Energy Flows through Ecosystems

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Transcript Energy Flows through Ecosystems

Chapter 3
Ecosystem Ecology
Ecological Organization
Ecology
Organisms
Populations
Communities
Ecosystems
Biosphere
Fig. 3-5, p. 58
Ecosystem Ecology Examines Interactions
Between the Living and Non-Living World
Abiotic
CLIMATE!!
Water
Air
Nutrients
Rocks
Heat
Solar energy
Biotic
Living and once
living
Fig. 3-6, p. 59
Ecosystem Boundaries
• ecosystems interact with other ecosystems
Energy Flows through Ecosystems
One-way flow of high-quality energy:
Sun → autotroph → heterotroph→ environment as heat → radiation to space
Photosynthesis and Respiration
Trophic Levels, Food Chains, and Food Webs
• Decomposers
• Consumers that
release nutrients
• Bacteria
• Fungi
• Detritivores
• Feed on dead bodies
of other organisms
• Earthworms
• Vultures
Fig. 3-9a, p. 61
Many of the World’s Most Important
Species Are Invisible to Us
Microorganisms
• Bacteria
• Protozoa
• Fungi
Fig. 3-10, p. 61
Heat
Abiotic chemicals
(carbon dioxide,
oxygen, nitrogen,
minerals)
Heat
Solar
energy
Heat
Producers
(plants)
Decomposers
(bacteria, fungi)
Heat
Consumers
(herbivores,
carnivores)
Heat
Fig. 3-14, p. 61
Ecosystem Productivity
• Energy captured
via
photosynthesis
over a given
amount of time.
• Energy captured
minus the energy
respired by
producers.
Productivity varies among ecosystems
• NPP = GPP – respiration by producers
• Measured in g C/m2/year
• Productivity = NPP/GPP*100
The amount of increase in organic matter per unit of time.
Usable Energy Decreases with Each Link in
a Food Chain or Web
• Biomass
• represents the chemical energy stored at
each energy level
• dry weight, water is neither a source of
energy, nor has any nutritional value
• Standing Crop
• amount of biomass at a given time
• may be high even if productivity is low
due to accumulation
Fig. 3-14, p. 65
Energy Flow in an Ecosystem: Losing
Energy in Food Chains and Webs
• Ecological efficiency
can range from 5-20%
across ecosystems
• Measured in Joules
• On average, 90% of
energy is lost with each
transfer through the
trophic pyramid
Figure 3-19
10% Rule AKA the
Ecological Rule of Thumb
• In accordance with the 2nd law of thermodynamics, there is a
decrease in the amount of energy available to each succeeding
organism in a food chain or web.
Most trophic
pyramids assume
10% ecological
efficiency
Nutrient Cycles in the Biosphere
Biosphere
Carbon
cycle
Phosphorus
cycle
Nitrogen
cycle
Water
cycle
Oxygen
cycle
Heat in the environment
Heat
Heat
Heat
Fig. 3-7, p. 55
The Hydrologic Cycle
Alteration of the hydrologic
cycle by humans
1. Withdrawal of large amounts of freshwater at
rates faster than nature can replace it
2. Clearing vegetation
3. Increased flooding
when wetlands
are drained
3-18, p. 68
69
Fig. 3-17,
The Carbon Cycle
• Animals also
release gases,
like CH4, as
flatulence or
burps.
• C is also released
as CH4 through
decomposition by
fungi and bacteria
Carbon's Special Knack for Bonding
Carbon Reservoirs in
Oceans
• shells, skeletons, coral reefs
• Biological pump: organisms in the
upper ocean sink to the bottom
• CO2 can dissolve into ocean
water OR can dissolve into
precipitation that ends up in the
ocean
• form carbonates, limestone,
dolomite
Carbon Reservoirs on
Land
• Old growth forests/trees that live for thousands of years
• Trapped in ice caps/glaciers
• CaCO3 (limestone or sedimentary rocks)
• Incorporated into the soil
• Freshwater wetlands/bogs
• Peat formation (burial of plant material under anaerobic
conditions)
• Dissolved in aquifers
Why Do We Need
Carbon?
• Carbon is the basic building block required to
form
• proteins
• carbohydrates
• fats
Effects of Human Activities
on Carbon Cycle
• We alter the carbon cycle by adding excess CO2 to the
atmosphere through:
1. Burning fossil fuels.
Coal: C (s) + O2  CO2
Natural gas: CH4 + 2O2  CO2 + 2H2O
Gasoline: 2C8H18 + 25O2  16CO2 + 18H2O
2. Clearing vegetation faster than it is replaced.
3. Burning biomass, trash, or waste releasing CO, CO2,
C particulates (slash & burn agriculture)
4. Release of CO2 by deep plowing or strip mining
5. Landfills release methane (CH4 )
Effects of Human Activities
on Carbon Cycle
5. Raising cows and other ruminants that burp and fart
6. Manufacture of carbon containing compounds like
CFCs
7. Destruction of wetlands
Breaking Carbon Bonds
8. Production of cement releases CO2
Consequences of Human Activities
on Carbon Cycle
1. Climate change
a. Loss of some species
b. Climate zones shift
c. Flooded habitats
2. Sea level rise
a. Coastal habitats flooded
3. Ice caps/glaciers melting
a. Flooding and habitat loss
4. Ocean acidification
a. Shells of marine organisms dissolve
b. Lower pH below tolerance level
The Nitrogen
Cycle
• Heavily dependent on
bacteria for each step:
1nitrogen-fixation,
2assimilation,
3ammonification,
4nitrification,
and
5denitrification.
