ABSTRACT
Nutrients are gained and lost by all communities in a variety of different ways. Nutrient budgets can be produced if people can calculate gains and losses for nutrients. In some communities, budgets may be more or less in balance, while in others inputs exceed outputs leading to the accumulation in the compartments of living biomass and dead organic matter. Atmospheric carbon dioxide is the source of carbon of terrestrial communities. A particular nutrient atom taken up by a plant may then be eaten by a herbivore which dies and decomposes, releasing the nutrient atom back into the soil from where it can be taken up once again by plant roots. Aquatic systems obtain most of their nutrients through streamflow. In streams, river communities and lakes with a stream outflow, export in outgoing stream water is an important factor. The pools of chemical elements available exist as pools in various compartments.
