Macroinvertebrate Field Survey
Purpose: This field
exercise will introduce students to a method for using macroinvertebrates as
indicators of stream quality.
Summary: The students will sort
macroinvertebrate samples to determine relative quantities of various organisms
and make an assessment of the general stream water quality.
Background: Benthic macroinvertebrates can be used
as indicator species to reveal information about the general water quality of
a stream or river. See "Macroinvertebrate
Clues" for more information.
Macroinvertebrates
vary in their tolerance to pollution levels. Usually the pollution is from excess nutrients or sediments
that cause low oxygen levels. Generally,
mayflies, stoneflies, and caddisflies have the lowest tolerance to pollution,
while midges, leeches, worms, and blackflies have the highest.
In the middle, "somewhat tolerant" range are crustaceans, beetles,
and craneflies.
In most streams
and rivers, the larval insects will tend to dominate the macroinvertebrate community.
These organisms cannot move far from their immediate habitat, and thus
must adjust to changes in water quality, including the food that's available
to them, the kind of stream bottom, predators, the temperature, and the speed
of the water. For this reason, these organisms are good
indicators of what has happened in the stream during their life cycle.
In most cases, the normal life cycle of one generation is four to six
months. In the Truckee River, regular macroinvertebrate surveys are
used to determine conditions in the river.
Materials:
- Bottom samples from several
locations along a stream or river.
Try to obtain samples both above and below sources of pollutants,
such as the influx of water from Steamboat Creek to the Truckee River.
- White ice cube trays
- Labeling tape and waterproof
markers for labeling trays
- Large shallow white trays or
pans
- Small shallow white plastic or
Styrofoam containers
- Tarp or other plastic sheet
- Tweezers, spatulas, white
plastic spoons, small paintbrushes, clear plastic pipets, etc. for sorting
bugs
- Hand lenses
- Disposable gloves
- Rinsing bucket
- Data sheet
- Macroinvertebrate keys
- Clipboard
- Pencils, colored and regular
- Graph paper
Procedure: Students should formulate a hypothesis
about which sampling site will have the best water quality, and which the
worst. Have them write out their
hypothesis and reasoning prior to making the field trip or doing the survey.
- Gather
stream bottom samples from several locations along a local stream or river
where differences in sample composition due to water quality changes might
be expected. For example, collect
samples (or request samples) from the Truckee River upstream of the confluence
with Steamboat Creek, directly downstream of the confluence in Lockwood, and
then at a location between Lockwood and Pyramid Lake such as Wadsworth.
For a sampling protocol, see p. 129, Streamkeeper's Field Guide, or
the EPAs Streamside Biosurvey instructions on the web, www.epa.gov/OWOW/monitoring/volunteer/stream/vms42.html. If it is unsafe to allow students
to access the waterbody, ask agency staff to collect samples when they do
their usual surveys. The samples will need to be preserved.
- Have
students label the sections of the ice cube trays with the following major
groups:
Mayflies
Stoneflies
Caddisflies
Dobsonflies/alderflies/fishflies
Dragonflies/damselflies
True
flies
Beetles
Crustaceans
Snails/clams
Worms/leeches
Other
- Spread
out the entire contents of the sample container into a large, shallow
white tray to make a thin layer of bugs. Add just enough water to cover the sample. If your sample is too large to
spread into a thin layer, transfer part into a second tray.
- Fill
the labeled ice cube trays with water. Line them up end to end so the labeled edges face
you. Carefully sort out the
debris, looking at each piece for benthic macroinvertebrates. Some of the macroinvertebrates may
blend extremely well into their habitat materials. Use spatula, tweezers, spoons, and
paintbrushes to sort the bugs into different sections of ice cube trays. Use the white plastic containers
to hold the bugs while you use a hand lens to examine and identify
them. Use the laminated
identification cards to help you.
Look at the shape of the body and head, and the location,
structure, and length of the gills, tails, eyes, mouthparts, antennae and
prolegs.
- Record
the numbers of macroinvertebrates on the macroinvertebrate survey
worksheet. Calculate water
quality index value. Is it
excellent, good, fair, or poor?
- Collect
equipment and clean up the site.
