Hydrogen sulfide is the chemical compound with the formula H2S. It is a colorless chalcogen hydride gas with the characteristic foul odor of rotten eggs, it is poisonous and flammable. Hydrogen sulfide is produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers. H2S occurs in volcanic gases, natural gas, in some sources of well water; the human body uses it as a signaling molecule. Swedish chemist Carl Wilhelm Scheele is credited with having discovered hydrogen sulfide in 1777; the British English spelling of this compound is hydrogen sulphide, but this spelling is not recommended by the International Union of Pure and Applied Chemistry or the Royal Society of Chemistry. Hydrogen sulfide is denser than air. Hydrogen sulfide burns in oxygen with a blue flame to form sulfur water. In general, hydrogen sulfide acts as a reducing agent in the presence of base, which forms SH−. At high temperatures or in the presence of catalysts, sulfur dioxide reacts with hydrogen sulfide to form elemental sulfur and water.
This reaction is exploited in the Claus process, an important industrial method to dispose of hydrogen sulfide. Hydrogen sulfide is soluble in water and acts as a weak acid, giving the hydrosulfide ion HS−. Hydrogen sulfide and its solutions are colorless; when exposed to air, it oxidizes to form elemental sulfur, not soluble in water. The sulfide anion S2− is not formed in aqueous solution. Hydrogen sulfide reacts with metal ions to form metal sulfides, which are insoluble dark colored solids. Lead acetate paper is used to detect hydrogen sulfide because it converts to lead sulfide, black. Treating metal sulfides with strong acid liberates hydrogen sulfide. At pressures above 90 GPa, hydrogen sulfide becomes a metallic conductor of electricity; when cooled below a critical temperature this high-pressure phase exhibits superconductivity. The critical temperature increases with pressure. If hydrogen sulfide is pressurized at higher temperatures cooled, the critical temperature reaches 203 K, the highest accepted superconducting critical temperature as of 2015.
By substituting a small part of sulfur with phosphorus and using higher pressures, it has been predicted that it may be possible to raise the critical temperature to above 0 °C and achieve room-temperature superconductivity. Hydrogen sulfide is most obtained by its separation from sour gas, natural gas with high content of H2S, it can be produced by treating hydrogen with molten elemental sulfur at about 450 °C. Hydrocarbons can serve as a source of hydrogen in this process. Sulfate-reducing bacteria generate usable energy under low-oxygen conditions by using sulfates to oxidize organic compounds or hydrogen. A standard lab preparation is to treat ferrous sulfide with a strong acid in a Kipp generator: FeS + 2 HCl → FeCl2 + H2SFor use in qualitative inorganic analysis, thioacetamide is used to generate H2S: CH3CNH2 + H2O → CH3CNH2 + H2SMany metal and nonmetal sulfides, e.g. aluminium sulfide, phosphorus pentasulfide, silicon disulfide liberate hydrogen sulfide upon exposure to water: 6 H2O + Al2S3 → 3 H2S + 2 Al3This gas is produced by heating sulfur with solid organic compounds and by reducing sulfurated organic compounds with hydrogen.
Water heaters can aid the conversion of sulfate in water to hydrogen sulfide gas. This is due to providing a warm environment sustainable for sulfur bacteria and maintaining the reaction which interacts between sulfate in the water and the water heater anode, made from magnesium metal. Hydrogen sulfide can be generated in cells via non enzymatic pathway. H2S in the body acts as a gaseous signaling molecule, known to inhibit Complex IV of the mitochondrial electron transport chain which reduces ATP generation and biochemical activity within cells. Three enzymes are known to synthesize H2S: cystathionine γ-lyase, cystathionine β-synthetase and 3-mercaptopyruvate sulfurtransferase; these enzymes have been identified in a breadth of biological cells and tissues, their activity has been observed to be induced by a number of disease states. It is becoming clear that H2S is an important mediator of a wide range of cell functions in health and in disease. CBS and CSE are the main proponents of H2S biogenesis.
