Galloway, J. N. University of Virginia,
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In the absence of human activities, biological N fixation is the primary source of reactive N, providing about 90-130 Tg N yr-1 (Tg = 1012 g) on the continents. Human activities have resulted in the fixation of an additional ~150 Tg N yr-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 the uncertainty around the magnitude of other sinks (e.g., retention in groundwater, soils, or vegetation or denitrification to N2 ) is large. 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 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.
Day: Tuesday, Feb. 2
Time: 08:30 - 9:00am
Location: Sweeney Center
Code: SS07TU0830S