There is more to wetlands than just being perpetually moist or wet. The presence of water determines or influences most of this area’s biogeochemistry. In other words, the biological, physical, chemical, and geological processes that occur in a wetland are greatly influenced by water.
The U.S. Fish and Wildlife Service provided a workable definition to specifically define what constitutes a wetland in 1979, the definition is as follows:
Wetlands are lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface, or the land is covered by shallow water. . . .
Wetlands must have one or more of the following three attributes:
1) at least periodically, the land supports predominantly hydrophytes;
2) the substrate is predominantly undrained hydric soil; and
3) the substrate is saturated with water or covered by shallow water at some time during the growing season of each year.
Most wetlands are found between upland and aquatic ecosystems. They are transitional zones between them. Not all wetlands are found between upland and aquatic ecosystems. Some are found scattered in upland areas as depressions that collect water or as areas where groundwater comes to the surface.
Wetlands vary greatly in their characteristics. For instance, some wetlands are flooded throughout the year, while others are only flooded during certain seasons. There are also wetlands that rarely flood. Regardless, all of these are wetlands for the soil remains saturated with water all year round. Due to this wetness, wetland-adapted plants would flourish and hydric soil characteristics would develop. The development of hydric soil would occur because of the prolonged saturation and low-oxygen conditions within the wetlands.
Each wetland-adapted plant species are adapted to a certain type of wetland. This is due to the fact that different types of wetlands would vary in the quantity, distribution, and movement of their water. These wetland-adapted plants are also called hydrophytes. ‘Hydro-’ pertaining to water and ‘-phytes’ pertaining to plants. This is an appropriate name as wetland-adapted plants are plant species that love soil that is saturated with water.
Besides water-loving flora, wetlands are important habitats for several wildlife species. A significant number of bird, insect, and other wildlife species depend on wetlands for critical stages in their life cycles. For some species, these wetlands are important feeding and or resting grounds.
Recently, wetlands have been gaining a lot of attention for they can contribute to improving water quality. Due to this, despite the fact that a lot of wetlands are privately owned, their protection has become a public concern. By protecting wetlands and by keeping them healthy, their biodiversity would improve. Hydrophytes would flourish and act as filtering systems that are capable of removing sediment, nutrients and pollutants from water.
Although it is a well-established fact that wetlands contribute to water quality, not all wetlands are capable of doing this. Some wetlands are able to impede drainage flow from urbanized areas. While doing so, these wetlands would also filter out pollutants from whatever water would flow through them. Despite this, there are wetlands that provide no significant water-quality benefits.
Wetlands are important to both humans and animals, yet they are under threat due to human activity and extreme weather conditions. These threats are capable of affecting the water flows, nutrient balance, and biodiversity of the wetlands.
Through the years, classification systems have been developed to distinguish wetland types. Wetlands can be categorized according to their hydrology, water chemistry, soils, and the plant species found there. However, these categorizations do not indicate how much each type would be able to contribute to improving water quality.
Wetlands can be characterized based on what kind of vegetation is dominant. The dominant vegetation could either be trees, shrubs, or herbaceous plants. These wetlands may obtain their water from precipitation, runoff, or groundwater. Due to this, wetlands would vary in their water chemistry ranging from very acidic to alkaline.
The defining characteristic of marshes is that they are located at the edges of rivers, streams, lakes, or ponds. Marshes could either be permanently flooded or flooded only during high water periods. Marshes are usually dominated by submersed, floating-leaved, or emergent vegetation, like cattails, pondweeds, water lilies, and various sedges, like rushes, spike rushes, grasses, and forbs. Marshes can be subcategorized further into emergent marsh and hemi-marsh.
The primary distinguishing feature of emergent marshes is that it is dominated by emergent narrow- and broad-leaved herbs and grass-like plants as well as floating-leaved herbs. They are usually shallow and are present along the shores of lakes and streams. Plants common in emergent marshes include water plantains, sedges, spike-rushes, pond-lilies, pickerelweed, arrowheads, bulrushes, and cattails.
