Transcript Ecosystems full

Feedback Loops
Ch 5, pgs 109-122
Earth’s environmental systems
• Our planet’s environment consists of complex networks
of interlinked systems
- Matter and molecules
- Organisms, populations, interacting species
- Nonliving things (rocks, air, water, etc.)
• A systems approaches assesses questions as a whole
- 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
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
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
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 lack of oxygen in the water
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
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
Systems are perceived in various ways
• Categorizing environmental systems helps make
Earth’s 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
Major Components of Systems
- Abiotic = nonliving
components;
physical and
chemical factors
- water, air, nutrients,
solar energy
- Biotic = living or
once living
components
Ecosystems
• Ecosystem = all organisms and nonliving objects that
occur and interact in a particular area at the same time
- It includes abiotic and biotic components
• Biological entities are tightly intertwined with chemical
and physical entities through interactions and feedback
loops
• Ecosystems receive, process and transform inputs of
energy while cycling and recycling matter
- Outputs produced include heat, water, wastes
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
Ecosystems interact spatially
• Ecosystems vary greatly in size
- From a puddle of water to a bay, lake or
forest
• Adjacent ecosystems may share components
and interact
- ex. prairie and forests interact where they
converge
• Ecotones = transitional zones between two
ecosystems
- Elements of each ecosystem mix
• Patches = form the landscape
- Example: forested patches within an
agricultural landscape
- Widely spaced patches endanger
organisms
Productivity
• The amount of photosynthesis that
takes place is one indicator of an
ecosystem’s productivity
• Primary productivity: amount of
biomass produced by
photosynthetic organisms
- Net Primary Productivity
(NPP): the left-over remains of
biomass available to use as food
for other consumers after the
producer has used some for their
own respiration
• Secondary productivity: amount
of biomass produced by organisms
that eat photosynthetic organisms
NPP (net primary productivity)
• NPP can be considered the rate at which
energy for use by consumers is stored in
new biomass (cells, leaves, roots, and
stems)
- Most productive ecosystems
- 1. algal beds and reefs
- 2. tropical rain forests
- 3. swamps and marshes
- Least productive ecosystems
- 1. desert
- 2. open ocean
- 3. tundra
Numbers equal biomass
Net primary productivity of ecosystems
High net primary productivity = ecosystems whose
plants rapidly convert solar energy to biomass
NPP variation causes global geographic
patterns
NPP increases with temperature and precipitation on
land, and with light and nutrients in aquatic ecosystems
NPP as a limiting factor
• Since producers are the
source of all food in an
ecosystem, NPP is
ultimately a limiting factor
- Humans now use, waste,
or destroy about 27% of
the earth’s total potential
NPP, and 40% of the
NPP of the planet’s
terrestrial ecosystems
Biodiversity
Ch 11
pgs 181-296
Levels of biological diversity (biodiversity)
• Humans are reducing Earth’s
diversity of life
• Biodiversity = variety of life at
all levels of organization
- Species diversity
- Genetic diversity
- Population and community
diversity
Species diversity
• Species = a set of individuals that share certain
characteristics and can interbreed
- Producing fertile offspring
• Species diversity = the number or variety of species
in a particular region
- Richness = the number of species
- Evenness (relative abundance) = the similarity in
numbers between species
• Speciation adds to species richness
- Extinction reduces species richness
Species diversity and evenness
Compared with the boxed area at the top:
Which area has greater species richness? Why?
Which has reduced richness? Why?
