Introduction

The following are a series of prototype investigations, developed for the Earth Curriculum project, that explore Biosphere 2 as a model for the interconnected physical, chemical, biological, and human systems of the Earth. The goal of the investigations is to highlight important aspects of how the Earth works by studying its key systems at a smaller scale, through interaction with real and real-time sensor data from the Biosphere 2 facility.

The major insight to be gained through the investigations is that physical, chemical, and biological processes interact with one another through a complicated network of relationships in nature. These interactions produce changes in the behavior of natural systems -- to temperature, relative humidity, carbon dioxide and other variables -- that feed back upon one another and produce additional changes to the system. At the planetary scale, changes in these parameters are produced by interactions and feedbacks between the global water cycle, carbon cycle, and Earth's energy balance.

Insights/Curriculum Highlights:

System behavior is related to underlying system structure.

Changes in light, temperature, relative humidity and CO2 in Biosphere 2 are tied together through a complicated network of interactions between physical, chemical and biological processes, which themselves are mediated by the physical and chemical properties of air, soils, plants, and water.

Understanding how this network of interactions is structured, and representing them with concept maps and models, can help explain the basic patterns of variation among these variables.

This collection of interacting biological, chemical and physical processes are often thought of/grouped together into separate, interacting systems: the hydrological cycle, carbon cycle, and energy balance. In Biosphere 2 and the Earth, these cycles are closely linked together.

Differences in the behavior of these variables inside Biosphere 2 and outside in the Earth can be tied to differences in the way that the cycles are structured within the two systems (e.g., the relative sizes of atmosphere, ocean, and biosphere, as well as the use of mechanical systems to simulate natural ones).

Like Biosphere 2, "Biosphere 1" (the Earth) is an energetically open, materially closed system. It does not, on average, gain or lose any materials.

Thinking skills / Pedagogy Highlights:

Making connections between data sets and the underlying patterns of interactions that produce their variance through time.

Thinking about four data parameters simultaneously.

Using previously-learned content knowledge (e.g., the temperature dependence of the air's ability to hold water; heat capacities of air, soil and water) to explain the connections between four variables (light, temperature, relative humidity and carbon dioxide).

Creating and representing mental models of the underlying system interactions in words and in concept maps.

Learning formal systems thinking concepts and basic software operations in Stella II environment.

Using formal systems thinking concepts to build, in Stella II, qualitative models of interactions and feedbacks inside Biosphere 2.

Thinking about similar sets of processes occurring over different scales of space and time, and in systems that are structured differently.

Using qualitative models to explain system behavior in Biospheres 1 and 2.

Directed investigations: Part 1: How are light, temperature, relative humidity and carbon dioxide connected?

Background materials:

The Biosphere 2 system: An introduction and overview

Introduction to Concept Maps

Data resources (in the Data Harvester):

CO2, light, temperature and relative humidity data from Biosphere 2; viewed for periods of days-weeks at a 15 minute sampling frequency.

CO2 data from Mauna Loa, Hawaii.

Additional resources:

Earth Curriculum Glossary:

- Photosynthesis

- Respiration

- Transpiration

- Concept map

- System

- Model

Introduction:

The purpose of this investigation is to examine sensor data from Biosphere 2, and use the data to make inferences about how the parameters measured relate to one another inside Biosphere 2. You will use the Data Harvester to examine temperature, relative humidity, light and carbon dioxide data from either the Rainforest or Desert biomes of Biosphere 2 (your choice). Data should be viewed for a duration of days to weeks at a 15 minute time interval.

On the basis of your observations, and utilizing the background materials and what you have learned in the previous investigations, you will then be asked to make a Concept Map that represents your understanding of how these variables relate to one another in the Biosphere 2 system.

Steps in the investigation:

1. Enter the Data Harvester and choose how you want to see the data (i.e., variables that change through time, through space, or with other variables).

2. On the following screen, choose which Biosphere 2 biome you want to see data from (Rainforest or Desert -- you choose) and examine all of the different combinations of two variables (i.e., CO2 and light, temperature and relative humidity etc.) that are possible to observe. Be sure to specify the date range and frequency of measurement you wish to see data for (for example, the past two weeks with hourly averages).

3. Observe how these parameters vary over the range of dates you have chosen, and how they appear to vary with respect to one another. Then answer the following questions and complete the activities.

Questions:

1. Describe in words how each parameter varies through the course of one day. What is the maximum and minimum value for each parameter? At what time of the day does each parameter reach its maximum and minimum values?

1a) Compare the daily variation in CO2 levels in Biosphere 2 with the seasonal-annual variations in CO2 observed over Mauna Loa, Hawaii. Why do CO2 levels vary more in one day inside Biosphere 2 than they do over almost 50 years on Earth? Why do CO2 levels rise and fall each year in the Mauna Loa data? Why are the observed CO2 concentrations increasing?

