Phosphate and nitrates are nutrients that are essential to life. In water, inorganic phosphorus occurs as ion phosphate PO43-. This is the form that phosphorus takes when it is dissolved in water. Phosphate is an important component of DNA (deoxyribonucleic acid) and ATP (adenosine triphosphate). DNA stores genetic information and allows an organism to grow and develop. Organisms store energy as ATP, but unlike fat, it’s a form that is immediately available for use. Therefore, both nutrients are in high demand. Phosphorus is relatively rare in the earth’s crust so in general it is in short supply and puts the brakes on growth. That is why the addition of fertilizer to your garden results in a more abundant crop. Phosphorus does not exist as a gas and therefore, unlike nitrogen, does not exist in the atmosphere.

The availability of nitrogen also limits growth. However, you would be right to point out that there is plenty of nitrogen in the atmosphere (78%). The hitch is that very few organisms can use nitrogen directly from the air. The exceptions are cyanobacteria (also known as blue-green algae) which transform nitrogen from the atmosphere into ammonium (NH4+). Some bacteria live in symbiosis in the roots of certain legumes such as beans that can do the same thing. Finally, a third group of bacteria transforms ammonium first into nitrite (NO-2) and then into nitrate (NO-3) which is taken up by plants. A bit complicated, but the bottom line is that animals and plants depend on other organisms to get the nitrogen they need to grow and survive. Nitrogen is also essential to photosynthesis, without it plants can’t make food. Nitrogen is in all amino acids which in turn are the building blocks for the proteins in our bodies. Like phosphate, the demand outstrips the availability except for organisms that can use nitrogen directly. For these reasons among others, phosphate and nitrate are two parameters frequently measured in water by watershed groups, including the Petitcodiac Watershed Alliance.

Having an abundance of phosphate and nitrate in the environment might seem like a good thing when it improves crop yields. However, when it reaches rivers and lakes it can lead to excessive growth of algae and plants. Lakes and rivers can become green.

Bloom of cyanobacteria in Irishtown Reservoir 2009. Photo: Alyre Chiasson

Algae and plants use oxygen at night. When the algae and plants eventually start to die at the end of their growing season their decomposition strips even more oxygen from the water. As a result, the fish die, they decompose, and even more oxygen is depleted. In the end, you have a dead smelly lake or river. This excessive enrichment in waters and the resulting algal growth is known as eutrophication. Cyanobacteria can also undergo rapid growth and can even overshadow the growth of regular good algae. Cyanobacteria are a normal inhabitant of all waters and only become a problem when overly abundant. Excessive growth of algae stops when nitrogen becomes depleted from the water, but cyanobacteria have no such limitation because they can use nitrogen directly from the air! They also do better at higher temperatures than regular algae. This might explain why serious blooms of cyanobacteria are becoming more common as temperatures rise with climate change. In 2019, Lake Winnipeg, Manitoba made the news with a dramatic cyanobacteria bloom, prompting an environmental and social crisis. In the late 1980s, as a student at the University of Manitoba, I visited Lake Winnipeg. It was a beautiful blue and supported an active commercial fishery. Needless to say, the lake is today facing difficulty on numerous fronts. In addition, cyanobacteria can produce deadly toxins, which can be fatal if ingested. This is why sites where algal and cyanobacteria blooms have occurred are posted with a warning.1

Lake Winnipeg cyanobacteria bloom, 2019.
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Canada can take credit for identifying phosphate as the main driver of algal and cyanobacteria blooms. That legacy can be seen today in the labeling of detergents as being phosphate-free. However, sewage, soil exposure from various practices, and intensive use of fertilizers have resulted in a worldwide problem. Even the oceans have not escaped, with coastal eutrophication on the rise2. Limiting runoff and the input of phosphates and nitrates from sewage and wastewater is an obvious solution. This requires the implementation of best management practices on land and adequate treatment of sewage3. Drinking water supplies are not exempt from blooms and the removal of potential cyanobacteria toxins can require expensive technology that might not be available nor affordable to all, particularly on a global scale.

What can you do? Support efforts that limit the input of phosphates and nitrates into waterways. If your property borders a waterway, a strip of vegetation adjacent to the water known as a riparian zone can intercept and absorb nutrients and pollutants. Limit fertilizer use, natural or artificial, to what is absorbed by the plants to prevent excess nutrients washed away into waterways by the rain. As an added bonus, your riparian zone helps stabilize the soil making your land less likely to erode away. In 2023, the New Brunswick Environmental Network released a toolkit for understanding and implementing riparian zones. You can find more about riparian zones by consulting their document at:

Warning of potentially dangerous cyanobacteria blooms. Photo: Alyre Chiasson

In the next issue, we will dive into the Petitcodiac River starting with the fish!
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