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60-504: Dyke Marsh is a freshwater wetland and wildlife preserve located on the west bank of the Potomac River south of Alexandria , Virginia between Old Town Alexandria and Mount Vernon . Dyke Marsh consists of about 380 acres (1.5 km) of tidal marsh , floodplain , and swamp forest. It formed 5,000 to 7,000 years ago. With a total size of 485 acres, Dyke Marsh is one of the largest remaining pieces of freshwater tidal wetlands left in

120-412: A beaver population is visible along the "Haul Road" and muskrat have been spotted numerous times. Little brown bats and red fox can be seen at night. Cottontail rabbit , gray squirrels , shrews , and field mice (the vole ) can also be found in and around the marsh. The most obvious inhabitant of Dyke Marsh is the red-winged blackbird , with its distinct call. The red-winged blackbird nests among

180-711: A sink or a source of carbon, depending on the specific wetland. If they function as a carbon sink, they can help with climate change mitigation . However, wetlands can also be a significant source of methane emissions due to anaerobic decomposition of soaked detritus , and some are also emitters of nitrous oxide . Humans are disturbing and damaging wetlands in many ways, including oil and gas extraction , building infrastructure, overgrazing of livestock , overfishing , alteration of wetlands including dredging and draining, nutrient pollution , and water pollution . Wetlands are more threatened by environmental degradation than any other ecosystem on Earth, according to

240-477: A floating mat. The erect stems grow to 2–4 m ( 6 + 1 ⁄ 2 –13 ft) tall, with the tallest plants growing in areas with hot summers and fertile growing conditions. The leaves are 18–60 centimetres (7– 23 + 1 ⁄ 2  in) long and 1–6 cm ( 1 ⁄ 2 – 2 + 1 ⁄ 4  in) broad. The flowers are produced in late summer in a dense, dark purple panicle , about 15–40 cm (6– 15 + 1 ⁄ 2  in) long. Later

300-402: A frequency and duration to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally included swamps, marshes, bogs, and similar areas.' For each of these definitions and others, regardless of the purpose, hydrology is emphasized (shallow waters, water-logged soils). The soil characteristics and

360-486: A high above ground biomass that blocks light to other plants allowing areas to turn into Phragmites monoculture very quickly. Decomposing Phragmites increases the rate of marsh accretion more rapidly than would occur with native marsh vegetation. Phragmites australis subsp. australis is causing serious problems for many other North American hydrophyte wetland plants, including the native P. australis subsp. americanus . Gallic acid released by phragmites

420-1248: A polar climate, wetland temperatures can be as low as −50 °C (−58 °F). Peatlands in arctic and subarctic regions insulate the permafrost , thus delaying or preventing its thawing during summer, as well as inducing its formation. The amount of precipitation a wetland receives varies widely according to its area. Wetlands in Wales , Scotland , and western Ireland typically receive about 1,500 mm (59 in) per year. In some places in Southeast Asia , where heavy rains occur, they can receive up to 10,000 mm (390 in). In some drier regions, wetlands exist where as little as 180 mm (7.1 in) precipitation occurs each year. Temporal variation: Surface flow may occur in some segments, with subsurface flow in other segments. Wetlands vary widely due to local and regional differences in topography , hydrology , vegetation , and other factors, including human involvement. Other important factors include fertility, natural disturbance, competition, herbivory , burial and salinity. When peat accumulates, bogs and fens arise. The most important factor producing wetlands

480-540: A portion of the overall water cycle, which also includes atmospheric water (precipitation) and groundwater . Many wetlands are directly linked to groundwater and they can be a crucial regulator of both the quantity and quality of water found below the ground. Wetlands that have permeable substrates like limestone or occur in areas with highly variable and fluctuating water tables have especially important roles in groundwater replenishment or water recharge. Substrates that are porous allow water to filter down through

540-400: A protective barrier to coastal shoreline. Mangroves stabilize the coastal zone from the interior and will migrate with the shoreline to remain adjacent to the boundary of the water. The main conservation benefit these systems have against storms and storm surges is the ability to reduce the speed and height of waves and floodwaters. Common reed Phragmites australis , known as

