Canada goose
The Canada goose is a large wild goose species with a black head and neck, white cheeks, white under its chin, a brown body. Native to arctic and temperate regions of North America, its migration reaches northern Europe, it has been introduced to the United Kingdom, New Zealand, Argentina and the Falkland Islands. Like most geese, the Canada goose is herbivorous and migratory. Successful at living in human-altered areas, Canada geese have proven able to establish breeding colonies in urban and cultivated areas, which provide food and few natural predators; the success of this common park species has led to its being considered a pest species because of their depredation of crops and their noise, aggressive territorial behavior, habit of begging for food. The Canada goose was one of the many species described by Carl Linnaeus in his 18th-century work Systema Naturae, it belongs to the Branta genus of geese, which contains species with black plumage, distinguishing them from the grey species of the genus Anser.
Branta is a Latinised form of Old Norse Brandgás, "burnt goose" and the specific epithet canadensis is a New Latin word meaning "from Canada". According to the Oxford English Dictionary, the first citation for the'Canada goose' dates back to 1772; the Canada goose is colloquially referred to as the "Canadian goose". The cackling goose was considered to be the same species or a subspecies of the Canada goose, but in July 2004, the American Ornithologists' Union's Committee on Classification and Nomenclature split them into two species, making the cackling goose into a full species with the scientific name Branta hutchinsii; the British Ornithologists' Union followed suit in June 2005. The AOU has divided the many subspecies between the two species; the subspecies of the Canada goose were listed as: Atlantic Canada goose, B. c. canadensis Interior Canada goose, B. c. interior Giant Canada goose, B. c. maxima Delacour, 1951 Moffitt's Canada goose, B. c. moffitti Aldrich, 1946 Vancouver Canada goose, B. c. fulva Dusky Canada goose, B. c. occidentalis Lesser Canada goose, B. c. parvipes The distinctions between the two geese have led to confusion and debate among ornithologists.
This has been aggravated by the overlap between the small types of Canada goose and larger types of cackling goose. The old "lesser Canada geese" were believed to be a hybrid population, with the birds named B. c. taverneri considered a mixture of B. c. minima, B. c. occidentalis, B. c. parvipes. The holotype specimen of taverneri is a straightforward large pale cackling goose however, hence the taxon is still valid today and was renamed "Taverner's cackling goose". In addition, the barnacle goose was determined to be a derivative of the cackling goose lineage, whereas the Hawaiian goose originated from ancestral Canada geese. Thus, the species' distinctness is well evidenced, A recent proposed revision by Harold C. Hanson suggests splitting Canada and cackling goose into six species and 200 subspecies; the radical nature of this proposal has provoked surprise in some quarters. The black head and neck with a white "chinstrap" distinguish the Canada goose from all other goose species, with the exception of the cackling goose and barnacle goose.
The seven subspecies of this bird vary in size and plumage details, but all are recognizable as Canada geese. Some of the smaller races can be hard to distinguish from the cackling goose, which overlap in mass. However, most subspecies of the cackling goose are smaller; the smallest cackling goose, B. h. minima, is scarcely larger than a mallard. In addition to the size difference, cackling geese have a shorter neck and smaller bill, which can be useful when small Canada geese comingle with large cackling geese. Of the "true geese", the Canada goose is on average the largest living species, although some other species that are geese in name, if not of close relation to these genera, are on average heavier such as the spur-winged goose and Cape Barren goose. Canada geese have a 127 -- 185 cm wingspan. Among standard measurements, the wing chord can range from 39 to 55 cm, the tarsus can range from 6.9 to 10.6 cm and the bill can range from 4.1 to 6.8 cm. The largest subspecies is the B. c. maxima, or the giant Canada goose, the smallest is B. c. parvipes, or the lesser Canada goose.
