Lab2_SystemDiagrams_LLL
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Lab 2—Reading and Constructing System Diagrams 24 Questions
Why is system diagram construction crucial to ESS?
How do you understand something as complex as climate change, or soil formation for that matter? Both are tremendously complicated with many factors, processes, and feedback loops involved. It can be mind boggling. Indeed, soil processes are a part of what influences climate (through carbon sequestration and soil microbe respiration), and climate influences soil processes (through controlling temperature and moisture). One complex system is embedded in
another in an interdependent relationship. The challenge is daunting, and one might be forgiven for giving up, but as our population grows and we must manage resources, there is great need for understanding complex systems. In addition, new tools provide opportunity to take on this challenging task. The answer to understanding the complex interwoven components of the earth we live on is that
you “pull out all the stops.” You have to look at everything, the component physics, chemistry, geology, and biology. Field observations, experimental studies and computer modeling all need to be integrated. Multi-disciplinary teams and dedicated scientific communities are necessary. ESS is arguably the most challenging scientific endeavor humanity has ever embarked on. Much remains to be done, but one can also be heartened by the tremendous progress that has been made in the last few decades. One fundamental tool used in tackling these types of complex scientific challenges is mapping out the linkages among the various components, processes, and variables that influence a complex system of interest (climate, soils, ecosystems ….). These maps take many forms, but often consist of diagrams with boxes and arrows, and can be constructed as formalized system diagrams
with their own meaningful iconography (symbology). They are fundamentally conceptual maps
, models for how the complex system works, although they can also be transformed into working models. You are probably already familiar with system diagrams in some form. They are often called cycles, and the water cycle, carbon cycle, and rock cycle mentioned in the first lab are just three
examples. We will start with these more familiar examples as we explore how one constructs systems diagrams. Knowing how to create system diagrams is also a skill that is useful in many other realms of life. For example, one could map out their financial situation or what influences their grade using system diagrams. Some people refer to “systems thinking.” One example of the application of system thinking to health science can be found here
, which might be worth reviewing if you are or intend to be connected to this field in the future. There is a tremendous amount of material on the web about systems thinking, in part because it is so powerful and multi-disciplinary, and it can be disorienting at first. The reason we start off this lab course in ESS with this exercise is because understanding and constructing system diagrams is not only fundamental to ESS, it is also a powerful tool to use throughout life. 1
Our experience in teaching system diagram material suggests to us that for many students learning how to build such diagrams is not easy. This is not mentioned to discourage you in any way. Experience also suggests that this material is also quite accessible at the introductory college level. Just be prepared to explore a way of thinking that may be unfamiliar at first. As in the first lab, the parts you need to answer to complete the lab are identified by green text.
Reading system diagrams as conceptual models (7 pts)
The water cycle is an attempt to understand how water moves above, on top of, and below the earth’s surface. Without water, not only would there be no life on earth, but the earth would behave very differently geologically. Water makes all sorts of things happen in our world, and this is why it is often introduced at the elementary school level. Below you will find a version of the water cycle from the USGS (
source: https://gpm.nasa.gov/education/images/usgs-water-cycle-
diagram
) that is very commonly used, and which you have seen in Lab 1. The USGS (the United States Geological Survey) is the agency responsible for helping to track and understand water resources, and provides a wealth of high quality geosciences information which we will tap into in subsequent labs. Read through the diagram carefully. If there are some words you are unfamiliar with (e.g. sublimation, or evapotranspiration) use your favorite web browser to look up
a definition. 2
Use the diagram and what you know of the water cycle to answer these questions to the best of your ability, and thereby get some practice in reading one form of a system diagram. Please write clear, complete, answers and make your text a different color
. Question 1:
Of all the possibilities mentioned in the diagram, where is the greatest quantity of the water at any one point in time? The greatest quantity of water at any one point in time would be located in the ocean.