600-589: A separate species, P. americanus ), is markedly less vigorous than European forms. The expansion of Phragmites in North America is due to the more vigorous, but similar-looking European subsp. australis . Phragmites australis subsp. australis outcompetes native vegetation and lowers the local plant biodiversity . It forms dense thickets of vegetation that are unsuitable habitat for native fauna . It displaces native plants species such as wild rice , cattails , and native orchids . Phragmites has

660-422: A strong influence on wetland water chemistry, particularly in coastal wetlands and in arid and semiarid regions with large precipitation deficits. Natural salinity is regulated by interactions between ground and surface water, which may be influenced by human activity. Carbon is the major nutrient cycled within wetlands. Most nutrients, such as sulfur , phosphorus , carbon , and nitrogen are found within

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720-410: A unique kind of wetland where lush plant growth and slow decay of dead plants (under anoxic conditions) results in organic peat accumulating; bogs, fens, and mires are different names for peatlands. Variations of names for wetland systems: Some wetlands have localized names unique to a region such as the prairie potholes of North America's northern plain, pocosins , Carolina bays and baygalls of

780-471: A weekly basis on the Mount Vernon Trail. Just off of the trail, there is a sitting area on a boardwalk over the marsh. The interior path is J-shaped and goes south from the marina entrance and then turns east onto a peninsula. Birdwatchers, animal lovers, and nature enthusiasts often visit the sitting area in an effort to catch a glimpse of what Dyke Marsh has to offer. Visitors also come at night to watch

840-508: A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota, particularly rooted plants, to adapt to flooding". Sometimes a precise legal definition of a wetland is required. The definition used for regulation by the United States government is: 'The term "wetlands" means those areas that are inundated or saturated by surface or ground water at

900-422: A wetland system includes its plants ( flora ) and animals ( fauna ) and microbes (bacteria, fungi). The most important factor is the wetland's duration of flooding. Other important factors include fertility and salinity of the water or soils. The chemistry of water flowing into wetlands depends on the source of water, the geological material that it flows through and the nutrients discharged from organic matter in

960-403: A wetland) affects hydro-periods (temporal fluctuations in water levels) by controlling the water balance and water storage within a wetland. Landscape characteristics control wetland hydrology and water chemistry. The O 2 and CO 2 concentrations of water depend upon temperature , atmospheric pressure and mixing with the air (from winds or water flows). Water chemistry within wetlands

1020-558: A whole. To replace these wetland ecosystem services , enormous amounts of money would need to be spent on water purification plants, dams, levees, and other hard infrastructure, and many of the services are impossible to replace. Floodplains and closed-depression wetlands can provide the functions of storage reservoirs and flood protection. The wetland system of floodplains is formed from major rivers downstream from their headwaters . "The floodplains of major rivers act as natural storage reservoirs, enabling excess water to spread out over

1080-577: A wide area, which reduces its depth and speed. Wetlands close to the headwaters of streams and rivers can slow down rainwater runoff and spring snowmelt so that it does not run straight off the land into water courses. This can help prevent sudden, damaging floods downstream." Notable river systems that produce wide floodplains include the Nile River , the Niger river inland delta, the Zambezi River flood plain,

1140-499: Is associated with larger methane emissions and greater carbon dioxide uptake than native New England salt marsh vegetation that occurs at higher marsh elevations. Common reed is suppressed where it is grazed regularly by livestock . Under these conditions it either grows as small shoots within the grassland sward, or it disappears altogether. In Europe , common reed is rarely invasive, except in damp grasslands where traditional grazing has been abandoned. In North America ,

1200-417: Is degraded by ultraviolet light to produce mesoxalic acid , effectively hitting susceptible plants and seedlings with two harmful toxins. Phragmites is so difficult to control that one of the most effective methods of eradicating the plant is to burn it over 2–3 seasons. The roots grow so deep and strong that one burn is not enough. Ongoing research suggests that goats could be effectively used to control

