school energy&environment

Primary productivity

The primary productivity of an ecosystem is defined as the speed at which the solar energy is turned into an organic substance by chlorophyll in the photosynthesis.
It is defined as follows:

•gross primary productivity (GPP), the total photosynthesis speed (therefore also called total photosynthesis);
• net primary productivity (NPP), the speed at which the organic matter produced is stored, net of that used by the plant to live (therefore also called apparent photosynthesis);
• net productivity of the community (NPC), it is the speed at which the organic matter not used by herbivore and carnivore animals is stored;
• secondary productivity (SP), it is the speed at which the organic matter is stored by consumers (i.e. the heterotrophic organisms that have not photosynthesis capability) for energy purposes.

A high primary productivity rate in the ecosystems is obtained when the physical factors (for instance: water, nutrients and climate) are favourable. The presence of some forms of secondary energy can also help to increase the primary productivity rate. An example is that of estuaries, one of the most productive ecosystems in the world. In estuaries, freshwater encounters seawater. The plants that live there form a wide photosynthetic carpet. Trunks and roots trap large amounts of food particles and, once their vital cycle is over, they decompose, thus supplying the ecosystem with more organic matter. Here, secondary energy is provided by the effect of tides, that on one side promotes the fast flow of nutrients and on the other side promotes the disposal of the produced waste, so that the organisms that live there (sea bass, gilthead, mullet, clam larvae) do not spend energy to find food or dispose of waste and can grow more quickly.