Biota of Rivers and Streams - Hydro-Environmental Analysis: Freshwater Environments - page 182

Light

Coarse
particulate
organic
matter

Larger plants
(mosses,
red algae)

Epilithic
algae

Microorganisms
(e.g., hyphomycete
fungi)

Dissolved
organic
matter

Microorganisms

Flocculation

Fine
particulate
organic
matter

Invertebrate
shredders

Invertebrate
scrapers

Invertebrate
collectors

Vertebrate
predators

Invertebrate
predators

FIGURE 6.19 General organic matter pathway. (From FISRWG, Stream Corridor Restoration: Principles,
Processes, and Practices , Federal Interagency Stream Restoration Working Group, 1998.)

6.4 SOURCES AND DISTRIBUTION OF ORGANIC MATTER
The general pathway of organic matter in aquatic systems is illustrated in Figure 6.19. The sources
of organic matter are autochthonous (instream sources) or allochthonous (out of stream) and the
relative importance of each varies, for example, with the stream order, as indicated by the RCC
(Figure 6.2).
In low-order streams, most of the organic matter is allochthonous. The organic materials are
produced outside the streams and then carried to them, such as coarse-sized leaves and litter fall-
ing into the river from riparian vegetations, dead organisms, and other particulate materials trans-
ported to the stream. Coarse particulate organic matter (CPOM) is considered to have a particle size
greater than about 1 mm. The organic material can also be dissolved organic compounds (dissolved
organic matter; DOM), such as materials leached from decaying materials. DOM can comprise the
largest pool of organic carbon in streams. In some Southern streams, highly colored tannic acid
and DOM derived from wetlands and often complexed with iron give the streams a characteristic
stained color and they are often called blackwater streams.