TEMPORAL AND SPATIAL PATTERNS IN CHLOROPHYLL CONCENTRATION OF TRANSPORTED 
ORGANIC MATTER IN THE UPPER MISSISSIPPI RIVER

Emily R. Forde and Michael D. Delong
Large River Studies Center and Biology Department, Winona State University, 
Winona MN, 55987

Recent studies have shown algal transport organic matter (TOM) to be an 
important influence on food web dynamics in large rivers.  Unfortunately, 
research has been limited to main channel habitats and addressed limited spatial 
scales.  This study examined how the abundance of algal TOM changed temporally 
in different habitats of the Upper Mississippi River.  This was addressed by 
sampling different particle sizes of TOM from April to September 2004 in side 
channel, backwater and main channel habitats of the Upper Mississippi River near 
Winona, MN.  Samples were drawn monthly from four point transects across the 
channel at a depth of 1 meter and divided into fine (FTOM; 100-1000 ?m) and 
ultrafine (UTOM; 1-100 ?m).  TOM samples were then split into algal and detrital 
fractions using colloidal silica. Chlorophyll concentrations were determined 
spectrophotometrically, using the monochromatic method. Similar temporal trends 
were evident for both UTOM and FTOM. Chlorophyll concentrations increased 
between April and May, which corresponded to a decrease in discharge. 
Concentrations declined from May to June as discharge increased to its spring 
maxima.  Both UTOM an FTOM increased to highest observed concentrations in 
August during baseflow condition. Only small differences in chlorophyll 
concentrations were evident between habitats, with all three exhibiting similar 
temporal patterns.  Overall, however, concentrations were slightly higher in the 
main channel.  This study indicated that an inverse relationship exists between 
chlorophyll concentrations of phytoplankton and discharge.  Small differences 
observed between habitats demonstrate the productivity capacity of lotic 
habitats within the river.

Keywords: chlorophyll concentration, Mississippi River, transport organic 
matter, food web, large river, habitat