Wetland | Wikipedia audio article


A wetland is a distinct ecosystem that is
inundated by water, either permanently or seasonally, where oxygen-free processes prevail.
The primary factor that distinguishes wetlands from other land forms or water bodies is the
characteristic vegetation of aquatic plants, adapted to the unique hydric soil. Wetlands
play a number of functions, including water purification, water storage, processing of
carbon and other nutrients, stabilization of shorelines, and support of plants and animals.
Wetlands are also considered the most biologically diverse of all ecosystems, serving as home
to a wide range of plant and animal life. Whether any individual wetland performs these
functions, and the degree to which it performs them, depends on characteristics of that wetland
and the lands and waters near it. Methods for rapidly assessing these functions, wetland
ecological health, and general wetland condition have been developed in many regions and have
contributed to wetland conservation partly by raising public awareness of the functions
and the ecosystem services some wetlands provide.Wetlands occur naturally on every continent. The main
wetland types are swamp, marsh, bog, and fen; sub-types include mangrove forest, carr, pocosin,
floodplains, mire, vernal pool, sink, and many others. Many peatlands are wetlands.
The water in wetlands is either freshwater, brackish, or saltwater.
Wetlands can be tidal (inundated by tides) or non-tidal. The largest wetlands include
the Amazon River basin, the West Siberian Plain, the Pantanal in South America, and
the Sundarbans in the Ganges-Brahmaputra delta.The UN Millennium Ecosystem Assessment determined
that environmental degradation is more prominent within wetland systems than any other ecosystem
on Earth.Constructed wetlands are used to treat municipal and industrial wastewater
as well as stormwater runoff. They may also play a role in water-sensitive urban design.==Definitions==
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 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. Mitsch and Gosselink write that wetlands exist
“…at 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.===Technical definitions===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.” There are four
main kinds of wetlands – marsh, swamp, bog and fen (bogs and fens being types of mires).
Some experts also recognize wet meadows and aquatic ecosystems as additional wetland types.
The largest wetlands in the world include the swamp forests of the Amazon and the peatlands
of Siberia.====Ramsar Convention definition====
Under the Ramsar international wetland conservation treaty, wetlands are defined as follows:
Article 1.1: “…wetlands are areas of marsh, fen, peatland or water, whether natural or
artificial, permanent or temporary, with water that is static or flowing, fresh, brackish
or salt, including areas of marine water the depth of which at low tide does not exceed
six metres.” Article 2.1: “[Wetlands] may incorporate riparian
and coastal zones adjacent to the wetlands, and islands or bodies of marine water deeper
than six metres at low tide lying within the wetlands.”====Regional definitions====
Although the general definition given above applies around the world, each county and
region tends to have its own definition for legal purposes. In the United States, wetlands
are defined as “those areas that are inundated or saturated by surface or groundwater at
a frequency and duration sufficient to support, and that under normal circumstances do support,
a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands
generally include swamps, marshes, bogs and similar areas”. This definition has been used
in the enforcement of the Clean Water Act. Some US states, such as Massachusetts and
New York, have separate definitions that may differ from the federal government’s.
In the United States Code, the term wetland is defined “as land that (A) has a predominance
of hydric soils, (B) is inundated or saturated by surface or groundwater at a frequency and
duration sufficient to support a prevalence of hydrophytic vegetation typically adapted
for life in saturated soil conditions and (C) under normal circumstances supports a
prevalence of such vegetation.” Related to this legal definitions, the term “normal circumstances”
are conditions expected to occur during the wet portion of the growing season under normal
climatic conditions (not unusually dry or unusually wet), and in the absence of significant
disturbance. It is not uncommon for a wetland to be dry for long portions of the growing
season. Wetlands can be dry during the dry season and abnormally dry periods during the
wet season, but under normal environmental conditions the soils in a wetland will be
saturated to the surface or inundated such that the soils become anaerobic, and those
conditions will persist through the wet portion of the growing season.==Ecology==
The most important factor producing wetlands is 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 fertility, natural disturbance,
competition, herbivory, burial and salinity. When peat accumulates, bogs and fens arise.==Characteristics==
Wetlands vary widely due to local and regional differences in topography, hydrology, vegetation,
and other factors, including human involvement.==Hydrology==
Wetland hydrology is associated with the spatial and temporal dispersion, flow, and physio-chemical
attributes of surface and ground water in its reservoirs. Based on hydrology, wetlands
can be categorized as riverine (associated with streams), lacustrine (associated with
lakes and reservoirs), and palustrine (isolated). Sources of hydrological flows into wetlands
are predominantly precipitation, surface water, and groundwater. Water flows out of wetlands
by evapotranspiration, surface runoff, and subsurface water outflow. Hydrodynamics (the
movement of water through and from 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 hydrochemistry. The O2 and CO2 concentrations
of water depend on temperature and atmospheric pressure. Hydrochemistry within wetlands is
determined by the pH, salinity, nutrients, conductivity, soil composition, hardness,
and the sources of water. Water chemistry of wetlands varies across landscapes and climatic
regions. Wetlands are generally minerotrophic with the exception of bogs.
