Gaseous carbon dioxide CO 2 is the most abundant form of carbon in the atmosphere, where it occurs in a concentration of about ppm 0. Model of the Global Carbon Cycle. Based on data from Blasing , Solomon et al. Atmospheric CO 2 is a critical nutrient for photosynthetic organisms, such as plants and algae.
Plants absorb this gas through tiny pores called stomata in their foliage, fix it into simple sugars, and then use the fixed energy to support their respiration and to achieve growth and reproduction.
The biomass of autotrophs is available to be consumed by heterotrophs and passed through food webs. All organisms release CO 2 to the atmosphere as a waste product of their respiratory metabolism. CO 2 is also the most common emission associated with the decomposition of dead organic matter. However, if this process occurs under anaerobic conditions in which oxygen, O 2 , is not present , then both CO 2 and CH 4 are emitted.
Because anaerobic decomposition is relatively inefficient, dead organic matter often accumulates in wetlands such as swamps and bogs, eventually forming peat. Under suitable geological conditions of deep burial, high pressure and temperature, and a lack of oxygen, peat and other organic materials may be slowly transformed into carbon-rich fossil fuels such as coal, petroleum, and natural gas see Chapter Atmospheric CO 2 also dissolves into oceanic water, forming the bicarbonate ion HCO 3 — , which can be taken up and fixed by photosynthetic algae and bacteria, which are the base of the marine food web.
Various marine organisms also use oceanic CO 2 and HCO 3 — to manufacture their shells of calcium carbonate CaCO 3 , an insoluble mineral that slowly accumulates in sediment and may eventually lithify into limestone also CaCO 3. Over almost all of geological time, the amount of CO 2 absorbed by the global biota from the atmosphere was similar to that released through respiration and decomposition. Consequently, the cycling of this nutrient can be viewed as a steady-state system.
In modern times, however, anthropogenic emissions have changed the atmospheric carbon balance. Global emissions of CO 2 and CH 4 are now larger than the uptake of these gases, an imbalance that has resulted in increasing concentrations in the atmosphere. This phenomenon appears to be intensifying the greenhouse effect of Earth and resulting in global warming see Chapter Nitrogen is another important nutrient for organisms, being an integral component of many biochemicals, including amino acids, proteins, and nucleic acids.
Like the carbon cycle, that of nitrogen has an important atmospheric phase. However, unlike carbon, nitrogen is not a significant constituent of rocks and minerals. Consequently, the atmospheric reservoir plays a paramount role in the cycling of nitrogen Figure 5. Model of the Global Nitrogen Cycle. Nitrogen occurs in three main compartments: the atmosphere, terrestrial organic material, and oceanic organic material. Based on data from Hutzinger and Freedman These trace gases typically occur in atmospheric concentrations much less than 1 ppm, although there may be larger amounts close to sources of anthropogenic emissions see Chapter Nitrogen occurs in many additional forms in terrestrial and aquatic environments.
These chemicals range in character from simple amino acids, through proteins and nucleic acids, to large and complex molecules that are components of humified organic matter. Nitrogen in ecosystems also occurs in a small number of inorganic compounds, the most important of which are N 2 and NH 3 gases and the ions nitrate, nitrite NO 2 — , and ammonium.
The nitrogen cycle involves the transformation and cycling of the various organic and inorganic forms of nitrogen within ecosystems. Because the two nitrogen atoms in dinitrogen gas are held together by a strong triple bond, N 2 is a highly unreactive compound.
For this reason N 2 can be directly used by only a few specialized organisms, even though it is extremely abundant in the environment. These nitrogen-fixing species, all of which are microorganisms, have the ability to metabolize N 2 into NH 3 gas, which can then be used for their nutrition. More importantly, the NH 3 also becomes indirectly available to the great majority of autotrophic plants and microorganisms that cannot fix N 2 themselves. Biological nitrogen fixation is a critical process — most ecosystems depend on it to provide the nitrogen that sustains their primary productivity.
In fact, because nitrogen is not an important constituent of rocks and soil minerals, N 2 fixation is ultimately responsible for almost all of the organic nitrogen in the biomass of organisms and ecosystems throughout the biosphere. The only other significant sources of fixed nitrogen for ecosystems are the atmospheric deposition of nitrate and ammonium in precipitation and dustfall, and the uptake of NO and NO 2 gases by plants.
