Lake Michigan environmental survey : final report / [edited] by John C. Ayers.

The samples were then dried or frozen, depending upon the intended method of
analysis.
Benthos samples were obtained in one of two ways, depending upon the
species of organisms present, water depth, and type of bottom. The preferred
method was to tow a sled net along the bottom. The sled carried a # 000 net
which trapped the benthic organisms but allowed the fine stirred-up sediment
to pass through. Exclusion of sediment was important to avoid contamination
of the sample. Metal-free samples were insured by covering all parts of the
sled around the mouth of the net with plastic tape and plastic spray coating.
A towing harness of synthetic line was used between the sled and the steel
towing cable. The organisms collected in the glass jar at the end of the net
were then concentrated by straining the excess water off through a piece of
nylon stocking stretched over a large plastic funnel. The organisms were
then rinsed lightly with distilled water and transferred by plastic spoons to
plastic bags for freezing.
The second method involved collecting sediments with the ponar dredge
and separating the benthos from the sediment on board ship. Each dredge sample
was placed in a plastic bucket or fiber-glass tub and thoroughly agitated with
lake water provided by the metal-free pump. The dense sediment would settle
out while the less dense benthos remained in suspension. The water was then
poured through the nylon stocking-plastic funnel strainer. The benthos collected on the stocking was placed in a plastic bag with a plastic spoon, rinsed
lightly with distilled water, and frozen.
The metal net hoops on both the phytoplankton and zooplankton nets were
covered with plastic tape. When it was necessary to use a steel towing cable,
about 20 feet of synthetic line was used as a buffer between the net and the
cable. Whenever possible the nets were towed with synthetic line.
Phytoplankton samples were collected with a # 20 plankton net. After
being towed, the phytoplankton net was suspended from the towing boom and the
sample concentrated in the bottom of the net by rinsing the sides of the net
with lake water provided by the metal-free pump. The concentrated phytoplankton sample was strained through a # 5 net into a # 20 net placed inside a large
plastic garbage pail. The garbage pail supported the # 20 net and prevented
metal contamination of the sample. By trapping the zooplankton in the # 5 net,
this method prevented contamination of the phytoplankton sample by zooplankton
caught in the phytoplankton tow. The net where the phytoplankton sample had

B-2