Environmental
systems: Connections,
energy, and
ecosystems
3
Key Terms
acidic
aquifers
atoms
autotrophs
basic
biogeochemical cycles
biomass
biomes
carbohydrates
carbon cycle
cells
cellular respiration
chaparral
chemical energy
climate diagrams
climatographs
compound
covalent bond
dead zone
denitrifying bacteria
deoxyribonucleic acid
(DNA)
desert
ecosystem
electrons
elements
energy
entropy
enzymes
eukaryotic
eutrophication
evaporation
feedback loop
first law of
thermodynamics
groundwater
Gulf of Mexico
heterotrophs
hydrocarbons
hydrologic cycle
hypoxia
igneous rocks
ionic bonds
ionic compounds
ions
isotopes
kinetic energy
lava
lipids
macromolecules
magma
metamorphic rock
molecules
negative feedback loop
net primary productivity
neutrons
nitrification
nitrogen cycle
nitrogen fixation
Key Terms Continued
nitrogen-fixing bacteria
nucleic acids
nutrient cycles
nutrients
organelles
organic compounds
phosphorus cycle
photosynthesis
plymers
positive feedback loop
potential energy
precipitation
primary producers
primary productivity
prokaryotic
proteins
protons
ribonucleic acid (RNA)
rock cycle
runoff
salts
savannas
second law of thermodynamics
sedimentary rock
sediments
system
taiga
temperate deciduous forest
temperate grasslands
temperate rainforest
transpiration
tropical dryforest
tropical rainforest
tundra
The Ecology of the Environment:
• The nature of systems
• Ecosystem-level ecology
• Earth’s biomes
• Nutrient cycles:
Nitrogen, Carbon,
Phosphorus
• The rock cycle
• The hydrologic cycle
Central Case: The Gulf of Mexico’s “Dead
Zone”
• Major fisheries off Louisiana were devastated by die-offs.
• Scientists found large regions of low oxygen in the Gulf.
• The recurring “dead zone” resulted from nitrogen
pollution traveling down the Mississippi River.
Earth’s environmental systems
Our planet consists of many complex, large-scale,
interacting systems.
System = a network of relationships among a group of
parts, elements, or components that interact with and
influence one another through the exchange of energy,
matter, and/or information
Feedback loop = a circular process whereby a system’s
output serves as input to that same system.
Feedback loops: Negative feedback
In a negative feedback loop, output acts as input that
moves the system in the opposite direction.
This compensation stabilizes the system
Figure 6.1a
Feedback loops: Positive feedback
In a positive
feedback loop,
output acts as
input that moves
the system further
in the same
direction.
This magnification
of effects
destabilizes the
system.
Figure 6.1b
An environmental system
• Mississippi River
as a system:
• Input of water,
fish, pollution,
etc.
• Output to Gulf
of Mexico
Figure 6.3
Two systems or one?
The Mississippi River system and the system of the Gulf of
Mexico interact.
Understanding the dead zone requires viewing the
Mississippi River and the Gulf of Mexico as a single
system.
This holistic kind of view is necessary for comprehending
many environmental issues and processes.
Eutrophication
Key to the dead zone =
Eutrophication: excess nutrient enrichment in
water, which increases production of organic matter...
… which when decomposed by oxygen-using
microbes can deplete water of oxygen
Creation of the hypoxic dead zone
Nitrogen input boosts phytoplankton…
…which die and are decomposed by microbes that suck
oxygen from water, killing fish and shrimp.
Figure 6.5
Ways To Organize Nature
Emergent Properties
Classification
Trophic Structures
Emergent Properties
When units, particles, or
moieties at one level of
organization are place together
in unique combinations to form
a new unit, particle, or moiety
at a higher level of organization,
the new properties emerge.
