1. Definition and Significance
Microorganisms growing on stones, sticks, aquatic macrophytes, and other submerged surfaces are useful in assessing the effects of pollutants on lakes, streams, and estuaries. Called periphyton,1,2 this group of organisms include zoogleal and filamentous bacteria, attached protozoa, rotifers, and algae, and free-living microorganisms that swim, creep, or lodge among the attached forms.
Unlike plankton, which often do not fully respond to pollution’s influence in rivers for a considerable distance downstream, periphyton show marked responses immediately below pollution sources. Examples are the beds of Sphaerotilus (see Section 10900, Plate 26:H) and other “slime organisms” commonly observed in streams below organic waste discharges. Because periphyton’s abundance and composition at a given location are governed by the water quality there, observations of their condition generally are useful in evaluating the waterbody’s conditions.
The use of periphyton in assessing water quality often is hindered by the lack of suitable natural substrata at the desired sampling station. Furthermore, it often is difficult to collect quantitative samples from natural substrata because of their physical complexity. To circumvent these problems, investigators have used artificial substrata to provide a uniform surface type, area, and orientation.