1260-440: Is determined by the pH , salinity , nutrients, conductivity , soil composition, hardness , and the sources of water. Water chemistry varies across landscapes and climatic regions. Wetlands are generally minerotrophic (waters contain dissolved materials from soils) with the exception of ombrotrophic bogs that are fed only by water from precipitation. Because bogs receive most of their water from precipitation and humidity from

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1320-412: Is hydrology, or flooding . The duration of flooding or prolonged soil saturation by groundwater determines whether the resulting wetland has aquatic, marsh or swamp vegetation . Other important factors include soil fertility, natural disturbance, competition, herbivory , burial, and salinity. When peat from dead plants accumulates, bogs and fens develop. Wetland hydrology is associated with

1380-510: Is some overlap in this character), and in culm characteristics. It is a helophyte ( aquatic plant ), especially common in alkaline habitats, and it also tolerates brackish water, and so is often found at the upper edges of estuaries and on other wetlands (such as grazing marsh ) which are occasionally inundated by the sea. A study demonstrated that P. australis has similar greenhouse gas emissions to native Spartina alterniflora . However, other studies have demonstrated that it

1440-416: Is the dominant species in the area. It normally develops its characteristic flower spike by June. Many other species of plant occupy the marsh including several types of Sagittaria , arrow arum, pickerelweed, sweetflag, spatter-pond lily, and northern wild rice . The rice attracts animals such as the red-winged blackbird and waterfowl . Dyke Marsh is much different than it used to be. It is estimated that

1500-451: Is the only place in the world where both crocodiles and alligators coexist. The saltwater crocodile inhabits estuaries and mangroves. Snapping turtles also inhabit wetlands. Birds , particularly waterfowl and waders use wetlands extensively. Mammals of wetlands include numerous small and medium-sized species such as voles , bats , muskrats and platypus in addition to large herbivorous and apex predator species such as

1560-545: Is usually saturated with water". More precisely, wetlands are areas where "water covers the soil , or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season". A patch of land that develops pools of water after a rain storm would not necessarily be considered a "wetland", even though the land is wet. Wetlands have unique characteristics: they are generally distinguished from other water bodies or landforms based on their water level and on

1620-693: The Baltimore-Washington Metropolitan Area . The marsh is managed by the National Park Service as part of the George Washington Memorial Parkway . Dyke Marsh contains a wide array of plant and animal life. "Haul Road" is a trail that leads visitors into the marsh. It is frequented by area birdwatchers. Dyke Marsh is located off the George Washington Memorial Parkway at the Belle Haven Marina exit. Here

1680-492: The Millennium Ecosystem Assessment from 2005. Methods exist for assessing wetland ecological health . These methods have contributed to wetland conservation by raising public awareness of the functions that wetlands can provide. Since 1971, work under an international treaty seeks to identify and protect " wetlands of international importance ." A simplified definition of wetland is "an area of land that

1740-740: The Mississippi River Delta , and the die-off of reed beds is believed to accelerate coastal erosion . The entire plant is edible raw or cooked. The young stems can be boiled, or later on be used to make flour. The underground stems can be used but are tough, as can the seeds but they are hard to find. Stems can be made into eco-friendly drinking straws . Many parts of the plant can be eaten. The young shoots can be consumed raw or cooked. The hardened sap from damaged stems can be eaten fresh or toasted. The stems can be dried, ground, sifted, hydrated, and toasted like marshmallows. The seeds can be crushed, mixed with berries and water, and cooked to make

1800-666: The Pantanal in South America, and the Sundarbans in the Ganges - Brahmaputra delta. Wetlands contribute many ecosystem services that benefit people. These include for example water purification , stabilization of shorelines, storm protection and flood control . In addition, wetlands also process and condense carbon (in processes called carbon fixation and sequestration ), and other nutrients and water pollutants . Wetlands can act as

1860-444: The atmosphere , their water usually has low mineral ionic composition. In contrast, wetlands fed by groundwater or tides have a higher concentration of dissolved nutrients and minerals. Fen peatlands receive water both from precipitation and ground water in varying amounts so their water chemistry ranges from acidic with low levels of dissolved minerals to alkaline with high accumulation of calcium and magnesium . Salinity has

