| In the summer of 2007, one cruise survey on terrestrial chromophoric dissolved organic matter (CDOM) was carried out in the Zhoushan Sea Area of the East China Sea. We determined the fluorescence intensities at excitation wavelength 370 nm /emission wavelength 460 nm and the absorption coefficients at wavelength 355 nm, which represent terrestrial CDOM concentrations. The fluorescence indices were also measured as the indicator of CDOM sources. The results showed that CDOM concentrations roughly tended to decrease in the direction from the land to the sea, but there was some phenomenon of vertical jump. High concentrations of CDOM in the surface water were observed in some sites of the northeast of the Zhoushan Sea Area from time to time, but they showed a great variability, which suggesting that the waters may be subject to the impact of estuarine plume of the Yangtze River. It was found in a continuous observation station that the concentrations of CDOM at low tide were often higher than those at high tide. During the mixing process between river water and sea water, the CDOM concentrations and light absorption coefficients at 355 nm had a significant negative linear relationship with the salinity. That is to say, CDOM took on the conservative behavior in general. However, CDOM concentrations were significantly lower than the theoretical dilution values in the low salinity zone (S <24), indicating a non-conservative removal behavior of CDOM in the suspended sediment front. Fluorescence indices were almost fixed at 1.50 in most of water samples with the salinity between 24 and 31, indicating that CDOM could be dominated with terrestrial sources. However, fluorescence indices varied from 1.70 to 1.90 and above in low salinity zone (S <24), indicating that CDOM could be dominated with marine sources; it is related to the significant removal of terrestrial fractions of CDOM in this zone with low salinity and high turbidity. These results prove that terrestrial organic matter can be used as a good tracer and indicate the variability of water quality in the coastal plume. |
