SNC 1D1 – Cycling of Matter in Ecosystems • cycles that involve both living things processes of the earth are called biogeochemical cycles. •Biogeochemical cycles include the water cycle, the carbon cycle and the nitrogen cycle among others.

The Water Cycle• liquid water evaporates, forming water vapour that moves through the atmosphere. Water vapour condenses and returns to earth as hail or snow. • water falling on land enters the groundwater and enters lakes or oceans.• water taken in by plant roots may be released by transpiration from plant leaves.

The Carbon Cycle• Carbon moves between the abiotic and biotic parts of an

ecosystem.• Large quantities of carbon cycle through photosynthesis and

cellular respiration.• Most of the earth’s carbon is not cycled but stored in carbon

rich deposits such as coal, oil or natural gas.• Some carbon is also stored in limestone formed from the

remains of marine organisms.• Large amounts of carbon are also contained in plant tissue

and dissolved CO2 levels in the ocean

Human Activities and the Carbon Cycles• Human activities have increased atmospheric CO2 levels to

those not seen in the last 800 000 years.• Increased atmospheric carbon dioxide levels result in climate

change.• Burning fossil fuels releases carbon dioxide into the

atmosphere.• Climate change can alter two critical abiotic factors:

temperature and water availability.• This can cause melting ice caps and glaciers, sea level rises

and disrupting ecosystems. • Deforestation also increases carbon dioxide in the

atmosphere.• Reforestation and reduced fossil fuel use can slow climate

change.

The Nitrogen Cycle• Nitrogen is extremely abundant in the atmosphere but is

difficult to obtain directly from the environment.• Nitrogen enters the atmosphere through a complex

biochemical pathway. • Most of the nitrogen used by living things is taken from the

atmosphere by nitrogen fixing bacteria. • These organisms convert nitrogen gas into nitrogen containing

compounds such as nitrates, nitrites and ammonia (nitrogen fixation).

• Lightning and ultraviolet light also fix small amounts of nitrogen (10%).

• Nitrates and nitrites in the soil are easily absorbed by producers (highly soluble).

• Nitrogen absorbed by plants then passes up food chains to consumers.

• A dead organism’s nitrogen rich compounds are taken in by decomposers and released back to the environment.

• These compounds are either recycled in the atmosphere or converted by denitrifying bacteria back into nitrogen gas.

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