Using the BioEarth Modeling Framework to Understand the Sources, Transport and Fate of Atmospheric Nitrogen in the Pacific Northwest

May 18, 2017
By Liz Allen

Researchers: Serena Chung, John Harrison, Brian Lamb, and Tsengel Nergui

Widespread use of synthetic nitrogen fertilizers and fossil fuel combustion have led to significant increases in reactive nitrogen emissions and deposition globally. Emissions are any transfer of nitrogen compounds from the Earth’s surface to the atmosphere, while deposition describes transfer from the atmosphere back to the surface. Excess nitrogen is a serious environmental concern for many reasons including causing eutrophication of terrestrial and aquatic systems and contributing to global climate change. Within the Northwest, there are pressing questions about the degree to which agricultural practices contribute to excess nitrogen and its associated environmental consequences.

WSU researchers at the Department of Civil and Environmental Engineering’s Laboratory for Atmospheric Research, the School of the Environment, and the School of Biological Sciences are working together to quantify nitrogen sources, fluxes, and fates—in other words, defining a nitrogen budget for the Pacific Northwest. This work is part of the BioEarth project, funded by a 5-year $3 million grant from the USDA National Institute of Food and Agriculture (NIFA), which has supported researchers in modeling regional nitrogen emissions and deposition under changing climate patterns. Having an understanding of major nitrogen sources and sinks in the region is a prerequisite for being able to compare nitrogen fluxes in the Northwest with other regions and designing effective nitrogen management policies. This research is vitally important because it supports “true cost accounting”, enabling decision-makers to assess the various costs and benefits of nitrogen in the environment—including the crop yield benefits derived from fertilizers and negative effects of nitrogen deposition in sensitive natural environments.

Sunrise Area at Mt. Rainier, © Homini, CC BY 2.0.

Transport of atmospheric nitrogen is controlled in part by natural inter-annual climate variability caused by the El Niño Southern Oscillation (ENSO). In the ENSO cycle, El Niño years are characterized by warmer than average winters and springs, while La Niña years typically are cooler and wetter than average. As part of the regional nitrogen budget effort, researchers used meteorological and chemical transport models to simulate atmospheric physical and chemical processes in the Northwest during the 1997/98 El Niño and the 1998/99 La Niña events.

Tsengel Nergui is a graduate student working with Brian Lamb and Serena Chung in the Laboratory for Atmospheric Research. Her dissertation research has focused on understanding the effect of climate variability on atmospheric nitrogen dynamics in the Northwest. The frequency of extreme El Niño events, such as the one that occurred during the time period that Nergui focused on for her research, is projected to double in the 21st century. Understanding nitrogen deposition patterns in recent history helps modelers make projections about the transport and fate of nitrogen in the future.

The figure below shows an approximate annual nitrogen budget for the Pacific Northwest in the year 2000. The combination of nitrogen emissions from transportation, urban, industrial, and agricultural sources accounted for 97% of total regional emissions. Total annual nitrogen emissions from the Northwest were estimated at 362 gigagrams, or nearly 400,000 tons. Regional nitrogen deposition is less than total emissions. For the study period, over half of all deposition occurred in forests, with substantial nitrogen deposition in grasslands and croplands as well. Regional deposition tends to follow the seasonal patterns in agricultural nitrogen emissions.

Approximate Pacific Northwest total nitrogen emissions and deposition for the year 2000.

This research advances understanding of atmospheric nitrogen sources, sinks, and net transport over the Northwest using an integrated modeling approach. Also, it reveals how natural climate variability can alter atmospheric transport and nitrogen deposition. Looking toward future research goals, ongoing measurements and modeling studies are needed to further examine the effects of climate variability and change on nitrogen dynamics in the atmosphere. There is also a great need to investigate the potential for new management practices and technologies that reduce nitrogen emissions.

A recent webinar featuring WSU graduate student researchers Tsengel Nergui and Will Forney explores regional nitrogen budget research in greater detail. That webinar with speaker bios and learning objectives can be found HERE.


This article is reprinted from the CSANR 2016 Annual Report.

Filed under Climate Change

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