Q.
What are the conditions in a stream that
make it produce an abundance of insects?
Isn’t a little pollution good in some streams?
A.
The short answer to your first question can
be summed up by saying a stream with an adequate
food base, the proper substratum conditions, and
a suitable environmental regime will usually
produce many insects. The long answer would
take more space than we have, but I’ll try to
add a bit about each of these. Obviously, if
the insects are to survive and reproduce they
must have an adequate food base; some utilize
algae growing on stones or sticks, others feed
on the fine detrital matter in the water column
or where it settles onto the stream bottom,
others shred coarse organic material such as
leaves, and others feed on other insects. Now
to have a proper algae food base, the right
environmental conditions in terms of sunlight
for photosynthesis, adequate dissolved nutrients
(mainly nitrogen and phosphorus), and a solid
substratum for attachment must be present. Thus,
the proper environmental regime includes such
things as the proper nutrient content, temperature
conditions that do not reach lethal levels,
and varying amounts of dissolved oxygen. In
terms of temperature conditions, each insect
requires a certain amount of thermal history
to develop; thus, the colder the stream, the
slower the development will be.
Your second question about a little pollution
being good is a bit tricky. In certain conditions,
and depending on the “pollution,” the answer is
“yes.” For instance, in an arctic stream where
the water temperature rarely gets much above
freezing, a little thermal “pollution” could
enhance development. A stream draining a basin
where the rocks were highly insoluble and thus
having low amounts of dissolved nutrients (N
and P) could benefit from some pollutant
containing these nutrients. Now having said
this, I don’t want to intimate that I condone
pollution; I’m just saying that in some
restricted examples, your term “a little
pollution” might be good.
If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584
Email: streamdoctor@aol.com
The ‘Stream Doctor’ is a retired professional stream ecologist and
author, now living in the West and spending way too much time
fly-fishing. You are invited to submit questions relating to
anything stream related directly to him for use in this Q & A Feature
at streamdoctor@aol.com.
Originally published November 22nd, 2004 on Fly Anglers Online by Robert Younghanz.