Genetic diversity
• Encompasses the differences in DNA among
individuals
• The raw material for adaptation to local conditions
• Populations with higher genetic diversity can survive
- They can cope with environmental change
• Populations with low genetic diversity are vulnerable
to environmental change or disease
• Inbreeding depression = genetically similar parents
mate and produce inferior offspring
- Cheetahs, bison, elephant seals
Ecosystem diversity
• Ecosystem diversity = the number and variety of
ecosystems
- Including different communities and habitats in an
area
• May include habitats, communities, or ecosystems at
the landscape level
- Sizes, shapes, and connections among patches
- Beaches, cliffs, coral reefs, ocean waters
• An area with a variety of vegetation holds more
biodiversity than the same size area with one plant type
Some groups have more species than others
• Species are not evenly
distributed among taxonomic
groups
- Insects predominate over all
other life-forms
- 40% of insects are beetles
• Groups accumulate species by:
- Adapting to local conditions
- Geographic speciation
- Low rates of extinction
Insects outnumber all other species
Measuring biodiversity is not easy
• Out of the estimated 3–100 million species on Earth, 1.8
million species have been identified and described
• Most widely accepted estimate of the number of species?
- 14 million
• It is very difficult to know how many species exist
- Small organisms are easily overlooked
- Many species look identical until thoroughly examined
- Many remote spots on Earth remain unexplored
• Entomologist Terry Erwin found 163 beetle species living
on one tree species
Biodiversity is unevenly distributed
• Living things are not
distributed evenly on Earth
• Latitudinal gradient =
species richness increases
toward the equator
Canada has 30–100 species of
breeding birds, while Costa Rica
has more than 600 species
Latitudinal gradient has many causes
• Climate stability, high plant
productivity, no glaciation
- More specialized habitats,
species coexistence
• Diverse habitats increase species
diversity and evenness
- Tropical rainforests and
drylands, ecotones
• Human disturbance can increase
habitat diversity, which leads to
species diversity
- But only at the local level
Biodiversity loss and species extinction
• Extinction = occurs when the last member of a species
dies and the species ceases to exist
• Extirpation = the disappearance of a population from a
given area, but not the entire species globally
- Can lead to extinction
• Extinction is a natural process
- 99% of all species that ever lived are now extinct
• Background rate of extinction = natural extinctions
- For mammal or marine species: each year 1 species out
of every 1–10 million goes extinct
Earth has had five mass extinctions
• Earth has had five mass extinctions in the past 440
million years
- Each event eliminated at least 50% of all species
• Humans are causing this sixth extinction event
- We will suffer as a result
People have hunted species to extinction
Extinctions followed human arrival on islands and continents
Current extinction rates are higher than
normal
• The current extinction rate is 100 to 1,000 times greater
than the background rate
• This rate will increase tenfold in future decades
- Human population growth and resource consumption
• The Red List = species facing high risks of extinction
- Mammal species (21%), bird species (12%)
- 17–74% of all other species
• In the U.S., in the last 500 years, 237 animal and 30 plant
species have been confirmed extinct
- Actual numbers are undoubtedly higher
Biodiversity loss has many causes
• Reasons for biodiversity losses are complex and
hard to determine
- Multiple factors interact in causing losses
• Four primary causes of population decline are:
- Habitat alteration
- Invasive species
- Pollution
- Overharvesting
• Global climate change now is the fifth cause
Habitat alteration causes biodiversity loss
• The greatest cause of biodiversity loss
• Habitats are destroyed, fragmented, and degraded
- Farming simplifies communities
- Grazing modifies grassland structure and composition
- Clearing forests removes resources organisms need
- Hydroelectric dams turn rivers into reservoirs
- Suburban sprawl replaces natural communities
A few species (e.g., pigeons,
rats) benefit from changing
habitats
Habitat fragmentation
• Habitat fragmentation =
gradual, piecemeal
degradation of habitat
- Farming, roads,
logging, etc.