An exceptionally large male of race B. c. maxima, which exceed 8 kg, weighed 10.9 kg and had a wingspan of 2.24 m. This specimen is the largest wild goose recorded of any species; the male Canada goose weighs 2.6–6.5 kg, averaging amongst all subspecies 3.9 kg. The female looks identical, but is lighter at 2.4–5.5 kg, averaging amongst all subspecies 3.6 kg, 10% smaller in linear dimensions than the male counterparts. The female possesses a different, less sonorous, honk than the male; this species is native to North America. It breeds in the northern United States in a wide range of habitats; the Great Lakes region maintains a large population of Canada geese
Strawberry
The garden strawberry is a grown hybrid species of the genus Fragaria, collectively known as the strawberries. It is cultivated worldwide for its fruit; the fruit is appreciated for its characteristic aroma, bright red color, juicy texture, sweetness. It is consumed in large quantities, either fresh or in such prepared foods as preserves, pies, ice creams and chocolates. Artificial strawberry flavorings and aromas are widely used in many products like lip gloss, hand sanitizers and many others; the garden strawberry was first bred in Brittany, France, in the 1750s via a cross of Fragaria virginiana from eastern North America and Fragaria chiloensis, brought from Chile by Amédée-François Frézier in 1714. Cultivars of Fragaria × ananassa have replaced, in commercial production, the woodland strawberry, the first strawberry species cultivated in the early 17th century; the strawberry is not, from a botanical point of view, a berry. Technically, it is an aggregate accessory fruit, meaning that the fleshy part is derived not from the plant's ovaries but from the receptacle that holds the ovaries.
Each apparent "seed" on the outside of the fruit is one of the ovaries of the flower, with a seed inside it. In 2016, world production of strawberries was 9.2 million tonnes, led by China with 41% of the total. The first garden strawberry was grown in Brittany, during the late 18th century. Prior to this, wild strawberries and cultivated selections from wild strawberry species were the common source of the fruit; the strawberry fruit was mentioned in ancient Roman literature in reference to its medicinal use. The French began taking the strawberry from the forest to their gardens for harvest in the 14th century. Charles V, France's king from 1364 to 1380, had 1,200 strawberry plants in his royal garden. In the early 15th century western European monks were using the wild strawberry in their illuminated manuscripts; the strawberry is found in Italian and German art, in English miniatures. The entire strawberry plant was used to treat depressive illnesses. By the 16th century, references of cultivation of the strawberry became more common.
People began using it for its supposed medicinal properties and botanists began naming the different species. In England the demand for regular strawberry farming had increased by the mid-16th century; the combination of strawberries and cream was created by Thomas Wolsey in the court of King Henry VIII. Instructions for growing and harvesting strawberries showed up in writing in 1578. By the end of the 16th century three European species had been cited: F. vesca, F. moschata, F. viridis. The garden strawberry was transplanted from the forests and the plants would be propagated asexually by cutting off the runners. Two subspecies of F. vesca were identified: F. sylvestris alba and F. sylvestris semperflorens. The introduction of F. virginiana from Eastern North America to Europe in the 17th century is an important part of history because this species gave rise to the modern strawberry. The new species spread through the continent and did not become appreciated until the end of the 18th century.
When a French excursion journeyed to Chile in 1712, it introduced the North American strawberry plant with female flowers that resulted in the common strawberry that we have today. The Mapuche and Huilliche Indians of Chile cultivated the female strawberry species until 1551, when the Spanish came to conquer the land. In 1765, a European explorer recorded the cultivation of the Chilean strawberry. At first introduction to Europe, the plants produced no fruit, it was discovered in 1766 that the female plants could only be pollinated by plants that produced large fruit: F. moschata, F. virginiana, F. ananassa. This is when the Europeans became aware that plants had the ability to produce male-only or female-only flowers; as more large-fruit producing plants were cultivated the Chilean strawberry decreased in population in Europe, except for around Brest where the Chilean strawberry thrived. The decline of the Chilean strawberry was caused by F. ananassa. Strawberry cultivars vary in size, flavor, degree of fertility, season of ripening, liability to disease and constitution of plant.
