Introduction: 

            By looking at the life found within a river (biological indicators), scientists can determine the relative quality of that river water.  They use the available information of the number and/or diversity of invertebrate (bug) populations in a given area in the river.  Invertebrates are often at the bottom of the food chain (just above plants) and are good indicators of the relative health of the river.  There are 2 indexes that we will use.  One is called the Biotic Index; the other is called an EPT Index.

            The Biotic Index evaluates the quality of the river by assigning point values to various insects.  Not all insects react to pollution the same way.  Some are very sensitive, others are more resistant.  Scientists have classified these insects into 3 groups:  Group 1 Taxa:  Highly Sensitive to Pollution; Group 2 Taxa: Somewhat Pollution -Sensitive; and Group 3 Taxa:  Pollution-Tolerant.  The insects that are the most sensitive are assigned the greatest number of points whereas the pollution tolerant insects are assigned low point values.  Water quality is evaluated as poor, fair, good or excellent.

            The EPT Index looks at the total variety of insects.  For instance, if only aquatic worms are found at a particular site, the water quality would be considered poor.  However, if there was a wide range of insects: caddis flies, aquatic worms, leeches, cranefly larva, dragonfly larva, snails, stonefly nymphs and Dobson flies then the area would be considered to be of good to excellent quality. Water quality is evaluated as poor, fair, good or excellent.

            Part of your responsibilities on the Farmington River trips will be to collect invertebrates with your group and record how many of each type you find.  Our team will return and then evaluate the data to help determine the quality of the water.  Today you will practice analyzing that data and will then collect insects and determine the health of Chinsey Brook behind the school.

            In your Farmington River packets are 2 Biotic Indexes of the sites we will visit (“Fast” and “Slow” water sites).  Use the table at the bottom of the spreadsheet to determine the water quality.

Questions/Analysis

1. How many insects TOTAL were found at the Slow water site? ______
2. What was the Total Biotic value of the stonefly (slow water)?_______
3. How many insects were collected by the Sample 4 group (slow water)? ____
4. What was the EPT index at the slow water site? _______
5. What does this tell you about the quality of water? _________________

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6. What was the Biotic Index at the Slow water site?___________________
7. What does this tell you about the quality of water at this site?__________

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8.  What kind of invertebrates would need to be found for the water to be considered “Excellent” quality water?_______________________________

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9.  At the fast water site, how many mayflies were found?______________

10.  How many organisms were found by the 1^st sample group? _____________

11.  How many organisms were found at the fast water site TOTAL?________

12.  How many more organisms were found at the fast water site compared to the slow water site? __________________

13.  Before looking at the indexes, what do you think this means about the fast water site’s health?_____________________________________________

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14.      What is the EPT index at the fast water site?____________________

15.      What quality water is it?_____________________________________

16.      What is the Biotic Index at the fast water site?____________________

17.      What quality water is it?_____________________________________

18.      Based upon some of your other research (March, April packets), what are some possible explanations for the differences in water quality at the two sites.

a)_________________________________________________________________________________________________________________________________________________________________________________________________

b)_________________________________________________________________________________________________________________________________________________________________________________________________

c)_______________________________________________________________

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