In food chains and webs, energy flows through trophic levels with reduced amounts of energy (approximately 10 %) making it to the next level. Eventually all the energy is lost, much of it as heat.
Nutrients however, may be cycled through the food chains endlessly. Such biogeochemical cycles involve living organisms, water, the atmosphere, and the soil. The elements are typically incorporated into organic compounds by autotrophs, pass through various consumers in a food web, and are recycled back to inorganic chemical as by the saprotrophs.
Carbon Cycle --------------------- Nitrogen Cycle