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