A stream is a body of water with surface water flowing within the bed and banks of a channel. The stream encompasses surface and groundwater fluxes that respond to geological, geomorphological and biotic controls. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams are called rivers. Streams are important as conduits in the water cycle, instruments in groundwater recharge, corridors for fish and wildlife migration; the biological habitat in the immediate vicinity of a stream is called a riparian zone. Given the status of the ongoing Holocene extinction, streams play an important corridor role in connecting fragmented habitats and thus in conserving biodiversity; the study of streams and waterways in general is known as surface hydrology and is a core element of environmental geography. Brook A stream smaller than a creek one, fed by a spring or seep, it is small and forded. A brook is characterised by its shallowness.
Creek In North America and New Zealand, a small to medium-sized natural stream. Sometimes navigable by motor craft and may be intermittent. In parts of Maryland, New England, the UK and India, a tidal inlet in a salt marsh or mangrove swamp, or between enclosed and drained former salt marshes or swamps. In these cases, the stream is the tidal stream, the course of the seawater through the creek channel at low and high tide. River A large natural stream, which may be a waterway. Runnel the linear channel between the parallel ridges or bars on a shoreline beach or river floodplain, or between a bar and the shore. Called a swale. Tributary A contributory stream, or a stream which does not reach a static body of water such as a lake or ocean, but joins another river. Sometimes called a branch or fork. There are a number of regional names for a stream. Allt is used in Highland Scotland. Beck is used in Lincolnshire to Cumbria in areas which were once occupied by the Danes and Norwegians. Bourne or winterbourne is used in the chalk downland of southern England.
Brook. Burn is used in North East England. Gill or ghyll is seen in Surrey influenced by Old Norse; the variant "ghyll" is used in the Lake District and appears to have been an invention of William Wordsworth. Nant is used in Wales. Rivulet is a term encountered in Victorian era publications. Stream Syke is used in lowland Cumbria for a seasonal stream. Branch is used to name streams in Virginia. Creek is common throughout the United States, as well as Australia. Falls is used to name streams in Maryland, for streams/rivers which have waterfalls on them if such falls have a small vertical drop. Little Gunpowder Falls and The Jones Falls are rivers named in this manner, unique to Maryland. Kill in New York, Pennsylvania and New Jersey comes from a Dutch language word meaning "riverbed" or "water channel", can be used for the UK meaning of'creek'. Run in Ohio, Michigan, New Jersey, Virginia, or West Virginia can be the name of a stream. Run in Florida is the name given to streams coming out of small natural springs.
River is used for larger springs like the Silver Rainbow River. Stream and brook are used in Midwestern states, Mid-Atlantic states, New England. Bar A shoal that develops in a stream as sediment is deposited as the current slows or is impeded by wave action at the confluence. Bifurcation A fork into two or more streams. Channel A depression created by constant erosion. Confluence The point at which the two streams merge. If the two tributaries are of equal size, the confluence may be called a fork. Drainage basin The area of land. A large drainage basin such as the Amazon River contains many smaller drainage basins. Floodplain Lands adjacent to the stream that are subject to flooding when a stream overflows its banks. Gaging station A site along the route of a stream or river, used for reference marking or water monitoring. Headwaters The part of a stream or river proximate to its source; the word is most used in the plural where there is no single point source. Knickpoint The point on a stream's profile where a sudden change in stream gradient occurs.
Mouth The point at which the stream discharges via an estuary or delta, into a static body of water such as a lake or ocean. Pool A segment where the water is deeper and slower moving. Rapids A turbulent, fast-flowing stretch of a stream or river. Riffle A segment where the flow is shallower and more turbulent. River A large natural stream, which may be a waterway. Run A somewhat smoothly flowing segment of the stream. Source The spring, or other point of origin of a stream. Spring The point at which a stream emerges from an underground course through unconsolidated sediments or through caves. A stream can with caves, flow aboveground for part of its course, underground for part of its course. Stream bed The bottom of a stream. Stream corridor Stream, its floodplains, the transitional upland fringe Streamflow The water moving through a stream channel. Thalweg The river's longitudinal section, or the line joining the deepest point in the channel at each stage from source to mouth. Waterfall or cascade The fall of water where the stream goes over a sudden drop called a knickpoint.