Bogs receive most of their water from the atmosphere; therefore, their water usually
has low mineral ionic composition. In contrast, groundwater has a higher concentration of
dissolved nutrients and minerals. The water chemistry of fens ranges from low
pH and low minerals to alkaline with high accumulation of calcium and magnesium because
they acquire their water from precipitation as well as ground water.===Role of salinity===
Salinity has a strong influence on wetland water chemistry, particularly in wetlands
along the coast. and in regions with large precipitation deficits. In non-riverine wetlands,
natural salinity is regulated by interactions between ground and surface water, which may
be influenced by human activity.===Soil===
Carbon is the major nutrient cycled within wetlands. Most nutrients, such as sulfur,
phosphorus, carbon, and nitrogen are found within 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. Wetland soils are identified by redoxymorphic mottles or low chroma, as
determined by the Munsell Color System.===Biota===
The biota of a wetland system includes its flora and fauna as described below. The most
important factor affecting the biota is the duration of flooding. Other important factors
include fertility and salinity. In fens, species are highly dependent on water chemistry. The
chemistry of water flowing into wetlands depends on the source of water and the geological
material in which it flows through as well as the nutrients discharged from organic matter
in the soils and plants at higher elevations in slope wetlands. Biota may vary within a
wetland due to season or recent flood regimes.====Flora====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 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 is usually small, like arrow arum (Peltandra
virginica). Trees and shrubs, where they comprise much
of the cover in saturated soils, qualify those areas in most cases as 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.
Examples include cypress (Taxodium) and mangrove.====Fauna====Fish are more dependent on wetland ecosystems
than any other type of habitat. Seventy-five percent of the United States’ commercial fish
and shellfish stocks depend solely on estuaries to survive. Tropical fish species need mangroves
for critical hatchery and nursery grounds and the coral reef system for food.
Amphibians such as frogs need both terrestrial and aquatic habitats in which to reproduce
and feed. While tadpoles control algal populations, adult frogs forage on insects. Frogs are used
as an indicator of ecosystem health due to their thin skin which absorbs both nutrient
and toxins from the surrounding environment resulting in an above average extinction rate
in unfavorable and polluted environmental conditions.Reptiles such as alligators and
crocodiles are common in wetlands of some regions. Alligators occur in fresh water along
with the fresh water species of the crocodile.The Florida Everglades is the only place in the
world where both crocodiles and alligators coexist. The saltwater crocodile inhabits
estuaries and mangroves and can be seen in the coastline bordering the Great Barrier
Reef in Australia.Snakes, lizards and turtles also can be seen throughout wetlands. Snapping
turtles are one of the many kinds of turtles found in wetlands.
Birds, particularly waterfowl and wading birds, use wetlands extensivelyMammals include numerous
small and medium-sized species such as voles, bats, and platypus in addition to large herbivorous
and apex species such as the beaver, coypu, swamp rabbit, Florida panther, and moose.
Wetlands attract many mammals due to abundant seeds, berries, and other vegetation components,
as well as abundant populations of prey such as invertebrates, small reptiles and amphibians.Insects
and invertebrates total more than half of the 100,000 known animal species in wetlands.
Insects and invertebrates can be submerged in the water or soil, on the surface, and
in the atmosphere====
Algae====Algae are diverse water plants that can vary
in size, color, and shape. Algae occur naturally in habitats such as inland lakes, inter-tidal
zones, and damp soil and provide a dedicated food source for many animals, including some
invertebrates, fish, turtles, and frogs. There are three main groups of algae: Plankton are algae which are microscopic,
free-floating algae. This algae is so tiny that on average, if 50 of these microscopic
algae were lined up end-to-end, it would only measure one millimetre. Plankton are the basis
of the food web and are responsible for primary production in the ocean using photosynthesis
to make food. Filamentous algae are long strands of algae
cells that form floating mats. Chara and Nitella algae are upright algae
that look like a submerged plant with roots.==Climates=====
Temperature===Wetlands are located in every climatic zone.
Temperatures vary greatly depending on the location of the wetland. Many of the world’s
wetlands are in temperate zones, midway between the North or South Pole and the equator. In
these zones, summers are warm and winters are cold, but temperatures are not extreme.
In a subtropical zone wetland, such as one along the Gulf of Mexico, a typical temperature
might be 11 °C (52 °F). Wetlands in the tropics are much warmer for a larger portion
of the year. Wetlands on the Arabian Peninsula can reach temperatures exceeding 50 °C (122
°F) and would therefore be subject to rapid evaporation. In northeastern Siberia, which
has a polar climate, wetland temperatures can be as low as −50 °C (−58 °F). Peatlands
insulate the permafrost in subarctic regions, thus delaying or preventing thawing of permafrost
during summer, as well as inducing the formation of permafrost.===Precipitation===
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: Perennial systems
Seasonal systems Episodic (periodic or intermittent) system
of the down Surface flow may occur in some segments, with
subsurface flow in other segments Ephemeral (short-lived) systems
Migratory species==
Uses of wetlands==Depending partly 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 the
following areas, for example: Water storage (flood control)
Groundwater replenishment Shoreline stabilisation and storm protection
Water purification Reservoirs of biodiversity
Pollination Wetland products
Cultural values Recreation and tourism
Climate change mitigation and adaptationAccording 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 a whole. Unless otherwise cited, ecosystem services
information is based on the following series of references.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.===Water storage (flood control)===
Major wetland type: floodplain and closed-depression wetlands
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 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 doesn’t run straight off the land
into water courses. This can help prevent sudden, damaging floods downstream.” Notable
river systems that produce large spans of floodplain include the Nile River, the Niger
river inland delta, [the Zambezi River flood plain], [the Okavango River inland delta],
[the Kafue River flood plain][the Lake Bangweulu flood plain] (Africa), Mississippi River (USA),
Amazon River (South America), Yangtze River (China), Danube River (Central Europe) and
Murray-Darling River (Australia). Human impact: Converting wetlands to upland
through drainage and development forces adjoining or downstream water channels into narrower
corridors. This accelerates watershed hydrologic response to storm events and this increases
the need in some cases for alternative means of flood control. That is because the newly
formed channels must manage the same amount of precipitation, causing flood peaks to be
[higher or deeper] and floodwaters to travel faster.