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1920-576: The beavers , coypu , swamp rabbit , Florida panther , jaguar , and moose . Wetlands attract many mammals due to abundant seeds, berries, and other vegetation as food for herbivores, as well as abundant populations of invertebrates, small reptiles and amphibians as prey for predators. Invertebrates of wetlands include aquatic insects such as dragonflies , aquatic bugs and beetles , midges, mosquitos , crustaceans such as crabs, crayfish, shrimps, microcrustaceans, mollusks like clams, mussels, snails and worms. Invertebrates comprise more than half of

1980-585: The cattails and feeds on insects and seeds. Nearly 300 species of birds have been seen in Dyke Marsh. It is known as one of the best birdwatching sites in the Washington Metropolitan Area . The lower Potomac is a natural migration route, especially for water birds. In 2014 a beetle species, Pterostichus sculptus , new to Virginia was discovered at Dyke Marsh. More than 360 species of plants have been found at Dyke Marsh. The narrow-leafed cattail

2040-624: The common reed , is a species of flowering plant in the grass family Poaceae . It is a wetland grass that can grow up to 20 feet (6 metres) tall and has a cosmopolitan distribution worldwide. Phragmites australis commonly forms extensive stands (known as reed beds ), which may be as much as 1 square kilometre (0.39 square miles) or more in extent. Where conditions are suitable it can also spread at 5 metres (16 feet) or more per year by horizontal runners , which put down roots at regular intervals. It can grow in damp ground, in standing water up to 1 m (3 ft 3 in) or so deep, or even as

2100-576: The Asian porcelain berry , Japanese honeysuckle , and Asiatic bittersweet have begun smothering parts of the floodplain forest. Yellow iris and the common reed are exotic plants that now inhabit the actual marsh. Efforts are being made to prevent the introduction of the purple loosestrife . Dyke Marsh is just east of the George Washington Memorial Parkway and the Mount Vernon Trail . Thousands of bicyclists, walkers, and runners go through Dyke Marsh on

2160-619: The Okavango River inland delta, the Kafue River flood plain, the Lake Bangweulu flood plain (Africa), Mississippi River (US), Amazon River (South America), Yangtze River (China), Danube River (Central Europe) and Murray-Darling River (Australia). Groundwater replenishment can be achieved for example by marsh , swamp , and subterranean karst and cave hydrological systems. The surface water visibly seen in wetlands only represents

2220-511: The Southeastern US, mallines of Argentina, Mediterranean seasonal ponds of Europe and California, turloughs of Ireland, billabongs of Australia, among many others. Wetlands are found throughout the world in different climates. Temperatures vary greatly depending on the location of the wetland. Many of the world's wetlands are in the temperate zones , midway between the North or South Poles and

2280-494: The US, the best known classifications are the Cowardin classification system and the hydrogeomorphic (HGM) classification system. The Cowardin system includes five main types of wetlands: marine (ocean-associated), estuarine (mixed ocean- and river-associated), riverine (within river channels), lacustrine (lake-associated) and palustrine (inland nontidal habitats). Peatlands are

2340-610: The United States' commercial fish and shellfish stocks depend solely on estuaries to survive. Amphibians such as frogs and salamanders need both terrestrial and aquatic habitats in which to reproduce and feed. Because amphibians often inhabit depressional wetlands like prairie potholes and Carolina bays, the connectivity among these isolated wetlands is an important control of regional populations. While tadpoles feed on algae, adult frogs forage on insects. Frogs are sometimes used as an indicator of ecosystem health because their thin skin permits absorption of nutrients and toxins from

2400-622: The equator. In these zones, summers are warm and winters are cold, but temperatures are not extreme. In subtropical zone wetlands, such as along the Gulf of Mexico , average temperatures might be 11 °C (52 °F). Wetlands in the tropics are subjected to much higher temperatures for a large portion of the year. Temperatures for wetlands on the Arabian Peninsula can exceed 50 °C (122 °F) and these habitats would therefore be subject to rapid evaporation. In northeastern Siberia , which has