The stream expends kinetic energy in "trying" to eliminate the
The dinoflagellates are a classification subgroup of protista. They are a large group of flagellate eukaryotes. Most are marine plankton, but they are common in freshwater habitats, their populations are distributed depending on salinity, or depth. Many dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey. In terms of number of species, dinoflagellates are one of the largest groups of marine eukaryotes, although this group is smaller than diatoms; some species are endosymbionts of marine animals and play an important part in the biology of coral reefs. Other dinoflagellates are unpigmented predators on other protozoa, a few forms are parasitic; some dinoflagellates produce resting stages, called dinoflagellate cysts or dinocysts, as part of their lifecycles. Dinoflagellates are considered to be protists, with Dinoflagellata. About 1,555 species of free-living marine dinoflagellates are described. Another estimate suggests about 2,000 living species, of which more than 1,700 are marine and about 220 are from fresh water.
The latest estimates suggest a total of 2,294 living dinoflagellate species, which includes marine and parasitic dinoflagellates. A bloom of certain dinoflagellates can result in a visible coloration of the water colloquially known as red tide, which can cause shellfish poisoning if humans eat contaminated shellfish; some dinoflagellates exhibit bioluminescence—primarily emitting blue-green light. In 1753, the first modern dinoflagellates were described by Henry Baker as "Animalcules which cause the Sparkling Light in Sea Water", named by Otto Friedrich Müller in 1773; the term derives from the Greek word δῖνος, meaning whirling, Latin flagellum, a diminutive term for a whip or scourge. In the 1830s, the German microscopist Christian Gottfried Ehrenberg examined many water and plankton samples and proposed several dinoflagellate genera that are still used today including Peridinium and Dinophysis; these same dinoflagellates were first defined by Otto Bütschli in 1885 as the flagellate order Dinoflagellida.
Botanists treated them as a division of algae, named Pyrrophyta or Pyrrhophyta after the bioluminescent forms, or Dinophyta. At various times, the cryptomonads and ellobiopsids have been included here, but only the last are now considered close relatives. Dinoflagellates have a known ability to transform from noncyst to cyst-forming strategies, which makes recreating their evolutionary history difficult. Dinoflagellates are unicellular and possess two dissimilar flagella arising from the ventral cell side, they have a ribbon-like transverse flagellum with multiple waves that beats to the cell's left, a more conventional one, the longitudinal flagellum, that beats posteriorly. The transverse flagellum is a wavy ribbon in which only the outer edge undulates from base to tip, due to the action of the axoneme which runs along it; the axonemal edge has simple hairs. The flagellar movement produces forward propulsion and a turning force; the longitudinal flagellum is conventional in appearance, with few or no hairs.
It beats with two periods to its wave. The flagella lie in surface grooves: the transverse one in the cingulum and the longitudinal one in the sulcus, although its distal portion projects behind the cell. In dinoflagellate species with desmokont flagellation, the two flagella are differentiated as in dinokonts, but they are not associated with grooves. Dinoflagellates have a complex cell covering called an amphiesma or cortex, composed of a series of membranes, flattened vesicles called alveolae and related structures. In armoured dinoflagellates, these support overlapping cellulose plates to create a sort of armor called the theca, as opposed to athecate dinoflagellates; these occur in various shapes and arrangements, depending on the species and sometimes on the stage of the dinoflagellate. Conventionally, the term tabulation has been used to refer to this arrangement of thecal plates; the plate configuration can be denoted with the plate tabulation formula. Fibrous extrusomes are found in many forms.
Together with various other structural and genetic details, this organization indicates a close relationship between the dinoflagellates, the Apicomplexa, ciliates, collectively referred to as the alveolates. Dinoflagellate tabulations can be grouped into six "tabulation types": gymnodinoid, gonyaulacoid–peridinioid, nannoceratopsioid and prorocentroid; the chloroplasts in most photosynthetic dinoflagellates are bound by three membranes, suggesting they were derived from some ingested algae. Most photosynthetic species contain chlorophylls a and c2, the carotenoid beta-carotene, a group of xanthophylls that appears to be unique to dinoflagellates peridinin and diadinoxanthin; these pigments give many dinoflagellates their typical golden brown color. However, the dinoflagellates Karenia brevis, Karenia mikimotoi, Karlodinium micrum have acquired other pigments through endosymbiosis, including fucoxanthin; this suggests their chloroplasts were incorporated by several endosymbiotic events involving colored or secondarily colorless forms.
