Environmental Engineering Reference
In-Depth Information
3.8 Annual oceanic NPP in parts of the Atlantic, Indian, and
Pacific oceans. Simplified from maps in IMCS 2000.
The global average for all terrestrial NPP is held low
because of the huge extent of water- and cold-stressed
ecosystems. With annual global NPP averaging only 15
MJ/m 2 and mean radiation reaching the Earth's surface
at 5 GJ/m 2 , the planetary efficiency of photosynthesis
would be just 0.3%. Similarly, with oceanic NPP averag-
ing 180 g, or roughly 3 MJ/m 2 , the global mean of phy-
toplanktonic fixation efficiency would be a mere 0.06%.
Detailed long-term studies measured efficiencies from
less than 0.092% in the oligotrophic Sargasso Sea to
0.9% in Nova Scotia's coastal waters and in excess of 5%
in Eniwetok Atoll (Parsons 1984). Thus both the terres-
trial and marine efficiencies of NPP differ by 2 OM, and
these differences are reflected, but far from perfectly mir-
rored, by the richness of standing phytomass as well as by
the diversity of heterotrophic life.
3.4 Phytomass Stores
Fresh phytomass has a highly variable content of water,
ranging from less than 5% for mature seeds to as high as
95% for young shoots (and values for phytoplankton cells
are even higher). The only way to ensure the uniformity
of comparisons is to express all masses in absolutely dry
terms (after desiccation of samples at 104 C-105 Cto
constant weight). Their densities are then 0.2-0.8 g/
cm 3 , with organic matter accounting for about 95% of
most species but with inorganic substances making up as
much as 50%, even 70% of the dry mass in many aquatic
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