Chapter 5 Topics
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Systems concepts
Ecosystems
 Matter
and energy
 Spatial patterns
 Services
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Biogeochemical cycles
 Water
 Carbon
 Nitrogen
 Phosphorus
 Human
impacts
Why “systems”?
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Our planet consists of innumerable parts connected
by myriad processes into a vast number of complex
networks
Systems approaches allow us to investigate and
understand these parts, processes, and networks in
both focused and comprehensive ways
Systems fundamentals
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System = a network of relationships among parts,
elements, or components that interact with and
influence one another and exchange energy, matter,
or information
When studying systems, scientists identify an
arbitrary “boundary” that defines what’s “inside”
the system and what’s “outside” the system
Because no system is truly isolated from its
surroundings, we must therefore consider “inputs to”
and “outputs from” the system being studied
Feedback loops
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Feedback loop = a circular process in which a
system’s output serves as input to that same system
Depending on the system response, the feedback
loop is called either “positive” or “negative”
Positive and negative feedback loops do not mean
“good” and “bad”
Positive feedback loop
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Positive feedback loop = the system response is
amplified (unidirectional), driving the system toward
an extreme condition
Rare in nature, but common in systems altered by
human actions
Negative feedback loop
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Negative feedback loop = the system response is
dampened (bidirectional), driving the system
toward a more-or-less stable condition
Most systems in nature operate in this way
Other systems concepts
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Dynamic equilibrium =
system processes move in
opposing directions
balancing their effects
Homeostasis = systems
seek to maintain constant
(stable) internal conditions
Emergent properties =
system characteristics that
are not evident in the
components alone
Earth’s systems – a reminder
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The framework of
Earth’s four systems
helps make complexity
comprehensible
 Lithosphere
= rock
 Atmosphere = air
 Hydrosphere = water
 Biosphere = life
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The boundaries overlap,
so the systems interact
Tools for studying systems - models
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A scientific model = a simplified representation of
a complex natural process that helps us understand
the process and make predictions
 Researchers
gather data
 Form a hypothesis about relationships
 The model predict how the system will behave
 New data refine and increase the model’s accuracy
Other tools
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Remote sensing allows a
whole-landscape
perspective – especially
important for studying
climate systems
Geographic information
system (GIS) = used to
analyze the spatial
arrangement of
landscape elements
Applying systems concepts
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Solving environmental
problems requires
considering all of the
parts and processes in
the system of interest
The Gulf of Mexico’s
“dead zone”, a region
of water so depleted of
oxygen (hypoxia) that
marine organisms are
killed or driven away
Eutrophication – excess nutrients
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Nutrients (nitrogen and phosphorous) are added to
the Mississippi River from
 Fertilizers
and manure from Midwestern farms
 Sewage treatment plants, run-off, and emissions
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Nutrient over-enrichment causes
 Phytoplankton
to grow rapidly and die, then…
 Bacteria eat dead phytoplankton and other wastes
 Explosions of bacteria deplete oxygen, causing…
 Fish and other aquatic organisms to suffocate
Eutrophication yields hypoxia
Ecosystems
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Ecosystem = all organisms and nonliving conditions
that exist and interact at a given place and time
Parts and processes…
 Living
organisms (biotic factors) are tightly intertwined
with chemical and physical conditions (abiotic factors)
 Through interactions and feedback loops
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Inputs and outputs…
 Energy
flows through ecosystems, arriving as solar
radiation and leaving as heat
 Matter is recycled within ecosystem, through food-web
relationships and decomposition
Energy and matter
Energy becomes biomass
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Productivity = rate at which biomass is generated
Primary production = conversion of solar energy to
chemical energy in sugars by autotrophs
Gross primary production (GPP) = the total amount
of energy assimilated by autotrophs
Net primary production (NPP) = the energy
converted by autotrophs into biomass (available for
consumption by heterotrophs)
Secondary production = biomass generated by
heterotrophs from consuming autotrophs
NPP by ecosystem
Global distribution of NPP
Ecosystems interact spatially
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The term “ecosystem” is most often applied to selfcontained systems of moderate geographic extent
Adjacent ecosystems, such as prairies and forests,
may share components and interact along their
boundaries
These transitional zones between ecosystems are
called ecotones
Landscape ecology
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Landscape ecology = studies how landscape structure
affects the abundance, distribution, and interaction of
organisms
The landscape is divided into patches whose size
depends on the relationships being studied
