MORE carbon dioxide is released from residential lawns than corn fields, and much of the difference can likely be attributed to soil temperature, according to a new study by researchers at Elizabethtown College in Pennsylvania.
The data, recently published online in the Soil Science Society of America Journal, suggest that urban heat islands may be working at smaller scales than previously thought.
These findings provide a better understanding of the changes that occur when agricultural lands undergo development and urbanization.
David Bowne, assistant professor of biology, led the study to look at the amount of carbon dioxide being released from residential lawns versus corn fields in Lancaster County, Pa.
Bowne said the study allowed him to look beyond the obvious impact of losing agricultural fields to development, i.e., the loss of food that was once produced on the land.
"That is a legitimate concern, but I wanted to look more at how this change could potentially impact the carbon cycle with the understanding that the carbon cycle has implications for global climate change," he explained.
To begin to understand how the carbon cycle is changing, Bowne and undergraduate researcher Erin Johnson measured carbon dioxide efflux, soil temperature and soil moisture under residential and corn production land uses. They found that both carbon dioxide efflux and soil temperature were higher in residential lawns than in corn fields, an announcement said.
Temperature had the most influence on the level of carbon dioxide efflux, followed by land use type.
"As you increase temperature, you increase biological activity — be it microbial, plant, fungal or animal," Bowne explained. That increased activity leads to more respiration and more carbon dioxide leaving the soils.
However, the surprise was that the higher temperatures found in residential lawns suggested urban heat islands working at small scales. Urban heat islands occur when development leads to large areas of dark-colored surfaces such as roofs, buildings and parking lots that absorb more heat and, therefore, cause an increase in temperature in the neighboring areas. This effect makes urban areas warmer than the surrounding countryside.
The urban heat islands in the areas Bowne was studying seem to operate on much smaller scales than previously thought. While heat islands are usually studied on large scales — such as comparing a large city to its surrounding rural areas — fewer studies have been done to evaluate how development may affect temperatures on a small scale, the announcement said.
"Within a developed area within a city or town, you could have local increases in soil temperature because of the amount of development within a really small area," Bowne said.
Bowne is planning further experiments to test soil temperatures over a range of development setups and sizes.
He also will test carbon sequestration. Along with the carbon dioxide efflux data, information about carbon sequestration would provide a bigger picture of carbon cycling that could then help researchers determine how various land uses and management practices — such as no-till agriculture or leaving grass clippings on lawns — can change the carbon cycle.
"If we go from one land use to another land use, how does that impact carbon cycling, which, in turn, can affect climate change? Our current study touches on one component of that cycle, and more research is needed to address this huge topic," Bowne said.