TEMPORAL VARIATIONS OF THE CHLOROPHYLL-a CONCENTRATION OFF THE CHANGJIANG (YANGTZE) RIVER MOUTH AND RESPONSE TO THE THREE GORGES DAM

Temporal variations of sea surface chlorophyll-a concentration off the Changjiang (Yangtze) River mouth were investigated using SeaWiFS and MODIS data over the period of 1997-2012. The datasets of water and sediment discharge at Datong Station were also collected in order to examine the relationship between chlorophyll-a concentration in Yangtze River estuary and the river water and sediment discharge, as well as to clarify its response to the TGD Project. The results showed that both the average annual chlorophyll-a concentration with the annual water discharge, and the average monthly chlorophyll-a concentration with the monthly water discharge showed a good linear relationship (R²=0.72; R²=0.89). But the chlorophyll-a concentration has a poorer relationship with the sediment discharge from Yangtze River, which showed that the contribution of water discharge carrying dissolved nutrients to phytoplankton is greater than the part provided by sediment. Besides, the annual chlorophyll-a concentration in the study area has a decrease tendency after the TGD, the monthly average chlorophyll-a concentration also showed a delay of the spring and summer peak. It may be related to the spring drought caused by more dry years after TGD, and the reservoir operation mechanism. Although the TGD operation mechanism increased the water discharge in the dry season, the chlorophyll-a concentration showed a decrease tendency because of the lower temperature and lower transparency caused by the strong sediment resuspension in the coastal area in winter time.