Undisturbed natural ecosystems are able to maintain a vibrant diversity of life because they incorporate intricate recycling systems that conserve essential materials. These materials include mineral nutrients, such as nitrogen or phosphorus, and important biological substances such as water or oxygen gas. Unlike energy, which generally flows into and out of an ecosystem, matter passes through various cycles that allow it to nourish one generation after another.
Recycle and Reuse
Matter cycling in an ecosystem is a specific application of a fundamental principle known as the conservation of mass, which states that matter changes forms but is never created or destroyed. In an environmental context, this indicates that an ecosystem must include mechanisms that recycle matter. Without these mechanisms, unusable residual matter would perpetually accumulate and no new matter could be created as a replacement. An individual ecosystem, however, is not a perfectly closed system. Some degree of nutrient transfer does occur between an ecosystem and the surrounding environment.
From Earth to Life to Earth
The systems that accomplish matter recycling are known as biogeochemical cycles. This informative term captures the fundamental aspects of ecological nutrient conservation. "Bio" means life -- the living organisms in an ecosystem -- and "geo" means earth, which serves as a reservoir for the "chemicals" that organisms need to build their physical structures and sustain their metabolic processes. The Earth is, in a sense, the beginning and end of each individual matter cycle, whereas the middle of the cycle is dominated by organisms that manipulate this matter in various ways.
The Great Nutrient Reservoir
An ecological nutrient is any element or molecule required for the growth, development or reproduction of an organism. These substances are initially supplied by the Earth -- for example, water originates from the ocean, nitrogen and oxygen from the atmosphere, and minerals, such as calcium and potassium, from rocks that slowly break down into soil. Many of these nutrients will cycle through an ecosystem for numerous generations, but small amounts are lost and returned to natural systems. This loss occurs, for example, as runoff that deposits mineral nutrients into lakes and oceans, fires that convert carbon to carbon dioxide gas, and microbiological activity that disperses soil nitrogen into the atmosphere.
Passing the Nutrients
The biological portion of matter cycling takes place the interactions between producers, consumers and decomposers. Producers, generally plants, absorb nutrients from soil and water and incorporate them into their tissues. Herbivorous consumers, such as deer, then incorporate these same nutrients into their tissues when they feed on producers, and carnivorous consumers, such as coyotes, receive these nutrients from herbivores or other carnivores. Without decomposers, these nutrients would then be locked up in waste generated by consumers and in the organic residue of dead producers and consumers. But bacteria, fungi, insects and other decomposers process this organic matter in a way that makes nutrients available to future generations of higher organisms.
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