Download Chemical cycling

Ecosystems
1. Energy Flow
2. Chemical cycles
water, carbon, nitrogen
3. Human effects on cycles
eutrophication, acid rain
• Ecosystem = community plus abiotic factors
- Conditions (temp, light)
Resources (water, nutrients)
• Energy flows from the sun, through plants,
animals, and decomposers, and is lost as heat
• Chemicals are recycled between air, water,
soil, and organisms
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• A terrarium ecosystem / Biosphere II
Chemical cycling
(C, N, etc.)
Light
energy
Chemical
energy
Heat
energy
Figure 36.8
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Chemicals are recycled between organic
matter and abiotic reservoirs
– Water cycle
- Carbon cycle
– Nitrogen cycle
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Solar
heat
Water vapor
over the sea
Precipitation
over the sea
(283)
Net movement
of water vapor
by wind (36)
Evaporation
from the sea
(319)
Water vapor
over the land
Evaporation
and
transpiration
(59)
Precipitation
over the land
(95)
Oceans
Flow of water
from land to sea
(36)
Surface water
and groundwater
Figure 36.14
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
salt water = 97.5%
freshwater = 2.5%
oceans
ice caps
and
glaciers
1.97%
ground- lakes, atmosphere
rivers,
0.001%
water
0.5% and soil
0.03%
Carbon cycle
• Carbon is taken from the atmosphere by
photosynthesis
– used to make organic molecules
returned to the atmosphere by cellular respiration,
decomposers
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
CO2 in atmosphere
Plants,
algae,
cyanobacteria
Cellular respiration
Burning
Higher-level
consumers
Photosynthesis
Primary
consumers
Wood and
fossil fuels
Decomposition
Detritivores
(soil microbes
and others)
Detritus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure
36.15
The nitrogen cycle relies heavily on bacteria
• Nitrogen is plentiful in the atmosphere as N2
– But plants and animals cannot use N2
• Some bacteria in soil and legume root nodules
convert N2 to compounds that plants can use:
ammonium (NH4+) and nitrate (NO3–)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Legumes and certain other plants house nitrogenfixing bacteria
• Legumes and
certain other
plants have
nodules in
their roots that
contain
nitrogen-fixing
bacteria
Shoot
Nodules
Roots
Figure 32.14A
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ATMOSPHERE
N2
Amino
acids
Nitrogen-fixing
bacteria
N2
NH4+
NH4+
(ammonium)
Soil
Ammonifying
bacteria
Organic
material
Nitrifying
bacteria
NO3–
(nitrate)
Root
Figure 32.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Nitrogen (N2) in atmosphere
Assimilation
by plants
Amino acids
and proteins in
plants and animals
Nitrogen
fixation
Denitrifying
bacteria
Detritus
Nitrates
(NO3–)
Nitrogen-fixing
bacteria in root
nodules of legumes
Detritivores
Nitrogen-fixing
bacteria in soil
Nitrogen
fixation
Decomposition
Nitrifying
bacteria
Ammonium (NH4+)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Human impact on chemical cycles
76%
naturally
occurring
24%
humancaused
Atmospheric
CO2
concentration
24%
naturally
occurring
58%
humancaused
Terrestrial
nitrogen
fixation
46%
available
54%
used
Accessible
surface
water
• Environmental changes caused by humans can
unbalance nutrient cycling over the long term
– Example: acid rain
– Sulfur dioxide, nitrogen oxides create strong
acids when dissolved in rain water.
– Low pH kills aquatic life, leaches nutrients from
soil
– Calcium deficiency affects everything in food
chain: plants, insects, birds. Weak egg shells.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
eutrophication • Algal bloom can cause a lake
to lose its species diversity
– Human-caused eutrophication wiped out
fisheries in Lake Erie in the 1950s and 1960s
– classic experiments on eutrophication led to
the ban on phosphates in detergents
Figure 36.19B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
What are the limits to human alteration of
chemical cycles and habitats?
• What should the limits be?
• How do we set priorities for what we value in
the natural world?
Aesthetic, economic, conservation, humans
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings