environmental systems: connections, energy, and ecosystems

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

PowerPoint® Lecture prepared by Jay Withgott

Scott Brennan • Jay Withgott

3Environmental

systems: Connections, energy, and ecosystems


This lecture will help you understand:

• 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


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


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


IonsAtoms 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


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


CellsBasic 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


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)


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.


Nutrient (biogeochemical) cyclesNitrogen, 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 biomesBiomes 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 variablePrecipitation stable through year Trees deciduous: lose leaves in fall, dormant in winterModerate diversity of broad-leafed treesNorth America, Europe, China

Figure 6.9


Temperate grassland

Temperature moderate, seasonally variablePrecipitation sparse but stableGrasses dominate; few treesLarge grazing mammalsNorth 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 stablePrecipitation highTrees tall; forest interior moist and darkExtremely high biodiversitySoil poor in organic matter; is abovegroundEquatorial regions

Figure 6.12


Tropical dry forest

Temperature warm, seasonally stablePrecipitation highly seasonally variableTrees deciduous: dormant in dry seasonHigh biodiversitySubtropical latitudes

Figure 6.13


Savanna

Temperature warmPrecipitation highly seasonally variableGrassland interspersed with treesLarge grazing mammalsAfrica and other dry tropical regions

Figure 6.14


Desert

Figure 6.15

Temperature warm in most, but always highly variable b/w day and nightPrecipitation extremely low Vegetation sparse; growth depends on periods of rainOrganisms adapted to harsh conditionsSouthwestern region of North America, Australia, Africa


Tundra

Temperature cold, seasonally variablePrecipitation very low Vegetation very low and sparse; no treesLow biodiversity; high summer productivityArctic regions

Figure 6.16


Taiga (boreal forest)

Temperature cool, seasonally variablePrecipitation low to moderate Coniferous (evergreen) trees dominate; monotypic forestsLow biodiversity; high summer productivitySubarctic regions

Figure 6.17


Chaparral

Temperature seasonally variablePrecipitation seasonally variableEvergreen shrubs dominatePlants resistant to fire; burns frequentlyCalifornia, 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.

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



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



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

environmental systems: connections, energy, and ecosystems

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