Investigate Your Watershed

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Investigate Your Watershed

• Using Aquatic Organisms to Assess Stream Water
  Quality
• Karin Readel, UMBC, Baltimore, MD

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Overview of Lesson

• Benthic Macroinvertebrates
• What are they?
• Why use them to assess water quality?
• Collection Techniques
• Identification of Organisms
• Introduction to dichotomous keys
• Determination of water quality
• Worksheet to calculate Pollution Tolerance Index
  Value
• Example

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Benthic MacroinvertebratesWhat are they?

• Benthic
• Refers to those organisms that live in the
  benthos- on top of, attached to or within the
  bottom substrate of a body of water
• Macro
• Large enough to see with the naked eye
• Invertebrates
• No backbone (insects, worms, mollusks, etc)

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How Do We Determine Water Quality?

• Chemical tests
• For Example
• Nitrates
• Phosphates
• Dissolved Oxygen
• Biological tests
• For Example
• Fecal Coliform
• Fish, Algae Surveys
• Benthic Macroinvertebrates

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Why Use These Organisms?
Benthic Macroinvertebrates

• have a varying sensitivity to pollution
• are not very mobile
• persist for relatively long periods of time in
  environment

They can indicate if there is a chronic water
quality problem
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Collection of Organisms

• Equipment Needed
• Kick Net
• Bucket
• Scrub Brush
• Sieve
• Rinsing Bottle
• Sorting Tray

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Location of Site

• Relatively shallow water (3-12 deep)
• Section with riffles- water moving relatively
  fast over rocks

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Collection Methods

• Downstream student holds net
• Upstream student kicks out a 1 m2 area in front
  of net for 60 seconds

Click here to play the video clip
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Net contents washed into bucket
Click here to play the video clip
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3 fist-sized rocks are scrubbed into bucket
Click here to play the video clip
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If needed process can be repeated 1or 2 times
moving upstream
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Buckets are carried back to lab
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Buckets are filtered through sieve or screen to
remove excess water
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Remaining insects, rocks, leaf litter, etc.
dumped onto tray
Click here to View Video Clip
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Students use forceps to pick through sample
organisms placed into vials of alcohol to
preserve for identification lab
Click here to play the video clip
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Identification of OrganismsUse of Dichotomous
Keys

• What are they?
• Tool used to categorize and uniquely identify
  organisms or objects

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Identification of OrganismsUse of Dichotomous
Keys

• How are they used?
• Start with all organisms in one big group
• Divide organisms into 2 subgroups by choosing
  being pairs of alternative characteristics
• For example Does the organism have 6 legs or
  less, OR does the organism have more than 6 legs?

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Dichotomous Keys can be viewed graphically as
trees.
All organisms
No Legs
Legs
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Example Construct a Key of Students in the Room

• Characteristics
• Gender
• Height
• Hair Color
• Age

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All students
Women
Men
Less than 56 Dusty
Taller than 56
Longer Hair
Hair lt 6 Anne
gt22 yrs old Joe
lt19 yrs old Meghan
gt19 yrs old Kim
lt22 yrs old Scott
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Click HERE to Link to Benthic Macroinvertebrate
Dichotomous KeyORContinue on to Learn How to
Use the Pollution Tolerance Index Worksheet
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Determination of Water Quality Using the
Pollution Tolerance Index Worksheet

• Once organisms have been identified they can be
  placed into 4 different groups based on
  sensitivity to pollution
• Intolerant
• Moderately tolerant
• Fairly tolerant
• Tolerant

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Pollution Tolerance Index

• Each group of organisms has its own weighting
  factor between 1.0 and 4.0
• Organisms intolerant to pollution have a
  weighting factor of 1.0
• Organisms tolerant to pollution have a weighting
  factor of 4.0
• You may find one to several taxa, or categories
  of organisms in each group, or you may find none
  at all!

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A Group Score is calculated for each group

• Group Score ( of Taxa Seen) x
• (Weighting Factor)

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Cumulative Index Value

• CIV Total of all group scores
• Total of taxa seen
• 1.0-2.0 Excellent water quality
• 2.1 2.5 Good water quality
• 2.6 3.5 Fair water quality
• Over 3.6 Poor water quality

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Pollution Tolerance Index Value Worksheet

• Click HERE to open the worksheet in MS Word for
  review or printing
• Follow this link to view an example of how to use
  the sheet

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Example

• After collecting organisms from this stream, you
  identified the following
• 2 Dobsonfly larvae
• 10 Mayfly larvae
• 3 Dragonfly nymphs
• 15 Midges
• 8 Aquatic worms
• 1 Leech

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Step 1 Indicate the of Each Organism

• Locate each identified organism (or taxon) on the
  left side of the worksheet and then place an X in
  the appropriate column in the middle, indicating
  how many of each organism you found

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Step 2 Calculate Group Scores

• For each of the 4 groups, write the number of
  taxa collected (not of individual organisms) in
  the column on the right. There are 2 taxa in in
  Group 1 in this example.
• Then multiply the of taxa seen by the weighting
  factor. The result is the Group Score for Group
  1.
• Group Score (2 taxa seen) x 1.0 2.0

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• Calculate Group Scores for all 4 groups.

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Step 3 Calculate the CIV

• The CIV is the sum of the Group Scores, divided
  by the sum of the taxa seen.
• In our example the CIV 15/6 or 2 ½.
• Converted to decimal format this is 2.5

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Step 4 Use CIV to Determine Water Quality

• Finally, compare the CIV to the values at the
  bottom of the worksheet in order to determine
  overall water quality.
• In our example the CIV 2.5.
• Based on the values on the right, this means the
  water quality is GOOD

• 1.0-2.0 Excellent water quality
• 2.1 2.5 Good water quality
• 2.6 3.5 Fair water quality
• Over 3.6 Poor water quality