= Ecosystem
{wiki}
An <ecosystem> is a system of interacting <organisms> and their nonliving surroundings. A pond study might include <algae>, <fish>, <bacteria>, <water>, dissolved <chemical compounds> and incoming <light>. The useful step is to state the boundary and time interval: the pond surface, bottom and shoreline might enclose the study region, but <water>, <organisms> and <energy> can cross them. The chosen boundary specifies what counts as internal storage, input or output; it does not make the <ecosystem> sealed. See https://openstax.org/books/biology-2e/pages/46-1-ecology-of-ecosystems[Clark, Douglas and Choi, Biology 2e, 46.1: ecosystems and their components].
For a toy pond <water> budget over one day, begin with $1000\,\mathrm{m^3}$, add $120\,\mathrm{m^3}$ crossing inward, and remove $90\,\mathrm{m^3}$ crossing outward. With all other transfers omitted by assumption, the final amount is $1000+120-90=1030\,\mathrm{m^3}$. The same bookkeeping asks whether a change inside an <ecosystem> came from internal processes or exchanges with its surroundings. Changing the boundary to include an upstream reservoir changes which transfers are internal, while preserving the accounting.
Back to article page
