To understand the extent to which human activities are polluting Earth’s atmosphere and oceans, it’s important to distinguish human-made pollutants from compounds that occur naturally. A recent study co-authored by a Brown University professor does just that for ammonium, a compound that is produced by human activities like agriculture, as well as by natural processes that occur in the ocean. The research, based on two years of rainwater samples taken in Bermuda, suggests that ammonium deposited over the open ocean comes almost entirely from natural marine sources, not from anthropogenic sources.
To understand the extent to which human activities are polluting Earth’s atmosphere and oceans, it’s important to distinguish human-made pollutants from compounds that occur naturally. A recent study co-authored by a Brown University professor does just that for ammonium, a compound that is produced by human activities like agriculture, as well as by natural processes that occur in the ocean.
The research, based on two years of rainwater samples taken in Bermuda, suggests that ammonium deposited over the open ocean comes almost entirely from natural marine sources, not from anthropogenic sources.
“That was a bit of a surprise,” said Meredith Hastings, the Joukowsky Assistant Professor of Earth, Environmental, and Planetary Sciences and one of the study’s co-authors. “We have some sense of what the ammonium emissions are in the United States, so we would expect to see that signature in Bermuda, but we don’t see it.”
The findings, published in Global Biogeochemical Cycles, don’t necessarily mean that ammonium emissions are lower than was previously thought, Hastings said. It could be that the ammonium is simply deposited closer to the continent before it reaches Bermuda, which is about 600 miles of the coast. Either way, the findings suggest that humans are not adding nearly as much ammonium to the ocean as some researchers had assumed.
Understanding the human contribution of ammonium is important because ammonium is a source of nitrogen. Too much nitrogen added to rivers and oceans can disrupt aquatic ecosystems.
“We see a lot of deleterious effects of increased nitrogen pollution on our waterways and our drinking water,” said Hastings, who is also a fellow in Brown’s Institute for the Study of Environment and Society. “So if you want to make policy to limit emissions and reduce these pollution impacts, we need to have a good handle on what sources are natural and what are anthropogenic.”
An ideal testing ground
The island of Bermuda is an ideal place to study the origins of pollutants, Hastings said. The weather over the island is dominated by tropical air masses that blow in from the south. But for part of the year, when tropical high pressure shifts, air masses coming off the continental United States work their way into the region. Those air masses can contain pollutants from industry, agriculture and other human activities on the continent.
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Ocean image via Shutterstock.
