Seasonal Variation in Nutrient Distribution in the Inner Area of the Ariake Sea

Abstract

In order to investigate the seasonal variation in nutrient distribution in the mudflat-shallow water system, we made field surveys once a month from August, 2007 to July, 2008 in the bay head of the Ariake Sea. The NH4-N concentration increased in autumn and exceeded the NO3-N concentration. Then the NO3-N concentration increased and topped in January. Since the river discharge was small, such an increase of nitrogen concentration would be caused by the flux from the bottom sediments. The PO4-P concentration was also increased in autumn moderately. It decreased from January to March and still low until June. Such a variation would be also affected by the seasonal variation in PO4-P release from the sediment. These facts suggest the important role of the variation in nutrient supply from the sediments of mudflat in this area.