"Hey Mom what's for dinner?" "Cycles, dear!" "No, not again!"
The Phosphorus Cycle
The phosphorus cycle is different from the water, carbon,
and nitrogen cycles because phosphorus is found in
sedimentary rock, not the atmosphere. Phosphorus is a
necessary element in DNA, in many molecules found in living
cells, and in the bones of vertebrate animals. A smaller,
less important source of phosphorus is the droppings
(guano) of fish-eating sea birds.
Erosion caused by rainfall and the runoff of streams
removes phosphorus from phosphate rock. This results in a
phosphorus supply in the soil which is available to plants.
The phosphorus is absorbed by the plants' roots and used to
make organic compounds. As animals eat the plants, the
phosphorus is passed along to them. Decomposing plant or
animal tissue and animal droppings return organic forms of
phosphorus to the water and soil.
Much of the phosphorus is eventually lost in the oceans.
The phosphorus in the soil is dissolved in water, which in
turn flows into bodies of water. Some of this phosphorus is
used by plankton, which in turn is eaten by fish. These
fish are then consumed by sea birds. But the majority of
phosphorus washed into the sea sinks to the ocean floor and
is not recycled.