These enzymes are characterized by the transfer of a sulfur atom from methionine to serine to form a cysteine molecule. 3-MST contributes to hydrogen sulfide production by way of the cysteine catabolic pathway. Dietary amino acids, such as methionine and cysteine serve as the primary substrates for the transulfuration pathways and in the production of hydrogen sulfide. Hydrogen sulfide can be synthesized by non-enzymatic pathway, derived from proteins such as ferredoxins and Rieske proteins. H2S has been shown to be involved in physiological processes like vasoconstriction in animals, increasing seed germination and stress responses in plants. Hydrogen sulfide signaling is innately intertwined with physiological processes that are known to be moderated by reactive oxygen species and reactive nitrogen species. H2S has been shown to interact with NO resulting in severa
The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat and other necessities available in the environment. In population biology, carrying capacity is defined as the environment's maximal load, different from the concept of population equilibrium, its effect on population dynamics may be approximated in a logistic model, although this simplification ignores the possibility of overshoot which real systems may exhibit. Carrying capacity was used to determine the number of animals that could graze on a segment of land without destroying it; the idea was expanded to more complex populations, like humans. For the human population, more complex variables such as sanitation and medical care are sometimes considered as part of the necessary establishment; as population density increases, birth rate increases and death rate decreases. The difference between the birth rate and the death rate is the "natural increase".
The carrying capacity could support a positive natural increase or could require a negative natural increase. Thus, the carrying capacity is the number of individuals an environment can support without significant negative impacts to the given organism and its environment. Below carrying capacity, populations increase, while above, they decrease. A factor that keeps population size at equilibrium is known as a regulating factor. Population size decreases above carrying capacity due to a range of factors depending on the species concerned, but can include insufficient space, food supply, or sunlight; the carrying capacity of an environment may vary for different species and may change over time due to a variety of factors including: food availability, water supply, environmental conditions and living space. The origins of the term "carrying capacity" are uncertain, with researchers variously stating that it was used "in the context of international shipping" or that it was first used during 19th-century laboratory experiments with micro-organisms.
A recent review finds the first use of the term in an 1845 report by the US Secretary of State to the US Senate. Several estimates of the carrying capacity have been made with a wide range of population numbers. A 2001 UN report said that two-thirds of the estimates fall in the range of 4 billion to 16 billion with unspecified standard errors, with a median of about 10 billion. More recent estimates are much lower if non-renewable resource depletion and increased consumption are considered. Changes in habitat quality or human behavior at any time might reduce carrying capacity. Research conducted by the Australian National University and Stockholm Resilience Centre mentioned that there is a risk for the planet to cross the planetary thresholds and reach “Hothouse Earth” conditions.. In this case, the Earth would see its carrying capacity reduced. In the view of Paul and Anne Ehrlich, "for earth as a whole, human beings are far above carrying capacity today."The application of the concept of carrying capacity for the human population has been criticized for not capturing the multi-layered processes between humans and the environment, which have a nature of fluidity and non-equilibrium, for sometimes being employed in a blame-the-victim framework.
Supporters of the concept argue that the idea of a limited carrying capacity is just as valid applied to humans as when applied to any other species. Animal population size, living standards, resource depletion vary, but the concept of carrying capacity still applies; the number of people is not the only factor in the carrying capacity of Earth. Waste and over-consumption by wealthy and near-wealthy people and nations, are putting significant strain on the environment together with human overpopulation. Population and consumption together appear to be at the core of many human problems; some of these issues have been studied by computer simulation models such as World3. When scientists talk of global change today, they are referring to human-caused changes in the environment of sufficient magnitude to reduce the carrying capacity of much of Earth to support organisms Homo sapiens; some aspects of a system's carrying capacity may involve matters such as available supplies of food, raw materials, and/or other similar resources.
In addition, there are other factors that govern carrying capacity which may be less instinctive or less intuitive in nature, such as ever-increasing and/or ever-accumulating levels of wastes, and/or eradication of essential components of any complex functioning system. Eradication of, for example, large or critical portions of any complex system can interrupt essential processes and dynamics in ways that induce systems failures or unexpected collapse. Thus, on a global scale and similar resources may affect planetary carrying capacity to some extent so long as Earth's human passengers do not dismantle, eradicate, or otherwise destroy critical biospheric life-support capacities for essential processes of self-maintenance, self-perpetuation, self-repair. Thus, car
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can be released to fuel the organisms' activities. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water – hence the name photosynthesis, from the Greek φῶς, phōs, "light", σύνθεσις, synthesis, "putting together". In most cases, oxygen is released as a waste product. Most plants, most algae, cyanobacteria perform photosynthesis. Photosynthesis is responsible for producing and maintaining the oxygen content of the Earth's atmosphere, supplies all of the organic compounds and most of the energy necessary for life on Earth. Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centres that contain green chlorophyll pigments. In plants, these proteins are held inside organelles called chloroplasts, which are most abundant in leaf cells, while in bacteria they are embedded in the plasma membrane.
