Environmental Sustainability in Practice

Water Pollution from Fertilizers

Farmers apply a range of nutrients (or fertilizers) to the soil to enhance plant growth. This generally occurs in early spring before crops are planted and sometimes in the autumn after crops are harvested. In the right quantities, these nutrients enhance the soil’s fertility and help produce a strong and healthy crop. However, fertilizers can also have negative impacts on the environment, and in particular on our water resources. Rain and other forms of precipitation can carry certain nutrients in fertilizers off the fields and into waterways (both above and below ground), polluting them. These nutrients can cause a whole range of problems when they enter our waterways. Here, we focus on two of the most common nutrients that tend to pollute our waters and have far-reaching impacts: nitrates and phosphorus.


Nitrates

Nitrate (NO3) is a very common inorganic compound needed for plant growth. It occurs both naturally (e.g., in animal manure) and synthetically produced as a fertilizer. An important property of nitrate is that it is very water soluble (it dissolves easily in water), thus when rain falls on a field where nitrate fertilizer has been applied, it is dissolved and transported by the water. Water can move across the landscape, collecting in streams and rivers that flow to lakes and oceans. It can also move downward into groundwater. Nitrate that ends up in lakes can contribute to plant growth in those water bodies which reduces the amount of oxygen available for other living organisms such as fish.

Nitrate that ends up in groundwater can be consumed by animals and people. The consumption of nitrates is especially dangerous for babies – it can cause what is called blue baby syndrome. This syndrome was more common in the past; now we recognize the causes and limit exposure by babies to nitrates. However, cases of blue baby syndrome still occur (Knobeloch et al., 2000).


Phosphorus

Another essential ingredient for plant growth that farmers apply to the field is phosphorus. Like nitrates, phosphorus can be found in both natural sources such as compost and can be produced synthetically from a mined material called ‘phosphate’. Phosphorus is applied to soil in much the same way as nitrates, and often these are mixed as part of a multi-nutrient fertilizer. However, phosphorus is less water soluble than nitrates, and tends to move with soil particles that are washed off the fields by large amounts of precipitation. Phosphorus tends to accumulate in larger bodies of water, along with water pollution from other sources (for example, industries and cities). Because phosphorus, like nitrates, feeds plants, it is a major contributor to the build up of algae and the eutrophication of water bodies. Eutrophication means that the water is less able to support fish and other living organisms because the oxygen in the water is reduced.

Algae contaminates water bodies, making them unsafe to drink and for recreation, and an unsuitable habitat for fish and other organisms. The combination of high levels of phosphorus in a water body and warm temperatures can lead to huge ‘blooms’ of algae. This is a serious concern in Lake Erie.

 

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