Assessment of eutrophication using remotely sensed chlorophyll-a in the Northwest Pacific region

The Northwest Pacific region, which includes parts of northeast China, Japan, Korea and southeast Russia, is one of the most densely populated areas of the world. Eutrophication is an emerging environmental problem in this region, where a significant number of red tides and hypoxic conditions have been reported in coastal waters - possibly due to anthropogenic influences such as extensive chemical fertilizer use and sewage effluent. To assess this problem, NOWPAP CEARAC, the Special Monitoring and Coastal Environment Assessment Regional Activity Centre of the Action Plan for the Protection, Management and Development of the Marine and Coastal Environment of the Northwest Pacific Region of the United Nations Environmental Programme, has developed Procedures for assessment of eutrophication status including the evaluation of land based sources of nutrients for the NOWPAP region (NOWPAP Common Procedures). The NOWPAP Common Procedures include the screening procedure to detect symptoms of eutrophication with selected parameters. One of the selected parameters is remotely sensed chlorophyll-a concentration (satellite Chl-a). To prepare a long-term consistent satellite Chl-a from 1998 to 2016, regression analysis was conducted by pixel to pixel using the daily composites of SeaWiFS and MODIS Remote Sensing Reflectance for overlapping period (July 2002 to December 2004). Two different empirical in-water algorithms, a NASA standard and a regionally developed one for turbid water, were applied to estimate Chl-a in the eastern and western parts of the Northwest Pacific region, respectively. The assessment of eutrophication was then conducted by the level and trend of satellite Chl-a.