Florida's climate boosts soil-carbon storage, cuts greenhouse emissions

Soil-stored carbon can slow the build-up of carbon-based gases in the atmosphere, a phenomenon believed to be a cause of global climate change. So it's vital to preserve soil carbon, said Sabine Grunwald, a UF soil and water science professor who led the research.

"The conservation of the 'black gold' below our feet, which is not only a natural part of Florida's soils but also helps to improve our climate and agricultural production, is a hidden treasure," said Grunwald, a member of the Institute of Food and Agricultural Sciences faculty. "Soils serve as a natural container to hold carbon that would otherwise be emitted into the atmosphere as greenhouse gases that accelerate global climate change."

In addition to environmental stewardship, landowners can make money by storing carbon. Participants in the state's Florida Stewardship Program are sitting on an estimated $300 million worth of carbon.

Because it's so wet, Florida's soil has historically stored more carbon than any state, except perhaps Alaska, which has not been studied extensively, Grunwald said.

With Florida's rapid population growth in the past 45 years, from 5 million to about 18 million, land use has changed considerably. More urban areas have sprung up, while agricultural, rangeland and forests have declined, Grunwald said. That change has caused carbon-rich wetlands to increase 140 percent, while carbon-poor agricultural land decreased about 20 percent, according to the study.

In the first study of its kind, UF researchers reviewed data from 1,251 soil samples collected across Florida from 1965 to 1996. They also collected 1,080 new soil samples statewide in 2010. They studied carbon sequestration rates from 1965 to 2010.

Researchers studied land use, land cover and climate change to see how those factors affect the soil's ability to store carbon. Organic carbon in soil includes dead plant and animal tissue and makes up most global soil carbon.

Land cover is what's on Earth's surface, whether it's dirt, pavement, water or trees, among other things. Land use means how people utilize public and private land, such as agriculture, forestry or conservation land.

Together, land use, land cover and climate change account for 46 percent of soil carbon sequestration, the study showed. Of that, land use and land cover account for 27 percent, while climate change account for 19 percent.

Researchers used temperature and rain to determine the effect of climate change. They found higher average annual temperatures correlated with higher soil carbon sequestration, specifically in crops, mesic upland forest, pineland and land converted from pine forests to urban use. Areas with higher average annual precipitation showed less sequestration in agricultural crops and pine forests.

Among land-use types, researchers also found sugarcane in the soils of the Everglades Agricultural area near Lake Okeechobee and wetlands stored the most soil carbon while crop, citrus and relatively dry upland forest sequestered the least.

Results of the study appear in the September issue of the journal Science of the Total Environment.