The Pearl River Estuary

located at the downstream of the Pearl River Delta

receives freshwater from multisources and is an active transition zone between river environments and maritime environments. The variation of water optical properties with tide remains to be further studied. Based on the fixed point measurement during 4 days in the Pearl River Estuary

The averaged CDOM (chromophoric dissolved organic matter) concentration a

g

(355)  is 1.01±0.31 m

-1

at flood tide while the value is 1.18±0.37 m

-1

at ebb tide. It shows the temporal feature that the values at ebb tide are higher than those at flood tide. From the spatial dimension

 a

g

(355) inside the estuary entrance is higher than that outside. It fluctuates weakly both inside the estuary entrance at ebb tide and outside the entrance at flood tide. The averaged S

g

(spectral slope of CDOM absorption coefficient) is 0.018 6±0.002 9 nm

-1

at flood tide and it shows a lower value (0.017 7±0.002 3 nm

-1

) at ebb tide. The values at ebb tide are closer to each other in space. S

g

has significantly positive correlation with the molecular size M (absorbance ratio between 250 and 365 nm)

both of them show high values at flood tide. In addition

there is remarkable negative correlation between a

g

(355) and salinity for the outer estuary. And the correlation at ebb tide is superior to that at flood tide. However they have no common bond inside the entrance during flood season. Therefore

the optical properties of CDOM at ebb tide appear to be more stable

particularly for those of the inner estuary. And the tidal effects should be considered in retrieving water quality parameters from remote sensing data.