In oceanography and earth sciences, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, rises from the bed of a body of water to near the surface. It refers to those submerged ridges, banks, or bars that rise near enough to the surface of a body of water as to constitute a danger to navigation. Shoals are known as sandbanks, sandbars, or gravelbars. Two or more shoals that are either separated by shared troughs or interconnected by past or present sedimentary and hydrographic processes are referred to as a shoal complex; the term shoal is used in a number of ways that can be either similar or quite different from how it is used in the geologic and oceanographic literature. Sometimes, this terms refers to either any shallow place in a stream, sea, or other body of water. Shoals are characteristically narrow ridges, they can develop where a stream, river, or ocean current promotes deposition of sediment and granular material, resulting in localized shallowing of the water.
Marine shoals develop either by the in place drowning of barrier islands as the result of episodic sea level rise or by the erosion and submergence of inactive delta lobes. Shoals can appear as a coastal landform in the sea, where they are classified as a type of ocean bank, or as fluvial landforms in rivers and lakes. A shoal–sandbar may seasonally separate a smaller body of water from the sea, such as: Marine lagoons Brackish water estuaries Freshwater seasonal stream and river mouths and deltas; the term bar can apply to landform features spanning a considerable range in size, from a length of a few metres in a small stream to marine depositions stretching for hundreds of kilometers along a coastline called barrier islands. They are composed of sand, although they could be of any granular matter that the moving water has access to and is capable of shifting around; the grain size of the material comprising a bar is related to the size of the waves or the strength of the currents moving the material, but the availability of material to be worked by waves and currents is important.
Wave shoaling is the process when surface waves move towards shallow water, such as a beach, they slow down, their wave height increases and the distance between waves decreases. This behavior is called shoaling, the waves are said to shoal; the waves may or may not build to the point where they break, depending on how large they were to begin with, how steep the slope of the beach is. In particular, waves shoal as they pass over submerged reefs; this can be treacherous for ships. Shoaling can diffract waves, so the waves change direction. For example, if waves pass over a sloping bank, shallower at one end than the other the shoaling effect will result in the waves slowing more at the shallow end, thus the wave fronts will refract. Refraction occurs as waves move towards a beach if the waves come in at an angle to the beach, or if the beach slopes more at one end than the other. Sandbars known as a trough bars, form where the waves are breaking, because the breaking waves set up a shoreward current with a compensating counter-current along the bottom.
Sometimes this occurs seaward of a trough. Sand carried by the offshore moving bottom current is deposited where the current reaches the wave break. Other longshore bars may lie further offshore, representing the break point of larger waves, or the break point at low tide. A harbor or river bar is a sedimentary deposit formed at a harbor entrance or river mouth by: the deposition of freshwater sediment, or the action of waves on the sea floor or up—current beaches. Where beaches are suitably mobile, or the river's suspended or bed loads are large enough, deposition can build up a sandbar that blocks a river mouth and damming the river, it can be a seasonally natural process of aquatic ecology, causing the formation of estuaries and wetlands in the lower course of the river. This situation will persist until the bar is eroded by the sea, or the dammed river develops sufficient head to break through the bar; the formation of harbor bars can prevent access for boats and shipping, can be the result of: construction up-coast or at the harbor — e.g.: breakwaters, dune habitat destruction.
