Nitrogen Pollution in the Northeastern United States: Sources, Effects, and Management Options

TLDR

The northeastern United States receives high anthropogenic nitrogen inputs from food imports, atmospheric deposition, fertilizer, feed, and leguminous crops, leading to tropospheric ozone, plant damage, altered forest nitrogen cycles, acidified surface waters, and coastal eutrophication. We applied the PnET‑BGC and WATERSN models to assess management strategies that reduce nitrogen inputs to forests and estuaries. Aggressive nitrogen emission cuts alone do not markedly improve forest stream acid–base status, whereas wastewater treatment removal yields larger estuarine nitrogen reductions, and comprehensive source‑targeted strategies provide the greatest ecological benefits.

Abstract

The northeastern United States receives elevated inputs of anthropogenic nitrogen (N) largely from net imports of food and atmospheric deposition, with lesser inputs from fertilizer, net feed imports, and N fixation associated with leguminous crops. Ecological consequences of elevated N inputs to the Northeast include tropospheric ozone formation, ozone damage to plants, the alteration of forest N cycles, acidification of surface waters, and eutrophication in coastal waters. We used two models, PnET-BGC and WATERSN, to evaluate management strategies for reducing N inputs to forests and estuaries, respectively. Calculations with PnET-BGC suggest that aggressive reductions in N emissions alone will not result in marked improvements in the acid–base status of forest streams. WATERSN calculations showed that management scenarios targeting removal of N by wastewater treatment produce larger reductions in estuarine N loading than scenarios involving reductions in agricultural inputs or atmospheric emissions. Because N pollution involves multiple sources, management strategies targeting all major pollution sources will result in the greatest ecological benefits.