Fig. 2-14, p. 45

Chemicalenergy(food)

Solarenergy

WasteHeat

WasteHeat

WasteHeat

WasteHeat

Mechanicalenergy

(moving,thinking,

living)

Chemical energy

(photosynthesis)

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 2-15Figure 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.

Fig. 2-16, p. 47

Recycleand

reuse

Low-quality Energy(heat)

Waste and

pollution

Pollutioncontrol

Sustainable low-waste economy

Waste and

pollution

Matter Feedback

Energy Feedback

Inputs (from environment)

Energyconservation

Matter

Energy

SystemThroughputs

Outputs(into environment)

5

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)

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 3-26Figure 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 3-27Figure 3-27

Carbon:

• The basic constituent of all organic compounds

• Photosynthesis and Respiration provide a link between the atmosphere and terrestrial

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 3-29Figure 3-29

The global nitrogen cycle

19

Major Components of Nitrogen Cycle

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 CycleNitrogen 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 orreleased into the atmosphere, where itbecomes 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 3-31Figure 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 3-32Figure 3-32

Why sulfur?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