Upriver development — e.g.: dams and reservoirs, riparian zone destruction, river bank alterations, river adjacent agricultural land practices, water diversions. Watershed erosion from habitat alterations — e.g.: deforestation, grading for development. Artificially created/deepened harbors. In a nautical sense, a bar is a shoal, similar to a reef: a shallow formation of sand, a navigation or grounding hazard, with a depth of water of 6 fathoms or less, it therefore applies to a silt accumulation that shallows the entrance to or course of a river, or creek. A bar can form a dangerous obstacle to shipping, preventing access to the river or harbour in unfavourable weather conditions or at some states of the tide. In addition to longshore bars discussed above that are small features of a beach, the term shoal can be applied to larger geological units that form off a coastline as part of the process of coastal erosion; these include spits and baymouth bars that
Rainwater harvesting is the accumulation and storage of rainwater for reuse on-site, rather than allowing it to run off. Rainwater can be collected from rivers or roofs, in many places, the water collected is redirected to a deep pit, a reservoir with percolation, or collected from dew or fog with nets or other tools, its uses include water for gardens, irrigation, domestic use with proper treatment, indoor heating for houses, etc. The harvested water can be used as drinking water, longer-term storage, for other purposes such as groundwater recharge. Rainwater harvesting is one of the simplest and oldest methods of self-supply of water for households financed by the user; the construction and use of cisterns to store rainwater can be traced back to the Neolithic Age, when waterproof lime plaster cisterns were built in the floors of houses in village locations of the Levant, a large area in Southwest Asia, south of the Taurus Mountains, bound by the Mediterranean Sea in the west, the Arabian Desert in the south, Mesopotamia in the east.
By the late 4000 BC, cisterns were essential elements of emerging water management techniques used in dry-land farming. Many ancient cisterns have been discovered in the entire Land of Israel. At the site believed by some to be that of the biblical city of Ai, a large cistern dating back to around 2500 BC was discovered that had a capacity of nearly 1,700 m3, it was carved out of solid rock, lined with large stones, sealed with clay to keep from leaking. The Greek island of Crete is known for its use of large cisterns for rainwater collection and storage during the Minoan period from 2,600 BC - 1,100 BC. Four large cisterns have been discovered at Myrtos–Pyrgos and Zakroeach; the cistern found at Myrtos-Pyrgos was found to have a capacity of more than 80 m3 and date back to 1700 BC. Around 300 BCE, farming communities in Balochistan, Kutch, used rainwater harvesting for agriculture and many other uses. Rainwater harvesting was done by Chola kings. Rainwater from the Brihadeeswarar temple was collected in Shivaganga tank.
During the Chola period, the Vīrānam tank was built in the Cuddalore district of Tamil Nadu to store water for drinking and irrigation purposes. Vīrānam is a 16-km-long tank with a storage capacity of 1,465,000,000 cu ft. Rainwater harvesting was common in the Roman Empire. While Roman Aqueducts are well-known, Roman cisterns were commonly used and their construction expanded with the Empire. For example, in Pompeii, rooftop water storage was common before the construction of the Aqueduct in the 1st century BC; this history continued for example the Basilica Cistern in Istanbul. Though little-known, for centuries the town of Venice depended on rainwater harvesting; the lagoon which surrounds Venice is brackish water, not suitable for drinking. The ancient inhabitants of Venice established a system of rainwater collection, based on man-made insulated collection wells. Water percolated down the specially designed stone flooring, was filtered by a layer of sand collected at the bottom of the well.
As Venice acquired territories on the mainland, it started to import water by boat from local rivers, but the wells remained in use, were important in time of war when access to the mainland water could be blocked by an enemy. A number of Canadians have started implementing rainwater harvesting systems for use in stormwater reduction, irrigation and lavatory plumbing. Substantial reform to Canadian law since the mid-2000s has increased the use of this technology in agricultural and residential use, but ambiguity remains amongst legislation in many provinces. Bylaws and local municipal codes regulate rainwater harvesting. Tamil Nadu was the first state to make rainwater harvesting compulsory for every building to avoid groundwater depletion; the scheme has been implemented in all rural areas of Tamil Nadu. Posters all over Tamil Nadu including rural areas create awareness about harvesting rainwater TN Govt site, it gave excellent results within five years, every state took it as a role model. Since its implementation, Chennai had a 50% rise in water level in five years and the water quality improved.
