Author(s)

K. Kakugawa, T. Futagami, M. Matsuda, H. Sakai, Y. Amano, Y. Fujiwara, H. Hattori & S. Sakurai

Abstract

A large number of hazards all over the world are caused by debris flows and landslides, and this is especially so every year in Japan. In June 1999, August 2005, July 2010 in the Hiroshima prefecture, and in July 2009 in the Yamaguchi prefecture, there were many hazardous occurrences of large debris flows and landslides owing to torrential downpours. Through the survey made of these hazards it seems that there are two main factors causing the increase of hazards and consequent risks. The two main factors are the contiguity of urbanization of hillsides and the bio-deterioration of mechanical structures of the ground on hillsides caused by eutrophication (nutrient enrichment). The eutrophication promotes microbial activities that deteriorate the mechanical structures of the ground on the hillside slopes. Microorganisms promote the weathering of rocks to soils and cause aggregation of soils by their metabolites. Aggregated structures of soils wet the ground to decrease the resistance to landslides. It seems that microbial activities accelerate the occurrence of debris flows. The eutrophication causes the bio-weathering of the ground. This contribution describes the investigation of the relationships between debris flows and microorganisms activated by eutrophication of hillside ecosystems in order to construct a precise model of occurrence of debris flows. The model may be able to mitigate the hazards. Identification of microorganisms in the subsurface of the hillside was obtained by using a molecular biological technique. It was observed that the values of the eutrophication index (TC and TN) are high in the weathered rock and low in the unweathered rock.

Keywords

debris flow, landslide, microorganisms, eutrophication of ground, bio-deterioration of ground, molecular biological technique, DNA, Denaturing Gradient Gel Electrophoresis, DGGE, natural hazard, ecological systems, mechanical deterioration of ground, aggr