QUESTIONS
Effect of Sewage OuHall on a Stream Ecosystem
347
At the laboratory, remove the plugs from the filter holder and add 1 ml of
M-Endo culture medium to the pad side, replace the plugs, and place the holder
(grid side down) in an incubator (35°C, 90% relative humidity) for 24 h.
I. Remove the filter from the filter holder-incubation holder withlorceps. Some
of the bacteria could be pathogenic. Do not touch the filter either to your
hands, to bench tops, or to equipment. Flame the tip ofthe forceps before and
after handling the filter. Place the gridded filter on a 5 x 7.6 cm glass slide and
examine it with a dissection microscope.
ii. Count the total number of colored colonies on the grid. Distinguish between
clones that are red, orange, or have a metallic sheen.
lll. The ratio of colonies with a metallic sheen to total colonies is an index of
"coliform contamination" and hence a rough measure of fecal contamination.
This index is used commonly as a measure of water pollution.
iv. Discard the filter into a container of alcohol.
5. Plot the distribution of the various variables along the logitudinal gradient of the
stream (e.g., temperature, pH, benthic fauna, sewage fungus).
1. What are the major ecological effects of sewage discharge on a stream ecosystem?
2. Which biotic components of the ecosystem are most sensitive to pollutants? Why?
3. How far downstream can the effects of a sewage outfall be observed? Are the
changes in the various parameters related or do they occur independently of each
other?
4. What is meant by the "assimilative capacity" of a stream? Is this a legitimate
ecological concept?
5. What is meant by "sewage fungus"?
6. In some areas remote from human habitation, there may be large concentrations of
coliform bacteria in streams. How would you explain this? [see Hanes et al. (1965).]
7. Do colonies of bacteria growing on a nutrient medium give a quantitative estimate
of the size of natural microbial populations? Why?
8. Is there a difference between eutrophication and pollution? [See Likens (1972).]
9. What additional toxic substances may have been present in the sewage discharge?
What about viruses? [See, e.g., Bertucci et al. (1977) and Borchardt et al. (1977).]
10. In some places sewage effluents are discharged onto land rather than into the
water courses. What are the advantages/disadvantages of this? What are the
advantages/disadvantages of discharges onto wetlend, marsh systems? [See
Hammer (1989).]
11. Protozoan populations often increase in size downstream of sewage outfalls. Why
do you think this happens?
12. What might be the effect of discharging heated water (e.g., effluent from a power
plant) into a stream containing domestic sewage?
APPARATUS AND SUPPLIES
1. Incubation chamber: 25°C, ca. 90% relative humidity.
2. Forceps.
3. Bacteriological Analysis Monitors (part MHWG 03700, Millipore Corp., Bedford,
MA).
Effect of Sewage OuHall on a Stream Ecosystem
347
At the laboratory, remove the plugs from the filter holder and add 1 ml of
M-Endo culture medium to the pad side, replace the plugs, and place the holder
(grid side down) in an incubator (35°C, 90% relative humidity) for 24 h.
I. Remove the filter from the filter holder-incubation holder withlorceps. Some
of the bacteria could be pathogenic. Do not touch the filter either to your
hands, to bench tops, or to equipment. Flame the tip ofthe forceps before and
after handling the filter. Place the gridded filter on a 5 x 7.6 cm glass slide and
examine it with a dissection microscope.
ii. Count the total number of colored colonies on the grid. Distinguish between
clones that are red, orange, or have a metallic sheen.
lll. The ratio of colonies with a metallic sheen to total colonies is an index of
"coliform contamination" and hence a rough measure of fecal contamination.
This index is used commonly as a measure of water pollution.
iv. Discard the filter into a container of alcohol.
5. Plot the distribution of the various variables along the logitudinal gradient of the
stream (e.g., temperature, pH, benthic fauna, sewage fungus).
1. What are the major ecological effects of sewage discharge on a stream ecosystem?
2. Which biotic components of the ecosystem are most sensitive to pollutants? Why?
3. How far downstream can the effects of a sewage outfall be observed? Are the
changes in the various parameters related or do they occur independently of each
other?
4. What is meant by the "assimilative capacity" of a stream? Is this a legitimate
ecological concept?
5. What is meant by "sewage fungus"?
6. In some areas remote from human habitation, there may be large concentrations of
coliform bacteria in streams. How would you explain this? [see Hanes et al. (1965).]
7. Do colonies of bacteria growing on a nutrient medium give a quantitative estimate
of the size of natural microbial populations? Why?
8. Is there a difference between eutrophication and pollution? [See Likens (1972).]
9. What additional toxic substances may have been present in the sewage discharge?
What about viruses? [See, e.g., Bertucci et al. (1977) and Borchardt et al. (1977).]
10. In some places sewage effluents are discharged onto land rather than into the
water courses. What are the advantages/disadvantages of this? What are the
advantages/disadvantages of discharges onto wetlend, marsh systems? [See
Hammer (1989).]
11. Protozoan populations often increase in size downstream of sewage outfalls. Why
do you think this happens?
12. What might be the effect of discharging heated water (e.g., effluent from a power
plant) into a stream containing domestic sewage?
APPARATUS AND SUPPLIES
1. Incubation chamber: 25°C, ca. 90% relative humidity.
2. Forceps.
3. Bacteriological Analysis Monitors (part MHWG 03700, Millipore Corp., Bedford,
MA).