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Bird poop brings 3.8 million metric tons of nitrogen out of the sea each year

Long before the rise of modern agriculture, humans relied on three things to bring nitrogen to barren soils: lightning strikes, nitrogen-fixing bacteria, and natural fertilizers. Among those, the nitrogen- and phosphorus-rich guano produced by millions of seabirds (such as nesting cormorants, above) was so prized it went by the name “white gold.” Now, a new study reveals just how rich that “gold” really is. A first-of-its-kind tally suggests that 804 million breeding seabirds and their chicks produce about 591,000 metric tons of nitrogen each year, researchers report today in Nature Communications. Together with guano from nonbreeders, seabirds produce about 3.8 million metric tons of the element annually—a shade higher than what’s transferred to land by all fishing activities, and 75% of the nitrogen fixed by either lightning or bacteria in rice paddies. A separate calculation estimates that nesting birds and chicks also excrete 99,000 metric tons of phosphorus each year. Now here’s the poop: Because about 12% of that nitrogen and 22% of that phosphorous is readily dissolvable, seabird colonies are nutrient “hot spots,” providing rich runoff to land and sea plants living downcurrent, the researchers say. That’s especially true in the waters around Antarctica and its nearby islands, because seabirds there typically are larger and have longer breeding seasons than seabirds elsewhere.