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nitrogen enters the world through free living and symbiotic bacteria.
Nitrogen,Phosphorus and Sulphur Cycles
The Nitrogen Cycle
Getting nitrogen into the living world is a difficult process.Plants and phytoplankton are not equipped to incorporate nitrogen from the atmosphere (which exists as tightly bonded, triple covalent N2) even though this molecule comprises approximately 78 percent of the atmosphere. Nitrogen enters the living world via free-living and symbiotic bacteria, which incorporate nitrogen into their macromolecules through nitrogen fixation (conversion of N2).
Cyanobacteria live in most aquatic ecosystems where sunlight is present; they play a key role in nitrogen fixation.Cyanobacteria are able to use inorganic sources of nitrogen to “fix” nitrogen. Rhizobium bacteria live symbiotically in the root nodules of legumes (such as peas, beans, and peanuts) and provide them with the organic nitrogen they need. Free-living bacteria, such as Azotobacter, are also important nitrogen fixers.
Organic nitrogen is especially important to the study of ecosystem dynamics. Many ecosystem processes, such as primary production and decomposition, are limited by the available supply of nitrogen. The nitrogen that enters living systems by nitrogen fixation is successively converted from organic nitrogen back into nitrogen gas by bacteria.
The conversion process occurs in three steps in terrestrial systems: ammonification, nitrification, and denitrification.
• The ammonification process converts nitrogenous waste from living animals or from the remains of dead animals into ammonium (NH4+) by certain bacteria and fungi.
• The ammonium is converted to nitrites (NO2-) by nitrifying bacteria, such as Nitrosomonas, through nitrification. Subsequently, nitrites are converted to nitrates (NO3) by similar organisms.
• The process of denitrification occurs, whereby bacteria, such as Pseudomonas and Clostridium, convert the nitrates into nitrogen gas, allowing it to re-enter the atmosphere.
Human activity can release nitrogen into the environment by two primary means:
• The combustion of fossil fuels, (which releases different nitrogen oxides)
• The use of artificial fertilizers in agriculture, (which are then washed into lakes, streams, and rivers by surface runoff).
A major effect from fertilizer runoff is saltwater and freshwater eutrophication, a process whereby nutrient runoff causes the excess growth of microorganisms, depleting dissolved oxygen levels and killing ecosystem fauna.A process occurs in the marine nitrogen cycle, where the ammonification, nitrification, and denitrification processes are performed by marine bacteria.
Some of this nitrogen falls to the ocean floor as sediment, which can then be moved to land in geologic time by uplift of the Earth’s surface and thereby incorporated into terrestrial rock. Although the movement of nitrogen from rock directly into living systems has been traditionally seen as insignificant compared with nitrogen fixed from the atmosphere, a recent study showed that this process may indeed be significant.
The Phosphorus Cycle
Phosphorus is an essential nutrient for living processes; it is a major component of nucleic acid and phospholipids, and, as calcium phosphate, makes up the supportive components of our bones. Phosphorus is often the limiting nutrient (necessary for growth) in aquatic ecosystems. Phosphorus occurs in nature as the phosphate ion (PO4), in addition to phosphate runoff as a result of human activity.Natural surface phosphate runoff occurs when it is leached from phosphate-containing rock by weathering, thus sending phosphates into rivers, lakes, and the ocean. This rock has its origins in the ocean. Phosphate-containing ocean sediments form primarily from the bodies of ocean organisms and from their excretions.
However, in remote regions, volcanic ash, aerosols, and mineral dust may also be significant phosphate sources. This sediment then is moved to land over geologic time by the uplifting of areas of the Earth’s surface.
Weathering of rocks and volcanic activity releases phosphate into the soil, water, and air, where it becomes available to terrestrial food webs. Phosphate enters the oceans via surface runoff, groundwater flow, and river flow. Phosphate dissolved in ocean water cycles into marine food webs. Some phosphate from the marine food webs falls to the ocean floor, where it forms sediment.
Excess phosphorus and nitrogen that enters ecosystems from fertilizer runoff and from sewage causes excessive growth of microorganisms and depletes the dissolved oxygen. This then leads to the death of many ecosystem fauna, such as shellfish and finfish. This process is also responsible for dead zones in lakes and many major rivers found in coastal areas of high population density.
A dead zone is an area within a freshwater or marine ecosystem where large areas are depleted of their normal flora and fauna. These zones can be caused by eutrophication, oil spills, dumping of toxic chemicals, and other human activities. The number of dead zones has been increasing for several years, and more than 400 of these zones were present as of 2008. One of the worst dead zones is off the coast of the United States in the Gulf of Mexico, where fertilizer runoff from the Mississippi River basin has created a dead zone of over 8463 square miles. Phosphate and nitrate runoff from fertilizers also negatively affect several lake and bay ecosystems including the Chesapeake Bay in the eastern United States.
