Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Ancient coral reef tells the history of Kenya's soil erosion

12.04.2007
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 over the years, Dunbar's team measured the ratio of two elements—barium and calcium—in the coral skeleton, which is composed of calcium carbonate. "It turns out that there is a lot of barium in soils," Dunbar said. "So whenever something changes the landscape and causes the soil to erode and wash into the rivers, the soil is delivered to the sea. And with that soil comes the barium."

The corals then incorporate the barium in well-developed bands that provide a record of annual growth, similar to tree rings, he added. To measure barium levels in the corals, Dunbar's team applied an innovative technique that quickly vaporizes the carbonate, then analyzes its chemical composition with a mass spectrometer.

"In the past we used a dentist drill," Dunbar said. "We drilled out a little bit of powder, and then we dissolved the powder and took it to the lab, where we measured the barium with a wet chemical technique. It was a very slow process, very painful. It took forever to get data." The new method, developed by researchers at the Australian National University, "increased the speed at which we could collect data by a factor of 50," he noted.

Equilibrium loss

An analysis of barium levels revealed that prior to about 1915, the Kenyan landscape was in equilibrium—rain washed out some soils moderately from decade to decade in a regular cycle that was only altered by periods of drought. "But in the late 1910s, the amount of barium coming down to the coast suddenly shoots up, and it keeps rising and rising," Dunbar said. "This represents colonial land change, when the British came in and tried some grand-scale experiments, like the clearing of bush to create coffee plantations."

Before the plantations were developed, the primary long-term land uses in the region were nomadic animal husbandry and small-scale agriculture—sustainable practices that were compatible with the natural vegetation, Dunbar said. But then the colonialists began clear-cutting some of the coastal forests and burning vegetation to make room for the plantation experiments. What followed was a drastic increase in soil erosion that turned the rivers muddy and brown. "It's a natural thing," Dunbar explained. "When you perturb a landscape and you cut down trees and bushes—the plants that normally help hold the soils together—the next time you have a big rain or a flood, the soils go to the rivers."

Although colonialism ended decades ago and plantations along the coast were abandoned, the landscape remains out of equilibrium, he said: "This would be a lesson for other parts of the planet: When you perturb a system by clear-cutting the natural vegetation and it responds in a negative way, it loses its essence, and it responds not just for a few years or a few decades but maybe a century or even more."

Population pressure

Another factor driving soil erosion in Kenya is human pressure. As the population grows, more trees are harvested for fuel, which contributes to erosion, Dunbar said.

"Furthermore, a dramatic increase in population following independence [in 1963] together with unregulated land use, deforestation and severe droughts in the early 1970s all contributed to an unprecedented rate of soil erosion and flux of suspended sediment [and barium] to Malindi reef between 1974 and 1980," the authors wrote. Erosion remains a serious problem today, they added, thanks in part to continued urban sprawl, deforestation, poor farming practices and other human activities.

The authors called for stronger soil conservation efforts—a goal that Kenya is unlikely to achieve on its own because of a lack of economic resources, they noted. However, if soil devastation continues, the socioeconomic consequences could be dire, Dunbar said. "Loss of soils constitutes loss of valuable natural capital for the people of East Africa," he noted. "A follow-on effect is that loss of the soils down the rivers can also have a damaging effect of the coastal zone, particularly the health of local fisheries and the corals reefs that drive a local tourist economy."

The Dunbar lab's next research effort will focus on mega-droughts—periods of severely reduced rainfall that lasted for decades in East Africa. The most recent mega-drought occurred between 1750 and 1820. "If you think how many people live in East Africa now, if a mega-drought happened today, it would be devastating," Dunbar said.

Mark Shwartz | EurekAlert!
Further information:
http://www.stanford.edu/news/
http://www.stanford.edu/dept/news/html/releases.html

More articles from Earth Sciences:

nachricht Climate satellite: Tracking methane with robust laser technology
22.06.2017 | Fraunhofer-Gesellschaft

nachricht How reliable are shells as climate archives?
21.06.2017 | Leibniz-Zentrum für Marine Tropenforschung (ZMT)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

Im Focus: Optoelectronic Inline Measurement – Accurate to the Nanometer

Germany counts high-precision manufacturing processes among its advantages as a location. It’s not just the aerospace and automotive industries that require almost waste-free, high-precision manufacturing to provide an efficient way of testing the shape and orientation tolerances of products. Since current inline measurement technology not yet provides the required accuracy, the Fraunhofer Institute for Laser Technology ILT is collaborating with four renowned industry partners in the INSPIRE project to develop inline sensors with a new accuracy class. Funded by the German Federal Ministry of Education and Research (BMBF), the project is scheduled to run until the end of 2019.

New Manufacturing Technologies for New Products

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Hubble captures massive dead disk galaxy that challenges theories of galaxy evolution

22.06.2017 | Physics and Astronomy

New femto-camera with quadrillion fractions of a second resolution

22.06.2017 | Physics and Astronomy

Rice U. chemists create 3-D printed graphene foam

22.06.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>