Biota of Rivers and Streams - Hydro-Environmental Analysis: Freshwater Environments - page 164

Leaf and stick
detritus in
margin

Boulder
cascade

Sand-silt
over cobbles

Transverse bar
over cobbles

Moss on
boulder

Fine gravel
patch

Debris dam

Stream segment Segment system Reach system Pool-rie system Microhabitat system

FIGURE 6.1 Hierarchical organization of a stream system and its habitat subsystems. (From FISRWG,
Stream Corridor Restoration: Principles, Processes, and Practices , Federal Interagency Stream Restoration
Working Group, 1998.)

as healthy as one with fewer numbers but with a greater diversity of organisms. Supporting a
diverse assemblage of organisms typically requires a diverse habitat. Many of the metrics used to
assess aquatic health as described in Chapter 7 and methods for stream restoration as described in
Chapter 8 consider multiple spatial scales of land cover, geologic setting, hydrologic setting, aquatic
habitat, and water chemistry. Some of the types of organisms that may occur in streams and rivers,
and their typical habitats, are described in the following section.

6.2 AUTOTROPHS

6.2.1 p erIpHyton , or b entHIc a utotropHS
Periphyton (from peri meaning around, about, or enclosing and phyto for plant; Figure 6.3) are algae
or plants (autotrophs), a deinition of which is “Algae attached to submerged substrate in aquatic
environment” (USEPA SESD 2007).
As illustrated in Figure 6.2 and according to the RCC, periphyton are most common in low-order
to mid-order rivers, where light reaches the bottom substrate. However, periphyton are found in
virtually all streams and rivers on virtually all surfaces that receive light (Allan and Castillo 2007).
The periphyton are variously identiied or classiied based on their taxonomy or the substrate on
which they reside. They are also distinguished in that they occur on substrates as opposed to other
algae that low with the current, for example, the phytoplankton or planktonic algae.
First, before continuing and to add to the confusion, these are not really plants, and not all
of them are really algae. Organisms can be subdivided into two separate domains, the highest
taxonomic level or rank, the Prokaryota and the Eukaryota. The general difference is that unlike
the eukaryotic organisms, the prokaryotic organisms lack a cell nucleus. The Prokaryota includes
bacteria. The Eukaryota may be further subdivided into kingdoms, such as Protista, Fungi, Plantae,
and Animalia. True plants are in the Animalia kingdom, while most algae (such as the periphyton
and phytoplankton) are protists. However, there are some planktonic and periphytic algae, known
as blue-green algae which are not really algae. They fall within the domain Prokaryota and are also
called Cyanobacteria. The most common forms of periphyton are diatoms and green algae (within
the divisions and Chlorophyta, respectively, of the Protista kingdom), and Cyanobacteria. Each of
these algal types may be composed of many thousands of subspecies. The level of taxonomic clas-
siication may differ, depending on the speciic study goals; however, some level of classiication is
usually necessary to either assess the health or manage the quality of rivers and streams.