Streams Reduce Nitrogen Pollution, Scientists Find

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The worst-case scenario is the creation of so-called dead zones, where nothing can live. The Gulf of Mexico, Chesapeake Bay, and Black Sea all have dead zones, with devastating consequences to marine life and the livelihoods of those who depend on the fisheries.

Nitrogen pollution has also been implicated in manatee deaths in Florida, noxious algal blooms, and the loss of marine habitat from overgrowth of algae, especially in coral reefs and seagrass beds. These near-coast habitats serve as nurseries for commercial and non-commercial fisheries, leading to long-term declines in coastal marine fisheries.

New Insight

Until now, scientists had not fully understood the processes of nitrogen uptake and release in streams. Newly available technology enabled the researchers in this study to track nitrogen through a stream's biological systems and find out what happens to it. The two-year study involved more than 100 researchers collecting data on 12 streams from Puerto Rico to Alaska. Small streams handle nitrogen in two ways, Webster explained. First, the algae, bacteria, and fungi in a stream use nitrogen as a nutrient. They grow quickly and become food for aquatic insects and fish.

"Then you have the dead gunk that falls to the bottom," said Webster. "That is converted by denitrifying bacteria back to a gas, which is vented back into the atmosphere."

The researchers found that the faster flowing water of rivers and channelized streams carries those sediments rather than letting them fall to the bottom.

According to the results, the smaller a stream is, the more efficient it is at "trapping" nitrogen; the nitrogen is removed more quickly and travels shorter distances downstream.

"What it means," said Webster, "is that you have to take care of the streams on the landscape."

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