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Lesson

Water Quality Monitoring:
Biomonitoring with
Benthic macroinvertebrates

 
   
  Because water is so important to living, we must care about its quality. Poor water quality can easily result in sickness and even death. Pollution and contamination can cause water quality to become poor.
biomonitoring One way to determine the water quality of a river, lake, or stream is to observe the life that it supports. With good water, we can expect to find a diversity of plants and animals living in and around it; poor water quality is generally accompanied by a limited variety of plant and animal life. Studying living things in determining a measure of water quality is known as biomonitoring.
benthic macro-invertebrates The creatures that live in a waterway can tell you a lot about water quality because all organisms require specific conditions to live. A common way to measure water quality uses the presence of certain creatures within the waterway known as benthic macroinvertebrates. Macroinvertebrates are large enough to see with the naked eye (macro) and have no backbone (invertebrate). Benthic macro-invertebrates live in the benthos, or stream bottom, and include insect larvae, adult insects and crustaceans.
Differences in tolerance to pollution by various species is the key to using benthic macro-invertebrates as indicators of water quality. Stream-bottom macroinvertebrates are good indicators of water quality because they differ in their sensitivity to water pollution. Some benthic macroinvertebrates are very sensitive to pollution and cannot survive in polluted water. Others are less sensitive to pollution and can be found even in very polluted streams. Benthic macroinvertebrates usually live in the same area of a stream for most of their lives. Sampling the benthic macroinvertebrates gives you a good sense of what the water quality has been for the past few months. If the water quality is generally poor, or if a polluting event occurred within the past several months, it will be reflected in the macroinvertebrate population.
categorized by pollution tolerance These aquatic macroinvertebrates are grouped into 3 categories based on their sensitivity to pollution for the purpose of classifying water quality.
very sensitive to pollution

Class 1 Organisms are pollution sensitive. They are associated with good water quality. They do not tolerate pollution well, and large numbers are observed only when good water quality is present.



Class 1 examples.

somewhat sensitive to pollution

Class 2 Organisms somewhat pollution tolerant. They tolerate water pollution better than Class 1 organisms. We can expect to see significant numbers of these animals when the water quality ranges from good to moderate.

Class 2 examples.

pollution tolerant

Class 3 Organisms are pollution tolerant. They are tolerant to even higher levels of pollution than are Class 2. When these animals dominate, poor water quality is generally the reason.

Class 3 examples.

Numbers and diversity of collected organisms are used to determine overall water quality. One method involves collecting a sample of macroinvertebrates from the stream, identifying the organisms and rating the water quality. Water quality ratings of excellent, good, fair and poor are based on the pollution tolerance levels of the organisms found and the diversity of organisms in the sample. A stream with excellent water quality should support organisms from all three pollution tolerance groups.
summary

Biomonitoring is the use of organisms to assess or monitor environmental conditions. Benthic macroinvertebrates are ideal for use in biomonitoring for several reasons:

  1. They are ubiquitous.
  2. They are relatively sedentary and long-lived.
  3. Some species of benthic macroinvertebrates are sensitive to pollution and some are tolerant.
  4. Benthic macroinvertebrates are easy to collect and identify.

Benthic macroinvertebrates act as continuous monitors of the water they live in. Unlike chemical monitoring, which provides information about water quality at the time of measurement, biological monitoring can provide information about past and/or episodic pollution.

 
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