Conference 4 - Biogeochemical
Cycles
Biogeochemical Cycles
Carbon Cycle
Starting with the carbon reservoirs, CO2 in the air and HCO3-
molecules in the water, plants, through photosynthesis break down the
CO2 molecules to build plant matter and release oxygen. As consumers eat
plants which gets the carbon into the food web. Through respiration,
animals will release carbon atoms into the air as CO2.
In aquatic systems there are two processes to note: 1) sedimentation in
solution and limestone formation of carbon. The later removes carbon
from the solution. 2) Weathering and combustion of fossil-fuel carbon.
Phosphorous
Cycle
The phosphorus cycle is representative of any of the other minerals. Its
importance is due to the fact that it is typically a limiting factor in
the environment. Unlike carbon, phosphorous does not have a gaseous
state. The phosphorous cycle starts in the rocks and soil of the
lithosphere. Plants absorb phosphate ions (PO43-)
dissolved in water and directly from the soil. Phosphate moves through
the food chain as plant material is consumed. It reenters the cycle as
waste from the consumers. Unlike carbon, phosphorous only reenters the
ecosystem it came from if the waste is deposited into the ecosystem it
came from. In short, as consumers move from ecosystem to ecosystem the
level of phosphate can change.
The phosphate cycle is disrupted more easily than other geochemical
cycles. For instance in tropical rainforests that are cut down, the
phosphorous in organisms is lost due to burning and removing of trees.
Since most ecosystems are essentially balanced, once the trees are cut
or burned the phosphorus is removed from the ecosystem by logging trucks
or washed downstream as ash and burned materials.
Nitrogen
Cycle
The main reservoir of nitrogen in the environment is the atmosphere,
which is about 78% nitrogen. Plants absorb nitrogen through water and
used to create plant material. Nitrogen continues its cycle as consumers
eat producers and release the nitrogen back into the environment through
waste, usually in the form of ammonium compounds.
Nitrogen also is removed from the air and transformed into useable forms
by nitrifying bacteria using the chemosynthetic process. This process
creates a usable form of nitrogen that plants can once again use to
continue the nitrogen cycle.
Nitrogen fixation is also another process that moves nitrogen into the
food chain. Through nitrogen fixation, nitrogen gas is converted to a
usable form of ammonium, which plants can once again use for creating
plant material.
Other processes that “fix” nitrogen are lightning, industrial fixation,
and denitrification. Lightning fixation occurs as lightning creates
ammonium as the energy electrifies the air. During industrial fixation,
combustion of fossil fuels creates ammonium which is released into the
air. The above two processes return the nitrogen to the surface as acid
rain. In denitrification, nitrate is oxidized by bacteria in soil that
is low in oxygen and released back into the atmosphere.
Visit www.FaulknerWeb.com
to see more
E-mail
me at Home |