Sunday, 12 June 2011

New data about Amazonian Dark Earth (ADE).

ResearchBlogging.org
The Journal of Archaeological Science has just published a new study on ADE. The study, of Birk et al. is entitled: “Faeces deposition on Amazonian Anthrosols as assessed from 5b-stanols”. I have just read it and this is my very first impression:
The new data are extremely interesting. The authors look at the presence of coprostanol (a marker for faeces) in Amazonian Dark Earth (ADE). They have found a clear change in the index used to asses different sources of stanols, when comparing samples from the topmost 10 cm with samples coming from a depth of 30-40 cm. It seems that litter degradation is responsible for this change. Moreover, it also seems that the normal indexes used to assess the human origin of the stanols do not work very well in Amazonia. This paper is going to be a valuable reference to similar studies performed in Amazonia in the future.
Natural Oxisol on the left; Terra preta on the right

However, while Birk et al. correctly notice that one of the most debated topics about ADE is its origin, they do not do very much to assess why the faeces were there and what is their meaning from an archaeological point of view. ADE is found in two different forms, terra preta and terra mulata. Terra preta is darker, contains more organic matter, P and charcoal and also contains lots of fragments of ceramic. Terra mulata is like a light version of terra preta, it contains more nutrients and charcoal compared with “natural” soils from the surroundings, but less compared to terra preta. Moreover, in the terra mulata sites there is no pottery. Terra preta is found in small patches of about 1 hectare and terra mulata if found surrounding the terra preta sites. Terra mulata can cover as much as 200 hectares. An interpretation could be that terra preta resulted from settlements while terra mulata resulted from agriculture. If this thesis was correct, the high fertility of terra preta would be a side effect of human waste disposal and not the intentional result of land fertilization. In the case of terra mulata, if we assume it has been produced by agricultural use, fertilization must have been intentional. In this case, it would have been very important to see if there is any coprostanol in terra mulata! But the study did not look at terra mulata. Many scholars talk about ADE as synonymous of terra preta, without making a distinction with terra mulata, despite the fact that the differences between the two are key to understanding the past of Amazonia (estimating past population density, the region’s carrying capacity, the levels of social complexity achieved, pre-Columbian settlement patterns, the extent of the human impact on pre-Columbian forest etc.)
Birk et al. only compared samples from 4 terra preta sites with samples from natural soils. I think they missed a great occasion. If they had also looked at 4 samples from terra mulata sites they might have been able to shed new light on the matter. Perhaps they did look at terra mulata and just decided to publish the results in a second paper…keeping us waiting GRRRR J



Birk, J. J., Teixeira, W.G., Neves, E.G., & Glaser, B. (2011). Faeces deposition on Amazonian Anthrosols as assessed from 5β-stanols Journal of Archaeological Science, 38 (6), 1209-1220 : doi:10.1016/j.jas.2010.12.015

3 comments:

  1. I concur......waiting for Mulata........ GRRRR,

    I did receive an encouraging proof of concept update on NASA's ABE hyperspectral imagery from Michael Palace, good ABE verses Non-ABE definitions in three bands. These bands are associated with increased phosphorus.
    Makes me think of a Rio conference video of Johannes Lehmann talking of the vast amounts of P at 8 foot depth that ABE trees can reach.
    NASA’s Space Archaeology; $364K Terra Preta Program
    http://archaeologyexcavations.blogspot.com/2010/08/time-traveling-via-satellite.html

    As for Pre-Colombian population the regrowth of trees tells a 5 billion ton tale;
    The Columbian encounter led to terrestrial biospheric carbon sequestration on the order of 2 to 5 GtC Climate Forcing.
    The Columbian Encounter and the Little Ice Age: Abrupt Land Use Change, Fire, and Greenhouse Forcing - Annals of the Association of American Geographers
    http://www.informaworld.com/smpp/content~db=all?content=10.1080/00045608.2010.50243

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  2. Umberto,

    their flying me to Montreal Monday;

    The Executive Director of the Commission for Environmental Cooperation, http://www.cec.org/Page.asp?PageID=1115&AA_SiteLanguageID=1
    has asked me to speak on biochar, a five minute talk, "unmediated face-time" with the top three environmental officials of north America.
    http://www.cec.org/Page.asp?PageID=1209&ContentID=17683&SiteNodeID=215&BL_ExpandID=

    A great opportunity to expand on the broad applications and benefits for soil-c solutions via thermal conversion directly to Lisa Jackson, Mr. Juan Rafael Elvira Quesada and Peter Kent.

    tomorrow I'll be posting my talk to the policy list under the thread; "Five Minutes with Lisa Jackson et al"
    http://tech.groups.yahoo.com/group/biochar-policy/

    Been talking to tons of folks for updates on char projects, Check out the updates I got from Artero,

    Agave Border Initiative (ABC),
    Arturo Velez sent his Agave-Derived Biofuels creation of a Bi-National Border Consortium to foster large-scale use of agave as energy crop.
    His steering committee; Dr. Soll Sussman, Coordinator of the Border Energy Forum, as well as the National Coordinators of the Bor­der 2012 Binational Environmental Program, Dr. Steve Kaffka, Director of the California Biomass Collaborative and Dr. Matthew A. Jenks, Coordinator for the Western Regional USDA-ARS Biomass Research Center, US Arid Land Agricultural Research Center, USDA.
    Government agencies, private initiative, farmers/ranchers/foresters associations, academia/researchers, NGO and entrepreneurs are welcome to participate.
    The Western US States produce only ~0.3% of the total USA biomass production, but by planting 25 million hectares of agave on marginal dryland, these States could produce 1.6+ Billion tonnes of dry biomass every year, the same amount the whole US currently produces.
    In Mexico he is working with CONOSIL, with six hundred and seventy thousand members. They own at least thirty million hectares of land. They are VERY interested in the Agave Project. Especially the States with more semiarid and arid land (upper half of Mexico).
    CONOSIL is a member of the International Family Forestry Alliance.
    CONOSIL: http://www.conosil.org.mx/ ,Arturo is the National Administrative Coordinator.

    http://www.slideshare.net/agaveproject/Agave-Project-Presentation

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  3. Erich,
    good luck with the talk!
    I'll be interested to read what you have to say at "Five Minutes with Lisa Jackson et al"

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