Water management engineering developments in the past century have degraded these wetlands
through the construction of artificial embankments. These constructions may be classified as dykes,
bunds, levees, weirs, barrages and dams but serve the single purpose of concentrating
water into a select source or area. Wetland water sources that were once spread slowly
over a large, shallow area are pooled into deep, concentrated locations. Loss of wetland
floodplains results in more severe and damaging flooding. Catastrophic human impact in the
Mississippi River floodplains was seen in death of several hundred individuals during
a levee breach in New Orleans caused by Hurricane Katrina. Ecological catastrophic events from
human-made embankments have been noticed along the Yangtze River floodplains since the middle
of the river has become prone to more frequent and damaging flooding. Some of these events
include the loss of riparian vegetation, a 30% loss of the vegetation cover throughout
the river’s basin, a doubling of the percentage of the land affected by soil erosion, and
a reduction in reservoir capacity through siltation build-up in floodplain lakes.===Groundwater replenishment===
Major wetland type: marsh, swamp, and subterranean karst and cave hydrological systems
The surface water which is the water visibly seen in wetland systems only represents a
portion of the overall water cycle which also includes atmospheric water and groundwater.
Wetland systems are directly linked to groundwater and a crucial regulator of both the quantity
and quality of water found below the ground. Wetland systems that are made of permeable
sediments like limestone or occur in areas with highly variable and fluctuating water
tables especially have a role in groundwater replenishment or water recharge. Sediments
that are porous allow water to filter down through the soil and overlying rock into aquifers
which are the source of 95% 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 too
high. Karst (cave) systems are a unique example of this system and are a connection of underground
rivers influenced by rain and other forms of precipitation. These wetland systems are
capable of regulating changes in the water table on upwards of 130 m (430 ft).
Human impact: Groundwater is an important source of water for drinking and irrigation
of crops. Over 1 billion people in Asia and 65% of the public water sources in Europe
source 100% of their water from groundwater. Irrigation is a massive use of groundwater
with 80% of the world’s groundwater used for agricultural production.Unsustainable abstraction
of groundwater has become a major concern. In the Commonwealth of Australia, water licensing
is being implemented to control use of water in major agricultural regions. On a global
scale, groundwater deficits and water scarcity is one of the most pressing concerns facing
the 21st century.===Shoreline stabilization and storm protection
===Wetland type: Mangroves, coral reefs, salt
marsh Tidal and inter-tidal wetland systems protect
and stabilize coastal zones. Coral reefs provide 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. Human impact: The sheer number of people who
live and work near the coast is expected to grow immensely over the next fifty years.
From an estimated 200 million people that currently live in low-lying coastal regions,
the development of urban coastal centers is projected to increase the population by fivefold
within 50 years. The United Kingdom has begun the concept of
managed coastal realignment. This management technique provides shoreline protection through
restoration of natural wetlands rather than through applied engineering. In East Asia,
reclamation of coastal wetlands has resulted in widespread transformation of the coastal
zone, and up to 65% of coastal wetlands have been destroyed by coastal development. One
analysis using the impact of hurricanes versus storm protection provided naturally by wetlands
projected the value of this service at US$33,000/hectare/year.===Water purification===
Wetland types: floodplain, closed-depression wetlands, mudflat, salt marsh, mangroves
Nutrient retention: Wetlands cycle both sediments and nutrients balancing terrestrial and aquatic
ecosystems. A natural function of wetland vegetation is the up-take, storage, and (for
nitrate) the removal of nutrients found in runoff from the surrounding soil and water.
In many wetlands, nutrients are retained until plants die or are harvested by animals or
humans and taken to another location, or until microbial processes convert soluble nutrients
to a gas as is the case with nitrate. Sediment and heavy metal traps: Precipitation
and surface runoff induces soil erosion, transporting sediment in suspension into and through waterways.
These sediments move towards larger and more sizable waterways through a natural process
that moves water towards oceans. All types of sediments which may be composed of clay,
sand, silt, and rock can be carried into wetland systems through this process. Wetland vegetation
acts as a physical barrier to slow water flow and trap sediment for short or long periods
of time. Suspended sediment often contains heavy metals that are retained when wetlands
trap the sediment. In some cases, certain metals are taken up through wetland plant
stems, roots, and leaves. Many floating plant species, for example, can absorb and filter
heavy metals. Water hyacinth (Eichhornia crassipes), duckweed (Lemna) and water fern (Azolla) store
iron and copper commonly found in wastewater. Many fast-growing plants rooted in the soils
of wetlands such as cattail (Typha) and reed (Phragmites) also aid in the role of heavy
metal up-take. Animals such as the oyster can filter more than 200 litres (53 US gal)
of water per day while grazing for food, removing nutrients, suspended sediments, and chemical
contaminants in the process. On the other hand, some types of wetlands facilitate the
mobilization and bioavailability of mercury (another heavy metal), which in its methyl
mercury form increases the risk of bioaccumulation in fish important to animal food webs and
harvested for human consumption. Capacity: The ability of wetland systems to
store or remove nutrients and trap sediment and associated metals is highly efficient
and effective but each system has a threshold. An overabundance of nutrient input from fertilizer
run-off, sewage effluent, or non-point pollution will cause eutrophication. Upstream erosion
from deforestation can overwhelm wetlands making them shrink in size and cause dramatic
biodiversity loss through excessive sedimentation load. Retaining high levels of metals in sediments
is problematic if the sediments become resuspended or oxygen and pH levels change at a future
time. The capacity of wetland vegetation to store heavy metals depends on the particular
metal, oxygen and pH status of wetland sediments and overlying water, water flow rate (detention
time), wetland size, season, climate, type of plant, and other factors.