2460-882: The fireflies in the marsh and trees. 38°46′04″N 77°02′55″W  /  38.76778°N 77.04861°W  / 38.76778; -77.04861 Wetland Wetlands exist on every continent , except Antarctica . The water in wetlands is either freshwater , brackish or saltwater . The main types of wetland are defined based on the dominant plants and the source of the water. For example, marshes are wetlands dominated by emergent herbaceous vegetation such as reeds , cattails and sedges . Swamps are dominated by woody vegetation such as trees and shrubs (although reed swamps in Europe are dominated by reeds, not trees). Mangrove forest are wetlands with mangroves , halophytic woody plants that have evolved to tolerate salty water . Examples of wetlands classified by

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2520-494: The following areas: According to the Ramsar Convention: The economic worth of the ecosystem services provided to society by intact, naturally functioning wetlands is frequently much greater than the perceived benefits of converting them to 'more valuable' intensive land use – particularly as the profits from unsustainable use often go to relatively few individuals or corporations, rather than being shared by society as

2580-481: The fresh water of the upper Potomac mixes with the salt water of the lower Potomac. The fresh water tends to float above the tidal salt water producing a tidal freshwater marsh. Dyke Marsh got its name because it was within a dike at one point. Earthen walls were built around the perimeter of the marsh in the 19th century to create more "fast land," land not inundated by tides . This land was used for farming purposes, mainly to graze livestock or to grow crops. One of

2640-464: The interface between truly terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet highly dependent on both." In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions. Under the Ramsar international wetland conservation treaty , wetlands are defined as follows: An ecological definition of

2700-462: The known animal species in wetlands, and are considered the primary food web link between plants and higher animals (such as fish and birds). Depending on a wetland's geographic and topographic location, the functions it performs can support multiple ecosystem services , values, or benefits. United Nations Millennium Ecosystem Assessment and Ramsar Convention described wetlands as a whole to be of biosphere significance and societal importance in

2760-546: The marsh once consisted of 650 acres (2.6 km). In the 1950s and 1960s, dredging took place, which reduced it to its current size and configuration. Shoreline erosion is noticeable along the Haul Road, showing that the dredging is still making an impact. Human influences have also led to the introduction of several types of exotic, or non-native, plants to the marsh. These plants are very opportunistic and often outcompete beneficial native species of plants. Exotic vines, such as

2820-652: The numerous long, narrow, sharp pointed spikelets appear greyer due to the growth of long, silky hairs. These eventually help disperse the minute seeds. Recent studies have characterized morphological distinctions between the introduced and native stands of Phragmites australis in North America. The Eurasian phenotype can be distinguished from the North American phenotype by its shorter ligules of up to 0.9 millimetres ( 1 ⁄ 32  in) as opposed to over 1 mm, shorter glumes of under 3.2 mm ( 1 ⁄ 8  in) against over 3.2 mm (although there

2880-594: The oldest photographs of Dyke Marsh is a circa 1909 picture postcard created for the Alexandria-Mt. Vernon trolley line (whose light rail tracks were replaced by the George Washington Memorial Parkway in 1932.) The photograph is labelled: The "Dyke," a favorite resort for fishermen and hunters on the line of the Mt. Vernon Railroad, near Alexandria, Va . Dyke Marsh has an abundance of wildlife. Evidence of

2940-832: The plants and animals controlled by the wetland hydrology are often additional components of the definitions. Wetlands can be tidal (inundated by tides) or non-tidal. The water in wetlands is either freshwater , brackish , saline , or alkaline . There are four main kinds of wetlands – marsh , swamp , bog , and fen (bogs and fens being types of peatlands or mires ). Some experts also recognize wet meadows and aquatic ecosystems as additional wetland types. Sub-types include mangrove forests , carrs , pocosins , floodplains , peatlands, vernal pools , sinks , and many others. The following three groups are used within Australia to classify wetland by type: Marine and coastal zone wetlands, inland wetlands and human-made wetlands. In

