Program
 
General Session 2: Marine & estuarine biogeochemistry
 
 
 
Poster
Absorbance photobleaching of chromophoric dissolved organic matter in the Yangtze River Estuary
GS2-39
Guisheng Song* , College of Marine and Environmental Sciences, Tianjin University of Science & Technology
Yijie Li, College of Marine and Environmental Sciences, Tianjin University of Science & Technology
Huixiang Xie, Institut des sciences de la mer de Rimouski, Universit¨¦ du Qu¨¦bec ¨¤ Rimouski, Canada
Presenter Email: guisheng_song@tust.edu.cn
The kinetics and temperature-, pH- and salinity-dependences of the absorbance photobleaching of chromophoric dissolved organic matter (CDOM) in the Yangtze River estuary (YRE) were evaluated using laboratory solar-simulated irradiations and compared to those of standard Suwannee River humic substances (SRHS). The photobleaching rate (RPB) increased with water temperature and the temperature dependence conformed to the linear Arrhenius equation. For a 20°C increase in temperature, photobleaching increased by ~44% in the headwater of the estuary and by 66%-84% in saltier water. In the pH range from 4 to 10, RPB for the YRE samples exhibited minima at pH from 6 to 7 and increased towards both lower and higher pH values, contrasting the consistent increase in photobleaching with pH demonstrated by the SRHS. However, the variation of salinity had insignificant effect on CDOM photobleaching for both the SRHS and the YRE samples. Photobleaching increased the spectral slope coefficient between 275 nm and 295 nm (S275-295) in summer, which matched the behavior of SRHS, but decreased it in winter, implying a difference in the molecular composition of chromophores between the two seasons. Temperature, salinity, and pH modified the photoalteration of the spectral shape but their effects varied spatially and seasonally. The summer-winter differences in CDOM photoreactivity and water temperature further amply the difference in photobleaching between the two seasons caused by the seasonality in solar irradiance.