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

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

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.

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.

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

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

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

Negative feedback

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

Positive feedback

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

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

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

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

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

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