富山湾の水塊構造と河川水・沿岸海底湧水による淡水フラックス

抄録

In Toyama prefecture, because of the steep slope from the mountains to the coast coupled with high precipitation, a large volume of river water flows into Toyama bay, and the submarine groundwater discharge (SGD) ranges widely on the steep continental shelf. However, the substance budget and its impacts to the coastal environment have not been previously studied. The purpose of this study is to clarify the water mass structure of Toyama bay and to estimate the fluxes of freshwater and its nutrients by using a box model. Using the T-S diagram it is clear that Toyama bay water is made up of coastal surface water, Tsushima Warm Current (TWO water and deep water (Japan Sea Proper Water). It demonstrates that the upper 200 m (Toyama Bay Shallow Water) is composed of high salinity water (TWC) and low salinity water derived from freshwater. The freshwater flux was calculated with a box model of the shallow water. The maximum SGD flux (2.3×10⁸ m³month^-1) was about 25% of the river water flux (9.1×10⁸ m³month^-1). And the nutrient fluxes via the SGD path were 55% (PO₄^3-) and 133% (NO₂^- + NO₃^-) of the river values. Furthermore the possibility was suggested from the N to P cocentration ratios that SGD entered the Toyama bay water colum primarily in the depth range of 〜100-180 m.