Download Determining Pollution Tolerance Index

BIO-MONITORING DATA SHEET
How Healthy is my Stream?
Determining Pollution Tolerance Index
Date: ______
Period: ______ Table #: _______
Introduction: Ecologists can assess the “health” of an ecosystem by the
presence or absence of particular species. Macroinvertebrates are often
used to assess the health of rivers and streams. These are animals with no
backbones that are visible without the aid of a microscope.
Team Member Names: ___________________________________________
Procedure:
1. Use the macroinvertebrate key to identify and classify the species in
your stream sample.
Group 1
____ Pouch Snail
____ Tubifex Worm
____ Blood Midge
____ Rat-tailed Maggot Larva
____ Riffle Beetle
Group 2
____ Midge (except Blood Midge)
____ Blackfly Larva
____ Flatworm
____ Leech
____ Water Mite
_____ Total present x 1 =
_____ Total present x 2 =
_____ Index value for Group 1
_____ Index value for Group 2
Group 3
____ Damselfly Nymph
____ Dragonfly Nymph
____ Aquatic Sowbug
____ Scud
____ Cranefly Larva
____ Clam
Group 4
____ Stonefly Nymph
____ Mayfly Nymph
____ Caddisfly Larva
____ Dobsonfly Nymph
____ Riffle Beetle
____ Water Penny
____ Gilled Snail
_____ Total present x 3 =
_____ Total present x 4 =
_____ Index value for Group 3
_____ Index value for Group 4
2. On the Bio-monitoring Data Sheet, place a check mark next to each
type of organism that was found in your sample. (NOTE: We are not
counting individuals, we are counting types of animals.)
3. Multiply the number of species in each group by its group number to
determine its index value.
4. Add the index values of all four groups and divide by the total
number of species found in your sample to determine the Pollution
Tolerance Index (PTI) for your stream.
5. Discuss the answers to the questions with your group members. Take
notes on your discussion in your science journal.
6. Write the answers in your journal in complete sentences that restate
the question and are supported with your data.
______________________________________________________________
Discussion Questions:
1. Describe the process your group used to identify organisms and
assess your stream sample.
2. Which animals were the most common in your sample?
3. Which animals were the least common in your sample?
4. What is the PTI of your stream according to your results?
Explain.
5. Infer: which of the organisms are the most tolerant to
pollution?
6. Which organisms must be present to indicate a healthy stream?
PTI = Sum of index values divided by total number of different animals
in sample
= ___________
PTI KEY:
4 = excellent quality 3 = good quality
2 = fair quality
1 = poor quality