- Conducting the test: A sample of sediment is taken from the bottom of the river. This sample is searched for benthic macroinvertebrates, and all that are found are identified and recorded.
- Testing: The presence of benthic macroinvertebrates in the sediment of the river. The macroinvertebrates are categorized into four sections: intolerant, moderately tolerant, fairly tolerant, and very tolerant. The more intolerant the species, the higher the water quality must be for it to survive.
- Importance: The number of macroinvertebrates from each of the four categories above can be an important indicator in the quality of the water. For example, a body of water that has only species from the very tolerant group is most likely a body with very low water quality, because these species will live in almost any type of water. On the contrary, a body of water with many species from the intolerant category would imply water of very high quality.
- Natural Occurrence: Water that is polluted naturally can result in only tolerant macroinvertebrates being present. Natural pollution occurs from a variety of sources, such as ash from an erupting volcano, algal blooms, and storms.
- Human Impact: Water that is polluted from human activity can have the same effect. Human sources of pollution are also very numerous. They include drainage pipes, fertilizer, and mines.
- Data: In the samples that we pulled from the river, benthic macroinvertebrates were found from each of the four categories. This implies that the water can sustain species requiring high quality water to survive. This test is measured with a pollution tolerance index rating, or PTI. The PTI rating for our sample was 29, which is considered an excellent score. According to this test, the water quality from our area of study is very high.
- Explanation of Results: The results from the benthic macroinvertebrates test are in agreement with the overall results of the other nine tests, which scored a high water quality index (as mentioned in the introduction). A number of factors contribute to this high water quality, including limited human intervention in the watershed and a healthy ecosystem in the area immediately surrounding the river.