There are several ways for emergent marshes to form. They could form as a result of continental glaciation, formation of lake basins, drainage networks, and poorly drained depressions that could support wetland vegetation.
Emergent marshes may require certain soil characteristics to develop. However, this type of wetland is still quite versatile for it can develop in soils with textures of glacial sediment, including rock, gravel, sand, silt, or clay. The primary difference between emergent marsh and peatlands is the type of sediment overlying their mineral soil. Emergent marshes would accumulate circumneutral to alkaline, fine organic sediments. Whereas peatlands accumulate acidic organic sediments.
Wetness in emergent marshes varies depending on the time of the year. In months where precipitation is high, emergent marshes can get flooded. In times of the year where water levels are low seed bank expression and seedling establishment occurs. Flooding in emergent marshes can lead to the formation of oxygen-deprived sediments and peat accumulation. There are animals that can significantly affect several properties of emergent marshes. For instance, muskrat’s can create openings in emergent marshes which would then be colonized by submergent and floating vegetation. Beavers could also create dams in nearby streams and divert water into the emergent marsh.
Marshes that feature a mixture of emergent and/or floating-leaved vegetation interspersed with a submersed plant community and are found in deeper waters is what is known as hemi-marsh. Sago pondweed, coontail, and wild celery are the usual plant species that are part of the submersed community. Broad-leaved cattail, American lotus, white water lily, and common bur-reed are the usual plant species that are part of the emergent or floating-leaved group.
Hemi-marshes feature a unique combination of emergent and floating-leaved plant species with open water. This creates an ideal habitat that provides sufficient food and cover conditions for many aquatic-dependent birds and amphibians. Birds would usually comb these areas to look for prey and or use them as areas for nesting and rearing their young. The rich vegetation also provides an exceptional nursery for young fish and is a great production area for the zooplankton and insects that are a critical part of the food web.
Sedge meadows, also known as wet meadows, are wetlands with soils that are permanently or near-permanently saturated with water. Sedge meadows are usually found between marshes and other wetlands with less-saturated soils, or in places where wet depressions and swales, or around where groundwater comes out of the soil. Sedge meadows are wet grasslands that are often dominated by sedges and grasses with relatively few forbs or broad-leaved flowering plants. A lot of bird, reptile, and amphibian species frequent sedge meadows.
Like the traditional prairie, a wet prairie is herbaceous and is dominated by graminoids and forbs. They are usually wetter than mesic prairies but are less wet than sedge meadows. There are wet prairies that resemble both wet prairie and mesic prairie. This type of prairie is what is known as wet-mesic prairie and is considered the driest type of wetland in the Midwestern area of the United States. Wet prairies are host to a wide variety of animals.
Fens and seeps
Fens and seeps are some types of wetlands that are fed by groundwater that seeps out of the soil’s surface. Different plant species vary with regards to what water chemistry and pH level they are adapted to. Thus, the water chemistry and pH level of the groundwater that seeps out would determine what plant species would dominate in these types of wetlands.
This type of wetland is usually fed by alkaline groundwater emerging from calcareous or dolomitic soils or bedrock zones. Aside from that, fens have a layer of peat formed from dead plant material. Vegetation in fens is composed mostly of herbaceous plants but it may also include some shrubs and trees.
Seeps or seepage marshes are usually present in the base of slopes, glacial moraines, wetland borders, headwater, or along stream drainages.
Bogs are wetlands that aren’t fed by streams or groundwater but are fed solely by precipitation instead. This type of wetland is dominated by peat moss, which may form a floating mat over deeper water that supports a rich assortment of specially adapted species. Peat moss is acidic and it acidifies the water, lowering the pH to as low as 3.0 in bogs. Due to the formation of a floating mat, bogs have a cool micro-climate. They are also nutrient-poor and have very low oxygen levels. These conditions are perfect for unique carnivorous plants such as sundews and pitcher plants.