Classification
Classification
Trophic Structures
Tertiary
consumers
10 kcal
Secondary
consumers
100 kcal
Primary
consumers
Producers
1,000 kcal
10,000 kcal
Figure 19.26
Chemistry and the environment
Chemistry is central to environmental science:
• Carbon dioxide and climate change
• Sulfur dioxide and acid rain
• Pesticides and public health
• Nitrogen and wastewater treatment
• Ozone and its atmospheric depletion
Atoms and elements
An element is a fundamental type of chemical substance.
Elements are composed of atoms.
Each atom has a certain
number of:
protons (+ charge)
electrons (– charge)
neutrons (no charge)
Figure 4.1
Atoms and elements
92 elements occur in nature, each with its characteristic
number of protons, neutrons, and electrons.
Figure 4.1
Chemical symbols
Each element is abbreviated with a chemical symbol:
H = hydrogen
C = carbon
N = nitrogen
O = oxygen
P = phosphorus
Cl = chlorine
Fe = iron
CHOPKINS CaFe
Isotopes
Isotopes are alternate
versions of elements,
which differ in mass by
having a different
number of neutrons.
Carbon-14 has two
extra neutrons beyond
normal carbon’s 6.
Figure 4.2
Ions
Atoms electrically charged, due to gain or loss of electrons
Figure 4.3
Molecules, compounds, and bonds
Molecules = combinations of two or more atoms
Compounds = molecules consisting of multiple elements
Atoms are held together by bonds:
covalent bond = uncharged atoms sharing
electrons (CO2)
ionic bond = charged atoms held together by
electrical attraction (NaCl)
Water is a unique compound
Hydrogen bonds give
water properties that
make it a vital molecule
for life:
• Is cohesive
• Resists temperature
change
• Ice insulates
• Dissolves many
chemicals
Figure 4.4
Acidity
In an aqueous solution,
If H+ concentration is greater than OH– concentration,
then solution is acidic.
If OH– is greater than H +,
then solution is basic.
pH scale
pH scale measures
acidity and basicity.
Pure water = 7
Acids < 7
Bases > 7
Figure 4.6
pH Scale
Organic compounds
Consist of carbon atoms and,
generally, hydrogen atoms
Joined by covalent bonds
May include other elements
Highly diverse; C can form many
elaborate molecules
Vitally important to life
ethane
Hydrocarbons
C and H only; major type of organic compound
Mixtures of hydrocarbons make up fossil fuels.
Figure 4.7
Macromolecules
Large molecules essential for life:
• Proteins
• Nucleic acids
• Carbohydrates
• Lipids
The first three are polymers, long chains of
repeated molecules.
Proteins
Consist of chains of amino acids; fold into complex shapes
For structure, energy, immune system, hormones, enzymes
Figure 4.8
Carbohydrates
Complex carbohydrates consist of chains of sugars.
For energy, also structural (cellulose, chitin)
Figure 4.11
Lipids
Do not dissolve in water
• Fats and oils
• Phospholipids
• Waxes
• Steroids
Nucleic acids
DNA and RNA
Encode genetic information and pass it on from generation
to generation
DNA = double-stranded chain (double helix)
RNA = single-stranded chain
Nucleic acids
Paired strands of
nucleotides make up
DNA’s double helix.
Figure 4.9
Genes and heredity
Genes, functional
stretches of DNA,
code for the synthesis
of proteins.
Figure 4.10
Cells
Basic unit of organismal organization; compartmentalize
macromolecules and organelles
Plant
cell
Animal
cell
Prokaryotic cell
Eukaryotic cell
Figure 4.12
Energy
Can change position, physical composition, or temperature
of matter
Potential energy = energy of position
(water held behind a dam)
Kinetic energy = energy of movement
(rushing water released from a dam)
Potential and kinetic energy
Potential energy stored in food is converted to
kinetic energy when we exercise.