The discovery of plastids in the Apicomplexa has led some to suggest they were inherited from an ancestor common to the two groups, b
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
The brown algae, comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Most brown algae live in marine environments, where they play an important role both as food and as habitat. For instance, Macrocystis, a kelp of the order Laminariales, may reach 60 m in length and forms prominent underwater kelp forests. Kelp forests like these contain a high level of biodiversity. Another example is Sargassum, which creates unique floating mats of seaweed in the tropical waters of the Sargasso Sea that serve as the habitats for many species. Many brown algae, such as members of the order Fucales grow along rocky seashores; some members of the class, such as kelps, are used by humans as food. Between 1,500 and 2,000 species of brown algae are known worldwide; some species, such as Ascophyllum nodosum, are important in commercial use because they have become subjects of extensive research in their own right.
They have environmental significance as well, through carbon fixation. Brown algae belong to the group Heterokontophyta, a large group of eukaryotic organisms distinguished most prominently by having chloroplasts surrounded by four membranes, suggesting an origin from a symbiotic relationship between a basal eukaryote and another eukaryotic organism. Most brown algae contain the pigment fucoxanthin, responsible for the distinctive greenish-brown color that gives them their name. Brown algae are unique among heterokonts in developing into multicellular forms with differentiated tissues, but they reproduce by means of flagellated spores and gametes that resemble cells of other heterokonts. Genetic studies show their closest relatives to be the yellow-green algae. Brown algae exist in a wide range of forms; the smallest members of the group grow as tiny, feathery tufts of threadlike cells no more than a few centimeters long. Some species have a stage in their life cycle that consists of only a few cells, making the entire alga microscopic.
Other groups of brown algae grow to much larger sizes. The rockweeds and leathery kelps are the most conspicuous algae in their habitats. Kelps can range in size from the two-foot-tall sea palm Postelsia to the giant kelp Macrocystis pyrifera, which grows to over 45 m long and is the largest of all the algae. In form, the brown algae range from small crusts or cushions to leafy free-floating mats formed by species of Sargassum, they may consist of delicate felt-like strands of cells, as in Ectocarpus, or of foot-long flattened branches resembling a fan, as in Padina. Regardless of size or form, two visible features set the Phaeophyceae apart from all other algae. First, members of the group possess a characteristic color that ranges from an olive green to various shades of brown; the particular shade depends upon the amount of fucoxanthin present in the alga. Second, all brown algae are multicellular. There are no known species that exist as single cells or as colonies of cells, the brown algae are the only major group of seaweeds that does not include such forms.
However, this may be the result of classification rather than a consequence of evolution, as all the groups hypothesized to be the closest relatives of the browns include single-celled or colonial forms. Whatever their form, the body of all brown algae is termed a thallus, indicating that it lacks the complex xylem and phloem of vascular plants; this does not mean that brown algae lack specialized structures. But, because some botanists define "true" stems and roots by the presence of these tissues, their absence in the brown algae means that the stem-like and leaf-like structures found in some groups of brown algae must be described using different terminology. Although not all brown algae are structurally complex, those that are possess one or more characteristic parts. A holdfast is a rootlike structure present at the base of the alga. Like a root system in plants, a holdfast serves to anchor the alga in place on the substrate where it grows, thus prevents the alga from being carried away by the current.
Unlike a root system, the holdfast does not serve as the primary organ for water uptake, nor does it take in nutrients from the substrate. The overall physical appearance of the holdfast differs among various brown algae and among various substrates, it may be branched, or it may be cup-like in appearance. A single alga has just one holdfast, although some species have more than one stipe growing from their holdfast. A stipe is a stalk or stemlike structure present in an alga, it may grow as a short structure near the base of the alga, or it may develop into a large, complex structure running throughout the algal body. In the most structurally differentiated brown algae, the tissues within the stipe are divided into three distinct layers or regions; these regions include a central pith, a surrounding cortex, an outer epidermis, each of which has an analog in the stem of a vascular plant. In some brown algae, the pith region includes a core of elongated cells that resemble the phloem of vascular plants both in structure and function.