• Continuous habitats are
broken into patches
- Species needing that
habitat disappear
• Landscape-level strategies
try to optimize areas to be
preserved
Habitat loss occurs in every biome
• Habitat loss is responsible for declines for 83% of
mammals and 85% of birds
• 99% of U.S. prairies have been converted to agriculture
- Grassland birds have declined 82–99%
Pollution causes biodiversity loss
• Pollution harms organisms in many ways
- Air pollution degrades forest ecosystems
- Water pollution impairs fish and amphibians
- Agricultural runoff harms terrestrial and aquatic
species
- Toxins, garbage, oil, and chemicals impact organisms
• Damage to wildlife and ecosystems caused by pollution
can be severe
- But it is less than the damage caused by habitat
alteration or invasive species
Overharvesting causes biodiversity loss
• Vulnerable species
- Large, few in number, longlived, and have few young
• The Siberian tiger is hunted
without rules and regulations
- Powerful economic incentives
increase poaching
• Many other species are affected
- Whales, sharks, gorillas
- The oceans contain only 10% of
the large animals they once did
Invasive species cause biodiversity loss
• Introduction of non-native
species to new areas
- Accidental: zebra
mussels, weeds
- Intentional: food crops,
exotic pets, ornamental
plants
• Island species are
especially vulnerable
Invaders cost billions of
• Invaders lack natural
predators, competitors, or dollars in damage each year
parasites
Climate change causes biodiversity loss
• Human manipulation of Earth’s climate system has
global impacts on biodiversity
• Emission of greenhouse gases warms temperatures
- Modifying global weather patterns
• The frequency of extreme weather events increases
- Droughts, etc.
• Increased stress forces organisms to shift their
geographic ranges
- Most animals and plants will not be able to adapt
- 20–30% of species are at increased risk of
extinction
Warming has been the greatest in the Arctic
Because of melting ice, polar bears can’t hunt seals, so
they were added to the endangered species list in 2008
Endangered Species
Ch 11, pgs 296-310
Biodiversity provides free ecosystem
services
• Provides food, fuel, fiber, and shelter
• Purifies air and water and detoxifies wastes
• Stabilizes climate, moderates floods, droughts,
wind, temperature
• Cycles nutrients, renews soil fertility
• Pollinates plants and controls pests and disease
• Maintains genetic resources
• Provides cultural and aesthetic benefits
• Allows us to adapt to change
The value of 17 ecosystem services = $46 trillion per year
Biodiversity helps maintain ecosystem
function
• It increases stability and resilience of natural systems
• Decreased biodiversity reduces a system’s ability to
function and provide services to our society
• The loss of a species affects ecosystems differently
- If the species can be functionally replaced by others,
it may make little difference
- Loss of key species and top predators causes other
species to decline or disappear
Biodiversity enhances food security
• Industrial agriculture has narrowed our diet
- Wild and rare species can improve food security
• New potential food crops are waiting to be used
- Serendipity berry is 3,000 times sweeter than sugar
• Genetic diversity within crops is enormously valuable
- Turkey’s wheat crops received $50 billion worth of
disease resistance from wild wheat
• Wild strains provide disease resistance
- Many grow back year after year without being
replanted
Organisms provide drugs and medicines
• Wild species produce
$150 billion/year of
drugs
• Taxol comes from the
Pacific yew tree
- Treats cancer
• Every species that goes
extinct is a lost
opportunity to cure
disease
Biodiversity generates economic benefits
• Biodiversity generates income through tourism
- Especially in developing countries
- Costa Rica: rainforests
- Australia: Great Barrier Reef
- Belize: reefs, caves, and rainforests
- Tanzania: savanna wildlife
• A powerful incentive to preserve natural areas
- Reduce impacts on the landscape and species
• But too many visitors to natural areas can degrade the
outdoor experience and disturb wildlife
Conservation biology: the search for
solutions
• Conservation biology = studies the factors behind the
loss, protection, and restoration of biodiversity
- Scientists became alarmed at the degradation of
natural systems
• An applied and goal-oriented science
• Conservation biologists integrate evolution, extinction,
ecology, and environmental systems
- Design, test, and enact ways to decrease our impacts
Conservation biology: the search for
solutions
• Conservation geneticists = study genetic attributes of
