Name______Class______Date______
Exploration LabFIELD ACTIVITY
Inferring Water Quality
A healthy stream that is free of pollutants and human disturbance provides a good habitat for a variety of invertebrate populations, the most common of which are insect larvae and nymphs. Various aquatic worms and small crustaceans, such as sow bugs, scuds, and crayfish, also are abundant in fresh water.
The health of a stream can be determined by testing its pH and its levels of dissolved oxygen and nitrogen compounds. However, these chemical tests require costly test kits and equipment. A less expensive method for gauging water quality is sampling the living water-quality indicators—populations of aquatic invertebrates that normally live there. Scientists divide these indicators into three major groups according to their sensitivity to pollution. You can see some of these organisms in Figure 1. If certain species are missing, there is a good chance that the stream has suffered some form of pollution. In this activity, you will monitor a local stream for living water-quality indicators.
FIGURE 1: LIVING WATER QUALITY INDICATORS
OBJECTIVES
Identifyliving water-quality indicators in samples of water.
Calculate Total Stream Quality.
Infer stream quality from collected data.
Evaluate methods of determining water quality.
MATERIALS
•hand lens
•macro-invertebrate identification key or pond life field guides
Inferring Water Quality continued
Procedure
1.Research some of the living water-quality organisms. What specific characteristics do these organisms have to make them indicators of good water?
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2.If the measured pH and dissolved-oxygen levels for a stream were in the normal range, which groups of macro-invertebrates would probably be present?
______
______
______
3.Select a portion of a rapidly moving body of water to conduct your study. For best results, find a place where the water is flowing over a rocky bottom. If the stream bottom in your area is not rocky, try to find sections of the stream that are clear and flowing.
4.Overturn some rocks upstream from where you intend to sample to dislodge those species using rocks as a refuge. Stir the bottom of the sample area with a stick or your feet to dislodge bottom dwellers. The water may be very cloudy at this point.
5.After the water runs clear, draw the plankton net through the water by the end of the cord. Tiny floating organisms will be funneled through the net into the attached bottle. Take the plankton net to shore, and separate species by placing each species into an egg carton compartment filled with water. Be careful not to drop any of the organisms.
6.Use the identification key or field guides to identify and count the number of each species collected. Record the count for each species in Table 1. Return the collected specimens to the stream.
Analysis
1.Organizing Data The letters A, B, or C are used in Table 1 to represent the numbers of organisms of each species collected in the field activity. A = 1 to9, B = 10 to 99, C = 100 or more. Record the appropriate letter designation beside the name of each species in the table to indicate the relative a bundance. Place a null sign, Ø, in the space next to the species name if no species were found.
2.Organizing Data Count the combined total of letters noted in the Most Sensitive Species column. (Do not count the null signs.) This sum is the Total Species Present (TSP). Record the total in the space for the TSP. Repeat this process for the Moderately Sensitive Species and the Tolerant Species.
Inferring Water Quality continued
TABLE 1: STREAM SURVEY DATA
Most Sensitive Species / Moderately Sensitive Species / Tolerant SpeciesName / Amount / Letter / Name / Amount / Letter / Name / Amount / Letter
caddisfly larvae / atherix / aquatic worms
gilled snails / alderfly larvae / blackfly larvae
hellgrammite / beetle larvae / leeches
mayfly nymphs / clams / midge larvae
rifle beetles / crane fly larvae / pouch snails
stonefly nymphs / crayfish
water penny larvae / damselfly nymphs
dragonfly nymphs
scuds
sowbugs
fishfly larvae
Total Species Present (TSP) / Total Species Present (TSP) / Total Species Present (TSP)
Index Factor / TSPX3 / TSPX2 / TSPX1
Index Value / + / +
Total value / =
Stream Quality / Poor (TV below 11) / Fair (TV 11-16) / Good (TV 17-22) / Excellent (TV over 22)
3.Examining the Data Multiply the TSP for each column by the specified Index Factor (IF) to get the Index Value for each species. Notice that the Most Sensitive column has an IF of 3, the Moderately Sensitive column has an IF of 2,and the Tolerant column has an IF of 1. Add the three Index Values together to get the Total Value. Stream quality is determined by the Total Value. According to your calculations, is your stream quality poor, fair, good, or excellent?
______
4.Analyzing Data The presence of a few organisms from the most sensitive or moderately sensitive category indicates higher water quality. Why do you think that the stream quality formulation is not based on the actual population number of each species present?
______
______
______
______
Inferring Water Quality continued
5.Identifying and Recognizing Patterns Why is the Index Value higher for the more sensitive species regardless of the count for each species?
______
______
______
______
Conclusions
6.Evaluating Results Compare your data with data from another test site on the same stream. If the Total Value numbers of the sites differ, which species groups created the variation?
______
______
______
- Evaluating Methods Explain how collecting data for more than one site and averaging the resulting Total Values is a more valid measurement of stream quality than individual Total Values. What kind of information would be missed by averaging the data?