In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. The hydrogen freed by the splitting of water is used in the creation of two further compounds that serve as short-term stores of energy, enabling its transfer to drive other reactions: these compounds are reduced nicotinamide adenine dinucleotide phosphate and adenosine triphosphate, the "energy currency" of cells. In plants and cyanobacteria, long-term energy storage in the form of sugars is produced by a subsequent sequence of light-independent reactions called the Calvin cycle. In the Calvin cycle, atmospheric carbon dioxide is incorporated into existing organic carbon compounds, such as ribulose bisphosphate. Using the ATP and NADPH produced by the light-dependent reactions, the resulting compounds are reduced and removed to form further carbohydrates, such as glucose; the first photosynthetic organisms evolved early in the evolutionary history of life and most used reducing agents such as hydrogen or hydrogen sulfide, rather than water, as sources of electrons.
Cyanobacteria appeared later. Today, the average rate of energy capture by photosynthesis globally is 130 terawatts, about eight times the current power consumption of human civilization. Photosynthetic organisms convert around 100–115 billion tonnes of carbon into biomass per year. Photosynthetic organisms are photoautotrophs, which means that they are able to synthesize food directly from carbon dioxide and water using energy from light. However, not all organisms use carbon dioxide as a source of carbon atoms to carry out photosynthesis. In plants and cyanobacteria, photosynthesis releases oxygen; this is called oxygenic photosynthesis and is by far the most common type of photosynthesis used by living organisms. Although there are some differences between oxygenic photosynthesis in plants and cyanobacteria, the overall process is quite similar in these organisms. There are many varieties of anoxygenic photosynthesis, used by certain types of bacteria, which consume carbon dioxide but do not release oxygen.
Carbon dioxide is converted into sugars in a process called carbon fixation. Carbon fixation is an endothermic redox reaction. In general outline, photosynthesis is the opposite of cellular respiration: while photosynthesis is a process of reduction of carbon dioxide to carbohydrate, cellular respiration is the oxidation of carbohydrate or other nutrients to carbon dioxide. Nutrients used in cellular respiration include amino acids and fatty acids; these nutrients are oxidized to produce carbon dioxide and water, to release chemical energy to drive the organism's metabolism. Photosynthesis and cellular respiration are distinct processes, as they take place through different sequences of chemical reactions and in different cellular compartments; the general equation for photosynthesis as first proposed by Cornelis van Niel is therefore: CO2carbondioxide + 2H2Aelectron donor + photonslight energy → carbohydrate + 2Aoxidizedelectrondonor + H2OwaterSince water is used as the electron donor in oxygenic photosynthesis, the equation for this process is: CO2carbondioxide + 2H2Owater + photonslight energy → carbohydrate + O2oxygen + H2OwaterThis equation emphasizes that water is both a reactant in the light-dependent reaction and a product of the light-independent reaction, but canceling n water molecules from each side gives the net equation: CO2carbondioxide + H2O water + photonslight energy → carbohydrate + O2 oxygen Other processes substitute other compounds for water in the electron-supply role.
In the first stage, light-dependent reactions or light reactions capture the energy of light and use it to make the energy-storage molecules ATP and NADPH. During the second stage, the light-independent reactions use these products to capture and reduce carbon dioxid
An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy is incorporated into plant tissue. By feeding on plants and on one-another, animals play an important role in the movement of matter and energy through the system, they influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be used by plants and other microbes. Ecosystems are controlled by internal factors. External factors such as climate, the parent material which forms the soil and topography, control the overall structure of an ecosystem, but are not themselves influenced by the ecosystem. Ecosystems are dynamic entities—they are subject to periodic disturbances and are in the process of recovering from some past disturbance.
Ecosystems in similar environments that are located in different parts of the world can end up doing things differently because they have different pools of species present. Internal factors not only control ecosystem processes but are controlled by them and are subject to feedback loops. Resource inputs are controlled by external processes like climate and parent material. Resource availability within the ecosystem is controlled by internal factors like decomposition, root competition or shading. Although humans operate within ecosystems, their cumulative effects are large enough to influence external factors like climate. Biodiversity affects ecosystem functioning, as do the processes of disturbance and succession. Ecosystems provide a variety of services upon which people depend; the term ecosystem was first used in 1935 in a publication by British ecologist Arthur Tansley. Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment.
