Influence of Tropical Cyclone on the Water Quality of Atsumi Bay

Abstract

Typhoon No. 14 that hit Japan on 30 th October 2010 brought a huge water mass that increased the water volume and nutrient into the Atsumi Bay estuary, Japan. The aims of this research were to clarify the impact of a typhoon on the physical properties and nutrient concentrations of Atsumi Bay. This study summarizes the effects of a typhoon on nutrient fluxes from rivers to the estuary, which is revealed by the less-saline surface coastal water. The elevated surface chlorophyll a concentrations along the Toyo River transect were possibly caused by phytoplankton uptake on nutrient supply. The greatest increases of concentrations of nitrogen and phosphorus after typhoon generally appeared in the surface waters along the Umeda River transect caused by high nutrient concentrations from Umeda River; but decreased along the Toyo River transect due to dilution by seawater and possibly caused by phytoplankton uptake. The pre-typhoon predominant species of dissolved nitrogen (DN) is dissolved organic nitrogen (DON), it was changed to be 54% of dissolved inorganic nitrogen (DIN) along the Umeda River transect after typhoon in the surface layer. The lower post-typhoon bottom concentration of nutrient along both the Toyo and Umeda River transects was influenced by the disturbances of hypoxic condition in the bottom layer.