#1: Nitrogen Fixation
• Atmospheric nitrogen is converted to ammonia or
ammonium ion by nitrogen-fixing bacteria that live in
legume root nodules or in soil OR atmospheric
nitrogen is converted to nitrogen oxides by lightening.
• N2 NH3 or NH4+
Nitrogen-fixing bacteria
•N2 NOx
Lightening
#2: Assimilation
• Plant roots absorb
ammonium ions and
nitrate ions for use in
making molecules such
as DNA, amino acids and
proteins.
• Consumers assimilate
nitrogen through eating
producers.
#3: Ammonification
• When plants and animals die, bacteria and fungi take up
some of the N-molecules.
• The remaining is released as ammonium ions or
ammonia gas.
• R- NH2 + H2O  NH4+  NH3 + OH- + CO2
Decomposing bacteria
•Assimilation can occur here also
#4: Nitrification
• Soil bacteria oxidize ammonia and ammonium ions
to nitrite & nitrate ions.
• NH3 or NH4+  NO2Soil bacteria
• NO2- + H2O  NO3- + 2H
#5: Denitrification
• Denitrifying bacteria reduce ammonia, nitrite, nitrate
back to nitrogen gas (under anaerobic conditions).
• NH3 or NO2- or NO3-  N2
Denitrifiying bacteria
Why Do We Need
Nitrogen?
• Your body needs nitrogen
• to make other amino acids to synthesize proteins
• for metabolic processes that depend upon enzymes
• to make DNA, which makes up your genes
• to make RNA, which is involved in protein synthesis
Human intervention in the
nitrogen cycle
1. Additional NO and N2O in atmosphere from burning
fossil fuels; also causes acid rain
2. N2O to atmosphere from bacteria acting on
fertilizers and manure
3. Destruction of forest, grasslands, and wetlands
4. Add excess nitrates to bodies of water
5. Remove nitrogen from topsoil
Effects of Human Activities
on the Nitrogen Cycle
• Human activities
such as production
of fertilizers now fix
more nitrogen than
all natural sources
combined.
Figure 3-30
The Phosphorus Cycle
• SLOW PROCESS
• Bacteria are not as
important
• Not usually found in
the atmosphere (only
as dust)
• Limiting factor for
plant growth (except
in Alabama!)
• Usually insoluble in
water and is not
found in most aquatic
environments
Why Do We
Need
Phosphorus?
• Your body needs phosphorus
• to make nucleotides (DNA & RNA)
• to make ATP in cells
• to make phospholipids (cell membranes)
• to give strength to your bones and teeth enamel
Effects of Human Activities
on the Phosphorous Cycle
1. Clearing forests
2. Removing large amounts of phosphate
from the earth to make fertilizers
3. Erosion leaches
phosphates into
streams
Excess Phosphorus
• Limiting factor in aquatic ecosystems
• Causes algal blooms
• Algae die
• Decomposers use lots of O2
• Hypoxic conditions result
• Comes from agriculture, residential
runoff & household detergents
Calcium, magnesium, and
potassium are important
macronutrients
• Regulate cellular processes
• Transmit signals between
cells
• Derived from rocks &
decomposing vegetation
• Attracted to soil particles by
positive charges
The Sulfur Cycle
• Generalized representation of sulfur oxides is SOx
• The primary air pollutant, sulfur dioxide, is oxidized, once in
the atmosphere, to sulfur trioxide.
• 2SO2 + O2  2SO3
• Sulfur trixoide dissolves
in atmospheric water
droplets to form
sulfuric acid.
• SO3 + H2O  H2SO4
Why Do We Need Sulfur?
• Sulfur is a part of
• some of the amino acids in your body and is involved
in protein synthesis
• several enzyme reactions
• the production of collagen (forms connective tissues,
cell structure and artery walls)
• keratin (gives strength to hair,
skin and nails)
We add sulfur dioxide to
the atmosphere by:
1. Burning coal and oil
2. Refining sulfur containing petroleum.
3. Convert sulfur-containing metallic
ores into free metals such as
copper, lead, and zinc
releasing sulfur dioxide
into the environment.
Ecosystems respond to disturbance
• An ecosystem has high
resistance when a
disturbance has no overall
effect on the flow of
matter and energy.
July 2001
• An ecosystem that returns
to its original state
quickly after a
disturbance has high
resilience.
August 2005
Restoration Ecology
The Intermediate Disturbance Hypothesis
• Ecosystems experiencing intermediate levels of
disturbance are more diverse than those with high or
low disturbance levels
Both extremes exist
Favor best competitors
Eliminate most species
Instrumental Values of Ecosystems
Support systems
Provisions
Regulating services
Instrumental Values of Ecosystems
Resilience
Regulating services
Intrinsic Values of Ecosystems
Should we value only what we can put a
price on as humans?