Diurnal Changes in a Stream Ecosystem
321
4. Using planimetry or by counting squares, determine the area of the curve that represents
gross primary productivity, net primary productivity, and ecosystem respiration as
g 02/m 3 -day. Based on an assumed or calculated respiratory quotient (see Exercise 29),
calculate the production and respiration values in terms of carbon.
5. Note: There may be some advantages (less data to manipulate, fewer compounded errors,
minimized stream heterogeneity) in using the single-curve method in this class exercise for
estimating stream metabolism [see Hall and Moll (1975)]. The procedure is the same as
above, except that the rate of 02-change curve is calculated for time intervals from data at
only one station. If possible, divide the class in half, obtain data from both stations, and
compare the results based on an average of the two single-curve analyses and the doublecurve analysis.
Questions
1. Why is it necessary to make a correction for exchange of oxygen (diffusion) with the
atmosphere? [See Owens (1969).] Will errors in this parameter significantly affect the overall
estimates of primary productivity and respiration?
2. What is the meaning ofthe net primary productivity value as determined by this method? [See
Wetzel (1975).]
3. How might you obtain a better estimate of net productivity? [See Kelly et al. (1974) and
Gallegos et al. (1977).]
4. What is the PIR ratio for the whole stream? If the value were less than 1, where would the extra
energy come from? If greater, where would the extra energy be going?
5. What are the main factors affecting stream metabolism? How do these differ from one stream
segment to another? From day to day or season to season?
6. In some streams, the dissolved oxygen values for the downstream station may be similar to the
upstream values. What does this mean? How is the rate-of-change method used in this case?
7. Attempt to construct a possible food web for the stream ecosystem. What are the energy
relationships?
OPTION 4. LABORATORY ANALYSES
Using the data in Fig. 24.lB and Table 24.2:
1. Calculate the channel cross-sectional areas for Stations I and II.
2. Calculate and plot the change in heat storage for each station throughout the diurnal period.
3. Calculate the difference in heat storage (budget) between the upstream and downstream
stations for the diurnal period (see Option 1).
4. Using data for N0 3 - and Na + (Table 24.2), complete Option 2.
5. Calculate the percent saturation values for the downstream station on Fig. 24.1 and plot them.
6. Determine a diffusion constant for each station, and correct the O2 rate-of-change curves
(Fig. 24.1D) for diffusion. Plot the corrected values and complete Parts 3 and 4 of Option 3.
7. Answer the questions for Options 1, 2, and 3.
Apparatus and Supplies (in addition to those other exercises cited)
1. Clipboards.
2. Flashlights.
3. Alarm clock.
4. Graph paper (linear and log).
5. Portable net radiometer (e.g., C.S.I.R.O. Net Radiometer, Model CN2, Middleton and Co.
Pty., Ltd., Port Melbourne, Victoria, Australia; or a small clock-driven pyrheliometer, e.g.,
Belfort Instruments Inc., Baltimore, MD).
321
4. Using planimetry or by counting squares, determine the area of the curve that represents
gross primary productivity, net primary productivity, and ecosystem respiration as
g 02/m 3 -day. Based on an assumed or calculated respiratory quotient (see Exercise 29),
calculate the production and respiration values in terms of carbon.
5. Note: There may be some advantages (less data to manipulate, fewer compounded errors,
minimized stream heterogeneity) in using the single-curve method in this class exercise for
estimating stream metabolism [see Hall and Moll (1975)]. The procedure is the same as
above, except that the rate of 02-change curve is calculated for time intervals from data at
only one station. If possible, divide the class in half, obtain data from both stations, and
compare the results based on an average of the two single-curve analyses and the doublecurve analysis.
Questions
1. Why is it necessary to make a correction for exchange of oxygen (diffusion) with the
atmosphere? [See Owens (1969).] Will errors in this parameter significantly affect the overall
estimates of primary productivity and respiration?
2. What is the meaning ofthe net primary productivity value as determined by this method? [See
Wetzel (1975).]
3. How might you obtain a better estimate of net productivity? [See Kelly et al. (1974) and
Gallegos et al. (1977).]
4. What is the PIR ratio for the whole stream? If the value were less than 1, where would the extra
energy come from? If greater, where would the extra energy be going?
5. What are the main factors affecting stream metabolism? How do these differ from one stream
segment to another? From day to day or season to season?
6. In some streams, the dissolved oxygen values for the downstream station may be similar to the
upstream values. What does this mean? How is the rate-of-change method used in this case?
7. Attempt to construct a possible food web for the stream ecosystem. What are the energy
relationships?
OPTION 4. LABORATORY ANALYSES
Using the data in Fig. 24.lB and Table 24.2:
1. Calculate the channel cross-sectional areas for Stations I and II.
2. Calculate and plot the change in heat storage for each station throughout the diurnal period.
3. Calculate the difference in heat storage (budget) between the upstream and downstream
stations for the diurnal period (see Option 1).
4. Using data for N0 3 - and Na + (Table 24.2), complete Option 2.
5. Calculate the percent saturation values for the downstream station on Fig. 24.1 and plot them.
6. Determine a diffusion constant for each station, and correct the O2 rate-of-change curves
(Fig. 24.1D) for diffusion. Plot the corrected values and complete Parts 3 and 4 of Option 3.
7. Answer the questions for Options 1, 2, and 3.
Apparatus and Supplies (in addition to those other exercises cited)
1. Clipboards.
2. Flashlights.
3. Alarm clock.
4. Graph paper (linear and log).
5. Portable net radiometer (e.g., C.S.I.R.O. Net Radiometer, Model CN2, Middleton and Co.
Pty., Ltd., Port Melbourne, Victoria, Australia; or a small clock-driven pyrheliometer, e.g.,
Belfort Instruments Inc., Baltimore, MD).