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Macroinvertebrates
Background Information
In most streams, the energy available to organisms is stored in plants and
made available to animal life either in the form of leaves and algae that
are eaten by macroinvertebrates. In turn, the macroinvertebrates are a source of energy
(food) for larger animals such as fish, which are a source of energy (food)
for birds, raccoons, and humans.
Besides being an important link in the food chain, macroinvertebrates can also
serve as an indicator of water quality. Some stream-bottom macroinvertebrates cannot survive in polluted
water while others can survive or even thrive in polluted water. A
healthy ecosystem supports diversity of organisms, so in a healthy stream, the stream-bottom community will include a
variety of pollution-sensitive macroinvertebrates. Conversely, an unhealthy
stream will support only a few types of nonsensitve macroinvertebrates.
In this project, macroinvertebrate sampling is coupled with chemical water
quality sampling. The reason for this is quite simple. The process
of identifying stream pollution with water analysis alone is time intensive
and can only provide information for the time of sampling. Even the presence of fish may not provide information about a pollution problem because fish
can move away to avoid polluted water and then return when conditions improve.
However, most stream-bottom macroinvertebrates cannot move to avoid pollution. A macroinvertebrate
sample may provide more information about pollution or overall water
quality that is not present at the time of sample collection.
Useful stream-bottom macroinvertebrate data are easy to collect without expensive
equipment.
Test Procedure
The two most common methods to sample macroinvertebrates include the kick net
or the dip net methods. The kick net is most efficient for sampling streams with rocky or gravel stream
beds where the velocity of the water will move the dislodged organisms into
the net. The dip net method can be used in a variety of habitats and
used like the kick net or used for scooping through the water.
The first step is to select a sampling site to ensure that the appropriate
equipment is obtained. Find a riffle that is typical of the stream. A good riffle for sampling will have
cobble-sized stones, fast-moving water, and a depth of 3 to 12 inches. Select a 3-foot
by 3-foot area within the riffle for sampling.
Position the kick net at the downstream end of the sampling area and proceed
slowly walking upstream. The net should be stretched out to its full 3-foot width with the
bottom edge lying firmly against the stream bed. No water should wash under or over the net.
If needed, small
rocks can be used to weigh down the bottom edge of the net. A
"kick" is a stationary sampling accomplished by using the toe or
heel of a boot and dislodging the upper layer of the stream bed one meter at a
time. If larger substrate is encountered, such as a large piece of wood,
the object should be picked up and rubber by hand or small brush to dislodge
the attached organisms.
NOTE: To avoid losing macroinvertebrates that should be part of the sample, do not stand in
or disturb the sampling area before the kick seine is in place.
Lift the kick seine out of the water with a forward scooping motion. The object is to avoid
losing any macroinvertebrate specimens
while the seine is lifted. This will be easier if one person holds the top of the kick seine handles while the other person holds the bottom of the
handles.
Carry the kick seine to the stream bank and spread it out flat on a piece of
white plastic. Carefully examine the net and
the collected debris for macroinvertebrates. Look carefully as many
specimens will be small and hard to see. Using tweezers or fingers, place all the specimens in white containers filled
with stream water. Sort them into different types as you remove them from the net, and place
each type in a separate container. Ice cube trays are very
effective for this process.
NOTE: If your plan is to transport the sample back to your "lab" before sorting and
identification, you can place the contents of the kick seine (including the debris) into a bucket
that is partly filled with stream water. If you put a lid on the bucket (recommended), you should
leave some air space above the water in the bucket to allow mixing of oxygen.
Once the macroinvertebrates are collected and sorted, they can be identified
by using the Save
Our Streams Macroinvertebrate Identification Key.
Record and submit the results to the project data base.
What to Expect
The Guidelines established by the Save Our Streams Program will be followed
for this project. Save Our Streams identifies three groups of
macroinvertebrates based on their sensitivity to pollution: pollution
sensitive, somewhat pollution tolerant and pollution tolerant. The Save
Our Streams method involves collecting a sample of macroinvertebrates from the
stream, identifying the organisms and rating the water quality. Water
quality ratings of excellent, good, fair, and poor are based on the pollution
tolerance levels of the organisms found and the diversity of organisms in the
sample. A stream with excellent water quality should support organisms
from all three pollution tolerance groups.
Indicators of good water quality
Mayfly larvae
Caddisfly larvae
Stonefly larvae
Gilled snails
Riffle Beetle - adult
Planaria
Water Peeny
Hellgramite
Indicators of fair water quality
Crayfish
Riffle Beetle - larva
Dragonfly
Cranefly larvae
Damselfly
Scuds
Alderfly
Sowbug
Watersnipe Fly
Whirligig Beetle - larva
Fishfly
Clam or Mussel
Indicators of poor water quality
Midge fly larvae
Blackfly larvae
Leeches
Aquatic worms
Lung snails
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