Where is nitrogen cycle slowest

In aquatic environments, blue-green algae really a bacteria called cyanobacteria are an important free-living nitrogen fixer. In addition to nitrogen-fixing bacteria , high-energy natural events such as lightning, forest fires, and even hot lava flows can cause the fixation of smaller, but significant, amounts of nitrogen.

The high energy of these natural phenomena can break the triple bonds of N 2 molecules , thereby making individual N atoms available for chemical transformation. Within the last century, humans have become as important a source of fixed nitrogen as all natural sources combined.

Burning fossil fuels, using synthetic nitrogen fertilizers, and cultivating legumes all fix nitrogen. Through these activities, humans have more than doubled the amount of fixed nitrogen that is pumped into the biosphere every year Figure 3 , the consequences of which are discussed below. When organisms nearer the top of the food chain like us!

After nitrogen is incorporated into organic matter , it is often converted back into inorganic nitrogen by a process called nitrogen mineralization , otherwise known as decay.

When organisms die, decomposers such as bacteria and fungi consume the organic matter and lead to the process of decomposition. During this process, a significant amount of the nitrogen contained within the dead organism is converted to ammonium. Once in the form of ammonium, nitrogen is available for use by plants or for further transformation into nitrate NO 3 - through the process called nitrification. Some of the ammonium produced by decomposition is converted to nitrate NO 3 - via a process called nitrification.

The bacteria that carry out this reaction gain energy from it. Nitrification requires the presence of oxygen, so nitrification can happen only in oxygen-rich environments like circulating or flowing waters and the surface layers of soils and sediments. The process of nitrification has some important consequences. The positive charge prevents ammonium nitrogen from being washed out of the soil or leached by rainfall. In contrast, the negatively charged nitrate ion is not held by soil particles and so can be washed out of the soil, leading to decreased soil fertility and nitrate enrichment of downstream surface and groundwater.

Through denitrification , oxidized forms of nitrogen such as nitrate NO 3 - and nitrite NO 2 - are converted to dinitrogen N 2 and, to a lesser extent, nitrous oxide gas NO 2. Denitrification is an anaerobic process that is carried out by denitrifying bacteria , which convert nitrate to dinitrogen in the following sequence:.

Nevertheless, certain processes do return some marine phosphorus to portions of the continental landscape. For example, some kinds of fish spend most of their life at sea but migrate up rivers to breed. When they are abundant, fish such as salmon import substantial quantities of organic phosphorus to the higher reaches of rivers, where it is decomposed to phosphate after the fish spawn and die. Fish-eating marine birds are also locally important in returning oceanic phosphorus to land through their excrement.

Soil is the principal source of phosphorus uptake for terrestrial vegetation. The phosphate ion PO 4 3— is the most important form of plant-available phosphorus. Although phosphate ions typically occur in small concentrations in soil, they are constantly produced from slowly dissolving minerals such as calcium, magnesium, and iron phosphates Ca 3 PO 4 2 , Mg 3 PO 4 2 , and FePO 4. Phosphate is also produced by the microbial oxidation of organic phosphorus, a component of the more general process of decay.

Water-soluble phosphate is quickly absorbed by microorganisms and by plant roots and used in the synthesis of a wide range of biochemicals. Aquatic autotrophs also use phosphate as their principal source of phosphorus nutrition. In fact, phosphate is commonly the most important limiting factor to the productivity of freshwater ecosystems. This means that the primary productivity will increase if the system is fertilized with phosphate, but not if treated with sources of nitrogen or carbon unless they first have sufficient PO 4 3— added; see Chapter Lakes and other aquatic ecosystems receive most of their phosphate supply through runoff from terrestrial parts of their watershed, and by the recycling of phosphorus from sediment and organic phosphorus suspended in the water column.

Humans are greatly affecting the global phosphorus cycle by mining it to manufacture fertilizer, and applying that material to agricultural land to increase its productivity. For some time, the major source of phosphorus fertilizers was guano, the dried excrement of marine birds. Guano is mined on islands, such as those off coastal Chile and Peru, where breeding colonies of seabirds are abundant and the climate is dry, allowing the guano to accumulate.

