These nine were selected because of their significant impact on aquatic organisms and because they are relatively inexpensive to perform. Furthermore, by performing these nine tests an overall water quality index can be determined. Biological monitoring can inexpensively screen for problems that are not specifically tested for using common chemical kits. The presence of heavy metals, pesticides, herbicides, and other toxins in a stream may be indicated by a lack of biodiversity in a stream. Since certain organisms can tolerate more pollution than others, the greater the variety of organisms - the better the water quality.
Biological monitoring can also indicate the presence of problems that extend over time.
Two important characteristics of streams is the velocity and volume of flow. Flow rate can control many other factors such as oxygen content, water temperature , composition of the stream bed, amount of food available, and pollution levels. These factors in turn directly affect the types and numbers of plant and animal species which exist in the stream ecosystem. Changes in land use in the watershed may shorten the length of time it takes for rainfall to enter the stream, resulting in sudden changes in velocity and volume of flow. Working to answer these focus questions will help you learn a lot about streams.