______
______
______
Extension
1.Designing Experiments Observe and keep representative organisms from each of the sensitivity columns in small aquariums for classroom observation. Note the habitat preferences and behavior of each. Compare their movement, anatomy, and coloration.
2.Designing Experiments How do you think samplings taken from a muddy bottom stream with marginal flow would compare to the results of this lab? Design an experiment to find out. With teacher permission, conduct your experiment and report your results to the class.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Environmental Science1Aquatic Ecosystems
TEACHER RESOURCE PAGE
Exploration LabFIELD ACTIVITY
Inferring Water Quality
Teacher Notes
TIME REQUIRED Two 45-minute periods
SKILLS ACQUIRED
Collecting data
Classifying
Organizing and analyzing data
Identifying and recognizing patterns
Predicting
Designing experiments
RATING
Teacher Prep–3
Student Set-Up–2
Concept Level–3
Clean Up–2
THE SCIENTIFIC METHOD
Make Observations Students gather data about water quality indicators in Procedure step 1.
Analyze Results Students organize data in Analysis questions 1 and 2. They analyze the data in questions 3–5.
Draw Conclusions Students draw conclusions and evaluate their methods in Conclusions questions 6 and 7.
MATERIALS
Try to have samples of the organisms in the classroom prior to fieldwork so that students can gain skills in identifying them. The plankton net called for in this activity consists of a cone-shaped net attached to a collecting bottle at the narrow end. The other end of the net is attached to a long cord. Alternate materials include a dip net or a seine net, which is a large, expensive mesh net that resembles a tennis court net. To use it a person wades out into the water and pulls on the end ropes to bring the catch to shore.
A simple dip net can be constructed by tightly taping an ordinary kitchen strainer to a 1-meter long (about 3-foot-long) long pole or old broomstick handle.
Small pocket notebooks for recording data and other observations, tote bags to carry supplies, and clipboards for holding papers are useful.
Inferring Water Quality continued
SAFETY CAUTIONS
Encourage students to wear comfortable, seasonal clothing. Old clothes and water proof shoes or boots are advisable when working in aquatic habitats. Tells students to watch out for slippery places on the rocks.
Be sure to check for any known student allergies to native plants students might encounter. Make sure students know how to identify poison ivy, poison oak, sumac, and other types of problem vegetation. Tell them to use insect repellent.
Warn students to stay away from areas around drain pipes and drainage ditches. These sites may be contaminated and are potentially hazardous.
DISPOSAL
Before leaving the stream or river, have students return all collected aquatic organisms to the water.
TIPS AND TRICKS
Groups of 4 to 6 students work well for this activity. Students should not work on out door field activities alone and should inform an adult of where they plan to collect samples.
Students probably need reference materials, such as guides to pond life, to answer question 1 in the Procedure. Also they might prepare for the lab by doing library and Internet research (if available) on the use of macro-invertebrates to monitor water quality.
Sample data is provided in the table on page 64. The letters do not factor into quality formulation other than to indicate if a particular species is present or absent. The values will vary depending on the species present during the field activity.
The Total Value calculation could be used for comparing different sites on one stream or to compare various streams.
The most sensitive organisms are considered “indicator species.” Their presence means that water quality conditions are high enough for the moderately sensitive and tolerant species to thrive.
If possible, visit the same freshwater area in different seasons, and have students observe any differences in the composition of the populations.
Name______Class______Date______
Exploration LabFIELD ACTIVITY
Inferring Water Quality
A healthy stream that is free of pollutants and human disturbance provides a good habitat for a variety of invertebrate populations, the most common of which are insect larvae and nymphs. Various aquatic worms and small crustaceans, such as sow bugs, scuds, and crayfish, also are abundant in fresh water.
The health of a stream can be determined by testing its pH and its levels of dissolved oxygen and nitrogen compounds. However, these chemical tests require costly test kits and equipment. A less expensive method for gauging water quality is sampling the living water-quality indicators—populations of aquatic invertebrates that normally live there. Scientists divide these indicators into three major groups according to their sensitivity to pollution. You can see some of these organisms in Figure 1. If certain species are missing, there is a good chance that the stream has suffered some form of pollution. In this activity, you will monitor a local stream for living water-quality indicators.
FIGURE 1: LIVING WATER QUALITY INDICATORS
OBJECTIVES
Calculate Total Stream Quality.
Infer stream quality from collected data.
Identify living water-quality indicators in samples of water.
Evaluate methods of determining water quality.
MATERIALS
•hand lens
•macro-invertebrate identification key or pond life field guides
Name______Class______Date______
Inferring Water Quality continued
Procedure
1.Research some of the living water-quality organisms. What specific characteristics do these organisms have to make them indicators of good water?
Answers may vary. Sample answer: These species require a clean stream habitat
in order to survive and reproduce. Many species have sensitive gill structures __
that are easily damaged by pollutants.______
2.If the measured pH and dissolved-oxygen levels for a stream were in the normal range, which groups of macro-invertebrates would probably be present?
