Environmental Engineering Reference
In-Depth Information
and average body weights (they have increased everywhere during the twentieth
century, but the difference between typical body masses in North America and
Europe, on the one hand, and in Asia, Africa, and Latin America on the other per-
sists) results in at least 170 Mt (35 Mt C) of domesticated zoomass in 1900 (more
than four times greater than the total zoomass of all wild land mammals) and at
least 600 Mt of live weight (120 Mt C) in the year 2000, a 3.5-fold increase in 100
years and roughly 25 times the values for the total wild mammalian zoomass. The
cattle zoomass alone (about 80 Mt C) is now at least 300 times greater than the
zoomass of all surviving African elephants, whose biomass is now less than 2% of
the zoomass of Africa's nearly 300 million bovines.
In some countries the presence of domestic animals has reached unprecedented
densities. In 2009 the Netherlands had nearly 4 million heads of cattle, more than
12 million pigs, and 1.1 million sheep and goats (PVE 2010), whose live-weight
zoomass added up to about 1.3 t/ha of crop and grazing land, three times the average
anthropomass per hectare—and in some parts of the country the difference was
twice as high. Even more remarkably, this high density of domesticated zoomass
was an order of magnitude greater than the combined biomass of all soil inverte-
brates and was surpassed only by the mass of soil bacteria. Even the extraordinarily
high Dutch crop yields could not support such densities, and the country is a major
importer of animal feed (Galloway et al. 2007).
With 500-800 Gt C, the biosphere's phytomass binds an equivalent of between
65% and 102% of the element's current atmospheric content (831 Gt C, corre-
sponding to 390 ppm CO
2
). In terms of penetration of the Earth's physical spheres,
the eukaryotic biomass constitutes a mere 7
10
-9
of the ocean's volume and less
than 0.01% of all the carbon in the ocean. Subterranean and subsea prokaryotes,
even when credited with very high cell totals, amount to just 6
×
10
-7
of the top 4
km of the crust, the generally accepted depth limit for the survival of extremophiles.
The uniform distribution of dry terrestrial phytomass over ice-free land would
produce a layer about 1 cm thick; the same process in the ocean would add a mere
0.03 mm of phytoplankton (in both cases I am assuming the average biomass density
to be equal to 1 g/cm
3
). I know of no better examples to illustrate the evanescent
quality of life.
×
Productivities and Harvests
During the millennia of prehistoric evolution the human impact on the biosphere,
however profound locally or regionally, was limited from spreading to a global scale
