Biogeochemical cycles - Carbon Cycle/Oxygen Cycle/Phosphorus Cycle December 19, 2017 Carbon Cycle This cycle contains any of the natural pathways by which essential elements of living matter are circulated. Biogeochemical cycles are named for the cycling of biological, geological and chemical elements through Earth and its atmosphere. • The cycles move substances through the biosphere, lithosphere, atmosphere and hydrosphere. Cycles are gaseous and sedimentary. • Gaseous cycles include nitrogen, oxygen, carbon, phosphorous, sulfur and water. • These elements cycle through evaporation, absorption by plants and dispersion by wind. Sedimentary cycles include the leeching of minerals and salts from the Earth’s crust, which then settle as sediment or rock before the cycle repeats. Energy flows through an ecosystem and is dissipated as heat, but chemical elements are recycled. • For the living components of a major ecosystem (e.g., a lake or a forest) to survive, all the chemical elements that make up living cells must be recycled continuously. • Energy flows directionally through Earth’s ecosystems, typically entering in the form of sunlight and exiting in the form of heat. However, the chemical components that make up living organisms are different (they get recycled). • Elements within biogeochemical cycles flow in various forms from the nonliving (a biotic) components of the biosphere to the living (biotic) components and back. • Repetition of the cycles is important. Plants absorb carbon dioxide and release oxygen, making the air breathable. Plants also acquire nutrients from sediment. Animals acquire nutrients from plants and other animals, and the death of plants and animals returns these nutrients to the sediment as they decay. The cycle then repeats and allows other living things to benefit. • The simplest example of biogeochemical cycles at work includes water. Water evaporates from the oceans, condenses as clouds and precipitates as rain, which returns the water back to the earth in a cycle. Many elements cycle through ecosystems, organisms, air, water, and soil. Many of these are trace elements. Other elements, including carbon, nitrogen, oxygen, hydrogen, sulfur, and phosphorus is critical components of all biological life. Each biogeochemical cycle can be considered as having a reservoir (nutrient) pool a larger, slow-moving, usually abiotic portion and an exchange (cycling) pool a smaller but more-active portion concerned with the rapid exchange between the biotic and abiotic aspects of an ecosystem. Types of Bio-geochemical Cycles: From the viewpoint of the ecosphere as a whole, biogeochemical cycles fall into two basic groups: Gaseous Types, in which the reservoir is in the atmosphere or the hydrosphere (ocean); and Sedimentary Types, in which the reservoir is in the crust of earth. CARBON CYCLE Carbon is a constituent of all organic compounds, many of which are essential to life on Earth. The source of the carbon found in living matter is carbon dioxide (CO2) in the air or dissolved in water. Carbon is found in all organic macromolecules and is also a key component of fossil fuels. Steps in the carbon cycle 1. Carbon enters the atmosphere as carbon dioxide from respiration and combustion. 2. Carbon dioxide is absorbed by producers to make carbohydrates in photosynthesis. 3. Animals feed on the plant passing the carbon compounds along the food chain. Most of the carbon they consume is exhaled as carbon dioxide formed during respiration. The animals and plants eventually die. 4. The dead organisms are eaten by decomposers and the carbon in their bodies is returned to the atmosphere as carbon dioxide. In some conditions decomposition is blocked. The plant and animal material may then be available as fossil fuel in the future for combustion. The cycle has four major reservoirs of carbon interconnected by pathways of exchange. The reservoirs are: 1. the atmosphere 2. the terrestrial biosphere (which usually includes freshwater systems and non-living organic material, such as soil carbon) 3. the oceans (which includes dissolved inorganic carbon and living and non-living marine biota 4. the sediments (which includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. Other facts: Algae and terrestrial green plants (producers) are the chief agents of carbon dioxide fixation through the process of photosynthesis, through which carbon dioxide and water are converted into simple carbohydrates. These compounds are used by the producers to carry on metabolism, the excess being stored as fats and polysaccharides. The stored products are then eaten by consumer organisms, from protozoans to man, which convert them into other forms. CO2 is added directly to the atmosphere by animals and some other organisms as a by-product of respiration. The carbon present in animal wastes and in the bodies of all organisms is released as CO2 by decay, or decomposer, organisms (chiefly bacteria and fungi) in a series of microbial transformations. Part of the organic carbon the remains of organisms has accumulated in Earth’s crust as fossil fuels (e.g., coal, gas, and petroleum), limestone, and coral. The carbon of fossil fuels, removed from the cycle in prehistoric time, is now being released in vast amounts as CO2 through industrial and agricultural processes, much of it quickly passing into the oceans and there being “fixed” as carbonates. If oxygen is scarce (as in sewage, marshes, and swamps), some carbon is released as methane gas. Human Impact on the Carbon Cycle: Felling of forests, coal-burning power plants, automobile exhausts, factory smokestacks, and other waste vents of the human environment contribute about 22 billion tons of carbon dioxide (corresponding to 6 billion tons of pure carbon) and other greenhouse gases into the earth’s atmosphere each year. This alters the Carbon Cycle drastically. Carbon dioxide emissions are now around 12 times higher than in 1900 because of increased quantities of coal, oil and gas consumption for energy. This serious imbalance in the Carbon cycle is responsible behind the phenomena like Green House Effect, Global Warming and Climate Change. It is now an established fact that this environmental impact will have disastrous consequences for the entire biosphere and humanity.