Ecosystems and the Physical

Environment

Chapter 5

Cycling of Materials within Ecosystems

Basics of biogeochemical cycling

Energy flows one way through ecosystems

Matter cycles continuously through biotic and abiotic components.

MATERIAL CYCLES• Carbon Cycle

– Begins with intake of CO2 during photosynthesis. Carbon atoms are incorporated into glucose and then:• Remain in plant material until death.

– Eaten by predator– Respiration– Excretion

» Death (Decomposers)

Cycling of Materials within Ecosystems

Carbon cycle:

Carbon Cycle

Nitrogen Cycle

• Plants uptake inorganic nitrogen from the environment and build protein molecules which are later eaten by consumers.– Nitrogen-fixing bacteria change nitrogen to a

less mobile, more useful form by combining it with hydrogen to make ammonia - used to build amino acids.

• Members of bean family (legumes) have nitrogen-fixing bacteria living in their root tissue.

Nitrogen Cycle– Nitrogen re-enters the environment:

• Death of organisms• Excrement and urinary wastes

– Nitrogen re-enters atmosphere when denitrifying bacteria break down nitrates into N2 and nitrous oxide (N2O)gases.

• Humans have profoundly altered nitrogen cycle via use of synthetic fertilizers, nitrogen-fixing crops, and burning fossil fuels.

Cycling of Materials within Ecosystems

Nitrogen cycle:Atmospheric nitrogen (N2)

Nitrogen fixation by humans

Biological nitrogen fixation

Nitrification

NH3 & NH4

-

NO3-

Assimilation

Denitrification

Plant & animal proteins

Decomposition

Internal cycling

Nitrogen Cycle

Phosphorous Cycle

• Phosphorous compounds are leached from rocks and minerals and usually transported in aqueous form.– Taken in and incorporated by producers.

• Passed on to consumers.– Returned to environment by decomposition.

Cycling of Materials within Ecosystems

Phosphorus cycle:

Phosphate rocksPhosphate mining Fertilizer

containing phosphates

Animals, crops

Soil phosphates

Internal cycling

Erosion

Erosion

Dissolved phosphates

Marine organisms

Excretion / decomposition

Internal cycling

Marine sediments

Phosphorous Cycle

Sulfur Cycle

• Most sulfur tied up in underground rocks and minerals. Inorganic sulfur released into air by weathering and volcanic eruptions.– Cycle is complicated by large number of

oxidation states the element can assume.– Human activities release large amounts of

sulfur, primarily by burning fossil fuels.• Important determinant in rainfall acidity.

Cycling of Materials within Ecosystems

Sulfur cycle:

Hydrologic Cycle

• Describes the circulation of water as it:– Evaporates from land, water, and organisms.

(Transpires from plants)• Enters the atmosphere.

–Condenses and precipitates back to the earth’s surfaces.

»Moves underground by infiltration or overland runoff into rivers, lakes and seas.

Cycling of Materials within Ecosystems

Hydrologic cycle:

Hydrologic Cycle

Hydrologic Cycle

• Solar energy drives the hydrologic cycle by evaporating surface water.– Evaporation - Changing liquid to a vapor below

its boiling point.– Sublimation - Changing water between solid

and gaseous states without ever becoming liquid.

Solar Radiation• Visible light passes through atmosphere

undiminished.• Ultraviolet light is absorbed by ozone in

the stratosphere.• Infrared radiation is absorbed by carbon

dioxide and water in the troposphere.– Albedo - Reflectivity

• Fresh clean snow 90%• Dark soil 3%• Net average of earth 30%

Solar Radiation

Solar Radiation

– Solar energy is unevenly distributed.• Sun strikes the equator directly all year.• Earth’s axis is tilted.

– Also rays of light entering the atmosphere at the poles must pass through a deeper envelope of air than light entering at the equator.

– This causes the sun’s energy to be scattered at the pole, producing lower temperature.

Solar Radiation

Temperature Changes with Latitude

Like equator Like at poles

Solar Radiation

Temperature Changes with Season

•Seasons are a result of the tilt of the earth.

•During half of the year, the northern hemisphere tilts towards the sun, and during the other half away from the sun.

The Atmosphere

Composition

Nitrogen 78%

Oxygen 21%

Carbon dioxideArgonWater vaporPollutantsHeliumEtc.

1%

The Atmosphere

Troposphere•Ranges in depth from 12.5 km over the equator to 8.0 km over the poles.

•All weather occurs here.•Composition is relatively uniform.•Air temperature drops rapidly with increasing altitude.

The Atmosphere

• Stratosphere– Extends from troposphere to about 45 km.