Question 2:
Which component(s) depicted in the diagram are especially significant for a location like Antarctica? Ice and snow are especially significant for a location like Antarctica. Question 3:
Calving is a process where large chunks of glacial ice fall into the ocean (this occurs where the glacier front is floating on the water, or just at the water’s edge and large pieces break off and fall into the sea). The resulting icebergs eventually melt. Is
that process displayed here, and if so, how? Calving is not on display in the diagram.
Question 4:
Does all of the water in the atmosphere that precipitates fall onto the land, and if not, where else can it fall? Is this represented in the diagram? Water can also fall into the ocean. It is not well represented in the diagram.
Question 5:
Where does water likely spend the shortest amount of time, on average? Google it if you don’t have a guess Water spends the shortest amount of time in the atmosphere.
Question 6:
Are “plant uptake” and “evapotranspiration” linked? If so, explain how. (evapotranspiration = evaporation of water from surfaces plus transpiration, which is evaporation of water from leaves
) Yes it is linked because plant uptake is the plant taking
in water from the soil and evaporating from its leaves. Question 7:
Is that linkage (Q6) explicitly shown on the diagram above?
I would say so because it shows the plant getting water from the soil and that it evaporates into the atmosphere.
This USGS water cycle diagram has the advantage of making a clear visual connection between the words and the real world. However, it has some disadvantages. Some of these are pointed out by the answers to the questions above. There are important processes that are not included in this diagram. Taking a more structured approach to creating system diagrams results in a more useful product, and a sounder conceptual understanding. Such system diagrams can also serve as the basis for more powerful, and predictive computer models for the
earth system under investigation, and versions of the water cycle adapted to specific localities are used to manage water with very important economic and social consequences. When it 3
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comes to recourse management, it is important to not only have a qualitative understanding, but
also a quantitative grasp of the situation.
Another example of a system diagram
Below is a diagram for the carbon cycle from NOAA (National Oceanic and Atmospheric Administration – another federal government source that has significant geosciences information). Find additional information on the carbon cycle (and image source) here
. Use the carbon cycle diagram above to answer the following questions.
Question 8:
Several arrows show transfer of carbon (C) from the atmosphere to vegetation. What is the name for the process that accomplishes this (where C in the form of CO
2
is taken up by plants)? The process of photosynthesis is where the plants capture carbon dioxide from the atmosphere.
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Question 9:
Calcite and aragonite are minerals with a chemical formula of CaCO
3
. Note they contain carbon, and thus are part of the carbon cycle. Calcite is a particularly common mineral. Corals are one type of marine organism (amongst a host) that can extract from seawater the components necessary for making their shells (often aragonite
or calcite). Eventually, corals and the shells of other marine organisms turn into a rock called limestone. Is this process explicit or implicit in any way in the diagram above, and if so how? I would say it is implicit. The diagram shows carbon going to the Marine Biota
and eventually turning into sediments and dissolved organic carbon but it is not specifically show this process.
Question 10:
In a couple of sentences, describe one way that you might modify this diagram to expand or improve it. One way I would modify this diagram is to give respective numbers to show just how much carbon is in use throughout these processes. The diagram shows how the carbon cycle works but I would add numbers or percentages to show how much each variable uses this carbon to see just how much they influence the carbon cycle.
Below is another diagram from NOAA that shows a different version of the carbon cycle (source:
http://www.pmel.noaa.gov/co2/file/Carbon+Cycle+Graphics
). Take a few moments to study the diagram. Consider how it differs from the one above. Pg stands for petagrams, which is 10E15 grams. “E” in this number stands for exponent and so 1 petagram = 1,000,000,000,000,000 grams. That is a lot of mass.
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Note that reading this type of diagram does take more effort, focus, and attention than the first diagram—that is because it is significantly more complex and contains more information. Notice the numbers attached to some of the components (specifically the arrows). The arrows show inflow or outflow for some “resting places” (reservoirs) of the carbon in units of petagrams/year, which are fluxes describing the rate of the transfer. The black numbers
represent the pre-
industrial amounts (before significant influence of humanity) and the red numbers
represent the
anthropogenic (human induced) amount during the period 2000-2005. The numbers in brackets
represent the amount of carbon in specific reservoirs. The two red numbers for plants and soils represent one anthropogenic activity that decreases the amount, and another that increases the amount. More details can be found at the website source provided above. Use this diagram to answer the questions below.