organisms to infer the status of their populations
• Minimum viable population size = how small a
population can become before it runs into problems
- Small populations are most vulnerable to extinction
and need special attention
Conservation focuses on endangered
species
• Endangered Species Act (ESA) (1973) = the primary
U.S. legislation for protecting biodiversity
• It forbids the government and citizens from taking actions
that destroy endangered species or their habitats
- Or trading in products made from endangered species
• The ESA’s goal is to prevent extinction
- Stabilize declining populations
- Enable populations to recover
• In 2010, the U.S. had 1,010 species listed as endangered
and 314 listed as threatened
The ESA has been successful
• Intensive management has saved or stabilized species
- 40% of declining populations are now stable
• These successes occur despite problems
- Underfunding of the U.S. Fish and Wildlife Service
and the National Marine Fisheries Service
- Recent political forces have tried to weaken the ESA
Peregrine falcons, brown
pelicans, bald eagles, and
others have recovered and
are no longer listed
The ESA is controversial
• Many Americans support protecting endangered species
• Opponents feel that the ESA values endangered
organisms more than the livelihood of people
- Protection will restrict land use and cost jobs
- “Shoot, shovel, and shut up” = landowners conceal the
presence of endangered species on their land
- But the ESA has stopped few development projects
• Habitat conservation plans and safe harbor agreements
- Landowners can harm species if they improve habitat
for the species in other places
Species protection can be controversial
• Protecting the northern
spotted owl slowed
logging in old-growth
rainforests
• Loggers feared for their
jobs
- Landowners feared
restrictions
International conservation efforts
• UN Convention on International Trade in
Endangered Species of Wild Fauna and Flora (1973)
- CITES protects endangered species by banning
international transport of their body parts
• Convention on Biological Diversity (1992)
- Seeks to conserve biodiversity
- Use biodiversity in a sustainable manner
- Ensure the fair distribution of biodiversity’s benefits
• By 2010, 193 nations had signed on to the Convention
- Only Andorra, the Vatican, and the U.S. did not join
The Convention on Biological Diversity
• The Convention aims to:
- Provide incentives to conserve biodiversity
- Manage access to and use of genetic resources
- Transfer technology (including biotechnology)
- Promote scientific cooperation
- Assess human effects on biodiversity
- Promote biodiversity education and awareness
- Provide funding for critical activities
- Encourage nations to report on conservation efforts
• Despite some successes, biodiversity is still being lost
Protecting biodiversity: captive breeding
• Captive breeding = individuals are bred and raised so
they can be reintroduced into the wild
- 65 plant and animal species exist only in captivity
• Reintroductions can be controversial
- Ranchers opposed reintroducing wolves to
Yellowstone National Park
- Fragmented habitat must be improved
before releasing animals
Biologists have raised condor
chicks in captivity with the
help of hand puppets that look like the
heads of adult condors
Protecting biodiversity: cloning
• Cloning creates more individuals and saves species from
extinction
- DNA from an endangered species is inserted into an
egg without a nucleus
- The egg is inserted into a closely related species
• Several mammal species have been cloned
- But these efforts are not enough to recreate lost
biodiversity
• Without ample habitat and protection in the wild, having
cloned animals in a zoo does little good
Forensics protects threatened species
• Forensic science (forensics) = analyzes evidence to
identify or answer questions relating to a crime
• Conservation scientists use forensics to protect species
- Researchers use DNA to identify a species or
subspecies and its geographic origin
• Detecting illegal activity helps enforce laws protecting
wildlife
- For example, whale meat is analyzed in Asian markets
- DNA from killed elephants shows many more were
killed than the Zambian government admitted
Umbrella species protect others
• Conservation biologists use particular species as tools
to conserve communities and ecosystems
• Umbrella species = species that, when protected, also
help protect other, less charismatic species
- Often large species that need large amounts of
habitat
- Protecting their habitat automatically protects
others
- Ex: Northern spotted owls. Molluscs and
salamanders are within the protective
boundaries of the northern spotted owl.
