Biogeochemical Cycles Biogeochemical Cycles biogeochemical cycles or nutrient

Biogeochemical Cycles

Biogeochemical Cycles • biogeochemical cycles or nutrient cycles are pathways which chemical elements and molecules move through the biotic and abiotic compartments of earth • these elements are recycled through these cycles • They can be stored for long periods of time in reservoirs where they accumulate – eg oceans or lakes for water

Water Cycle • Water is recycled by evaporation, condensation and precipitation where it falls back to earth clean and fresh

Biogeochemical Cycles • The most well known cycles are: – carbon cycle – nitrogen cycle – oxygen cycle – water cycle • Cycles involve a balance between the different compartments which can be distributed on a global scale

The Carbon Cycle • Essential to life on earth – Half the dry weight of most organisms is carbon • Carbon cycle reservoirs: – atmosphere – land mass of earth (including underground) – earth’s water – all living things • Carbon moves between these reservoirs by different pathways of exchange

The Carbon Cycle • Atmosphere – Mostly in the form of carbon dioxide – Small percent (~0. 04%) but critical for supporting life: plants breath it in and convert it – 750 billion tons in atmosphere

The Carbon Cycle • Earth’s Landmass – largest reservoir – sedimentary rock contains 80 quadrillian tons – most is trapped and inaccessible deep underground – Close to surface some can move through the carbon cycle

The Carbon Cycle • Oceans – 36 trillion tons – mostly bicarbonate ion (over 90%) with most of the rest carbonate ion

The Carbon Cycle • Living Biomass – 575 billion tons – most in vegetation – most found in organic compounds such as carbohydrates (molecules made of carbon, hydrogen and oxygen)

The Carbon Cycle • Two main paths: – 1) photosynthesis – plants use sun’s energy to convert CO 2 to glucose (releases O 2) • CO 2 + H 2 O + energy glucose + O 2 • removes carbon dioxide from atmosphere – 2) cellular respiration – reverse of photosynthesis • glucose + O 2 CO 2 + H 2 O + energy • This energy powers living things • puts carbon back into atmosphere

The Carbon Cycle • Carbon also returned to atmosphere by: – decay of plants and animals releases methane gas (CH 4) – burning carbon based materials (eg fossil fuels, wood) releases CO 2 – warming seawater releases dissolved CO 2 – volcanic eruptions release CO 2

The Carbon Cycle

Disturbing the Carbon Cycle • Usually there is a balance in the carbon cycle so that the amount of carbon entering and leaving different reservoirs maintains them at fairly constant levels • Scientists have documented and regular increase in carbon levels in the atmosphere in modern times indicating that there is a disturbance in the cycle • What do you think are some possible causes for such a disturbance in the carbon cycle?

Disturbing the Carbon Cycle • Natural Events: – forest fires – combustion releases CO 2 – volcanoes • break down rocks which releases CO 2 • ash in atmosphere lowers photosynthesis thus less CO 2 is removed from atmosphere

Disturbing the Carbon Cycle • Human Activities – Deforestation – reduces photosynthesis – Burning fossil fuels – adds CO 2 to atmosphere – Agriculture – cattle farts (methane gas)