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On the fate of anthropogenic nitrogen.

ABSTRACT: 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 approximately 35 and 15 TgN/yr, respectively. Greater denitrification in terrestrial soils and wetlands may account for the loss of approximately 17 TgN/yr from the land surface, calculated by a compilation of data on the fraction of N(2)O 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 (NO(x) and NH(x)) 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 N(2) endproduct.

SUBMITTER: Schlesinger WH

PROVIDER: S-EPMC2613040 | biostudies-literature | 2009 Jan

REPOSITORIES: biostudies-literature

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On the fate of anthropogenic nitrogen.

Schlesinger William H WH

Proceedings of the National Academy of Sciences of the United States of America 20081231 1

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 approximately 35 and 15 TgN/yr, respectively. Greater denitrification in terrestrial soils and wetlands may account ...[more]

PMID: 19118195

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Project description:Nitrogen, the most dominant constituent of Earth's atmosphere, is critical for the habitability and existence of life on our planet. However, its distribution between Earth's major reservoirs, which must be largely influenced by the accretion and differentiation processes during its formative years, is poorly known. Sequestration into the metallic core, along with volatility related loss pre- and post-accretion, could be a critical process that can explain the depletion of nitrogen in the Bulk Silicate Earth (BSE) relative to the primitive chondrites. However, the relative effect of different thermodynamic parameters on the alloy-silicate partitioning behavior of nitrogen is still poorly known. Here we present equilibrium partitioning data of N between alloy and silicate melt ( DNalloy/silicate ) from 67 new high pressure (P = 1-6 GPa)-temperature (T = 1500-2200 °C) experiments under graphite saturated conditions at a wide range of oxygen fugacity (logfO2 ~ΔIW - 4.2 to - 0.8), mafic to ultramafic silicate melt compositions (NBO/T = 0.4 to 2.2), and varying chemical composition of the alloy melts (S and Si contents of 0-32.1 wt.% and 0-3.1 wt.%, respectively). Under relatively oxidizing conditions (~ΔIW - 2.2 to - 0.8) nitrogen acts as a siderophile element ( DNalloy/silicate between 1.1 and 52), where DNalloy/silicate decreases with decrease in fO2 and increase in T, and increases with increase in P and NBO/T. Under these conditions DNalloy/silicate remains largely unaffected between S-free conditions and up to ~17 wt.% S content in the alloy melt, and then drops off at > ~20 wt.% S content in the alloy melt. Under increasingly reduced conditions (< ~ ΔIW - 2.2), N becomes increasingly lithophile ( DNalloy/silicate between 0.003 and 0.5) with DNalloy/silicate decreasing with decrease in fO2 and increase in T. At these conditions fO2, along with Si content of the alloy under the most reduced conditions (< ~ΔIW - 3.0), is the controlling parameter with T playing a secondary role, while, P, NBO/T, and S content of the alloy have minimal effects. A multiple linear least-squares regression parametrization for DNalloy/silicate based on the results of this study and previous studies suggests, in agreement with the experimental data, that fO2 (represented by Si content of the alloy melt and FeO content of the silicate melt), followed by T, has the strongest control on DNalloy/silicate . Based on our modeling, to match the present-day BSE N content, impactors that brought N must have been moderately to highly oxidized. If N bearing impactors were reduced, and/or there was significant disequilibrium core formation, then the BSE would be too N-rich and another mechanism for N loss, such as atmospheric loss, would be required.

Dataset Information

On the fate of anthropogenic nitrogen.

Publications

On the fate of anthropogenic nitrogen.

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