However, these are generally minor sources in comparison with biological N 2 fixation. The best known of the N 2 -fixing microorganisms are bacteria called Rhizobium, which live in specialized nodules on the roots of leguminous plants, such as peas and beans. Some non-legumes, such as alders, also live in a beneficial symbiosis a mutualism; see Chapter 9 with N 2 -fixing microorganisms.
So do most lichens, which are a mutualism between a fungus and an alga. Many other N 2 -fixing microbes are free-living in soil or water, such as cyanobacteria blue-green bacteria. Non-biological nitrogen fixation also occurs, for instance during a lightning event when atmospheric N 2 combines with O 2 under conditions of great heat and pressure. Humans can also cause N 2 to be fixed. For example, nitrogen fertilizer is manufactured by combining N 2 with hydrogen gas H 2 , which is manufactured from CH 4 , a fossil fuel in the presence of iron catalysts to produce NH 3.
In addition, NO gas is formed in the internal combustion engines of vehicles, where N 2 combines with O 2 under conditions of high pressure and temperature. Large amounts of NO are emitted to the atmosphere in vehicle exhaust, contributing to air pollution Chapter This is a globally important component of the modern nitrogen cycle and is comparable in magnitude with non-human N 2 fixation about million tonnes per year. Most species in the pea family Fabaceae , such as these soybeans, develop a mutualism with Rhizobium bacteria.
The Rhizobium live in nodules on the roots and fix nitrogen gas N 2 into ammonia NH 3 , which the plant can use as a nutrient. Source: D. After an organism dies, its organically bound nitrogen must be converted to inorganic forms; otherwise, the recycling of its fixed nitrogen would not be possible Figure 5. As such, ammonification is a component of the complex process of decay, but one that is specific to the nitrogen cycle.
Ammonification is carried out by a variety of microorganisms. The resulting ammonium is a suitable source of nutrition for many species of plants, particularly those that live in environments with acidic soil.
Nitrification is the process by which nitrate is synthesized from ammonium. Once the nitrite is formed, it is rapidly oxidized to nitrate by Nitrobacter bacteria. Because Nitrosomonas and Nitrobacter are sensitive to acidity, nitrification does not occur in acidic soil or water. This is why plants growing in acidic habitats must be able to use ammonium as their source of nitrogen. Important Transformations of Fixed Nitrogen in Ecosystems.
The diagram indicates the key transformations of nitrogen among its most important inorganic forms in soil and aquatic ecosystems. Source: Modified from Freedman In denitrification, also performed by a wide variety of microbial species, nitrate is converted to either of the gases N 2 O or N 2 , which are released to the atmosphere. Denitrification occurs under anaerobic conditions, and its rate is greatest when there is a large concentration of nitrate, for example in fertilized agricultural land that is temporarily flooded.
In some respects, denitrification can be considered a counter-balancing process to nitrogen fixation. In fact, global rates of nitrogen fixation and denitrification are in a rough balance, so the total amount of fixed nitrogen in the biosphere is not changing much over time. Phosphorus is a key constituent of many biochemicals, including fats and lipids, nucleic acids such as the genetic materials DNA and RNA, and energy-carrying molecules such as ATP.
However, phosphorus is required by organisms in much smaller quantities than nitrogen or carbon. Nevertheless, phosphorus is often in short supply and so it is a critical nutrient in many ecosystems, particularly in freshwater and agriculture. In contrast to the carbon and nitrogen cycles, that of phosphorus does not have a significant atmospheric phase.
Although phosphorus compounds do occur in the atmosphere, as trace quantities in particulates, the resulting inputs to ecosystems are small compared with the amounts available from soil minerals or from the addition of fertilizer to agricultural land. Phosphorus tends to move from the terrestrial landscape into surface waters and then eventually to the oceans, where it deposits to sediment that acts as a long-term sink.
Although some phosphorus minerals in oceanic sediment are eventually recycled to the land by geological uplift associated with mountain building, this is an extremely slow process and is not meaningful in ecological time scales.