2. Using your knowledge of basic biology and the Biosphere 2 system, and recalling the earlier "When Does it Rain?" and "Solstice and Seasons" investigations, what do think are the relationships between the observed parameters? Write down your answer in words (a "word model"), making sure to be clear about how each parameter relates to the others.

Activities:

1. Based on your answer to question 2, draw out a concept map that represents the interactions between the parameters you observed. Include any elements of the Biosphere 2 system (biolgical processes, physical-chemical properties that you have learned about, mechanical systems of Biosphere 2) that link together the observed parameters.

Directed investigations: Part 2: From mapping to modeling: Making a Stella model of interactions inside the Biosphere 2 system

Background materials:

Select readings on system dynamics and modeling, more intro to Stella II

- From the Road Maps series and the Creative Learning Exchange, MIT System Dynamics in Education Project

Additional resources:

Earth Curriculum Glossary of Concepts and Terms

Biology, chemistry textbooks

Introduction:

In the previous investigation you drew upon what you have learned earlier in the Earth Curriculum, new background materials, and your own knowledge of biology to map out the connections between different parameters inside Biosphere 2. In this investigation you will take your concept map and turn it into a more formal, qualitative model in Stella to represent these interactions.

Beginning with the background materials, you will learn how to use the basic tools of system modelers -- scientists who build models of different natural systems (such as the interactions between populations in an ecosystem). Your ultimate goal for this investigation will be to turn your original Biosphere 2 concept maps into formal, qualitative system models in Stella II by applying your new knowledge of how to build system models, and by tying what you learn about plant-level interactions with the atmosphere to biome (or system) level changes in the observed parameters.

Steps in the investigation:

1. Using what you have learned about the way that modelers represent system components with formal definitions and symbols, take each component of your concept map and identify what formal system building block (reservoir, flow, converter, connector) it represents. Then begin to build your model by deploying all of the reservoirs that you have identified from your concept map into a new system diagram in Stella.

2. What processes increase and decrease the levels of the stocks you deployed on your system diagram? Answer this question in a short, three-paragraph essay (one paragraph for each stock). Represent those processes as appropriate flows on your system diagram.

3. Represent temperature and relative humidity on your system diagram with the appropriate system symbol (i.e., how you defined them in step 1 of this investigation). Recall how you defined temperature and relative humidity in the first directed investigation, and represent these definitions with the appropriate set of systems symbols (connectors and flows). You may need to add other components to your system diagram (i.e., other converters or reservoirs) in order to do this.

4. Complete your model by thinking about how any so-far unconnected components of the model are linked to one another, and representing those interactions with appropriate systems symbols. You may need to employ the "ghost" function of Stella in order to keep your model diagram clear and uncluttered.

Questions:

What are the major feedback loops that you can identify in your system diagram?

Starting at dawn, explain in words -- drawing on the conceptual logic of your system diagram -- how the observed parameters (light, temperature, relative humidity, and CO2) change over the course of one day inside Biosphere 2. Be sure to explain all changes with reference to your model -- nothing in your explanation should be missing from your model, and vice-versa.

If light levels were to double, predict how all of the observed parameters would be likely to change in Biosphere 2 over the course of a day. Again, base your prediction on the logic and structure of your system diagram, with particular reference to any important feedbacks evident in the model. Make your prediction in words, and by drawing a graph that tracks changes in the parameters over the course of the hypothetical day. What would happen if light levels were half their normal amount?

If atmospheric CO2 levels were to double on Earth, use your model to predict how temperature and relative humidity might change over the course of a number of years. Again, base your prediction on the logic and structure of your system diagram, with particular reference to any important differences in model structure between Biosphere 2 and Earth. What, ultimately, will happen to CO2 levels? Why?

Note: The final question will be expanded into an exploratory investigation.

Appendix: Review of Content highlights

At the end of "When does it Rain?" students will have come to understand the connections between air temperature and the ability of the air to hold water, through lab experiments, observation of data from different ecosystems, and visualizations of the physical-chemical properties that are involved. In "Solstice and Seasons", by exploring the well-known lag between the solstices and the warmest/coldest times of the year, students will also have learned about such fundamental concepts as heat capacity, and how heat is transferred between types of materials. Through these investigations, students have thus begun to learn some of the fundamental physical and chemical principles that govern how energy and materials flow through the Earth.

As with the previous investigations, students discover the insights of the Biosphere investigation by beginning with the observation and exploration of sensor data (air temperature, relative humidity, light and carbon dioxide) from an ecosystem -- in this case, either the Rainforest or Desert biomes within the closed system of Biosphere 2. All of these parameters vary over a time scale of hours to days inside the biomes of Biosphere 2, making it easier to see that tight connections between them through the small scale and material closure of the system.