Karnataka: In Bangalore, adoption of rainwater harvesting is mandatory for every owner or the occupier of a building having the site area measuring 60 ft × 40 ft and above and for newly constructed building measuring 30 ft × 40 ft and above dimensions. In this regard, Bangalore Water Supply and Sewerage Board has initiated and constructed “Rain Water Harvesting Theme Park” in the name of Sir M. Visvesvaraya in 1.2 acres of land situated at Jayanagar, Bangalore. In this park, 26 different type of rainwater harvesting models are demonstrated along with the water conservation tips; the auditorium on the first floor is set up with a "green" air conditioning system and will be used to arrange the meeting and showing of a video clip about the rainwater harvesting to students and general public. An attempt has been made at the Department of Chemical Engineering, IISc, Bangalore to harvest rainwater using upper surface of a solar still, used for water distillation In Rajasthan, rainwater harvesting has traditionally been practised by the people of the Thar Desert.
Many ancient water harvesting systems in Rajasthan have now been revived. Water harvesting systems are used in other areas of Rajasthan, as well, for example the chauka system from the Jaip
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
Freshwater swamp forest
Freshwater swamp forests, or flooded forests, are forests which are inundated with freshwater, either permanently or seasonally. They occur along the lower reaches of rivers and around freshwater lakes. Freshwater swamp forests are found in a range of climate zones, from boreal through temperate and subtropical to tropical. In the Amazon Basin of Brazil, a seasonally flooded forest is known as a várzea, a use that now is becoming more widespread for this type of forest in the Amazon. Igapó, another word used in Brazil for flooded Amazonian forests, is sometimes used in English. Varzea refers to whitewater-inundated forest, igapó to blackwater-inundated forest. Peat swamp forests are swamp forests where waterlogged soils prevent woody debris from decomposing, which over time creates a thick layer of acidic peat. Eastern Congolian swamp forests Niger Delta swamp forests Western Congolian swamp forests. Northern New Guinea lowland rain and freshwater swamp forests Southern New Guinea freshwater swamp forests Borneo peat swamp forests Chao Phraya freshwater swamp forests Irrawaddy freshwater swamp forests Peninsular Malaysian peat swamp forests Ratargul Swamp Forest Sundarbans freshwater swamp forests in Bangladesh and India Red River freshwater swamp forests Southwest Borneo freshwater swamp forests Tonle Sap-Mekong peat swamp forests Wathurana freshwater swamp forest Myristica swamp Nelapattu Bird Sanctuary Cantão igapó forest Gurupa várzea Iquitos várzea Marajó várzea Monte Alegre várzea Orinoco Delta swamp forests Pantanos de Centla Paramaribo swamp forests Purus várzea Coniferous swamp forest
Soil conservation is the prevention of soil loss from erosion or prevention of reduced fertility caused by over usage, salinization or other chemical soil contamination. Slash-and-burn and other unsustainable methods of subsistence farming are practiced in some lesser developed areas. A sequel to the deforestation is large scale erosion, loss of soil nutrients and sometimes total desertification. Techniques for improved soil conservation include crop rotation, cover crops, conservation tillage and planted windbreaks, affect both erosion and fertility; when plants trees, die they decay and become part of the soil. Code 330 defines standard methods recommended by the U. S. Natural Resources Conservation Service. Farmers have practiced soil conservation for millennia. In Europe, policies such as the Common Agricultural Policy are targeting the application of best management practices such as reduced tillage, winter cover crops, plant residues and grass margins in order to better address the soil conservation.
Political and economic action is further required to solve the erosion problem. A simple governance hurdle concerns how we name and value the land and what we call it and this can be changed by cultural adaptation. Contour ploughing orients furrows following the contour lines of the farmed area. Furrows move right to maintain a constant altitude, which reduces runoff. Contour ploughing was practiced by the ancient Phoenicians, is effective for slopes between two and ten percent. Contour ploughing can increase crop yields from 10 to 50 percent as a result of greater soil retention. Terracing is the practice of creating nearly level areas in a hillside area; the terraces form a series of each at a higher level than the previous. Terraces are protected from erosion by other soil barriers. Terraced farming is more common on small farms and in underdeveloped countries, since mechanized equipment is difficult to deploy in this setting. Keyline design is an enhancement of contour farming, where the total watershed properties are taken into account in forming the contour lines.
