On the dispersal of riverine colored dissolved organic matter over the West Florida Shelf

We investigated the optical properties of surface water in areas of the Wes t Florida Shelf influenced by riverine discharge and by the occurrence of a phytoplankton plume. Results of absorption and fluorescence spectroscopy a nalyses and determination of dissolved organic carbon (DOC) concentration s howed that the injection of riverine colored dissolved organic matter (CDOM ) strongly affected the optical properties and DOC concentrations over the shelf. Riverborne nutrients contributed to an increase hi primary productiv ity. However, during the study period, the increase in primary productivity did not result in the production of significant amounts of CDOM. Fluorescence spectroscopy results showed that optical properties of riverin e CDOM were lost close to the mouth of the rivers. A simple mathematical mo del describing mixing between riverine and marine end-members demonstrated that most of the observed changes in optical properties of CDOM along salin ity gradients can be explained by mixing. Laboratory mixing experiments bet ween riverine water and seawater indicated that flocculation of organic mat ter during estuarine mixing did not affect the optical properties of CDOM.