In others, the center of the stipe is hollow and filled with gas that serves to keep that part of the alga buoyant. The stipe may be flexible and elastic in species like Macrocystis pyrifera that grow in strong currents, or may be more rigid in species like Postelsia palmaeformis that are exposed to the atmosphere at low tide. Many algae have a flattened portion that may resemble a leaf, this is termed a blade, lamina, or frond; the name blade is most applied to a single undivided structure, while frond may be
River ecosystems are flowing waters that drain the landscape, include the biotic interactions amongst plants and micro-organisms, as well as abiotic physical and chemical interactions of its many parts. River ecosystems are part of larger watershed networks or catchments, where smaller headwater streams drain into mid-size streams, which progressively drain into larger river networks. River ecosystems are prime examples of lotic ecosystems. Lotic refers from the Latin lotus, meaning washed. Lotic waters range from springs only a few centimeters wide to major rivers kilometers in width. Much of this article applies to lotic ecosystems in general, including related lotic systems such as streams and springs. Lotic ecosystems can be contrasted with lentic ecosystems, which involve still terrestrial waters such as lakes and wetlands. Together, these two ecosystems form the more general study area of freshwater or aquatic ecology; the following unifying characteristics make the ecology of running waters unique among aquatic habitats.
Flow is unidirectional. There is a state of continuous physical change. There is a high degree of temporal heterogeneity at all scales. Variability between lotic systems is quite high; the biota is specialized to live with flow conditions. The non living components of an ecosystem are called abiotic components. E.g stone,air,soil,etc. Unidirectional water flow is the key factor in lotic systems influencing their ecology. Stream flow can be intermittent, though. Stream flow is the result of the summative inputs from groundwater and overland flow. Water flow can vary between systems, ranging from torrential rapids to slow backwaters that seem like lentic systems; the speed or velocity of the water flow of the water column can vary within a system and is subject to chaotic turbulence, though water velocity tends to be highest in the middle part of the stream channel. This turbulence results in divergences of flow from the mean downslope flow vector as typified by eddy currents; the mean flow rate vector is based on variability of friction with the bottom or sides of the channel, sinuosity and the incline gradient.
In addition, the amount of water input into the system from direct precipitation, and/or groundwater can affect flow rate. The amount of water in a stream is measured as discharge; as water flows downstream and rivers most gain water volume, so at base flow, smaller headwater streams have low discharge, while larger rivers have much higher discharge. The "flow regime" of a river or stream includes the general patterns of discharge over annual or decadal time scales, may capture seasonal changes in flow. While water flow is determined by slope, flowing waters can alter the general shape or direction of the stream bed, a characteristic known as geomorphology; the profile of the river water column is made up of three primary actions: erosion and deposition. Rivers have been described as "the gutters down which run the ruins of continents". Rivers are continuously eroding and depositing substrate and organic material; the continuous movement of water and entrained material creates a variety of habitats, including riffles and pools.
Light is important to lotic systems, because it provides the energy necessary to drive primary production via photosynthesis, can provide refuge for prey species in shadows it casts. The amount of light that a system receives can be related to a combination of internal and external stream variables; the area surrounding a small stream, for example, might be shaded by surrounding forests or by valley walls. Larger river systems tend to be wide so the influence of external variables is minimized, the sun reaches the surface; these rivers tend to be more turbulent and particles in the water attenuate light as depth increases. Seasonal and diurnal factors might play a role in light availability because the angle of incidence, the angle at which light strikes water can lead to light lost from reflection. Known as Beer's Law, the shallower the angle, the more light is reflected and the amount of solar radiation received declines logarithmically with depth. Additional influences on light availability include cloud cover and geographic position.
