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 August 9th, 2004 on Fly Anglers Online by Robert Younghanz.