Science JunctionLesson 1
 
 

Introductory Lesson-Determination of Overall Water Quality Using a Quantitative Macroinvertebrate Survey

Objectives:
Students will be able to: Materials:
Water sample from a local stream or pond (sample must be fresh and contain debris from the bottom and edges of the water)
Macroinvertebrate Identification charts
Assorted trays and petri dishes for separation of sample
Dissecting microscope and hand lenses
Small paintbrushes
Pipets

Procedure:
1. Working with a partner, take an approximate 500 ml sample of the water including the debris.
2. Pour a portion of the sample into a petri dish and examine it under low power on the microscope.
3. Using the identification charts, count and identify 100 macroinvertebrates. Try not to hunt for only the large ones or your sample will be biased. If you can not find 100 macroinvertebrates in your sample, take an additional 500 ml sample. Continue this procedure until you and your partner have counted and indentified 100 macroinvertebrates.
4. Identify and count the numbers of each type of organism listed below.
5. Multiply the number of each type by its biotic value.
6. Add up all the numbers and divide by 10. This gives the Biotic Index Value. Check the Biotic Value chart at the bottom of the page to determine the quality of your water sample.
7. Compare your group value with the class values. Do they agree? Why or why not?


Class I    Pollution intolerant: These organisms are highly sensitive to pollution.
Class II   Somewhat pollution tolerant: These organisms will be found in clean and slightly polluted waterways.
Class III  Pollution tolerant: These organisms will be found in polluted, as well as clean aquatic ecosystems.
 
Class I 
 
Biotic Value
Number
Found
 Class II  Biotic 
Value		 Number 
Found		 Class III  Biotic 
Value		 Number 
Found
Stonefly nymph 
10
   Beetle larva 
8
   Midge fly larva 
5
  
Mayfly nymph 
10
   Sowbug 
8
   Snails 
4
  
Dobsonfly larva 
10
   Scud 
6
   Leech 
2
  
Caddisfly larva 
10
   Clams, Mussels 
6
   Aquatic worms 
0
  
Riffle beetle 
10
   Crayfish 
6
  
 
    
Water penny 
10
   Cranefly larva 
6
        
      Dragonfly nymph 
6
        
      Damselfly nymph 
6
        
      Black fly larva 
6
        
Total      Total      Total     
For example if you find:
25 mayflies 25 x 10 = 250
15 caddisflies 15 x 10 = 150
20 stoneflies 20 x 10 = 200
20 scuds 20 x  6 = 120
20 midge larva 20 x  5 = 100
Total =  820 / 10 = 82
Based on the Biotic Index value the water quality is excellent.

Biotic Index
Excellent >70
Good 60-79
Fair 40-59
Poor <40
 
|Water Quality and Macroinvertebrates | Water What-ifs Home |
 
 

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©1998 April J. Cleveland for Science Junction, NC State University. All rights reserved.
page design by Lisa Leonor Grable and April J. Cleveland 
URL: http://www.ncsu/scijunct/depot/experiments/water/lessons/macro/macrolesson1.html 
Last Modified: 6/3/98

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