Where, exactly, does this nitrogen come from? That’s what IBES graduate affiliate Emily Joyce wants to know. A mentee of biogeochemist Meredith Hastings, famed for her expertise in isolating nitrogen isotopes and identifying their sources, Joyce is devoting her time at Brown to understanding how much of the nitrogen in Narragansett Bay is deposited by precipitation, and how much is deposited by other city sources. 

“Using precipitation samples that were collected year-round in Providence in 2017, we can now better estimate the amount of nitrogen deposited into Narragansett Bay through precipitation,” she says, explaining that this work only considers a process known as “wet” deposition. “We found that total nitrogen wet deposited from the atmosphere has increased today by at least a factor of around 2.5 times since 1990.”

Now, she and her fellow lab members are working to quantify the amount of “dry” nitrogen deposition on Narragansett Bay, which occurs via gases and particles. This calculation is vital for understanding the biogeochemistry of the Bay, but had previously only ever been estimated.

Joyce believes that quantifying total urban nitrogen deposition is vital to ensure a healthy Bay today, and in the future.

“Understanding the sources of excess nitrogen is key for effective nitrogen pollution management; however, our understanding of the contribution of nitrogen from atmospheric deposition is limited by a significant lack of observations conducted, especially for dry deposition.” says Joyce. “Our preliminary results for wet deposition suggest that total nitrogen deposition has increased considerably over the past 30 years, which may have important implications for future environmental policy.”