Stream Ecosystem Field Activity

Engage:

Outdoor Activity:  To engage students in the lesson they should have the opportunity to explore the stream and make observations about the habitat in and around the stream where sampling will take place. When planning this part of the lesson allow time for students to change into waders as well as travel to and from the stream.  Safety and stream conditions should be a priority.  If water levels are too high and the current too strong do not allow students in the stream.  It is important to err on the side of safety when making these decisions.

 If you do not have waders and the weather is warm enough students may enter the stream in old sneakers or water shoes.  If students are unable to enter the stream, bringing students to observe the site is still an important part of the lesson.  Students can still make observations of the streams and surrounding areas.  Students may sketch the site and fill out the “Habitat Data Sheet” provided by the Leaf Pack Network. A short hike along the stream bank may help students observe different microhabitats as well as terrestrial abiotic factors that might influence the stream biota (shade from trees, steepness of banks, etc).

Bring students to the stream, equipped with boots, kick nets, white dishpans and plastic spoons. Depending on the class size and number of boots, split students into two groups.  Each group will get 15-20 minutes to explore the stream with their kick nets.  At this time do not be concerned with identifying the critters that you find.  The goal of this exercise is to give the students the opportunity to experience the stream and the habitats in and around it.  Any unusual or interesting critters that are found should be brought back to the classroom for further identification and observation.

 To use a kick net, students should pair up with one student holding the net in the water with the opening facing upstream.  The other student stands in front of the net and kicks the substrate for about 1 minute, making sure to disturb the rocks and gravel on the bottom of the stream.  This dislodges the invertebrates that live in these areas and the current washes them into the net.  Lift the net and empty it into the plastic dishpan that has been filled with about two inches of water. 

 While one group is in the creek, the other group should be collecting data on the habitat around the creek (stream habitat data sheet). This is a good time to review the terms biotic and abiotic and for students to be thinking about their observations in these terms.  They should be answering and thinking about questions such as: What plant community dominates the creek bank? How steep is the land around the creek?  Are there a lot of rocks in the creek?  Can they pick out the pools and the riffles in the creek itself? 

As students are exploring the creek, water chemistry data from both the pool and riffle should be collected.  Handheld probes can be used to easily collect dissolved oxygen and temperature data in both the pool and riffle.  If time permits this can be done as a whole group or it can be done with just few students who are waiting for their turn to go in the water. Take three measurements of Dissolved oxygen, pH, air temperature, and water temperature at each microhabitat to calculate an average. Depending on the location of the pool and riffles, the flow of the water, or recent rainfall events you may or may not see differences in these data.  This is also the time to be collecting leaf packs or kick net samples for students to analyze back in the classroom/lab (see protocol for instructions).

Explore:

Classroom preparation:  The white dishpans should be set up with at least one dishpan for every two students.  Along with a dishpan each pair of students should have a smaller white container to place macroinvertebrates into, 3- 5 petri dishes or white yogurt cups to sort macroinvertebrates into, and two plastic spoons.  It is helpful if you fill all of these containers with 1-2 inches of water before the program begins. 

Lab Activity:  As students enter the room, pair them up and have them stand across the table from each other with the dishpan and other sorting materials between them.

Before samples are handed out to students the instructor should spend about 15 minutes reviewing with students how the experiment was set up. Using individual whiteboards (or on the classroom board) students should be asked to think about and write down questions that might be answered by exploring their samples (this should be a review from the PowerPoint pre-lesson).  The guiding questions of this study are:

1) “Do different macroinvertebrates live in pools versus riffles?” 

2) “What are the characteristics of these microhabitats that might affect what lives there?”   

Students should be able to name biotic vs. abiotic factors that they observed in the stream.Abiotic factors include:  water temperature, dissolved oxygen, speed of the water, and substrate.  If students mention temperature, probe students further and ask how does one portion of the stream become cooler then another?  Trees and shade are one way that water is cooled in a stream; this is an important example of how a biotic factor (trees) may affect an abiotic condition (temperature) and should be highlighted to the students.  Keeping your list of biotic and abiotic factors on the board or chart paper is helpful for use later during the closing discussion. 

Explain to students the procedure that will take place to collect data from their samples.  Students should be reminded that methods of collecting data are extremely important in any experiment.  Detailed protocols are used to reduce the amount of variability and human error in data collection. (Note: If collecting data from leaf packs, it is very important not to mix up materials from different leaf packs, our final numbers of organisms will be “per leaf pack” (i.e. 25 mayflies per leaf pack), so we need to keep data from different leaf packs separate.)  For this experiment data collection will take place in three major steps: 1) Pick, 2) Sort/Identify, and 3) Count.  Review each step with the students.  Pass out the samples making sure half of the class gets a sample from the riffle packs and half from the pool packs.  Distribute the samples so that each station has an equal amount (e.g., ¼ of the leaf pack or kick net sample at each station).  Also add some of water to the students dishpans.  It is extremely important that students immediately write down “pool” or “riffle” on their data sheet (can use the “Team Data Sheet: Macroinvertebrate Data” found in the Stroud leaf pack network data sheets below), as well as the sample number they are working on.

