Why Aquatic

Invertebrates?

Many government agencies that are in charge of monitoring water quality rely on testing of water samples for pollutants.  Does that mean that this is the best approach?  Not necessarily.  Consider a spill of some pollutant into a stream.  It may only be detectable for a few days before it is diluted and washed downstream.  If no one is there to take a sample, it would go undetected.  As a result, effective water quality monitoring using water samples requires numerous samples to be taken.  In addition, water samples require expensive equipment  to be analyzed.

The advantage that aquatic invertebrates have is that by living in the stream, they are always in effect "sampling" the water quality.  Most of the organisms found in streams are the larval stage of insects.  These insects will go through a metamorphosis, changing into adult forms that may or may not remain in the stream.  The larval and adult stages that live in the stream have different tolerances to pollution.  If there is pollution in a stream, only those organisms that are more tolerant will survive.  If we find invertebrates that are intolerant to pollution, we can safely say that there has no been significant pollution in that stream recently.  And because some aquatic insects live for a year or more, we tell about the history of pollution in a stream well into the past.  As a result, by sampling invertebrates only once a year we can effectively monitor the water quality of a stream.

In addition, sampling aquatic invertebrates requires no expensive equipment.  With a homemade kick-net and a hand magnifying glass you can identify most invertebrates for monitoring.

One concern that many people have about monitoring with aquatic insects is that they will be difficult to identify.  To a beginner, they can be intimidating due to their small size and their lack of familiarity.  But with a little instruction from someone with experience, anyone can learn.  For example, there are many groups of schoolchildren across the country who are monitoring water quality using aquatic invertebrates.  There are many resources available to aid in identifying them, as well.  A good list of resources can be found in the Links section of this page.  You can also find images of aquatic invertebrates to help in identification in the Construct a key section.

One disadvantage of aquatic invertebrate monitoring is that it does not always tell us the source or type of pollution present.  Invertebrate sampling is often done in conjunction with simple sampling of stream habitat.  A good source of information on stream monitoring, especially for farmers, is the Monitoring Toolbox, produced by LSP.