Matter is recycled in an ecosystem through various cyclical processes, such as the oxygen cycle, carbon cycle, water cycle and nitrogen cycle. The oxygen cycle, for example, is driven by photosynthesis and enables the exchange of carbon dioxide and oxygen. In the water cycle, the processes of evaporation, sublimation and transpiration move water through an ecosystem.
The substances required by living organisms in an ecosystem are recycling continuously and their movements have no beginning or end. They move through both the living, or biotic, components of an ecosystem, and through the non-living, or abiotic, components. These components interact and are linked by energy flows and nutrient cycles. Because these interactions and cycles take place across both living and non-living components, they are referred to as an ecosystem's geochemical cycles.
When a recycling substance remains within the confines of one component for a relatively short time, such as a few days, that component is called an exchange pool. An example is Earth's atmosphere, which is an abiotic component that only holds water for a few days before it is returned to the land. When a component of an ecosystem holds on to a recycling substance for a much longer period time, it is called a reservoir. The oceans are a good example, and can hold water in place for thousands of years in the deeper sections.