He refined the term, describing it as "The whole system... including not only the organism-complex, but the whole complex of physical factors forming what we call the environment". Tansley regarded ecosystems not as natural units, but as "mental isolates". Tansley defined the spatial extent of ecosystems using the term ecotope. G. Evelyn Hutchinson, a limnologist, a contemporary of Tansley's, combined Charles Elton's ideas about trophic ecology with those of Russian geochemist Vladimir Vernadsky; as a result, he suggested. This would, in turn, limit the abundance of animals. Raymond Lindeman took these ideas further to suggest that the flow of energy through a lake was the primary driver of the ecosystem. Hutchinson's students, brothers Howard T. Odum and Eugene P. Odum, further developed a "systems approach" to the study of ecosystems; this allowed them to study the flow of material through ecological systems. Ecosystems are controlled both by internal factors. External factors called state factors, control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem.
The most important of these is climate. Climate determines the biome. Rainfall patterns and seasonal temperatures influence photosynthesis and thereby determine the amount of water and energy available to the ecosystem. Parent material determines the nature of the soil in an ecosystem, influences the supply of mineral nutrients. Topography controls ecosystem processes by affecting things like microclimate, soil development and the movement of water through a system. For example, ecosystems can be quite different if situated in a small depression on the landscape, versus one present on an adjacent steep hillside. Other external factors that play an important role in ecosystem functioning include time and potential biota; the set of organisms that can be present in an area can significantly affect ecosystems. Ecosystems in similar environments that are located in different parts of the world can end up doing things differently because they have different pools of species present; the introduction of non-native species can cause substantial shifts in ecosystem function.
Unlike external factors, internal factors in ecosystems not only control ecosystem processes but are controlled by them. They are subject to feedback loops. While the resource inputs are controlled by external processes like climate and parent material, the availability of these resources within the ecosystem is controlled by internal factors like decomposition, root competition or shading. Other factors like disturbance, succession or the types of species present are internal factors. Primary production is the production of organic matter from inorganic carbon sources; this occurs through photosynthesis. The energy incorporated through this process supports life on earth, while the carbon makes up much of the organic matter in living and dead biomass, soil carbon and fossil fuels, it drives the carbon cycle, which influences global climate via the greenhouse effect. Through the process of photosynthesis, plants capture energy from light and use it to combine carbon dioxide and water to produce carbohydrates and oxygen.
The photosynthesis carried out by all the plants in an ecosystem is called the gross primary production. About half of the GPP is consumed in plant respiration; the remainder, that portion of GPP, not used up by respirati
Thiosulfate is an oxyanion of sulfur. The prefix thio- indicates that the thiosulfate ion is a sulfate ion with one oxygen replaced by sulfur. Thiosulfate has a tetrahedral molecular shape with C3v symmetry. Thiosulfate occurs and is produced by certain biochemical processes, it dechlorinates water and is notable for its use to halt bleaching in the paper-making industry. Thiosulfate is useful in smelting silver ore, in producing leather goods, to set dyes in textiles. Sodium thiosulfate called hypo, was used in photography to fix black and white negatives and prints after the developing stage; some bacteria can metabolise thiosulfates. Thiosulfate is produced by the reaction of sulfite ion with elemental sulfur, by incomplete oxidation of sulfides, sodium thiosulfate can be formed by disproportionation of Sulfur dissolving in sodium hydroxide. Thiosulfates are stable only in neutral or alkaline solutions, but not in acidic solutions, due to disproportionation to sulfite and sulfur, the sulfite being dehydrated to sulfur dioxide: S2O2−3 + 2 H+ → SO2 + S + H2O This reaction may be used to generate an aqueous suspension of sulfur and demonstrate the Rayleigh scattering of light in physics.
If white light is shone from below, blue light is seen from sideways and orange from above, due to the same mechanisms that color the sky at mid-day and dusk.. Thiosulfates react with halogens differently, which can be attributed to the decrease of oxidizing power down the halogen group: 2 S2O2−3 + I2 → S4O2−6 + 2 I− S2O2−3 + 4 Br2 + 5 H2O → 2 SO2−4 + 8 Br− + 10 H+ S2O2−3 + 4 Cl2 + 5 H2O → 2 SO2−4 + 8 Cl− + 10 H+ In acidic conditions, thiosulfate causes rapid corrosion of metals. Addition of molybdenum to stainless steel is needed to improve its resistance to pitting. In alkaline aqueous conditions and medium temperature, carbon steel and stainless steel are not attacked at high concentration of base, thiosulfate and in presence of fluoride ion; the natural occurrence of the thiosulfate group is restricted to a rare mineral sidpietersite, Pb4O22, as the presence of this anion in the mineral bazhenovite was disputed. Thiosulfate extensively forms complexes with transition metals hence a common use is dissolving silver halides in film photography developing.
