The Effects of Topography and Soil Properties on Radiocesium Concentrations in Forest Soils in Fukushima, Japan

Abstract

The radioactive plume released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) during the accident in March 2011 contaminated the environment in the nearby towns. This project collected soil samples in a village in Fukushima, Japan, during the summers of 2016, 2017, and 2018 and then examined the radioactive contamination levels in forest soils. Forests provide valuable water and nutrient resources to farming activities as well as places for various leisure activities. In Fukushima, about 70 percent of the land is covered with forests. However, collecting a large number of field samples in forests or decontaminating forests in the aftermath of a massive radioactive contamination event faces challenges because of the rugged topography. Thus, this project focused on Cesium-137 (Cs-137), a radionuclide with a half-life of 30.17 years, and aimed to demonstrate the methodology to extract as much knowledge as possible about the Cs-137 behavior from a small number of samples. The raw data was conceptually defined and reorganized to present the contamination patterns in a forest using statistical models. The effects of five topographic parameters and two soil properties on the contamination patterns were compared. One significant finding was that the topographic parameters and soil properties demonstrated similar model performance for explaining Cs-137 concentration levels throughout the 30 cm depth. This finding confirms the co-functionality of topography and soil properties on a radionuclide’s subsurface migration. Understanding how radionuclides move and accumulate in forests is critical to avoiding the negative impacts on human health and protecting lowlands from harmful radioactivity levels while protecting the forests' ecosystems. This dissertation hopes that the collected data and results in the following sections will contribute to future remediation measures in the aftermath of a radioactive contamination event.