[Terrapreta] What does Carbon Sequestration really mean?

[Sean K. Barry]

Hi Kevin & the terrapreta list,

This discussion we all have been having about increased plant growth with increased CO2 concentration and the supposed increased microbial growth with charcoal in the soil, etc. has had me thinking very hard this morning.   I've been digging a trench out in the yard for four hours now.  Its amazing what looking at dirt and mud and rocks can do for cerebral activity.

What I have been pondering is how Terra Preta could possibly do anything to change the CO2 concentration in the atmosphere.
I've spent some time in these recent few days, typing postings to this list, trying to say that I do not think increased plant growth is going to reduce atmospheric CO2 levels.  Plants grow faster with higher CO2 concentrations.  I knew this.  I agreed with this when people were trying to beat me over the head about it.  Nonetheless, even with all the increased growth that increased CO2 concentration in the atmosphere could bring, I do not see that it can reduce the atmospheric concentration of CO2.  Plants live finite lives.  Then they decompose.  Decomposers expire CO2.  Decomposition of a living tree occurs at a higher rate than a tree grows.
Ergo more outgo.  Get it?

Focus for a bit on an observation that the living ecology of plants, animals, microbes, and soil actually expires CO2 into the atmosphere as well as inspires it.  There is a graph of continuous atmospheric CO2 readings.  It has been made rather famous by Al Gore, in his movie, "An Inconvenient Truth".  One of his college professors had started and been recording atmospheric CO2 levels since some time in the early 60s.  The graph has a SAWTOOTH appearance and an overall rising slope.  The sawtooth is clear evidence that the influx and outflux of CO2 to/from the atmosphere follows a seasonal pattern.  He said this in the movie.  Brian and Jon have both pointed out recently, that CO2 probably cycles diurnally as well.  The rising slope of the graph indicates that there is more carbon in the atmosphere than there was previously.  Feel free to argue any of these points with me.

CO2 is part of the living respiration of the Earth.  If there is more carbon available to the living Bipsphere, then I think the concentrations of carbon in ALL parts of the overall system will increase.  The living systems just kind of push carbon around, passing it in and out of the atmosphere.   Plants are always performing photosynthesis in the spring and early summer, combining CO2 and H2O, with energy from the sunlight, to get at some of that energy, and they build carbohydrate structures (made with carbon bearing molecules) to get at more of that energy.  They slow at this in the fall and winter, releasing CO2 and/or not inspiring so much as at other times.  Animals and microbes are always pulling off the energy that is carried in complex carbon bearing molecules.  We all eat carbohydrates and expire CO2.  Humans "burn" hydrocarbons and expire CO2, also.

Now, I come to something Kevin Chisholm said some time ago.  He was saying that carbon has to be removed from the Biosphere in order to be sequestered.  I hope this is an acceptable paraphrasing of your statement, Kevin?  I understood this to mean that carbon could not be sequestered, if it was still somehow involved in the living systems.  In light of this recent discussion about CO2 off-gassing by soil fauna and animals and CO2 uptake (and/or off-gassing) by flora, I have begun to believe that we cannot just invest carbon (in the form of charcoal) into living soil, and hope that it will somehow reduce atmospheric concentrations of CO2.

It may force carbon to reside for a while in soil, but the overall affect of TP soil to increase both plant growth and soil microbiological growth, may not necessarily change the flux of carbon into/out of the atmosphere.  It is not absolutely clear, either, that charcoal stays permanently in the soil.  It seems to have a much longer half-life in soil than carbohydrates, though.

Fossil carbon fuels are the difference.  The carbon they contain (in complex hydrocarbon molecules) had once been in the Biosphere.
Fossil fuels are fossils of plants that grew on the Terra Firma once.  But, they have been buried, very deep, in the subsoil, below the livng soil, and out of the living Biosphere for a very long time (circa 300 million years).  Does everyone realize that humans have actually SET the half-life of fossil fuel carbon in the ground at circa ~300,000,150 years?!  Here it is now, with us and the rest of the animals and the plants, up here, above the lifeless subsoil ground, and all participating again in the global climatic cycling of carbon.

Methinks, that putting it only as deep as Terra Preta, only as deep as the living part of the soil, IS NOT going to change the concentration of it in any part of the living Biosphere.  The living soil and the atmosphere, and the plants and animals are all part
of the Biosphere together.  The carbon concentrations are up.   They are likely to increase everywhere.

We CANNOT "Sequester Carbon", if we sequester it where there is life.  This is just my considered opinion.  You people can kick it all apart, as many of you are want to do.  This realization of mine has diminished my enthusiasm somewhat for Terra Preta.
I hope to hell someone soon will be able to prove that Terra Preta soils do not need as much fertilizer as other soils to grow productive crops.  This may be its only redeeming value.  I am retracting my staunch statements of belief that Terra Preta can "Sequester Carbon".  I don't believe it can provide "carbon negative" energy, either.




Regards,

SKB
-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/terrapreta_bioenergylists.org/attachments/20070921/10cc8a76/attachment.html 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 253 bytes
Desc: not available
Url : /pipermail/terrapreta_bioenergylists.org/attachments/20070921/10cc8a76/attachment.gif