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Energy is not the only substance necessary for life. Biogeochemical cycles are a way in which other important materials move through and are recycled in ecosystems. When properly functioning, these cycles maintain balance in ecosystems and ensure vital nutrients are available for life.
Water Cycle
The water cycle describes the movement of water through the environment. The four main processes in this cycle are condensation, precipitation, evaporation, and transpiration. Water starts in the atmosphere as a gas. When temperatures cool, the water condenses and falls as precipitation in a variety of forms. This water is consumed by organisms, infiltrates into the soil, or flows into rivers which lead to other bodies of water. Surface water can then evaporate back into the atmosphere completing the cycle. Transpiration, the release of water from plants, also returns water to their atmosphere.
Carbon Cycle
The carbon cycle describes how carbon moves through the environment. The four main processes in this cycle are photosynthesis, cellular respiration, decomposition, and combustion. Specifically, it addresses how carbon is exchanged between the atmosphere, living organisms, and soil. Carbon dioxide starts as a gas in the atmosphere as CO2. It is then absorbed by plants and converted to sugars during photosynthesis. This carbon moves up the food chain into animals and eventually is broken down into organic matter by decomposers when organisms die. This carbon can then be stored in the soil. Carbon dioxide is produced and released into the atmosphere by respiration of plants and animals or through the burning of fossil fuels.
Nitrogen Cycle
The nitrogen cycle describes how nitrogen moves through the environment. The five main processes in this cycle are nitrogen fixation, assimilation, ammonification, nitrification, and denitrification. Nitrogen gas is found in the atmosphere. Nitrogen-fixing bacteria are able to convert this nitrogen to a form that is usable by other organisms. Plants use this form of nitrogen to build molecules and proteins which are then consumed and used by other organisms. The organisms release nitrogen through urine or are broken down by decomposers and released back into the soil.
Phosphorus Cycle
The phosphorus cycle describes how nitrogen moves through the environment. The main source of phosphorus is from rocks. This is released into the environment via weathering and is absorbed by plants. This is then transferred into other organisms through the food chain and returned to the soil via decomposition.
