1 AP Environmental Science Earth’s Environmental Systems Mr. GrantLesson 32Earth’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 systemsMatter and moleculesOrganisms, populations, interacting speciesNonliving entities (rocks, air, water, etc.)A systems approaches assesses questions holisticallyHelping address complex, multifaceted issuesBut 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 componentsThey interact with and influence one anotherThey exchange energy, matter, or informationSystems receive inputs of energy, matter, or informationThey process these inputs and produce outputsFeedback loop = a circular process in which a system’s output serves as input to that same systemNegative 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 inputThat moves the system in the other directionInput and output neutralize one anotherStabilizes the systemExample: predator – prey interactionsMost systems in nature
9 Positive feedback loop Positive feedback loop = instead of stabilizing a system, it drives it further toward one extreme or anotherExponential growth in human population, erosion, melting sea iceRare in natureBut is common in natural systems altered by humans
11 Systems are activeDynamic equilibrium = system processes move in opposing directionsBalancing their effectsHomeostasis = a system maintains constant (stable) internal conditionsEmergent properties = system characteristics are not evident in the components aloneThe whole is more than the sum of the partsIt 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 systemsFor example, river systems consist of hundreds of smaller tributary subsystemsImpacted 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 shellfishGulf “dead zone” = a region of water so depleted of oxygenThat marine organisms are killed or driven awayHypoxia = low concentrations of dissolved oxygen in waterFrom 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 wastesExplosions of bacteria deplete oxygen, causing…Fish and other aquatic organisms to suffocateSources of nitrogen and phosphorus include:Agricultural sources, nitrogen-fixing cropsLivestock manure, sewage treatment plants, street runoff, industrial and vehicle emissions
15 Eutrophication The process of nutrient over-enrichment leads to: Blooms of algaeIncreased production of organic matterDecomposition and hypoxia
16 Systems are perceived in various ways Categorizing environmental systems helps make Earth’s dazzling complexity comprehensibleFor example, the Earth consists of structural spheresLithosphere = rock and sedimentAtmosphere = the air surrounding our planetHydrosphere = liquid, solid or vapor waterBiosphere = the planet’s living organisms and the abiotic (nonliving) portions of the environmentBoundaries overlap, so the systems interact