Picking: Separating organisms from detritus and gravel/sand (as adapted
from River Watch Network).
Materials needed:
5 gallon bucket
2 500-micron sieves
Squirt bottle
Tweezers
Clear casserole dish
"Decanting" the Sample:
Pour stream water through a 500 micron sieve into a 5-gallon bucket
until the bucket is 2/3 full.
Empty the sample into the bucket. Swirl the contents of the bucket.
Because the benthic macroinvertebrates are lighter than sand, they will
float. Pour off the critters with any other lighter material into a 500
micron sieve. Note: use a clean sieve that was NOT used to filter stream
water.
Repeat steps 2 & 3 until all that is left in the bucket is gravel and
sand. This may take 20 repetitions of this procedure until the sample is
cleaned.
Empty the sieve with the cleaned material into a clear casserole dish
filled with 1" of filtered steam water. Use a squirt bottle to remove any
organisms attached to the sieve.
Using tweezers, pick off any organisms clinging to leaves or sticks.
Put these organisms with the rest of the sample.
Check the material left in the bucket for any organisms left in the
sand/gravel mixture.
