Nguyen Hao Quang
The University of Tokyo, Japan
Turbidity, an indicator of water pollution, is an important water quality parameter directly related to underwater light penetration and thus affects the primary productivity in a water body. This study aims to investigate the variation of turbidity in Cam Ranh Bay and Thuy Trieu Lagoon as well as major factors affecting its spatiotemporal patterns by using remote sensing data. The algorithm for turbidity retrieval was developed based on the correlation between in situ measurements and red band of Landsat 8 OLI with R2 = 0.84, p < 0.05, Root Mean Square Error (RMSE) = 0.28 and Scatter Index (SI) = 0.22. Simulating WAves Nearshore (SWAN) model was used to compute bed shear stress, major factor affecting turbidity in shallow waters. In addition, the relationships between turbidity and bed shear stress, rainfall and tidal regime in study area were also analyzed, and found that: (1) During the dry season, turbidity was low in middle of the Bay but high in shallow waters and near coastlines. Resuspension of bed sediment was the major factor controlling turbidity in the time without raining. (2) During the rainy season as well as short time after raining in the dry season, turbidity was high due to the large amount of run-off entering into the study area. (3) Under tidal condition especially the flood tide regime, clear open ocean water entered into the Bay and diluted highly turbid waters resulted in decreasing turbidity. In deep waters, tidal regime combined with rainfall was the significant cause of highly turbid waters.