Therefore, aspects of the global phosphorus cycle represent a flow-through system. 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. Gas exchange through the atmosphere and water is one way that the carbon cycle connects all living organisms on Earth.
The movement of carbon through the land, water, and air is complex and, in many cases, it occurs much more slowly than the biological carbon cycle. As stated, the atmosphere, a major reservoir of carbon in the form of carbon dioxide, is essential to the process of photosynthesis. The level of carbon dioxide in the atmosphere is greatly influenced by the reservoir of carbon in the oceans.
The exchange of carbon between the atmosphere and water reservoirs influences how much carbon is found in each location; each affects the other reciprocally. Carbon dioxide CO 2 from the atmosphere dissolves in water, combining with water molecules to form carbonic acid.
It then ionizes to carbonate and bicarbonate ions. Formation of bicarbonate : Carbon dioxide reacts with water to form bicarbonate and carbonate ions. More than 90 percent of the carbon in the ocean is found as bicarbonate ions.
Some of these ions combine with seawater calcium to form calcium carbonate CaCO 3 , a major component of marine organism shells. These organisms eventually form sediments on the ocean floor. Over geologic time, the calcium carbonate forms limestone, which comprises the largest carbon reservoir on earth.
On land, carbon is stored in soil as a result of the decomposition of living organisms or the weathering of terrestrial rock and minerals.
This carbon can be leached into the water reservoirs by surface runoff. Deeper underground, on land and at sea, are fossil fuels: the anaerobically-decomposed remains of plants that take millions of years to form. Fossil fuels are considered a non-renewable resource because their use far exceeds their rate of formation.
A non-renewable resource is either regenerated very slowly or not at all. Another way for carbon to enter the atmosphere is from land by the eruption of volcanoes and other geothermal systems. Carbon sediments from the ocean floor are taken deep within the earth by the process of subduction: the movement of one tectonic plate beneath another.
Carbon is released as carbon dioxide when a volcano erupts or from volcanic hydrothermal vents. Carbon dioxide is also added to the atmosphere by the breeding and raising of livestock. This is another example of how human activity indirectly affects biogeochemical cycles in a significant way. Although much of the debate about the future effects of increasing atmospheric carbon on climate change focuses on fossils fuels, scientists take natural processes, such as volcanoes and respiration, into account as they model and predict the future impact of this increase.
Nitrogen, the most abundant gas in the atmosphore, is cycled through the biosphere via the multi-step process of nitrogen fixation, which is carried out by bacteria.
Getting nitrogen into the living world is difficult. Plants and phytoplankton are not equipped to incorporate nitrogen from the atmosphere which exists as tightly-bonded, triple-covalent N 2 , 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 N 2.
Cyanobacteria live in most aquatic ecosystems where sunlight is present; they play a key role in nitrogen fixation. Rhizobium bacteria live symbiotically in the root nodules of legumes such as peas, beans, and peanuts , providing 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 as 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. This process occurs in three steps in terrestrial systems: ammonification, nitrification, and denitrification. Third, 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.
Nitrogen fixation : Nitrogen enters the living world from the atmosphere via nitrogen-fixing bacteria. This nitrogen and nitrogenous waste from animals is then processed back into gaseous nitrogen by soil bacteria, which also supply terrestrial food webs with the organic nitrogen they need. Human activity can release nitrogen into the environment by two primary means: the combustion of fossil fuels, which releases different nitrogen oxides, and 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 similar process occurs in the marine nitrogen cycle, where the ammonification, nitrification, and denitrification processes are performed by marine bacteria.
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 and should be included in any study of the global nitrogen cycle.
Phosphorus is an essential element of living things, but, in excess, it can cause damage to ecosystems. Phosphorus is an essential nutrient for living processes. It is a major component of nucleic acid, both DNA and RNA; of phospholipids, the major component of cell membranes; and, as calcium phosphate, makes up the supportive components of our bones. Phosphorus is often the limiting nutrient necessary for growth in aquatic ecosystems. In addition to phosphate runoff as a result of human activity, natural surface 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. 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. Phosphorus is also reciprocally exchanged between phosphate dissolved in the ocean and marine ecosystems. The movement of phosphate from the ocean to the land and through the soil is extremely slow, with the average phosphate ion having an oceanic residence time between 20, and , years.
