RESPONSE OF DETRITAL TRANSPORTED ORGANIC MATTER TO 
TEMPORAL AND SPATIAL CONDITIONS IN THE UPPER MISSISSIPPI 
RIVER 

Danh C. Voong and Michael D. Delong
Large River Studies Center, Biology Department, Winona State University, Winona, MN  
55987

Recent studies have suggested that the quality of detrital organic matter transported in the 
water column (detrital TOM) changes temporally in correlation with increased 
phytoplankton production.  High quality detrital TOM could, therefore, serve as a 
supplement to the food web, particularly if increases in quality correspond to periods of 
greater invertebrate and fish production. This study examined changes in the chlorophyll 
a concentration of detrital transported organic matter in main channel and backwater 
habitats of the Upper Mississippi River over four sample dates (June – August).  Sample 
collection followed established LRSC procedures for collection of transported organic 
matter.  Algal and detrital components of TOM were separated using colloidal silica 
centrifugation.  Highest chlorophyll concentrations of detrital TOM were observed in 
both main channel and backwater when phytoplankton were most abundant.  The rate of 
increase of chlorophyll concentration was higher in the main channel than in backwaters.  
Carbon:chlorophyll a ratio, a measure of organic matter quality, was also greatest when 
phytoplankton abundance was highest. We propose that senescing phytoplankton 
represent the bulk of detrital transported organic matter during periods of high 
phytoplankton production, resulting in greater detrital quality and the potential for detrital 
TOM to contribute substantially more to the diet of primary consumers than during other 
times of the year.


Keywords:  transported organic matter, temporal, detritus, chlorophyll, backwater, main 
channel