On average, a strawberry has about 200 seeds on its external membrane. Some vary in foliage, some vary materially in the relative development of their sexual organs. In most cases, the flowers appear hermaphroditic in structure, but function as either male or female. For purposes of commercial production, plants are propagated from runners and, in general, distributed as either bare root plants or plugs. Cultivation follows one of two general models—annual plasticulture, or a perennial system of matted rows or mounds. Greenhouses produce a small amount of strawberries during the off season; the bulk of modern commercial production uses the plasticulture system. In this method, raised beds are formed each year and covered with plastic to prevent weed growth and erosion. Plants obtained from northern nurseries, are planted through holes punched in this covering, irrigation tubing is run underneath. Runners are removed from the plants as they appear, in order to encourage the plants to put most of their energy into fruit development.
At the end of the harvest season, the plastic is removed and the plants are plowed into the ground. Because strawberry plants more than a year or two old begin to decline in productivity and fruit quality, this system of replacing the plants each year allows for improved yields and denser plantings. However, because it requires a longer growing season to allow for estab
Striped bass
The striped bass called Atlantic striped bass, linesider, rock or rockfish, is an anadromous Perciforme fish of the family Moronidae found along the Atlantic coast of North America. It has been introduced into inland recreational fisheries across the United States. Striped bass found in the Gulf of Mexico are a separate strain referred to as Gulf Coast striped bass; the striped bass is the state fish of Maryland, Rhode Island, South Carolina, the state saltwater fish of New York, New Jersey and New Hampshire. The history of the striped bass fishery in North America dates back to the Colonial period. Many written accounts by some of the first European settlers describe the immense abundance of striped bass, along with alewives and spawning up most rivers in the coastal Northeast; the striped bass is a typical member of the Moronidae family in shape, having a streamlined, silvery body marked with longitudinal dark stripes running from behind the gills to the base of the tail. Common mature size is 20 to 40 pounds.
The largest specimen recorded was 124 pounds, netted in 1896. Striped bass are believed to live for up to 30 years; the maximum weight can be north of eighty pounds. The average size in length is twenty to thirty five inches and five to just shy of twenty pounds. Striped bass are native to the Atlantic coastline of North America from the St. Lawrence River into the Gulf of Mexico to Louisiana, they are anadromous fish that migrate between salt water. Spawning takes place in fresh water. Striped bass have been introduced to the Pacific Coast of North America and into many of the large reservoir impoundments across the United States by state game and fish commissions for the purposes of recreational fishing and as a predator to control populations of gizzard shad; these include: Elephant Butte Lake in New Mexico. Striped bass have been introduced into waters in Ecuador, Latvia, Russia, South Africa, Turkey for sport fishing and aquaculture; the spawning success of striped bass has been studied in the San Francisco Bay-Delta water system, with a finding that high total dissolved solids reduce spawning.
At levels as low as 200 mg/l TDS, an observable diminution of spawning productivity occurs. They can be found in lakes, ponds and wetlands. Though the population of striped bass was growing and repopulating in the late 1980s and throughout the 1990s, a study executed by the Wildlife and Fisheries Program at West Virginia University found that the rapid growth of the striped bass population was exerting a tremendous pressure on its prey; this pressure on their food source was putting their own population at risk due to the population of prey not coming back to the same spawning areas. In the United States, the striped bass was designated as a protected game fish in 2007, executive agencies were directed to use existing legal authorities to prohibit the sale of striped bass caught in federal waters in the Atlantic Ocean and Gulf of Mexico. In Canada, the province of Quebec designated the striped bass population of the Saint Lawrence as extirpated in 1996. Analysis of available data implicated dredging in the disappearance.
In 2002, a reintroduction program was successful. Striped bass spawn in fresh water, although they have been adapted to freshwater habitat, they spend their adult lives in saltwater. Four important bodies of water with breeding stocks of striped bass are: Chesapeake Bay, Massachusetts Bay/Cape Cod, Hudson River, Delaware River. Many of the rivers and tributaries that emptied into the Atlantic, had at one time, bred stock of striped bass; this occurred until the 1860s. One of the largest breeding areas is the Chesapeake Bay, where populations from Chesapeake and Delaware bays have intermingled; the few successful spawning populations of freshwater striped bass include Lake Texoma, Lake Weiss, the Colorado River and its reservoirs downstream from and including Lake Powell, the Arkansas River, as well as Lake Marion that retained a landlocked breeding population when the dam was built. Stocking of striped bass was discontinued at Lake Mead in 1973 once natural reproduction was verified. Striped bass have been hybridized with white bass to produce hybrid striped bass known as wiper, whiterock bass, sunshine bass, palmetto bass, Cherokee bass.