Question 11:
What percentage of the carbon in the atmosphere is anthropogenic in origin (you will need to make a simple calculation: anthropogenic C/total C)? About 25.7% of carbon in the atmosphere is anthropogenic.
Question 12:
Where is most of the carbon stored (what reservoir or sink holds it)? The ocean stores the most carbon. Question 13:
It turns out that cement production from carbonate rocks also releases carbon dioxide into the atmosphere. What percent of the total anthropogenic release of C to the atmosphere is due to cement production from carbonates (make a simple calculation: cement emissions/total anthropogenic atmospheric C)? About 3.5% of total anthropogenic atmospheric carbon is from cement emissions.
Question 14:
In this model, is volcanism a significant contributor of C to the atmosphere? Volcanism is not a significant contributor of carbon to the atmosphere. Volcanism is responsible for less than 1 Pg of carbon.
As you can see there is quite a bit more information in this type of diagram, but it also raises questions as to where all these numbers come from.
Constructing system diagrams as the foundation for predictive models (5 pts)
The next two sections of this lab provide a foundation for constructing system diagrams. Read them carefully as you will then be asked to create a more detailed diagram of the hydrologic cycle. There are 4 fundamental parts
to a system diagram/model: Reservoirs, Transfer Processes, Variables, and Rules
. Reservoirs
: These are the core of the diagram. They are different places that some quantity of interest resides. The quantity of interest can be a compound (e.g. water), an element (e.g. carbon), energy, individuals in a population, mass, or a great variety of other possibilities, depending on what kind of system diagram you are constructing. You should be able to capture the quantity as a number in some way and so there will be units involved. For water, the units could be gallons (volume) or grams (mass), or for population the units could be the number of individuals.
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Transfer Processes
: Transfer processes are ways that the quantity of interest is transferred (moves) into or out of a reservoir. Inflows
transfer the quantity of interest into a specific reservoir, and outflows
transfer the quantity of interest out of a specific reservoir (and possibly act as an inflow to another reservoir). Typically, the transfer process is shown by lines with arrows that link reservoirs and indicate the direction of movement of the quantity of interest. Variables
: Variables influence the rate of a transfer process. In some cases, they are variables in an equation that governs the transfer process (the equation itself is a rule – described below).
Temperature is a very common variable, and there are many others. Variables are linked to the transfer process by a line (or are otherwise associated with the transfer process) to show which transfer process the variable is influencing. Rules
: These are equations, if-then statements, or other guidelines for establishing the amount of inflow or outflow associated with a transfer process. For example, for snow versus rain, the rule might be “if T<32 Fahrenheit then transfer to snow reservoir, else transfer to surface water.”
Full rules often are not shown directly on the system diagram, but their general form can be identified on the diagram iconically, by a label or ornamentation of the line linking the variable to the transfer process. A general form of a rule could be “as variable x increases, inflow increases” and the associated line could be ornamented with a + sign. If the inflow decreases as the variable x increases (an inverse relationship) then the associated linking line could be ornamented with a minus sign. The rules are what allows the qualitative model to become operational so that one can have some initial conditions (a starting point), and then model how the system should behave with time. Guidelines for constructing system diagrams
Here are some guidelines for how to construct system diagrams. Again, it will be worth your time to read this carefully.
A consistent iconography should be used, with distinct and different symbols for reservoirs versus transfer processes versus variables, and with distinctly different lines for linking reservoirs by transfer processes versus linking variables to transfer processes
(it may be easier to associate the variable to the transfer process without a line).
A reservoir can only be connected to another reservoir by an intervening transfer process (and not directly). There should be arrows to indicate the direction of transfer (i.e. to differentiate an inflow from an outflow).
