Sampling Process: Collecting Sample
From STREAM BUGS AS BIOMONITORS
Guide to Pacific Northwest Macroinvertebrate Monitoring and Identification
Jeff Adams
with Mace Vaughan and Scott Hoffman Black - The Xerces Society (www.xerces.org)
Step-by-step macroinvertebrate collection - Oregon DEQ Protocols, 2003
NOTE: Keep all activity downstream of where macros will be collected; and be careful
to not lose organisms at any step along the way!
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Your sample site location should have been chosen based on your study questions
and design (random, upstream/downstream, etc.). Unless it deals directly with
your study question, you should avoid sites directly above or below bridges,
culverts, or other features that could influence your samples. Now that you're at
the stream, take a look to make sure no adult salmon are present, and that you
don't see freshly turned gravels that may indicate a spawning redd.
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Take 4 wetted width (wet margin to wet margin) measurements at the first riffle
downstream of your sample site location. Add the 4 widths together, then multiply
by 10; that will give you a stream reach length that is approximately 40x the
width (150m or 500 feet minimum and 300m or 1000' maximum).
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Walk along the banks for a bit, if you haven't already, and get a feel for whether
or not there are at least 8 riffles within the reach. Riffles are sections of streams
where the water is shallower and rougher and the substrate is larger. If there are
plenty of riffles available, you will take one sample from each of 8 riffles; if there
aren't a lot of riffles in the reach, you will take 2 samples from each of four riffles.
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Think of a 9 section grid system to select the sample location in each riffle. leave out the edge habitat (outer 10%) then think of the riffle as 3 rows and 3
columns and number them 1 to 9 from left to right and downstream to upstream
(see diagram below, click for enlargement); when sampling 8 riffles, sample in
the middle of section 1 in the first riffle, section 2 in riffle 2, and so on; when
sampling 4 riffles, sample sections 1 and 5 in the first riffle; sections 2 and 6 in
the second, 3 and 7 in the third, and 4 and 8 in the fourth. If fewer than 4 riffles
are available, split your samples as evenly as possible between the available
riffles and avoid sampling sections that are adjacent to each other. You don't need
to measure all this out exactly, but it's a good way to reduce our personal biases
from the selection of sample locations.
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Now it's time to collect the sample. First, make sure your sample jar is properly
labeled inside and out. In the middle of section 1 of the first riffle, place the Dframe kicknet or Surber sampler on the riffle bottom such that the current is
flowing directly into the net (this may be slightly different than the direction of
the stream as a whole). Remember, the goal of getting all bugs from a 1 square
foot area and 4 inches depth, off the substrate and into the net.
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squat behind or to the side of the net (not upstream)
use your fingers to make sure the bottom of the net is flush against
the stream bottom; shift any rocks or cobbles that are keeping it
from settling
measure 1 foot upstream of the net (hint: the net is 1 foot wide)
pick up all large rocks and debris within that area and scrub
thoroughly in the net (a typical kitchen scrub brush is often
helpful); be sure to look the rocks over for any clinging macros,
then set them to the side (hint: if you set the rocks to the sides of
the front corners of the net, they can help direct the flow of water
into the net)
once only gravels (smaller than a golf ball) remain, use your trowel
to disturb the substrate to about 4" depth if possible
once thoroughly disturbed, use your boot heel to give the area a
last shuffle
tilt the net back and lift it off the riffle bottom; use the current and
water to wash the material to the bottom of the net
immediately remove any fish or amphibians that were
accidentally captured in the net and record them on your
datasheet
gently invert the net into the sample tub and go to the next riffle
 (hint: after the last sample only, use the current a couple
more times to rinse material to the bottom; then use forceps
to pick off any clinging macroinvertebrates
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Repeat the above process at the next riffle upstream, and so on, until you have
collected 8 samples that represent a total of 8 square feet of stream bottom.
Remove any large debris from the tub (use your forceps and squirt bottle to
carefully pick off all macros); then slowly pour the water out of the tub, through a
sieve, so only the sample remains. Also squirt and pick macros and debris that
was captured on the sieve.
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Material from all 8 sample locations is placed into the same sample jar - if a
sample fills more than half of the sample jar, it will probably need to be split into
more jars that are labeled exactly the same, but have "1 of 4", "2 of 4", etc. on the
inside and outside labels.
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Filter water out of the sample jar one more time, then fill the jar with 95-100%
alcohol.
That's it for the bugs! However, habitat data is important as well.
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Now that the bugs are safely preserved, gather the required habitat data (water
temperature, air temperature, wetted width, and substrate size - use the .pdf of
field data form), as well as any other chemical and physical data of interested. If
you have several volunteers, those measuring substrate and wetted width can do
so while the macroinvertebrate collectors are gathering their samples, as long as
they always stay downstream of those collecting macros.
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temperature - if you can leave a continuous temperature recording device
in the water over the course of the summer, that's wonderful, but if you
can't, tie a bit of flagging around an armored thermometer and let it rest in
an area of moderate flow for a few minutes; then quickly read the
temperature after you remove it
twenty-one width/substrate transects are needed along the length of the
reach - divide your reach into 20 segments; each segment is equal to two
times the average the 4 wetted widths you used to calculate your reach
length, with a minimum of 25' (7.5m) and maximum of 50' (15m); you'll
collect a total of 21 evenly spaced transects (1 at the beginning, 19 in the
middle, and 1 at the end)
at each transect, measure the wetted width - this is the distance from wet
margin to wet margin of the stream (see or click on the image to the right)
o
gather substrate size information using a modified Wolman pebble count for each transect and without looking, put your foot at the left wet margin,
1/4 width, 1/2 width, 3/4 width, and at the right wet margin; pick the
substrate particle up (if you can) that your finger hits at the tip of your
boot and classify it from silt to boulder or bedrock based on its medium
length (not the longest edge and not the shortest edge); record the
information in the field data form; collect at all 5 points on each transect
for a total of 105 sediment size measurements for the entire reach
o
finally, collect any other information you might be interested in; then
double check that all the necessary field data has been recorded, and that
your sample is labeled correctly, and you're done. NICE WORK!
As a final note, you should put fresh alcohol in the samples after a day or two. This will
ensure adequate preservation for storage or shipping.