Figure 4.13
Electromagnetic Energy
Sun
High energy, short
wavelength
Low energy, long
wavelength
Nonionizing radiation
Ionizing radiation
Cosmic
rays
Gamma
rays
10-14
X rays
10-12
Visible
Far
Near
ultraviolet ultraviolet waves
waves
waves
10-8
Wavelength in meters (not to scale)
10-7
10-6
Near
infrared
waves
10-5
Far
infrared
waves
Microwaves
10-3
TV
waves
10-2 10-1
Radio
waves
1
15
10
Visible
5
Ultraviolet
Energy emitted from sun (Kcal/cm2/min)
Energy Distribution in Sunlight
0
0.25
Infrared
1
2
2.5
3
Wavelength (micrometers)
Energy Quality
High Quality
Low Quality
Solid
Gas
Salt
Solution of salt in water
Coal
Coal-fired power
plant emissions
Gasoline
Automobile emissions
Aluminum can
Aluminum ore
Transmission of Energy
Convection
Conduction
Radiation
Heating water in the
bottom of a pan causes
some of the water
vaporize into bubbles.
Because they are lighter
than the surrounding
water, they rise. Water
then sinks from the top to
replace the rising bubbles.
This up and down
movement (convection)
eventually heats all of the
water.
Heat from a stove burner
causes atoms or
molecules in the pan’s
bottom to vibrate faster.
The vibrating atoms or
molecules then collide
with nearby atoms or
molecules, causing them
to vibrate faster.
Eventually, molecules or
atoms in the pan’s
handles are vibrating so
fast it becomes too hot to
touch.
As the water boils,
hear from the hot
stove burner and pan
radiate into the
surrounding air, even
though air conducts
very little heat.
Energy Quality
Electricity
Very–high-temperature
heat (greater than 2,500°C)
Nuclear fission (uranium)
Nuclear fusion (deuterium)
Concentrated sunlight
High-velocity wind
High-temperature heat
(1,000–2,500°C)
Hydrogen gas
Natural gas
Gasoline
Coal
Food
Normal sunlight
Moderate-velocity wind
High-velocity water flow
Concentrated
geothermal energy
Moderate-temperature heat
(100–1,000°C)
Wood and crop wastes
Dispersed geothermal energy
Low-temperature heat
(100°C or lower)
Source of Energy
Very high
Very–high-temperature heat
(greater than 2,500°C)
for industrial processes
and producing electricity to
run electrical devices
(lights, motors)
High
Mechanical motion (to move
vehicles and other things)
High-temperature heat
(1,000–2,500°C) for
industrial processes and
producing electricity
Moderate
Moderate-temperature heat
(100–1,000°C) for industrial
processes, cooking,
producing steam,
electricity, and hot water
Low
Relative Energy Quality
(usefulness)
Low-temperature heat
(100°C or less) for
space heating
Energy Tasks
Relationship between Energy Quality and
Pollution Streams System
Throughputs
Inputs
(from environment)
High-quality energy
Matter
Output
(intro environment)
Unsustainable
high-waste
economy
Low-quality energy (heat)
Waste matter and pollution
Laws of thermodynamics
First Law: Energy can change form, but cannot be created
or lost.
Second Law: Energy will tend to progress from a moreordered state to a less-ordered state (increase in entropy).
Increase in entropy
Burning firewood demonstrates the second law of
thermodynamics.
Figure 4.14
Energy from the sun
Energy from the sun powers most living systems.
Visible light is only part of the sun’s electromagnetic
radiation.
Figure 4.15
Autotrophs and photosynthesis
The sun’s energy is used by autotrophic organisms,
or primary producers (e.g., plants), to manufacture
food.
Photosynthesis turns light energy from the sun into
chemical energy that organisms can use.
Photosynthesis
In the presence of chlorophyll
and sunlight,
Water and carbon dioxide
are converted to
sugars and oxygen.
Figure 4.16
Photosynthesis
6 CO2 + 12 H2O + energy from sun
————>
C6H12O6 (sugar) + 6 O2 + 6 H2O
Streamlined
6 CO2 + 6 H2O + energy from sun
————>
C6H12O6 (sugar) + 6 O2
Respiration and heterotrophs
Organisms use stored energy via respiration, which splits
sugar molecules to release chemical energy.
This occurs in autotrophs and in the heterotrophs (animals,
fungi, most microbes) that eat them.
