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Lecture Outlines
Chapter 5
Environment:The Science behind theStories
4th Edition
Withgott/Brennan
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Study Guide:
•Environmental systems
•Ecosystems and theirservices
•How living and nonlivingentities interact
•Landscape ecology, GISand ecological modeling
•The water, carbon,nitrogen, and phosphoruscycles
•Human impacts on thesecycles
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Central Case: The Gulf of Mexico’s “DeadZone”
•The Gulf of Mexico brings in abillion pounds/year of shrimp,fish, and shellfish
•Gulf “dead zone” = a region ofwater so depleted of oxygen
-That marine organisms arekilled or driven away
•Hypoxia = low concentrationsof dissolved oxygen in water
-From fertilizer, fossil fuelemissions, runoff, sewage
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Earth’s environmental systems
•Our planet’s environment consists of complex networksof 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 tounderstand and predict
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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, orinformation
-They process these inputs and produce outputs
•Feedback loop = a circular process in which asystem’s output serves as input to that same system
•Negative and positive feedback loops do not meanbad and good
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Negative feedback loop
•Negative feedback loop = output from a system movingin 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
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Negative feedback
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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
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Positive feedback
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Systems are active
•Dynamic equilibrium = systemprocesses move in opposing directions
-Balancing their effects
•Homeostasis = a system maintainsconstant (stable) internal conditions
•Emergent properties = systemcharacteristics are not evident in thecomponents alone
-The whole is more than the sum ofthe parts
It is hard to fully understand systems; they connect to other systemsand do not have sharp boundaries
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Environmental systems interact
•Environmental entities: complex, interacting systems
•For example, river systems consist of hundreds ofsmaller tributary subsystems
-Impacted by farms, cities, fields, etc.
•Solving environmental problems means consideringall appropriate components in the system of interest
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Eutrophication: a systems perspective
•Fertilizer from Midwestern farms adds nutrients to theMississippi 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, streetrunoff, industrial and vehicle emissions
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Eutrophication
•The process of nutrient over-enrichment leads to:
-Blooms of algae
-Increased production of organic matter
-Decomposition and hypoxia
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Systems are perceived in various ways
•Categorizing environmental systems helps makeEarth’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 theabiotic (nonliving) portions of the environment
•Boundaries overlap, so the systems interact
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Ecosystems
•Ecosystem = all organisms and nonliving entities thatoccur and interact in a particular area at the same time
-It includes abiotic and biotic components
•Biological entities are tightly intertwined with chemicaland physical entities
-Through interactions and feedback loops
•Ecosystems receive, process and transform inputs ofenergy
-While cycling and recycling matter
-Outputs produced include heat, water, wastes
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Systems of interacting entities in ecosystems
•Energy from the sun flows in one direction
-Arriving as radiation and leaving as heat
•Matter is recycled within ecosystem
-Through food-web relationships and decomposition
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Energy is converted to biomass
•Primary production = conversion of solar energy tochemical energy in sugars by autotrophs
•Gross primary production (GPP) = assimilation ofenergy by autotrophs
•Net primary production (NPP) = energy remainingafter respiration which is used to generate biomass
-Available for consumption by heterotrophs
•Secondary production = biomass generated byheterotrophs from consuming autotrophs
•Productivity = rate at which ecosystems generatebiomass
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Net primary productivity of ecosystems
High net primary productivity = ecosystems whoseplants rapidly convert solar energy to biomass
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NPP variation causes global geographicpatterns
NPP increases with temperature and precipitation onland, and with light and nutrients in aquatic ecosystems
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Nutrients can limit productivity
•Nutrients = elements and compounds required forsurvival that are consumed by organisms
•Macronutrients = required in larger amounts
-Nitrogen, carbon, phosphorus
•Micronutrients = nutrients needed in smaller amounts
•Nutrients stimulate plant production
-Nitrogen and phosphorus are important for plant andalgal growth
Dramatic growth of algae inwater treated with phosphate
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Nutrient runoff is devastating aquaticsystems
•Nitrogen is the more important limiting factor forprimary productivity
-In coastal ocean waters
-Iron is an effective nutrient for open ocean waters
•Satellite imagery gives scientists an improved view ofproductivity at regional and global scales
Phytoplankton blooms off theLouisiana coast
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Worldwide marine dead zones
•Over 400 dead zones occur globally
-Most are off the coasts of Europe and the U.S.
