Trophic levels Ecosystems can be represented as a pyramid of production and consumption. After level 2 the remaining energy or biomass presents little opportunity for further levels of consumption. Nutrient cycles Trophic levels give a unidirectional impression of energy or biomass flows. They are useful in analyzing carrying capacity of natural and agricultural ecosystems. They do not show the full path of nutrient flows, which are important in understanding the sustainability of systems over time.
Organisms are continually absorbing and returning nutrients to their environments.
Physical processes such as air and water movement influence the fates of these nutrients to variable extents. The water cycle essentially involves physical processes of evaporation, precipitation and water flow with solar energy providing the driving force. However, organisms and especially plants modify evaporation and precipitation. The presence of water in oceans and atmosphere make this a global cycle. The nitrogen cycle is perhaps the most complex in that so many organisms are involved in the transformations.