biogeochemical cycle
46.3 | Biogeochemical Cycles By the end of this section, you will be able to: Discuss the biogeochemical cycles of water, carbon, nitrogen, phosphorus, and sulfur Explain how human activities have impacted these cycles and the potential consequences for Earth Energy flows directionally through ecosystems, entering as sunlight or inorganic molecules for chemoautotrophs and leaving as heat during the many transfers between trophic levels. However, the matter that makes up living organisms is conserved and recycled. The six most common elements associated with organic moleculescarbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfurtake a variety of chemical forms and may exist for long periods in the atmosphere, on land, in water, or beneath the Earths surface. Geologic processes, such as weathering, erosion, water drainage, and the subduction of the continental plates, all play a role in this recycling of materials. Because geology and chemistry have major roles in the study of this process, the recycling of inorganic matter between living organisms and their environment is called a biogeochemical cycle. Water contains hydrogen and oxygen, which is essential to all living processes. The hydrosphere is the area of the Earth where water movement and storage occurs: as liquid water on the surface and beneath the surface or frozen rivers, lakes, oceans, groundwater, polar ice caps, and glaciers , and as water vapor in the atmosphere. Carbon is found in all organic macromolecules and is an important constituent of fossil fuels. Nitrogen is a major component of our nucleic acids and proteins and is critical to human agriculture. Phosphorus, a major component of nucleic acid along with nitrogen , is one of the main ingredients in artificial fertilizers used in agriculture and their associated environmental impacts on our surface.