Swamps are often found near rivers and streams. They are low-elevation floodplains that collect water from the aforementioned water bodies. They drain the water back to the rivers and streams but at a slow rate. Swamps are usually woody. There are times of the year where the water is stagnant. Swamps are nutrient-rich and have shallow waters. Due to these characteristics, swamps are important habitats for wildlife such as wild ducks, fish, otters, snakes, freshwater crustaceans, and more. There are two major classes of swamps and these are forested swamps and shrub swamps.
Just like regular forests, forested swamps are dominated by trees but only the water-tolerant ones.
Small- to medium-sized perennial woody plant species or shrubs dominate shrub swamps.
Wetland Types for the purpose of Evaluating Water-quality Benefits
Wetlands can be categorized into two broad categories when it comes to determining their water-quality benefits. These categories include riparian wetlands and interstream divide wetlands.
Wetlands that are adjacent to streams and are periodically soaked due to surface and subsurface water flows towards them are known as riparian wetlands. These wetlands tend to be narrow. Soils in riparian wetlands are usually deposited by flowing water or are alluvial.
Interstream divides are usually large and the soil present in them are nonalluvial or were not deposited by water. Poor drainage in flat areas where rainfall exceeds evapotranspiration leads to the formation of Interstream divides.
Riparian and interstream divide wetlands are similar with regard to wetness. However, they vary in several aspects that they also make different contributions to water quality. To understand how wetlands can improve water quality, a deeper understanding of the natural vegetation, or in other words the dominant plant species, needs to be developed.
The Importance of Wetlands
Due to the fact that wetlands can improve water quality and are an important habitat for a wide array of species, they are considered a valuable natural resource. They are capable of slowing down runoff which reduces erosion and prevents sediment transport. This is highly beneficial for environments downstream, especially that the productivity of some habitats such as estuaries, seagrasses, and reefs are sensitive to the negative effects of water sediments. Healthy wetlands can soak up excess nutrients from any flowing water that flows through them. They are also capable of capturing, processing, and storing contaminants. Moreover, if the natural flow of water through the wetlands is left undisturbed, potential environmental stressors such as sediments, nutrients, acids and/or metals present in the soil wouldn’t be released into the water. Wetlands are important when it comes to the management of urban stormwater and effluent for they can assist in the removal of bacteria and or other harmful microorganisms in the water. This, along with the fact that they can remove nutrients and suspended materials in the water before the water is returned to their corresponding water body. The best thing about wetlands is that they are capable of improving water quality through natural processes.
Wetlands present in a watershed have essential hydrologic, geochemical and biological functions. They are capable of reducing water flow velocity which is important for flood mitigation. The vegetation present in wetlands can facilitate the movement of water through the soil which leads to groundwater recharge. As discussed earlier, they are capable of improving water quality. Aside from that, wetland vegetation is capable of absorbing carbon dioxide. They are important habitats for wildlife as well.
Wetlands and their effects on Surface Water Quality
Be it urban or rural upland areas, their drainage water must pass through the riparian area before reaching the stream or any other body of water. While this water travels through the riparian area, chemical, physical, and biological processes in the riparian area can alter the quality of the passing water.
Flood Water Management
Besides improving water quality, riparian wetlands are capable of mitigating storm runoff as well. Since riparian wetlands are depressions found in elevated areas, runoff would collect in them first before moving downwards to areas of low elevation. Due to this, the runoff would lose velocity. The water that collects in the riparian wetlands may either contribute to streamflow when full or contribute to groundwater movement. Essentially, riparian wetlands act as a holding area for large quantities of surface water and they are capable of releasing their stored surface water slowly. A one-acre wetland, one foot deep, can hold approximately 330,000 gallons of water. Without the riparian wetland, stormwater would rush down the slope without being slowed down. This high-velocity runoff could easily damage agricultural lands, structures, natural habitats, etc.
Removal of Nutrient and Sediments
Agricultural activity would usually make a land area susceptible to sediment generation and nutrient buildup. Wetlands are capable of mitigating this negative effect of agricultural activity by removing nutrients and sediments from the water.
