Environmental Systems Topic - 1 Systems and Models Statements: 1.H – 1.L

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??

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: With the person sitting next to you; One person describe steady state equilibrium and the other explain an example.

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 systems can be either negative or positive

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.

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.

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?

Example of negative feedback in the environment?

Positive Feedback Positive is usually Bad Occurs when a change to a system causes more of the change to occur. Feedback that amplifies or increases change and accelerates deviation away from equilibrium. It is a destabilizing, 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….

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

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. People avoid the gullies, which causes the paths to widen and more vegetation loss and erosion, etc…

Evaluation of Models Strengths: (in other words why do we use models?) Limitations: (issues surrounding the use of models) Discuss this with the 3 to 4 people in your area, coming up with 3 for each. Discuss as a class.