环境科学论文代写 Opportunities Exist For Their Restoration And Creation
Wetlands contribute towards some of the most biologically diverse ecosystems that exist on our planet, providing habitats for a huge variety of both aquatic and terrestrial wildlife and plants by acting as biological and genetic pathways between water and land. They also support endemic and migratory species by providing valuable rearing and breeding habitats. In fact, within British wetlands, there are more than 3,500 species of invertebrates, 150 aquatic plants, 22 ducks and 39 wader species, as well as Britain's native amphibians that depend on these wetlands for breeding (1). Occurring naturally on almost all continents of the Earth, wetlands are ecologically important in the environment and provide many essential processes for example water purification, flood control and shoreline stability. These provide a variety of aquatic habitats such as swamps, marshes and bogs. In addition, they are important buffers against extreme weather; absorbing water during heavy rain to help prevent flooding and providing the surrounding areas with water during draughts. They support and restore underground water systems, store sediments and process pollution while being home to a huge variety of species. With controlled flooding, wetland habitats can increases fish abundance and species richness (2,3). The water found in such habitats includes freshwater (4).
The hydrological cycle is an essential process regarding wetlands and is vital in keeping a constant balance of water, both above and below sea level. Water is transferred from one reservoir to another via processes including condensation, evaporation, infiltration and precipitation, providing a global water recycling system and contributing towards producing a critical resource for human well-being; clean running water (5). Freshwater wetlands rely on the hydrological cycle because as the cycle proceeds, the water is purified, which in turn produces freshwater.
Freshwater habitats are among the most productive ecosystems in Britain and include both flowing waters (lotic ecosystems) such as rivers, and still standing waters (lentic ecosystems) such as lakes. They can regulate flooding, erosion, sedimentation, local climates and water quality, and also facilitate the dilution and disposal of pollutants (6). In particular, freshwater ecosystems control runoff processes from the land to rivers, floods and droughts (7) and water quality (8). This is absolutely essential for the ecosystems and wildlife to which they supply for.
The distribution of freshwater and wetland habitats across Britain is uneven, with Scotland holding the majority of the freshwater in the UK, specifically 70% by area, and more than 90% by volume (9). In addition, there are almost 570 lakes in Wales and a much larger number of smaller ponds and wetland pools (6).
However, despite this, lowland wetland and freshwater habitats have now become a conservational priority in Britain, following a dramatic decline of area within the last century. They are now among the rarest and most threatened habitats in Britain, which of course has dramatic consequences and effects for the plants and animals to which they provide resources for. Both lowland raised bogs and fen are referred to as priority habitats within the UK Biodiversity Action Plan. Also, there are six separate lowland wetland habitat types under Annex I of the EU Habitats Directive (10).
These habitats and the plants and wildlife they support are subject to many various pressures and threats. These must be fully understood before any action can be taken to restore, protect and recreate the habitat and associated ecosystem. The three primary threats regarding these habitats are land-use disturbances, altered hydrologies, and the introduction of non-native species (11).
环境科学论文代写 Opportunities Exist For Their Restoration And Creation
环境科学论文代写 Opportunities Exist For Their Restoration And Creation
Perhaps the most relevant threat to freshwater and wetland habitats is the issue of climate change. An assessment of water balance was undertaken for Britain using both current and future climate scenarios (12). Results showed that water availability could increase in winter across the whole of Britain, and northwest Ireland and northwest Scotland could have some increased water availability in summer. Other regions would have decreased water availability during summer months. Significant seasonal stresses could occur due to this climate change and the associated lowering of water levels. Any major water loss can severely damage these habitats. This also includes the extraction of freshwater for drinking water, which is of increasingly high demand as the Earth's population continues to grow exponentially. This may consequently affect the natural differences in water quality between ground water and surface water that many species depend upon. In addition, the usual wetland species may be invaded by other species which are more adapted to a drier environment. These may consequently out-compete the usual wetland species due to better adaptations, leading to possible declines in population and, in worst cases, extinction of the native wetland species. Natural lowland raised bogs receive water inputs from precipitation alone, so they are particularly sensitive to any additional inputs of surface or ground water, especially if these are polluted or enriched. Water pollution can have severe effects. This is an example of altered hydrologies and the introduction of non-native species.
