Re: Barley Straw explanation

From: Chris Teichreb (
Date: Thu Jun 24 1999 - 09:32:55 PDT

Date: Thu, 24 Jun 1999 09:32:55 -0700 (PDT)
From: Chris Teichreb <>
Message-Id: <aabcdefg2305$foo@default>
Subject: Re: Barley Straw explanation

Hi Chris,

> Chris,
> Wow, love your explanation. Don't understand it all, so I hope you
> won't mind clarifying a few things for me.

        No problem. I was, as they say, feeling a little cheeky and high
and mighty that day. Working on revision for my thesis which deals with
this issue in terms of global climate change in the arctic. Anyways, here
follows a quick follow up to your questions.

> DOC = a mixture of several compounds?

        Yes, a mixture of numerous organic carbon compounds. Essentially,
dissolved organic carbon is any carbon which is smaller than 0.45um in
diameter. Don't ask me why that size was chosen, it just was. It arises
from the breakdown of plant material, but can also be formed through
decomposition of animals. To be blunt, if you rotted a human corpse in a
lake, organic carbon would eventually be leached out. Since there's not a
lot of human bodies floating in lakes, it's mainly from plants.

> PAR = light? of certain
> wavelengths?

        PAR=photosynthetically active radiation. Yes, this is light which
includes the visible spectrum (visible to the human eye). Can't remember
the exact wavelengths off the top of my head, but it goes from 320nm
(violet) to about 680nm (red). Below 320nm is ultraviolet radiation,
above 680nm is infrared.

        Green photosynthetic plants use light primarily in the blue and
red regions. The reason they appear green, is because green light is not
readily absorbed, but rather is reflected back, giving the overall
greenish appearance.

> exogenous, heterotrophic, macrophyte = ?

        Exogenous means external. In terms of what I was saying,
exogenous enzymes are those enzymes formed by bacteria or algae and
excreted to the exterior of the cell wall into the water to break down
phosphorus which has been bound to organic carbon, iron, or other
elements. It costs a lot of energy to form these enzymes, so if they're
constantly having to do this, they have less energy for reproduction which
means fewer new algal cells.

        Heterotrophic bacteria are those which rely on a external carbon
source. Those organisms capable of making their own carbon sources (such
as plants through photosynthesis) are referred to as autotrophic. There
are no homotrophic bacteria ;) (sorry, couldn't resist!).

        Macrophyte, in terms of aquatic plants, are ones which are visible
to the naked eye, as opposed to microphyte. This includes all of the
aquatic plants you see for sale in the local aquarium shops. It's a very
general term used to encompass a lot of various classes of plants.

> Do floating plants still apply to a tank that gets light from the
> side?

        Well, perhaps not. Although they will remove some of the excess

> (on windowsill) Does blackwater extract do the same (or
> more/less) as peat or barley straw?

        Yes, this is an organic extract from the Amazon. Formed through
the breakdown of rainforest vegetation.

> You said that I might change
> the water frequently, but wouldn't I risk adding more phosphorus (or
> other things for that matter) if I do that?

        No, not unless your tap water has very high phosphorus levels.
Essentially, you have all sorts of aquatic organisms ranging from bacteria
to algae to protozoans to aquatic plants, and perhaps a snail or two.
These are constantly growing and dying. When they die, they decompose and
the phosphorus is released back into the water and will build up over time
if you're just topping off with tap water which adds even more phosphorus.

> Seems to me that if I
> leave the water as it is, the phosphorus would get used up. Also,
> don't the plants themselves need that phosphorus? Or is that an
> element they get from their prey?

        I'm not sure if Utrics and Aldrovanda get phosphorus from their
prey, but in general, phosphorus is needed in very very small amounts.
There's a term called the Redfield ratio, which looks at the balance of
carbon to nitrogen to phosphorus in aquatic organisms. In general, most
aquatic plants have about a 150:10:1 C:N:P ratio, and they try to maintain
this ratio through various processes. Since aquatic Utrics and Aldrovanda
already come from relatively low nutrient waters, they need even less

> Sorry about all these questions. This is quite interesting to me.
> If you choose to reply, you can answer in point form to save
> yourself some time typing.
> Thanks.

        No problem. I hope the above clarifies what I said in my previous
answer. In reply to Fernando's suggestion of using rice straw, I would
agree that would be better than barley, since most rice is growing in wet
areas to begin with and will be slightly more natural.

        For my own experience, although I've never seen Aldrovanda in the
wild, I have seen plenty of Utrics. They almost always occur in
shallow calm lakes, amongst cattails, Equisetum, rushes and other plants
growing along the shore. I beleive this is due to the fact that they are
rootless, and get blown to the shores and tangled up amongst these plants.
I've taken water samples from these lakes, and they're usually very low in
phosphorus and nitrogen concentrations (for those of you who have to know,
[P]<1uM, [N]<6uM) and high in humic DOC concentrations (at least 3mg*l-1
and above). In most places I've seen them, they bloom in late summer,
mainly in response to water temperature (I've seen U.vulgaris in Inuvik,
Northwest Territories, where there is nearly 24 hour light throughout most
of the summer). This often corresponds with low water levels, but I think
this is merely a case of lowest precipitation and runoff levels occuring
during this period.

        On a final note, you can make your own DOC extract through boiling
peat. Simply place some peat in a watertight container, pour boiling
water over it, stir for a couple of minutes, and leave for about a week.
You'll notice the water turn a dark brown, strain this through screening
of some sort, and you'll have a very natural extract, no worries about
excess nutrients being added. Peat is ultimately where most of the DOC in
the north comes from, and I've seen U.vulgaris up to 6 feet long! Don't
add too much to your aquarium, enough to give a nice yellowish tinge to
the water.

> Chris F.
> P.S. Know any good chemistry books for the not completely stupid on
> the subject kind of person like me?

        Most of what I've been talking about is out of journal articles.
Since my work focuses on aquatic systems, that's where most of my info is
from. A good general text on limnology (freshwater ecology) is Wetzel and
Likens 'Limnological Analyses', which gives a good overview of some of the
stuff I've gone over here.

        For really really detailed picky picky ;) methods on growing
aquatic plants without growing lots of algae, visit the Krib
(, I think!) and go to the aquatic plants section. These
people really know what they're doing, and I consider them _the_ experts
on how to keep small aquariums from becoming algal cultures!

Happy growing,


Chris Teichreb
Department of Biological Sciences
Simon Fraser University
Burnaby, B.C.

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