Thiosulfate is used to extract or leach gold and silver from their ores as a less toxic alternative to cyanide. Thiosulfate is an acceptable common name; the external sulfur has an oxidation state of –2 while the central sulfur atom has an oxidation number of +6. The enzyme rhodanase catalyzes the detoxification of cyanide by thiosulfate: CN− + S2O2−3 → SCN− + SO2−3. Sodium thiosulfate has been considered as an empirical treatment for cyanide poisoning, along with hydroxocobalamin, it is most effective in a pre-hospital setting, since immediate administration by emergency personnel is necessary to reverse rapid intracellular hypoxia caused by the inhibition of cellular respiration, at complex IV. It activates TST in mitochondria. TST is associated with protection against obesity and type II diabetes. Tetrathionate Thiosulfuric acid Thiosulfate ion General Chemistry Online, Frostburg State University
An autotroph or primary producer, is an organism that produces complex organic compounds from simple substances present in its surroundings using energy from light or inorganic chemical reactions. They are the producers such as plants on land or algae in water, they do not need a living source of energy or organic carbon. Autotrophs can reduce carbon dioxide to make organic compounds for biosynthesis and create a store of chemical energy. Most autotrophs use water as the reducing agent, but some can use other hydrogen compounds such as hydrogen sulfide; some autotrophs, such as green plants and algae, are phototrophs, meaning that they convert electromagnetic energy from sunlight into chemical energy in the form of reduced carbon. Autotrophs can be chemoautotrophs. Phototrophs use light as an energy source, while chemotrophs use electron donors as a source of energy, whether from organic or inorganic sources; such chemotrophs are lithotrophs. Lithotrophs use inorganic compounds, such as hydrogen sulfide, elemental sulfur and ferrous iron, as reducing agents for biosynthesis and chemical energy storage.
Photoautotrophs and lithoautotrophs use a portion of the ATP produced during photosynthesis or the oxidation of inorganic compounds to reduce NADP+ to NADPH to form organic compounds. The Greek term autotroph was coined by the German botanist Albert Bernhard Frank in 1892, it stems from the ancient Greek word τροφή, meaning "nourishment" or "food". Some organisms rely on organic compounds as a source of carbon, but are able to use light or inorganic compounds as a source of energy; such organisms are not defined rather as heterotrophic. An organism that obtains carbon from organic compounds but obtains energy from light is called a photoheterotroph, while an organism that obtains carbon from organic compounds but obtains energy from the oxidation of inorganic compounds is termed a chemoheterotroph, chemolithoheterotroph, or lithoheterotroph. Evidence suggests that some fungi may obtain energy from radiation; such radiotrophic fungi were found growing inside a reactor of the Chernobyl nuclear power plant.
Autotrophs are fundamental to the food chains of all ecosystems in the world. They take energy from the environment in the form of sunlight or inorganic chemicals and use it to create energy-rich molecules such as carbohydrates; this mechanism is called primary production. Other organisms, called heterotrophs, take in autotrophs as food to carry out functions necessary for their life. Thus, heterotrophs — all animals all fungi, as well as most bacteria and protozoa — depend on autotrophs, or primary producers, for the energy and raw materials they need. Heterotrophs obtain energy by breaking down organic molecules obtained in food. Carnivorous organisms rely on autotrophs indirectly, as the nutrients obtained from their heterotroph prey come from autotrophs they have consumed. Most ecosystems are supported by the autotrophic primary production of plants that capture photons released by the sun. Plants can only use a fraction of this energy for photosynthesis 1% is used by autotrophs; the process of photosynthesis splits a water molecule, releasing oxygen into the atmosphere, reducing carbon dioxide to release the hydrogen atoms that fuel the metabolic process of primary production.
