As I prepared students for field trips to a stream, I knew that I needed a simple reading selection to explain the biotic index. Unfortunately, I had trouble finding one! At the same time, I was working on selections for a problem and solution text structure activity. I realized that the story of the biotic index is a great topic for problem and solution--and if students are going on a stream study field trip, it is a topic that they can live and experience.
You can get a formatted version of this text along with student-ready activities here: Problem and Solution Texts for Teaching Text Structure.
Reading level: Fifth grade, lexile 860
For more advice on leading stream studies, check out this blog post: Leading Stream Studies for Kids.
--------------------------------------------------------------------------------------------------------------------------
Does this stream look polluted?
It’s important to know if a stream is polluted. When scientists know that a waterway has poor water quality, they can try to find the source of the pollution. Many scientists work to keep track of
pollution levels in creeks, streams, and rivers.
But it’s not always easy to find pollution. Some pollutants, like sewage, dirt, and certain chemicals, are easy to see. But other pollutants, like nitrogen and phosphorus, are less obvious. Making the matter even more difficult is the fact that pollution might not be visible every day. A chemical pollutant might be present in a stream one day, but absent the next.
Using chemical tests to find pollution can become expensive. Different pollutants are found with different tests. To get a good picture of the overall water quality, a scientist would need many test kits. Luckily, scientists have developed an easy and inexpensive way to see if a stream has good water quality—the biotic index.
Pollution Tolerant or Pollution Sensitive?
“Biotic” refers to living things. So the biotic index is a survey of living things in the waterway. While all creatures are affected by pollution, some are more sensitive than others. By looking at which creatures are in a creek, a scientist can make a good guess about the water quality of the creek.
The creatures on the biotic index share some common traits. They are all invertebrates, which means that they don’t have a backbone. They all have short life spans, usually under a year. They are all large enough to see without a magnifying glass. While some of them might be familiar, like crayfish, others are less well known, like caddisfly larva and isopods.
But the creatures have many differences. Stonefly larva, mayfly larva, and crayfish are all sensitive to pollution. This means that they would probably not be found in polluted water. On the other hand, leeches and gilled snails can tolerate pollution. These creatures may be found in polluted water. Of course, just finding a leech does not mean that a waterway is polluted. To carry out a full biotic index, a volunteer counts how many different kinds of creatures are found, and in what numbers.
A biotic index is easy to use. In fact, people who are not scientists can quickly learn how to identify stream creatures and record data. And this is good news, because, with miles and miles of streams and creeks, many volunteers are needed to keep tabs on water quality.
Look at the stream picture again. Suppose that you found three mayfly nymphs, two crayfish, and five stonefly larva in the water. What guess might you make about the water quality?
Keeping waterways healthy is an important task. With the help of the biotic index, everyone has an easy way to find out the quality of the water in a creek.
by Emily Kissner
©2024. Permission granted for single classroom use. This text may not be resold or included in any products offered for sale.
No comments:
Post a Comment