Tswaing Meteorte Wetlands

A wetland is a land area that is saturated with water, either permanently or seasonally, such that it takes on the characteristics of a distinct ecosystem.  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 roles in the environment, principally water purification, flood control, carbon sink and shoreline stability. Wetlands are also considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life.

Wetlands occur naturally on every continent except Antarctica, the largest including the Amazon River basin, the West Siberian Plain, and the Pantanal in South America.  The water found in wetlands can be freshwater, brackish, or saltwater. The main wetland types include swamps, marshes, bogs, and fens; and sub-types include mangrove, carr, pocosin, and varzea.

Constructed wetlands can be 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 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 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.

Characteristics

Wetlands vary widely due to local and regional differences in topography, hydrology, vegetation, and other factors, including human involvement. Wetlands can be divided into two main classes. They are tidal and non-tidal areas.

Hydrolog

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 their water from the atmosphere; therefore, their water 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. 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 vegetation zones and structure as well as animal populations. 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

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).

Forested wetlands are generally known as swamps. The upper level of these swamps is determined by high water levels, which are negatively 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 reptilian species. Alligators are found in fresh water along with the fresh water species of the crocodile. The saltwater crocodile is found in estuaries and mangroves and can be seen in the coastline bordering the Great Barrier Reef in Australia. The Florida Everglades is the only place in the world where both crocodiles and alligators coexist. Snakes, lizards and turtles also can be seen throughout wetlands. Snapping turtles are one of the many kinds of turtles found in wetlands.

Mammals include numerous species of small mammals in addition to large herbivorous and apex species such as the beaver, swamp rabbit, and Florida panther, live within and around wetlands. The wetland ecosystem attracts mammals due to its prominent seed and vegetation sources, abundant populations of invertebrates, small reptiles and amphibians.

Monotremes such as the platypus (Ornithorhynchus anatinus) is found in eastern Australia living in freshwater rivers or lakes. Much like the beaver, the platypus creates dams and burrows for shelter and protection. The platypus swims through the use of webbed feet. The platypus feeds on insect larvae, worms, or other freshwater insects hunting mainly by night by the use of their bill. It turns up mud on the bottom of the lake or river, and with the help of the electroreceptors located on the bill, unearths freshwater insects. The platypus stores their findings in special pouches behind their bill and consumes its prey upon returning to the surface.

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 animals, fish, and invertebrates. 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

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. However, wetlands found in the tropics, around the equator, are warm all year round. Wetlands on the Arabian Peninsula, for example, can reach 50 °C  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 . In a moderate zone, such as the Gulf of Mexico, a typical temperature might be 11 °C . Wetlands are also located in every climatic zone.

Rainfall

The amount of rainfall a wetland receives varies widely according to its area. Wetlands in Wales, Scotland, and western Ireland typically receive about 1,500 mm per year. In some places in Southeast Asia, where heavy rains occur, they can receive up to 10,000 mm . In the northern areas of North America, wetlands exist where as little as 180 mm of rain falls 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

Human-disturbance:

• Encroachment
  • Drainage
  • Development
  • Over-grazing
  • Mining
  • Unsustainable water use
• Ecosystem Stress
  • Water Scarcity
  • Endangered species
  • Disruption of breeding grounds
  • Imbalance in sediment load and nutrient filtration

Uses of wetlands

Aquaculture

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.

The function of natural wetlands can be classified by their ecosystem benefits. United Nations Millennium Ecosystem Assessment and Ramsar Convention found wetlands to be of biosphere significance and societal importance in the following areas:

• Flood control
• Groundwater replenishment
• Shoreline stabilisation and storm protection
• Water purification
• Reservoirs of biodiversity
• Wetland products
• Cultural values
• Recreation and tourism
• Climate change mitigation and adaptation

According to the Ramsar Convention:

Flood control

Major wetland type: floodplain

Storage reservoirs and flood protection: The wetland system of floodplains is formed from major rivers downstream from their headwaters. 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). "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."

Human impact: Converting wetlands through drainage and development have contributed to the issue of irregular flood control through forced adaption of water channels to narrower corridors due to loss of wetland area. These new 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 on 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.

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 the 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 stabilisation 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.