Human impact: The capacity of a wetland to store sediment, nutrients, and metals can
be diminished if sediments are compacted such as by vehicles or heavy equipment, or are
regularly tilled. Unnatural changes in water levels and water sources also can affect the
water purification function. If water purification functions are impaired, excessive loads of
nutrients enter waterways and cause eutrophication. This is of particular concern in temperate
coastal systems. The main sources of coastal eutrophication are industrially made nitrogen,
which is used as fertilizer in agricultural practices, as well as septic waste runoff.
Nitrogen is the limiting nutrient for photosynthetic processes in saline systems, however in excess,
it can lead to an overproduction of organic matter that then leads to hypoxic and anoxic
zones within the water column. Without oxygen, other organisms cannot survive, including
economically important finfish and shellfish species.
Examples: An example of how a natural wetland is used to provide some degree of sewage treatment
is the East Kolkata Wetlands in Kolkata, India. The wetlands cover 125 square kilometres (48
sq mi), and are used to treat Kolkata’s sewage. The nutrients contained in the wastewater
sustain fish farms and agriculture.===Constructed wetlands===The function of most natural wetland systems
is not to manage wastewater. However, their high potential for the filtering and the treatment
of pollutants has been recognized by environmental engineers that specialize in the area of wastewater
treatment. These constructed wetland systems are highly controlled environments that intend
to mimic the occurrences of soil, flora, and microorganisms in natural wetlands to aid
in treating wastewater effluent. Constructed wetlands can be used to treat raw sewage,
storm water, agricultural and industrial effluent. They are constructed with flow regimes, micro-biotic
composition, and suitable plants in order to produce the most efficient treatment process.
Other advantages of constructed wetlands are the control of retention times and hydraulic
channels. The most important factors of constructed wetlands are the water flow processes combined
with plant growth. Constructed wetland systems can be surface
flow systems with only free-floating macrophytes, floating-leaved macrophytes, or submerged
macrophytes; however, typical free water surface systems are usually constructed with emergent
macrophytes. Subsurface flow-constructed wetlands with a vertical or a horizontal flow regime
are also common and can be integrated into urban areas as they require relatively little
space.===Reservoirs of biodiversity===
Wetland systems’ rich biodiversity is becoming a focal point at International Treaty Conventions
and within the World Wildlife Fund organization due to the high number of species present
in wetlands, the small global geographic area of wetlands, the number of species which are
endemic to wetlands, and the high productivity of wetland systems. Hundred of thousands of
animal species, 20,000 of them vertebrates, are living in wetland systems. The discovery
rate of fresh water fish is at 200 new species per year. The impact of maintaining biodiversity
is seen at the local level through job creation, sustainability, and community productivity.
A good example is the Lower Mekong basin which runs through Cambodia, Laos, and Vietnam.
Supporting over 55 million people, the sustainability of the region is enhanced through wildlife
tours. The U.S. state of Florida has estimated that US$1.6 billion was generated in state
revenue from recreational activities associated with wildlife.
Biodiverse river basins: The Amazon holds 3,000 species of freshwater fish species within
the boundaries of its basin, whose function it is to disperse the seeds of trees. One
of its key species, the Piramutaba catfish, Brachyplatystoma vaillantii, migrates more
than 3,300 km (2,100 mi) from its nursery grounds near the mouth of the Amazon River
to its spawning grounds in Andean tributaries, 400 m (1,300 ft) above sea level, distributing
plants seed along the route. Productive intertidal zones: Intertidal mudflats
have a level of productivity similar to that of some wetlands even while possessing a low
number of species. The abundance of invertebrates found within the mud are a food source for
migratory waterfowl. Critical life-stage habitat: Mudflats, saltmarshes,
mangroves, and seagrass beds have high levels of both species richness and productivity,
and are home to important nursery areas for many commercial fish stocks.
Genetic diversity: Populations of many species are confined geographically to only one or
a few wetland systems, often due to the long period of time that the wetlands have been
physically isolated from other aquatic sources. For example, the number of endemic species
in Lake Baikal in Russia classifies it as a hotspot for biodiversity and one of the
most biodiverse wetlands in the entire world. Evidence from a research study by Mazepova
et al. suggest that the number of crustacean species endemic to Baikal Lake (over 690 species
and subspecies) exceeds the number of the same groups of animals inhabiting all the
fresh water bodies of Eurasia together. Its 150 species of free-living Platyhelminthes
alone is analogous to the entire number in all of Eastern Siberia. The 34 species and
subspecies number of Baikal sculpins is more than twice the number of the analogous fauna
that inhabits Eurasia. One of the most exciting discoveries was made by A. V. Shoshin who
registered about 300 species of free-living nematodes using only six near-shore sampling
localities in the Southern Baikal. “If we will take into consideration, that about 60%
of the animals can be found nowhere else except Baikal, it may be assumed that the lake may
be the biodiversity center of the Eurasian continent.”Human impact: Biodiversity loss
occurs in wetland systems through land use changes, habitat destruction, pollution, exploitation
of resources, and invasive species. Vulnerable, threatened, and endangered species number
at 17% of waterfowl, 38% of fresh-water dependent mammals, 33% of freshwater fish, 26% of freshwater
amphibians, 72% of freshwater turtles, 86% of marine turtles, 43% of crocodilians and
27% of coral reef-building species. Introduced hydrophytes in different wetland systems can
have devastating results. The introduction of water hyacinth, a native plant of South
America into Lake Victoria in East Africa as well as duckweed into non-native areas
of Queensland, Australia, have overtaken entire wetland systems suffocating the wetlands and
reducing the diversity of other plants and animals. This is largely due to their phenomenal
growth rate and ability to float and grow on the surface of the water.===Wetland products and productivity===
Wetland productivity is linked to the climate, wetland type, and nutrient availability. Low
water and occasional drying of the wetland bottom during droughts (dry marsh phase) stimulate
plant recruitment from a diverse seed bank and increase productivity by mobilizing nutrients.
