Nitrogen deposition near roadways in south-central New York

Background/Question/Methods Atmospheric deposition is a major input of nitrogen (N) to terrestrial and aquatic ecosystems and N pollution is a major concern in human-dominated landscapes. Deposition of N can be spatially heterogeneous. Deposition measurements at locations far away from the pollution sources may underestimate regional inputs and be less useful in analyzing local patterns of N biogeochemistry. We studied N deposition in areas adjacent to interstate highways and urban traffic corridors in the south-central New York, headwaters of the N-polluted Chesapeake Bay. Two forested sites and two open shrub/grassland sites were selected and in each site, bulk collectors (collecting both wet and dry deposition) were deployed at incremental distances from the roadways. A fifth reference site was established in the Nature Preserve at Binghamton University, with a total of 52 collectors. Deposition samples were collected weekly from June to August 2009 and bi-weekly during Fall 2009. Deposition volume, pH, and conductivity were measured immediately after each collection, and filtered samples subsequently measured for NH₄-N and NO₃-N using a Lachat automated analyzer.

Results/Conclusions Concentrations of NO₃-N from collectors immediately adjacent to the roads (0 m lines) were similar among four sample sites, ranging from 0.15-0.71 mg/L. In two open sites, we found no clear trend of declining NO₃-N away from the roads. In one of the forested sites, significantly higher NO₃-N concentrations were found away from the road and under the canopy (mean NO₃-N concentrations of 0.338, 0.587, and 0.917 mg/L at 0 m, 15 m, and 40 m distances respectively). Contamination from bird droppings prevented us from calculating an accurate input of NH₄-N. The comparisons of median NH₄-N and NO₃-N values indicate that NH₄-N from traffic sources was generally lower than NO₃-N. Budget estimates of NO₃-N and NH₄-N inputs ranged from 110 to 153 mg/m² in the summer, extrapolating to yearly inorganic N inputs of 0.44 - 0.612 g/m². Our data suggest limited N deposition near roadways. That is in contrast to the exponential decline in metal deposition (Ca, Mg, Al, Sr, Zn, Cu, Pb) away from the roads measured at the same sites. Traffic-generated N pollutants thus could travel long distances and affect the regional environment. However, landscape plant cover may also affect the fate of this N pollution.