ENVIRONMENTAL STUDIES OF PHOSPHORUS IN THE UPPER MISSISSIPPI
RIVER, 1994-1998.  

D. Kent Johnson.   Environmental Monitoring and Assessment
Section, Metropolitan Council Environmental Services, Mears Park
Centre, 230 East Fifth Street, St. Paul, MN 55101.  

The issue of phosphorus in the Upper Mississippi River came to
the forefront during the 1987-1988 drought in the Upper Midwest. 
Low river flows and an abundance of phosphorus combined to create
excessive algal blooms in Lake Pepin (Pool 4) during the summer
of 1988.  These algal blooms caused unsightly surface scums, bad
odors, low oxygen levels, and localized fish kills.  The
Metropolitan Wastewater Treatment Plant (Metro Plant), owned and
operated by the Metropolitan Council Environmental Services
(MCES), is the largest point source of phosphorus upstream from
Lake Pepin.  The 220 mgd facility provides advanced secondary
treatment and discharges to mid-Pool 2 of the Mississippi River
in St. Paul, MN.  Minnesota state statutes require municipal
wastewater facilities to remove phosphorus to 1 mg/1 where the
discharge is directly to or affects a lake or reservoir.  After
the 1987-1988 drought, a question arose about the effect of Metro
Plant phosphorus on the water quality of Lake Pepin and Spring
Lake, a smaller lake in lower Pool 2.  To address this question,
a study was conducted in 1990-1992 by MCES and several
cooperating agencies.  The study reached a number of conclusions: 
1.  The Upper Mississippi River, Pools 2-4, contains an abundance
of phosphorus in the water column and sediment bed; 2.  The Metro
Plant is only one of numerous point and nonpont sources of
phosphorus; 3.  Phosphorus reductions at the Metro Plant alone
will result in little short-term reduction of algal blooms in
Lake Pepin; 4.  Basin-wide phosphorus reductions are needed
before long-term improvements in water quality will be achieved. 
Despite these findings, a number of unresolved issues remained. 
Low river flows did not occur during the study period, leaving an
inadequate data set for targeted conditions.  Much data were
collected on phosphorus loadings, but not much was known about
the fate and transport of phosphorus in the river--in particular,
the role of sediment in transporting phosphorus.  Finally, the
study found that internal loading of phosphorus in Lake Pepin was
important, but more research was needed on release rates and
mechanisms.  In 1993, the NPDES permit for the Metro Plant was
reissued with several phosphorus requirements, including an
effluent limit of 4.0 mg/l, implementation of phosphorus removal
in 25% of the wastestream, and continuing environmental studies
of phosphorus.  From 1994 to 1998, additional studies were
conducted to determine the effect of phosphorus loadings from the
Metro Plant and other sources on the water quality of the
Mississippi River (specifically algal blooms in Lake Pepin and
Spring Lake), and to project the water quality benefits to the
river of reduced phosphorus loadings.  The five major components
of the 1994-1998 environmental studies of phosphorus were as
follows:  1. "Citizen Monitoring of Lake Pepin and Spring Lake",
conducted by the Minnesota-Wisconsin Boundary Area Commission to
evaluate water quality goals from the user perspective; 2.
"Phosphorus Sources and Upper Mississippi River Water Quality",
conducted by the MCES to analyze historical river data; 3.
"Phosphorus Sources and Lake Pepin Water Quality", conducted by
the U.S. Army Engineers Waterway Experiment Station to analyze
nutrient and seston fluxes and phytoplankton dynamics; 4. "Lake
Pepin Sediment History", conducted by the Science Museum of
Minnesota to study changes in sediment and phosphorus loadings
over the past 200 years; and 5.  "Advanced Eutrophication
Modeling of the Upper Mississippi River", conducted by HydroQual,
Inc. to project water-quality improvements under various
phosphorus management strategies.  Four of the studies are
presented after this introduction.  The 1994-98 environmental
studies of phosphorus lend additional support to the conclusions
of the earlier study and provide further insights on phosphorus,
sediment, and algal dynamics in the Upper Mississippi River,
Pools 2-4.  The need for phosphorus removal at the Metro Plant
has been identified, and biological phosphorus removal will be
employed to meet an annual effluent limit of 1.0 mg/1 by 2005. 
However, long-term improvements in Lake Pepin water quality will
only be achieved through additional basin-wide reductions in
phosphorus loadings from both point and nonpoint sources.  

Keywords:  Upper Mississippi River, Lake Pepin, phosphorus,
eutrophication, water quality