There are several ways for chemicals and nutrients to enter a riparian wetland.
Chemicals and nutrients are dissolved in the runoff water itself and enter the riparian wetland directly.
The sediments that are carried by the runoff are laced with chemicals and nutrients and are deposited in the riparian wetland.
Groundwater may seep into the riparian wetland and could carry the chemicals of the rocks that it percolates through.
Nitrogen and phosphorus are the two most common inorganic nutrient pollutants that would enter wetlands. However, the wetlands are capable of removing these nutrient pollutants from the water by either transferring them to the sediment, by having the vegetation absorb them or by transforming them into atmospheric chemicals.
In upland areas, nitrates present in the soil are lost primarily through subsurface drainage. In riparian wetlands, these nitrates are either absorbed by the plants or converted to nitrogen gas and lost to the atmosphere through an anaerobic process called denitrification which is carried out by microorganisms. There are wetlands that are capable of removing up to 80% of a water’s nitrate concentration through the denitrification process.
Nitrogen in the form of ammonium may enter wetlands mainly through surface runoff. The plants present in the wetlands would absorb the ammonia and use it as a source of nitrogen. Wetlands are home to a wide variety of microorganisms, some of them play an important role in the nitrogen cycle because they can convert ammonia to nitrogen gas. The ammonia could also be converted to nitrate which is more readily removed from the water by the wetland plants.
Through agricultural runoff or by wastewater effluent, phosphorus enriched runoff may enter water bodies which may lead to blooms of nuisance algae that clog water intakes, increased turbidity of water bodies, a decline of aquatic macrophytes due to shading, and many other water quality concerns. Wetlands are capable of retaining phosphorus through these mechanisms:
Adsorption onto peat and clay particles
Precipitation of insoluble phosphates with metals (iron, calcium, and aluminum) under aerobic conditions; and
Incorporation into living biomass of bacteria, algae, and macrophytes
Several studies have estimated that wetlands are capable of removing up to 92% of the phosphorus from the overland runoff. In other studies, it was revealed that wetlands are capable of reducing up to 46% of the phosphorus in rivers.
Particles that float in moving water such as fine clay particles, silt, sand, and gravel are what are referred to as sediments. These sediments are capable of carrying chemicals such as phosphorus, organic nitrogen, and some metals such as iron or aluminum as these chemicals are capable of attaching to these particles. There are certain kinds of pesticides that can attach to sediments as well. Since wetlands can significantly reduce runoff velocity by holding the water, they would allow these sediments to settle on the wetland bottom. Besides carrying chemicals, the sediments themselves have the potential to damage aquatic ecosystems by clogging fish gills, suffocating bottom-dwelling or benthic organisms, reducing fish reproductive habitat or the benthic substrata, reducing water clarity, reducing primary productivity due to physical burial and reduced light availability. Studies have shown that wetlands can reduce sedimentation by as much as 98%. This would vary depending on local hydrology. There are other studies that investigated the effects of wetlands on watersheds. In these studies, they discovered that watersheds made up of 40% wetlands have up to 90% lower sediment loads compared to watersheds with no wetlands.
Wetlands may exhibit seasonality with regards to their function. For instance, during summer and early fall, the emergent and submerged aquatic plants present in the wetlands would grow faster. Due to this, they take up large quantities of nutrients from the water and sediment. Since the plants would take up large quantities of nutrients they would act as a sort of “nutrient sink”. Thus, during summer, wetlands are capable of reducing the possibility of nutrient pollution.
Runoff water that passes through developed areas like agricultural fields could pick up large amounts of nitrate-nitrogen and phosphorus. These are nutrients that are important for crop growth. However, they can be harmful to humans and animals in reasonably high doses. Moreover, these nutrients can end up in water bodies which may stimulate algae growth in them. This stimulated algae growth may lead to the depletion of the water’s dissolved oxygen. Once the oxygen is depleted, fish and other aquatic organisms that depend on oxygen would die off. This would lead to the disruption of aquatic food chains. There are studies that demonstrate that a significant amount of nitrate-nitrogen is stripped away from subsurface flow as they pass through the riparian areas.