During the twentieth century, however, deposits of sedimentary phosphate minerals were discovered in several places, such as southern Florida. Phosphorus had become geologically concentrated in sedimentary deposits in these places through the deposition of marine organisms over millions of years. These deposits are now being mined to supply mineral phosphorus used to manufacture agricultural fertilizer.

However, when these easily exploitable mineral deposits become exhausted, phosphorus may turn out to be a limiting factor for agricultural production in the not-so-distant future. About 50 million tonnes of phosphorus fertilizer are manufactured each year.

This is a highly significant input to the global phosphorus cycle, in view of the estimate that about million tonnes of phosphorus per year are absorbed naturally from soil by vegetation.

Where colonial seabirds are abundant, their excrement guano can be mined as a source of phosphorus-rich fertilizer. This is a view of a large colony of fish-eating guanay cormorants Phalacrocorax bougancillii near Paracas off the coast of Peru. The dried guano is periodically scraped from the rocks and used for agricultural purposes. Enviromental Issues 5.

Too Much of a Good Thing — Pollution by Nutrients Nutrients are essential to the healthy metabolism of organisms and to the proper functioning of ecosystems. Often, an increase in the supply of certain nutrients will enhance the productivity of wild and cultivated plants — this is the principle behind the use of fertilizer in agriculture. However, there are also cases in which an excessive supply of nutrients has caused important environmental problems. However, the use of agricultural fertilizer can result in concentrations of NO 3 — in drinking water that are high enough to be toxic to humans, especially to infants see Chapter Yet gaseous NO and N 2 O are air pollutants if they occur in high concentrations, especially in sunny environments where they are involved in the photochemical production of toxic ozone see Chapter There are other examples of environmental problems caused by excessive nutrients.

For instance, CO 2 is one of the most important plant nutrients because carbon comprises about half of plant biomass. But this critical nutrient occurs in a relatively small atmospheric concentration — only about 0.

This well-documented change is contributing to global warming, an important environmental problem see Chapter Eutrophication, or an excessive productivity of waterbodies, is another environmental problem related to an excessive supply of nutrients. It is most often caused by an excess of PO 4 3— , usually because of sewage dumping or runoff from fertilized agricultural land see Chapter Highly eutrophic lakes are degraded ecologically and may no longer be useful as a source of drinking water or for recreation.

Clearly, these examples show that there is a fine balance between chemicals serving as beneficial nutrients, or as damaging pollutants. Sulphur is a key constituent of certain amino acids, proteins, and other biochemicals. Sulphur is abundant in some minerals and rocks and has a significant presence in soil, water, and the atmosphere. Atmospheric sulphur occurs in various compounds, some of which are important air pollutants see Chapter Sulphur dioxide SO 2 , a gas, is emitted by volcanic eruptions and is also released by coal-fired power plants and metal smelters.

SO 2 is toxic to many plants at concentrations lower than 1 ppm. In some places, such as the Sudbury area, important ecological damage has been caused by this gas Chapter In the atmosphere, SO 2 becomes oxidized to the anion negatively charged ion sulphate SO 4 2— , which occurs as tiny particulates or is dissolved in suspended droplets of moisture.

Hydrogen sulphide H 2 S , which has a smell of rotten eggs, is emitted naturally from volcanoes and deep-sea vents. It is also released from habitats where organic sulphur compounds are being decomposed under anaerobic conditions, and from oxygen-poor aquatic systems where SO 4 2— is being reduced to H 2 S. Dimethyl sulphide is another reduced-sulphur gas that is produced in the oceans and emitted to the atmosphere. In oxygen-rich environments, such as the atmosphere, H 2 S is oxidized to sulphate, as is dimethyl sulphide, but more slowly.

Most emissions of SO 2 to the atmosphere are associated with human activities, but almost all H 2 S emissions are natural. An important exception is the emission of H 2 S from sour-gas wells and processing facilities, for example, in Alberta.