The Sulphur Cycle
Sulphur is an essential element for the macromolecules of living things. As a part of the amino acid cysteine, it is involved in the formation of disulfide bonds within proteins, which help to determine their 3-D folding patterns, and hence their functions. sulphur cycles between the oceans, land, and atmosphere. Atmospheric sulfur is found in the form of sulphur dioxide and enters the atmosphere in three ways: from the decomposition of organic molecules, from volcanic activity and geothermal vents, and from the burning of fossil fuels.
Sulphur dioxide from the atmosphere becomes available to terrestrial and marine ecosystems when it is dissolved in precipitation as weak sulphuric acid or when it falls directly to the Earth as fallout. Weathering of rocks also makes sulphates available to terrestrial ecosystems. Decomposition of living organisms also helps to returns sulphates to the ocean, soil and atmosphere.
On land, sulphur is deposited in four major ways:
• direct fallout
• rock weathering
• geothermal vents
Atmospheric sulphur is found in the form of sulphur dioxide, as rain falls through the atmosphere, sulphur is dissolved in the form of weak sulfuric acid.
The weathering of sulphur-containing rocks releases sulphur into the soil. These rocks originate from ocean sediments that are moved to land by the geologic uplifting of ocean sediments.
Terrestrial ecosystems can then make use of these soil sulphates (SO4-), and upon the death and decomposition of these organisms,release the sulphur back into the atmosphere as hydrogen sulphide (H2S) gas.
Sulphur enters the ocean via runoff from land, from atmospheric fallout, and from underwater geothermal vents. Some ecosystems rely on chemoautotrophs using sulphur as a biological energy source. This sulphur then supports marine ecosystems in the form of sulphates.
Human activities have played a major role in altering the balance of the global sulphur cycle. The burning of large quantities of fossil fuels, especially from coal, releases larger amounts of hydrogen sulphide gas into the atmosphere. As rain falls through this gas, it creates the phenomenon known as acid rain. Acid rain is corrosive, and is caused by rainwater passing through sulphur dioxide gas as it falls to the ground , turning it into weak sulfuric acid, which causes damage to aquatic ecosystems.
Acid rain damages the natural environment by lowering the pH of lakes, which kills many of the resident fauna; it also affects the man-made environment through the chemical degradation of buildings,monuments and statues. Many marble monuments, such as the Lincoln Memorial in Washington DC, in the US, have suffered significant damage from acid rain over the years. These examples show the wide-ranging effects of human activities on our environment and the
challenges that remain for our future.
The process whereby oxygen is depleted by the growth of microorganisms due to excess nutrients in aquatic systems is called?
a. dead zoning, b. eutrophication, c. retrofication, d. depletion
Answer B) A major effect from fertilizer runoff is saltwater and freshwater eutrophication, a process whereby nutrient runoff causes the excess growth of microorganisms, depleting dissolved oxygen levels and killing ecosystem fauna
What is the process called, whereby nitrogen is brought into organic molecules?
a. nitrification, b. denitrification, c. nitrogen fixation, d. nitrogen cycling
Answer A) Nitrification. Ammonium is converted to nitrites by nitrifying bacteria, through nitrification. Subsequently, nitrites are converted to nitrates by similar organisms.
acid rain corrosive rain caused by rainwater falling to the ground through sulfur dioxide gas, turning it into weak sulfuric acid; can damage structures and ecosystems
biogeochemical cycle cycling of mineral nutrients through ecosystems and through the non-living world
biomagnification increasing concentrations of persistent, toxic substances in organisms at each trophic level, from the primary producers to the apex consumers
biomass total weight, at the time of measurement, of living or previously living organisms in a unit area within a trophic level
dead zone area within an ecosystem in lakes and near the mouths of rivers where large areas of ecosystems are depleted of their normal flora and fauna; these zones can be caused by eutrophication, oil spills, dumping of toxic chemicals, and other human activities
ecosystem dynamics study of the changes in ecosystem structure caused by changes in the environment or internal forces
ecosystem community of living organisms and their interactions with their abiotic environment
equilibrium steady state of an ecosystem where all organisms are in balance with their environment and each other
eutrophication process whereby nutrient runoff causes the excess growth of microorganisms, depleting dissolved oxygen levels and killing ecosystem fauna
fallout direct deposit of solid minerals on land or in the ocean from the atmosphere
food web graphic representation of a holistic, non-linear web of primary producers, primary consumers, and higher-level consumers used to describe ecosystem structure and dynamics
resilience (ecological) speed at which an ecosystem recovers equilibrium after being disturbed
resistance (ecological) ability of an ecosystem to remain at equilibrium in spite of disturbances
subduction movement of one tectonic plate beneath another
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