Following on from this, air pollution also has an effect on these habitats. Air pollution is where chemicals and pollutants are introduced into the atmosphere which usually cause discomfort and disease to humans and also damage to food crops and ecosystems. The deposition of unwanted or toxic nutrients onto these habitats due to such air pollution can alter the pH, nutrient values and ratios in such habitats. pH and nutrient values are usually kept relatively constant in ecosystems. If they are not, damage to organisms can occur. These changes as a result of pollution may cause invasion by other organisms that are well adapted to the new pH and nutrient values. This again may cause out-competition. Deposition of ammonia due to air pollution is very high in Britain. This is another example of altered hydrologies and the introduction of non-native species.
In addition, this could cause eutrophication. This is a process where water acquires a high concentration of nutrients, especially nitrates and phosphates. These cause excessive growth of algae which then die and decompose. This induces the high level of organic material and decomposition organisms to deplete the water of oxygen, which in turn causes the death of other aquatic organisms, for example fish. Eutrophication is a natural process for water but is greatly sped up due to human activity.
Furthermore, these sites have been destroyed even further due to peat extraction. This is where peat has been extracted and bogs have been converted to agriculture, forestry or urban development. In response, the valuable habitats have been completely demolished and again have effects on the ecosystem and species they support. Many organisms will have been forced to migrate, others will have declined in population, and some may have become extinct. It has been observed that many losses of fen sites through conversion to agriculture have been very widespread (13). This is an example of land-use disturbances and shows how human activity is affecting wetland and freshwater habitats and ecosystems in Britain.
Habitat fragmentation is another cause of destruction in lowland freshwater and wetland habitats. Habitat fragmentation occurs by either natural geological processes that alter the layout of an environment, or by human activity such as land conversion and urbanisation which occurs at a much faster rate and causes extinction of many species (14). Most surviving sites are small in size and isolated from other patches of similar habitat. This means that opportunities for species to disperse between sites and re-colonise restored sites are limited and immigration may be impossible (13). In addition to this, it also means that on each individual fragment there may be increased crowding and competition for resources. This is a common cause for species becoming threatened or endangered. One explanation for this is due to the organisms only being able to reproduce with others on the same fragment, which may eventually lead to inbreeding and a loss of genetic variation. As a consequence, if a disease then breaks out or if environmental conditions suddenly change, the subpopulation is less likely to be able to adapt to the new environment, causing possible extinction. This is another example of land-use disturbances. One solution to this problem is to establish pathways between the fragments of the habitats. This can be achieved by preserving or planting corridors of native vegetation which aims to increase reproduction between the isolated subpopulations, providing much needed genetic variation within the population as a whole.
But with much of Britain's wetlands disappearing how can they be restored or, if necessary, created? This is needed in order to maximise benefits of the ecosystem services they provide.
It is a tough question when thinking of restoration because throughout history our wetlands and freshwater habitats have been manipulated for our means. Water levels have been kept at a stable constant to give us a fresh water source but also flood protection. This means the natural hydrological means are unknown, making it hard to predict how a 'natural wetland' should be (15).
When renewing wetlands, the problem causing the degradation must first be removed. In many cases this is enough to restore the land to its original state, this is the passive approach and allows nature to restore plant communities and allow animals to re-colonise the area over time. It also means soils revert back to their original state thus helping growth back to the previous system. The passive approach is only effective if the site still has the overall characteristics of a wetland and degradation will halt once the problem has been removed. Such approach is desirable because it means minimal cost, low management and a high success rate.
