Nutrient cycling is the first basic principle of ecosystem sustainability. It is the repeated pathway of particular nutrients or elements from the environment through one or more organisms back to the environment. Some examples include carbon cycle, the nitrogen cycle, and the phosphorus cycle; which are driven directly or indirectly by incoming solar energy and gravity. The earth's chemical cycles also connect past, present, and future forms of life. The nutrient cycle is important in two ways. First is that it prevents waste and the second reason is it assures that the ecosystem will not run out of essential elements. An these two lead to what is know as the first basic principle of ecosystem sustainability, which is the ecosystems dispose of waste and replenish nutrients by recycling all elements.
The hydrologic cycle or water cycle that collects, purifies, and distributes the earth's water supply is in the ecosystem. The water cycle is powered by energy from the sun and by gravity. The carbon cycle is based on carbon dioxide gas. Carbon Dioxide is a key component of nature's thermostat. Lighting and certain bacteria convert gaseous nitrogen gas into compounds that can enter food webs as part of the nitrogen cycle. In the Phosphorus cycle, phosphorus moves slowly from phosphate deposits on land and in shallow ocean sediments to living organisms, and then much more slowly backs to the land and ocean. Bacteria are less important here to the nitrogen cycle. Sunlight as a source of energy is fundamental to sustainability because it is both nonpolluting and non-depletable.