Alternative Field Sampling Techniques
Equipment Needs
- Baby food jars with lids
- Turkey baster
- Long-handled net
- Drift nets (purchase or make)
- Eyedroppers
- Pans
1) Substrate/Rock Rubbing:
This collection is to be done along the side of the stream where the current slows and offers a different habitat for macroinvertebrates. Collectors should work in groups of two. Have baby food jars filled with water or alcohol. One person can turn over the algae covered rocks and debris and the other should gently scrape the macroinvertebrates into the baby food jar. Have water in the jar for field identification. For lab identification, preserve the specimens in ethanol.
2) Vegetation:
There are a wide variety of organisms found in the vegetation along stream and
pool edges. Use a D-net to sweep back and forth
through the base of the plants below water level. If you use this method consistently
at your site, choose a standard number of sweeps to use each time. Record the
number on the data sheet.
3) Woody Debris and Root Balls:
Look for roots exposed along banks and submerged branches or logs. Place your D-net downstream of this material and agitate or shake the roots and branches, keeping the net close to the debris. Empty the net in the collection pan and proceed with identification.
B. Rolling Rocks
This is a simple technique and can be used to practice macroinvertebrate identification without seriously altering the habitat. Wade into the stream and select any rocks for investigation. Turn the rocks over and look quickly for organisms. You may be able to identify some upon first glance. Then, shake or rinse the rocks in the collection pan to dislodge any organisms for further study. You may want to mark seven to ten rocks as reference rocks for seasonal studies.
C. Drift Nets
For this, you need nets that you can leave anchored (with the mouth of the net pointing upstream) for several hours or overnight. They are checked later and the organisms are collected and identified.
D. Muddy Bottom/Stagnant Pool Sampling
If no riffles are present, an alternative collection method is needed. With little or no flow to bring the "bugs" into the net, you should sweep the net through a standard sample area of 50 square feet. Walk along the designated area with your D-net, scraping the surface of tree roots, scooping up leaf debris and bottom materials. Dip the mud-laden net up and down in the water to rinse out the mud and leave the organisms behind. Dump the net contents into your pan and proceed with sorting and identification as described for riffle sampling.
E. Artificial Substrate
You may have a site that is inappropriate habitat for benthic macroinvertebrates, such as a deep river or lake. In this case you may alter the habitat with the addition of an artificial residence. One easy way to arrange for artificial habitat is to make a wire net bag and load it with several six to ten inch rocks. Tie this device off and submerge it at your site for five to seven weeks. At the end of this time, remove the bag of rocks and observe and identify the macroinvertebrate populations.
Another artificial substrate is the Hester-Dendy, a series of plexiglass plates that also serve as macroinvertebrate habitat. (The LCRA has these available with detailed instructions for use.) This apparatus will illustrate what sort of macroinvertebrate populations would be possible if adequate habitat was present.
F. Kick Seine-Net Operation
This net is an alternative to the D-net and can also be used to sample a riffle area. See Appendix G for construction techniques. It is easier to build than a D-net but is a little more difficult to manipulate when dumping contents into the sorting pan.
1. Avoid wading through the area to be sampled.
2. Three people will be needed: two to hold the net (one on each side) firmly against the bottom of the creek and the third person to be the kicker.
3. Use a large flat bottom net (Appendix G) with a mesh size no larger than .60 mm.
4. The kicker will stand one meter in front of the net with his/her back toward the current, so that the current hits the back of their legs. The kicker should kick up the substrate for three minutes, as continually as possible. This should be done while moving slowly toward the net.
5. During the three-minute kick, approximately one square meter of substrate should be disturbed. Hand rub or scrub the cobble and larger rocks in the area to loosen benthics that may still be attached to the rocks.
6. Slowly pick the net up from the bottom, tip it downstream (back away from the kicker) and take the net to the shoreline. Dump and rinse the contents into the pan for picking sorting and identification.