Most lotic species are poikilotherms whose internal temperature varies with their environment, thus temperature is a key abiotic factor for them. Water can be heated or cooled through radiation at the surface and conduction to or from the air and surrounding substrate. Shallow streams are well mixed and maintain a uniform temperature within an area. In deeper, slower moving water systems, however, a strong difference between the bottom and surface temperatures may develop. Spring fed systems have little variation as springs are from groundwater sources, which are very close to ambient temperature. Many systems show strong diurnal fluctuations and seasonal variations are most extreme in arctic and temperate systems; the amount of shading and elevation can influence the temperature of lotic systems. Water chemistry in river ecosystems varies depending on which dissolved solutes and gases are present in the water column of the stream. River water can include, apart from the water itself, dissolved inorganic matter and major ions dissolved inorganic nutrients suspended and dissolved organic matter gases (nitrogen, nitrous oxide, carbon dioxide, oxyge
Aquatic plants are plants that have adapted to living in aquatic environments. They are referred to as hydrophytes or macrophytes. A macrophyte is an aquatic plant that grows in or near water and is either emergent, submergent, or floating, includes helophytes. In lakes and rivers macrophytes provide cover for fish and substrate for aquatic invertebrates, produce oxygen, act as food for some fish and wildlife. Aquatic plants require special adaptations for living submerged at the water's surface; the most common adaptation is aerenchyma, but floating leaves and finely dissected leaves are common. Aquatic plants can only grow in water or in soil, permanently saturated with water, they are therefore a common component of wetlands. Fringing stands of tall vegetation by water basins and rivers may include helophytes. Examples include stands of Equisetum fluviatile, Glyceria maxima, Hippuris vulgaris, Carex, Sparganium, yellow flag and Phragmites australis; the principal factor controlling the distribution of aquatic plants is the depth and duration of flooding.
However, other factors may control their distribution and growth form, including nutrients, disturbance from waves and salinity. Aquatic vascular plants have originated on multiple occasions in different plant families. Seaweeds are not vascular plants. A few aquatic plants are able to survive in brackish and salt water; the only angiosperms capable of growing submerged in seawater are the seagrasses. Examples are found in genera such as Zostera. Although most aquatic plants can reproduce by flowering and setting seed, many have extensive asexual reproduction by means of rhizomes and fragments in general. One of the largest aquatic plants in the world is the Amazon water lily. Many small aquatic animals use plants like duckweed for a home, or for protection from predators, but areas with more vegetation are to have more predators; some other familiar examples of aquatic plants might include floating heart, water lily and water hyacinth. Based on growth form, macrophytes can be classified as: Emergent macrophytes Floating-leaved macrophytes Submerged macrophytes Free floating macrophytes An emergent plant is one which grows in water but which pierces the surface so that it is in air.
Collectively, such plants are emergent vegetation. This habit may have developed because the leaves can photosynthesize more efficiently above the shade of cloudy water and competition from submerged plants but the main aerial feature is the flower and the related reproductive process; the emergent habit permits pollination by flying insects. There are many species of emergent plants, among them, the reed, Cyperus papyrus, Typha species, flowering rush and wild rice species; these may be found growing in fens but less well owing to competition from other plants. Some species, such as purple loosestrife, may grow in water as emergent plants but they are capable of flourishing in fens or in damp ground. Floating-leaved macrophytes have root systems attached to the substrate or bottom of the body of water and with leaves that float on the water surface. Common floating leaves macrophytes are pondweeds. Submerged macrophytes grow under water with root attached to the substrate or without any root system.
Free-floating macrophytes are aquatic plants that are found suspended on water surface with their root not attached to substrate or sediment or bottom of water body. They are blown by air and provide breeding ground for mosquito. Example include Pistia spp called water lettuce, water cabbage or Nile cabbage The many possible classifications of aquatic plants are based upon morphology. One example has six groups as follows: Amphiphytes: plants that are adapted to live either submerged or on land Elodeids: stem plants that complete their entire lifecycle submerged, or with only their flowers above the waterline Isoetids: rosette plants that complete their entire lifecycle submerged Helophytes: plants rooted in the bottom, but with leaves above the waterline Nymphaeids: plants rooted in the bottom, but with leaves floating on the water surface Pleuston: vascular plants that float in the water Macrophytes perform many ecosystem functions in aquatic ecosystems and provide services to human society.
One of the important functions performed by macrophyte is uptake of dissolve nutrients from water. Macrophytes are used in constructed wetlands around the world to remove excess N and P from polluted water. Beside direct nutrient uptake, macrophytes indirectly influence nutrient cycling N cycling through influencing the denitrifying bacterial functional groups that are inhabiting on roots and shoots of macrophytes. Macrophytes promote the sedimentation of suspended solids by reducing the current velocities, impede erosion by stabilising soil surfaces. Macrophytes provide spatial heterogeneity in otherwise unstructured water column. Habitat complexity provided by macrophytes like to increase the richness of taxonomy and density of both fish and invertebrates; some aquatic plants are used by humans as a food source. Examples include wild rice, water caltrop, Chinese wa
Chlorine is a chemical element with symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are intermediate between them. Chlorine is a yellow-green gas at room temperature, it is an reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the Pauling scale, behind only oxygen and fluorine. The most common compound of chlorine, sodium chloride, has been known since ancient times. Around 1630, chlorine gas was first synthesised in a chemical reaction, but not recognised as a fundamentally important substance. Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, this was confirmed by Sir Humphry Davy in 1810, who named it from Ancient Greek: χλωρός, translit. Khlôros, lit.'pale green' based on its colour.
