Nitrogen levels have been building up in soil and leaking into water systems, according to a recent study conducted by UW Prof. Nandita Basu of the department of earth and environmental sciences and doctoral student Kim Van Meter. The study, published in <em>Environmental Research Letters,</em> stated that even if nitrogen use was stopped today, its effects on human health and the environment could still be felt through what are called “time lags.” </p>
One prominent issue is the difficulty in measuring soil nitrogen levels. Van Meter explained that this comes from nitrogen “legacies” in the soil.
“You may go down to a local stream and measure the nitrogen and say, ‘well the nitrogen levels are X this year,’ but you don’t know if that really came from what was applied to the landscape this year or if it came from … 10 or 20 years ago, because the time lag from when nitrogen is applied to when it comes out in the water can be quite long.”
This way, an excess of nitrogen in the soil and water creates a number of risks to health and the environment.
A health risk that is associated with excess nitrogen is known as “blue baby syndrome.” When young babies are exposed to high nitrate levels in drinking water, it can “impair the ability of their blood to carry oxygen,” which is the reason behind the name, according to Van Meter. There may also be links to certain types of cancer with high nitrogen levels but those links aren’t as well established.
In water, an increase of nitrogen levels can lead to hypoxic conditions where there is a lack of oxygen in the water. This often stems from a process called eutrophication, which is especially apparent along coastal zones. The excess nitrogen causes an increase in algae growth, and the oxygen levels in the water are severely depleted as the algae was decomposed creating areas called “dead zones” where nothing is able to grow. An example of this is along the Gulf of Mexico, which is one of the largest dead zones in the world.
The time lags can also be troublesome for farmers looking for quick improvement.
“When farmers are doing different kinds of practices to improve water quality, we would expect that when they do something they would see the benefit of that,” Basu said. “The benefit will actually come much, much later which is something that needs to be acknowledged.”
“I like to say it’s like going on a diet and not losing any weight,” Van Meter said. “How long do you want to stay committed to a diet when you’re not losing any weight? I think it’s really important for people to understand that these legacies are there and that the time lags can be very long, so that you can get people excited about doing something to make a change, and keep them committed to those practices over time.”
For farmers, nitrogen fertilizer is important to improve plant growth and crop yields. Simply discontinuing the use of nitrogen fertilizers without an alternative could significantly affect crop yields. There has been some research done that says crops could do with little nitrogen, but according to Basu, “there needs to be more research and [translation] of the research so that there is more confidence in using less [nitrogen].”
Currently, there are a number of practices to help reduce the amount of nitrogen in soil such as covering crops. However, the time lags make it difficult to see immediate change.