Environmental Engineering Reference
In-Depth Information
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FIGURE 22.10
Ranges and means of production by various ecosystems (data from Whit-
taker, 1975).
dry terrestrial habitats have very low production (Robarts
et al.,
1995).
Freshwater marshes have very high rates of production; peatlands and
deepwater swamps have lower rates of production (Table 22.4). Produc-
tion of methane appears to follow primary production trends, with more
productive wetlands producing greater amounts of methane. Greater pro-
duction presumably increases the extent of anoxia and leads to greater
methane production (Table 22.4).
The majority of primary production by macrophytes is not grazed di-
rectly by herbivores in wetlands (Mitsch and Gosselink, 1993), rather it is
deposited as detritus, and much of this organic production can be stored
in the sediment (Fig. 22.11) or consumed by invertebrates. Although less
than 4% of the earth's surface is wetlands, wet soils contain about one-
third of all organic matter stored in the world's soils. The vast deposits of
coal are remnants of such organic storage from the swamps of the Car-
boniferous period. Given this potentially great production of carbon, vari-
able rates of storage, respiration, and hydrological throughput, wetlands
can serve as either sinks or sources of organic matter in the landscape. Nat-
ural wetlands with high hydrological throughput can be significant sources
of organic C in the watershed (Mulholland and Kuenzler, 1979). However,
artificial wetlands are used as sewage treatment systems; in this case, the
wetland has a net consumption of organic carbon.
Wetlands represent a hybrid between terrestrial systems and aquatic
systems. The carbon flux diagram of Creeping Swamp, North Carolina, il-
lustrates some unique features of wetland ecosystems (Fig. 22.12). Carbon
production was dominated by trees, followed by algae and small plants.
The production of carbon in coarse particulate organic material fuels the
food web of the wetland. Most of the carbon in ecosystem compartments
is in trees and sediments. The majority of the carbon flux into the detrital
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