Tree and ground-cover are effective perimeter treatment for soil erosion prevention, by impeding surface flows. A special form of this perimeter or inter-row treatment is the use of a “grass way” that both channels and dissipates runoff through surface friction, impeding surface runoff and encouraging infiltration of the slowed surface water. Windbreaks are sufficiently dense rows of trees at the windward exposure of an agricultural field subject to wind erosion. Evergreen species provide year-round protection. Cover crops such as legumes plant, white turnip and other species are rotated with cash crops to blanket the soil year-round and act as green manure that replenishes nitrogen and other critical nutrients. Cover crops help suppress weeds. Soil-conservation farming involves no-till farming, “green manures” and other soil-enhancing practices; such farming methods attempt to mimic the biology of barren lands. They can revive damaged soil, minimize erosion, encourage plant growth, eliminate the use of nitrogen fertilizer or fungicide, produce above-average yields and protect crops during droughts or flooding.
The result is lower costs that increase farmers' profits. No-till farming and cover crops act as sinks for nitrogen and other nutrients; this increases the amount of soil organic matter. Repeated plowing/tilling degrades soil, killing its beneficial earthworms. Once damaged, soil may take multiple seasons to recover in optimal circumstances. Critics argue that no-till and related methods are impractical and too expensive for many growers because it requires new equipment, they cite advantages for conventional tilling depending on the geography and soil conditions. Some farmers claimed that no-till complicates weed control, delays planting and that post-harvest residues for corn, are hard to manage. Salinity in soil is caused by irrigating with salty water. Water evaporates from the soil leaving the salt behind. Salt breaks down causing infertility and reduced growth; the ions responsible for salination are: sodium, calcium and chlorine. Salinity is estimated to affect about one third of the earth’s arable land.
Soil salinity adversely affects crop metabolism and erosion follows. Salinity occurs in areas with shallow saline water tables. Over-irrigation deposits salts in upper soil layers as a byproduct of soil infiltration; the best-known case of shallow saline water table capillary action occurred in Egypt after the 1970 construction of the Aswan Dam. The change in the groundwater level led to high salt concentrations in the water table; the continuous high level of the water table led to soil salination. Use of humic acids may prevent excess salination given excessive irrigation. Humic acids can eliminate them from root zones. Planting species that can tolerate saline conditions can be used to lower water tables and thus reduce the rate of capillary and evaporative enrichment of surface salts. Salt-tolerant plants include saltbush, a plant found in much of North America and in the Mediterranean regions of Europe; when worms excrete egesta in the form of casts, a balanced selection of minerals and plant nutrients is made into a form accessible for root uptake.
Earthworm casts are five times richer in available nitrogen, seven times richer in available phosphates and eleven times richer in available potash than the surroundi
The Atchafalaya Basin, or Atchafalaya Swamp, is the largest wetland and swamp in the United States. Located in south central Louisiana, it is a combination of wetlands and river delta area where the Atchafalaya River and the Gulf of Mexico converge; the river stretches from near Simmesport in the north through parts of eight parishes to the Morgan City southern area. The Atchafalaya is different among Louisiana basins because it has a growing delta system with wetlands that are stable; the basin contains about 30 % marsh and open water. It contains the largest contiguous block of forested wetlands remaining in the lower Mississippi River valley and the largest block of floodplain forest in the United States. Best known for its iconic cypress-tupelo swamps, at 260,000 acres, this block of forest represents the largest remaining contiguous tract of coastal cypress in the US; the Atchafalaya Basin and the surrounding plain of the Atchafalaya River is filled with bayous, bald cypress swamps, marshes, which give way to brackish estuarine conditions, end in the Spartina grass marshes where the Atchafalaya River meets the Gulf of Mexico.
