Chapter 4Biogeochemical Cycles

What IS a “biogeochemical cycle”?

BIO = “life” GEO = “earth” CHEMICAL = “elements – C, O, N, P, S

• a cycling of nutrients (water, carbon, oxygen, nitrogen, phosphorus, sulphur) from the abiotic components of the ecosystem (water, air, soil, rock) through the biotic components (plants, animals, fungi, bacteria)

Objectives:

Identify and describe the flow of nutrients in each biogeochemical cycle.

Explain the impact that humans have on the

biogeochemical cycles.

Objectives:

Identify and describe the flow of nutrients in each biogeochemical cycle.

Explain the impact that humans have on the biogeochemical cycles.

What Sustains Life on Earth?

• Solar energy, the cycling of matter, and gravity sustain the earth’s life.

Figure 3-7

Two Secrets of Survival: Energy Flows and Matter Cycles

An ecosystem survives by a combination of energy flow (from Sun to Earth) and matter cycling.

Remember: the Earth is a CLOSED system

Figure 3-14

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.

Water’s Unique Properties There are strong forces of attraction between

molecules of water. (due to H bonds) 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. (due to polar nature of water) Water expands when it freezes.

Fig. 3-26, p. 72

PrecipitationPrecipitation

Transpiration

Condensation

Evaporation

Ocean storage

Transpiration from plants

Precipitation to land

Groundwater movement (slow)

Evaporation from land Evaporation

from ocean Precipitation to ocean

Infiltration and Percolation

Rain clouds

RunoffSurface runoff

(rapid)

Surface runoff (rapid)

THE HYDROLOGIC (WATER) CYCLE

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.

Fig. 3-27, pp. 72-73

Effects of Human Activities on Carbon Cycle

We alter the carbon cycle by adding excess CO2 to the atmosphere through: Burning fossil fuels. Clearing vegetation

faster than it is replaced

photosynthesis = CO2

Figure 3-28

THE NITROGEN CYCLE

THE NITROGEN CYCLE

Effects of Human Activities on the Nitrogen Cycle

We alter the nitrogen cycle by: Adding nitrous oxide to the atmosphere from

vehicles and factories which contributes to acid rain.

Contaminating ground water from nitrate ions in inorganic fertilizers.

Releasing nitrogen into the troposphere through deforestation (less N assimilated by trees).

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

Fig. 3-31, p. 77

Dissolvedin Ocean

Water

Marine Sediments Rocks

uplifting overgeologic time

settling out weatheringsedimentation

LandFoodWebs

Dissolvedin Soil Water,Lakes, Rivers

death,decomposition

uptake byautotrophs

agriculture

leaching, runoff

uptake byautotrophs

excretion

death,decomposition

mining Fertilizer

weathering

Guano

MarineFoodWebs

THE PHOSPHORUS CYCLE

Effects of Human Activities on the Phosphorous Cycle

We remove large amounts of phosphate from the earth to make fertilizer.

We reduce phosphorous in tropical soils by clearing forests.

We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers – excess phosphorus causes algal blooms

Algal blooms

Fig. 3-32, p. 78

Hydrogen sulfide

Sulfur

Sulfate salts

Decaying matter

Animals

Plants

Ocean

IndustriesVolcano

Hydrogen sulfideOxygen

Dimethyl sulfide

Ammoniumsulfate

Ammonia

Acidic fog and precipitationSulfuric acid

WaterSulfurtrioxide

Sulfur dioxide

Metallicsulfidedeposits

THE SULPHUR CYCLE

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

Assignment: Put the 6 cycles together on one poster!

Draw the hydrologic, carbon, oxygen, nitrogen, phosporus and sulphur cycles onto one piece of poster paper.

Include the required terminology Follow the criteria on the rubric provided Assessment will be done by performance

(explanation of the cycles by the group)

The Gaia Hypothesis: Is the Earth Alive?

Some have proposed that the earth’s various forms of life control or at least influence its chemical cycles and other earth-sustaining processes. The strong Gaia hypothesis: life controls the

earth’s life-sustaining processes. The weak Gaia hypothesis: life influences the

earth’s life-sustaining processes.