CYCLING OF MATTER IN ECOSYSTEMS 2.6 Matter cannot be created or destroyed, so all water and nutrients must be obtained from chemicals already in the environment. Chemicals on Earth are continuously consumed, rearranged, stored, and used in a series of cycles called biogeochemical cycles. The Water Cycle The water cycle is the cycling of water through the environment. biogeochemical cycles water cycle The water cycle

The Carbon Cycle 2.6 Carbon moves between the abiotic and biotic parts of an ecosystem in the carbon cycle Most of this exchange occurs between carbon dioxide in air or water and photosynthesizing organisms. Most of Earth’s carbon is stored in carbon-rich deposits such as fossil fuels. Large quantities of carbon are also contained in plant tissue and dissolved in the oceans. By burning fossil fuels, humans release stored carbon into the atmosphere. This has a dramatic effect on the carbon cycle. Deforestation also increases the concentration of carbon dioxide in the atmosphere. The concentration of carbon dioxide in the atmosphere is higher now than it has been for the past 800 000 years. This change is causing global climatic change. carbon cycle

The Carbon Cycle (continued) 2.6

The Nitrogen Cycle 2.6 Nitrogen is very abundant in the atmosphere. It enters and leaves the atmosphere through a complex biochemical pathway in the nitrogen cycle. Nitrogen is taken from the atmosphere by certain bacteria in a process called nitrogen fixation. Nitrogen is returned to the atmosphere by denitrifying bacteria. nitrogen cycle The nitrogen cycle