Overall, the global emission of all sulphur-containing gases is equivalent to about million tonnes of sulphur per year. Sulphur occurs in rocks and soils in a variety of mineral forms, the most important of which are sulphides, which occur as compounds with metals. Iron sulphides such as FeS 2 , called pyrite when it occurs as cubic crystals are the most common sulphide minerals, but all of the heavy metals such as copper, lead, and nickel can exist in this mineral form.

Wherever metal sulphides become exposed to an oxygen-rich environment, the bacterium Thiobacillus thiooxidans oxidizes the mineral, generating sulphate as a product. This autotrophic bacterium uses energy from this chemical transformation to sustain its growth and reproduction. This kind of primary productivity is called chemosynthesis in parallel with the photosynthesis of plants. In places where large amounts of sulphide are oxidized, high levels of acidity are associated with the sulphate product, a phenomenon referred to as acid-mine drainage see Chapter Sulphur also occurs in a variety of organically bound forms in soil and water.

These compounds include proteins and other sulphur-containing substances in dead organic matter. Soil microorganisms oxidize organic sulphur to sulphate, an ion that plants can use in their nutrition. Plants satisfy their nutritional requirements for sulphur by assimilating its simple mineral compounds from the environment, mostly by absorbing sulphate dissolved in soil water, which is taken up by roots.

In environments where the atmosphere is contaminated by SO 2 , plants can also absorb this gas through their foliage. However, too much absorption can be toxic to plants — there is a fine line between SO 2 as a plant nutrient and as a poison. Human activities have greatly influenced certain fluxes of the sulphur cycle. Important environmental damage has been caused by SO 2 toxicity, acid rain, acid-mine drainage, and other sulphur-related problems.

However, sulphur is also an important mineral commodity, with many industrial uses in manufacturing and as an agricultural fertilizer.

Nutrients are chemicals that are essential for the metabolism of organisms and ecosystems. If they are insufficient in quantity, then ecological productivity is less than it potentially could be.

Nutrients can also be present in excess, in which case environmental damage may be caused by toxicity and other problems. Nutrients routinely cycle among inorganic and organic forms within ecosystems.

Key aspects of nutrient cycles are illustrated by the carbon, nitrogen, phosphorus, and sulphur cycles. Although nitrogen's lurking basically everywhere, it's not terribly abundant in the Earth's crust , and it's incredibly difficult for living things to capture atmospheric nitrogen and use it for their purposes.

Since nitrogen is a limited resource on this planet, a nitrogen atom doesn't spend much time doing nothing when it's in a form living things can use — scientists call this nitrogen "fixed.

This is the cycle of a nitrogen atom on Earth, and its journey starts either very quietly or with a humongous bang. Believe it or not, lightning and bacteria are primarily responsible for turning atmospheric nitrogen into nitrogen living things can use.

Atmospheric nitrogen N2 is very stable, so it takes an incredible amount of energy to convert it to a different form. If you've ever wondered why your outdoor plants seem happier after a rain than they do when you turn a sprinkler on them, there's a reason for that: Lightning electrifies atmospheric nitrogen N2 and water H2O to reconfigure them into ammonia NH3 and nitrates NO3.

This falls to the ground as rain, where plants slurp it up and use it for their biological processes. On the other end of the spectrum, the most common way nitrogen is made available to organisms is when atmospheric nitrogen is fixed by bacteria, some of which live free in the soil and others of which enjoy a symbiotic relationship with certain plant species. When the excess plant material is broken down, the decomposing bacteria can use up all the oxygen in the water causing dead zones.

Most bodies of water gradually become more productive over time through the slow, natural accumulation of nutrients in a process called eutrophication. Hypertrophication on the Potomac River : The bright green color of the water is the result of algae blooms in response to the addition of phosphorous based fertilizers.

The nitrogen cycle is the process by which nitrogen is converted from organic to inorganic forms; many steps are performed by microbes. The nitrogen cycle describes the conversion of nitrogen between different chemical forms. Complex species interactions allow organisms to convert nitrogen to usable forms and exchange it between themselves. Nitrogen is essential for the formation of amino acids and nucleotides. It is essential for all living things.

