Le Journal | La chronique de Mister Oli Le paléo-fleuve Manche |
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Il
y a 20 000 ans, à la fin du
Pléistocène(1), les eaux de la Seine, de la
Tamise, du Rhin et de l'Elbe se jettaient dans le plus grand fleuve que
l'Europe ait connu(2). Le fleuve Manche alimenté par les
rivières d'Europe du Nord et les eaux de fonte des calottes
anglo-irlandaise et fennoscandienne se jettait dans le golfe de
Gascogne comme le montrent les reconstitutions effectuées
à partir des carottes sédimentaires
prélevées dès 1995 par le navire
océanographique Marion-Dufresne.![]() le fleuve Manche il y a 20 000 ans |
Le
niveau de la mer était alors 130 m plus bas qu'aujourd'hui
à
cause de l'énorme quantité d'eau
stockée dans les glaces continentales
qui recouvraient le nord de l'Europe, la Sibérie, les
principaux
massifs montagneux, le Groenland et le Canada(3).
L'épaisseur maximum
des calottes glaciaires est alors estimée à 3000
m. A son extension
maximum lors de la dernière glaciation, la calotte glaciaire
atteignait
le sud de l'Angleterre. La Grande-Bretagne était
reliée au continent. L'analyse de la proportion relative des isotopes de l'oxygène 16O et 18O dans les sédiments permet d'étudier les apports massifs d'eau douce dans l'océan au moment de la fonte des glaces et aide à comprendre les effets du réchauffement climatique sur la circulation océanique. Références (1) Article Pléistocène, fr.wikipedia.org, avril 2009 (2) printempsdeschercheurs.fr/spip.php?rubrique47, avril 2009 (3) Detailed global paleogeography: jan.ucc.nau.edu/~rcb7/globaltext2.html, avril 2009 |
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| The Chihuahua's Word Composting Yard Trimmings and Household Refuse |
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| Composting
is an efficient way of reducing the quantity of garbage to be
transported to the landfill or incinerator. Composting vegetable and
fruit peels reduces the quantity of garbage produced by a household by
30 to 50%. As for yard trimmings, transporting huge quantities of
vegetable material costs tax payers money and profits professional
composters who sell them back to households who purchase their products. Producing valuable compost is easy in a garden and also possible inside a house or an apartment provided the decomposition process is well understood and mastered. Compostable materials can be divided into green materials (vegetable and fruit peels, grass, green leaves) and brown (dry grass, straw, woodchips, paper, dead leaves). Green material in excess contribute to creating anaerobic conditions. Anaerobic decomposition occurs when little or no oxygen is present. Excessive humidity and green material content create anaerobic conditions that generate smells as H2S and NH4. The result of this decomposition is a thick paste. Aerobic decomposition requires extensive ventilation to allow oxygen consuming bacteria to develop. This decomposition does not produce smells and the final humus is a light brown powder. Ventilation can be either active or passive: active by turning compost periodically or passive with worms digging galleries. When it is digested by worms, it is called vermicompost. |
Temperature
rises during decomposition and may need to be kept under control. A
large mass of compost helps heat building up. Streaks of smokes may be
observed in cold weather. Overheating above 70°C kills
worms and useful bacteria and delays decomposition. A large compost may
also catch fire. Small scale outdoor decomposition does not require much care and it rarely matters what type of decomposition is involved. In a garden, it may not need to be optimized. However a poorly maintained compost may not be able to digest all the yard trimming of the year. ![]() A beautiful garden compost built by the marquis de Oliveras for his estates. An hexagonal frame offers a smaller perimeter than a square one for the same surface. |
Industrial or
agricultural large scale facilities demand speed, efficiency and
control of temperature and gas emission. Having a compost in an
apartment also requires a good understanding of the different
mecanisms involved to avoid anaerobic decomposition generating smells
and an optimized decomposition is also required so that worms get
enough food and are able to digest all compostable household refuse.
References (1) Misra, Roy, Hiraoka, Méthodes de compostage au niveau de l'exploitation agricole, FAO, 2005, ISSN 1729-0554 (2) Agence de l'Environnement et de la Maîtrise de l'Energie www.ademe.fr/particuliers/Fiches/compost, February 2010 (3) Metro Vancouver www.metrovancouver.org/SERVICES/SOLIDWASTE/ COMPOSTING/Pages/default.aspx, February 2010 ![]() |