These hybrids have been stocked in many freshwater areas across the US. Striped bass are of significant value for sport fishing, have been introduced to many waterways outside their natural range. A variety of angling methods are used, including trolling and surf casting with topwater lures a good pick for surf casting, as well as bait casting with live and dead bait. Striped bass will take a number of live and fresh baits, includ
Ocean
An ocean is a body of water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean; these are, in descending order by area, the Pacific, Indian and Arctic Oceans. The word "ocean" is used interchangeably with "sea" in American English. Speaking, a sea is a body of water or enclosed by land, though "the sea" refers to the oceans. Saline water covers 361,000,000 km2 and is customarily divided into several principal oceans and smaller seas, with the ocean covering 71% of Earth's surface and 90% of the Earth's biosphere; the ocean contains 97% of Earth's water, oceanographers have stated that less than 5% of the World Ocean has been explored. The total volume is 1.35 billion cubic kilometers with an average depth of nearly 3,700 meters. As the world ocean is the principal component of Earth's hydrosphere, it is integral to life, forms part of the carbon cycle, influences climate and weather patterns; the World Ocean is the habitat of 230,000 known species, but because much of it is unexplored, the number of species that exist in the ocean is much larger over two million.
The origin of Earth's oceans is unknown. Extraterrestrial oceans may be composed of water or other compounds; the only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their geologic histories and Venus are theorized to have had large water oceans; the Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, a runaway greenhouse effect may have boiled away the global ocean of Venus. Compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of natural satellites; the Solar System's giant planets are thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may exist on exoplanets and exomoons, including surface oceans of liquid water within a circumstellar habitable zone.
Ocean planets are a hypothetical type of planet with a surface covered with liquid. The word ocean comes from the figure in classical antiquity, the elder of the Titans in classical Greek mythology, believed by the ancient Greeks and Romans to be the divine personification of the sea, an enormous river encircling the world; the concept of Ōkeanós has an Indo-European connection. Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases. Though described as several separate oceans, the global, interconnected body of salt water is sometimes referred to as the World Ocean or global ocean; the concept of a continuous body of water with free interchange among its parts is of fundamental importance to oceanography. The major oceanic divisions – listed below in descending order of area and volume – are defined in part by the continents, various archipelagos, other criteria.
Oceans are fringed by smaller, adjoining bodies of water such as seas, bays and straits. The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system, part of every ocean and the longest mountain range in the world; the continuous mountain range is 65,000 km long. The total mass of the hydrosphere is about 1.4 quintillion metric tons, about 0.023% of Earth's total mass. Less than 3% is freshwater; the area of the World Ocean is about 361.9 million square kilometers, which covers about 70.9% of Earth's surface, its volume is 1.335 billion cubic kilometers. This can be thought of as a cube of water with an edge length of 1,101 kilometers, its average depth is about 3,688 meters, its maximum depth is 10,994 meters at the Mariana Trench. Nearly half of the world's marine waters are over 3,000 meters deep; the vast expanses of deep ocean cover about 66% of Earth's surface. This does not include seas not connected to the World Ocean, such as the Caspian Sea; the bluish ocean color is a composite of several contributing agents.
