In an ecosystem materials circulate from
environment through producers,
consumers, and reducers back to environment. The processes of transfer and
concentration of materials in ecosystems have great, and increasingly urgent,
significance to communities that draw their resources from them.
The dynamics of dissolved phosphate in
bodies of still water illustrate some of the
general principles of nutrient circulation, especially the ways parts of ecosystems
are related to one another by nutrient transfer and moving water.
The word "nutrient"' can apply
to any substance taken into an organism that is
metabolised or becomes part of ionic balances excluding toxins and substances
used only as signals for behavior. The phosphate model illustrates the principles of
chemical exchanges between organisms and environment and between different
organisms. The same principles could be illustrated using other inorganic
elements and ions such as calcium and potassium, and nitrate, that are present in
water and soil and may be taken up to become factors in the maintenance of
community function.
