Urbanization is a widespread type of land-use change that, until recently, received very little attention from ecosystem ecologists. Colorado State University ecologists now have found important changes in the carbon exchange due to urbanization along the Front Range of Colorado.
Indy Burke, professor of forest sciences, and Jason Kaye, postdoctoral forest sciences research associate at Colorado State, found that rapid urbanization during the past five decades has altered the regional carbon budget by changing the rates at which plants and soil microorganisms use and generate carbon dioxide and by changing the rates of nitrogen greenhouse gas production.
"It is now recognized that the most important global changes are land-use changes," said Burke. "To date, ecological scientists have not studied what is probably the most important land-use change: urbanization. Water and air quality at local-to-global scales are significantly influenced by how we alter carbon and nitrogen balance."
Along the Front Range of Colorado, the burgeoning urban metropolis is deriving new land from adjacent prime agricultural land and unmanaged grasslands. Kaye and Burke measured soil respiration – carbon dioxide released into the air by living organisms in the soil -in urban ecosystems and nearby dryland agriculture, irrigated agriculture and unmanaged grasslands in north-central Colorado.
The study found soil respiration to be four times greater in urban ecosystems than dryland agriculture because of the large amount of fertilized and irrigated lawns in urban areas. Urban ecosystems also had higher rates of soil respiration than cultivated, irrigated agricultural land. Plant growth, which takes carbon dioxide out of the air and stores it in live plants and soils, also is higher in urban ecosystems, leading to a net storage of carbon over a century or more.
While urban ecosystems may remove more carbon dioxide from the atmosphere, the team also found that the impact of urbanization on the atmosphere is mixed. The positive result of urban ecosystems has been more carbon storage in the soil. However, working with Arvin Mosier, U.S. Department of Agriculture researcher and affiliate faculty member at Colorado State, the team found that there also is a negative effect from fertilization and irrigation – higher nitrogen gas fluxes which contribute to the greenhouse effect.
More widespread studies of the Front Range are planned in the next two years. The researchers plan to evaluate whether increased carbon storage in urban soils compensates for increased nitrogen release into the atmosphere.
"Understanding the changes of carbon storage and nitrogen release into the environment is important because, without a doubt, it will have an effect on the environment we live in," said Kaye.