Transcript 1. energy & cycles BEST

Chemical
energy
(photosynthesis)
Solar
energy
Waste
Heat
Mechanical
energy
(moving,
thinking,
living)
Chemical
energy
(food)
Waste
Heat
Waste
Heat
Waste
Heat
Fig. 2-14, p. 45
SUSTAINABILITY AND
MATTER AND ENERGY LAWS
• Unsustainable High-Throughput
Economies: Working in Straight Lines
– Converts resources to goods in a manner that
promotes waste and pollution.
Figure 2-15
Sustainable Low-Throughput
Economies: Learning from Nature
• Matter-Recycling-and-Reuse Economies:
Working in Circles
– Mimics nature by recycling and reusing, thus
reducing pollutants and waste.
– It is not sustainable for growing populations.
Inputs
(from environment)
Energy
Matter
System
Throughputs
Outputs
(into environment)
Energy
conservation
Waste
and
pollution
Low-quality
Energy
(heat)
Sustainable
low-waste
economy
Pollution
control
Matter
Feedback
Waste
and
pollution
Recycle
and
reuse
Energy Feedback
Fig. 2-16, p. 47
Biogeochemical Cycling
The cycling of nutrients through
ecosystems via food chains and food
webs, including the exchange of
nutrients between the biosphere and
the hydrosphere, atmosphere and
geosphere (e.g., soils and sediments)
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MATTER CYCLING IN
ECOSYSTEMS
• Nutrient Cycles: Global Recycling
– Global Cycles recycle nutrients through the
earth’s air, land, water, and living organisms.
– Nutrients are the elements and compounds
that organisms need to live, grow, and
reproduce.
– Biogeochemical cycles move these
substances through air, water, soil, rock and
living organisms.
Transfer v Transformation
• Transfers flow through a system and
involve a change in location
• Transformations lead to interaction within
a system in the formation of a new end
product or involving a change of state.
• As we discuss various cycles, underline
transfers, and circle transformations.
Flows v Storage
• Sometimes matter flows through a cycle
and sometimes it is stored.
• When a material is flowing through a cycle
(conversion), color it green.
• When it is being stored (sink), color it red.
Nutrient cycles and energy flow
The Water Cycle
Figure 3-26
Water’s Unique Properties
• There are strong forces of attraction between
molecules of water.
• Water exists as a liquid over a wide
temperature range.
• Liquid water changes temperature slowly.
• It takes a large amount of energy for water to
evaporate.
• Liquid water can dissolve a variety of
compounds.
• Water expands when it freezes.
Effects of Human Activities
on Water Cycle
• We alter the water cycle by:
– Withdrawing large amounts of freshwater.
– Clearing vegetation and eroding soils.
– Polluting surface and underground water.
– Contributing to climate change.
The global carbon cycle
The Carbon Cycle:
Part of Nature’s Thermostat
Figure 3-27
Carbon:
• Photosynthesis and Respiration provide a link
between the atmosphere and terrestrial
• The basic constituent of all organic compounds
environments.
• Decomposition recycles carbon to the soil and
back to atmosphere
• Fires oxidize organic material to CO2 (burning)
Organic detritus, under intense pressure,
changes into coal and petroleum in rock.
