ORGANIC-CARBON AND NITROGEN-CONTENT ASSOCIATED WITH COLLOIDS AND SUSPENDED PARTICULATES FROM THE MISSISSIPPI RIVER AND SOME OF ITS TRIBUTARIES

Suspended material samples were collected at 16 sites along the Missis sippi River and some of its tributaries during July-August 1991, Octob er-November 1991, and April-May 1992, and separated into colloid and p articulate fractions to determine the organic carbon content of these two fractions of suspended material. Sample collection involved centri fugation to isolate the suspended particulate fraction and ultrafiltra tion to isolate the colloid fraction. For the first time, particulate and colloid concentrations and organic carbon and nitrogen content wer e investigated along the entire reach of the Mississippi River from ab ove Minneapolis Minnesota,to below New Orleans, Louisiana. Organic car bon content of the colloid (15.2 percent) was much higher than organic carbon content of the particulate material (4.8 percent). Carbon/nitr ogen ratios of colloid and particulate phases were more similar to rat ios for microorganisms than to ratios for soils, humic materials, or p lants.