Environmental Engineering Reference
In-Depth Information
freshwater and coastal wetlands—whose limited areas have been subject to exten-
sive conversion to cropland, urban, and industrial uses—have phytomass stores
commonly in excess of 50 t/ha.
Energy losses along the food webs mean that the heterotrophic biomass must be
dominated by tissues of short-lived microorganisms. Prokaryotes—unicellular bac-
teria and archaea—are abundant not only in soils and near-surface waters but also
in extreme environments (undersea sediments, deep ocean thermal vents, and rocks
up to several kilometers below the Earth's surface, hot springs, and highly alkaline
lakes), and they are also (often symbiotically) active inside plants and animals;
nitrogen-i xing bacteria in legumes and gut microbes in ruminants are excellent
examples of unusually rewarding symbioses. Biomass totals diminish rapidly at
higher trophic levels: the biomass of soil invertebrates is much smaller than that of
soil bacteria, and the zoomass of large mammalian herbivores is much larger than
that of the carnivores that prey on them. The top predators (large felids, tuna,
sharks) have large bodies, but their aggregate zoomass is a very small fraction of
the overall biomass of their respective ecosystems.
Compared to quantii cations of phytomass, quantii cations of heterotrophic
biomass are relatively uncommon. Bacteria, both autotrophic and heterotrophic, are
present in soils in quantities ranging from 10
1
to 10
3
g/m
2
(Coleman and Crossley
1996). Earthworms (Oligochaeta) are the most conspicuous soil invertebrates, and
their biomass usually dominates the total for soil macrofauna; in soils of the tem-
perate zone it usually adds up to just around 5 g/m
2
, and in cultivated soils rich in
organic matter it can surpass 10 g/m
2
(Edwards and Lofty 1972; Hartenstein 1986).
Barros et al. (2002) found similar densities in Amazonian farmland soils (between
1 and 9 g/m
2
), but maxima above 100 g/m
2
in some Amazonian pastures. Millipedes
(Diplopoda) add only between 1 and 5 g/m
2
. The most common range for all
soil macrofauna (dominated by earthworms, ants, and termites) is between 5 and
15 g/m
2
.
The biomass of ants (Hymenoptera) is usually well below 0.5 g/m
2
(Brian 1978),
while typical densities of termites (Isoptera) are an order of magnitude higher. Aver-
ages in Amazonian rain forests are 2-2.5 g/m
2
. Very similar rates (1-3 g/m
2
) prevail
in the region's croplands and pastures, and in the annually l ooded
várzea
forest
termite densities are just 0.1 g/m
2
(Martius 1994; Barros et al. 2002).Values around
5 g/m
2
are typical for the four dominant species in the tropical woodlands of
Australia's Queensland (Holt and Easy 1993), and means of 10 g/m
2
were found
in the Atlantic forest in northeastern Brazil, in São Paulo state, and in the dry ever-
green forest of northeast Thailand (Inoue et al. 2001; Costa-Leonardo, Casarin, and