-Mostly due to farm, city and industrial pollution
-Some are seasonal, others are permanent
•Fisheries and ecosystems are devastated
-Causing over $2 billion/year in lost harvests
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Ecosystems interact spatially
•Ecosystems vary greatly in size
-From a puddle of water to a bay, lake or forest
•The term “ecosystem” is most often applied to self-contained systems of moderate geographic extent
•Adjacent ecosystems may share components and interact
-I.e. prairie and forests interact where they converge
•Ecotones = transitional zones between two ecosystems
-Elements of each ecosystem mix
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•Landscape ecology = studies how landscape structure affectsthe abundance, distribution, and interaction of organisms
-Helpful for sustainable regional development
•Patches = form the landscape
-Are spread spatially in complex patterns (a mosaic)
-I.e. forested patches within an agricultural landscape
-Widely spaced patches endanger organisms
Landscape ecology
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Metapopulations and conservation biology
•Metapopulation = a network of subpopulations
-Most members stay within patches
-Some individuals may move among patches or matewith those of other patches
-Individuals in small, isolated patches risk extinction
•Conservation biologists = study the loss, protection, andrestoration of biodiversity
•Human development fragments habitat
-Creating small, isolated patches
-Habitat corridors that link patches protect biodiversity
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Remote sensing applies landscape ecology
•Remote sensing allows scientiststo take a landscape perspective
•Geographic information system(GIS) = computer software used inlandscape ecology research
-Analyzes how elements of alandscape are arranged
-Helps in planning and land-usedecisions
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Modeling helps us understand systems
•A model = a simplified representation of a complexnatural process
-Helps us understand the process and make predictions
•Ecological modeling = constructs and tests models
-To explain and predict how ecological systems work
•Researchers gather data and form a hypothesis aboutrelationships
-Models predict how the system will behave
-New data refine and increase the model’s accuracy
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Ecological modeling
Ecological modeling resembles the scientific method
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Ecosystems provide vital services
•Human society depends on healthy, functioningecosystems
-They provide goods and services we need to survive
•Ecosystem services = provided by the planet’s systems
-Soil formation, water and air purification, pollination
-Breakdown of some pollutants and waste
-Quality of life issues (inspiration, spiritual renewal)
-Nutrient cycling
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Ecosystem goods and services
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Nutrients circulate through ecosystems
•Matter is continually circulated in ecosystems
•Nutrient (biogeochemical) cycles = the movement ofnutrients through ecosystems
-Atmosphere, hydrosphere, lithosphere, and biosphere
•Pools (reservoirs) = where nutrients reside for varyingamounts of time (the residence time)
•Flux = the rate at which materials move between pools
-Can change over time
-Is influenced by human activities
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Main components of a biogeochemical cycle
•Source = a pool that releases more nutrients than itaccepts
•Sinks = a pool that accepts more nutrients than it releases
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The hydrologic cycle
•Water is essential for biochemical reactions
-It is involved in nearly every environmental system
•Hydrologic cycle = summarizes how liquid, gaseous andsolid water flows through the environment
-Oceans are the main reservoir
•Evaporation = water moves from aquatic and landsystems into the atmosphere
•Transpiration = release of water vapor by plants
•Precipitation, runoff, and surface water = water returnsto Earth as rain or snow and flows into streams, oceans,etc.
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Transpiration
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Groundwater
•Aquifers = underground reservoirs of sponge-likeregions of rock and soil that hold…
-Groundwater = water found underground beneathlayers of soil
•Water table = the upper limit of groundwater in anaquifer
-Water may be ancient (thousands of years old)
•Groundwater becomes exposed to the air where the watertable reaches the surface
-Exposed water runs off to the ocean or evaporates
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The hydrologic cycle
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Human impacts on the hydrologic cycle
•Removing forests and vegetation increases runoff anderosion, reduces transpiration and lowers water tables
•Irrigating agricultural fields depletes rivers, lakes andstreams and increases evaporation
•Damming rivers increases evaporation and infiltration
•Emitting pollutants changes the nature of precipitation
•The most threatening impact: overdrawing groundwaterfor drinking, irrigation, and industrial use
-Water shortages create worldwide conflicts
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The carbon cycle
•Carbon is found in carbohydrates, fats, proteins, bones,cartilage and shells
•Carbon cycle = describes the route of carbon atomsthrough the environment
•Photosynthesis by plants, algae and cyanobacteria
-Removes carbon dioxide from air and water
-Produces oxygen and carbohydrates
-Plants are a major reservoir of carbon
•Respiration returns carbon to the air and oceans
-Plants, consumers and decomposers
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Sediment storage of carbon
•Decomposition returns carbon to the sediment
-The largest reservoir of carbon
-May be trapped for hundreds of millions of years
•Aquatic organisms die and settle in the sediment
-Older layers are buried deeply and undergo highpressure
-Ultimately, it may be converted into fossil fuels
•Oceans are the second largest reservoir of carbon
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The carbon cycle
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Humans affect the carbon cycle
•Burning fossil fuels moves carbon from the ground to theair
•Cutting forests and burning fields moves carbon fromvegetation to the air
•Today’s atmospheric carbon dioxide reservoir is thelargest in the past 800,000 years
