Summer satellite-driven chlorophyll-a variations in the East China Sea during 1998-2014: before and after impoundment of Three Gorges Dam, China

Abstract

The purpose of this study is to investigate climatological variations from the temporal and spatial surface satellite-driven chlorophyll concentration and to understand their related environmental changes that affect the distribution of chlorophyll in the East China Sea (ECS) during 1998-2014, especially summer season (June ~ August). 17-year monthly mean values of surface satellite-driven chlorophyll-a concentration (SeaWiFS and MODIS), nutrients and recorded Changjiang River discharge data were used to determine reduced summer biological activity. A linear trend analysis of chlorophyll data reveals that, during recent 17 years, the summer chlorophyll-a concentration showed decreased trend. To determine more detailed spatial and temporal variations, we used empirical orthogonal function (EOF) analysis. First mode is temporally correlated with the area influenced by the Changjiang River discharge and spatially correlated with north-west and south-east patterns. Regional trend between chlorophyll and river discharge determined by K mean analysis showed that reduced summer chlorophyll-a concentrations were correlated with reduced summer Changjiang River discharge in the south of Jeju, Korea. Since the Changjiang River is a major source of nutrients in the ECS, the decreased summer chlorophyll seemed to be related with the change in nutrients in the coastal area before and after impoundment of Three Gorges Dam (orophyll in the East China Sea (ECS) during 1998-2014, especially summer season (June ~ August). 17-year monthly mean values of surface satellite-driven chlorophyll-a concentration (SeaWiFS and MODIS), nutrients and recorded Changjiang River discharge data were used to determine reduced summer biological activity. A linear trend analysis of chlorophyll data reveals that, during recent 17 years, the summer chlorophyll-a concentration showed decreased trend. To determine more detailed spatial and temporal variations, we used empirical orthogonal function (EOF) analysis. First mode is temporally correlated with the area influenced by the Changjiang River discharge and spatially correlated with north-west and south-east patterns. Regional trend between chlorophyll and river discharge determined by K mean analysis showed that reduced summer chlorophyll-a concentrations were correlated with reduced summer Changjiang River discharge in the south of Jeju, Korea. Since the Changjiang River is a major source of nutrients in the ECS, the decreased summer chlorophyll seemed to be related with the change in nutrients in the coastal area before and after impoundment of Three Gorges Dam (