We can measure pollution in a stream in a number of different ways. We can measure physical conditions in the water like the temperature and the amount of sediments. We can measure chemical levels of many different kinds of compounds that get into the stream from agricultural areas (fertilizer components such as nitrogen and phosphorous; organic chemicals used in herbicides and pesticides), industrial wastes (chemicals, organic wastes), and urban runoff (oil and grease, chemicals, lawn fertilizers). We can also measure biological conditions. We could culture bacteria from streams and find out if they are carrying any diseased organisms. For example, you may have heard of E. Coli bacteria that are common in the digestive systems of mammals. Certain strains can cause severe problems in people if they are taken in through the food or water supply. Typhoid and cholera are also spread through the water.
Aside from measuring these pollutants, we can also measure the biological health of a stream by measuring the diversity of the species found in the river. Since we expect the highest diversity in a healthy stream, streams that are under stress from habitat or pollution changes will have fewer species than those without those stresses. Since the species live in the stream all the time, measuring the biology is a more complete indication of stream health than going to the stream periodically and measuring chemical levels.
There are several specific measures of biological quality that have been used by the EPA:
- The Index of Biotic Integrity or IBI is a measure of the health of the fish community in a stream
- The Invertebrate Community Index or ICI is a measure of the health of the macroinvertebrate (aquatic insect) community in a stream
- The Qualitative Habitat Evaluation Index or QHEI is a measure of the quality of the stream habitat including the riparian zone, substrate, presence of meanders, etc.
You can click on the links above to find out more specifically how these things are measured. You can also explore other parts of this website for definitions and more explanation of water quality measures.
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