Invertebrate Data Collection Protocols
Stream Invertebrate Survey
An additional method for assessing the quality of a stream, river, or lake is through an examination of the life forms which live in it. Small animals, known as invertebrates because they have no internal skeleton and are related to the insects, crustaceans, worms, clams, and snails are often used as indicators of water quality. The approach which follows is a simplified method for getting an idea of the life forms in a stream and evaluating what these life forms can tell us about water quality.
Simplified Invertebrate Sampling Procedure
This method is useful if you are interested in a quick look at invertebrates in a stream. However, many organisms, including those that live deeper in the stream bed are overlooked. Choose a shallow riffle area with moderately fast flow and stones about 5 to 25 cm in diameter. Pick up several rocks and brush or rub the surfaces into a small bucket of water. Pick up the invertebrates carefully with a spoon or eye dropper and examine them. Use the Identification Chart in Appendix 1 to identify them and sort them into Pollution Tolerance Categories. Return the invertebrates,unharmed, to the stream. If most organisms you examine are pollution intolerant, your site probably is healthy. If there are very few pollution intolerant organisms, your site probably has some problems. A more complete sampling procedure is better for answering these questions.
Collect the Samples
Approach the first sampling area from downstream. Do not disturb the sampling area by walking in it or upstream of it. Place a Surber sampler, D-net, or simple net on the downstream edge of the sample area, so the opening faces into the flow. Push the frame a little way into the stream substrate. Brush all stones and debris 5 cm or larger within the
sampling area. Pick up a stone, hold it under water in front of the net and rub it gently with a brush or your hands. The loosened invertebrates will be swept into the net. Place the cleaned rocks outside the sampling area. Starting at the upstream end, gently agitate the streambed to a depth of 2 to 5 cm to loosen any remaining invertebrates.
Take the net to stream bank and turn it inside out in a bucket, half full of cool stream water. Transfer the invertebrates and debris into the bucket by carefully rinsing or shaking the net, then scraping it with a plastic spoon. Gently pick off organisms that cling to the net. Handle them carefully to avoid injuring them and keep them in the shade. Make sure the entire sample is in the bucket. Check larger pieces of debris in the bucket for bugs, then discard the debris.
Take two more samples and combine them with the first one. Analyse and report the results for the three combined samples. Invertebrates are not distributed evenly in streams, so, even at one station, you can expect to find some samples with very few invertebrates and others with many.
Identify and Count the Invertebrates A .) Sort the sample:
Pour some invertebrates from the bucket into a shallow
tray of water, preferably one with a white background. Fill the compartments of two ice cube trays with stream water. Handle the
invertebrates gently with tweezers, spoons, or eye droppers. Many will be active. Sort them into
separate compartments of the ice cube trays based on obvious differences in appearance.
Continue sorting until there are no invertebrates left in the bucket.
B.) Identify the invertebrates:
Use the an Invertebrate Field Key or Identification Chart to identify the organisms. Figure
5 illustrates the terms for various parts of their bodies. Most simple field charts identify only
major taxa or groups (classes, orders, families), not species. There are thousands of species and
most are difficult to identify. Taxon (plural taxa) is a general term referring to identifiable groups
like species, genera, families, orders, or classes. Two different looking organisms usually are
different taxa, although sometimes they are two life stages (e.g., larva, pupa) of the same
species. Within each broad taxonomic group, distinguish as many kinds of organisms as possible,
based on appearance. For example, there may be a few obvious types of caddisflies in a sample.
You do not need to name them, just recognize them as different. Use a hand lens (lOX
magnification) or magnifying glass to examine small organisms.
Count the invertebrates:
Record the total numbers counted and the number of identifiable taxa for each broad
taxonomic group on the Invertebrate Survey Field Data Sheet. Record the most abundant or
predominant taxon. Return the organisms to the area of the stream you sampled. Occasionally, you may
want to preserve a sample for future analysis or teaching, but we usually do not recommend it.
To prepare a sample, remove as much water as possible and add concentrated isopropyl or
ethyl alcohol to make a 70% solution of alcohol in water. Transfer the sample to a labelled bottle.
You can use a tray marked with a grid on it if you find high numbers of one type of organism in
the sample. First, remove all the different looking invertebrates, then spread the remaining ones
on the gridded tray. Examine a few grid squares and count the average number of individuals
per square. Multiply the average number per square by the total number of squares on the tray to
get the total number.
Many stream invertebrates are aquatic stages in the life cycles of insects. The mosquito, for example, spends a great deal of its life in water. People may often not associate the aquatic stages, nymphs and larvae, with the flying, non-aquatic adults. The diagram above illustrates some of the body parts which may be referred to in field guides to aquatic invertebrates.
Collecting, Reporting, and Evaluating Information from Stream Invertebrate Surveys.
Invertebrate surveys detect moderate to severe degradation of stream habitat. Table 2 lists common responses to pollution. For example, organic pollution usually results in low numbers of pollution-sensitive organisms and high numbers of a few species of pollution-tolerant species.
Information collected from several locations in the area provides baseline data that can help you identify habitat concerns and choose appropriate restoration projects. When you survey the same stations over several years, you can recognize changes in water quality. If the results of your invertebrate survey are inconclusive or suggest poor conditions, you may wish to examine habitat and water quality to find answers to the problem.
Before you react strongly to evidence of poor water quality, remember that your survey uses simplified versions of scientific techniques. Although the results of your tests usually are reliable, there are exceptions to any rule. Sometimes stream conditions appear abnormal, but are natural in a particular area . Make sure you have reliable background data to compare with data from problem sites.
| WARNING SIGN | PROBLEM | high diversity, lots of pollution sensitive invertebrates | no problem, good water quality |
| low diversity, high numbers, lots of scrapers and collectors | organic enrichment/pollution or lots of algal growth resulting from nutrient enrichment |
| high diversity and low numbers; or no insects, but the stream appears clean | toxic pollution (e.g. chlorine, acids, heavy metals, pesticides, or, another severe problem of unknown origin |
| reduced numbers of all types of invertebrates | physical problem (e.g., downstream of dam, sediment from erosion) or somctimes streams are unproductive for natural reasons (glacier-fed streams, spring-fed streams) |
Assess the Water Quality
Pollution Tolerance Index: The Identification Chart and Field Data Sheet categorize the broad taxonomic groups according to their tolerance of organic pollution. Category 1 includes pollution sensitive species found only in high quality water. Category 2 includes species that tolerate some pollution and are found in high or fair quality water. Category 3 includes pollution tolerant species that are found in a wide range of conditions.
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