Respiration
The equation for respiration is the exact opposite of the
equation for photosynthesis.
Some organisms and communities live without sunlight
and are powered by chemosynthesis.
C6H12O6 (sugar) + 6 O2
————>
6 CO2 + 6 H2O + chemical energy
Ecosystems
Ecosystem = all the interacting organisms and abiotic
factors that occur in a particular place and time
Energy and nutrients flow among all parts of an ecosystem.
Conception of an ecosystem can vary in scale:
small pond
large forest
entire planet
Energy in ecosystems
Energy from sun
converted to
biomass (matter in organisms)
by producers
through photosynthesis
Rapid conversion = high primary productivity
(coral reefs)
Rapid plant biomass availability for consumers = high net
primary productivity
(wetlands, tropical rainforests)
Flow of Energy in Ecosystems
(photosynthesis)
Waste
heat
Mechanical
energy
Chemical
energy
(food)
Chemical
energy
Solar
energy
Waste
heat
(moving,
thinking,
living)
Waste
heat
Waste
heat
Nutrient (biogeochemical) cycles
These describe how particular chemicals cycle
through the biotic and abiotic portions of our
environment.
Nutrients = elements and compounds organisms
consume and require for nutrition and survival
A carbon atom in your body could have been part
of a dinosaur 100 million years ago.
Energy Flow Animation
Click to view
animation.
Nutrient (biogeochemical) cycles
Nitrogen, carbon, and phosphorus are key nutrients.
Nitrogen:
Phosphorus:
78% of atmosphere
In ADP and ATP for
metabolism
In proteins and DNA
In limited supply to
organisms; requires
lightning or bacteria to
become usable
A potent fertilizer
Carbon:
In DNA and RNA
Key component of
organic molecules
In limited supply to
organisms
Atmospheric CO2
regulates climate
A potent fertilizer
The nitrogen cycle
How nitrogen (N) moves through our environment
• Atmospheric N2 is fixed by lightning or specialized
bacteria and becomes available to plants and animals in the
form of ammonium ions (NH4+).
• Nitrifying bacteria turn ammonium ions into nitrite (NO2–)
and nitrate (NO3–) ions. Nitrate can be taken up by plants.
• Animals eat plants, and when plants and animals die,
decomposers consume their tissues and return ammonium
ions to the soil.
• Denitrifying bacteria convert nitrates to gaseous nitrogen
that reenters the atmosphere.
The nitrogen cycle
Figure 6.25
Human impacts on the nitrogen cycle
Haber and Bosch during WWI developed a way to fix
nitrogen artificially.
Synthetic nitrogen fertilizers have boosted agricultural
production since then.
Today we are fixing as much nitrogen artificially as the
nitrogen cycle does naturally.
We have thrown the nitrogen cycle out of whack.
Human impacts on the nitrogen cycle
Figure 6.26
Nitrogen and the dead zone
Excess nitrogen flowing down the Mississippi River into the
Gulf causes hypoxia, worse in some regions than others.
From The Science behind the Stories
Nitrogen and the dead zone
The size of the hypoxic zone in the northern Gulf of Mexico,
had grown since 1985, and was largest in 2002.
From The Science behind the Stories
Viewpoints: The dead zone
Terry
Roberts
“Evidence that nitrogen fertilizer
is polluting the Gulf of Mexico
is not conclusive… Used
correctly, fertilizer increases
food production and helps
protect the environment.”
Paul
Templet
“The Dead Zone is driven
by a massive influx of
nutrients into a system no
longer able to process them.
… We need to act now to
save these resources.”
From Viewpoints
The carbon cycle
How carbon (C) moves through our environment
• Producers pull carbon dioxide (CO2) from the air and use it
in photosynthesis.
• Consumers eat producers and return CO2 to the air by
respiration.
• Decomposition of dead organisms, plus pressure
underground, forms sedimentary rock and fossil fuels.
This buried carbon is returned to the air when rocks are
uplifted and eroded.