Water purification

Wetland types: floodplain, 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 and storage of nutrients found in the surrounding soil and water. These nutrients are retained in the system until the plant dies or is harvested by animals or humans. Wetland vegetation productivity is linked to the climate, wetland type, and nutrient availability. 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).

Sediment traps: Rainfall run-off is responsible for moving sediment 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. Reedbeds or forests located in wetlands act as physical barriers to slow waterflow and trap sediment.

Water purification: Many wetland systems possess biofilters, hydrophytes, and organisms that in addition to nutrient up-take abilities have the capacity to remove toxic substances that have come from pesticides, industrial discharges, and mining activities. The up-take occurs through most parts of the plant including the stems, roots, and leaves. Floating plants 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 of water per day while grazing for food, removing nutrients, suspended sediments, and chemical contaminants in the process.

Capacity: The ability of wetland systems to store nutrients and trap sediment 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 see dramatic biodiversity loss through excessive sedimentation load. The capacity of wetland vegetation to store heavy metals is affected by waterflow, number of hectares (acres), climate, and type of plant.

Human impact: 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 ecosystem due to their phenomenal growth rate and ability to float and grow on the surface of the water.

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, and are used to treat Kolkata's sewage. The nutrients contained in the wastewater sustain fish farms and agriculture.

List of wetland types

The following list is that used within Australia to classify wetland by type:

• A—Marine and Coastal Zone wetlands

1. Marine waters—permanent shallow waters less than six metres deep at low tide; includes sea bays, straits
2. Subtidal aquatic beds; includes kelp beds, seagrasses, tropical marine meadows
3. Coral reefs
4. Rocky marine shores; includes rocky offshore islands, sea cliffs
5. Sand, shingle or pebble beaches; includes sand bars, spits, sandy islets
6. Intertidal mud, sand or salt flats
7. Intertidal marshes; includes saltmarshes, salt meadows, saltings, raised salt marshes, tidal brackish and freshwater marshes
8. Intertidal forested wetlands; includes mangrove swamps, nipa swamps, tidal freshwater swamp forests
9. Brackish to saline lagoons and marshes with one or more relatively narrow connections with the sea
10. Freshwater lagoons and marshes in the coastal zone
11. Non-tidal freshwater forested wetlands

• B—Inland wetlands

1. Permanent rivers and streams; includes waterfalls
2. Seasonal and irregular rivers and streams
3. Inland deltas (permanent)
4. Riverine floodplains; includes river flats, flooded river basins, seasonally flooded grassland, savanna and palm savanna
5. Permanent freshwater lakes (> 8 ha); includes large oxbow lakes
6. Seasonal/intermittent freshwater lakes (> 8 ha), floodplain lakes
7. Permanent saline/brackish lakes
8. Seasonal/intermittent saline lakes
9. Permanent freshwater ponds (< 8 ha), marshes and swamps on inorganic soils; with emergent vegetation waterlogged for at least most of the growing season
10. Seasonal/intermittent freshwater ponds and marshes on inorganic soils; includes sloughs, potholes; seasonally flooded meadows, sedge marshes
11. Permanent saline/brackish marshes
12. Seasonal saline marshes
13. Shrub swamps; shrub-dominated freshwater marsh, shrub carr, alder thicket on inorganic soils
14. Freshwater swamp forest; seasonally flooded forest, wooded swamps; on inorganic soils
15. Peatlands; forest, shrub or open bogs
16. Alpine and tundra wetlands; includes alpine meadows, tundra pools, temporary waters from snow melt
17. Freshwater springs, oases and rock pools
18. Geothermal wetlands
19. Inland, subterranean karst wetlands

• C—Human-made wetlands

1. Water storage areas; reservoirs, barrages, hydro-electric dams, impoundments (generally > 8 ha)
2. Ponds, including farm ponds, stock ponds, small tanks (generally < 8 ha)
3. Aquaculture ponds; fish ponds, shrimp ponds
4. Salt exploitation; salt pans, salines
5. Excavations; gravel pits, borrow pits, mining pools
6. Wastewater treatment; sewage farms, settling ponds, oxidation basins
7. Irrigated land and irrigation channels; rice fields, canals, ditches
8. Seasonally flooded arable land, farm land

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