1)    PICK  – Students will get about 15 minutes to pick through their sample (in the dishpan) using the plastic spoons at their station.  During this time students should simply pick out as many living things as possible from their dishpan.  We are not worried about identifying the organisms at this time – there will be time for that later.  The goal is to get all of the macroinvertebrates out of the pans into the medium sized white container.  Depending on what is being found this may be a difficult task for some students. Having the goal of completing this task in 15 minutes helps to keep students focused.  Having a large timer projected on a screen and reminders of how much time is left also helps students to focus on the task at hand. If students do not finish in the allotted time give them a few more minutes to finish going through all the leaf packs.  If some groups finish early, and there is still leaf pack material that needs to be picked through feel free to give them more.  Make sure to give them a new data sheet and sorting tray with their new sample as to not mix up data between samples.

2)    SORT/IDENTIFY  - Remove the large dishpans from the table.  Students should be left with their medium size dishpans containing the organisms they found and 3-5 petri dishes or yogurt containers.  Pass out identification cards, sorting sheets, field guide and any other identification resources (the NYS DEC provides video identification of many of the common macroinvertebrates).  Students should sort the animals from the medium size white containers to the smaller containers based on taxa.  (Taxa are listed on their data sheets along with some pictures.)  Students should be able to identify one or two distinguishing characteristics of each taxa (i.e. mayflies generally have 3 tails, stoneflies generally have 2 tails, etc.).

3)    COUNT  – Have students tally the number of each taxa onto their data sheets. As one large group it is now time to tally all the data for the pools and then the riffles.  You should end up with two numbers for each taxa (the number in the pool and the number in the riffle) as well as a total number of individuals for the pool vs. the riffle, and a count of the number of different taxa in the pool vs. the riffle.

(Methods for counting the number of adult insects emerging from the stream are described in Lesson 6)

After students have tallied up their macroinvertebrate counts, and discussed their results, they should fill out the Venn Diagram exercise as a wrap up to their field trip (See Evaluate section below).

Explain:

Understanding the difference between biotic and abiotic is an important concept when learning about interactions within ecosystems.  Basic definition of the terms can be explained to students as follows:

• Abiotic– something that not alive and was never living such as water, rocks, and air.  Abiotic factors in an ecosystem include temperature and light.
• Biotic – refers to anything that is alive or once was alive.  Obvious examples include trees and animals, but examples that might become confusing to students include dead leaves, wood, paper, bones, and feathers.

Abiotic and biotic factors are constantly interacting with each other to determine the distribution and abundance of living things in an ecosystem.  Students are often easily able to give examples of how abiotic factors influence the biota of an area.  For example, when discussing stream ecosystems students will be able to articulate that the amount of water or temperature might affect the types of fish that live in a stream.  They are also usually able to identify biotic interactions such as predator-prey relationships.   It is much more difficult for students to identify examples of how biotic factors influence the abiotic.  Throughout this lesson it is important to identify and discuss all types of interactions when appropriate.  Ask students to come up with their own examples of these interactions.  Help them think about the observations they made at the stream in biotic and abiotic terms and how these observations are connected.  Some examples that you might want to highlight include:

Abiotic affecting Biotic:

• The speed of water in each microhabitat affects the types of macroinvertebrates that live there.  What physical adaptations do the invertebrates have that helps them “hold on” in fast moving water?
• Lower Dissolved Oxygen levels in pools might affect the types of macroinvertebrates that live there. What physical adaptations do the inverts have that allows them to breath in water with low dissolved oxygen levels?

Biotic affecting Biotic:

• Many types of fish eat macroinvertebrates.  How does the amount or type of macroinvertebrate affect the fish population?  How might the fish affect the macroinvertebrate population?
• Some taxa of macroinvertebrates eat dead and decaying leaves, how might the terrestrial plant community affect the macroinvertebrate population in the stream?
• Emerging adult macroinvertebrates are an important food source for many forest dwelling animals such as birds and spiders.  How would timing of emergence affect the local migratory bird population?

 Biotic affecting Abiotic:

• Trees living next to the creek produce shade that is affecting the temperature of the water.  What would happen to the water temperature if all the trees along the creek were cut down?
• Submerged plants or algae in a stream might influence the amount of dissolved oxygen in the water. How do plants affect the amount of dissolved oxygen in the water?

Evaluate

Have students create a Venn diagram for the pool and riffle microhabitats using the Lesson 3 Venn Diagram worksheet.  Students should include in their diagram observations that they made in the field as well as organism that were collected in the leaf packs.  Specifically, ask students to identify which of these characteristics are biotic and which are abiotic.  You may want to have students distinguish between the abiotic and biotic by writing the words in different color pens.

Extend

Have students create a food chain/web based on what they saw while they were in the stream.  This can be done together on the main classroom board or in small groups.  Make sure students include connection to the terrestrial ecosystem as well as microorganisms that they probably can’t see.  Other smaller organisms from a water sample can also be seen under a dissecting scope (daphnia, copepods, etc.) (Leaf pack users: If compound microscopes are available, scrape some biofilm off of the leaves in the leaf pack and have students observe it under the microscope.)