There is one study which was conducted in a wetland in North Carolina that investigated the effects of riparian vegetation on the nitrate-nitrogen concentration that is present in shallow groundwater. In this study, researchers observed that the nitrate-nitrogen concentration dropped from 15 milligrams per litre to 2 milligrams per litre. This reduction is significant because a nitrate-nitrogen concentration of 10 milligrams per litre or higher is considered unsafe according to the Environmental Protection Agency. The researchers noted that the significant reduction in nitrate-nitrogen concentration happened only after the contaminated water passed through 30 to 50 feet of the riparian areas. There are published longitudinal studies that measured the amount of nitrate-nitrogen content that riparian areas removed annually. In one study, they found that riparian areas are capable of removing nearly 85 percent annually. There are also studies that investigated how much nitrate-nitrogen is removed per acre of wetlands. According to one study, an acre of wetland found at the edge of an agricultural field is capable of removing 27 pounds of nitrate-nitrogen while an acre of wetland found near the stream can remove 4 pounds.
Although there are several processes present in a wetland that could eliminate nitrate-nitrogen, most researchers believe that denitrification is the foremost process that does this. In the denitrification process, certain soil bacteria species convert nitrate-nitrogen to nitrogen gas. This nitrogen gas would eventually return to the atmosphere.
With regards to water quality improvement, the location of wetlands is more important than either the degree of wetness or the size of the wet area. Denitrification can occur in both narrow areas of vegetation and large downstream areas. Most of the wetlands would have already removed most of the nutrients before the water even reaches the downstream areas. Soil near streams which are wet because of the surface or subsurface water flows towards them are effective at removing nitrate-nitrogen from agricultural and other runoff waters.
Benefits of Interstream Divide Wetlands
The soil in the interstream divides either drain poorly or very poorly. While riparian wetlands are present immediately adjacent to a stream or other similar bodies of water, interstream divides are located some distance away from them. Generally, interstream divides are located at a higher elevation compared to riparian wetlands.
Due to the fact that interstream divides are relatively flat and are often located miles from a naturally occurring drainage outlet, water moves slowly across their surface and excess rainfall would take weeks to dissipate. The degree of wetness in interstream divides depends on rainfall and evapotranspiration. Since rainfall and precipitation are affected by the seasons, water would tend to pool in interstream divides during winter and spring. It is during these seasons that precipitation greatly exceeds evapotranspiration. However, during summer and fall, precipitation is equal to or less than evapotranspiration. Thus, the soil dries faster and the water table drops more than 3 feet below the soil surface during these seasons.
Pollutant Concentrations are Diluted
Runoff water usually does not pass through interstream divide wetlands. Thus, interstream divides are not able to remove pollutants from surface runoff water. Due to the fact that interstream divides are located at high elevations, they are capable of contributing to surface runoff to some extent. They serve as sources of water that flow downstream. The water that collects in interstream divides is usually rainwater. Undeveloped interstream divides usually have soil that has very little plant nutrients. As the nutrient-poor-runoff exits the interstream divide, they pick up nutrients especially from agricultural areas close to the stream along the way. As a result, the nutrients and sediments present in the runoff near the stream, or similar water bodies, are diluted. This dilution effect that interstream divides are capable of providing improves surface water quality, albeit in a passive sense.