3000-429: The soil and underlying rock into aquifers which are the source of much of the world's drinking water . Wetlands can also act as recharge areas when the surrounding water table is low and as a discharge zone when it is high. Mangroves , coral reefs , salt marsh can help with shoreline stabilization and storm protection. Tidal and inter-tidal wetland systems protect and stabilize coastal zones. Coral reefs provide

3060-537: The soil of wetlands. Anaerobic and aerobic respiration in the soil influences the nutrient cycling of carbon, hydrogen, oxygen, and nitrogen, and the solubility of phosphorus thus contributing to the chemical variations in its water. Wetlands with low pH and saline conductivity may reflect the presence of acid sulfates and wetlands with average salinity levels can be heavily influenced by calcium or magnesium. Biogeochemical processes in wetlands are determined by soils with low redox potential. The life forms of

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3120-412: The soils and plants at higher elevations. Plants and animals may vary within a wetland seasonally or in response to flood regimes. There are four main groups of hydrophytes that are found in wetland systems throughout the world. Submerged wetland vegetation can grow in saline and fresh-water conditions. Some species have underwater flowers, while others have long stems to allow the flowers to reach

3180-515: The sources of water include tidal wetlands , where the water source is ocean tides ); estuaries , water source is mixed tidal and river waters; floodplains , water source is excess water from overflowed rivers or lakes; and bogs and vernal ponds , water source is rainfall or meltwater . The world's largest wetlands include the Amazon River basin , the West Siberian Plain ,

3240-406: The spatial and temporal dispersion, flow, and physio-chemical attributes of surface and ground waters. Sources of hydrological flows into wetlands are predominantly precipitation , surface water (saltwater or freshwater), and groundwater. Water flows out of wetlands by evapotranspiration , surface flows and tides , and subsurface water outflow. Hydrodynamics (the movement of water through and from

3300-536: The species. Since 2017, over 80% of the beds of Phragmites in the Pass a Loutre Wildlife Management Area have been damaged by the invasive roseau cane scale ( Nipponaclerda biwakoensis ), threatening wildlife habitat throughout the affected regions of the area. While typically considered a noxious weed, in Louisiana the reed beds are considered critical to the stability of the shorelines of wetland areas and waterways of

3360-442: The status of Phragmites australis australis is a source of confusion and debate. It is commonly considered a non-native and often invasive species , introduced from Europe in the 1800s. However, there is evidence of the existence of Phragmites as a native plant in North America long before European colonization of the continent. The North American native subspecies, P. a.  subsp. americanus (sometimes considered

3420-709: The surface of the water. When trees and shrubs comprise much of the plant cover in saturated soils, those areas in most cases are called swamps . The upland boundary of swamps is determined partly by water levels. This can be affected by dams Some swamps can be dominated by a single species, such as silver maple swamps around the Great Lakes . Others, like those of the Amazon basin , have large numbers of different tree species. Other examples include cypress ( Taxodium ) and mangrove swamps. Many species of fish are highly dependent on wetland ecosystems. Seventy-five percent of

3480-490: The surface. Submerged species provide a food source for native fauna, habitat for invertebrates, and also possess filtration capabilities. Examples include seagrasses and eelgrass . Floating water plants or floating vegetation are usually small, like those in the Lemnoideae subfamily (duckweeds). Emergent vegetation like the cattails ( Typha spp.), sedges ( Carex spp.) and arrow arum ( Peltandra virginica ) rise above

3540-457: The surrounding environment resulting in increased extinction rates in unfavorable and polluted environmental conditions. Reptiles such as snakes , lizards , turtles , alligators and crocodiles are common in wetlands of some regions. In freshwater wetlands of the Southeastern US, alligators are common and a freshwater species of crocodile occurs in South Florida. The Florida Everglades

3600-440: The types of plants that live within them. Specifically, wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants . A more concise definition is a community composed of hydric soil and hydrophytes . Wetlands have also been described as ecotones , providing a transition between dry land and water bodies. Wetlands exist "...at

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