• Ocean water also absorbs carbon from multiple sources,
eventually storing it in sedimentary rock or providing it to
aquatic plants.
The carbon cycle
Figure 6.27
Human impacts on the carbon cycle
We have increased CO2 in the atmosphere by burning fossil
fuels and deforesting forests.
Atmospheric CO2 concentrations may be the highest now in
420,000 years.
This is driving global warming and climate change.
The phosphorous cycle
How phosphorus (P) flows through our environment.
P is most abundant in rocks. Weathering releases phosphate
(PO43–) ions from rocks into water.
Plants take up phosphates in water, pass it on to consumers,
which return it to the soil when they die.
Phosphates dissolved in lakes and oceans precipitate, settle,
and can become sedimentary rock.
The phosphorous cycle
Figure 6.28
The hydrologic cycle
How water flows through our environment
Water enters the atmosphere by evaporation and by
transpiration from leaves.
It condenses and falls from the sky as precipitation.
It runs off the land surface into streams, rivers, lakes, and
eventually the ocean.
Water infiltrates into aquifers, becoming groundwater.
The hydrologic cycle
Figure 6.23
The rock cycle
A key environmental system
Rocks change from one form to another over time
Igneous rock = of volcanic origin; cooled magma
Sedimentary rock = mineralized sediments
(layers of mud, dust, or sand)
Metamorphic rock = transformed by extreme heat or
pressure
The rock cycle
Figure 6.20
Biomes
Biome = major regional complex of similar plant
communities
A large ecological unit defined by its dominant plant type
and vegetation structure
Biomes are determined primarily by a region’s climate, esp.
temperature and precipitation.
Biome distribution
Figure 6.7
Climate and biomes
Biomes change with temperature and precipitation.
Figure 6.8
Climatographs
These climate diagrams show monthly temperature and
precipitation variation for a particular site.
Climate patterns tend to be similar within a given biome.
Figure 6.10
Temperate deciduous forest
Temperature moderate,
seasonally variable
Precipitation stable through
year
Trees deciduous: lose
leaves in fall, dormant in
winter
Moderate diversity of
broad-leafed trees
North America, Europe,
China
Figure 6.9
Temperate grassland
Temperature moderate,
seasonally variable
Precipitation sparse but
stable
Grasses dominate; few
trees
Large grazing mammals
North America, Asia, South
America
Figure 6.10
Temperate rainforest
Temperature moderate
Precipitation very high
Trees grow tall
Dark moist forest interior
Pacific northwest region of
North America, Japan
Figure 6.11
Tropical rainforest
Temperature warm,
seasonally stable
Precipitation high
Trees tall; forest interior
moist and dark
Extremely high biodiversity
Soil poor in organic matter;
is aboveground
Equatorial regions
Figure 6.12
Tropical dry forest
Temperature warm,
seasonally stable
Precipitation highly
seasonally variable
Trees deciduous: dormant in
dry season
High biodiversity
Subtropical latitudes
Figure 6.13
Savanna
Temperature warm
Precipitation highly
seasonally variable
Grassland interspersed with
trees
Large grazing mammals
Africa and other dry tropical
regions
Figure 6.14
Desert
Temperature warm in most,
but always highly variable
b/w day and night
Precipitation extremely low
Vegetation sparse; growth
depends on periods of rain
Organisms adapted to harsh
conditions
Southwestern region of
North America, Australia,
Africa
Figure 6.15
Tundra
Temperature cold,
seasonally variable
Precipitation very low
Vegetation very low and
sparse; no trees
Low biodiversity; high
summer productivity
Arctic regions
Figure 6.16
Taiga (boreal forest)
Temperature cool,
seasonally variable
Precipitation low to
moderate
Coniferous (evergreen)
trees dominate;
monotypic forests
Low biodiversity; high
summer productivity
Subarctic regions
Figure 6.17
Chaparral
Temperature seasonally
variable
Precipitation seasonally
variable
Evergreen shrubs
dominate
Plants resistant to fire;
burns frequently
California, Chile, West
Australia
Figure 6.18
Aquatic “biomes”
Aquatic systems also show patterns of variation and can be
categorized like biomes.