Agricultural Drainage Treatment
Plant nutrients and sediments present in agricultural drainage water are reduced by up to 30 to 100 percent when this drainage water is pumped into a wetland first instead of discharging them directly to a stream or any similar body of water. The longer the drainage water remains in the wetland, the more it loses its pollutants, the lesser the amount of pollutants entering the stream or similar water bodies. Temperature, wind speed, and humidity are the major meteorological factors that affect runoff velocity, while precipitation affects the volume of the runoff. If the conditions are correct, the runoff would have its volume and speed increased. As a consequence of the increased runoff volume and speed, the amount of nutrients and sediment carried by the runoff increases as well. Moreover, this increases the amount of nutrients and sediments that reach the stream. In essence, undeveloped interstream divide wetlands can act as a sort of sink for agricultural drainage. However, a pump must be used to move the agricultural drainage water up towards the elevated interstream divide wetlands. Aside from that, a diffuser canal is needed so that the agricultural drainage can be distributed evenly in the interstream divide. The diffuser canal is essential because, without them, runoff channels would develop which would reduce the amount of time the drainage water would remain in the wetland. Due to this, the wetland’s benefits towards water quality would be reduced. Since interstream divide wetlands need to be modified extensively to act as a drainage sink, their water-quality benefit is deemed marginal.
Wetlands Effect on Groundwater Quality
Wetlands have a significant effect on groundwater quality and quantity. The thick vegetation present in wetlands allows the water to readily percolate through the soil. Unfertilized wetland soils replenish the groundwater with a supply of good quality water. However, wetlands recharge the groundwater at a slow rate.
There are two main reasons why wetlands are damp.
First, wetlands receive a large volume of water from both surface runoff and rainfall.
Second, water in wetlands percolates slowly through the soil.
Linking Groundwater and Surface Water
Wetlands act as a sort of link between groundwater and surface water. Wetlands can collect runoff water and would either release the collected water slowly or let the collected water percolate into the soil to recharge groundwater supplies. Due to this, wetlands are able to make positive contributions to soil moisture, especially in agricultural settings. Wetlands are also capable of mitigating damage from flooding and water erosion by acting as a catch basin. Depending on the type of wetland, their surface water may be present all year round or come and go depending on the season. The volume of the surface water affects the rate at which groundwater supplies are recharged. Intentionally draining wetlands can negatively affect their capacity to recharge groundwater. This could also adversely affect the surrounding soil moisture, especially during dry periods. Seasonal changes in precipitation can influence the direction of where the groundwater would flow within a wetland. During springtime, there is higher precipitation and the wetland water level may be higher than the water table. When the wetland water level is higher than the water table’s, they would act as a point of recharge for the groundwater. However, during summertime, precipitation is usually sparse. Due to this, the wetland water level would drop below the water table’s level. The water would then move from the groundwater table and into the wetland. In essence, the wetland acts as a point of groundwater discharge during seasons of low precipitation.
Benefits of Riparian Wetlands
Riparian wetlands, since they are located in a relatively low area, tend to receive large volumes of runoff from upslope areas such as agricultural fields and or interstream divide wetlands. The water that moves through the soil surface of riparian wetland moves quickly when it is moving towards an outlet. Due to this fast movement of water, the riparian wetland is not able to recharge the groundwater. Yet, they are still capable of removing and trapping pollutants. Riparian areas adjacent to streams and similar water bodies are capable of discharging groundwater into them.
Benefits of Interstream Divide Wetlands
Due to the fact that interstream divide wetlands are located in elevated areas, their primary source of water is rainfall. Water that collects in interstream divide wetlands remains fresh because their soils are usually unfertilized. However, interstream divide wetlands are flat and poorly drained that their water percolates the wet soils very slowly. Due to this, only a small amount of their water reaches the groundwater supply. There is a study conducted in North Carolina which estimated the groundwater recharge rate of poorly drained wet soils like those found in interstream divide wetlands. In this study, researchers estimated that poorly drained wet soils usually have a groundwater recharge rate of 1 inch per year or less. Well-drained soils, on the other hand, have a recharge rate of 10 inches per year or more.
Other Water-quality benefits
Removal of a wide range of Contaminants
Several contaminants present in both agricultural and urban runoff such as pesticides, metals, and landfill leachate can be eliminated or be made less harmful by wetlands. Processes that are facilitated by wetlands such as photolysis and adsorption are capable of dealing with the aforementioned contaminants. Due to the fact that plants grow at a faster rate in wetlands, the wetland is able to provide a huge surface area for adsorption, plant sequestration, microbial degradation, and exposure to light for photolysis.
