What Aquatic Insects Tell Us About Water Quality

Macroinvertebrate Sampling to Monitor Water Quality

Water quality sampling net and tray.
Water quality can be assessed by sampling the aquatic insects in a stream or pond. Getty Images/Dorling Kindersley/Will Heap

The types of insects and other invertebrates living in the world's lakes, rivers or oceans can tell us if that water source has very high or very little water pollutants.

There are a number of ways that the scientific community and environmental agencies measure water quality, such as taking the temperature of the water, testing the pH and water clarity, measuring the level of dissolved oxygen, as well as determining the levels of nutrients and toxic substances.

It seems looking at insect life in the water might be the easiest and perhaps most cost-effective method especially if the surveyor can tell the difference from one invertebrate to the next upon visual examination. It can eliminate the need for frequent, costly chemical tests.

"Bioindicators, which are sort of like a canary in a coalmine—are living organisms that indicate the quality of their environment by their presence or absence," according to Hannah Foster, postdoctoral researcher in bacteriology at the University of Wisconsin-Madison. "The main reason to use bioindicators is that chemical analysis of water provides only a snapshot of the quality of a body of water."

Importance of Water Quality Monitoring

Adverse changes to the water quality of one stream can impact all the bodies of water it touches. When water quality degrades, changes to plant, insect and fish communities may occur and can affect the entire food chain.

Through water quality monitoring, communities can assess the health of their streams and rivers over time. Once baseline data on the health of a stream is collected, subsequent monitoring can help identify when and where pollution incidents occur.

Using Bioindicators for Water Sampling

Doing a survey of bioindicators, or biological water quality monitoring, involves collecting samples of aquatic macroinvertebrates. Aquatic macroinvertebrates live in water for at least part of their life cycle. Macroinvertebrates are organisms without backbones, which are visible to the eye without the aid of a microscope. Aquatic macroinvertebrateslive on, under and around rocks and sediment on the bottoms of lakes, rivers and streams. They include insects, worms, snails, mussels, leeches and crayfish.

For example, sampling macroinvertebrate life in a stream when monitoring water quality is useful because these organisms are easy to collect and identify, and tend to stay in one area unless environmental conditions change. Simply put, some macroinvertebrates are highly sensitive to pollution, while others tolerate it. Certain types of macroinvertebrates found thriving in a body of water can tell you if that water is clean or polluted.

Highly Sensitive to Pollution

When found in high numbers, macroinvertebrates like adult riffle beetles and gilled snails can serve as bioindicators of good water quality. These creatures are usually highly sensitive to pollution. These organisms tend to require highly dissolved oxygen levels. If these organisms were once abundant, but subsequent sampling shows a decline in numbers, it may indicate that a pollution incident occurred. Other organisms that are highly sensitive to pollution include:

  • mayflies (nymphs)
  • caddisflies (larvae)
  • stoneflies (nymphs)
  • water pennies
  • hellgrammites (dobsonfly larvae)

Somewhat Tolerant of Pollution

If there is an abundance of a certain type of macroinvertebrates, like clams, mussels, crayfish and sowbugs, that can indicate that the water is in fair to good condition. Other macroinvertebrates that are somewhat tolerant to pollutants include:

Pollution Tolerant

Certain macroinvertebrates, like leeches and aquatic worms, thrive in poor quality water. An abundance of these organisms suggests environmental conditions in a body of water have deteriorated. Some of these invertebrates use "snorkels" to access oxygen at the water's surface and are less dependent on dissolved oxygen to breathe. Other pollution-tolerant macroinvertebrates include:

  • black flies (larvae)
  • midge flies (larvae)
  • lunged snails