Invertebrate sampling
Why sample macroinvertebrates?
Macroinvertebrates are useful indicators of the health or condition of wetlands and other water bodies. They respond to many kinds of pollution, including chemical pollution and physical disturbance to the landscape around the site, wetland structure, and hydrology. There are several advantages of using macroinvertebrates:
- Invertebrates are commonly and widely found in many types of wetlands.
- Invertebrates respond with a range of sensitivities to many kinds of pollution, for this reason they are commonly used in toxicity testing to develop water quality standards.
- Many aquatic invertebrates complete their life cycles in wetlands, so they are exposed directly to the physical, chemical and biological conditions within the wetland. Invertebrates with longer life cycles such as dragonflies, may signal that conditions remained healthy for the duration of their development.
- Aquatic invertebrates are important in wetland food webs for wildlife.
(Taken from "A Citizen's Guide to Biological Assessment of Wetlands, the Macroinvertebrate Index of Biological Integrity" Dr. Judy Helgen, MPCA 2002)
How do we sample?
Volunteers work as a team to collect one complete dipnet sample and one complete bottletrap sample from each wetland site. The dipnet sample is collected by sweeping a large net through the water in or near vegetation. This sampling technique provides the widest number of species. A bottletrap sample is collected by submerging specially designed 2 liter bottles, mounted on a dowel, about 6 inches below the surface of the water. Bottletrapping allows us to catch the actively swimming predators.
For more specific sampling information refer to:
Macroinvertebrate sampling protocols:
Taken from: "A Citizen's Guide to Biological Assessment of Wetlands, The Macroinvertebrate Index of Biological Integrity", Dr. Judy Helgen, MPCA 2000.
When to sample:
Macroinvertebrates should be sampled during the month of June, or at the latest, early July. Monitoring occurs during this time of year for two primary reasons.
1. To ensure that the macroinvertebrates are a size that is easy to identify.
2. To ensure that the majority of the macroinvertebrates collected matured in the site
sampled. If it is later in the season, there is a greater chance that the macroinvertebrates
may have flown in from another nearby wetland.
Where to sample:
Samples should be collected in the shallow, near-shore area not deeper than 3 feet (1 meter). The same general area should be used for the bottletrap placement and the dipnet sampling. If there is a cattail fringe (or other emergent vegetation), sample in the area between the cattails and the shore. If there is no water between the emergent vegetation and the shore, then sample within the cattails and to the outer edge of the cattails towards the open water. If there is no emergent vegetation, sample very near shore in water up to 3 feet deep.
Refer to diagrams. DN=Dipnet sampling location BT=Bottletrap placement
Setting bottletraps:
1. Use 6 bottletraps per site. Set the traps out in 3 pairs, the members of each pair about 3-6 ft. apart.
Spread the 3 pairs along the shore, with pairs roughly 20ft. apart. You will combine the data
from all 6 traps for metrics.
2. Put at least 2 of the traps in very shallow water near shore, the others in shallow water not deeper
than about 2-3 ft.
3. Set the traps 2 nights before collecting them. Be aware of rain events prior to bottle placement and
after. Wetland water levels can fluctuate quickly.
4. Fill traps with water with no air bubbles (tip trap under water so bubbles escape).
5. Press funnel into trap opening so it snaps in tightly. Again, remove air bubbles.
6. Lower bottle on dowel, orient bottle horizontally in water.
7. Put bottletraps about one hand length under the water.
Collecting bottletraps:
1. Collect each pair of bottletraps each into one jar (3 jars total for 3 pairs of BTs), unless the sample
occupies more than 1/4 volume of the jar. If so, use a second jar.
2. Raise trap up the dowel, remove the funnel, pour the trap contents through your sieve.
3. Dislodge any critters stuck to the inside walls of the bottle. What's on the outside of the bottle
is not part of the sample.
4. Collect the second trap of the pair and pour contents into sieve.
5. Backflush the contents of the sieve into your sample jar with 95% alcohol.
NOTE:
a. If you have a lot of leeches or other organisms in your traps, you may need to use more jars
to preserve the sample.
b. If you have fish, tadpoles or salamanders you should note these on your field data sheet and
leave them at the site. Note approximate numbers.
6. Label properly. Put pencil or India ink label inside the jars. Label outside for convenience. See further labeling information below.
Collecting a dipnet (DN) sample:
You collect one dipnet sample per site. Each DN sample consists of two dipnetting efforts. Dipnet in the near-shore shallow areas in water up to one meter deep. "Sample close to edge and in the veg." Use a 12 x 16" wood framed 1/2" hardware cloth screen over a tray (or 2 Coleman cooler trays) of water. The tray(s) of water should sit within a larger kitty litter pan or dishpan. This can float on the wetland.
FIRST DIPNETTING EFFORT
1. Put water in your collecting pans that sit underneath your hardware cloth screen.
2. Place the framed hardware cloth screen over the water so its edges don't hang over the edge of
the pans. This way the critters go down into the water in the pans.
3. Hold the long-handled dip net vertically, one hand near net, one hand up handle.
4. Using strong strokes, sweep the net through the water towards you about 3-5 times.
5. Be sure to sample right into the vegetation near shore.
6. Invert all the net contents onto the hardware cloth screen. Get everything out of the net.
7. Spread the vegetation, loosen it. Do this periodically for up to 10 minutes. This allows the
critters to get down into the water in the pans.
8. After 10 minutes, remove the vegetation and do the second dipnetting effort.
SECOND DIPNETTING EFFORT
1. Move to a different shallow area.
2. Repeat the steps described in 1-7 above.
3. After spreading out the vegetation for 10 minutes, remove it, and pour the water from the
collecting pans through your sieve. Be sure to dislodge the leeches and snails which might
attach to the pan.
4. Backflush the sieve contents into your sample jar with 95% alcohol. Be sure to get any critters
which attach to the sieve walls. Use two jars if critters and debris occupy more than 1/4 of the
jar volume.
Sample labeling:
1. Record sample code on field data sheet, especially if different from site name.
2. Use pencil or truly permanent India ink on 100% cotton cardstock or index card.
3. Indicate Site Name, Sample Code, Date, County, Collector's name, if DN or BT sample. Indicate
if there is more than one jar--jar #1 of 2, jar #2 of 2.
4. Place label INSIDE jar. This is the only label you trust.
5. For convenience, label also on the outside of the jar.
6. Remember alcohol is flammable. Keep lids tight. Store away from flame or heat.
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