1. AP Environmental Science Earth’s Environmental Systems
Mr. Grant
Lesson 32
Earth’s Environmental Systems

2. Objectives:
Define the terms negative feedback loop and positive feedback loop.
Describe the nature of environmental systems.

3. Define the terms negative feedback loop and positive feedback loop.
Negative Feedback Loop: A feedback loop in which output of one type acts as input that moves the system in the opposite direction. The input and output essentially neutralize each other’s effects, stabilizing the system.
Positive Feedback Loop: A feedback loop in which output of one type acts as input that moves the system in the same direction. The input and output drive the system further toward one extreme or another.

4. Describe the nature of environmental systems.
Earth’s natural systems are complex, so environmental scientists often take a holistic approach to studying environmental systems.
Systems are networks of interacting components that generally involve feedback loops, show dynamic equilibrium and result in emergent properties.
Negative feedback stabilizes systems, whereas positive feedback destabilizes systems. Positive feedback often results from human disturbance if natural systems.
Because environmental systems interact and overlap, one’s delineation of systems depends on the questions in which one is interested.
Hypoxia in the Gulf of Mexico, resulting from nutrient pollution in the Mississippi River, illustrates how systems are interrelated.

5. Earth’s environmental systems
Our planet’s environment consists of complex networks of interlinked systems
Matter and molecules
Organisms, populations, interacting species
Nonliving entities (rocks, air, water, etc.)
A systems approaches assesses questions holistically
Helping address complex, multifaceted issues
But systems can show behavior that is hard to understand and predict

6. Systems show several defining properties
System = a network of relationships among parts, elements, or components
They interact with and influence one another
They exchange energy, matter, or information
Systems receive inputs of energy, matter, or information
They process these inputs and produce outputs
Feedback loop = a circular process in which a system’s output serves as input to that same system
Negative and positive feedback loops do not mean bad and good

7. Negative feedback loop
Negative feedback loop = output from a system moving in one direction acts as input
That moves the system in the other direction
Input and output neutralize one another
Stabilizes the system
Example: predator – prey interactions
Most systems in nature

8. Negative feedback

9. Positive feedback loop
Positive feedback loop = instead of stabilizing a system, it drives it further toward one extreme or another
Exponential growth in human population, erosion, melting sea ice
Rare in nature
But is common in natural systems altered by humans

10. Positive feedback

11. Systems are active
Dynamic equilibrium = system processes move in opposing directions
Balancing their effects
Homeostasis = a system maintains constant (stable) internal conditions
Emergent properties = system characteristics are not evident in the components alone
The whole is more than the sum of the parts
It is hard to fully understand systems; they connect to other systems and do not have sharp boundaries

12. Environmental systems interact
Environmental entities: complex, interacting systems
For example, river systems consist of hundreds of smaller tributary subsystems
Impacted by farms, cities, fields, etc.
Solving environmental problems means considering all appropriate components in the system of interest

13. Central Case: The Gulf of Mexico’s “Dead Zone”
The Gulf of Mexico brings in a billion pounds/year of shrimp, fish, and shellfish
Gulf “dead zone” = a region of water so depleted of oxygen
That marine organisms are killed or driven away
Hypoxia = low concentrations of dissolved oxygen in water
From fertilizer, fossil fuel emissions, runoff, sewage

14. Eutrophication: a systems perspective
Fertilizer from Midwestern farms adds nutrients to the Mississippi River, which causes…
Phytoplankton to grow, then…
Bacteria eat dead phytoplankton and wastes
Explosions of bacteria deplete oxygen, causing…
Fish and other aquatic organisms to suffocate
Sources of nitrogen and phosphorus include:
Agricultural sources, nitrogen-fixing crops
Livestock manure, sewage treatment plants, street runoff, industrial and vehicle emissions

15. Eutrophication The process of nutrient over-enrichment leads to:
Blooms of algae
Increased production of organic matter
Decomposition and hypoxia

16. Systems are perceived in various ways
Categorizing environmental systems helps make Earth’s dazzling complexity comprehensible
For example, the Earth consists of structural spheres
Lithosphere = rock and sediment
Atmosphere = the air surrounding our planet
Hydrosphere = liquid, solid or vapor water
Biosphere = the planet’s living organisms and the abiotic (nonliving) portions of the environment
Boundaries overlap, so the systems interact