3

Environmental systems: Connections,

energy, and ecosystems

Key Termsacidicaquifersatomsautotrophsbasicbiogeochemical cyclesbiomassbiomescarbohydratescarbon cyclecellscellular respirationchaparralchemical energyclimate diagramsclimatographscompoundcovalent bonddead zonedenitrifying bacteria

igneous rocksionic bondsionic compoundsionsisotopeskinetic energylavalipidsmacromoleculesmagmametamorphic rockmoleculesnegative feedback loopnet primary productivityneutronsnitrificationnitrogen cyclenitrogen fixation

deoxyribonucleic acid (DNA)desertecosystemelectronselementsenergyentropyenzymeseukaryoticeutrophicationevaporationfeedback loopfirst law of thermodynamicsgroundwaterGulf of Mexicoheterotrophshydrocarbonshydrologic cyclehypoxia

Key Terms Continuednitrogen-fixing bacterianucleic acidsnutrient cyclesnutrientsorganellesorganic compoundsphosphorus cyclephotosynthesisplymerspositive feedback looppotential energyprecipitationprimary producersprimary productivityprokaryoticproteinsprotons

ribonucleic acid (RNA)rock cyclerunoffsaltssavannassecond law of thermodynamicssedimentary rocksedimentssystemtaigatemperate deciduous foresttemperate grasslandstemperate rainforesttranspirationtropical dryforesttropical rainforesttundra

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 zoneNitrogen 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

Figure 19.26

Tertiary consumers

Secondary consumers

Primary consumers

Producers

10 kcal

100 kcal

1,000 kcal

10,000 kcal

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 byelectrical 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 lifeethane

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

Figure 4.12Eukaryotic cell

Animal cell

Plant cell

Prokaryotic cell

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, shortwavelength

Low energy, longwavelength

Ionizing radiation Nonionizing radiation

Cosmicrays

Gammarays

X rays Farultraviolet

waves

Nearultraviolet

waves

Visiblewaves

Nearinfraredwaves

Farinfraredwaves

Microwaves TVwaves

Radiowaves

Wavelength in meters (not to scale)

10-14 10-12 10-8 10-7 10-6 10-5 10-3 10-2 10-1 1

Energy Distribution in Sunlight

En

erg

y e

mit

ted

fro

m s

un

(K

cal/c

m2/m

in)

0

5

10

15

0.25 1 2 2.5 3Wavelength (micrometers)

Visible

Infrared

Ultr

avio

let

Energy Distribution in Sunlight

En

erg

y e

mit

ted

fro

m s

un

(K

cal/c

m2/m

in)

0

5

10

15

0.25 1 2 2.5 3Wavelength (micrometers)

Visible

Infrared

Ultr

avio

let

Energy QualityHigh Quality

Solid

Salt

Coal

Gasoline

Aluminum can

Low Quality

Gas

Solution of salt in water

Coal-fired powerplant emissions

Automobile emissions

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 QualityElectricityVery–high-temperature heat (greater than 2,500°C)Nuclear fission (uranium)Nuclear fusion (deuterium)Concentrated sunlightHigh-velocity wind

High-temperature heat (1,000–2,500°C)Hydrogen gasNatural gasGasolineCoalFood

Normal sunlightModerate-velocity windHigh-velocity water flowConcentrated geothermal energyModerate-temperature heat (100–1,000°C)Wood and crop wastes

Dispersed geothermal energyLow-temperature heat (100°C or lower)

Very high

High

Moderate

Low

Source of Energy Relative Energy Quality(usefulness)

Energy Tasks

Very–high-temperature heat (greater than 2,500°C) for industrial processes and producing electricity to run electrical devices (lights, motors)

Mechanical motion (to move vehicles and other things)High-temperature heat (1,000–2,500°C) for industrial processes and producing electricity

Moderate-temperature heat (100–1,000°C) for industrial processes, cooking, producing steam, electricity, and hot water

Low-temperature heat(100°C or less) for

space heating

Relationship between Energy Quality and Pollution Streams

Inputs(from environment)

High-quality energy

Matter

SystemThroughputs

Output(intro environment)

Unsustainablehigh-wasteeconomy

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 more-ordered 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.

RespirationThe 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 pondlarge forestentire planet

Energy in ecosystems

Energy from sunconverted 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

Solarenergy

Wasteheat

Chemicalenergy

(photosynthesis)

Wasteheat

Wasteheat

Wasteheat

Chemicalenergy(food)

Mechanicalenergy(moving,thinking,

living)

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:

78% of atmosphere

In proteins and DNA

In limited supply to organisms; requires lightning or bacteria to become usable

A potent fertilizer

Carbon:

Key component of organic molecules

Atmospheric CO2 regulates climate

Phosphorus:

In ADP and ATP for metabolism

In DNA and RNA

In limited supply to organisms

A potent fertilizer

The nitrogen cycleHow 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

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.”

“Evidence that nitrogen fertilizer is polluting the Gulf of Mexico is not conclusive… Used correctly, fertilizer increases food production and helps protect the environment.”

From Viewpoints

The carbon cycleHow 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 (PO4

3–) 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

Figure 6.15

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

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: SolutionsDecreasing 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 DataNitrogen 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…?

Figure 4.7

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

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