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Chapter 3

Chapter 3.docx

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Department
Environment
Course Code
ENV100Y5
Professor
Monika Havelka

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Chapter 3: Earth’s Environmental Systems: • Consists of complex networks of interlinked systems • Between living and non-living System: is a network of relationships among parts, elements or components that interact with and influence one another through exchanges of energy, matter or information Types of systems – properties of boundaries: • Isolated system: neither energy nor matter can be exchanged across the boundaries • Closed system: energy can be exchanged across the boundaries, but matter cannot o Systems receive inputs and produce outputs of energy o Consequences:  Resources are finite and limited  There is no “away” to throw things to  “What goes around, comes around” - Principle of Environmental Unity • Open system: both matter and energy can be exchanged across the boundaries o System receive inputs of both energy and matter and produce outputs of both Sometimes cycles are affected by feedback loops: • Positive feedback: o Output from the system acts as an input that drives the system farther in the same direction – toward one extreme or another o Self-reinforcing, self-perpetuating o “vicious” cycle o Stabilizes the system o E.g. removal of soil by water or wind (erosion) • Negative feedback: o Output from the system acts as an input that moves the system in the opposite direction – stabilizing it or returning it to the starting point o Self-regulating, homeostatic o “equilibrium” cycle Systems show several basic properties: • Dynamic equilibrium – systems are constantly changing, interacting, balancing • Homeostasis – many systems tend to maintain stable internal conditions o Resistance: strength to remain constant o Resilience: some systems (not all) recover easily from disturbances • Emergent properties – system characteristics not evident in components on their own Complex systems have multiple subsystems: • Systems seldom have well-defined boundaries so deciding where one system ends and another begins can be difficult Environmental systems may be perceived in warious ways: • Major Earth spheres: o Geosphere: is the rock and sediment beneath our feet (uppermost layer – lithosphere) o Atmosphere: is composed of the air surrounding our planet o Hydrosphere: encompasses all water – salt or fresh, liquid, ice or vapour – in surface water bodies and glaciers near the underground  The subsystem that consists of the perennially frozen parts of the hydrosphere has its own name - crysophere o Biosphere: consists of all the planet’s living organisms o Arguing: anthrosphere/technospehre – encompasses the parts of the environment that are built or modified by humans for human use Ecosystem ecology: study of interactions among organisms and their physical environment as an integrated system • a way of looking at organisms and their interactions with the environment as an integrated system • focuses on functions, processes, fluxes (energy, nutrients), biogeochemical cycles, etc. • ecosystems are nested and hierarchical • ecosystems are dynamic • inputs, outputs, feedback loops, resistance & resilience, emergent properties • boundary between the biotic and abiotic components is often blurred • ecosystem stability: resistance and resilience • 4 main components: o abiotic env’t (water, soil minerals, atmospheric gases) o 1° producers o consumers o decomposers • species are not usually treated as separate units; functional role is what is important • abiotic components are of equal importance as biotic components (movement of nutrients & energy are focus of investigation) • human activities are often important (e.g. deposition of pollutants, harvesting of species, etc.) • ecosystems are nested and hierarchical, thus we can study them on a number of different spatial and temporal scales • spatial boundaries: o often indistinct boundary o organisms may move between aquatic & terrestrial environment; trees drop leaves into pond • temporal scale: o instantaneous o seasonal o successional o evolutionary history o geologic history • Energy flow in ecosystem: o ecosystem is an economy; energy is the currency o ecosystems based on autotrophs o autotrophs transform energy from sunlight or inorganic compounds into chemical energy stored in sugars o energy converted by primary producers: growth, maintenance (respiration), reproduction  Net Primary Productivity (NPP) = Gross Primary Productivity(GPP) - respiration by autotrophs  NPP = energy available to consumers & decomposers • terrestrial ecosystems: max NPP in wet tropics • marine ecosystems: max NPP along coastlines Limit to productivity in aquatic ecosystem: o coastlines more productive than open ocean o depth of photic zone; nutrients o Systems and cycles consist of interconnected reservoirs: • Acycle is: o a system of two or more connected reservoirs, in which material (or energy) is transferred in a cyclical fashion. o a way of understanding and modeling where substances come from, where they go, where they “reside” in the Earth system, and how they are transferred and transformed. • Matter is endlessly recycled through environmental systems, changing form as it goes. • Energy comes into the Earth system, cycles around, is used and degraded, and then exits the system. Biogeochemical Cycle: • Nutrients moving ecosystems • Travel through atmosphere, hydrosphere, geosphere and from one organism to another in dynamic equilibrium • Reservoir: a location where materials in a cycle remain for a period of time before moving to another reservoir o Residence time: average time the material remains in the reservoir o If Sources = Sinks: Steady State • Flux: movement of material/energy among reservoir o amount of material transferred, described in terms of mass or volume per unit of time o Fluxes are controlled by rates of transfer processes and capacities of reservoirs • Sources: a reservoir that releases more material than it takes in • Source: where the flux is coming from o gives out more than it takes in • Sink: where the fl
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