Non-conservative mixing behavior of colored dissolved organic matter in a humic-rich, turbid estuary

The estuarine mixing behavior of colored dissolved organic matter (CDOM) absorbance was investigated in combined field and laboratory studies. From February to October 1998, surface water samples were collected along 9 transects in the Tyne estuary, Northeast England, from the tidal limit into the coastal North Sea. In 8 of these transects, mixing plots of absorbance vs. salinity indicated substantial removal of CDOM absorbance (average: 32%) in the upper estuary. Results from laboratory studies under simulated estuarine conditions suggest that an average of 21% (range: 9-39%) of riverine CDOM may be removed by adsorption onto suspended sediment, while CDOM flocculation accounted for an average removal of only 6% (range: 0-18%). We propose that adsorptive removal exerts a major control on CDOM in estuaries with elevated turbidity levels.