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Re: bluegreen algae and biogenic decalcification

> Date: Tue, 8 Jul 1997 04:20:10 -0400 (EDT)
> From: ac554 at freenet_carleton.ca (David Whittaker)
> Subject: Re: bluegreen algae control

> If it was truly competition, then green algae should have prospered
> immediately after the destruction of the cyanobacteria by the erythro-
> mycin, and not just on those occasions when the "outbreaks ended
> without any effort."

The green algae very well may have prospered in the chemically induced
cases, but in the cases where I treated the tanks I wasn't looking closely
for other changes.

> Conditions that favour green algae also tend to favour macrophytes.
> You also have plants in your tank which benefitted from the better
> lighting and increased nutrients.

True, but the tank was a low-light tank with slow-growing plants (crypts
and anubias).  The macrophytes showed no visible response to the
treatments until after the cb was essentially gone.

> Although your statement mentions no quantities, it would seem that
> there was more than enough light and nutrients to provide for both
> types of algae. So how do you explain the disappearance of the
> cyanobacteria?

The conditions I changed were selected to favor green algae:  I added
ammonium because I suspected that green algae would grow better on it than
they would on nitrate, and because the cb (some of which have their own
nitrogen-fixing capabilities) should profit less by its addition.  I
removed the filter media so the ammonium would stay in the tank longer.  I
increased the light because the cb seems to grow better under low light
than does green algae.

Certainly there was enough light and macronutrients for both.  This says
nothing about trace and micronutrient levels or of availability of
cellular precursors (i.e. vitamins, cofactors, essential amino acids,
etc.) that might be required by cb but not by green algae.  It also
doesn't address toxins that either competitor might use to gain an
advantage over the other.  I don't know the actual mechanism of
competition.  I wish I did.  My hope (and my hypothesis) was that when
given a small edge the green algae would use whatever mechanism it had
available to suppress its competition.

> As the mass of green algae increases, so do oxygen levels in the
> tank. This starts to inhibit the reproduction of the cyanobacteria,
> The older bacteria eventually die out except in those locations least
> aerobic. There they await the return of more favorable circumstances.

I didn't measure O2 levels, so this is plausible.  I have measured O2
repeatedly on some of my other tanks and I've never found levels much
below saturation.  "Saturation" at my altitude (about a mile above sea
level) is a little lower than it is most places because of the reduced
atmospheric pressure.

> That's my theory. Horeman and Rataj, and at least one other author
> casually mention that cyanobacteria and oxygen don't mix well, but
> don't go into details.

It seems like one way to use your theory would be to shut off circulation
in a brightly lit tank.  O2 will supersaturate (at least, that's what
happens when my pumps fail).  Shouldn't this wipe out the cb?

> - --
> Dave Whittaker
> ac554 at FreeNet_Carleton.ca

When we get right down to it, any method that works has got to be
better than chemical treatment.

> ------------------------------
> Date: Tue, 8 Jul 97 8:43:05 MDT
> From: "Marshall F. Wilkinson" <wilkinso at acs_ucalgary.ca>
> Subject: Re: biogenic decalcification


> My understanding of this process is that it is NOT the preferred
> method of meeting the Carbon needs of these plants, i.e. they
> prefer to use carbon available as dissolved CO2.

That is my understanding, as well.  I think that biogenic decalcification
cuts in when normal metabolism has already reduced CO2 levels to unusable

I also speculate that using HCO3 requires more energy than using CO2.
Also, there would be a potential barrier the plants have to overcome -
they have to manufacture the chemical "machinery" needed to import and use
the HCO3.  I wonder if a plant that is normally capable of using HCO3 may
starve instead if it doesn't get enough light to get through the barrier
and to support the added energy cost.

> Marshall Wilkinson
> Calgary Alberta
> ------------------------------
> Date: Tue, 8 Jul 1997 10:42:06 -0500
> From: krombhol at felix_teclink.net (Paul Krombholz)
> Subject: Re: peat or soil as DIC (CO2) substitute


> Back in March Roger Miller wrote that he had some crypts doing quite well
> in a sunlit tank with Vallisneria, Ceratophyllum and Elodea and the pH over
> 9.  In this same tank, Hygrophila polysperma died.  This was a very
> significant post for me, because I always assumed that Crypts were high CO2
> plants. Possibly they were getting a lot of CO2 via their roots.  Maybe
> they can compete successfully for CO2 in the water with Elodea et. al.
> Definitely they have some arrows in their quiver that I never suspected.

Now that you mention it... The tank has a good-sized population of trumpet
snails.  Their habit of burrowing in the daytime would place their
respiratory waste CO2 in the root zone while the tank was lit and when the
CO2 was most needed.

I've also noticed Anubia thriving under fairly low CO2 conditions (not CO2
depleted conditions,though) and attributed their well being to the fact
that some fish and all the shrimp I've ever had prefer hiding in the
shelter of the anubia's roots and leaves.  This means that their waste CO2
would be a direct supplement to the plant's CO2 supply.  Pretty nice
arrangement, isn't it?

> Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174, in
> cooler Jackson, Mississippi.

Roger Miller
In Albuquerque, watching thunderstorms roll off the continental divide.