United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
Research and Development
EPA-600/S3-82-065 Oct. 1982
Project Summary
Photosynthesis and
Respiration Rates in the
Monticello Experimental
Streams: 1976/77 Diel Field
Data and Computed Results
Douglas J. Fuller), John S. Gulliver, and Heinz G. Stefan
Two-station diel dissolved oxygen
measurements collected during
1976-77 at the Monticello Ecological
Research Station (Monticello, MN)
were analyzed by a graphical-
analytical method and by a computer
model. Dissolved Oxygen Routing
Model (DORM), to determine daily
community respiration and photo-
synthesis. A third set of values was
generated by using the DORM model
to simulate the graphical method. The
complete DORM included surface
oxygen exchange, longitudinal disper-
sion, a higher-order curve extrapola-
tion between upstream dissolved
oxygen measurements, and the depend-
ence of respiratory rate on water
temperature and dissolved oxygen
concentrations: however, neither the
graphical nor the simulated graphical
models included these factors. The
complete DORM gave consistently
higher rates of respiration and photo-
synthesis than either the graphical-
analytical method or the computer
simulation.
This Project Summary was devel-
oped by EPA's Environmental Re-
search Laboratory, Duluth. MN. to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
During 1976 and 1977, two-station
diel dissolved oxygen (D.O.) measure-
ments were taken at the Monticello
Ecological Research Station in ambient
and heated experimental streams. The
data were made available to the authors
for analysis. Three methods of analysis
were used in treating the data: a
graphical-analytical routing method, a
numerical dissolved oxygen routing
method (DORM) and a computer
simulated graphical method.
In the graphical-analytical method,
the hydraulic residence time in a
channel reach was calculated, after
which the upstream station diel oxygen
curve with the residence time added to
the dissolved oxygen time was plotted
on the same graph with the
downstream station diel oxygen curve.
The difference in D.O. during the night
hours divided by the residence time
yielded an hourly nighttime respiration
rate. All nighttime respiration rates
were averaged and used as an estimate
of the respiration rate that occurred
during daylight hours. The photosyn-
thetic rate was graphically determined
by measuring the D.O. difference each
hour during the daylight. Each value
was divided by the residence time to
give an hourly rate; adding the average
respiration rates gave an hourly photo-
synthetic rate (g m"3 hr~1). The photo-
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synthetic rates were multiplied by the
hydraulic mean depth to produce photo-
synthetic rates per unit surface area
(g m"2 hr~1). Addition of all hourly photo-
synthetic rates yielded an accumulated
rate for the period of record.
The numerical Dissolved Oxygen
Routing Model (DORM) involved
determination of total stream commun-
ity photosynthesis and respiration rates
through successive routing of the two-
station die! D.O. measurements. This
model included surface oxygen ex-
change, longitudinal dispersion, a higher
order curve extrapolation between up-
stream D.O. measurements, and de-
pendence of respiratory rate on water
temperature and D.O. concentration. A
sensitivity analysis was conducted with
DORM to investigate the influence of
residence time on respiration and photo-
synthesis rates.
The graphical-analytical procedure
was also simulated by DORM numeric-
ally. This was accomplished by making
the same assumptions as in the
graphical method; namely, no surface
oxygen exchange (reaeration) or
longitudinal dispersion occurred,
respiration was independent of temper-
ature and D.O. concentration, and a linear
interpolation between D.O. measure-
ments was used.
Conclusions
The complete routing (DORM) gave
consistently higher rates of respiration
and photosynthesis than either the
graphical method or its simulation by
DORM. This was due to the omission of
reaeration (surface oxygen exchange) in
these methods. The effect of reaeration
on photosynthesis and respiration
appeared to be channel-position
dependent, at least in spring and late
summer
Total daily rates of respiration and
total daily rates of photosynthesis
obtained by the graphical method were
consistently smaller than those
obtained by DORM. The average
fractions were 87% and 89%, respec-
tively, for the upper channel reach and
76% and 81 %, respectively, for the lower
channel reach.
Photosynthesis and respiration rates
increased with increasing residence
time m the channel in a nonlinear
relationship For a +20% change in
residence time, respiration changed
from +1.7% to +11.0%; for a -20%
change in residence time, respiration
changed between -2.3% to -9.6%. The
associated rate changes for photosyn-
thesis were +2.9% to +13.6%, and -2.6%
to -12.7%.
Recommendations
In future studies using diel dissolved
oxygen routing, particular care must be
taken to measure channel cross
sections and flow rates or hydraulic
residence time directly by tracer routing
Application of a constant correction
coefficient to the results of the graphics I
method implies that reaeration effects
are of the same magnitude m spring,
summer and fall Application of the
numerical method DORM wouldelimm-
ate the assumption
Douglas J. Fullen, John S. Gulliver, and Heinz G. Stefan are with the St. Anthony
Falls Hydraulic Laboratory, University of Minnesota, Minneapolis, MN 55414.
Kenneth E. F. Hokanson is the EPA Project Officer (see below).
The complete report, entitled "Photosynthesis and Respiration Rates m the
Monticello Experimental Streams: 1976/77 Diel Field Data and Computed
Results," (Order No. PB 82-242 066; Cost: $16.50, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:«
Monticello Ecological Research Station
EnvironmentaLResearch Laboratory—Duluth
P.O. Box 50d "
U.S. Environmental Protection Agency
Monticello, MN 55362
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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