Excess phosphorus and nitrogen that enters these ecosystems from fertilizer runoff and from sewage causes excessive growth of microorganisms and depletes the dissolved oxygen, which leads to the death of many ecosystem fauna, such as shellfish and finfish. This process is responsible for dead zones in lakes and at the mouths of many major rivers. Dead zones : Dead zones occur when phosphorus and nitrogen from fertilizers cause excessive growth of microorganisms, which depletes oxygen, killing flora and fauna.
Worldwide, large dead zones are 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; more than of these zones were present as of 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 8, 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, which was one of the first ecosystems to have identified dead zones.
Sulfur is deposited on land as precipitation, fallout, and rock weathering, and reintroduced when organisms decompose. Sulfur 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. Sulfur cycles exist between the oceans, land, and atmosphere.
Sulfur cycle : Sulfur dioxide from the atmosphere becomes available to terrestrial and marine ecosystems when it is dissolved in precipitation as weak sulfuric acid or when it falls directly to the earth as fallout. Weathering of rocks also makes sulfates available to terrestrial ecosystems. Decomposition of living organisms returns sulfates to the ocean, soil, and atmosphere. On land, sulfur is deposited in four major ways: precipitation, direct fallout from the atmosphere, rock weathering, and decomposition of organic materials.
Atmospheric sulfur is found in the form of sulfur dioxide SO 2. As rain falls through the atmosphere, sulfur is dissolved in the form of weak sulfuric acid H 2 SO 4 , creating acid rain. Sulfur can also fall directly from the atmosphere in a process called fallout. The weathering of sulfur-containing rocks also releases sulfur into the soil.
These rocks originate from ocean sediments that are moved to land by the geologic uplift. Upon the death and decomposition of these organisms, sulfur is released back into the atmosphere as hydrogen sulfide H 2 S gas. Sulfur may also enter the atmosphere through geothermal vents. Sulfur vents : At this sulfur vent in Lassen Volcanic National Park in northeastern California, the yellowish sulfur deposits are visible near the mouth of the vent.
Sulfur enters the ocean via runoff from land, fallout, and underwater geothermal vents. Some marine ecosystems rely on chemoautotrophs, using sulfur as a biological energy source. This sulfur then supports marine ecosystems in the form of sulfates.
Human activities have played a major role in altering the balance of the global sulfur cycle. The burning of large quantities of fossil fuels, especially from coal, releases large amounts of hydrogen sulfide gas into the atmosphere, creating acid rain.
Acid rain is corrosive rain that causes damage to aquatic ecosystems and the natural environment by lowering the pH of lakes, which kills many of the resident fauna; it also affects the human-made environment through the chemical degradation of buildings. For example, many marble monuments, such as the Lincoln Memorial in Washington, DC, 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. Privacy Policy.
Skip to main content. Search for:. Biogeochemical Cycles. Biogeochemical Cycles The elemental components of organic matter are cycled through the biosphere in an interconnected process called the biogeochemical cycle. Learning Objectives Summarize the concept of biogeochemical cycles.
Materials are recycled via erosion, weathering, water drainage, and the movement of tectonic plates. Water is essential to all living processes, while carbon is found in all organic macromolecules. Nitrogen and phosphorus are major components of nucleic acids and play major roles in agriculture. Sulfur plays a role in the three-dimensional folding of proteins and is released into the atmosphere by the burning of fossil fuels.
Key Terms hydrosphere : combined mass of water found on, under, and over the surface of a planet biogeochemical cycle : cycling of mineral nutrients through ecosystems and through the non-living world. The Water Hydrologic Cycle Water has a large effect on climate, ecosystems, and living organisms and is continuously cycled through the environment. Learning Objectives Explain the path of the hydrologic cycle and its importance.
Key Takeaways Key Points Water cycling affects the climate, transports minerals, purifies water, and replenishes the land with fresh water. Water with a longer residence time, such as water in oceans and glaciers, is not available for short-term cycling, which occurs via evaporation.
Surface water evaporates water to water vapor or sublimates ice to water vapor , which deposits large amounts of water vapor into the atmosphere.
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