But the “biome” concept has historically been applied to
terrestrial systems.
Aquatic systems are shaped not by air temperature and
precipitation, but by water temperature, salinity, dissolved
nutrients, currents, waves, etc.
Conclusions: Challenges
The Gulf of Mexico’s dead zone threatens coastal
ecosystems and fishing economies.
We are depleting groundwater supplies.
We have doubled Earth’s nitrogen fixation.
We have increased CO2 concentrations in the atmosphere.
An understanding of chemistry is crucial to many questions
in environmental science.
An understanding of energy fundamentals is important for
ecology and human use of energy resources.
Conclusions: Solutions
Decreasing fertilizer application and finding other ways to
lessen nitrogen runoff into the Mississippi River should
mitigate the dead zone.
Conservation, desalination, and equitable distribution are
solutions to groundwater depletion.
Modifications in the way we pursue agriculture can reduce
artificial nitrogen fixation.
Reducing fossil fuel use and forest loss can reverse CO2
enrichment of the atmosphere.
Energy fundamentals inform our understanding of ecology
and human use of energy resources.
QUESTION: Review
Which biome has warm stable temperatures, highly seasonal
rainfall, deciduous trees, and high biodiversity?
a. Tropical rainforest
b. Tropical dry forest
c. Temperate rainforest
d. Taiga
QUESTION: Review
Water enters the atmosphere through the process of…?
a. Precipitation
b. Transpiration
c. Infiltration
d. Runoff
QUESTION: Review
Carbon enters the atmosphere as carbon dioxide when… ?
a. Animals respire.
b. Sedimentary rocks are uplifted and eroded.
c. Humans burn fossil fuels.
d. All of the above take place.
QUESTION: Weighing the Issues
If farmers’ use of fertilizers affects shrimp fishermen far
downstream, who should be responsible for developing
policies to address the problem?
a. Governments of the farming states upstream
b. Governments of the fishing states downstream
c. The federal government
d. Both state and federal governments
QUESTION: Interpreting Graphs and Data
In this climatograph for Los Angeles, California, in the
chaparral biome, summers are… ?
a. Warm and dry
b. Warm and wet
c. Mild and dry
d. Mild and wet
Figure 6.18
QUESTION: Interpreting Graphs and Data
Nitrogen inputs from fertilizer…?
a. Have decreased
since 1950.
b. Are less than inputs
from animal
manure.
c. Equal 8 million
metric tons/year.
d. Became the primary
nitrogen source in
the 1960s.
Figure 6.26
QUESTION: Viewpoints
What should be done about the Gulf of Mexico’s dead
zone?
a. Mandate that Midwestern farmers reduce use of
fertilizers.
b. Work with Midwestern farmers to find ways to
lessen fertilizer runoff.
c. Nothing yet; more research is needed to
determine the causes of the hypoxia.
QUESTION: Review
Which of the following is a heterotroph?
a. Pine tree
b. Photosynthetic algae
c. Squid
d. Hydrogen sulfide
QUESTION: Review
The second law of thermodynamics states that…?
a. Energy cannot be created or destroyed
b. Things tend to move toward a less-ordered state
c. Matter tends to remain stable
d. Potential and kinetic energy are interchangeable
QUESTION: Interpreting Graphs and Data
A molecule of the hydrocarbon ethane contains…?
a. 2 carbon atoms and 6
hydrogen atoms
b. 2 carbon molecules and
6 hydrogen enzymes
c. Carbon and hydrogen
DNA
d. Eight different isotopes
Figure 4.7
QUESTION: Interpreting Graphs and Data
Which is listed from most
acidic to most basic?
a. Ammonia, baking
soda, lemon juice
b. Stomach acid, soft
soap, HCl
c. Acid rain, NaOH, pure
water
d. HCl, acid rain,
ammonia
Figure 4.6