In contrast, high water during deluges (lake marsh phase) causes turnover in plant populations
and creates greater interspersion of element cover and open water, but lowers overall productivity.
During a cover cycle that ranges from open water to complete vegetation cover, annual
net primary productivity may vary 20-fold. The grasses of fertile floodplains such as
the Nile produce the highest yield including plants such as Arundo donax (giant reed),
Cyperus papyrus (papyrus), Phragmites (reed) and Typha (cattail, bulrush).
Wetlands naturally produce an array of vegetation and other ecological products that can be
harvested for personal and commercial use. The most significant of these is fish which
have all or part of their life-cycle occur within a wetland system. Fresh and saltwater
fish are the main source of protein for one billion people and comprise 15% of an additional
two billion people’s diets. In addition, fish generate a fishing industry that provides
80% of the income and employment to residents in developing countries. Another food staple
found in wetland systems is rice, a popular grain that is consumed at the rate of one
fifth of the total global calorie count. In Bangladesh, Cambodia and Vietnam, where rice
paddies are predominant on the landscape, rice consumption reach 70%. Some native wetland
plants in the Caribbean and Australia are harvested sustainably for medicinal compounds;
these include the red mangrove (Rhizophora mangle) which possesses antibacterial, wound-healing,
anti-ulcer effects, and antioxidant properties.Food converted to sweeteners and carbohydrates
include the sago palm of Asia and Africa (cooking oil), the nipa palm of Asia (sugar, vinegar,
alcohol, and fodder) and honey collection from mangroves. More than supplemental dietary
intake, this produce sustains entire villages. Coastal Thailand villages earn the key portion
of their income from sugar production while the country of Cuba relocates more than 30,000
hives each year to track the seasonal flowering of the mangrove Avicennia.
Other mangrove-derived products: Fuelwood
Salt (produced by evaporating seawater) Animal fodder
Traditional medicines (e.g. from mangrove bark)
Fibers for textiles Dyes and tanninsHuman impact: Over-fishing
is the major problem for sustainable use of wetlands. Concerns are developing over certain
aspects of farm fishing, which uses natural waterways to harvest fish for human consumption
and pharmaceuticals. This practice has become especially popular in Asia and the South Pacific.
Its impact upon much larger waterways downstream has negatively affected many small island
developing states.Aquaculture is continuing to develop rapidly throughout the Asia-Pacific
region specifically in China with world holdings in Asia equal to 90% of the total number of
aquaculture farms and 80% of its global value. Some aquaculture has eliminated massive areas
of wetland through practices seen such as in the shrimp farming industry’s destruction
of mangroves. Even though the damaging impact of large scale shrimp farming on the coastal
ecosystem in many Asian countries has been widely recognized for quite some time now,
it has proved difficult to check in absence of other employment avenues for people engaged
in such occupation. Also burgeoning demand for shrimps globally has provided a large
and ready market for the produce Threats to rice fields mainly stem from inappropriate
water management, introduction of invasive alien species, agricultural fertilizers, pesticides,
and land use changes. Industrial-scale production of palm oil threatens the biodiversity of
wetland ecosystems in parts of southeast Asia, Africa, and other developing countries.
Over-exploitation of wetland products can occur at the community level as is sometimes
seen throughout coastal villages of Southern Thailand where each resident may obtain for
themselves every consumable of the mangrove forest (fuelwood, timber, honey, resins, crab,
and shellfish) which then becomes threatened through increasing population and continual
harvest.===Additional functions and uses of wetlands
===Some types of wetlands can serve as fire breaks
that help slow the spread of minor wildfires. Larger wetland systems can influence local
precipitation patterns. Some boreal wetland systems in catchment headwaters may help extend
the period of flow and maintain water temperature in connected downstream waters. Pollination
services are supported by many wetlands which may provide the only suitable habitat for
pollinating insects, birds, and mammals in highly developed areas. It is likely that
wetlands have other functions whose benefits to society and other ecosystems have yet to
be discovered.==Wetlands and climate change==
Wetlands perform two important functions in relation to climate change. They have mitigation
effects through their ability to sink carbon, converting a greenhouse gas (carbon dioxide)
to solid plant material through the process of photosynthesis, and also through their
ability to store and regulate water. Wetlands store approximately 44.6 million tonnes of
carbon per year globally. In salt marshes and mangrove swamps in particular, the average
carbon sequestration rate is 210 g CO2 m−2 y−1 while peatlands sequester approximately
20–30 g CO2 m−2 y−1. Coastal wetlands, such as tropical mangroves and some temperate
salt marshes, are known to be sinks for carbon that otherwise contributes to climate change
in its gaseous forms (carbon dioxide and methane). The ability of many tidal wetlands to store
carbon and minimize methane flux from tidal sediments has led to sponsorship of blue carbon
initiatives that are intended to enhance those processes.However, depending on their characteristics,
some wetlands are a significant source of methane emissions and some are also emitters
of nitrous oxide which is a greenhouse gas with a global warming potential 300 times
that of carbon dioxide and is the dominant ozone-depleting substance emitted in the 21st
century. Excess nutrients mainly from anthropogenic sources have been shown to significantly increase
the N2O fluxes from wetland soils through denitrification and nitrification processes
(see table below). A study in the intertidal region of a New England salt marsh showed
that excess levels of nutrients might increase N2O emissions rather than sequester them.
