In Tokyo Bay, water quality has been deteriorated due to human activities in river basins flowing into Tokyo Bay. Anoxia or hypoxia is one of the most significant water quality problems in Tokyo Bay, and previous studies revealed that the occurrence of hypoxia is controlled by wind stress, river discharge and strong wind effect. In particular, strong wind has a great role in the sudden increase in dissolved oxygen in the lower layer of the bay head. In recent years, meteorological conditions have changed evidently, such as flood disaster due to the increase in strong rainfall intensity. The change in meteorological conditions may also change wind speed and wind direction in the future. Therefore, to project water quality in Tokyo Bay, it is important to understand the future wind conditions. This study thus aims to investigate the applicability of Global Circulation Model (GCM) into the projection of wind conditions over Tokyo Bay by using 12 different GCM models. As a result, it is found that bias correction using cumulative density function should be used for the projection instead of using bias correction based on normal distribution.
It is demonstrated that duration of strong wind is one of the main factors which may enhance recovery from hypoxia in Tokyo Bay. Meteorological conditions are revealed to change, which may have caused more flood disaster, greater typhoon and so on in terms of climate change. Therefore, strong wind pattern is also expected to change and to have an effect on water quality in Tokyo Bay. This study thus aims to clarify the impact of meteorological change on the occurrence of and recovery from hypoxia by using Global Climate Model (GCM) outputs. As a result, it is suggested that the duration of strong wind decreases in the future.
1 学生会員 北見工業大学大学院 寒冷地・環境・エネルギー工学専攻(〒090-8507 北見市公園町165番 地) 2 正会員 博(工) 北見工業大学工学部 社会環境工学科(〒090-8507 北見市公園町165番地)The Shiretoko is a pennusla where a unique interaction occurs between the terrestrial and oceanic systems, which are linked by nutrient exchange processes. Nutrient rich floating sea ice is transported to the coast from the Okhotsk Sea and salmon and trout move upstream and feed inland animals, such as bears and birds. Conversely, nutrients flow into the ocean through rivers. It has been reported that this unique nutrient circulation is being disrupted by climate change and it is thus important to understand what mechanisms drive nutrient circulation in Shiretoko and maintain a unique ecological system. In this study, stable isotope analysis is used in combination to determine the contribution of land-derived (LDN) and marine-derived nutrients (MDN) in the Rausu River basin. Stable isotopes ratios, 13 C and 15 N, show a higher contribution of MDN before the snow-melt floods, and that MDN are distributed largely in the downstream region of the basin.
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