estimation of nutrient budget using underwater nutrient analyzer system

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To quantify the nutrient budget in semi-enclosed bay, we developed underwater nutrient analyzer systems. Field observation was carried out using newly developed sensor with current and water quality sensors at Odaiba in Tokyo Bay, Japan. As a result, we successfully observed variation of nitrate and ammonia with per hour interval within half year. These nutrients significantly varied with changes in tidal elevation, river discharge and phytoplankton concentration. These results also showed the important characteristics of water quality variation in the observation area. For example, phytoplankton generally increased under calm weather condition and decreased during precipitation event. This kind of phenomena continued for about 2 weeks if precipitation exceeded about 50 mm/day. However, if precipitation was small (ca. 5 mm/day), phytoplankton sharply increased since it originated from river. These results will contribute in the improvement of the water quality environment in Tokyo Bay.