Washing Soils Away

Abstract

GEOLOGY Soil erosion and land degradation are serious threats to developing countries. Not only do they diminish food security and threaten terrestrial ecosystems, but they also cause substantial damage to near-shore marine environments. As the causes and extent of soil erosion are explored with an aim toward combating the problem, historical records are needed to place modern rates in perspective. Fleitmann et al. document how erosion has affected East Africa, a region particularly vulnerable to the loss of fertile soil, by analyzing a 300-year-long record of Ba/Ca ratios in corals found off the coast of Kenya. These ratios serve as a good proxy for soil erosion because most of the Ba flux to the seawater stems from river discharge at the location where the samples were acquired. Shortly after the year 1900, Ba/Ca ratios began to increase steadily beyond their comparatively low values in the preceding 200 years; the initial increase could be due to British settlement of the fertile highlands of Kenya around that time. If effective soil conservation policies are not instituted, the situation will probably worsen in the future because of the country's growing population, leading to more intensive land use, as well as the increased rains expected with global warming. — HJS Geophys. Res. Lett. 34 , L04401 (2007).