Topics 2.3 & 2.4
Flows of energy and matter
★
The fate of solar radiation reaching the Earth
★
Productivity
★
Flows of energy and matter
Main concepts:
➔
As
Solar radiation
enters the
atmosphere
some
energy
becomes
unavailable
for
ecosystems
as it is
absorbed
by organic matter or
reflected
back
➔
The loss of radiation is through reflection and absorption
➔
Pathways of energy:
◆
Light energy to chemical energy
◆
Transfer of chemical energy from one trophic level to another, with different efficiencies
◆
ultraviolet and visible light to heat energy
◆
Reradiation of heat energy to the atmosphere
➔
Conversion of energy into biomass for a period of time =
productivity
➔
Gross secondary productivity
= total energy / biomass
assimilated by consumers. (food eaten - fecal
loss)
➔
Net primary productivity
= GPP - respiratory losses
➔
Net secondary productivity
= GSP - respiratory losses
➔
Maximum sustainable yields = net primary/net secondary productivity of a system
➔
Flows of matter: transfers and transformations
➔
Carbon and nitrogen cycles: illustrate flow of matter using flow diagrams
➔
Storages in the carbon cycle:
organisms, forests
,
atmosphere, soil, fossil fuels and oceans
Organic
Inorganic
➔
Flows in the carbon cycle: consumption, death and decomposition, photosynthesis,
respiration, dissolving
and fossilisation.
➔
Storages in the nitrogen cycle:
organisms
,
soil, fossil
fuels, atmosphere and water bodies
➔
Flows in the nitrogen cycle: nitrogen fixation, absorption, assimilation, consumption,
excretion, death and
decomposition, denitrification
➔
Human activities: burning fossil fuels, deforestation, urbanization and agriculture impact
energy flows as
well as the carbon and nitrogen cycle
Key points
Almost all energy comes from the sun
Solar radiation is made up of visible wavelengths (lights) and those invisible to humans
(ultraviolet and
infrared)
60% of energy is absorbed by atmospheric gases and dust particles
Nearly all ultraviolet light is absorbed by ozone
Infrared light (heat) is absorbed by carbon dioxide, clouds and water vapours
Ultraviolet and visible light energy (short wave) are converted to heat energy (long wave)
The systems depend on the amount of energy that reaches the ground, not the
atmosphere. This amount
varies according to time, season, clouds, etc
Most energy is reflected or absorbed and re radiated as heat
35% of energy is reflected back to space by ice, snow, water and land
Some of the energy absorbed heats up the land and seas
Only 1-4% of energy is available to plants on the surface
Green plants: light energy to chemical energy
Chemical energy: one trophic level to another