THE CHARACTERISTIC CHANGE OF FINE PARTICULATE ORGANIC MATTER DUE TO A FLOOD IN THE NANAKITA RIVER

抄録

Sediment sampling was conducted at three locations before and after a flood in the Nanakita river. The sediment samples were analyzed to obtain the information on the particle size distribution, the amount of resuspendable fine particulate organic matter (FPOM) available on the bed, and the composition of the basic nutrients, carbon, nitrogen and phosphorous, in the FPOM. The data suggest that there is an equilibrium state in which the amount of FPOM on the bed is constant in the low flow condition. The behavior of FPOM is found to show strong locality; the amount of FPOM on the bed increases during floods at some locations while it decreases during floods at other locations. In the analysis of nutrients and the microscopic observation, it is suggested that FPOM accumulated on the bed during floods is directly originated from the terrestrial area. FPOM that accumulated in the sediment after flood at all locations are found to be gradually changed in size and composition because biological activities are in process and dominant in the low flow condition.