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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