NUTRIENTS IN THE UPPER MISSISSIPPI RIVER:  TRANSPORT, PROCESSING, AND EFFECTS 
ON THE RIVER.

Houser, Jeffrey N. 
Richardson, William B.
USGS Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road, La 
Crosse, WI  54601

Nutrient concentrations and loads in the Upper Mississippi River (UMR) have 
been substantially affected by changes in land use, climate, hydrology, and 
river management/engineering over the last century.  An important consequence 
of these changes is the contribution of nutrients from the UMR to the hypoxic 
zone in the Gulf of Mexico.  The sources of nutrients in the basin and the 
factors that control their input to the river have received much study. Past 
research has generally focused on nutrient inputs to the river (e.g. the 
relationship between catchment characteristics nutrient export to the river) 
and the effects of nutrient outputs from the river on the Gulf of Mexico.  As 
a result, many aspects of nutrient inputs to, and outputs from, the river are 
reasonably understood. Less work has been done on the effects of in-river 
processes on nutrient retention, cycling, and transformation.  Also, the 
effects of elevated nutrient loads and changes in hydrology (e.g. hydrologic 
connectivity) on the functioning of river ecosystems and the biota they 
contain are poorly understood.  Less understood local effects of increased 
nutrient inputs likely include increased hypoxia in off channel areas, 
excessive phytoplankton and cyanobacterial production, and accumulation of 
nitrogen and phosphorus in sediments.  Recent research on nitrogen cycling 
has emphasized the linkages between river hydrology, geomorphology and 
connectivity among aquatic areas as determinants of biogeochemical process 
rates and N removal.  Recent research on riverine primary productivity has 
suggested (1) a strong relationship exists between nutrient concentrations in 
channels and rates of planktonic productivity; (2) backwater algal community 
structure is linked to N:P ratios that are largely related to hydrologic 
connectivity and river stage. Evidence from the UMR and other large rivers 
suggests that to understand the processing of nutrients within the river we 
need to better incorporate spatial and temporal patterns in hydrologic 
connectivity. 

Keywords:  Nitrogen, Phosphorus, eutrophication, denitrification, primary 
production

Presenting author:
Jeff Houser
USGS Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road, La 
Crosse, WI  54601
Ph:  608-781-6262
Fax: 608-498-5753
Email:  jhouser@usgs.gov  (please don’t post email on the web site, post my 
homepage if you’d like http://www.umesc.usgs.gov/staff/bios/jnh0.html)

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