• Limestone keeps carbon out of circulation
– Weathering of exposed limestone releases carbon
• A carbon atom cycles about every six years
Human impacts on the carbon cycle
• Human intrusion into the cycle is significant
• We are diverting or removing 40% of the
photosynthetic effect of land plants
• Burning fossil fuels has increased
atmospheric CO2 by 35%
• Deforestation and soil degradation release
significant amounts of CO2 to the
atmosphere
– Recent reforestation and changed agricultural
practices have improved this somewhat
The Nitrogen Cycle:
Bacteria in Action
Figure 3-29
The global nitrogen cycle
Major Components of Nitrogen Cycle
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The nitrogen cycle
• Is a unique cycle
– Bacteria in soils, water, and sediments perform
many steps of the cycle
– Nitrogen is in high demand by aquatic and
terrestrial plants
• Air is the main reservoir of nitrogen (N)
– Nonreactive nitrogen: most organisms can not
use it
• Reactive nitrogen (Nr): other forms of
nitrogen that can be used by organisms
Plants take up nitrogen
• Plants in terrestrial ecosystems (“non-N-fixing
producers”)
– Take up Nr as ammonium (NO4) and incorporate it into
proteins and nucleic acid compounds
– The nitrogen moves through the food chain to
decomposers, releasing nitrogen wastes
• Soil bacteria (nitrifying bacteria) convert ammonium
to nitrate to obtain energy
– Nitrate is available for plant uptake
• Nitrogen fixation: bacteria and cyanobacteria can
use nonreactive N and convert it to a usable form
The Nitrogen Cycle
Nitrogen Fixation:
Bacteria convert gaseous nitrogen to ammonia:
(N2)
(NH3)
Some ammonia enters the ground normally through waste and
decay as well (pee, poop and dead things).
Different bacteria convert ammonia to nitrite:
(NH3)
(NO2-)
Bacteria use nitrite as an energy source,
and give off nitrate (NO3-) as waste:
Nitrate is then taken up by plants or
released into the atmosphere, where it
becomes gaseous N2 again.
(NO3-)
(N2)
Nitrogen fixation
Effects of Human Activities
on the Nitrogen Cycle
• We alter the nitrogen cycle by:
– Adding gases that contribute to acid rain.
– Adding nitrous oxide to the atmosphere through
farming practices which can warm the atmosphere
and deplete ozone.
– Contaminating ground water
from nitrate ions in inorganic
fertilizers.
– Releasing nitrogen into the
troposphere through
deforestation.
The global phosphorus cycle
The Phosphorous Cycle
Figure 3-31
The phosphorus cycle
• Mineral elements originate in rock and soil minerals
– A shortage of phosphorus is a limiting factor
– Excessive phosphorus can stimulate algal growth
• As rock breaks down, phosphate is released
– Replenishes phosphate lost through leaching or runoff
• Organic phosphate: incorporated into organic
compounds by plants from soil or water
Human impacts on the
phosphorus cycle
• The most serious intrusion comes from fertilizers
• Phosphorus is mined and made into fertilizers,
animal feeds, detergents, etc.
• When added to soil, it can stimulate production
– Human applications have tripled the amount reaching
the oceans, accelerating the cycle
– It can’t be returned to the soil
• Excess phosphorus in water leads to severe
pollution
– Can cause too many bacteria and fish kills
The Sulfur Cycle
Figure 3-32
Why sulfur?
-In nature, it can be found as the pure
element and as sulfide and sulfate minerals.
-It is an essential element for life and is
found in two amino acids: cysteine and
methionine.
-Its commercial uses are primarily in
fertilizers, but it is also widely used in black
gunpowder, matches, insecticides and
fungicides.
Effects of Human Activities
on the Sulfur Cycle
• We add sulfur dioxide to the atmosphere
by:
– Burning coal and oil
– Refining sulfur containing petroleum.
– Convert sulfur-containing metallic ores into
free metals such as copper, lead, and zinc
releasing sulfur dioxide into the environment.
Serious consequences of
fertilization
• Nitric acid has destroyed lakes, ponds, and forests
• Atmospheric nitrogen oxides adds to ozone pollution,
climate change, and stratospheric ozone depletion
• Abundant nitrates are not incorporated into organisms
– They are released into the soil, where they leach calcium
and magnesium
• Eutrophication of waterways
• Nitrogen cascade: complex of ecological effects as
Nr moves through the environment
Comparing the cycles
• Carbon is mainly found in the atmosphere
– Directly taken in by plants
• Nitrogen and phosphorus are limiting factors
• All three cycles have been sped up by
human actions
– Acid rain, greenhouse gases, eutrophication
• Other cycles exist for other elements (e.g.,
water)
– All go on simultaneously
– All come together in tissues of living things