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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Biology > Cycling Systems

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Decaying material sinks to the bottom of ponds/lakes/seas.

Problem the producers (phytoplankton) are at the surface ( where there is light ) so nutrients from decay must be brought to the surface by water currents.

1. Winter - water circulates freely. Cold water at surface sinks, circulating nutrients but cold temperatures and little light reduce productivity.
2. Spring - nutrients are available , increased temperatures and increased daylight result in increased productivity (Spring bloom)
3. Summer - warm water rises and so colder water is trapped below a thermocline so nutrients are trapped at the bottom. Nutrients at top are quickly used up by plants resulting in decrease in productivity and decreased number of consumers dependent on plant life.
4. Autumn - water at surface cools and sinks allowing recycling of the nutrients and increased productivity (Autumn bloom). Growth is limited by reducing temperatures and light availability.

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