The global nitrogen cycle: changes and consequences
Citation
James N Galloway, The global nitrogen cycle: changes and consequences: .
Summary
In the absence of human activities, biological N fixation is the primary source of reactive N, providing about 90–130 Tg N year−1 (Tg = 1012 g) on the continents. Human activities have resulted in the fixation of an additional 150 Tg N year−1 by energy production, fertilizer production, and cultivation of crops (e.g., legumes, rice). Some sinks of anthropogenic N have been estimated (e.g., N2O accumulation in the atmosphere; loss to coastal oceans), however due to the uncertainty around the magnitude of other sinks (e.g., retention in groundwater, soils, or vegetation or denitrification to N2) a possibly large portion of the N fixed by humans is missing. While we know that N is accumulating in the environment, we do not know [...]
Summary
In the absence of human activities, biological N fixation is the primary
source of reactive N, providing about 90–130 Tg N
year−1 (Tg = 1012 g) on the continents. Human
activities have resulted in the fixation of an additional 150 Tg N
year−1 by energy production, fertilizer production,
and cultivation of crops (e.g., legumes, rice). Some sinks of
anthropogenic N have been estimated (e.g., N2O accumulation in the
atmosphere; loss to coastal oceans), however due to the uncertainty
around the magnitude of other sinks (e.g., retention in groundwater,
soils, or vegetation or denitrification to N2) a possibly large portion
of the N fixed by humans is missing. While we know that N is
accumulating in the environment, we do not know the rate of
accumulation. Due to the myriad of effects of excess N on humans,
ecosystems, and the atmosphere, and their cascading nature (i.e., one
atom of N can have a large number of excess N on humans, ecosystems, and
the atmosphere, and their cascading nature (i.e., one atom of N can have
a large number of different effects as it is transformed to different N
species), this lack of knowledge is unfortunate. There are limited
options available to society to reduce the amount of N mobilized by
human action because there is, in effect, a N imperative
— it is required for food production. As population
and per capita consumption of food (especially animal products)
increase, more and more N will be converted from unreactive to reactive
forms in the future. This is especially true in less developed regions.
Published in Environmental Pollution, volume 102, issue 1, on pages 15 -
24, in 1998.
