It turns out that fertilizer may pollute water for years. Scientists found that dangerous nitrate levels in drinking water could persist for decades, increasing the risk for health concerns.
Nitrogen fertilizer has been applied by farmers to fields for more than 80 years. This fertilizer then flows into rivers and lakes and can leech into drinking water. That's why researchers have decided to take a closer look at how long this particular nutrient load may impact our drinking water in the future.
"A large portion of the nitrogen applied as fertilizer has remained unaccounted for over the last decades," said Nandita Basu of Canada's University of Waterloo. "The fact that nitrogen is being stored in the soil means it can still be a source of elevated nitrate levels long after fertilizers are no longer being applied."
In this latest study, the researchers analyzed long-term data from more than 2,000 soil samples throughout the Mississippi River Basin. This revealed a systematic accumulation of nitrogen in agricultural soils. In fact, in many areas, this accumulation was hidden 25 to 100 cm below the surface of the soil. While this won't impact the top soil layer, it does mean that nitrogen may seep into groundwater sources.
"We hypothesize that this accumulation occurred not only because of the increased use of fertilizers, but also increases in soybean cultivation and changes in tillage practices over the past 80 years," said Kim Van Meter, a doctoral student in the Department of Earth and Environmental Sciences in the Faculty of Science.
When too much nitrogen is added as fertilizer, the excess washes into waterways and can even journey as far as the Gulf of Mexico. What's more worrying is if this enters drinking water. Exposure to excess nitrate in drinking water can cause methemoglobinemia or blue baby syndrome in infants.
"The presence of this legacy nitrogen means it will take even longer for best management practices to have a measurable benefit," Basu said. "If we're going to set policy goals, it's critical we quantify nitrogen legacies and time lags in human impacted landscapes."
The findings were published in the March edition of the journal Environmental Research Letters.