Sample answer: If the stream conditions were chemically sound, members from_
all sensitivity groups would be found. Many of the most sensitive species would_
be present to monitor the stream environment.______
3.Select a portion of a rapidly moving body of water to conduct your study. For best results, find a place where the water is flowing over a rocky bottom. If the stream bottom in your area is not rocky, try to find sections of the stream that are clear and flowing.
4.Overturn some rocks upstream from where you intend to sample to dislodge those species using rocks as a refuge. Stir the bottom of the sample area with a stick or your feet to dislodge bottom dwellers. The water may be very cloudy at this point.
5.After the water runs clear, draw the plankton net through the water by the end of the cord. Tiny floating organisms will be funneled through the net into the attached bottle. Take the plankton net to shore, and separate species by placing each species into an egg carton compartment filled with water. Be careful not to drop any of the organisms.
6.Use the identification key or field guides to identify and count the number of each species collected. Record the count for each species in Table 1. Return the collected specimens to the stream.
Analysis
1.Organizing Data The letters A, B, or C are used in Table 1 to represent the numbers of organisms of each species collected in the field activity. A = 1 to9, B = 10 to 99, C = 100 or more. Record the appropriate letter designation beside the name of each species in the table to indicate the relative abundance. Place a null sign, Ø, in the space next to the species name if no species were found.
2.Organizing Data Count the combined total of letters noted in the Most Sensitive Species column. (Do not count the null signs.) This sum is the Total Species Present (TSP). Record the total in the space for the TSP. Repeat this process for the Moderately Sensitive Species and the Tolerant Species.
Name______Class______Date______
Inferring Water Quality continued
TABLE 1: STREAM SURVEY DATA
Most Sensitive Species / Moderately Sensitive Species / Tolerant SpeciesName / Amount / Letter / Name / Amount / Letter / Name / Amount / Letter
caddisfly larvae / atherix / aquatic worms
gilled snails / alderfly larvae / blackfly larvae
hellgrammite / beetle larvae / leeches
mayfly nymphs / clams / midge larvae
rifle beetles / crane fly larvae / pouch snails
stonefly nymphs / crayfish
water penny larvae / damselfly nymphs
dragonfly nymphs
scuds
sowbugs
fishfly larvae
Total Species Present (TSP) / Total Species Present (TSP) / Total Species Present (TSP)
Index Factor / TSPX3 / TSPX2 / TSPX1
Index Value / + / +
Total value / =
Stream Quality / Poor (TV below 11) / Fair (TV 11-16) / Good (TV 17-22) / Excellent (TV over 22)
3.Examining the Data Multiply the TSP for each column by the specified Index Factor (IF) to get the Index Value for each species. Notice that the Most Sensitive column has an IF of 3, the Moderately Sensitive column has an IF of 2,and the Tolerant column has an IF of 1. Add the three Index Values together to get the Total Value. Stream quality is determined by the Total Value. According to your calculations, is your stream quality poor, fair, good, or excellent?
Answers may vary______
4.Analyzing Data The presence of a few organisms from the most sensitive or moderately sensitive category indicates higher water quality. Why do you think that the stream quality formulation is not based on the actual population number of each species present?
Sample answer: The sensitivity type of the aquatic species is a better indicator of
water quality than the population size because the mere presence of these species
regardless of number, indicates that the aquatic conditions are optimal for life._
Name______Class______Date______
Inferring Water Quality continued
5.Identifying and Recognizing Patterns Why is the Index Value higher for the more sensitive species regardless of the count for each species?
Sample answers: One might be conducting the study when the population______
number of a species is at an ebb (during its reproductive cycle) or, conversely,__
at its peak. The water quality may remain excellent throughout the ebb and flow
of the insect’s cycle.______
Conclusions
6.Evaluating Results Compare your data with data from another test site onthe same stream. If the Total Value numbers of the sites differ, which species groups created the variation?
Answers may vary, but the weight of the Index Factor for the most sensitive and
moderately sensitive species will change the Total Value numbers of the sites___
more dramatically than that of the tolerant species.______
7.Evaluating Methods Explain how collecting data for more than one site and averaging the resulting Total Values is a more valid measurement of stream quality than individual Total Values. What kind of information would be missed by averaging the data?
Averaging may be a valid method of measurement and may offer a more______
realistic Total Value because individual site measurements could have small____
errors in data collection. Calculating the Total Value for each site may help____
identify sources of pollution entering a site that averaging would miss______
Extension
1.Designing Experiments Observe and keep representative organisms from each of the sensitivity columns in small aquariums for classroom observation. Note the habitat preferences and behavior of each. Compare their movement, anatomy, and coloration.
2.Designing Experiments How do you think samplings taken from a muddy bottom stream with marginal flow would compare to the results of this lab? Design an experiment to find out. With teacher permission, conduct your experiment and report your results to the class.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Environmental Science1Aquatic Ecosystems