SPATIAL HETEROGENEITY IN ATMOSPHERIC REACTIVE NITROGEN DEPOSITION TO URBANIZING LANDSCAPES: IMPLICATIONS FOR WATER QUALITY, ECOSYSTEM, AND HUMAN HEALTH

National wet and dry deposition monitoring networks are the foundation for our understanding of atmospheric nitrogen deposition to landscapes. However, it has recently been shown that wet and dry deposition measured at National Trends Network (NTN) and CASTNET sites in the Northeastern U.S. are more heavily influenced by nitrate originating as NO_x emitted from regional power plants than vehicular emissions (Elliott et al. 2007; 2009). Although vehicular NO_x emissions comprise the single largest NO_x source in the U.S. (54%), these recent studies suggest the fate of vehicular NO_x in the environment may be much different than that of power plant NO_x emissions. Here, in three ongoing studies, we: 1) characterize isotopic composition of major NO_x emission sources; 2) examine more closely the fate of vehicular NOx emissions using the isotopic composition of gaseous reactive nitrogen, plants, and soils along a gradient perpendicular to a major interstate; and 3) further examine the role of atmospherically deposited nitrogen as a factor in urban surface water quality during base- and storm-flow conditions.

Together, the results from these studies indicate that: 1) we are underestimating the total load of atmospheric N deposited to landscapes; 2) this load is not uniform in pattern, but rather heavily concentrated near highways and urban areas; and 3) the implications of this spatial distribution need to be considered as a factor influencing urban surface water quality.