It includes the Lower Atchafalaya River, Wax Lake Outlet, Atchafalaya Bay, the Atchafalaya River and bayous Chêne, Black navigation channel. See maps and photo views of the Atchafalaya Deltas centered on 29°26′30″N 91°25′00″W; the Basin, susceptible to long periods of deep flooding, is sparsely inhabited. The Basin is about 20 miles in width from east 150 miles in length; the Basin is the largest existing wetland in the United States with an area of 1,400,000 acres, including the surrounding swamps outside of the levees that were connected to the Basin. The Basin contains nationally significant expanses of bottomland hardwoods, swamplands and back-water lakes; the Basin's thousands of acres of forest and farmland are home to the Louisiana black bear, on the United States Fish and Wildlife Service threatened list since 1992. The few roads that cross the Basin follow the tops of levees. Interstate 10 crosses the basin on elevated pillars on a continuous 18.2 mile bridge from Grosse Tete, Louisiana, to Henderson, near the Whiskey River Pilot Channel at 30°21′50″N 91°38′00″W.
The Atchafalaya National Wildlife Refuge was established in 1984 to improve plant communities for endangered and declining species of wildlife, migratory birds and alligators. The Atchafalaya Basin has a long relationship with the Mississippi River throughout the Holocene epoch, the geology of the modern basin is a direct manifestation of that relationship; the Atchafalaya Basin has been part of three historic depositional lobes of the Mississippi River Delta Plain that formed south Louisiana, active delta lobe development is occurring at the mouth of the Atchafalaya River and Wax Lake Outlet. The geology of the current basin has been driven by flows of Atchafalaya River water and sediment that flowed into open water areas through relict Mississippi River distributary channels; the Atchafalaya Basin contains lacustrine and coastal delta landscapes. Natural filling of the basin with sediment was accentuated with the building of the flood control levees that were completed in the 1940s. After the levees, sediment was directed into an area about one-third the size of the original basin.
An example of the lacustrine delta development can be seen at Lake Fausse Pointe State Park, where levees severed the connection between the Grand Bayou distributary and the lake, delta development was frozen in time. Geologically, the Atchafalaya River has been a backswamp, low area between the paths of the Mississippi River through the process of delta switching, which has built the extensive delta plain of Louisiana; the natural levees of the Mississippi River and the levees along its previous course on the west define the Atchafalaya Basin. The central basin is further bordered by man-made levees designed to contain and funnel floodwaters released from the Mississippi at the Old River Control Structure and the Morganza Spillway south toward Morgan City and to the Gulf of Mexico. There were small and few channel connections to the Mississippi River; the historic lack of significant channel connection indicates that the Atchafalaya River Basin did not receive significant sediment from the Mississippi except during large floods.
During the mid-19th century, manmade channel alterations, including the removal of a large log jam and dredging, permanently connected the Atchafalaya River to the Mississippi River. From until the completion of the Old River Control Structure in 1963, the Mississippi was diverting flow into the shorter and steeper path of the Atchafalaya channel. By law, a regulated 30 percent of the latitudinal flow water from the Mississippi and Black rivers is diverted into the Atchafalaya at the Old River Control Structure; this flow diverts on average 25 percent of the Mississippi River flow down the Atchafalaya. In times of extreme flooding, the US Army Corps of Engineers may open the Morganza Spillway and other spillways to relieve pressure on levees and control structures along the Mississippi. On May 13, 2011, in the face of a rising Mississippi River that threatened to flood New Orleans and other populated parts of Louisiana, the USACE ordered the Morganza Spillway opened for the first time since 1973.
This water floods the Atchafalaya Basin between the levees along the western and eastern limits of the Morganza and Atchafalaya basin fl
A constructed wetland is an artificial wetland to treat municipal or industrial wastewater, greywater or stormwater runoff. It may be designed for land reclamation after mining, or as a mitigation step for natural areas lost to land development. Constructed wetlands are engineered systems that use natural functions vegetation and organisms to treat wastewater. Depending on the type of wastewater the design of the constructed wetland has to be adjusted accordingly. Constructed wetlands have been used to treat both on-site wastewater. Primary treatment is recommended when there is a large amount of suspended solids or soluble organic matter. To natural wetlands, constructed wetlands act as a biofilter and/or can remove a range of pollutants from the water. Constructed wetlands are a sanitation technology that have not been designed for pathogen removal, but instead, have been designed to remove other water quality constituents such as suspended solids, organic matter and nutrients. All types of pathogens are expected to be removed to some extent in a constructed wetland.
