1. Chapter 3: Systems and Change What is a system? Simply put, a system is any part of the universe, (or Earth) that can be isolated for observation or study. Ex: a river system, the ocean, a forest, the atmosphere.

2. A system can be very large and complex, such as the Amazon Rainforest or the Earth. Systems can also be fairly small and discrete, such as a local pond. In any case, the system in question has many variables, and is in a constant state of transition. No ecological system is constant. Why do you suppose this is?

3. Open vs. Closed Systems A system may be open or closed in regards to the materials or energy within them. A system that exchanges a material with another system is open with regard to that material. Ex: The ocean system and the atmosphere constantly exchange water. They are open with regard to water.

4. A closed system does not exchange certain materials or energy. Ex: for all purposes, the Earth is a closed system in regards to material. The amount arriving is negligible, as is the amount man has removed from the planet. However, Earth is open as far as energy. Why is this so? Give an example.

5. Earth’s Incoming Energy The Earth (and therefore its ecosystems) receives the bulk of its energy from the sun. 99.998% - Incoming solar radiation.002% - Heat from within the earth transferred to ecosystems.

6. Incoming: 5.5 million exajoules of solar radiation. Reflected back into Space: 1.9 million exajoules of solar radiation. (~35%) Absorbed by the Atmosphere: 0.96 million exajoules of solar radiation. (~17%) Absorbed by the Earth: 2.6 million exajoules of solar radiation. (~47%)

7. Outgoing Energy 1.9 million exajoules of incoming energy is reflected by the atmosphere. 3.6 million exajoules of energy is Re-radiated by the Earth back into space. Total: 5.5 million exajoules of energy

8. Notice that the Incoming and Outgoing energy numbers are EQUAL. This satisfies the Law of Conservation of Energy, which states that the total amount of energy in the universe can not change.

10. The Character of Energy Incoming Energy: Our Earth receives energy from the sun in the form of the full electromagnetic spectrum. Only a very small portion of this spectrum is visible to the human eye. 700 to 400 nanometer wavelength light is visible (ROYGBIV!)

12. Most of Earth’s energy is re-radiated into Space as heat, or infra-red energy. This energy is longer wavelength energy, and is invisible to the human eye. Wavelength of over 700 nanometers.

14. Systems need to respond to inputs and in turn, have outputs of their own. Ex: Suppose an estuary ecosystem gets an input on excess nitrogen (fertilizer). The ecosystem initially responds by greatly increasing the growth of algae. The algae eventually dies off, causing an increase in bacteria, which uses up all of the oxygen.

15. Systems and Feedback A special type of response occurs when a system output also serves as an input and leads to changes in the nature of the system. The output that changes the system is called feedback.

16. Feedback can be positive, and increase the output further. Ex: An uncontrolled fire in the forest. A small fire starts, and gradually dries out more wood, which causes a larger fire, and so on…..

17. Positive Feedback Caused by Off Road Vehicles

18. Feedback can also be negative, and cause a decrease in output. Negative feedback is more desirable, because it causes a stabilization in the system. Ex: an increase in the fish population in a pond. Increased population will lead to increased competition, which will lower the population.

20. Environmental Unity The concept of Environmental Unity is Fundamental in Environmental Science. Basically stated, Environmental Unity means that one change in an ecosystem or environment affects something else.

21. Some Examples: -Poor agricultural practices do not prevent runoff of sediment….sediment is flushed into streams, causing habitat destruction of organisms needing rocky streams. -Global warming caused by increased carbon dioxide from industrialized nations causes increased typhoons in 3 rd world.

22. Lessons Learned from Environmental Unity In the Pacific Northwest, it was common practice to clear-cut all logs from an area. Clear cutting causes excessive runoff, and degrades streams (sediment, lack of shade). In an effort to make the streams more “salmon friendly” all obstacles such as stumps in the water were removed.

23. -Removal of large logs and debris from streams causes a reduction in deep pools where salmon reproduce. Salmon population actually declines more because of this practice. Clear cutting near streams is regulated, some stumps are actually placed into streams to act as habitat.

24. The Lesson: Environmental Unity needs to be taken into account when planning. -There is a need to study the relations between physical and biological systems before actions are taken. It is often too late to go back and correct a mistake, forethought is the key.

25. Uniformitarianism “The present is key to the past” First suggested by James Hutton in 1785, this principle suggests that processes that occur today are the same as occurred in the past, and are therefore directly related. Ex: rates of erosion, geologic uplift, deposition of sediments.

26. The importance of uniformitarianism: -since it is the key to the past, it must also be the key to the future. Ex: we can predict the rate at which a particular event might take place, based on our previous experience with it. We can also measure our impact on an event, and see if we are speeding it up or slowing it down.

27. Ex: based on growth rings, we can see how growth of trees has been affected by the environment. (Dendrochronology) Since we know what the growth rate was, why is is faster or slower now?

28. Dynamic Equilibrium A system that has a balance of input and output of whatever is being measured is said to be in a steady state. Other terms for this are Dynamic Equilibrium, and Homeostasis. All imply a balance, which needs to be maintained.

30. Sustainable development and agriculture are based on the concept of a steady state. Removal of resources only as they are replenished leaves a net change of zero. The sustainability of a system is based on the average residence time of particular materials.

31. Average residence time is calculated as: the total size of the system (S) divided by the average rate of transfer through the System (F). Ex: If the total nitrogen within an ecosystem is 10,000 pounds, and 1000 pounds is lost or gained each day, the average residence time is 10 days. ART = 10,000/1000 = 10 days

32. Average residence time can be used to measure all kinds of flux, or flow, through a system. Some man-made substances have ART’s of decades, or hundreds of years. Ex: PCB’s, DDT These types of toxins cause chronic, or long term damage, rather than acute, or immediate damage.

33. Systems with a high rate of change (Low ART) are more susceptible to acute damage from pollutants. Conversely, the pollutant will leave the system quickly.

34. A system with a slow rate of change (High ART) are less susceptible to acute damage from a pollutant, but the toxins will remain for a longer time, and cause more chronic damage.

35. The Gaia Hypothesis: –Named for Gaia, the Greek goddess Mother Earth –States that the surface environment of the Earth, with respect to such factors as the atmospheric composition of gases acidity-alkalinity of waters Surface temperature are actively regulated by the sensing, growth, metabolism and other activities of the biota. –Or, life manipulates the environment for the maintenance of life.