Biogeochemistry - Ecosystems

Question 1

Cycles

Answer 1

Earth receives constant influx of energy but chemical elements are available in fixed amounts.
Cycles involve biotic and abiotic (geological and chemical) components, hence biogeochemical cycles

Question 2

Global and local cycles

Answer 2

Cycles of elements that occur in gaseous forms (C O S N) are global.
Heavier elements (P K Ca), that dont occur as gases, have more local cycles

Question 3

General model of chemical cycling

Answer 3

Elements occur in four major reservoirs (Organic material available as nutrients, Org mat unavailable as nutrients, Inorganic materials unavailable as nutrients, Inorganic mat available as nutrients)
A variety of biotic and abiotic processes move elements between reservoirs

Question 4

Fossilization and burning of fossil fuels

Answer 4

Formation of peat > coal and oil. Burning fossil fuel - releases organic and inorganic molecules (nitrogen oxides, sulfur dioxide, VOCs, heavy metals)

Question 5

Sedimentary rock formation

Answer 5

Deposition/sedimentation of particulate materials and detritus (typically in aquatic environments). Major process on ecological time scales

Question 6

Weathering and erosion

Answer 6

Weathering caused by atmosphere (wind n water) and wildlife. May be physical or chemical.
Erosion - transportation and deposition of weathered material

Question 7

The carbon cycle

Answer 7

Major component of organic molecules. Key cycling processes - Photosynthesis, respiration, decomposition. Major reservoirs - Fossil fuels, soils, aquatic ecosystem sediments

Question 8

Nitrogen cycle

Answer 8

Nitrogen an essential component of proteins and nucleic acids
Key roles: Microbes - nitrogen fixation, nitrificaction, and denitrification plants - assimilation, ammonification
Major reservoirs - Atmosphere, soils, sediments, surface water, groundwater, biomass

Question 9

Phosphorus cycle

Answer 9

Phosphorus important component of: Nucleic acids, phospholipids, energy metabolism (ATP), bones/teeth. Major reservoirs: marine sedimentary rocks, soil, ocean (in dissolved form), living organisms

Question 10

Water cycle

Answer 10

Water essential for life (solvent, source of H for carbohydrates) and can play an important role in ‘moving’ elements/nutrients

Question 11

Nutrient enrichment

Answer 11

Most chemical cycles now disrupted/dominated by human activities. Excess nutrients can have toxic effects. Eg gulf of Mexico dead zone - Nutrient enrichment stimulates Phytoplankton blooms, decomposition leads to oxygen depletion

Question 12

Greenhouse gases and global warming

Answer 12

Fossil fuel burning has lead to rapid increases in atmospheric CO2 concentrations. Increasing emissions from habitat destruction (eg. forest clearance)