Students will attempt to build concept maps (see Process/Pedagogy Highlights below) that represent how the above-mentioned parameters are related to one another in either the Rainforest or Desert biome of Biosphere 2. In order to make such maps, insights from the previous investigations must be utilized. For example, air temperature changes as a function of light, the heat capacity of the air and soil, and the heat transfer between the air and soil; relative humidity changes as a function of the temperature, which increases or decreases the ability of air to hold water (as well as determining the rates of evapotranspiration).

But explaining changes in the carbon dioxide data, a dataset that they have not yet seen, force students to consider the role that plant-level processes have on the whole system. At least two plant processes play a major role in producing variation in the observed parameters. First, photosynthesis (which is driven by light and temperature) has an obvious and direct effect on CO2 levels. Second, transpiration from plants (also temperature dependent) moves water from the soil into the atmosphere, and thus influences the relative humidity of the air. In building the concept maps, students will be forced to weave together what they know about individual processes/phenomena (e.g., photosynthesis, heat capacity) to explain behavior that is occurring at the level of the whole system -- this advance in thinking skills is dicussed below in more detail.

The central insight of the first Biosphere 2 directed investigation is that light, temperature, relative humidity and carbon dioxide are all connected by a set of physical, chemical, and biological processes in the atmosphere, plants and soils. In the second Biosphere 2 directed investigation (and subsequent exploratory investigation), students focus on understanding and modeling formally the mechanisms by which the parameters are connected. The goal of the investigation is to build a qualitative (i.e., non-numerical) Stella model of the interactions between the observed parameters, based on (but extending) the original concept maps. By building simple yet qualitatively rigorous models of these interactions in Biosphere 2, utilizing the formal building blocks of system models, students will be pushed to construct a deeper understanding of the actual mechanisms -- the real processes -- that are at work inside the system.

Process/Pedagogy highlights

The fundamental content goal here is to have students work to build a systems-based understanding of how physical, chemical, and biological processes interact with one another to produce changes in temperature, relative humidity, and carbon dioxide levels. The route taken to earn these insights is in many ways similar -- and in some ways very different -- from the previous investigations. Figures 1 and 2 below show the pathway from data to insight that the first directed investigation seeks to illuminate.

In the first directed portion of the Biosphere investigation the "Point A" is the students making a set of observations about sets of data. The "Point B" is the end product of the investigation: a simple concept map that represents the student's understanding of how certain relevant properties and processes (e.g., heat capacity, photosynthesis, etc.) bind the data sets together in a web of interconnections. The question is how to have the students get from Point A to Point B.

The challenges here will be: a) for the students to connect things that are given (i.e., the observed parameters) to the insights that they have learned in previous investigations -- but which they have not yet connected to one other, b) to tie together these newly-learned insights to the student's basic knowledge of biology (e.g., the processes of photosynthesis and transpiration) -- which thus far has not been introduced into the Earth Curriculum, and c) to represent their understanding of these connections in the visual representation of a concept map.

A good way to begin the first directed investigation would be to engage students in building sample concept maps of very simple processes (examples are listed in the investigation below). This activity will hone their skills in representing connections between familiar things. After this activity, students can begin observing time series data for a biome of their choice ("Point A"). As suggested in the investigation below, students can begin by looking at different combinations of two parameters (i.e., light and CO2, light and temperature, temperature and relative humidity, etc.) for some fixed period of days. Questions will stimulate students to begin thinking about how the parameters might be connected to one another, and ask them to observe closely how the parameters vary through time.

Figure 1: Light, air temperature, relative humidity, and soil temperature data from the rainforest biome of Biosphere 2 (note: temp. and RH data should be put on a different scale in the Data Harvester to see relative changes along with PAR and CO2)

Figure 2: From data to simple concept map tying together observed parameters

Additional questions will engage students in comparing the daily variance in CO2 levels in Biosphere 2 to seasonal and annual changes in CO2 in the Earth's atmosphere. Here the idea is to get students thinking about the different scales over which biological processes can occur in nature, and their effect on atmospheric composition. Biosphere 2 provides an engaging point of departure for this.

Finally, students are asked to draw on their new skill in drawing concept maps, what they learned in previous investigations and what they know of basic biology, and what they observed in the data, to represent the nature of the relationships between the parameters, both in words and with a concept map ("Point B"). Here, little guidance need be given. Students can be given acetate (overhead) sheets for trial and error, with a final map submitted on paper. As for evaluating the concept map, recall that the goal here is to have students make connections between content knowledge that they should already know, using a skill that they have just developed. Thus, it is reasonable to expect the maps to include not only the parameters themselves, but at least all of the components placed on the example concept map above. Additional components could certainly have been placed on the map, including those that are specific to Biosphere 2 (for example, the air handler units, which regulate both temperature and relative humidity in the biomes).

