From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Sun Jul 13 2003 - 06:48:58 MDT
On Sun, 13 Jul 2003, Jeff Davis wrote:
> --- "Amara D. Angelica" <amara@kurzweilai.net> wrote:
> > However, the report also states: " FAO-UNESCO values
> > indicate that the amount of soil organic carbon in the
> > world is about 3000 x 10^15 g," so I'm confused.
>
> Here's a **possible** explanation. A living plant or
> animal is clearly biomass. When it dies, or is
> harvested, it's still biomass. But as it decomposes,
> perhaps its category status changes gradually. Is
> peat, loam, compost, or sewage/fecal material still
> biomass? As the decay process proceeds, a substantial
> quantity of the breakdown products remain in the soil.
I think that may be a little oversimplified.
I suspect that many people consider "biomass" to be the
mass in a "living organism" -- but if you consider where
most of the mass is (probably in trees) it is cellulose
and lignin -- technically not "living" at all -- but an
accumulated store of "organic carbon". Though most people
for energy production purposes classify "dead wood" as
"biomass".
Now, with respect to the soil. I (a) question the numbers
in the reference cited by Hal
http://www.icsu-scope.org/downloadpubs/scope13/index.html
because it was published in 1979 and I think we have learned
a fair amount about the global carbon cycle since then.
But assuming that it is accurate, Hal's statements may be
somewhat misleading. Why? Because Table 1.1 seems to point
out that the amount of carbon (inorganic) in the oceans
is an order of magnitude greater than the amount of carbon
on land or in the soil, or present as organic matter in
the oceans. (Of course these numbers are subject to revision
given my post of the Science News article the other day
indicating that scientists haven't previously looked for
bacteriophage quantities previously.)
But the number that *really* skews things is the amount of
carbon in sediments -- which seems to be ~3-4 orders of
magnitude larger than those present in other sources.
The question *then* becomes how much of the carbon in
sediments is "inorganic" (effectively graphite or coal?),
how much is "organic" (oil, peat, leaves or their decay
products, etc.) and how much is living material (primarily
bacteriophages [if you stretch the definition of "living"],
bacteria (mostly anaerobic), and perhaps a small fraction
of multicellular organisms (nematodes, etc.))].
Now, the organic carbon that is "living" material is probably
not classified as "biomass" for energy production purposes
(though peat might be). On the other hand for for ecological
purposes and global carbon cycle purposes one probably includes
much of the carbon in the process of converting from living
to organic to inorganic in the quantification of "biomass".
So there are some real problems with the question as Amara
posed it in that I think the definitions of "biomass" (and
"living") are very context sensitive from a scientific viewpoint.
Inorganic and organic are fairly well defined. But as the diagrams
in chapter 1 of the ref. cited above point out the global carbon
cycles are *very* complex (and still being worked out 20+ years later).
So Amara, if you want a good answer to the question I think you need to
refine the definitions a bit. For example with respect to the "depletion"
aspect -- burning of rain forest increases the atmospheric CO2
concentration which then further increases the oceanic CO2 concentration
(global warming, if it increases storm activity/rainfall, may also assist
in this process) [anything that increases the amount of water surface area
exposed to air will increase the rate at which CO2 disolves into the
water]. Increasing the oceanic CO2 concentration probably increases net
biomass production in the oceans (which may offset the losses on land) --
but there are other limiting nutrients as well such as iron and
phosphorus. The raping of the oceans of biomass (in the form of human
consumed species) probably allows a greater fraction of the oceanic carbon
to remain in the form of smaller organisms (e.g. photosynthetic bacteria).
The phages attack them resulting in the release of their organic material
then rains to the bottom of the oceans and accumulates in the sediments.
That may get released in part as methane gas by the bacteria most of which
probably ends up as methane clathrates. Some of the organic material
and/or bacteria in the sediments will get slowly converted into oil or coal.
Some will also eventually get subducted and released as CO2 from volcanoes.
[But one might be able to make a reasonable argument that an increase in
oceanic bacteria supports a larger mass of oceanic biomass that is eventually
consumed by humans and respired as atmospheric CO2...]
I wouldn't put very much money on statements by scientists that they
*really* understand these cycles completely yet (obviously human
interventions, e.g. everything from oil consumption to fishing are
changing them so they are going after a moving target).
Robert
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