|
If you find: |
Look for: |
|
Little variety of insects, with lots of each kind |
Water overly enriched with organic matter |
|
Only one or two kinds of insects in great abundance |
Severe organic pollution |
|
A variety of insects, but only a few of each kind, or NO
insects, but the stream appears clean |
Toxic pollution |
Macroinvertebrate Survey Worksheet
Stream_______________________________________________ Date__________________
Collection
Site__________________________________________ State__________________
Macroinvertebrate
Count
Sensitive:
o ____ caddisfly larvae
o ____ mayfly larvae
o ____ stonefly larvae
o ____ dobsonfly larvae
(hellgrammite)
o ____ gilled snails
o ____ riffle beetle adult
o ____ water penny larvae
Boxes checked X 3 = ________ index value
Somewhat Sensitive:
o ____ beetle larvae
o ____ clams
o ____ crane fly larvae
o ____ crayfish
o ____ damselfly larvae
o ____ dragonfly larvae
o ____ scuds
o ____ sowbugs
o ____ fishflylarvae
o ____ alderfly larvae
o ____ watersnipe larvae
Boxes checked X 2 = ________ index value
Tolerant:
o ____ aquatic worms
o ____ black fly larvae
o ____ leeches
o ____ midge larvae
o ____ lunged snails
Boxes checked X 1 = ________ index value
o Good (17-22) o Poor (<11)
Practice Data Sheet
Benthic
Macroinvertebrates in Sample
Sensitive:
o ____ caddisfly larvae
x_ 1_ mayfly larvae
x_ 1_ stonefly larvae
o ____ dobsonfly larvae
(hellgrammite)
o ____ gilled snails
x__2_ riffle beetle adult
x __1_ water penny larvae
Boxes checked X 3 = _4 x 3 = 12_______ index value
Somewhat Sensitive:
o ____ beetle larvae
o ____ clams
o ____ crane fly larvae
o ____ crayfish
o ____ damselfly larvae
x __3_ dragonfly larvae
o ____ scuds
x__2_ sowbugs
o ____ fishflylarvae
o ____ alderfly larvae
o ____ watersnipe larvae
Boxes checked X 2 = 2 x 2 = 4_______ index value
Tolerant:
x __2_ aquatic worms
x__4_ black fly larvae
o ____ leeches
o ____ midge larvae
o ____ lunged snails
Boxes checked X 1 = _ 2 x 1 = 2_______ index value
x Good (17-22) o Poor (<11)
Alternate Method to Assess Water Quality
|
Group 1: Most Intolerant |
Group 2: Moderately Intolerant |
Group 3: Fairly Tolerant |
Group 4: Most Tolerant |
|
o Stonefly larva |
o Caddisfly larva |
o Black fly larva |
o Aquatic worm |
|
o Alderfly larva |
o Mayfly larva |
o Midge larva |
o Leech |
|
o Dobsonfly larva |
o Riffle beetle larva |
o Sowbug |
o Left-hand/pouch snail |
|
o Snipefly larva |
o Water penny adult |
o Right-hand/other snail |
o Bloodworm midge larva |
|
|
o Dragonfly nymph |
o Scud |
|
|
|
o Damselfly nymph |
|
|
|
|
o Cranefly larva |
|
|
|
|
o Crayfish |
|
|
|
|
o Clam/mussel |
|
|
Totals and Weighting
Sample Summary |
|||
|
# of
types in Group 1 = |
# of
types in Group 2 = |
# of
types in Group 3 = |
# of
types in Group 4 = |
|
# of
types x 1 = |
# of
types x 2 = |
# of
types x 3 = |
# of
types x 4 = |
Sum of weighted scores = ____+____+____+____=____
Total number of different types = ____
Weighted average = sum of
weighted scores divided by # of types = ____
|
Weighted Average |
Water Quality |
|
1.0 - 2.0 |
Excellent |
|
2.1 - 2.5 |
Good |
|
2.6 - 3.5 |
Fair |
|
Over 3.6 |
Poor |
Alternate
Method (Sample Calculations)
|
Group 1: Most Intolerant |
Group 2: Moderately Intolerant |
Group 3: Fairly Tolerant |
Group 4: Most Tolerant |
| x Stonefly larva |
o Caddisfly larva |
x Black fly larva |
x Aquatic worm |
|
o Alderfly larva |
x Mayfly larva |
o Midge larva |
o Leech |
|
o Dobsonfly larva |
x Riffle beetle larva |
x Sowbug |
o Left-hand/pouch snail |
|
o Snipefly larva |
x Water penny adult |
o Right-hand/other snail |
o Bloodworm midge larva |
|
|
x Dragonfly nymph |
o Scud |
|
|
|
o Damselfly nymph |
|
|
|
|
o Cranefly larva |
|
|
|
|
o Crayfish |
|
|
|
|
o Clam/mussel |
|
|
Totals and Weighting
Sample Summary |
|||
|
# of
types in Group 1 = 1 |
# of
types in Group 2 = 4 |
# of
types in Group 3 = 2 |
# of
types in Group 4 = 1 |
|
# of
types x 1 = 1 |
# of
types x 2 = 8 |
# of
types x 3 = 6 |
# of
types x 4 = 4 |
Sum of weighted scores = 1 + 8 + 6 + 4 = 19
Total number of different types = 9
Weighted average = sum of
weighted scores divided by # of types = 19/8 = 2.375
Good water quality
|
Weighted Average |
Water Quality |
|
1.0 - 2.0 |
Excellent |
|
2.1 -2.5 |
Good |
|
2.6 -3.5 |
Fair |
|
Over 3.6 |
Poor |
Analyze the Macroinvertebrate Results in the Classroom
- Use the alternate
method to assess water quality.
Are the results different from that found using the survey
worksheet? Why might they be
different?
- Draw a graph showing
the relative numbers of sensitive, somewhat sensitive, and tolerant
macroinvertebrates. Include
data from all sampling sites on the same graph. You will need to share your data with other groups.
- Which sampling
location has the best water quality rating? _____________________________
- Which sampling
location has the poorest water quality rating? ___________________________
- Why do you think the
results varied from site to site?
- Was your hypothesis
correct?
- What other
information would you need to collect to confirm your results?
- What can be done to
improve or protect the water quality in the Truckee River and its
tributaries?
Resources
Aquatic
Macroinvertebrate Identification Key, web-based interactive key,
http://www.people.virginia.edu/~sos-iwla/Stream-Study/Key/Key1.HTML
A Community Water Quality
Monitoring Manual for Waterwatch Victoria, web resource, www.vic.waterwatch.org.au/fortheteacher/manual/index.htm
(see section on macroinvertebrates under "Biological Surveys"
Field Guide to Aquatic
Macroinvertebrates, 2003, Izaak Walton League, www.iwla.org
Lippy, K., Friesem, J.,
Vanderburg, S., Usher, L., and Lynn, B, 1995, Discover Wetlands, A Curriculum
Guide. Washington State Department
of Ecology, Publication #88-16-a, http://www.ecy.wa.gov/pubs/8816a.pdf
Monitor's Guide to Aquatic
Macroinvertebrates, 1992, Loren Larkin Kellog, The Izaak Walton League of
America, www.iwla.org