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What is an Ecosystem?
Now that your students have an understanding of the Hudson River's geography and the watershed that feeds it, it is important to teach them the concept of an ecosystem. Ecosystems are defined units of study with boundaries that are often chosen for convenience. The connections between ecosystems are so strong that some ecologists argue that all life on Earth is held in a single ecosystem-the biosphere, with humans as the dominant species. However ecologists usually find it convenient to study smaller subunits and then conceptualize how the whole is put together. Here students will learn about the Hudson River Ecosystem. The Hudson's ecosystem is connected by the streams, rainfall, runoff and seepage to the forest, atmosphere, and groundwater systems that are in its watershed. This is lifted from the IES strategic plan- permission to use needed.
Lesson 1- Hudson Food Webs
Once students have a sense of what components make up an ecosystem, they need to investigate what lives in the river. Using online visuals and a reading as research tools, students view plankton under a microscope and then use data to explore the changes that have taken place in the Hudson's food webs after the arrival of the zebra mussel. Images are provided to help students identify different types of plankton. The answer key is for the student calculations on the summary worksheet, where students compare percent changes in various population groups and explain how the pre and post-invasion food webs differ.
Lesson 2- Biomanipulation
Students set up mini-ecosystems in a jar or aquaria with phytoplankton, and then add different species of zooplankton. Over time, students will be able to observe a response in turbidity and the algal population. While this lesson also touches upon eutrophication, it can be used as an extension lab activity after the Hudson Food Webs lesson.
Lesson 3- An Aquatic Ecosystem
During this outdoor activity, students will use inquiry to discover living organisms in their local aquatic ecosystem. Ask students to read the Organisms in a Pond reading to understand the different kinds or organisms that live in a pond ecosystem. Use the pond exploration worksheet to guide students at a local pond to collect organisms for later identification in the lab. This lesson can be adapted to a stream if a pond is inaccessible. After returning to the classroom, students complete a macroinvertebrate survey to analyze the results of their collections and create a representative food web. Use the pond and stream invertebrate briefs to learn more about the different types of animals. Use the key to identify the organisms you and your students found in their stream or pond. Alternatively, you can give your students just the pictures of common pond and stream organisms and have them try to identify what they collected by comparing them with the pictures.
Lesson 4- Ecosystem Disturbance
Using data from Hubbard Brook Experimental Forest, students analyze the changes that take place in an ecosystem after deforestation. This lesson is expanded on at: http://tiee.ecoed.net in the "Ecology of Disturbance" activity by Charlene D'Avanzo, School of Natural Sciences, Hampshire College. Students should have some familiarity with ecological concepts such as aboveground primary production and the nitrogen cycle. Use the next lesson to introduce the Nitrogen Cycle.
Lesson 5- The Nitrogen Cycle
Learning about the different forms of nitrogen is a daunting challenge, with many students simply memorizing chemical formulas and terms they don't understand. This lesson strives to deepen students' knowledge by beginning with a nitrogen cycle 'game', similar to that often used in the water cycle (this game is modified from the University Corporation for Atmospheric Research, www.windows.ucar.edu ). During the game, students are introduced to the various forms of nitrogen in both disturbed and undisturbed settings. Next, students design and implement a long-term experiment that increases nitrogen concentrations in either an aquatic or terrestrial ecosystem. Two versions of the lab sheet are provided; version 1 offering a more open-ended format for advanced students, while version 2 provides more structure. For homework, students can use the Nitrogen Cycle Visuals as well as the internet to answer the questions on the computer assignment.
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