Patches can take on complex patterns, called mosaics,
leading to the development of metapopulations,
subpopulations in which most members remain within a
patch but others move among patches
Widely spaced patches can lead to speciation or
endanger an organism’s survival
Ecotones, patches, and mosaics
Ecosystems provide vital services
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Humans depend on healthy, functioning ecosystems
They provide goods & services we need to survive
Ecosystem services = economically beneficial
services provided by the planet’s natural systems
 Soil
formation, water and air purification, pollination
 Breakdown of some pollutants and waste
 Quality of life issues (inspiration, spiritual renewal)
 Nutrient cycling
Ecosystem goods and services
Nutrients
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Nutrients = elements and compounds required for
survival that are consumed by organisms
Macronutrients = required in larger amounts
Micronutrients = nutrients needed in smaller amounts
Nitrogen and phosphorus are the primary nutrients
needed for plant and algal growth
 Phosphorous
in a “limiting nutrient” for freshwater
 Nitrogen and iron are the “limiting nutrients” for
saltwater
Nutrient cycles
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Because of the their importance for plant growth,
the cycling of carbon, nitrogen, and phosphorous
are of special interest for ecosystems
These are known as biogeochemical cycles and
are characterized by their
 Pools
(reservoirs) where nutrients reside for varying
amounts of time (the residence time)
 Flux = the rate at which materials move between pools
which can change over time
Nutrient sources and sinks
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Pools function as sources and sinks for nutrients
depending on relative rates of in-flux and out-flux,
yielding different residence times
The hydrologic (water) cycle
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Process (flux) terms
Evaporation
 Condensation
 Precipitation
 Run-off
 Infiltration
 Uptake
 Transpiration
 Extraction
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Groundwater terms
Groundwater = water
contained in soil/rock
 Aquifer = a soil/rock
layer that transmits and
produces water easily
 Water table = the upper
surface of groundwater
in unconfined aquifers
 Discharge = the release
of groundwater to
surface water bodies
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Hydrologic cycle diagram
Human impacts to hydrologic cycle
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Removing forests and vegetation increases runoff and
erosion, reduces transpiration and lowers water tables
Irrigating agricultural fields depletes rivers, lakes and
streams and increases evaporation
Damming rivers increases evaporation and infiltration
Emitting pollutants changes the nature of precipitation
The most threatening impact: overdrawing groundwater
for drinking, irrigation, and industrial use
Water shortages create worldwide conflicts
The carbon cycle
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Carbon cycle = describes the route of carbon
atoms through the environment
Photosynthesis by plants, algae and cyanobacteria
removes carbon dioxide from air and water
Respiration returns carbon to the air and oceans
Sedimentary rocks are the primary long-term sink
for carbon
The oceans, atmosphere, plants, and soil are also
important pools
Carbon cycle diagram
Human impacts to carbon cycle
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Burning fossil fuels moves carbon from geologic
pools into the atmosphere
Cutting forests and burning fields moves carbon
from vegetation into the atmosphere
Today’s atmospheric carbon dioxide reservoir is the
largest in the past 800,000 years
Elevated atmospheric carbon dioxide is the driving
force behind climate change
Ocean acidification results when carbon moves from
the atmosphere into the ocean
The nitrogen cycle
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Nitrogen cycle = describes the routes that nitrogen
atoms take through the environment
Nitrogen gas comprises 78% of our atmosphere but
cannot be used by organisms
Nitrogen fixation = lightning or nitrogen-fixing
bacteria combine (fix) nitrogen with hydrogen to
form ammonium (NH4+)
Nitrogen cycle processes
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Nitrification = bacteria convert ammonium ions first
into nitrite and nitrate ions which plants can take up
Animals obtain nitrogen by eating plants (animals)
Decomposers release NH4+ to nitrifying bacteria
Denitrifying bacteria = convert nitrates in soil or
water to gaseous nitrogen releasing it back to the
atmosphere
Nitrogen cycle diagram
Human impacts to nitrogen cycle
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Haber-Bosch process = production of fertilizers by
combining nitrogen and hydrogen to synthesize ammonia
Fixing atmospheric nitrogen with fertilizers
 Increases emissions of greenhouse gases and smog
 Washes calcium and potassium out of soil
 Acidifies water and soils
 Moves nitrogen into terrestrial systems and oceans
 Reduces diversity of plants adapted to low-N soils
 Changes estuaries and coastal ecosystems and fisheries
The phosphorus cycle
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Phosphorus cycle = describes the routes that
phosphorus atoms take through the environment
Sediments and sedimentary rocks are the primary
pool
There is no significant atmospheric component
With naturally low environmental concentrations
phosphorus is a limiting factor for plant growth
The phosphorus cycle
Humans impacts to phosphorus cycle
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Mining rocks for fertilizer moves phosphorus from
the soil to water systems
Wastewater discharges also release phosphorus
Runoff containing phosphorus causes eutrophication
of aquatic systems