Prominent contributors include dissolved organic chlorophyll. Mariners and other seafarers have reported that the ocean emits a visible glow which extends for miles at night. In 2005, scientists announced that for the first time, they had obtained photographic evidence of this glow, it is most caused by bioluminescence. Oceanographers divide the ocean into different vertical zones defined by physical and biological conditions; the pelagic zone includes all open ocean regions, can be divided into further regions categorized by depth and light abundance. The photic zone includes the oceans from the surface to a depth of
Mourning dove
The mourning dove is a member of the dove family, Columbidae. The bird is known as the American mourning dove or the rain dove, erroneously as the turtle dove, was once known as the Carolina pigeon or Carolina turtledove, it is one of the most widespread of all North American birds. It is a leading gamebird, with more than 20 million birds shot annually in the U. S. both for meat. Its ability to sustain its population under such pressure is due to its prolific breeding; the wings make an unusual whistling sound upon a form of sonation. The bird is a strong flier, capable of speeds up to 88 km/h, it is the national bird of the British Virgin Islands. Mourning doves are light grey and brown and muted in color. Males and females are similar in appearance; the species is monogamous, with two squabs per brood. Both parents care for the young. Mourning doves eat exclusively seeds, but the young are fed crop milk by their parents; the mourning dove is related to the eared dove and the Socorro dove. Some authorities describe them as forming a superspecies and these three birds are sometimes classified in the separate genus Zenaidura, but the current classification has them as separate species in the genus Zenaida.
In addition, the Socorro dove has at times been considered conspecific with the mourning dove, although several differences in behavior and appearance justify separation as two different species. While the three species do form a subgroup of Zenaida, using a separate genus would interfere with the monophyly of Zenaida by making it paraphyletic. There are five subspecies of mourning dove: Eastern Z. m. carolinensis Clarion Island Z. m. clarionensis West Indian Z. m. macroura Western Z. m. marginella Panama Z. m. turturilla The ranges of most of the subspecies overlap a little, with three in the United States or Canada. The West Indian subspecies is found throughout the Greater Antilles, it has invaded the Florida Keys. The eastern subspecies is found in eastern North America, as well as Bermuda and the Bahamas; the western subspecies is found including parts of Mexico. The Panamanian subspecies is located in Central America; the Clarion Island subspecies is found only on Clarion Island, just off the Pacific coast of Mexico.
The mourning dove is sometimes called the "American mourning dove" to distinguish it from the distantly related mourning collared dove of Africa. It was formerly known as the "Carolina turtledove" and the "Carolina pigeon"; the genus name was bestowed in 1838 by French zoologist Charles L. Bonaparte in honor of his wife, Princess Zénaide, macroura is from Ancient Greek makros, "long" and oura, "tail"; the "mourning" part of its common name comes from its call. The mourning dove was thought to be the passenger pigeon's closest living relative based on morphological grounds until genetic analysis showed Patagioenas pigeons to be more related; the mourning dove was suggested to belong to the same genus and was listed by some authors as E. carolinensis. The mourning dove has a large range of nearly 11,000,000 km2; the species is resident throughout the Greater Antilles, most of Mexico, the Continental United States, southern Canada, the Atlantic archipelago of Bermuda. Much of the Canadian prairie sees these birds in summer only, southern Central America sees them in winter only.
The species is a vagrant in northern Canada and South America. It has been spotted as an accidental at least seven times in the Western Palearctic with records from the British Isles, the Azores and Iceland. In 1963, the mourning dove was introduced to Hawaii, in 1998 there was still a small population in North Kona; the mourning dove appeared on Socorro Island, off the western coast of Mexico, in 1988, sixteen years after the Socorro dove was extirpated from that island. The mourning dove is a medium-sized, slender dove 31 cm in length. Mourning doves weigh 112–170 g closer to 128 g; the elliptical wings are broad, the head is rounded. Its tail is tapered. Mourning doves have perching feet, with three toes forward and one reversed; the legs are short and reddish colored. The beak is short and dark a brown-black hue; the plumage is light gray-brown and lighter and pinkish below. The wings have black spotting, the outer tail feathers are white, contrasting with the black inners. Below the eye is a distinctive crescent-shaped area of dark feathers.
