Salinity status of the 2011 Tohoku-oki tsunami affected agricultural lands in northeast Japan

Abstract

As Japan has abundant annual rainfall (1,000 to 2,500 mm), soil salinity of agricultural lands has rarely been a major problem. Following the 2011 earthquake in the Pacific, large stretches of land along the coast in northeast Japan were devastated by a powerful tsunami. Saltwater damage of agricultural lands was so severe that agricultural crops could not be grown on large parts of the tsunami-inundated farmlands even two years after the disaster. This paper summarizes the status of agricultural lands in northeast Japan's Tohoku region that were affected by the tsunami. The paper presents the results of a field study of agricultural lands in Miyagi Prefecture, where the extent of the seawater damage was the most severe, representing 67% of the total tsunami-affected agricultural lands. Forty samples from surface and underlying (undisturbed) soil were collected from 30 different locations in coastal and tsunami-inundated farmlands and from inland sites located beyond the limit of the tsunami inundation. The analyses and measurements showed that the extent of soil salinity varied greatly across these sites, with the highest electrical conductivity (EC) value of 3.72 dS m−1 found in the surface soil of Minamisanriku cho. In addition, two study sites adjacent to each other, Watari cho and Yamamoto cho, had maximum and minimum EC values of 2.0 dS m−1 and 0.21 dS m−1, respectively, in their underlying soils. A comparison of the major soil properties revealed that the salinity status of the tsunami-inundated farmlands was dependent on particle size distribution and therefore on the infiltration rate of the soil, as well as the relative physical position (elevation) of the farmland. This study led us to carry out further investigations and experiments (still on-going) related to restoration and mitigation work in the tsunami-inundated agricultural lands, giving the highest priority to the major soil properties of different field sites in Miyagi Prefecture.

Keywords

• Agricultural land
• Salinity
• Soil properties
• Tsunami
• Northeast Japan