Reservoirs must be of the same type, i.e. containing the same kind of quantity of interest. For example, you should not directly link a water reservoir with an energy or carbon dioxide reservoir (although you can link them indirectly via a common variable to create a more complex diagram that models more than one quantity); rather, you should connect one water reservoir with another water reservoir.
Variables only influence a transfer process and cannot be linked to reservoirs. Think of variables as controls.
The quantity in one reservoir can be a variable in a transfer process. For example, the number of people in a reservoir (e.g. in a country) can be a variable that influences the inflow of people into that reservoir (indeed this only makes sense given that the number 7
of births is related to how many people exist in the reservoir). This type of relationship is shown by running the variable linking line from the reservoir to the transfer process affected. This geometry, by the way, can form a very important phenomena known as a feedback loop (which we will focus on in subsequent labs). Practicing system diagram component identification
Let’s change gears a bit. Consider the human population on an island as a reservoir of a quantity of interest. Hawaii could be an example. In this section you will practice thinking about what parts would need to be included in a system diagram that attempts to model how and why the human population could change with time. What are the two inflows (transfer processes) that could increase
the island human population? (hint: think about what mechanisms cause population to grow, or how people are added to a location)
Question 15:
[A] Transfer process inflow 1: Repopulation or the amount of births on the island.
Question 16:
[B] Transfer process inflow 2: Immigration or outside people coming to the island.
What are the two outflows (transfer processes) that could decrease
the island human population? (hint: think about what mechanisms cause population to decline, or how people are lost from a location)
Question 17:
[C] Transfer process outflow 1: Emigration or people leaving the island.
Question 18:
[D] Transfer process outflow 2: The deaths of the people on the island.
Now list 4 variables (there are a good number more than 4) that influence one or another of these transfer processes and indicate which of the transfer processes [above] each variable influences. (hint: think about why
populations change—this could be anything that impacts population increase or decrease, from political stability to resource availability, etc.) Question 19:
Variable 1: Economy and Jobs Linked to transfer process (A, B, C, or D): Linked B (Immigration)
Question 20:
Variable 2: Natural Disaster Linked to transfer process (A, B, C, or D): Linked with D (deaths) Question 21:
Variable 3: Amount of available space
. Linked to transfer process (A, B, C, or D): Linked with A (births)
Question 22:
Variable 4: Education 8
Linked to transfer process (A, B, C, or D): Linked with C (emigration) or B (Immigration)
Question 23:
Describe one rule
for how one of the 4 variables you chose influences the transfer process (e.g. when the variable increases or decreases, the transfer process increases/decreases). If a natural disaster were to happen, then there would be an increase of deaths. The more occurrences of disasters like hurricanes, earthquakes, and other natural disasters would increase the amount of deaths.
(optional) For extra practice, find a system diagram on the web for some sort of quantity of interest in earth science other than water or carbon. There are many possibilities. Key search terms such as nitrogen cycle, sulfur cycle, iron cycle, nutrient cycle, and energy cycle will help you find a diagram. Test your understanding by answering the following questions.
What is the cycle/quantity of interest you chose?
Identify and list at least 4 reservoirs evident in your system diagram.
Identify and list at least 2 transfer processes evident in your system diagram
Identify and list at least 2 variables and indicate which transfer process(es) they influence. If variables are not shown, infer them from what you know. Water cycle construction exercise (3 pts)
Above, we introduced a water cycle diagram, and noted some of its shortcomings. Since water is so important to the earth it is worthwhile to develop a better system model/diagram for it. Open the companion PowerPoint file for this lab.
Read the instructions on the first slide carefully. Then use the components on the next two slides to construct your version of a hydrologic cycle on the fourth page in the PowerPoint file. You will need to spend some time working on this. Make your diagram as complete as you can. Question 24:
Insert your version of the water cycle system diagram below (you should be
able to simply copy and paste the whole slide from PowerPoint into this word document):
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