Data on nitrous oxide fluxes from wetlands in the southern hemisphere are lacking, as
are ecosystem-based studies including the role of dominant organisms that alter sediment
biogeochemistry. Aquatic invertebrates produce ecologically-relevant nitrous oxide emissions
due to ingestion of denitrifying bacteria that live within the subtidal sediment and
water column and thus may also be influencing nitrous oxide production within some wetlands.===Peatswamps in Southeast Asia===
In Southeast Asia, peatswamp forests and soils are being drained, burnt, mined, and overgrazed,
contributing severely to climate change. As a result of peat drainage, the organic carbon
that was built up over thousands of years and is normally under water is suddenly exposed
to the air. It decomposes and turns into carbon dioxide (CO2), which is released into the
atmosphere. Peat fires cause the same process to occur and in addition create enormous clouds
of smoke that cross international borders, such as happens every year in Southeast Asia.
While peatlands constitute only 3% of the world’s land area, their degradation produces
7% of all fossil fuel CO2 emissions. Through the building of dams, Wetlands International
is halting the drainage of peatlands in Southeast Asia, hoping to mitigate CO2 emissions. Concurrent
wetland restoration techniques include reforestation with native tree species as well as the formation
of community fire brigades. This sustainable approach can be seen in central Kalimantan
and Sumatra, Indonesia.==Wetland Disturbance==
Wetlands, the functions and services they provide as well as their flora and fauna,
can be affected by several types of disturbances. The disturbances (sometimes termed stressors
or alterations) can be human-associated or natural, direct or indirect, reversible or
not, and isolated or cumulative. When exceeding levels or patterns normally found within wetlands
of a particular class in a particular region, the predominant ones include the following
Enrichment/Eutrophication Organic Loading and Reduced Dissolved Oxygen
Contaminant Toxicity Acidification
Salinization Sedimentation
Altered Solar Input (Turbidity/Shade) Vegetation Removal
Thermal Alteration Dehydration/Aridification
Inundation/Flooding Habitat Fragmentation
Other Human PresenceDisturbances can be further categorized as follows: Minor disturbance
Stress that maintains ecosystem integrity. Moderate disturbance
Ecosystem integrity is damaged but can recover in time without assistance.
Impairment or severe disturbance Human intervention may be needed in order
for ecosystem to recover.Just a few of the many sources of these disturbances are
Drainage Development
Over-grazing Mining
Unsustainable water use They can be manifested partly as:
Water scarcity Impacts to Endangered species
Disruption of wildlife breeding grounds Imbalance in sediment load and nutrient filtration===
Water Chemistry===Anthropogenic nitrogen inputs to aquatic systems
have drastically effected the dissolved nitrogen content of wetlands, introducing higher nutrient
availability which leads to eutrophication., Due to the low dissolved oxygen (DO) content,
and relatively low nutrient balance of wetland environments, they are very susceptible to
alterations in water chemistry. Key factors that are assessed to determine water quality
include: Major Anion Analysis: (HCO3-,Cl-,NO3-,SO42-)
Major Cation Analysis (Ca2+, Mg2+, Na+, K+) pH
Conductivity- Conductivity increases with more dissolved ions in the water
Turbidity Dissolved Oxygen
Temperature Total Dissolved SolidsThese chemical factors
can be used to quantify wetland disturbances, and often provide information as to whether
a wetland is surface water fed or groundwater fed due to the different ion characteristics
of the two water sources. Wetlands are adept at impacting the water chemistry of streams
or water bodies that interact with them, and can withdraw ions that result from water pollution
such as acid mine drainage or urban runoff.,==
Conservation==Wetlands have historically been the victim
of large draining efforts for real estate development, or flooding for use as recreational
lakes or hydropower generation. Some of the world’s most important agricultural areas
are wetlands that have been converted to farmland. Since the 1970s, more focus has been put on
preserving wetlands for their natural function yet by 1993 half the world’s wetlands had
been drained.In order to maintain wetlands and sustain their functions, alterations and
disturbances that are outside the normal range of variation should be minimized.===Balancing wetland conservation with the
needs of people===Wetlands are vital ecosystems that provide
livelihoods for the millions of people who live in and around them. The Millennium Development
Goals (MDGs) called for different sectors to join forces to secure wetland environments
in the context of sustainable development and improving human wellbeing. A three-year
project carried out by Wetlands International in partnership with the International Water
Management Institute found that it is possible to conserve wetlands while improving the livelihoods
of people living among them. Case studies conducted in Malawi and Zambia looked at how
dambos – wet, grassy valleys or depressions where water seeps to the surface – can be
farmed sustainably to improve livelihoods. Mismanaged or overused dambos often become
degraded, however, using a knowledge exchange between local farmers and environmental managers,
a protocol was developed using soil and water management practices. Project outcomes included
a high yield of crops, development of sustainable farming techniques, and adequate water management
generating enough water for use as irrigation. Before the project, there were cases where
people had died from starvation due to food shortages. By the end of it, many more people
had access to enough water to grow vegetables. A key achievement was that villagers had secure
food supplies during long, dry months. They also benefited in other ways: nutrition was
improved by growing a wider range of crops, and villagers could also invest in health
and education by selling produce and saving money.===Ramsar Convention===The Convention on Wetlands of International
Importance, especially as Waterfowl Habitat, or Ramsar Convention, is an international
treaty designed to address global concerns regarding wetland loss and degradation. The
primary purposes of the treaty are to list wetlands of international importance and to
promote their wise use, with the ultimate goal of preserving the world’s wetlands. Methods
include restricting access to the majority portion of wetland areas, as well as educating
the public to combat the misconception that wetlands are wastelands. The Convention works
closely with five International Organisation Partners. These are: Birdlife International,
the IUCN, the International Water Management Institute, Wetlands International and the
World Wide Fund for Nature. The partners provide technical expertise, help conduct or facilitate
field studies and provide financial support. The IOPs also participate regularly as observers
