Coral reefs, like tree rings, are natural archives of climate change. But oceanic corals also provide a faithful account of how people make use of land through history, says Robert B. Dunbar of Stanford University.
In a study published in the Feb. 22 issue of Geophysical Research Letters, Dunbar and his colleagues used coral samples from the Indian Ocean to create a 300-year record of soil erosion in Kenya, the longest land-use archive ever obtained in corals. A chemical analysis of the corals revealed that Kenya has been losing valuable topsoil since the early 1900s, when British settlers began farming the region.
"We found that soil erosion in Kenya increased dramatically after World War I, coinciding with British colonialism and a series of large-scale agricultural experiments that provoked a dramatic change in human use of the landscape," said Dunbar, a professor of geological and environmental sciences. "Today, the Kenyan landscape continues to lose topsoil to the Indian Ocean, primarily because of human pressure."
Erosion is a serious threat, he noted, because the loss of fertile soil often is accompanied by a decrease in food production. According to one recent study, soil erosion is a global problem that has caused widespread damage to agriculture and animal husbandry, placing about 2.6 billion people at risk of famine. "This is particularly worrisome in East and sub-Saharan Africa, where per capita food production has declined for the last half-century," Dunbar said.
Coral bands
For the study, Dunbar and his colleagues donned scuba gear and dove to the Malindi coral reef near the mouth of the Sabaki River, the second longest river in Kenya. Draining about 11 percent of Kenya's landmass, the Sabaki transports sediments to the sea.
The researchers took core samples from two large coral colonies, each more than 12 feet tall and about 15 feet wide. To find out how sediment flux has varied ove
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
10-Apr-2007