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On the fate of anthropogenic nitrogen

Schlesinger, William H.
Proceedings of the National Academy of Sciences of the United States of America 2009 v.106 no.1 pp. 203-208
nitrogen, biogeochemistry, biogeochemical cycles, nitrogen fertilizers, fertilizer application, environmental impact, water pollution, leaching, groundwater contamination, losses from soil, runoff, denitrification, ammonium nitrogen, nitrate nitrogen
This article provides a synthesis of literature values to trace the fate of 150 Tg/yr anthropogenic nitrogen applied by humans to the Earth's land surface. Approximately 9 TgN/yr may be accumulating in the terrestrial biosphere in pools with residence times of ten to several hundred years. Enhanced fluvial transport of nitrogen in rivers and percolation to groundwater accounts for [almost equal to]35 and 15 TgN/yr, respectively. Greater denitrification in terrestrial soils and wetlands may account for the loss of [almost equal to]17 TgN/yr from the land surface, calculated by a compilation of data on the fraction of N₂O emitted to the atmosphere and the current global rise of this gas in the atmosphere. A recent estimate of atmospheric transport of reactive nitrogen from land to sea (NOx and NHx) accounts for 48 TgN/yr. The total of these enhanced sinks, 124 TgN/yr, is less than the human-enhanced inputs to the land surface, indicating areas of needed additional attention to global nitrogen biogeochemistry. Policy makers should focus on increasing nitrogen-use efficiency in fertilization, reducing transport of reactive N to rivers and groundwater, and maximizing denitrification to its N₂ endproduct.