NITROGEN MASS BALANCE BUDGET FOR THE UPPER MISSISSIPPI RIVER
BASIN.  

Dennis M. Wasley 1, 2, D.M. Soballe1, D.R. Deuschle 1, 2, and R.J. Haro 2. 
 1 U.S. Geological Survey, Upper Midwest Environmental Sciences
Center, 2630 Fanta Reed Road, P.O. Box 818, La Crosse, WI 54602-
0818, USA; 2 River Studies Center, Department of Biology and
Microbiology, University of Wisconsin-La Crosse, La Crosse, WI
54601 USA.  

We used nitrogen and streamflow data from the Long Term Resource
Monitoring Program, the U.S. Geological Survey and other sources
to calculate average annual loads of total nitrogen, ammonia and
nitrate+nitrite (NOx) for twenty-seven tributaries of the upper
Mississippi River.  Average annual tributary loads were summed
and compared with average annual loads of the Mississippi River
at Alton, IL.  The selected tributaries covered 90% of the upper
Mississippi River Basin.  Thus, total nitrogen inputs were
adjusted to compensate for the unmonitored portion of the basin. 
Approximately 95% of the total nitrogen at Alton could be
accounted for from tributary loads and Mississippi River loads
upstream of impoundment.  Smaller scale navigational pool budgets
on pools 4, 8 and 13 indicate that total nitrogen is conserved as
it passes through these pools.  Tributary inputs of NOx) and
ammonia exceed loads at Alton indicating that some of the
inorganic nitrogen delivered from the tributaries is being
converted to organic nitrogen.  Conversion of NOx) and ammonia to
organic nitrogen is inconclusive in navigational pool scale
budgets.  Typically, NOx) and ammonia loads have higher residual
variance due to their volatile concentration shifts while TN
loads have lower residual variance due to the conservative nature
of total nitrogen concentrations.  Different collecting agencies
and varying periods of tributary data also increased uncertainty
associated with this budget of the upper Mississippi River.  This
budget offers a preliminary estimate of the nitrogen dynamics of
a large river system, and establishes a framework for
understanding the nitrogen dynamics of the upper Mississippi
River.  

Keywords:  Nutrients, Mississippi River, Nitrogen, Mass Balance,
Watershed