Plants convert and store the energy of the photon into the chemical bonds of simple sugars during photosynthesis. These plant sugars are polymerized for storage as long-chain carbohydrates, including other sugars and cellulose; when autotrophs are eaten by heterotrophs, i.e. consumers such as animals, the carbohydrates and proteins contained in them become energy sources for the heterotrophs. Proteins can be made using nitrates and phosphates in the soil. Electrolithoautotroph Organotroph Electrotroph Primary nutritional groups Heterotrophic nutrition
Ecosystem ecology is the integrated study of living and non-living components of ecosystems and their interactions within an ecosystem framework. This science examines how ecosystems work and relates this to their components such as chemicals, soil and animals. Ecosystem ecology examines physical and biological structures and examines how these ecosystem characteristics interact with each other; this helps us understand how to maintain high quality water and economically viable commodity production. A major focus of ecosystem ecology is on functional processes, ecological mechanisms that maintain the structure and services produced by ecosystems; these include primary productivity and trophic interactions. Studies of ecosystem function have improved human understanding of sustainable production of forage, fiber and provision of water. Functional processes are mediated by regional-to-local level climate and management, thus ecosystem ecology provides a powerful framework for identifying ecological mechanisms that interact with global environmental problems global warming and degradation of surface water.
This example demonstrates several important aspects of ecosystems: Ecosystem boundaries are nebulous and may fluctuate in time Organisms within ecosystems are dependent on ecosystem level biological and physical processes Adjacent ecosystems interact and are interdependent for maintenance of community structure and functional processes that maintain productivity and biodiversityThese characteristics introduce practical problems into natural resource management. Who will manage which ecosystem? Will timber cutting in the forest degrade recreational fishing in the stream? These questions are difficult for land managers to address while the boundary between ecosystems remains unclear. We need better understanding of the interactions and interdependencies of these ecosystems and the processes that maintain them before we can begin to address these questions. Ecosystem ecology is an inherently interdisciplinary field of study. An individual ecosystem is composed of populations of organisms, interacting within communities, contributing to the cycling of nutrients and the flow of energy.
The ecosystem is the principal unit of study in ecosystem ecology. Population and physiological ecology provide many of the underlying biological mechanisms influencing ecosystems and the processes they maintain. Flowing of energy and cycling of matter at the ecosystem level are examined in ecosystem ecology, but, as a whole, this science is defined more by subject matter than by scale. Ecosystem ecology approaches organisms and abiotic pools of energy and nutrients as an integrated system which distinguishes it from associated sciences such as biogeochemistry. Biogeochemistry and hydrology focus on several fundamental ecosystem processes such as biologically mediated chemical cycling of nutrients and physical-biological cycling of water. Ecosystem ecology forms the mechanistic basis for regional or global processes encompassed by landscape-to-regional hydrology, global biogeochemistry, earth system science. Ecosystem ecology is philosophically and rooted in terrestrial ecology; the ecosystem concept has evolved during the last 100 years with important ideas developed by Frederic Clements, a botanist who argued for specific definitions of ecosystems and that physiological processes were responsible for their development and persistence.
Although most of Clements ecosystem definitions have been revised by Henry Gleason and Arthur Tansley, by contemporary ecologists, the idea that physiological processes are fundamental to ecosystem structure and function remains central to ecology. Work by Eugene Odum and Howard T. Odum quantified flows of energy and matter at the ecosystem level, thus documenting the general ideas proposed by Clements and his contemporary Charles Elton. In this model, energy flows through the whole system were dependent on biotic and abiotic interactions of each individual component. Work demonstrated that these interactions and flows applied to nutrient cycles, changed over the course of succession, held powerful controls over ecosystem productivity. Transfers of energy and nutrients are innate to ecological systems regardless of whether they are aquatic or terrestrial. Thus, ecosystem ecology has emerged from important biological studies of plants, terrestrial and marine ecosystems. Ecosystem services are ecologically mediated functional processes essential to sustaining healthy human societies.
Water provision and filtration, production of biomass in forestry and fisheries, removal of greenhouse gases such as carbon dioxide from the atmosphere are examples of ecosystem services essential to public health and economic opportunity. Nutrient cycling is a process fundamental to forest production. However, like most ecosystem processes, nutrient cycling is not an ecosystem characteristic which can be “dialed” to the most desirable level. Maximizing production in degraded systems is an overly simplistic solution to the complex problems of hunger and economic security. For instance, intensive fertilizer use in the midwestern United States has resulted in degraded fisheries in the Gulf of Mexico. Regrettably, a “Green Revolution” of intensive chemical fertilization has been recommended for agriculture in developed and developing countries; these strategies risk alteration of ecosystem processes that may be difficult to restore when applied at broad scales without adequate assessme