QUESTIONS COME IN ALL KINDS
great aspect of being a naturalist, which includes anyone who appreciates
nature and thrives on new discoveries, is that intriguing environmental
mysteries abound. No one can answer all questions arising from outdoor
observations. But somewhere out there is an expert who can answer certain
ones. When I received the question below, I turned to Gary Mills, former
colleague at the University of Georgias Savannah River Ecology
Laboratory, and currently research professor at the University of South
Carolina Aiken. Gary is an organic chemist.
I was hiking in the Smokies, and in Abrams Creek, Tenn., a swiftly flowing
stream, were piles of yellowish foam. I assume it is natural but do
not know what causes it. So, what does cause it, and is it a problem?
Great question, and one I am sure many naturalists have wondered about.
Knowing the origin of the foam is especially important in this environmentally
unspoiled stream that flows to the Little Tennessee River from Cades
Cove. Abrams Creek is enjoyed by many for angling, boating and swimming.
It turns out that foam in a stream is a result of natural processes,
when dissolved organic carbon results from decaying vegetation upstream.
So the yellowish color is a good sign. Human-caused foam resulting from
pollution by detergents is usually white. Natural foam is generally
tan or brownish, depending on the type of vegetation contributing to
the dissolved carbon.
Mills points out, These foams can form in all aquatic environments.
He explains that their origin is from what is called the surface
microlayer (SML), a film at the water-air interface. The SML,
or biofilm, may be no thicker than the surface of a soap bubble but
can be full of life, supporting a rich community of microorganisms,
including bacteria. Many people have a negative view of bacteria
because of the few that are harmful to us, but most have positive environmental
roles and are essential to healthy ecosystems. The activities of bacteria
are constant and essential in all natural habitats.
microenvironment is rich in organic substances derived from decaying
leaves, wood and algae in the water itself, as well as material that
leaches out from humus in the soil of the adjacent forest. In the Smokies,
decaying vegetation would be a natural occurrence from conifers and
other streamside vegetation. Gary notes that generally, the SML
is not visually evident, but when the concentration of organic matter
is high and there is turbulence in the water, a bubbly froth will form
at the surface.
with beaver dams, large rocks or logs, foam will form below the obstruction
and be most apparent there; it can also drift downstream. Sometimes
foam is skimmed off the water surface and can collect on small limbs
or other objects in the stream. The same phenomenon of natural foam
can be seen at the beach in coastal areas. When marine algae are
blooming, they release organic matter into the water. A biofilm
like that in a stream will form on the surface, and as waves break on
shore the turbulence will produce foam that will sometimes blow
across the beach. The presence of foam in streams, lakes and the
ocean can be a little disconcerting if youre not sure whether
its the result of natural processes or is evidence of pollution.
Fortunately, because of strict environmental regulations, clean waters
are often the norm in many areas these days, so that natural foam is
what we get.
the hikers question for several reasons. First, it shows environmental
awareness and intellectual curiosity, a desire to know whether an observed
phenomenon is natural or a matter of concern. Second, it emphasizes
that complex environmental events are under way in any habitat we explore,
including life we cannot see. Finally, it underscores the intricacies
of natural environments and reveals how they can be appreciated more
fully once they are understood.
you have an environmental question or comment, email