Long-Lasting Nitrate in Streams Disturbs Water Quality

Hydrologic researchers from the USGS found that nitrate from fertilizers takes decades to travel through groundwater and into streams, disturbing the water quality of streams and even large rivers for many more years to come.

Researchers from the U.S. Geological Survey (USGS) have discovered that nitrate from nitrogen-based fertilizers end up in groundwater, which then takes 10 years and longer to travel into streams and rivers. Once the nitrate makes it into those waterways, the water quality is negatively affected for several years. The slow traveling nitrate makes it difficult for water quality experts to closely estimate the amount of nitrate that is expected to be in those waterways in the future.

"This study provides direct evidence that nitrate can take decades to travel from recharge at the land surface to discharge in streams," said Jerad Bales, acting USGS associate director for water. "This is an important finding because long travel times will delay direct observation of the full effect of nutrient management strategies on stream quality."

During their study, researchers looked at surface and ground waters at seven different sites across the U.S. and discovered that watersheds with the most groundwater held the highest nitrate levels. Then they used an age dating tracer to find out how long it takes the groundwater to reach the stream, discovering that the nitrate levels found in the water was older than a decade.

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