What are biogeochemical cycles?
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Hydrologic Cycle
Processes
The movement of water through the biosphere is known as the hydrologic cycle. There are several steps to this process. The sun’s solar energy provides the energy needed for photosynthesis to occur. This causes the release of water from the plant’s leaves – called transpiration. Water that is released into the earth’s atmosphere cools down and forms clouds, then causing precipitation to occur. After rain falls it can take several different paths. First, it can be released into the atmosphere by evaporation or transpiration. The combined amount of evaporation and evapotranspiration – the combined amount of evaporation and transpiration. Second, water can be absorbed into the soil and filter into the groundwater. Third, water can travel as runoff across the earth’s surface and into streams and rivers, and will ultimately reach the ocean (the ultimate pool of water on Earth). As water reaches the ocean, the cycle begins again.
The water cycle’s reservoirs include oceans, rivers, lakes, ponds, and areas underground.
Humans have a major impact on the water cycle. A major concern is that of deforestation. By harvesting trees, it reduces the plant biomass, ultimately reducing evapotranspiration. Clear-cutting of a mountain can lead to erosion and flooding due to the increase in runoff. Paving roads has a similiar effect because it also increases runoff due to a decrease in percolation. Another important issue is the diversion of water to provide for drinking. irrigation, and industrial uses which has a major effect on the hydrologic cycle.
Pools
Human Impact
Carbon Cycle
Processes
The carbon cycle is the movement of carbon around the biosphere. There are several processes that are involved in the carbon cycle, including photosynthesis, respiration, exchange, sedimentation, burial, extraction, and combustion. During photosynthesis, producers take in CO2 and incorporate it into their tissues. Some of this carbon is returned as CO2 when they respire or die. When producers do die, decomposers break down the dead material, which returns CO2 back into the atmosphere via respiration. The amount of carbon released from the ocean into the atmosphere equals around the same amount of atmospheric CO2 that diffuses into the water. When dissolved in the ocean, CO2 combines with calcium ions in the water to form calcium carbonate. This is a compound that can precipitate out of water and from limestone and dolomite rock through sedimentation and burial. Although sedimentation moves at an almost stagnant pace, it contributes to the largest carbon pool (in the slow part of the cycle). The last stages of the cycle include extraction and combustion. Extraction of fossil feuls is a more recent process that has become more popular due to our reliance on coal, oil, and natural gas. Extraction itself does not have an effect on the carbon cycle, it’s the aftermath that does – combustion. Combustion of fossil fuels by humans, and also the natural combustion of carbon (fires, volcanoes) releases carbon into the atmosphere as CO2 or into the soil as ash.
Pools
The carbon cycle's reservoirs include the atmosphere, fossil fuels, living organisms, ocean, and rocks.
Human Impact
The best-known and most significant human impact on the carbon cycle is the combustion of fossil fuels. This increases atmospheric carbon concentrations. The excess CO2 in the atmosphere acts to increase the retention of heat energy in the biosphere, resulting in global warming. Tree harvesting almost impacts the carbon cycle. Trees are a huge source of carbon since they store large amounts of carbon in their wood. The destruction of forests by cutting and burning increases the amount CO2 in the atmosphere.
Nitrogen Cycle
Processes
The nitrogen cycle is the movement of nitrogen around the biosphere. There are five major transformations in the nitrogen cycle: nitrogen fixation, nitrification, assimilation, mineralization, and denitrification. Nitrogen fixation is the process that converts nitrogen gas in the atmosphere (N2) into forms of nitrogen that producers can use. Nitrogen fixation by organisms, lightning, or human activites converts nitrogen gas into ammonium (NH4+) or nitrate (NO3-). Nitrification is a process that converts ammonium into nitrite (NO2-) and then into nitrate (NO3-). Once producers take up nitrogen as ammonia, ammonium, nitrite, or nitrate, they incorporate it into their tissues in a process called assimilation. Eventually, organisms die and their tissues decompose and are converted to ammonium in a process called mineralization. Finally, denitrification returns nitrogen to the atmosphere.
Pools
The nitrogen cycle's reservoirs include the atmosphere, food web (DNA/proteins), soil, and ocean sediments.
Human Impact
Nitrogen is a limiting nutrient in most ecosystems, so an excess of nitrogen can have detrimental results. One problem revolves around fertilizers. Adding nitrogen to soils in fertilizers increases the atmospheric concentrations of nitrogen where the fertilizers are used. This excess nitrogen can be transported through the atmosphere and deposited by rainfall, altering the abundance of species. In a study on fertilizers, scientists found that adding nitrogen reduced the number of species in a plot by up to 48 percent.
Phosphorus cycle
Processes
The phosphorus cycle involves a large pool of phosphorus in rock that is formed but the precipitation of phosphate onto the ocean floor. Geologic forces can lift these sediments and form mountains. The phosphorus in the mountains can be made available to producers either by weathering or by mining. Producers assimilate phosphorus from the soil or water and consumers assimilate it when they eat producers. The waste products and dead bodies of organisms experience mineralizations, which returns phosphorus to the environment where it can be ultimately transferred back to the ocean.
Pools
The phosphorus cycle's reservoirs include the food web, ocean water and sediments, rocks/fossils, fertilizer from farms, sewage from water treatment plants and mining waste from mines.
Human Impact
Phosphorus is used in fertilizers. This becomes a problem when these fertilizers are used and the excess phosphorus can leach into water bodies. Because aquatic environments are commonly limited by a low availability of phosphorus, even small inputs of phosphorus inot these systems can significantly increase the growth of producers. Phosphorus inputs can lead to an increase in the algal population (also known as algal bloom). When the algae die, the decomposition process consumes large amounts of oxygen, causing the water to become hypotoxic (low in oxygen). This results in the death of fish and other aquatic organisms. Another problem that results in an excess of phosphorus in waterways is the use of detergents. Because phosphorus causes significant environmental and economic damage, manufacturers stopped adding phosphates to detergents.
Sulfur Cycle
Processes
Calcium, magnesium, and potassium are derived from rock and can be held by soils. Producers can assimilate these elements, and mineralization of waste products and dead organisms returns the elements back to the environment. Most sulfur exists in the form of rocks and is released through the process of weathering, which makes it available for plant assimilation. Some sulfur exists as a gas in the form of sulfur dioxide (SO2), which can be produced by volcanic eruptions and the burning of fossil fuels. In the atmosphere, SO2 is converted into sulfuric acid (H2SO4) when it mixes with water. The sulfuric acid can then be carried back to the ground when it rains or snows.
Pools
The sulfur cycle's reservoirs include disolved sulfur, atmospheric sulfur, sulfur-bearing minerals, living organisms, and sulfur in soil.
Human Impact
There are several human acts that have a major impact on the sulfur cycle. These effects are include the burning of fossil fuels and mining.
