Abstract
The mega-tsunami resulting from the Tohoku earthquake destroyed most of the forests along the eastern Pacific coastline of Japan. Seawater inundation of costal forest soils carried a large influx of sea salt, leading to excessive adsorption of salt in buried 2A horizons under sea sand deposits. Forest soils that were inundated by seawater in turn caused severe damage, including needle discoloration, debilitation, droop, and finally death, to broad areas of the eastern Pacific coastal forests. Rehabilitation of tsunami-created saline soils in these forested lands generally requires the removal of sea salt, which is particularly difficult because most Japanese forests have poor irrigation facilities. Efficient removal of sea salt from the soils must therefore rely on high-precipitation events, such as typhoons and precipitation events in the rainy season. In this study, we monitored the progress of improvement in seawater-inundated forest soils in Hachinohe, Aomori Prefecture, and Watari-cho, Miyagi Prefecture, over time to evaluate the role of natural precipitation in desalinizing seawater-inundated forest soils. Measures of soil chemistry in tsunami-hit forests, such as exchangeable calcium and potassium content, initially showed decreasing tendencies, reached a state of equilibrium with time, then showed alteration in soil conditions. The results indicate that continuous and frequent rainfall events caused gradual removal of sea salt from seawater-inundated forest soils with time, and lead to a general recovery from the chemical condition caused by salination damage.