This can happen occasionally through a lightning strike, but the bulk of nitrogen fixation is done by free living or symbiotic bacteria. These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia. It is then further converted by the bacteria to make their own organic compounds. Some nitrogen fixing bacteria live in the root nodules of legumes where they produce ammonia in exchange for sugars.

The role of soil bacteria in the Nitrogen cycle : Nitrogen transitions between various biologically useful forms. It is usually performed by soil living bacteria, such as nitrobacter.

This is important because plants can assimilate nitrate into their tissues, and they rely on bacteria to convert it from ammonia to a usable form. Nitrification is performed mainly by the genus of bacteria, Nitrobacter.

Nitrification can also work on ammonium. It can either be cycled back into a plant usable form through nitrification or returned to the atmosphere through de-nitrification. De-Nitrification: Nitrogen in its nitrate form NO 3 — is converted back into atmospheric nitrogen gas N 2 by bacterial species such as Pseudomonas and Clostridium, usually in anaerobic conditions.

These bacteria use nitrate as an electron acceptor instead of oxygen during respiration. Many bacteria can reduce sulfur in small amounts, but some bacteria can reduce sulfur in large amounts, in essence, breathing sulfur. The sulfur cycle describes the movement of sulfur through the atmosphere, mineral forms, and through living things. Although sulfur is primarily found in sedimentary rocks or sea water, it is particularly important to living things because it is a component of many proteins.

Sulfur is released from geologic sources through the weathering of rocks. Once sulfur is exposed to the air, it combines with oxygen, and becomes sulfate SO 4. Plants and microbes assimilate sulfate and convert it into organic forms. As animals consume plants, the sulfur is moved through the food chain and released when organisms die and decompose.

Some bacteria — for example Proteus, Campylobacter, Pseudomonas and Salmonella — have the ability to reduce sulfur, but can also use oxygen and other terminal electron acceptors. Others, such as Desulfuromonas, use only sulfur. These bacteria get their energy by reducing elemental sulfur to hydrogen sulfide.

They may combine this reaction with the oxidation of acetate, succinate, or other organic compounds. The most well known sulfur reducing bacteria are those in the domain Archea, which are some of the oldest forms of life on Earth. They are often extremophiles, living in hot springs and thermal vents where other organisms cannot live.

Lots of bacteria reduce small amounts of sulfates to synthesize sulfur-containing cell components; this is known as assimilatory sulfate reduction. By contrast, the sulfate-reducing bacteria considered here reduce sulfate in large amounts to obtain energy and expel the resulting sulfide as waste. This process is known as dissimilatory sulfate reduction.

In a sense, they breathe sulfate. Sulfur metabolic pathways for bacteria have important medical implications. For example, Mycobacterium tuberculosis the bacteria causing tuberculosis and Mycobacterium leprae which causes leoprosy both utilize sulfur, so the sulfur pathway is a target of drug development to control these bacteria. Iron is an important limiting nutrient required for plants and animals; it cycles between living organisms and the geosphere.

Iron Fe follows a geochemical cycle like many other nutrients. Iron is typically released into the soil or into the ocean through the weathering of rocks or through volcanic eruptions. The Terrestrial Iron Cycle: In terrestrial ecosystems, plants first absorb iron through their roots from the soil. Iron is required to produce chlorophyl, and plants require sufficient iron to perform photosynthesis.

Animals acquire iron when they consume plants, and iron is utilized by vertebrates in hemoglobin, the oxygen-binding protein found in red blood cells. Animals lacking in iron often become anemic and cannot transmit adequate oxygen. Bacteria then release iron back into the soil when they decompose animal tissue. The Marine Iron Cycle: The oceanic iron cycle is similar to the terrestrial iron cycle, except that the primary producers that absorb iron are typically phytoplankton or cyanobacteria.

Iron is then assimilated by consumers when they eat the bacteria or plankton. He hypothesized that iron was the limiting nutrient in these areas. Scientists hoped that by adding iron to ocean ecosystems, plants might grown and sequester atmospheric CO2.