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Title: NITROGEN EMISSIONS ALONG THE COLORADO FRONT RANGE: RESPONSE TO POPULATION GROWTH, LAND AND WATER USE CHANGE, AND AGRICULTURE

Author
item BARON, J - USGS
item Del Grosso, Stephen - Steve
item OJIMA, D - CSU, FT. COLLINS, CO
item THEOBALD, D - CSU, FORT COLLINS, CO
item PARTON, W - CSU, FORT COLLINS, CO

Submitted to: American Geophysical Union
Publication Type: Book / Chapter
Publication Acceptance Date: 6/1/2004
Publication Date: 11/1/2004
Citation: Baron, J.S., Del Grosso, S.J., Ojima, D.S., Theobald, D.M., Parton, W.J. 2004. Nitrogen emissions along the colorado front range: response to population growth, land and water use change, and agriculture. American Geophysical Union.

Interpretive Summary: Biologically available nitrogen (fixed N) has a strong influence on species composition and growth rates in aquatic and terrestrial ecosystems. Application of N based fertilizers for crop production and lawns directly increases fixed N in agricultural and urban systems. In addition, N from fertilizers and other human activities can be emitted to the atmosphere, transported, and deposited in relatively pristine ecosystems. We investigated the sources and fate of N emissions generated in northeastern Colorado. The Colorado Front Range experienced rapid population growth from 1980 to 2000 and this is expected to continue in the near future. N emissions have also increased, due primarily to transportation, electricity generation, and industrial processes. Emissions from cropped soils have remained stable while emissions from livestock increased only slightly since 1980 because of more cattle and hogs in feedlots. Total emissions from transportation, power generation, and industry are more than 3 times higher than emissions from agriculture and non-agricultural emissions are more highly correlated with increased population. Although cause and effect relationships between increased N emissions and eutrophication of particular ecosystems are difficult to establish, higher N deposition has been observed at alpine sites west of the Colorado Front Range commensurate with the rise in emissions.

Technical Abstract: While N emissions are not commonly linked to land use change, the production of fixed nitrogen is strongly related to activities associated with urbanization, such as construction, production of energy, and development and use of transportation corridors. Agricultural intensification, brought about by application of synthetic N fertilizers and industrial-scale animal feeding operations, is another land use change that increases N emissions. The Colorado Front Range experienced rapid population growth from 1980 (1.9 million) to 2000 (2.9 million). Emissions from point (power plants and industry) and mobile (highway and off road vehicles) sources were responsible for most of the increase in emissions since 1980. Agriculture (cropped and grazed land and livestock) was the other important source of N emissions. Soil emissions from cropped and grazed lands remained stable while livestock emissions increased slightly due to more cattle and hogs in feedlots. Although cause and effect relationships between increased N emissions and eutrophication of particular ecosystems are difficult to establish, higher N deposition has been observed at alpine sites near the headwaters of the South Platte River commensurate with the rise in emissions. The ecosystem response of alpine systems to N deposition are likely to be the result, albeit an indirect one, of land use change.