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BIOL 215 Lecture Notes - Fossil Fuel, Kerogen, Denitrification

Biology (Sci)
Course Code
BIOL 215
Neil Price

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BIOL215 Lecture 24 Notes
Do terrestrial and aquatic ecosystems operate in a similar way? It seems that because of differences
in consumptions efficiencies, only a small portion of primary production is used by herbivores in
terrestrial systems compared to ocean and aquatic systems. Thus, large amounts of NPP are either
available or funnel through detrital food web, which are used by decomposers and fungi
Energy Flow in a Grassland Ecosystems:
99% of solar energy unavailable for use by second trophic level: primary producers only capture
roughly 1% of sun energy
Below ground NPP > above ground NPP
The conspicuous animals contribute little to consumption and secondary production
As energy losses between trophic levels accumulate eventually there is insufficient energy left to
support a viable population at a higher trophic level
Introduction to Nutrient Cycling:
The Earth is an open system with respect to energy input (energy is constantly supplied by the
The Earth is a closed system with respect to nutrient input (ignoring the periodic bombardment by
material from outer space)
Nutrients are cycled, between biotic and abiotic reservoirs (and among organic and inorganic
abiotic reservoirs) - can get locked in a chemical form that is not useable by all organisms
Movement, or cycling, of nutrients ultimately requires energy input into ecosystems, e.g., to
initiate chemical reactions - critically dependent on energy supply
What are nutrients?
Nutrients are the chemical forms of elements used for growth of all organisms
Nitrogen is one essential element - it exists in many chemical forms in the environment
Not all of these forms are directly available to all organisms - elemental or nutrient cycling
The conversion of one form of a nutrient to another involves nutrient cycling
Why are ecosystem ecologists interested in nutrient cycling?
Some nutrients limit primary producers (an consumers)
Human activities are dominating the cycles of many nutrients causing environmental problems
Carbon is a nutrient that is accumulating in the atmosphere and warming the planet
Because N is often a nutrient limiting production on land and in the ocean much attention is focused
on the Nitrogen Cycle
Coupling between productivity and nutrient use:
Organisms need essential elements to grow - these elements are required in constant proportions
In aquatic ecology this ration is known as the Redfield ratio which applies to primary producers:
106C:16N:1P [6.6C:1N] (as mols) - phytoplankton and roughly 50-150C:1N (as mols) - higher plants
How can we use the Redfield ratio?
To predict which nutrient will be limiting to growth
i.e. Phytoplankton require N:P = 16:1 and if the environment contains N:P = 30:1, P will ultimately
limit growth
If the environment contains N:P = 5:1, then N will ultimately limit growth
Liebig's Law of the Minimum - The resource is lowest abundance relative to an organism's
requirements will limit plant growth
To predict consumption of one nutrient from another
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