Encyclopedia of Environmental Science and Engineering, Volume I and II

LIMNOLOGY 615

The food chain concept involves the flow of energy

among the lake organisms and the recycling of nutrients.

Each trophic level (food chain level) transfers only 10 to

20 percent of the energy received up the chain to the next

trophic level (Kozlovsky, 1968; Gulland, 1970). This means

that a few large piscivorous fish depend on a large supply

of smaller planktivorous fish which depend on a very large

supply of zooplankton which depend on a successively

much larger base of photosynthetic production by phyto-

plankton and other aquatic plants. By constantly producing

wastes and eventually dying, all of these organisms provide

nourishment to detritus-eating organisms in the sediments,

which obtain their energy by decomposing organic matter.

Organic matter decomposition results in the recycling of

nutrients that are required for further plant production (U.S.

EPA, 1990).

PISCIVOROUS

FISH

EAT

EAT

EAT

USE

NUTRIENTS

RECYCLE

NUTRIENTS

ALGAE

PLANKTIVOROUS

FISH

ZOOPLANKTON

BENTHIC

ORGANISMS

MICROSCOPIC

1/10 IN

6"-1 FT

1–2 FT

FIGURE 5 Aquatic food chain (U.S. EPA, 1990).

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