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Exercise 24
OPTION 1. SOME ASPECTS OF AN ENERGY BUDGET
1. Collect and plot the values for net radiation at each of the two study sites. Use a portable net
radiometer if available; otherwise, adjust estimated values from a local climatologic data
station for the amount offorest canopy if the section of the stream is located in a forested area
(see Exercise 4). Alternatively, a photographic light meter, calibrated against measurements at
a local climatologic data station, could be used to approximate the input of solar radiation.
2. Collect and plot the air temperature, 10 cm above the water surface, and the surface water
temperature at each study site. Plot the direction of sensible heat flux between air and water
throughout the diurnal period.
3. Determine and plot the instantaneous amount of heat stored in the water at each sampling
time for each study site throughout the diurnal period: Ow = Tw' V' s' p, where Ow is the heat
content of the stream water in calories*, Tw is water temperature in DC, V is volume in cm 3 of
discharge, s is specific heat of water in cal/g-DC, and p is density in g/cm 3 . Superimpose these
curves on the same graph, adjusting the real time for the diwnstream site by the time of flow
between the two sites. Compute with an electronic digitizer, by planimetry, or by counting
squares the change in heat content between the two sites throughout the diurnal period (see
Exercise 3). Construct a graph to show this change in stored heat with time between the two
sites [see e.g., Wright and Horrall (1967)].
4. Calculate the difference in potential energy between the two sites: Difference in potential
energy (kg-m) = (Wlh l ) - (W2h2), where WI and W2 are weights of 1 m 3 of water in kilograms
at upstream and downstream sites, respectively, and hi and h2 are heights (in m above mean
sea level) of the gravitational centers of the channel cross sections at the two sites.
Questions
1. What other components of the heat budget have not been evaluated in this exercise? Do you
think these components would be important? Explain.
2. Why does the stream lose heat at night? Would the heat loss be greater or less than that
expected from a pond of the same depth? Why?
3. At what times during the diurnal period were the maximum and minimum air and water
temperatures observed? How do you explain this?
4. What do you think the biological and chemical responses are to these temperature
fluctuations?
5. What would be the effects of a rainstorm on the heat budget of a stream?
6. How would you expect the heat budget of a stream to be affected by the presence or absence of
forest vegetation? [See Burton and Likens (1973).J
7. How might the biological community of the stream utilize the potential energy lost as the
water flows downstream?
OPTION 2. SOME ASPECTS OF A CHEMICAL MASS BALANCE
(INPUT/OUTPUT BUDGET)
1. Determine and plot the concentrations of P0 4 3 -, N0 3 -, alkalinity, H+, and dissolved
organic carbon for each site throughout the diurnal period. Optionally, particulate matter can
be collected with a I-mm mesh net stretched across the stream. The amounts of finer
particulate matter can be determined by filtering a subsample of water, which had passed
through the I-mm net, through a tared, OA5-flm pore size Millipore filter and then measuring
its dry weight [see Eaton et al. (\969) for precautions]. Samples also can be filtered through
* \ g calorie (mean) x 4.\862 = I joule.
Exercise 24
OPTION 1. SOME ASPECTS OF AN ENERGY BUDGET
1. Collect and plot the values for net radiation at each of the two study sites. Use a portable net
radiometer if available; otherwise, adjust estimated values from a local climatologic data
station for the amount offorest canopy if the section of the stream is located in a forested area
(see Exercise 4). Alternatively, a photographic light meter, calibrated against measurements at
a local climatologic data station, could be used to approximate the input of solar radiation.
2. Collect and plot the air temperature, 10 cm above the water surface, and the surface water
temperature at each study site. Plot the direction of sensible heat flux between air and water
throughout the diurnal period.
3. Determine and plot the instantaneous amount of heat stored in the water at each sampling
time for each study site throughout the diurnal period: Ow = Tw' V' s' p, where Ow is the heat
content of the stream water in calories*, Tw is water temperature in DC, V is volume in cm 3 of
discharge, s is specific heat of water in cal/g-DC, and p is density in g/cm 3 . Superimpose these
curves on the same graph, adjusting the real time for the diwnstream site by the time of flow
between the two sites. Compute with an electronic digitizer, by planimetry, or by counting
squares the change in heat content between the two sites throughout the diurnal period (see
Exercise 3). Construct a graph to show this change in stored heat with time between the two
sites [see e.g., Wright and Horrall (1967)].
4. Calculate the difference in potential energy between the two sites: Difference in potential
energy (kg-m) = (Wlh l ) - (W2h2), where WI and W2 are weights of 1 m 3 of water in kilograms
at upstream and downstream sites, respectively, and hi and h2 are heights (in m above mean
sea level) of the gravitational centers of the channel cross sections at the two sites.
Questions
1. What other components of the heat budget have not been evaluated in this exercise? Do you
think these components would be important? Explain.
2. Why does the stream lose heat at night? Would the heat loss be greater or less than that
expected from a pond of the same depth? Why?
3. At what times during the diurnal period were the maximum and minimum air and water
temperatures observed? How do you explain this?
4. What do you think the biological and chemical responses are to these temperature
fluctuations?
5. What would be the effects of a rainstorm on the heat budget of a stream?
6. How would you expect the heat budget of a stream to be affected by the presence or absence of
forest vegetation? [See Burton and Likens (1973).J
7. How might the biological community of the stream utilize the potential energy lost as the
water flows downstream?
OPTION 2. SOME ASPECTS OF A CHEMICAL MASS BALANCE
(INPUT/OUTPUT BUDGET)
1. Determine and plot the concentrations of P0 4 3 -, N0 3 -, alkalinity, H+, and dissolved
organic carbon for each site throughout the diurnal period. Optionally, particulate matter can
be collected with a I-mm mesh net stretched across the stream. The amounts of finer
particulate matter can be determined by filtering a subsample of water, which had passed
through the I-mm net, through a tared, OA5-flm pore size Millipore filter and then measuring
its dry weight [see Eaton et al. (\969) for precautions]. Samples also can be filtered through
* \ g calorie (mean) x 4.\862 = I joule.