Chapter 4 Biogeochemical Cycles What IS a biogeochemical

Chapter 4 Biogeochemical Cycles

What IS a “biogeochemical cycle”? Ø BIO = “life” Ø GEO = “earth” Ø 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: Ø Identify and describe the flow of nutrients in each biogeochemical cycle. Ø 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 Ø An ecosystem survives by a combination of energy flow (from Sun to Earth) and matter cycling. Ø Remember: the Earth is a CLOSED system Figure 3 -14

MATTER CYCLING IN ECOSYSTEMS Ø Nutrient Cycles: Global Recycling l l l 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 Ø There are strong forces of attraction between molecules of water. (due to H bonds) Ø Water exists as a liquid over a wide temperature range. Ø Liquid water changes temperature slowly. Ø It takes a large amount of energy for water to evaporate. Ø Liquid water can dissolve a variety of compounds. (due to polar nature of water) Ø Water expands when it freezes.

THE HYDROLOGIC (WATER) CYCLE Condensation Rain clouds Transpiration Evaporation Transpiration Precipitation to land from plants Precipitation Runoff Surface runoff (rapid) Precipitation Evaporation from land Evaporation from ocean Precipitation to ocean Surface runoff (rapid) Infiltration and Percolation Groundwater movement (slow) Ocean storage Fig. 3 -26, p. 72

Effects of Human Activities on Water Cycle Ø We alter the water cycle by: l l 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 Ø We alter the carbon cycle by adding excess CO 2 to the atmosphere through: l l l Burning fossil fuels. Clearing vegetation faster than it is replaced photosynthesis = CO 2 Figure 3 -28

THE NITROGEN CYCLE

Effects of Human Activities on the Nitrogen Cycle Ø We alter the nitrogen cycle by: l l l 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 Ø Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined. Figure 3 -30

THE PHOSPHORUS CYCLE mining excretion Guano Fertilizer agriculture uptake by weathering autotrophs leaching, runoff Dissolved Land Marine Dissolved in Soil Water, Food in Ocean Lakes, Rivers Webs Water death, decomposition weathering sedimentation settling out uplifting over geologic time Rocks Marine Sediments Fig. 3 -31, p. 77

Effects of Human Activities on the Phosphorous Cycle Ø We remove large amounts of phosphate from the earth to make fertilizer. Ø We reduce phosphorous in tropical soils by clearing forests. Ø We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers – excess phosphorus causes algal blooms

Algal blooms

THE SULPHUR CYCLE Sulfur trioxide Water Acidic fog and precipitation Sulfuric acid Ammonia Oxygen Sulfur dioxide Ammonium sulfate Hydrogen sulfide Plants Dimethyl sulfide Volcano Industries Animals Ocean Sulfate salts Metallic sulfide deposits Decaying matter Sulfur Hydrogen sulfide Fig. 3 -32, p. 78

Effects of Human Activities on the Sulfur Cycle Ø We add sulfur dioxide to the atmosphere by: l l l 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. Ø Include the required terminology Ø Follow the criteria on the rubric provided Ø Assessment will be done by performance (explanation of the cycles by the group) Ø

The Gaia Hypothesis: Is the Earth Alive? Ø Some have proposed that the earth’s various forms of life control or at least influence its chemical cycles and other earth-sustaining processes. l l The strong Gaia hypothesis: life controls the earth’s life-sustaining processes. The weak Gaia hypothesis: life influences the earth’s life-sustaining processes.