1.The diversity of organisms in the sample;
2.The percentage of each organism in the sample;
3.The number of organisms per unit area;
4.The sample diversity (the combination of the previous three aspects);
5.The relative pollution tolerances of the organisms in the sample. The various environmental problems of freshwater streams can be detected by these five aspects. The problems affecting streams can be grouped into three general categories:
a. Physical - such as stream alterations reduced flow, or temperature extremes, including excessive sediment input from erosion or construction which unfavorably alters riffle characteristics. The result of physical impacts to a stream range from a general reduction in the numbers of all organisms to a reduction in the diversity of taxa.
b. Organic Pollution and Enrichment - the introduction of large quantities of human and livestock wastes, as well as agricultural fertilizers. The result of mild organic enrichment is usually a reduction in diversity, resulting from a marked increase in the types and numbers of macroinvertebrates that feed directly on organic materials. Because of the organic enrichment, excessive blooms of algae and other aquatic plants provide a plentiful food supply, favoring these detritus feeders. Organic pollution, however, presents a more severe problem, as can be found, for instance, below the outfall of an inadequate sewage treatment plant. Severe oxygen depletion often occurs. The situation can become so critical that the sensitive types of macroinvertebrates are eliminated and replaced by organisms that can tolerate extremely low oxygen levels.
c. Toxicity - this includes chemical pollutants such as chlorine, acids, metals, pesticides, oil, and so forth. It is very difficult to generalize the effects of toxic compounds upon macroinvertebrates since a number of the organisms vary in their tolerance to chemical pollutants. Generally speaking, however, a toxicity problem is usually the only condition that will render a stream totally devoid of macroinvertebrates.
Traditionally, macroinvertebrate samples have been taken in a very precise and careful manner for later identification to the generic or species level. Normally, each sample requires up to an hour to collect and process for storage. Actual sample analysis may take up to several days using expensive equipment. This process, while essential to providing data of scientific and legal quality, also results in an extended period between sample collection and subsequent analysis.
For the purpose of the Water Watch Biological Monitoring Project, a much more simplified method is used. The intent is to identify pronounced stream quality problems, as well as to gather information that will be useful in the long-term monitoring of stream health. The methods employed provide a rapid means of sampling several riffle areas to detect moderate to-severe stream quality degradation. The findings are produced within a short period of time after sample collection while still at the stream site. If a problem is indicated, additional samples can be taken to verify the findings. Should poor quality conditions be indicated, upstream sampling can then be undertaken to identify the source of the problem.