The eyes are dark, with light skin surrounding them. The adult male has bright purple-pink patches on the neck sides, with light pink coloring reaching the breast; the crown of the adult male is a distinctly bluish-grey color. Females are similar in appearance, but with more brown coloring overall and a little smaller than the male; the iridescent feather patches on the neck above the shoulders are nearly absent, but can be quite vivid on males. Juvenile birds have a scaly appearance, are darker. All five subspecies of the mourning dove look similar and are not distinguishable; the nominate subspecies possesses shorter wings, is darker and more buff-colored than the "average" mourning dove. Z. m. carolinensis has longer wings and toes, a shorter beak, is darker in color. The western subspecies has longer wings, a longer beak, sh
Weir
A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and results in a change in the height of the river level. There are many designs of weir, but water flows over the top of the weir crest before cascading down to a lower level. There is no single definition as to what constitutes a weir and one English dictionary defines a weir as a small dam originating from Middle English were, Old English wer, derivative of root of werian, meaning "to defend, dam". Weirs are used to prevent flooding, measure water discharge, help render rivers more navigable by boat. In some locations, the terms dam and weir are synonymous, but there is a clear distinction made between the structures. A dam is specifically designed to impound water behind a wall, whilst a weir is designed to alter the river flow characteristics. A common distinction between dams and weirs is that water flows over the top of a weir or underneath it for at least some of its length. Accordingly, the crest of an overflow spillway on a large dam may therefore be referred to as a weir.
Weirs can vary in size both horizontally and vertically, with the smallest being only a few inches in height whilst the largest may be hundreds of metres long and many metres tall. Some common weir purposes are outlined below. Weirs allow hydrologists and engineers a simple method of measuring the volumetric flow rate in small to medium-sized streams/rivers or in industrial discharge locations. Since the geometry of the top of the weir is known and all water flows over the weir, the depth of water behind the weir can be converted to a rate of flow. However, this can only be achieved in locations where all water flows over the top of the weir crest and at locations where the water that flows over the crest is carried away from the structure. If these conditions are not met, it can make flow measurement complicated, inaccurate or impossible; the discharge calculation can be summarised as: Q = C L H n Where: Q is the volumetric flow rate of fluid C is the flow coefficient for the structure. L is the width of the crest H is the height of head of water over the crest n varies with structure However, this calculation is a generic relationship and specific calculations are available for the many different types of weir.
Flow measurement weirs must be well maintained. As weirs are a physical barrier they can impede the longitudinal movement of fish and other animals up and down a river; this can have a negative effect on fish species that migrate as part of their breeding cycle, but can be useful as a method of preventing invasive species moving upstream. For example, weirs in the Great Lakes region have helped to prevent invasive sea lamprey from colonising further upstream. Mill ponds are created by a weir that impounds water that flows over the structure; the energy created by the change in height of the water can be used to power waterwheels and power sawmills, grinding wheels and other equipment. Weirs are used to control the flow rates of rivers during periods of high discharge. Sluice gates can be altered to decrease the volume of water flowing downstream. Weirs for this purpose are found upstream of towns and villages and can either be automated or manually operated. By slowing the rate at which water moves downstream slightly a disproportionate effect can be had on the likelihood of flooding.
On larger rivers, a weir can alter the flow characteristics of the waterway to the point that vessels are able to navigate areas inaccessible due to extreme currents or eddies. Many larger weirs will have features built in that allow boats and river users to "shoot the weir" and navigate by passing up or down stream without having to exit the river. Weirs constructed for this purpose are common on the River Thames, most are situated near each of the river's 45 locks; because a weir impounds water behind it and alters the flow regime of the river, it can have an effect on the local ecology. The reduced river velocity upstream can lead to increased siltation that reduces the water oxygen content and smothers invertebrate habitat and fish spawning sites; the oxygen content returns to normal once water has passed over the weir crest, although increased river velocity can scour the river bed causing erosion and habitat loss. Weirs can have a significant effect on fish migration. Any weir that exceeds either the maximum height a species can jump or creates flow conditions that cannot be bypassed limits the maximum point upstream that fish can migrate.
