Atmospheric deposition of nitrogen in New York City and Boston

Thomas Whitlow1, Yoshiki Harada2, Pamela Templer3 and Lucy Hutyra4

Nitrogen emissions from electrical power plants, automobile exhaust and fertilizer applications are the major sources of nitrogen deposition in rain and snow onto ecosystems of the northeastern United States. Small amounts of nitrogen deposition can serve as fertilizer and stimulate growth of plants. However, high rates of nitrogen deposition can lead to a series of negative consequences, including reductions in plant diversity, acidification of soils and waterways, and harmful effects on human health. The Clean Air Act Amendments in 1990 led to declining rates of nitrogen deposition in the northeastern U.S., but rates remain significantly elevated (more than 10X pre-industrial levels) and they occur as hot spots in urban areas.

We established two urban monitoring programs of atmospheric deposition in 2015, with one in Boston, MA and the other in New York City. We found that rates of atmospheric deposition are higher near the ground than on rooftops at the Brooklyn Grange in NYC. This difference makes intuitive sense in cities, where vehicles emit a variety of heavy metals and NOx from mechanical wear and fuel combustion. We also found that deposition and downspout drainage are relatively low, but leachate directly beneath the planting beds is very high. This pattern suggests that denitrification is occurring in the drainage zone between the beds and the roof drains. Further experiments using Br and nitrate pulses and underway to determine whether N is disproportionately leaving the system. We also established two new urban sites in the National Atmospheric Deposition Program in Boston, MA, with one site at Boston University and one at the Arnold Arboretum of Harvard University. Data from these urban sites provide a more complete understanding of the nitrogen fluxes in precipitation around the greater Boston and New York City areas and will contribute to our understanding of nitrogen pollution around the United States. Ultimately, our work will create a better understanding of how atmospheric nitrogen pollution affects nitrogen inputs to our terrestrial ecosystems and nearby waterways, providing policy-relevant data with implications for both ecosystem and human health.

 

1Cornell University, thw2@cornell.edu
2Cornell University
3Boston University, ptempler@bu.edu
4Boston University