Of course, the students' concept maps will likely be fairly incomplete. And even if complete, they are not likely to display consistency or formality in representation. This lack of clarity reflects the absence of clear thinking about what is really going on in the system -- the actual mechanisms that conncect light, temperature, relative humidity, and carbon dioxide. But with the addition of more "vocabulary" about how to make formal system diagrams, and with more clues about how the biological processes of plants can tie together all of the observed parameters when they occur within a closed system, students will have a more extensive tool set with which to improve upon their original concept maps.

The "Point A" of the second Biosphere directed investigation begins with the concept maps that students built. "Point B," as depicted in Figure 3, is a formal, qualitative model in Stella II that represents both the connections and the mechanisms that tie together the observed parameters. Again, the question is: how to get from Point A to Point B?

Figure 3: Sample qualitative model linking light, air temperature, relative humidity, and atmospheric CO2 levels in rainforest biome of Biosphere 2

The first step will certainly involve learning both the formal vocabulary of systems (e.g., reservoirs, flows, converters and connectors, feedbacks, etc.), and their symbolic representation and mechanical manipulation in the Stella II software environment. Initial activities, drawn from the rich resources available on-line, will help students to accomplish this.

Students will then apply their new "systems" skills to their concept maps. The first step will be to ask students to identify what type of system model building block is represented by each component and arrow of the concept map. This activity will form the foundation for the building of the model, as it will help students to define formally each model component. At the end of the exercise, three reservoirs should be defined by the students: carbon dioxide in the atmosphere, water in the atmosphere, and heat/energy in the system. The teacher will most likely have to do some "coaching" so that students in fact do correctly identify these reservoirs, a particularly difficult challenge because there are many equivalent ways to represent many of the other model/concept map components. For example, photosynthesis can be represented as a converter that influences the rate of CO2 transfer out of the atmosphere (as above), or as a flow that itself takes CO2 out. Both are equivalent representations of the same thing. So, a challenge for the teacher will be to -- on the one hand -- encourage students' creativity in representing what is going on in the system and -- on the other -- to make sure that there is consistency and conceptual rigor behind their representations.

After this exercise of defining model components, the next activity will be to deploy the three reservoirs on the system diagram in Stella, and to ask students what processes transfer the "stuff" of those reservoirs in and out of the reservoirs. For example, what processes directly increase the amount of CO2 in the atmosphere? What processes decrease the amount of CO2 in the atmosphere? Here you will ask students to answer these questions verbally -- forcing them to define and understand the actual mechanisms that change the levels of the reservoirs -- and to represent their answers with the appropriate placement of flows on their emerging system model diagram. The figures below, which are taken from different information sources on the web, are examples of supplementary resources that could serve as useful reference material for the teacher in illustrating these mechanisms. They illustrate the role of plants in the processes of transpiration and photosynthesis, provide a simple view of energy balance in a closed system, and provide a "global" view of the hydrological cycle inside Biosphere 2 (not really, yet). Such diagrams, combined with readings that explain them, will provide a stronger base of process information to deepen the student's understanding of the connections between the parameters. However, none of the diagrams really link together all of the parameters -- they are just pictures of individual plants doing specific things. The conceptual linkage that ties the plant-level processes to the levels of water and CO2 of the whole atmosphere will have to be made by the student -- and is a very important foundation for scaling their understanding up to global processes (in the exploratory investigations).

Figure 4: Earth's energy balance (need a better diagram here -- one that is Bio2-specific) -- this should build upon investigation #2.

Having answered these questions and represented them on the system diagram, a next step will be for the student to define the quantities of temperature and relative humidity and represent them appropriately on the system diagram. Once that task is complete, the student(s) should be left alone to complete the task of making appropriate connections among the model components (as, for example in Figure 3). In evaluating these models, attention should be paid to the formality of representation of model components, and the extent to which the model -- regardless of the particulars of its structure -- accurately represents the mechanisms that link together light, temperature, relative humidity and carbon dioxide. Again, the model above is very simple. Students will have a wealth of information at their disposal regarding the specific mechanical techniques used to produce rain and control temperatures inside Biosphere 2, and should be encouraged to represent these processes in their models -- as long as, of course, they are represented with conceptual rigor.

Figures 5 and 6: Evapotranspiration and photosynthesis in plants (add evaporation from soils)

Figure 7: The global hydrological cycle (Need one that is Bio2-specific)

Through these directed activities, students will have begun to build their own understanding of the complex interactions between atmosphere, biosphere, and water cycle at the global scale, first by beginning with observation of data, later by making simple concept maps, and finally by linking (with the help of formal system building blocks) plant-level biological processes to the system-level parameters (CO2, RH, etc.). These activities should help the student begin thinking about how differences in the structure and scale of these interactions produce different types of behavior -- in Biosphere 2 and the Earth system whose key features it seeks to model.

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