There are three zones, littoral, limnetic and profundal. The littoral zone, which is closest to the shore with shallow water region, allows easy penetration of light. It is warm and occupied by rooted plant species. The limnetic zone refers the open water of the pond with an effective penetration of light and domination of planktons. The deeper region of a pond below the limnetic zone is called profundal zone with no effective light penetration and predominance of heterotrophs. The bottom zone of a pond is termed benthic and is occupied by a community of organisms called benthos (usually decomposers).

Circulation of nutrients within the ecosystem or biosphere is known as biogeochemical cycles and also called as 'cycling of materials.' There are two basic types,
(I) Gaseous cycle - It includes atmospheric Oxygen, Carbon and Nitrogen cycles.
(II) Sedimentary cycle - It includes the cycles of Phosphorus, Sulphur and Calcium - Which are present as sediments of Earth.

(1) pyramid of number
(2) pyramid of biomass
(3) pyramid of energy.

Detritus food chain is a type of food chain which begins with dead organic matter which is an important source of energy. A large amount of organic matter is derived from the dead plants, animals and their excreta. This- type of food chain is present in all ecosystems. The transfer of energy from the dead organic matter, is transferred through a series of organisms called detritus consumers (detritivores)- small carnivores -large (top) carnivores with repeated eating arid being eaten respectively. This is called the detritus food chain.
Fallen leaves   ➝    Earth worm   ➝    Black bird     ➝         Hawk
Detritus               Detritivores      Small carnivores  Top carnivores

Primary productivity depends upon the plant species of an area, their photosynthetic capacity, availability of nutrients, solar radiation, precipitation, soil type, topographic factors (altitude, latitude and direction), and other environmental factors.