When degradation is too high and the passive approach is unlikely to achieve the desired goals, an active approach must be used, meaning intervention by humans. The methods involved could mean redirecting water flow with man-made structures, re-contouring the lands, controlling non-native species, intensive planting and seeding and bringing appropriate soils to the site which encourage native plants to thrive. Along with this approach comes significant planning and management resulting in a much more costly restoration.
One active approach which has shown success in increasing plant diversity in China is soil seed banks. By taking records of the seeds in a given habitat, it is possible to measure the change over time and season, giving an idea into what the habitat should look like from a plant species perspective. Knowing the seed bank information and controlling natural conditions promotes short term favourable plant communities (16). This can be taken even further by using artificial cultivation and seed planting to aid seed germination of submerged or emerged plants where the water is perhaps too deep (17). Combining these techniques is important when restoring the landscape of a wetland because it is often found that there is a lack of large flowering plants. These techniques are great because of low impact on the current environment; however they do have high costs due to the time needed to gain a full annual seed bank.
On a pessimistic note, recent research has shown some wetland habitats to be beyond restoration. In Holland, drained fens resisted calciphilic plants upon rewetting even with surface water treatment and calcium to reverse acidification (15).
Freshwater habitats such as streams are usually urbanised because of their freshwater and as a means of disposing of pollution. This causes stress on the habitats but there are four main restoration techniques used to help urbanised freshwater habitats, the first is stormwater management. There is often a network of pipes and structures designed to move water quickly off the landscape and into a catchment to prevent property damage. Stormwater management is now being taken further by using smaller catchment areas such a small ponds or porous pavements to reduce peak water flow. In theory, this should mimic a natural landscape and improve water quality treatment (18). There is still research that remains to be done on the overall effect of stormwater management on the entire ecology of urban streams (19).
环境科学论文代写 Opportunities Exist For Their Restoration And Creation
环境科学论文代写 Opportunities Exist For Their Restoration And Creation
Secondly, bank stabilisation can be used to minimise erosion to streams. Structural materials, bio-engineered products, and stream bank re-grading can all be used to re-enforce the bank (18). Mats of geotextile fabrics can be placed over a bank while plants germinate and root, thus giving it even more natural protection. This technique is very effective in rural freshwater habitats; however is not usually enough for urbanised areas due to high peak flows as a result of storm flows (20).
Thirdly, channel reconfiguration and grade control are two techniques but are often used together because they both involve heavy manipulation to the stream. These techniques aim to repair heavily incised channels, improve water conveyance and improve streambed and bank stability (18). Often the re-structuring of a stream with the intent of moving water in a desired way, perhaps to alleviate pressure on a certain bank, causes structural problems further downstream thus hindering success of many of these projects.
Finally, riparian replanting and management is a technique that has been used for urban and rural freshwater habitat restoration. This first means removing invasive exotic species and will typically require management to keep their populations low. The replanting of plants gives banks more structural stability but also increases aquatic biodiversity (18). Using this technique is great; however in urban areas land is expensive and will incur a higher cost than in rural areas. Land is also limited in urban areas because of pavements and development along river banks, however even small plant restoration is enough for a positive effect (18).
Creating freshwater and wetland habitats is much more difficult than restoring current ones because conditions have to be specific and exact in order to keep them sustained (21). A wetland creation project usually takes six months to complete before showing results, whereas a restoration project is usually two weeks. It requires much more planning and the constructed wetlands are often specific in function, mainly being used as stormwater management and pollution control. Constructed wetlands lack the full range of wetting and drying ranges because their water levels are dominated by surface runoff. This makes it hard for constructed wetlands to support wide species diversity (22).
Wetland and freshwater habitats are an important landscape for many different reasons but still they are disappearing at an alarming rate. Unfortunately there is little research about restoration and creation of both habitats, making the success rates of such projects "hit and miss". It is also very time consuming and expensive. It seems clear that the most effect approach to saving wetland and freshwater habitats is educating the public to their importance and begin preventing degradation and therefore less repair systems will be required.
环境科学论文代写 Opportunities Exist For Their Restoration And Creation