• Flagship species = large and charismatic species used
as spearheads for biodiversity conservation
- The World Wildlife Fund’s panda bear
• Some organizations are moving beyond the singlespecies approach to focus on whole landscapes
Parks and protected areas
• Setting aside land in parks and preserves conserves
habitats, communities, ecosystems, and landscapes
- 12% of the world’s area is in parks, wilderness,
reserves, etc.
• But these areas are not all managed for biodiversity
- They are used for recreation, water protection, etc.
- They are also illegally logged, etc.
- Many are not large enough to preserve whole systems
Biodiversity hotspots
• Biodiversity hotspots = prioritizes regions most
important globally for biodiversity
- Support a great number of endemic species = species
found nowhere else in the world
• The area must have at least 1,500 endemic plant species
(0.5% of the world total)
- It must have lost 70% of its habitat
due to humans
Focusing on hotspots protects the
greatest number of species per unit
effort
There are 34 global biodiversity hotspots
2.3% of the planet’s land surface contains 50% of the world’s
plant species and 42% of all terrestrial vertebrate species
Using innovative economic strategies
• Debt-for-nature swap = a conservation organization pays
off a portion of a developing country’s international debt
• In exchange, the country promises to set aside reserves to:
- Fund environmental education and
- Better manage protected areas
• The U.S.’s Tropical Forest Conservation Act
- Paid $218 million in debt payments to 13 developing
countries for conservation efforts
• Conservation concession = conservation organizations pay
nations to conserve, and not sell, resources
We can restore degraded ecosystems
• The best way to safeguard biodiversity and natural
systems?
- Protect natural areas before they become degraded
• Ecological restoration = restores degraded areas to some
semblance of their former condition
• Restoration ecology = restoring damaged systems to
bring back species and reestablish ecological processes
- Filter pollutants, clean water and air, build soil, etc.
Restoring Iraq’s wetlands
• Southern Iraq’s wetlands were drained in the 1970s and
1980s under Saddam Hussein, devastating the area
• After the 2003 U.S. invasion, a multi-million dollar
international restoration effort began
- Although successful, 2010’s drought caused Turkey
and Syria to divert water from the rivers
Drainage and
Restoration
Community-based conservation
• Developing nations often do not support conservationists
from developed nations trying to preserve areas
• Community-based conservation = conservation
biologists engage local people to protect land and wildlife
- It offers education, health care, and development aid
• Conservation efforts help local people
- People are retrained and income is supplemented
- Poaching is reduced
• It ensures that local resources can be sustainably used
Biogeochemical Cycles
Ch 5, pgs 122-132
Nutrients circulate through ecosystems
• Matter is continually circulated in ecosystems
• Nutrient (biogeochemical) cycles = the movement of
nutrients through ecosystems
- Atmosphere, hydrosphere, lithosphere, and biosphere
• Pools (reservoirs) = where nutrients reside for varying
amounts of time
- Flux = the rate at which materials move between pools
- Can change over time
- Is influenced by human activities
Main components of a biogeochemical cycle
• Source = a pool that releases more nutrients than it
accepts
• Sinks = a pool that accepts more nutrients than it releases
The hydrologic cycle
• Water is essential for biochemical reactions
- It is involved in nearly every environmental system
• Hydrologic cycle = summarizes how liquid, gaseous and
solid water flows through the environment
- Oceans are the main reservoir
• Evaporation = water moves from aquatic and land
systems into the atmosphere
• Transpiration = release of water vapor by plants
• Precipitation, runoff, and surface water = water returns
to Earth as rain or snow and flows into streams, oceans,
etc.