In some cases this can mean that huge lengths of breeding habitat are lost and over time this can have a significant impact of fish populations. In many countries, it is now a requirement by law to build fish ladders into the design of a weir that ensures that fish can bypass the barrier and access upstream habitat. Unlike dams, weirs do not prevent downstream fish migration, although they can create flow conditions that injure juvenile fish. Recent studies suggest that navigation locks have potential to provide increased access for a range of biota, including poor swimmers. Though the water around weirs can ofte
Estuary
An estuary is a enclosed coastal body of brackish water with one or more rivers or streams flowing into it, with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environments, they are subject both to marine influences—such as tides and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment. The mixing of sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world. Most existing estuaries formed during the Holocene epoch with the flooding of river-eroded or glacially scoured valleys when the sea level began to rise about 10,000–12,000 years ago. Estuaries are classified according to their geomorphological features or to water-circulation patterns, they can have many different names, such as bays, lagoons, inlets, or sounds, although some of these water bodies do not meet the above definition of an estuary and may be saline.
The banks of many estuaries are amongst the most populated areas of the world, with about 60% of the world's population living along estuaries and the coast. As a result, many estuaries suffer degradation from a variety of factors including: sedimentation from soil erosion from deforestation and other poor farming practices; the word "estuary" is derived from the Latin word aestuarium meaning tidal inlet of the sea, which in itself is derived from the term aestus, meaning tide. There have been many definitions proposed to describe an estuary; the most accepted definition is: "a semi-enclosed coastal body of water, which has a free connection with the open sea, within which sea water is measurably diluted with freshwater derived from land drainage". However, this definition excludes a number of coastal water bodies such as coastal lagoons and brackish seas. A more comprehensive definition of an estuary is "a semi-enclosed body of water connected to the sea as far as the tidal limit or the salt intrusion limit and receiving freshwater runoff.
This broad definition includes fjords, river mouths, tidal creeks. An estuary is a dynamic ecosystem having a connection to the open sea through which the sea water enters with the rhythm of the tides; the sea water entering the estuary streams. The pattern of dilution varies between different estuaries and depends on the volume of fresh water, the tidal range, the extent of evaporation of the water in the estuary. Drowned river valleys are known as coastal plain estuaries. In places where the sea level is rising relative to the land, sea water progressively penetrates into river valleys and the topography of the estuary remains similar to that of a river valley; this is the most common type of estuary in temperate climates. Well-studied estuaries include the Severn Estuary in the United Kingdom and the Ems Dollard along the Dutch-German border; the width-to-depth ratio of these estuaries is large, appearing wedge-shaped in the inner part and broadening and deepening seaward. Water depths exceed 30 m.
Examples of this type of estuary in the U. S. are the Hudson River, Chesapeake Bay, Delaware Bay along the Mid-Atlantic coast, Galveston Bay and Tampa Bay along the Gulf Coast. Bar-built estuaries are found in place where the deposition of sediment has kept pace with rising sea level so that the estuaries are shallow and separated from the sea by sand spits or barrier islands, they are common in tropical and subtropical locations. These estuaries are semi-isolated from ocean waters by barrier beaches. Formation of barrier beaches encloses the estuary, with only narrow inlets allowing contact with the ocean waters. Bar-built estuaries develop on sloping plains located along tectonically stable edges of continents and marginal sea coasts, they are extensive along the Atlantic and Gulf coasts of the U. S. in areas with active coastal deposition of sediments and where tidal ranges are less than 4 m. The barrier beaches that enclose bar-built estuaries have been developed in several ways: building up of offshore bars by wave action, in which sand from the sea floor is deposited in elongated bars parallel to the shoreline, reworking of sediment discharge from rivers by wave and wind action into beaches, overwash flats, dunes, engulfment of mainland beach ridges due to sea level rise and resulting in the breaching of the ridges and flooding of the coastal lowlands, forming shallow lagoons, elongation of barrier spits from the erosion of headlands due to the action of longshore currents, with the spits growing in the direction of the littoral drift.
Barrier beaches form in shallow water and are parallel to the shoreline, resulting in long, narrow estuaries. The average water depth is less than 5 m, exceeds 10 m. Examples of bar-built estuaries are Barnegat Bay, New Jersey. Fjords were formed where pleistocene glaciers deepened and widened existing river valleys so that they become U-shaped in cross s
