2. Environmental Systems Topic - 1 Systems and Models Assessment Statements 1.1.5-1.1.10

3. Steady-State Equilibrium The most stable state of a system and is a common property of most open systems in nature. The average condition of the system remains unchanged over time. No net change in the system… what does this mean??

4. Steady-State Equilibrium Some systems may undergo long-term changes to their equilibrium, while retaining an integrity to the system. Although there is continual input and output of matter and energy, the state of the system remains constant. This can be compared to Static Equilibrium - Properties of the system are constant and unchanged over time… this does not often occur in nature. Examples of Steady-State:

5. How systems stay at Equilibrium Systems remain balanced or unbalanced because of their feedback mechanisms. Systems always want to be in homeostasis, or balanced, and usually have a mechanism to get there. Feedback can be negative or positive

6. Feedback Loops Feedback Loop (IB): a relationship in which a change to one part of a system influences another part of the system in a way that either reinforces (increases) or slows the original change. (Or) A change to a system can either increase change or take the system back to equilibrium. Feedback loops involve time lags. Why? Not all systems have feedback loops... there must be a change to the system first.

7. Negative Feedback Negative is Good Occurs when a change to a system causes a response that is in the opposite direction of the output. A self-regulating method of promoting stability…leads of steady-state equilibrium. Example input = sun rays hitting your body response = body heats up Output = (Sweat)body cools down Without this response, what would happen?

8. Negative Feedback Loops Example: temperature regulation in humans involves a negative feedback loop, in which increased temperature leads to decrease in temperature by sweating. Without this response, what would happen?

9. Other Examples of Negative Feedbacks?

10. *Negative Feedback is desirable because it promotes equilibrium and self regulation*

11. Positive Feedback Positive is Bad  Occurs when a change to a system causes an increase change to that system. Feedback that amplifies or increases change and accelerates deviation away from equilibrium. A vicious cycle. Example: System = a forest Change to system = flame Response = wood dries Feedback = more fire and more wood drying, which leads to more fire, etc….

12. Positive Feedback Loops Example: exponential population growth involves a positive feedback loop in which more individuals lead to increased numbers of births.

13. Another Example of Positive Feedback: Off-Road Vehicle Use As vehicle use occurs, tires uproot and kill plants. This increases erosion rates and causes gullies. Erosion causes more vegetation loss. As people avoid the gullies, which causes the paths to widen and more vegetation loss and erosion, etc…

14. *Positive Feedback is undesirable because it is destabilizing!*

15. Transfers within a system Transfer - when matter or energy is moved from one location to another. Examples?

16. Transformations within a System Transformation - interaction within a system that forms a new end product or involves a change in state. Examples?

17. Why Systems Change Inputs - Anything introduced to the system. Outputs – Anything leaving a system or the response to an input. Stock (or Storage) – Anything remaining in a system that responds to input

18. Stock size is dependant on both the input and the output. Tree farm planting = cutting Use of Fossil fuels Pollution of lakes with pesticides

19. Evaluation of Models Strengths: Allows scientists to simplify a system Can change variables to predict different scenarios/events without waiting. Predictions/outcomes  plan of actions Limitations: Simplify  Inaccurate Rely on expertise of whoever made model. Different interpretations Vested interest?  Bias Dif. Models/same data = dif. predictions.