• Air temperature is stable • -45deg C to -75 degC (part closest to Earth)• Fraction ozone is 1000x more than in the

troposphere.• Absorbs UV

• Steady wind• Relatively calm

The Atmosphere

• Mesosphere– Middle Layer.

• Minimum temperature is about - 138o C.• Thermosphere

– Extends from 80-500 km.• Ionized and thin air

–Ionosphere - Lower Thermosphere»Aurora borealis (northern lights)

• high temperatures. (-1000 deg C+)• Absorbs UV and X-ray

The Atmosphere

Atmospheric Circulation

Circulation spawned by heating / cooling

Prevailing winds

Generated by pressure differences and Coriolis effect

The Atmosphere

The Coriolis Effect The influence of Earth’s rotation which tends to turn fluids towards the right in the Northern Hemisphere and towards the left in the Southern Hemisphere.

Coriolis effect

How does the airplane fly?

Coriolis effect

• Deflects air in North hemisphere to right

• Deflects air in South hemisphere to left

• Currents flow clockwise in the North and counter-clockwise in the South.

• Most noticed in higher latitudes.

Other Winds

• Prevaling winds

• Polar easterlies

• Westerlies

• Trade

The Global Ocean

Patterns of Circulation in the Ocean•Surface winds cause ocean currents (gyres).

The Global Ocean

Patterns of Circulation in the Ocean

Influenced by:

1) Coriolis Effect

2) Land Masses (freer to move in the S. Hemisphere)

The Global Ocean

Vertical Mixing of Ocean Water

•Cold salty water is more dense that warmer water.

•As a result, warm less salty water floats above the colder water.

Ocean Conveyor Belt

El Nino Southern Oscillation (ENSO)

• Large pool of warm surface water in Pacific Ocean moves back and forth between Indonesia and South America.

– Most years, the pool is held in western Pacific by steady equatorial trade winds.

• Every three-five years the Indonesian low collapses and the mass of warm surface water surges back east.

The Global Ocean

Ocean Interactions with the AtmosphereENSO alters the climate in many areas remote from the Pacific Ocean.

The Global Ocean

Ocean Interactions with the AtmosphereCoastal Upwelling – deep waters come to the surface due to strong trade winds bringing nutrients.

This decreases during El Niño

Increases during La Niña

El Nino Southern Oscillation

– Weak trade winds, expand warm mass of water, currents slow, prevents upwells

– Devastates S. Hemi fishing industry– Nutrient poor waters– Some species thrive, ie shrimp and scallops

– During an El Nino year, the northern jet stream pulls moist air from the Pacific over the US.

• Intense storms and heavy rains.– During intervening La Nina years, hot, dry weather is often

present.

– Pacific Decadal Oscillation - Very large pool of warm water moving back and forth across the North Pacific every 30 years.

Weather and Climate• Weather - A description of physical

conditions of the atmosphere.

• Climate - A description of the long-term weather pattern in a particular area.– Weather and climate are primary

determinants of biomes and ecosystem distribution.

Weather and Climate

Precipitation: any form of water that falls from the atmosphere

• Driest place on earth– Atacama Desert in Chile = 0.05 cm / year

• Wettest place on earth– Mount Waialeale in Hawaii = 1200 cm / year

Weather and Climate

Rain shadowsMountains cause air to rise . As the air rises it takes moisture with it, which

forms a cloud when temperatures decreases (with greater elevation), and precipitation occurs. As the air moves down the other side of the mountain it is warmed. This decreases the chance of precipitation.

Insert Fig 5.19 b

Weather and Climate

Severe weather events:

1) Tornados: form when a mass of cool dry air collides with

warm moist air

Source: University of Wyoming, Department of Atmospheric Science

Frequency of tornados annually per 100,000 km2

Tornado Alley (US) 40

Sydney, Australia 8

United Kingdom 1

Bangledesh 0.6

Weather and Climate

Severe weather events:

2) Tropical cyclones

Atlantic Ocean = hurricanes

Pacific Ocean = typhoons

Indian Ocean = cyclones

Weather and Climate

But, all are the same severe weather event:

• hurricane

• typhoon

• cyclone

Internal Planetary ProcessesPlate tectonics: study of the movements of plates

Internal Planetary Processes

Plate boundaries

Internal Planetary Processes

Plate boundaries

Internal Planetary Processes

Volcanoes

Most volcanoes occur along subduction zones

Internal Planetary Processes

Volcanoes

Some occur along spreading zones

Few, such as Hawaiian Islands, not associated with plates.

Internal Planetary Processes

Earthquakes

• caused by release of built up stress, typically along faults

• movement releases seismic waves

Typical side effects include:

1) Landslides

2) Tsunamis