in all meetings of the Conference of the Parties and the Standing Committee and as full members
of the Scientific and Technical Review Panel.==Valuation==
The value of a wetland to local communities, as well as the value of wetland systems generally
to the earth and to humankind, is one of the most important valuations that can be conducted
for sustainable development. This typically involves first mapping a region’s wetlands,
then assessing the functions and ecosystem services the wetlands provide individually
and cumulatively, and evaluating that information to prioritize or rank individual wetlands
or wetland types for conservation, management, restoration, or development. Over a longer
period, it requires keeping inventories of known wetlands and monitoring a representative
sample of the wetlands to determine changes due to both natural and human factors. Such
a valuation process is used to educate decision-makers such as governments of the importance of particular
wetlands within their jurisdiction.===Assessment===
Rapid assessment methods are used to score, rank, rate, or categorize various functions,
ecosystem services, species, communities, levels of disturbance, and/or ecological health
of a wetland or group of wetlands. This is often done to prioritize particular wetlands
for conservation (avoidance) or to determine the degree to which loss or alteration of
wetland functions should be compensated, such as by restoring degraded wetlands elsewhere
or providing additional protections to existing wetlands. Rapid assessment methods are also
applied before and after a wetland has been restored or altered, to help monitor or predict
the effects of those actions on various wetland functions and the services they provide. Assessments
are typically considered to be “rapid” when they require only a single visit to the wetland
lasting less than one day, which in some cases may include interpretation of aerial imagery
and GIS analyses of existing spatial data, but not detailed post-visit laboratory analyses
of water or biological samples. Due to time and cost constraints, the levels of various
wetland functions or other attributes are usually not measured directly but rather are
estimated relative to other assessed wetlands in a region, using observation-based variables,
sometimes called “indicators”, that are hypothesized or known to predict performance of the specified
functions or attributes. To achieve consistency among persons doing
the assessment, rapid methods present indicator variables as questions or checklists on standardized
data forms, and most methods standardize the scoring or rating procedure that is used to
combine question responses into estimates of the levels of specified functions relative
to the levels estimated in other wetlands (“calibration sites”) assessed previously
in a region. Rapid assessment methods, partly because they often use dozens of indicators
pertaining to conditions surrounding a wetland as well as within the wetland itself, aim
to provide estimates of wetland functions and services that are more accurate and repeatable
than simply describing a wetland’s class type. A need for wetland assessments to be rapid
arises mostly when government agencies set deadlines for decisions affecting a wetland,
or when the number of wetlands needing information on their functions or condition is large.
In North America and a few other countries, standardized rapid assessment methods for
wetlands have a long history, having been developed, calibrated, tested, and applied
to varying degrees in several different regions and wetland types since the 1970s. However,
few rapid assessment methods have been fully validated. Done correctly, validation is a
very expensive endeavor that involves comparing rankings of a series of wetlands based on
results from rapid assessment methods with rankings based on less rapid and considerably
more costly, multi-visit, detailed measurements of levels of the same functions or other attributes
in the same series of wetlands.===Inventory===
Although developing a global inventory of wetlands has proven to be a large and difficult
undertaking, many efforts at more local scales have been successful. Current efforts are
based on available data, but both classification and spatial resolution have sometimes proven
to be inadequate for regional or site-specific environmental management decision-making.
It is difficult to identify small, long, and narrow wetlands within the landscape. Many
of today’s remote sensing satellites do not have sufficient spatial and spectral resolution
to monitor wetland conditions, although multispectral IKONOS and QuickBird data may offer improved
spatial resolutions once it is 4 m or higher. Majority of the pixels are just mixtures of
several plant species or vegetation types and are difficult to isolate which translates
into an inability to classify the vegetation that defines the wetland. Improved remote
sensing information, coupled with good knowledge domain on wetlands will facilitate expanded
efforts in wetland monitoring and mapping. This will also be extremely important because
we expect to see major shifts in species composition due to both anthropogenic land use and natural
changes in the environment caused by climate change.===Monitoring===
A wetland needs to be monitored over time to assess whether it is functioning at an
ecologically sustainable level or whether it is becoming degraded. Degraded wetlands
will suffer a loss in water quality, loss of sensitive species, and aberrant functioning
of soil geochemical processes. Mapping
Practically, many natural wetlands are difficult to monitor from the ground as they quite often
are difficult to access and may require exposure to dangerous plants and animals as well as
diseases borne by insects or other invertebrates..Therefore, mapping using aerial imagery is one effective
tool to monitor a wetland, especially a large wetland, and can also be used to monitor the
status of numerous wetlands throughout a watershed or region. Many remote sensing methods can
be used to map wetlands. Remote-sensing technology permits the acquisition of timely digital
data on a repetitive basis. This repeat coverage allows wetlands, as well as the adjacent land-cover
and land-use types, to be monitored seasonally and/or annually. Using digital data provides
a standardized data-collection procedure and an opportunity for data integration within
a geographic information system. Traditionally, Landsat 5 Thematic Mapper (TM), Landsat 7
Enhanced Thematic Mapper Plus (ETM+), and the SPOT 4 and 5 satellite systems have been
used for this purpose. More recently, however, multispectral IKONOS and QuickBird data, with
spatial resolutions of 4 by 4 m (13 by 13 ft) and 2.44 by 2.44 m (8.0 by 8.0 ft), respectively,
have been shown to be excellent sources of data when mapping and monitoring smaller wetland
habitats and vegetation communities. For example, Detroit Lakes Wetland Management
District assessed area wetlands in Michigan, USA, using remote sensing. Through using this
technology, satellite images were taken over a large geographic area and extended period.
