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The bar graph below compares the recovery rates for froth flotation and tub (Struever 1968) flotation using modern carbonized seeds.
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A Comparison of the light-fraction recovery of carbonized modern seeds using froth and tub flotation
Note that the 2 MOST SIGNIFICANT Differences in light-fraction recovery (z value)
are for NON-BUOYANT carbonized seed types. This indicates that FROTH flotation
recovers not only buoyant seed types but is FAR SUPERIOR in non-buoyant seed recovery.
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So why is non-buoyant recovery important? Because not all carbonized seed species normally float, because smaller seeds and seed fragments may not float due to their lowered bulk densities, because porous or damaged seeds may tend to sink, because carbonized plant material may become waterlogged during the flotation process and lose buoyancy, and because in arid regions, it is common for calcium carbonate to coat carbonized plant material and prevent it from floating.
(M. Pendleton, 1983, American Antiquity 48(3):615-616.)
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Chart Data from M. Pendleton (1980) M.A. Thesis, California State University Chico, Chico, California.
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In the study above, modern seeds commonly available from nursuries were carbonized and added to one liter of topsoil per sample. Identical samples were processed using tub flotation (S. Struever (1968), American Antiquity 33:352-362) and froth flotation. Coded samples were analysed following processing to determine percentages of seed recovery for both flotation methods.
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