Removal of Pathogenic Microorganisms
Some diseases are spread by the consumption of water that is contaminated by pathogenic microorganisms. These illnesses are called waterborne diseases. Wetlands can help decrease the risk of waterborne diseases by trapping the pathogenic microorganisms through sedimentation or adsorption, or by the natural predation of pathogens by other microorganisms. Research has estimated that wetlands can remove up to 80 to 90 percent of pathogens in the water.
Other Benefits of Wetlands
Wetlands are diverse. They vary with regards to their depth, length of flooding, and the characteristics of their surrounding land. Each wetland is unique and they provide habitats with unique characteristics that can support a wide array of animal species.
Even wetlands that do not have any standing water at certain times in the year, still provide valuable habitat for many species. The unique vegetation that grows around the edge of wetlands provides food and shelter for many wildlife species, especially migratory animals.
Small aquatic invertebrates would increase during times when the wetland’s water level is high. During dry months, the aquatic invertebrates can enter a dormant stage to survive. When spring comes around, the wetland’s water would increase and the invertebrates would exit the dormant stage and become active. The hatching of aquatic invertebrates also usually coincides with the arrival of migratory animals.
Wetlands that are perpetually wet throughout the year may contain emergent, submerged, and floating vegetation throughout most of their area. This vegetation has certain characteristics that allow them to support a wide variety of wildlife species.
Plants around the edges and shallow areas of deep-water wetlands can provide food and shelter for various wildlife species. Wetlands with deep water have properties that make them a suitable habitat for various aquatic species. Deep-water wetlands also offers a source of recreation such as fishing, canoeing, and swimming.
How are our Wetlands Today?
More and more people are becoming aware of the benefits of wetlands. Unfortunately, the damage has been done and there are already significant losses in wetlands. These losses have attracted significant attention from the public. In the United States alone, 50 percent of the wetlands in North Carolina have been converted to other uses. The other 30 percent, about 5 million acres, are located near the interstream divide, and the remaining 20 percent, about 1 million acres are riparian areas adjacent to the streams. Due to the fact that these wetlands are adjacent to streams, they provide water quality benefits for that body of water. 300,000 to 500,000 acres of the lost wetland can be restored as narrow, vegetated strips. However, it is still difficult to determine if the restored wetlands could provide adequate or cost-effective water-quality protection.
There are several threats to wetlands. These include earthworks, drainage, water extraction, climate change, poor agricultural practices, feral animals such as wild pigs, invasive plants, and uncontrolled fires. These activities and encroachments have the following effects:
Erosion - which may result in increased sediment and ultimately block out light that is essential to aquatic plants and could smother aquatic animals.
Reduction in the wetland’s ability to remove herbicides, insecticides, and fungicides
The wetland’s ability to remove nutrients from the water would be significantly reduced which leads to the rapid and uncontrolled growth of plants and algae. This sudden overgrowth can block out light and, in the case of toxin-producing microorganisms, the water becomes toxic for wildlife, livestock, and humans.
The loss of wetlands leads to the loss of vegetation which leads to rising water tables.
Sodium that is naturally present in the soil would move closer to the surface which causes increased soil salinity which hinders plant growth.
The loss of wetlands facilitates the release of acids and metals into the soil and water. This could then lead to water quality deterioration. Water quality deterioration would then lead to a drop in fish population which could then allow acid-tolerant species to dominate. This could also lead to groundwater contamination. The acidity and presence of metals could also reduce agricultural productivity. The acidity of damaged wetlands could also cause damage to infrastructure near them through corrosion.
What should we do for our wetlands now?
A more reliable method for determining how well wetlands can improve water quality, something similar to a rating system, needs to be developed. This theoretical rating system would aid policymakers in coming up with decisions with regards to the use of wetlands. For instance, if the theoretical rating system would rate a certain wetland as having marginal water quality benefits, then the argument that this wetland is better off being utilized for other purposes would hold more weight. On the flip side, wetlands that do offer water quality benefits would be protected.