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Re: Cyanobacteria, algae, etc.

On Mon, 10 Jul 2000, Zach K. wrote:

>     Are you saying, more or less, that levels between .00 and .05 are
> generally ample?

Yes, but depending on other conditions in your tank and what you want out
of it, levels of 0 to 0.05 might be low.

> (snip)
> - -I don't know that parasitism is likely.  Interestingly (to me, anyway)
> - -aquatic plants apparently "leak" fairly large amounts of organic material
> - -into the water.  I'm not real clear on the details of that.
>     That's interesting to me too.  Do you know if they do it all the time?
> I'll try and learn about that when I can.

I think they leak some all the time, but the amounts may vary.  Some
background just in case someone has the time and inclination to dig into
the question...

Many years ago plants in one of my experimental tanks ceased to grow;
plants that survived into this period (mostly val) were light colored and
stunted. The tank was sunlit and when light was on the tank the vals would
bubble a lot, but there was very little new growth.  The bubbles seemed
like pretty direct evidence that photosynthesis was going on, but I
couldn't figure out where the products might be going.  It seemed like
the products could either be stored or simply leaked.  Vals don't have any
noticable storage structures, so I guessed they must be leaked.

The same thing happened more recently, and the stunting and lack of growth
was accompanied by an odd but flourishing hair algae clinging to the val.
I can't remember whether the hair algae was around for the first incident
or not.  This time I reasoned not only that the val was leaking whatever
it managed to photosynthesize but that the algae seemed to profit by the

The fundamental problem turned out to be a shortage of both iron and
phosphorus.  When I fixed the shortages the plants resumed normal growth
and the algae went away.

I read in Raven's "Energetics and Transport in Aquatic Plants" that algae
are capable of living in complete darkness on organics dissolved in the

I found a Biology professor at the University of New Mexico with an
interest in the role of dissolved organics in aquatic ecosystems, so I
asked him if plants stressed by nutrient deficiency could leak their
photosynthesized product and whether algae could live off from it.  He
responded that he didn't know if plants would leak that way, but algae
does and that algae could live off from leaked organics but that bacteria
would usually outcompete algae for the food source.

I subsequently read in a set of lecture notes from an ecology course at
the U. of Colorado that plants in terrestrial systems typically lose about
10% of their gross production through root exudates.  One function
fulfilled by the exuded organics is recovery of iron and other trace metal
nutrients from the substrate. I expect that loss might increase under
nutrient-deficient conditions.  I also have a rusty memory from a synopsis
of an early, important work on quantitative ecology (and of course, I
can't remember the reference) on a pond and surrounding area that there
was a substantial loss of organic material from the aquatic plants into
the water.

Finally last winter I found the review article "Competition and
Allelopathy in Aquatic Plant Communities" by Gopal and Goel (Botanical
Review, July-Sept, 1993, vol 59, no. 3, pp 155-210) where there are
several references to organics leaked from aquatic plants.  Most of their
emphasis was on allelopathic interactions, which I don't find interesting
because I see little direct evidence for allelopathy in planted tanks.
There are several references to a nutritive role for the leaked organics,
but that wasn't the author's emphasis, so they glossed over the topic.
I got the implication from this article that the leakage of nutritive
organics is common and that it evolved in the plants to fulfill an
ecological role.  That apparently was due to some work by R.G. Wetzel,
who's one of the most widely published limnologists around.

I haven't had the time since then to hunt down further references in this
paper trail.  The publications are often a little obscure, not locally
available, and the cost of getting them sent from Uncover or through
interlibrary loan builds up.

What little information I've been able to glean suggests to me that
organics leaked by aquatic plants (whether or not they're
nutrient-stressed) could play a role in some odd problems we see in
planted tanks, including some cyanobacteria problems.

Obviously, this isn't much information to go on.  One problem is an
apparent dirth of information on dissolved organics in planted tanks.
Diana Walstad, in her book, placed some much-needed emphasis on the role
of dissolved organics in planted tanks, but she concentrated on metal
complexes and allelopathy, and she didn't have direct evidence from
planted tanks.

A simple test for general concentrations would be nice, and I guess if you
have a spectroscope you can do one.  The only other approach that I can
think of is a crude biological oxygen demand test using a winkler oxygen
kit.  Any other ideas?

Roger Miller