Global Nitrogen Cycle

Abstract

Human activity has significantly altered nitrogen (N) cycle. Prior to the industrialization and agricultural revolution, the vast majority of reactive N (Nr) on the Earth was created by microorganisms through biological N fixation, and this creation was balanced over geological time by denitrification. Over the past century, development of new agricultural practices to satisfy growing global demand for food has drastically disrupted the N cycling. Anthropogenic creation of Nr through Haber-Bosch process now rivals the rate of natural terrestrial N fixation. The unintentional creation of Nr during fossil fuel combustion also adds to the global N cycle. The anthropogenic influences on the N cycling vary across regions of the globe. To date, the largest changes in N cycling have occurred in developed countries in temperate zone. However, this is changing as fertilizer use and fossil fuel combustion increase in South Asia and tropical South America. The significant consequences of anthropogenic acceleration of N cycle is the eutrophication of estuaries and coastal waters, leading to hypoxic zones in many areas, as well as increased global inventories of potent greenhouse gas N2O.