In addition, using this technique was less costly and time-consuming compared to the
older method using visual interpretation of aerial photographs. In comparison, most aerial
photographs also require experienced interpreters to extract information based on structure
and texture while the interpretation of remote sensing data only requires analysis of one
characteristic (spectral). However, there are a number of limitations
associated with this type of image acquisition. Analysis of wetlands has proved difficult
because to obtain the data it is often linked to other purposes such as the analysis of
land cover or land use. Further improvements
Methods to develop a classification system for specific biota of interest could assist
with technological advances that will allow for identification at a very high accuracy
rate. The issue of the cost and expertise involved in remote sensing technology is still
a factor hindering further advancements in image acquisition and data processing. Future
improvements in current wetland vegetation mapping could include the use of more recent
and better geospatial data when it is available.==Restoration==
Restoration and restoration ecologists intend to return wetlands to their natural trajectory
by aiding directly with the natural processes of the ecosystem. These direct methods vary
with respect to the degree of physical manipulation of the natural environment and each are associated
with different levels of restoration. Restoration is needed after disturbance or perturbation
of a wetland. Disturbances include exogenous factors such as flooding or drought. Other
external damage may be anthropogenic disturbance caused by clear-cut harvesting of trees, oil
and gas extraction, poorly defined infrastructure installation, over grazing of livestock, ill-considered
recreational activities, alteration of wetlands including dredging, draining, and filling,
and other negative human impacts. Disturbance puts different levels of stress on an environment
depending on the type and duration of disturbance. There is no one way to restore a wetland and
the level of restoration required will be based on the level of disturbance although,
each method of restoration does require preparation and administration.===Levels of restoration===
Factors influencing selected approach may includeBudget
Time scale limitations Project goals
Level of disturbance Landscape and ecological constraints
Political and administrative agendas Socioeconomic prioritiesPrescribed Natural
Regeneration There are no biophysical manipulation and
the ecosystem is left to recover based on the process of succession alone. The focus
of this method is to eliminate and prevent further disturbance from occurring. In order
for this type of restoration to be effective and successful there must be prior research
done to understand the probability that the wetland will recover with this method. Otherwise,
some biophysical manipulation may be required to enhance the rate of succession to an acceptable
level determined by the project managers and ecologists. This is likely to be the first
method of approach for the lowest level of disturbance being that it is the least intrusive
and least costly. Assisted Natural Regeneration
There are some biophysical manipulations however they are non-intrusive. Example methods that
are not limited to wetlands include prescribed burns to small areas, promotion of site specific
soil microbiota and plant growth using nucleation planting whereby plants radiate from an initial
planting site, and promotion of niche diversity or increasing the range of niches to promote
use by a variety of different species. These methods can make it easier for the natural
species to flourish by removing competition from their environment and can speed up the
process of succession. Partial Reconstruction
Here there is a mix between natural regeneration and manipulated environmental control. These
manipulations may require some engineering and more invasive biophysical manipulation
including ripping of subsoil, agrichemical applications such as herbicides and insecticides,
laying of mulch, mechanical seed dispersal, and tree planting on a large scale. In these
circumstances the wetland is impaired and without human assistance it would not recover
within an acceptable period of time determined by ecologists. Again these methods of restoration
will have to be considered on a site by site basis as each site will require a different
approach based on levels of disturbance and ecosystem dynamics.
Complete Reconstruction The most expensive and intrusive method of
reconstruction requiring engineering and ground up reconstruction. Because there is a redesign
of the entire ecosystem it is important that the natural trajectory of the ecosystem be
considered and that the plant species will eventually return the ecosystem towards its
natural trajectory.===Important considerations===
Constructed wetlands can take 10–100 years to fully resemble the vegetative composition
of a natural wetland. Artificial wetlands do not have hydric soil.
The soil has very low levels of organic carbon and total nitrogen compared to natural wetland
systems, and this reduces the performance of several functions.
Organic matter added to degraded natural wetlands can in some cases help restore their productivity.===Legislation===
International EffortsRamsar Convention North American Waterfowl Management PlanCanadian
National EffortsThe Federal Policy on Wetland Conservation
Other Individual Provincial and Territorial Based Policies==List of wetland types==
The following list is that used within Australia to classify wetland by type:
A—Marine and Coastal Zone wetlandsMarine waters—permanent shallow waters less than
six metres deep at low tide; includes sea bays, straits
Subtidal aquatic beds; includes kelp beds, seagrasses, tropical marine meadows
Coral reefs Rocky marine shores; includes rocky offshore
islands, sea cliffs Sand, shingle or pebble beaches; includes
sand bars, spits, sandy islets Intertidal mud, sand or salt flats
Intertidal marshes; includes saltmarshes, salt meadows, saltings, raised salt marshes,
tidal brackish and freshwater marshes Intertidal forested wetlands; includes mangrove
swamps, nipa swamps, tidal freshwater swamp forests
Brackish to saline lagoons and marshes with one or more relatively narrow connections
with the sea Freshwater lagoons and marshes in the coastal
zone Non-tidal freshwater forested wetlandsB—Inland
wetlandsPermanent rivers and streams; includes waterfalls
Seasonal and irregular rivers and streams Inland deltas (permanent)
Riverine floodplains; includes river flats, flooded river basins, seasonally flooded grassland,
savanna and palm savanna Permanent freshwater lakes (>8 ha); includes
large oxbow lakes Seasonal/intermittent freshwater lakes (>8
ha), floodplain lakes Permanent saline/brackish lakes
Seasonal/intermittent saline lakes Permanent freshwater ponds (8 ha) Ponds, including farm ponds, stock ponds,
small tanks (generally

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