Among other things, it causes a high level of phosphorus and nitrogen in the water as well as a higher presence of fecal coliforms. 

According to many experts, the presence of phosphorus in water is not alarming in itself. It is even essential to the productivity of freshwater ecosystems. On the other hand, due to human activities such as agriculture, there is far too much phosphorus in our waterways. Indeed, according to researchers in a study from the University of Montreal and McGill University studying data between 1985 and 2011, 19 of 23 Watershed studied crossed the threshold of 2.1 tonnes per square kilometer. According to their estimates, it would take hundreds (perhaps even thousands) of years to return below an acceptable threshold. 

The nitrogen contamination level is less important than for phosphorus, but it should still not be neglected. In 1981, “80 % of agricultural land in Canada was in the “very low” risk category for the risk of nitrogen water contamination”. In 2016, only 49 %s were at “very low” risk. Unsurprisingly, the regions that have undergone more intense densification in recent years are those where the risk is greatest. The following map shows some of the most at-risk regions in a darker color. 

Risque de contamination de l'eau de surface par l'azote au Canada en 2016
Risk of surface water contamination by nitrogen in Canada in 2016. Source : Nitrogen indicator

Consequences of contaminants

Phosphorus and nitrogen are in fact found in several fertilizers, which sometimes also include potassium, and in manure. During spreading periods, farmers cover their land with a layer of fertilizer and manure. Phosphorus and nitrogen then become fixed in the soil, sometimes saturating it. When there is rain, or any other water discharge, the precipitation runs off and flows, carrying contaminants with it until they reach surface and groundwater. 

Similarly, during erosion, saturated soils contaminate banks and water. Then, present in too large quantities in water, nitrogen can be harmful to human health while phosphorus rather causeseutrophication. Remember that agricultural land is often located near watercourses; the streaming drops therefore have a higher concentration than if the drops took a longer trip. 

Moreover, in addition to generating phosphorus, spreading practices also contaminate water with fecal coliforms. Indeed, fecal coliforms are bacteria contained in excrement. By the same principles of runoff and erosion, manure contaminates waterways. Thus, it becomes impossible to swim or navigate in water with too high levels of fecal coliforms.

Credit: Olivier Duval/Flickr

Cumulative effects 

With these forms of contamination, we often notice a cumulative effect. Since the farms are often quite close to each other, the contaminants emitted by each of them are added to the others. In other words, by having several farms rather than one farm, we increase the total volume of phosphorus emitted within a 10 km radius. Moreover, there is currently no obligation to characterize the location of all farms in Quebec. The regional county municipalities (MRC) will do this in their development plan for the agricultural zone. Thus, the permits granted do not take into consideration the activity of the neighborhood.

This proximity effect also has an effect on withdrawals, because if there is only one farm within a 10 km radius, its withdrawals are not likely to affect the watercourses. However, a region with a hundred farms within a 10 km radius can have serious repercussions. Unlike contaminants, water samples are declared to the Ministry of the Environment and the Fight against Climate Change (MELCC) and are therefore counted. 

In addition, between them, the different contaminants can have a cumulative effect. Indeed, the presence of fecal coliforms will, for example, deprive water of oxygen just like phosphate. Thus, when several different contaminants are found, eutrophication can be even more rapid.  

Let us understand clearly: agriculture is essential to meeting the needs of society, but in the interests of environmental protection and social justice, its practices deserve to be reviewed and better supervised. Reducing exports, diversifying our industries for greater autonomy, limiting the quantity of large farms and prioritizing human-scale farms that promote local agriculture are avenues to explore. 

Main photo: Hindrik Sijens


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