Evaluation for the effect of non-stationary nutrient transport on the coastal seaweed cultivation in western Japan

In order to evaluate the effects of non-stationary nutrient transport on the coastal seaweed cultivation, variations of the seaweed yield, nutrient condition of seawater, rainfall and nutrient transport from the river, observed over the last 40 years were examined to characterize the long-term trends and the influencing factors on the variation of seaweed yield. The results show that seaweed yield increased until 1973, then decreased in recent years. The recent condition of nutrients in seawater is relatively severe for seaweed farming. The results suggest that river-derived nutrient supply to coastal area will decrease further by the decrease of river discharge. For the future prospect, it is important to evaluate the variation of other nutrient supply such as from groundwater, offshore or bottom sediment as well as river discharge.