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Exercise 13
a. Several nets could be placed across the stream channel to measure spatial variations in
drift.
b. Nets could be placed at the downstream end of a rime and just below a pool.
c. Diurnal variations could be examined by installing drift nets and collecting organisms
at about 1 h before sunset and sunrise.
2. Transfer the organisms and debris from the drift nets to small plastic bags (Whirl-a-pacs),
add 70% alcohol, and transport to the laboratory.
3. Sort and identify the organisms in the drift samples.
4. Determine the weight of the organisms and organic debris by dry weight and organic weight
analyses.
5. Knowing the numbers of organisms drifting into the nets per unit time and the stream
discharge rate (see Exercise 5), calculate the drift rate [numbers per time from the (number/
cm 3 x cm 3 /time)] for the whole stream. From the amount of stream volume passing through
the net(s), calculate the drift density [as numbers per m\ calculated from the area of the
net opening (cm 2 ), velocity (cm/sec), and time; thus, volume = cm 2 x cm/sec x sec = cm 3 ].
6. Using your results, test the variability of sampling and the spatial and temporal heterogeneity
of distribution of drifting organisms.
7. Answer the following questions.
Questions
1. What are the advantages and disadvantages of a Surber or Hess sampler for collecting
samples of benthic invertebrates in streams?
2. What are the advantages and disadvantages of emergence traps in collecting benthic
invertebrates in streams?
3. How would you design a better sampler? [See Merritt and Cummins (1984).]
4. Which is richer in stream invertebrates, a pool or a rime'? Compare numbers and biomass.
How do you explain the results?
5. What types of benthic fauna predominate in rimes? In pools?
6. What are the effects and interrelationships of current and sediment type on distribution
and abundance of stream invertebrates?
7. How far into the sediments or into the banks do you think stream invertebrates may be
found? [See Hynes (1974) and Williams, (1984).]
8. What was the relationships between drift of organisms and drift of organic debris in your
studies? Did this change diurnally? How do you explain this?
9. What differences would you expect in benthic invertebrates between upstream and
downstream locations? Would problems of sampling differ? How?
10. Why would the placement of nets in the center of a rime tend to overestimate rates of
invertebrate drift for the entire stream? What would be the result of placing drift nets near
the shore line?
1l. What percentage of the total benthic fauna might move downstream as drift? [See Waters
(1972).]
12. Also, see questions for Exercise 12.
Equipment and Supplies*
l. Modified Hess sampler.
2. Surber sampler (Wildco Instruments, Saginaw, MI).
3. Drift net (Wildco Instruments, Saginaw, MI).
4. White enameled or plastic pans.
5. Forceps.
6. Balance.
*See Exercise 12 for additional supplies.
Exercise 13
a. Several nets could be placed across the stream channel to measure spatial variations in
drift.
b. Nets could be placed at the downstream end of a rime and just below a pool.
c. Diurnal variations could be examined by installing drift nets and collecting organisms
at about 1 h before sunset and sunrise.
2. Transfer the organisms and debris from the drift nets to small plastic bags (Whirl-a-pacs),
add 70% alcohol, and transport to the laboratory.
3. Sort and identify the organisms in the drift samples.
4. Determine the weight of the organisms and organic debris by dry weight and organic weight
analyses.
5. Knowing the numbers of organisms drifting into the nets per unit time and the stream
discharge rate (see Exercise 5), calculate the drift rate [numbers per time from the (number/
cm 3 x cm 3 /time)] for the whole stream. From the amount of stream volume passing through
the net(s), calculate the drift density [as numbers per m\ calculated from the area of the
net opening (cm 2 ), velocity (cm/sec), and time; thus, volume = cm 2 x cm/sec x sec = cm 3 ].
6. Using your results, test the variability of sampling and the spatial and temporal heterogeneity
of distribution of drifting organisms.
7. Answer the following questions.
Questions
1. What are the advantages and disadvantages of a Surber or Hess sampler for collecting
samples of benthic invertebrates in streams?
2. What are the advantages and disadvantages of emergence traps in collecting benthic
invertebrates in streams?
3. How would you design a better sampler? [See Merritt and Cummins (1984).]
4. Which is richer in stream invertebrates, a pool or a rime'? Compare numbers and biomass.
How do you explain the results?
5. What types of benthic fauna predominate in rimes? In pools?
6. What are the effects and interrelationships of current and sediment type on distribution
and abundance of stream invertebrates?
7. How far into the sediments or into the banks do you think stream invertebrates may be
found? [See Hynes (1974) and Williams, (1984).]
8. What was the relationships between drift of organisms and drift of organic debris in your
studies? Did this change diurnally? How do you explain this?
9. What differences would you expect in benthic invertebrates between upstream and
downstream locations? Would problems of sampling differ? How?
10. Why would the placement of nets in the center of a rime tend to overestimate rates of
invertebrate drift for the entire stream? What would be the result of placing drift nets near
the shore line?
1l. What percentage of the total benthic fauna might move downstream as drift? [See Waters
(1972).]
12. Also, see questions for Exercise 12.
Equipment and Supplies*
l. Modified Hess sampler.
2. Surber sampler (Wildco Instruments, Saginaw, MI).
3. Drift net (Wildco Instruments, Saginaw, MI).
4. White enameled or plastic pans.
5. Forceps.
6. Balance.
*See Exercise 12 for additional supplies.