Because of its great reactivity, all chlorine in the Earth's crust is in the form of ionic chloride compounds, which includes table salt. It is the second-most abundant halogen and twenty-first most abundant chemical element in Earth's crust; these crustal deposits are dwarfed by the huge reserves of chloride in seawater. Elemental chlorine is commercially produced from brine by electrolysis; the high oxidising potential of elemental chlorine led to the development of commercial bleaches and disinfectants, a reagent for many processes in the chemical industry. Chlorine is used in the manufacture of a wide range of consumer products, about two-thirds of them organic chemicals such as polyvinyl chloride, many intermediates for the production of plastics and other end products which do not contain the element; as a common disinfectant, elemental chlorine and chlorine-generating compounds are used more directly in swimming pools to keep them clean and sanitary. Elemental chlorine at high concentrations is dangerous and poisonous for all living organisms, was used in World War I as the first gaseous chemical warfare agent.
In the form of chloride ions, chlorine is necessary to all known species of life. Other types of chlorine compounds are rare in living organisms, artificially produced chlorinated organics range from inert to toxic. In the upper atmosphere, chlorine-containing organic molecules such as chlorofluorocarbons have been implicated in ozone depletion. Small quantities of elemental chlorine are generated by oxidation of chloride to hypochlorite in neutrophils as part of the immune response against bacteria; the most common compound of chlorine, sodium chloride, has been known since ancient times. Its importance in food was well known in classical antiquity and was sometimes used as payment for services for Roman generals and military tribunes. Elemental chlorine was first isolated around 1200 with the discovery of aqua regia and its ability to dissolve gold, since chlorine gas is one of the products of this reaction: it was however not recognised as a new substance. Around 1630, chlorine was recognized as a gas by the Flemish chemist and physician Jan Baptist van Helmont.
The element was first studied in detail in 1774 by Swedish chemist Carl Wilhelm Scheele, he is credited with the discovery. Scheele produced chlorine by reacting MnO2 with HCl: 4 HCl + MnO2 → MnCl2 + 2 H2O + Cl2Scheele observed several of the properties of chlorine: the bleaching effect on litmus, the deadly effect on insects, the yellow-green color, the smell similar to aqua regia, he called it "dephlogisticated muriatic acid air" since it is a gas and it came from hydrochloric acid. He failed to establish chlorine as an element. Common chemical theory at that time held that an acid is a compound that contains oxygen, so a number of chemists, including Claude Berthollet, suggested that Scheele's dephlogisticated muriatic acid air must be a combination of oxygen and the yet undiscovered element, muriaticum. In 1809, Joseph Louis Gay-Lussac and Louis-Jacques Thénard tried to decompose dephlogisticated muriatic acid air by reacting it with charcoal to release the free element muriaticum, they did not succeed and published a report in which they considered the possibility that dephlogisticated muriatic acid air is an element, but were not convinced.
In 1810, Sir Humphry Davy tried the same experiment again, concluded that the substance was an element, not a compound. He announced his results to the Royal Society on 15 November that year. At that time, he named this new element "chlorine", from the Greek word χλωρος, meaning green-yellow; the name "halogen", meaning "salt producer", was used for chlorine in 1811 by Johann Salomo Christoph Schweigger. This term was used as a generic term to describe all the elements in the chlorine family, after a suggestion by Jöns Jakob Berzelius in 1826. In 1823, Michael Faraday liquefied chlorine for the first time, demonstrated that what was known as "solid chlorine" had a structure of chlorine hydrate. Chlorine gas was first used by French chemist Claude Berthollet to bleach textiles in 1785. Modern bleaches resulted from further work by Berthollet, who first produced sodium hypochlorite in 1789 in his laboratory in the town of Javel, by passing chlorine gas through a solution of sodium carbonate; the resulting liqu