Estimation of Changes in the Nutrient Release Rate from Sediments after a Tsunami by an Incubation Experiment

A tsunami induced by the Nankai Trough earthquake may disturb marine sediments in the inner part of Osaka Bay. Since nutrient release from marine sediments has a significant impact on nu-trient concentrations in seawater, an incubation experiment was conducted to estimate the release rates of NH4-N and PO4-P in order to understand the present rates and to quantify the changes in the rates caused by tsunamis in Osaka Bay. The current release rate of NH4-N is an extension of the decreasing trend since 2000. The PO4-P release rate has remained at a low level since 2008. The release rate of redeposited sediments after exposure to the aerobic environment caused by a tsunami may decrease to approximately 70% of the current level for NH4-N and 60% for PO4-P. Nutrient concentrations and fishing have begun to decline in Osaka Bay. A reduction in the nutrient release rate by tsunamis may further limit primary production under the current situation where the contribution of release to nutrients in seawater is significant.