A Limnology Study of Drainage Ditches

by Therese Clark

Notes for the teacher:

Required of students:

Students are required to chemically test the water, observe microscopic organisms in the classroom and screen the grab sample for macroinvertebrates.

Preparation time:

• 1 class period for learning how to use various test kits.
• 1 class period for learning how to use a microscope.
• 1 class period for identifying macroinvertebrates.

Class time needed:

Since these activities are part of an ongoing project, information from these various tests can be used throughout the curriculum. Chemical and biological data can be used during ecosystem studies, population studies, and invertebrate studies along with other topics.

Abstract:

Studying populations of macroinvertebrates is an innovative activity/learning experience in the biological sciences that involves all students. Bottom samples collected provide material for sediment study and an opportunity to study a substrate of macroinvertebrates. Macroinvertebrates can be a key indicator of the biological integrity within a body of water. They can reveal the general water quality over an extended period of time since they are less mobile than vertebrates. The impact of nutrients and the effects of surface pollutants can be illustrated by the types of macroinvertebrates collected at the site. The types of organisms found are dependent on both the biotic and abiotic factors of the water source.

A limnological water study includes the chemical, biological and physical changes that take place in bodies of water. Chemical tests include pH, dissolved oxygen, conductivity, carbon dioxide, ammonia-nitrogen, nitrate/phosphate, alkalinity, silica, chlorides, sulfides, and hardness. These tests are used to detect any water pollution at the site. Tests such as dissolved oxygen and pH can be used on their own as excellent water quality parameters of a site if funds are limited.

This project accomplishes the following goals:

1. it promotes hands-on education and critical thinking skills about water quality and its impact on living things
2. it documents changes in the benthic community
3. it involves students, faculty, and parents as biomonitors
4. it educates participants about drainage ditch ecology and the diversity of small life forms
5. it promotes an understanding of water quality protection and environmental stewardship.

This activity/project allows our students to investigate the interrelationships of the various science courses taken in high school. This study encourages students that are afraid of science to become involved and enjoy the fun. Students find a niche in the various opportunities offered from this study, such as collecting samples, testing samples, recording data, graphing data, photographing the sites and collected samples, and presenting results.

Background:

What question does this activity help students to answer?

Macroinvertebrates can tell students about the chemical and biological factors of a body of water. The types of macroinvertebrates illustrate the nutrient/organic enrichment and the effects of toxic contamination on a body of water. This activity is designed to integrate chemistry and biology. Chemical tests performed at the water site along with biological grab samples can show the students the relationship between these two sciences.

Project

Materials Needed:

Test kits for the following water quality factors:

• Dissolved oxygen*
• pH*
• Alkalinity
• Carbon dioxide
• Ammonia-nitrogen
• Chlorides
• Hardness
• Nitrate/Phosphate
• Silica
• Sulfides
• Grab Sampler
• Various screen sizes

*these two tests can give an accurate reading for water quality

Test kits and grab sampler can be purchased from LaMotte Company, PO Box 329, Chestertown, Maryland 21620.

Activity

1. Assign the following tasks to student teams before collecting the water sample:
1. Sample collection - one team

   This team is responsible for correctly retrieving the water sample. The sample should be taken at least one foot below the surface of the water. It should be free of any foreign matter. Water samples can be obtained by using any type of container, and can be taken by a bucket grab or taken at the water's edge.
    

2. Sample testing - one team/test

   Each team is responsible for following the directions for the test they are performing. The following tests must be made at the time of sampling: dissolved oxygen, pH, sulfide, and carbon dioxide. There is no special treatment or time limitation for the following tests: chlorides, silica and hardness. If the sample is refrigerated, the alkalinity test can be performed within 24 hours. Nitrates and phosphates can be delayed; directions can be found with the test kit. Test kit directions can be retyped and laminated so that these can be taken out to do the field testing.
   

3. Data recording - one team

   Graphing the data requires this team to express the information so that changes occurring over time can be documented. These graphs provide an analytical look at the various chemical factors and their changes seasonally and from human impact.
   

4. Data graphing - one team

   Graphing the data requires this team to express the information so that changes occurring over time can be documented. These graphs provide an analytical look at the various chemical factors and their changes seasonally and from human impact.
   

5. Site description/photographs - one team

   A site description should include the following: water color, water depth, turbidity , water odor, wind speed, wind direction, present weather, amount of rainfall since last testing and days since last rainfall. Photographs can show types and amounts of vegetation around the site.
   

6. Sample description/photographs - one team

   This team must screen the grab sample and perform a sediment sample description (size of sediments and possible composition) and determine the amounts and types of macroinvertebrates found. After the sample is screened, portions of the sample can be analyzed using a stereoscope or a magnifier to find macroinvertebrates. Samples should be kept moist during this examination period so as to not stress any macroinvertebrates. Insect larvae and various types of mollusks are popular in our samples. Grab samples may be refrigerated for further study. It is important that samples are moist while being refrigerated. The moisture will prevent dessication.
   

7. Presentation of results - a member from each team

   A backboard with the results of each team along with photographs is a good way to exhibit the teamwork developed by your classes during this project. It provides closure and allows the team to summarize and analyze their results. A written report compiled by this team can be published to record the results of their testing.

2. Establish a regular monitoring pattern. This pattern can be weekly, monthly or whatever time schedule best fits your curriculum. Samples should be taken at the same time of day. This pattern will allow for more consistent measurement.

3. Be sure the work load is evenly distributed. These tests and samples can be easily done in an hour if everyone is working. Small amounts of a benthic sample can give an accurate cross-section of macroinvertebrate populations. Too much benthic sample can be overwhelming.

Method of Assessment/Evaluation

1. Students should design a form sheet that will list all the items to be tested and a space to record the results. These sheets should be easy to follow and read by other students. A good evaluation of this process is to ask students from another class to use the sheet.

2. Test kit instructions should be followed accurately and completely. A simple checklist will inform the student of any errors made during a practice session. Cooperative learning practices are very usable at this stage since students can become evaluators for other students performing the tests. Having several monitors performing the same test will also give an average of readings instead of a single reading.

3. Observations of test kit results should be recorded accurately. Measurements should be recorded in the correct scale. Any averages in measurements should be averaged correctly. This step is also a form of cooperative learning since opinions can be taken and instrument readings can be checked by other students.

4. The proper screening of samples can be evaluated by observing the sediments found in each screen. Samples larger in size than the screen size will be trapped in the screen. Sample sizes can be measured and an average calculated.

5. Examination of sediment samples and macroinvertebrates under a magnifier/stereoscope should include measurement size, composition of sediment, and the proper identification of the macroinvertebrates.

6. Assessing the proper use of an identification key can be done by using the components of the key as clues and each choice takes the students to the next station. Each station offers additional clues and choices. Finding the correct identification of the benthic organism is the goal of this activity.
   

Extensions/Reinforcements/Additional Ideas:

1. Enlarging the print on the instructions sheets and the identification keys and then laminating the sheets make convenient reference sheets for field use.

2. A multiple choice response for certain site descriptions will limit the number of responses and increase the accuracy of your records. For example: Water odor a) none, b) fishy, c) sewage, d) other.

3. Use photo album to keep photographs for establishing habitat characteristics and documenting seasonal changes. The photographs along with the site description will allow the students to see the changes that occur not only naturally, but also from human impact.

4. Use small rulers that can be placed on the stage of a stereoscope when measuring the benthic organisms. This will make the organism much easier to accurately measure.

Fellows Collection Index

1996 AE Collection Index

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