Text on this page was adapted from Stream Biology, a web site developed by:
Cristi Cave, B.S., Fisheries, 1998, School of Fisheries, University of Washington.
Filamentous algae in ATV damaged
section of Amity Creek
Primary Producers (algae)
in Lake Superior Streams
If you look into a cold, clear, fast-flowing stream, you'll notice that you can't see any plants. Does
this mean that nothing lives there?
Local streams usually flow much too fast to allow large plants to live in them. And most algae is washed away quickly.
However, you may see long, very thin strands of green waving downstream from their attachment to a rock or submerged branches.
If it feels sort of "ropy" and not slimy, then these long strands are probably an alga called, Cladophora,
that likes turbulence. But most of the plants in the stream won't be visible to you; that is, unless you know what to look for.
Cladophora also grows naturally on the rocky shoreline of Lake Superior and where there are excess nutrients
(eutrophication) can grow to produce massive amounts of organic material and become
a huge problem such as at Lake Michigan the past few years.
Something's Amuck provides more
detailed information.
There has been some concern about increasing algal growth in North Shore streams.
Check out this 2003 report
for a qualitative assessment on increasing periphyton in some local streams.
Anyone who has ever tried to walk across a stream knows that
the rocks under the water are slippery. If you were to scrape
a bit of that slime off and put it on a glass slide, and look
at it under a microscope, you would see a community of diatoms,
blue-green, and green algae, single-celled animals, bacteria,
fungi and lots of organic matter. This is what makes the rocks
slippery. It so happens that these plants are the favorite
food of many of the stream's herbivores!
Aquatic Plants: Algae
The MPCA (streams
and lakes)
and MN DNR
and WI DNR
all have information about algae including the potentially toxic species in lakes that have been in the media lately;
what's natural and what isn't; and how they can be managed if necessary and allowable.
Go here to overload on algae.
Diatoms of many different types cover all the
wet surfaces of the stream: the rocks, the leaves and sticks
and logs that have fallen in, and various kinds of debris.
In fact, the streambed is coated with plants!
In most small streams, however, often the
greatest contributor of plant food of all is the riparian
zone: the margins along the stream that are filled
with vegetation. These plants, like all plants, drop their
leaves--which fall into or are washed into the stream. This is allochthonous
matter (from outside the stream), as opposed to autochthonous
matter (from inside the stream, like algae and diatoms).
These leaves can't make oxygen, since they are dead, but they
provide food to the creatures in the stream. Not only
the leaves themselves can be eaten, but also whatever bacteria or fungus is
covering the leaves, rotting them. It is this bacteria
and fungus that is what crayfish are really after when they eat decaying
plant matter.
For more detailed information about algae and aquatic plants, how to identify them, and how to measure their
abundance, visit Water On the Web (WOW) -- lake modules
[2+3]
and [8+9],
stream modules [4+5],
and the Lake Access section on aquatic plants.
