Global trends and uncertainties in terrestrial denitrification and N2O emissions

Abstract

Soil nitrogen (N) budgets are used in a global, distributed flow-path model with 0.5° × 0.5° resolution, representing denitrification and N2O emissions from soils, groundwater and riparian zones for the period 1900-2000 and scenarios for the period 2000-2050 based on the Millennium Ecosystem Assessment. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N2 fixation and atmospheric N deposition increased from 155 to 345 Tg N yr-1 (Tg 1/4 teragram; 1 Tg 1/4 1012 g) between 1900 and 2000. Depending on the scenario, inputs are estimated to further increase to 408-510 Tg N yr21 by 2050. In the period 1900-2000, the soil N budget surplus (inputs minus withdrawal by plants) increased from 118 to 202 Tg yr-1, and this may remain stable or further increase to 275 Tg yr-1 by 2050, depending on the scenario. N2 production from denitrification increased from 52 to 96 Tg yr21 between 1900 and 2000, and N2O-N emissions from 10 to 12 Tg N yr-1. The scenarios foresee a further increase to 142 Tg N2-N and 16 Tg N2O-N yr-1 by 2050. Our results indicate that riparian buffer zones are an important source of N2O contributing an estimated 0.9 Tg N2O-N yr-1 in 2000. Soils are key sites for denitrification and are much more important than groundwater and riparian zones in controlling the N flow to rivers and the oceans. © 2013 The Author(s) Published by the Royal Society. All rights reserved.