Transpiration
Groundwater
• Aquifers = underground reservoirs of sponge-like
regions of rock and soil that hold…
- Groundwater = water found underground beneath
layers of soil
• Water table = the upper limit of groundwater in an
aquifer
- Water may be ancient (thousands of years old)
• Groundwater becomes exposed to the air where the water
table reaches the surface
- Exposed water runs off to the ocean or evaporates
The hydrologic cycle
Human impacts on the hydrologic cycle
• 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
• Carbon is found in carbohydrates, fats, proteins, bones,
cartilage and shells
• Carbon cycle = describes the route of carbon atoms
through 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
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 high
pressure
- Ultimately, it may be converted into fossil fuels
• Oceans are the second largest reservoir of carbon
The carbon cycle
Humans affect the carbon cycle
• Burning fossil fuels moves carbon from the ground to the
air
• Cutting forests and burning fields moves carbon from
vegetation to the air
• Today’s atmospheric carbon dioxide reservoir is the
largest in the past 800,000 years
- It is the driving force behind climate change
• The missing carbon sink: 1-2 billion metric tons of
carbon are unaccounted for
- It may be taken up by plants or soils of northern
temperate and boreal forests
The phosphorus cycle
• Phosphorus (P) is a key component of cell membranes,
DNA, RNA, ATP and ADP
• Phosphorus cycle = describes the routes that phosphorus
atoms take through the environment
- Phosphorous is NOT found in the atmosphere (NO
GAS STAGE!), but instead in sedimentary rocks and
does not depend on action of bacteria.
- It is released by weathering of rocks
• With naturally low environmental concentrations
- Phosphorus is a limiting factor for plant growth
The phosphorus cycle
Humans affect the phosphorus cycle
• Mining rocks for fertilizer moves phosphorus from the
soil to water systems
• Wastewater discharge also releases phosphorus
• Runoff containing phosphorus causes eutrophication of
aquatic systems
- Produces murkier waters
- Alters the structure and function of aquatic systems
- Do not buy detergents that contain phosphate
Sulfur Cycles
• Most sulfur is found in underground
rocks and deep oceanic deposits
• Natural release comes from weathering
of rock and gases released from seafloor
vents and volcanic eruptions, and
decomposition of dead organisms
• Human activities affect the sulfur cycle
- Burn sulfur-containing coal and oil
- Refine sulfur-containing petroleum
- Convert sulfur-containing metallic
mineral ores (smelting)
- Produce lare amounts of sulfur
dioxide (SO2) and hydrogen
sulfide gases (H2S)
The nitrogen cycle
• Nitrogen comprises 78% of our atmosphere
- It is contained in proteins, DNA and RNA
• Nitrogen cycle = describes the routes that nitrogen
atoms take through the environment
- Nitrogen gas in the atmosphere (N2) cannot be
used by organisms
- Has to be in the form of ammonia (NH3) or
nitrates (NO3-)
Steps
• 1. Nitrogen fixation = lightning or nitrogen-fixing
bacteria combine (fix) nitrogen with hydrogen
- Change N2 to ammonium ions NH4+
- These are then used by plants
• 2. Nitrification = soil bacteria converts ammonium NH4+
to nitrites (NO2- ) and then nitrates (NO3- )
• 3. Assimilation = Plants absorb ammonium (NH3),
ammonia ions (NH4+ ), and nitrate ions (NO3-)through
their roots. Other organisms gain this energy when they
consume the plants
Nitrogen Cycle Continued
• 4. Ammonification = decomposing
bacteria convert dead organism and other
waste to ammonia (NH3) or ammonium
(NH4+ ) which can be reused by plants
• 5. Denitrification = Specialized bacteria
convert ammonia (NH3) back into nitrites
(NO2- ) and nitrates (NO3- ) and then back
into nitrogen gas (N2)and nitrous oxide
gas (N2O), releasing them back into the
air
The nitrogen cycle
Humans affect the nitrogen cycle
• Haber-Bosch process = production of fertilizers by
combining 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-nitrogen
soils
- Changed estuaries and coastal ecosystems and fisheries
Humans put nitrogen into the environment
Fully half of nitrogen entering the environment is of human origin
Solutions to the dead zone
• The Harmful Algal Bloom and Hypoxia Research and
Control 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
Decreasing pollution
• Scientists, farmers and policymakers
are 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