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Preliminary assessment of eutrophication by remotely sensed chlorophyll-a in Toyama Bay,the Sea of Japan |
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| Authors: | Genki Terauchi Ryo Tsujimoto Joji Ishizaka Hideaki Nakata |
| Institution: | 1. Northwest Pacific Region Environmental Cooperation Center, Toyama, Japan 2. Graduate School of Science and Technology, Nagasaki University, Nagasaki, Japan 3. Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya, Japan 4. Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, Nagasaki, Japan |
| Abstract: | Time series of the chlorophyll-a concentration (Chl-a) observed by ocean color satellites from 1998 to 2009 were used to assess eutrophication in Toyama Bay, the Sea of Japan. An overall mean of Chl-a during the 12-year period was used to divide the study area into “high” or “low” Chl-a areas based on a reference condition of 5 mg m?3. The annual maximum monthly mean Chl-a trend was estimated pixel-wise and its significance examined by the Sen slope test at a 90 % confidence level. By combining the level and trend of remotely sensed Chl-a, Toyama Bay was then classified into six eutrophication states: high-increasing, high-no trend, high-decreasing, low-increasing, low-no trend and low-increasing. Our study indicates that the combined use of both the level and trend of remotely sensed Chl-a can be an efficient method to preliminarily assess eutrophication of coastal waters after a quality screening process with level 2 flags and validation with in situ Chl-a data. |
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