Subsurface wetland provide greater pathogen removal than surface wetlands. There are two main types of constructed wetlands: subsurface flow and surface flow constructed wetlands; the planted vegetation plays an important role in contaminant removal. The filter bed, consisting of sand and gravel, has an important role to play; some constructed wetlands may serve as a habitat for native and migratory wildlife, although, not their main purpose. Subsurface flow constructed wetlands are designed to have either horizontal flow or vertical flow of water through the gravel and sand bed. Vertical flow systems have a smaller space requirement than horizontal flow systems. Many terms are used to denote constructed wetlands, such as reed beds, soil infiltration beds, treatment wetlands, engineered wetlands, man-made or artificial wetlands. A biofilter has some similarities with a constructed wetland, but is without plants; the term of constructed wetlands can be used to describe restored and recultivated land, destroyed in the past through draining and converting into farmland, or mining.
A constructed wetland is an engineered sequence of water bodies designed to filter and treat waterborne pollutants found in sewage, industrial effluent or storm water runoff. Constructed wetlands are used for greywater treatment, they can be used after a septic tank for primary treatment in order to separate the solids from the liquid effluent. Some constructed wetland designs however do not use upfront primary treatment. Vegetation in a wetland provides a substrate upon which microorganisms can grow as they break down organic materials; this community of microorganisms is known as the periphyton. The periphyton and natural chemical processes are responsible for 90 percent of pollutant removal and waste breakdown; the plants remove about seven to ten percent of pollutants, act as a carbon source for the microbes when they decay. Different species of aquatic plants have different rates of heavy metal uptake, a consideration for plant selection in a constructed wetland used for water treatment. Constructed wetlands are of two basic types: surface flow wetlands.
Constructed wetlands are one example of nature-based solutions and of phytoremediation. Many regulatory agencies list treatment wetlands as one of their recommended "best management practices" for controlling urban runoff. Physical and biological processes combine in wetlands to remove contaminants from wastewater. An understanding of these processes is fundamental not only to designing wetland systems but to understanding the fate of chemicals once they enter the wetland. Theoretically, wastewater treatment within a constructed wetland occurs as it passes through the wetland medium and the plant rhizosphere. A thin film around each root hair is aerobic due to the leakage of oxygen from the rhizomes and rootlets. Aerobic and anaerobic micro-organisms facilitate decomposition of organic matter. Microbial nitrification and subsequent denitrification releases nitrogen as gas to the atmosphere. Phosphorus is coprecipitated with iron and calcium compounds located in the root-bed medium. Suspended solids filter out as they settle in the water column in surface flow wetlands or are physically filtered out by the medium within subsurface flow wetlands.
Harmful bacteria and viruses are reduced by filtration and adsorption by biofilms on the gravel or sand media in subsurface flow and vertical flow systems. The dominant forms of nitrogen in wetlands that are of importance to wastewater treatment include organic nitrogen, ammonium and nitrite. Total nitrogen refers to all nitrogen species. Wastewater nitrogen removal is important because of ammonia’s toxicity to fish if discharged into watercourses. Excessive nitrates in drinking water is thought to cause methemoglobinemia in infants, which decreases the blood's oxygen transport ability. Moreover, excess input of N from point and non-point sources to surface water promotes eutrophication in rivers, lakes and coastal oceans which causes several problems in aquatic ecosystems e.g. toxic algal blooms, oxygen depletion in water, fish mortality, loss of aquatic biodiversity. Ammonia removal occurs in constructed wetlands – if they are designed to achieve biological nutrient removal – in a similar ways as in sewage treatment plants, except that no external, energy-intensive addition of air is needed.
It is a