-It is the driving force behind climate change
•The missing carbon sink: 1-2 billion metric tons ofcarbon are unaccounted for
-It may be taken up by plants or soils of northerntemperate and boreal forests
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The nitrogen cycle
•Nitrogen comprises 78% of our atmosphere
-It is contained in proteins, DNA and RNA
•Nitrogen cycle = describes the routes that nitrogenatoms take through the environment
-Nitrogen gas cannot be used by organisms
•Nitrogen fixation = lightning or nitrogen-fixingbacteria combine (fix) nitrogen with hydrogen
-To form ammonium
-Which can be used by plants
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Nitrification and denitrification
•Nitrification = bacteria convert ammonium ions first intonitrite ions then into nitrate ions
-Plants can take up these ions
•Animals obtain nitrogen by eating plants or other animals
•Decomposers get it from dead and decaying plants orother animals
-Releasing ammonium ions to nitrifying bacteria
•Denitrifying bacteria = convert nitrates in soil or waterto gaseous nitrogen
-Releasing it back into the atmosphere
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The nitrogen cycle
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Humans affect the nitrogen cycle
•Haber-Bosch process = production of fertilizers bycombining nitrogen and hydrogen to synthesize ammonia
-Humans overcame the limits on crop productivity
•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-nitrogensoils
-Changed estuaries and coastal ecosystems and fisheries
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Humans put nitrogen into the environment
Fully half of nitrogen entering the environment is of human origin
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The phosphorus cycle
•Phosphorus (P) is a key component of cell membranes,DNA, RNA, ATP and ADP
•Phosphorus cycle = describes the routes that phosphorusatoms take through the environment
•Most phosphorus is within rocks
-It is released by weathering
-There is no significant atmospheric component
•With naturally low environmental concentrations
-Phosphorus is a limiting factor for plant growth
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The phosphorus cycle
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Humans affect the phosphorus cycle
•Mining rocks for fertilizer moves phosphorus from thesoil to water systems
•Wastewater discharge also releases phosphorus
•Runoff containing phosphorus causes eutrophication ofaquatic systems
-Produces murkier waters
-Alters the structure and function of aquatic systems
-Do not buy detergents that contain phosphate
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Solutions to the dead zone
•The Harmful Algal Bloom and Hypoxia Research andControl Act (1998)
-Called for an assessment of hypoxia in the dead zone
•Solutions outlined included:
-Reduce nitrogen fertilizer use in Midwestern farms
-Apply fertilizer at times which minimize runoff
-Use alternative crops and manage manure better
-Restore wetlands and create artificial ones
-Improve sewage treatment technologies
-Evaluate these approaches
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Decreasing pollution
•Scientists, farmers and policymakersare encouraged to
-Decrease fertilizer use
-While safeguarding agriculture
•Offering insurance and incentives
•Using new farming methods
•Planting cover crops
•Maintaining wetlands
•There have been some successes
-Despite a lack of funding
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Conclusion
•Thinking in terms of systems teaches us how to avoiddisrupting Earth’s processes
-How to mitigate any disruptions we cause
•Life interacts with its nonliving environment in ecosystems
-Through which energy flows and matter recycles
•Understanding biogeochemical cycles is crucial
-Humans are significantly changing the ways thesecycles function
•Environmental systems have survived
-Sustainability means learning from natural systems
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QUESTION: Review
Which of the following describes a negative feedback loop?
a)It drives a system towards an extreme
b)It stabilizes the system
c)It causes the system to move in one directionat a time
d)It is rare in nature
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QUESTION: Review
Which of the following statements is NOT correct?
a)A system is a network of relationships amongvarious components.
b)In a dynamic equilibrium, system processes move inopposing directions to balance their effects.
c)A system in homeostasis is not able to maintainconstant (stable) internal conditions.
d)A system with emergent properties has characteristicsthat are not evident in the components alone.
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QUESTION: Review
Which of the following is a correct statement?
a)Energy and matter flow in one direction only
b)Energy and matter both cycle repeatedly
c)Energy flows in one direction, while matter recycles
d)Matter flows in one direction, while energy recycles
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QUESTION: Review
What is the definition of secondary production?
a)Biomass generated by heterotrophs fromconsuming autotrophs
b)Elements and compounds that are required forsurvival
c)Energy remaining after respiration that is used togenerate plant biomass
d)Assimilation of energy by autotrophs
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QUESTION: Review
Which biogeochemical cycle uses photosynthesis andrespiration to cycle its atoms?
a)Carbon
b)Nitrogen
c)Water
d)Phosphorus
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QUESTION: Review
Which biogeochemical cycle is being affected byincreased fertilizer production through the Haber-Boschprocess?
a)Carbon
b)Nitrogen
c)Water
d)Phosphorus
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QUESTION: Review
Which of the following is NOT a way to decreasehypoxia?
a)Reduce fertilizer use in the MidwesternUnited States
b)Apply fertilizer during spring rains
c)Restoring wetlands
d)Improving sewage treatment technologies
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QUESTION: Weighing the Issues
Which of the following ecosystem services do you thinkis the most important?
a)Providing services such as water purification
b)Providing goods such as food
c)Enhancing the quality of our lives, such asspiritual renewal
d)All of these are fundamentally important
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QUESTION: Interpreting Graphs and Data
How many terrestrial patchesare located in this figure?
a) 5
b) 2
c)1
d)3
