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Systems diagrams
Positive Feedback Feedback that enhances a change in the
system and it is destabilized and pushed to a new equilibrium. This feedback may cause the process to speed up until the system collapses, resulting in a "vicious circle".
Example: Positive feedback in a bank account
Human population growth
Melting permafrost and global warming
You try!Warmer global temperatures.Melt more ice and snow.The Earth’s albedo decreases.More energy from the sun is absorbed by the surface of the Earth.
Positive feedback
Warmer global temperatures
Snow and glaciers melt
The Earth’s albedo decreases
More energy is absorbed by the surface of the
Earth
Production, consumption and human population You try!
Production, consumption and population
Climate Change.. Increase in the temperatures can cause
more evaporation. Water is a greenhouse gas…
Negative Feedback Feedback that tends to neutralize or
counteract any deviation from equilibrium, returning the system to a stead-state equilibrium.
Negative feedback example
Another example: air conditioner
You try!Increasing global temperatures.Increases evaporation of water.Increases formation of clouds.More light is reflected by the clouds.The temperature cools.
Negative feedback in ecosystems Predator Prey relationships
Disease
Food supply
Complete the diagram with increase/decrease
Identify Transformations and transfers in the hydrological cycle below:
Which flows will increase from climate change?
Answer:
1. A small glacier receives an input of 20 units of ice in the form of snowfall each year. As the ice melts, 19 units are lost through run-off, and 2 units through evaporation.
(a) Draw a labeled flow diagram showing these processes and their relationships. [3]
(b) State what would happen to the glacier if these inputs and outputs were to remain constant for several years.
Complete this example
Sketch a simplified energy flow diagram to show how energy flows in a named ecosystem
A simplified energy flow diagram for a tropical forest food chain is shown
Local ecosystem energy flow
sunlight Espino treeDegu and
other rodents eats the nuts
And so on…
Answers the questions about the diagram on the next slideState, giving one reason, what kind of system feedback is illustrated by the descending spiral. [1]
(b) Discuss the meaning of the term sustainable development with reference to Figure 2. [2]
(c) Evaluate the strengths and limitations of the models shown in Figure 2.
Answers(a) positive feedback because the effects of the problem make the problem worse; [1]
(b) traditionally defined as development which meets the needs of the currentgeneration without compromising ability of future generations to meet their own needs; but in this context it suggests development which has a positive role in enhancing the environment; and is dependent in some way on a healthy population; [2 max]
(c) simple, easy to see the connections; shows clearly how actions in one area can have a knock on effect on the originalDevelopment; can distinguish between positive and negative actions and consequences;
but far too simple, detail of what constitutes sustainable as opposed to inappropriate development is not clear; exact natures of the causal relationships are not explained; [2 max]
Soil degradation in Madagascar – make a model
Sample Madagaskar model
deforestation
Soil left to dry in sun
unprotected
Erosion from wind and rain
Leacing of nutrients
Soil becomes degraded
Madagascar answers.. protective forest cover removed; directly by
logging/farming/mining/industry/settlement; soil exposed to rain and easily washed
away/eroded; soil exposed to high temperatures and
baked/dried out; nutrients leached away; soil loses fertility and can no longer support
plants; soil degraded and useless as a resource for
humans; [4 max] Award [3 max] if no climatic factors are mentioned, or
the fact that soil is naturally poor.
Suggest how the differences in the size of comparable storages of the two ecosystems can be explained in terms of their different climates.
answer continued:
Which is in a steady state equilibrium? Why?
The temperate forest is in steady state equilibrium The flows are all the same size.
Draw a labeled flow diagram showing the flows and storages of inorganic nitrogenthat normally occur within soil. Show on your diagram how these flows provide a linkbetween the storages of dead organic matter and biomass.
Answer:
The diagram below shows the energy flow in a river ecosystem in temperate latitudes. All energy values are kJ m−2 yr−1. The system is in steady state equilibrium, calculate the value of X.
X = 10670 kJ m-2 yr-1