TOPIC: ROLE OF CONSTRUCTED WETLANDS IN IMPROVING WATER QUALITY AT DANDENONG CREEK CATCHMENT
Wetlands are essential ecosystems that provide various benefits in different parts of the world. Despite the notable benefits, many wetlands are threatened due to overexploitation heightened by the increase in human activities, economic motives, and change in land uses Lukacs and Finlayson (2010, p. 598). The global problem of climate change also contributes to loss of various wetlands due to extreme cases of droughts and reduction in the amount of rainfall to recharge the ecosystems. Undoubtedly, one of the major benefits of the wetlands is maintaining and improving water quality through various processes including filtration, trapping of sediments, and other purification mechanisms. A healthy wetland is composed of a rich diversity of animal and plants, which provides the insight of how the ecosystems offer habitat for many species of organism.
The biodiversity, particularly the macrophyte species also perform the functions of filtering and removing of water contaminants; thus, contributing to water purification. The essence of improving the quality of water entails removal of nutrients, sediments, hydrocarbons, pathogens, and other biophysical or chemical contaminants. Despite the mentioned essentialities, the natural wetlands around the world are under threat and are continually being destroyed particularly because of the changes in land uses, which are facilitated by the economically motivated world. As such, the remedial measures that many countries including Australia, which is the context of this study, have diverted to the construction of artificial wetlands to carry out the same purpose as the natural wetlands.
It is undeniable that wetlands are one of the world’s most productive ecosystems comparable to coral reefs and rainforests. They have an immense diversity of plant and animal species including microbes and higher organisms such as insects, amphibians, birds, reptiles, mammals, fish, and plants. However, as Sani et al. (2013 p. 1) noted, the Australian wetlands are under pressure caused by poor agricultural activities, climate change, earthworks, water extraction, and drainage amongst other factors. Such threats have led to various negative impacts such as erosion, which result in an increase of sediment which clouds the water and reduces the quality. Too much sediment also causes a reduction in the volume of water in the wetland and smoothers the aquatic life.
Industrial activities and poor agricultural practices have also led introduction and mobilization of different water pollutants such as insecticides, herbicides, and fungicides. Yu et al. (2015 p. 99) highlighted various anthropological stressors that change the quality of water to include dissolved organic carbon, agricultural run-offs, nitrates phosphates, and other natural organic matter. Markedly, the water quality of wetlands is influenced by the biophysical and chemical, mechanisms that alter water composition. Hey et al. (1994 p. 381) measured the concentration of suspended solids, nitrates, and phosphorous at the inlet and outlets of the Wetlands in River Des Plaines in the United States of America to demonstrate how construction of wetlands improve water quality. The results showed that the wetlands remove substantial quantities of the dissolved and suspended pollutants through trapping, filtration, and settling out of sediments in addition to reducing the velocity of the storm waters.
The solution to the threat of the natural wetlands is the construction of artificial wetlands to mimic the natural processes and provide the same benefits. As Sun et al. (2015 p. 511) mentioned, the built wetlands are engineered to simulate the common processes that occur in the natural wetland ecosystems. Most importantly, the wetlands are constructed to allow sufficient treatment of wastewaters. For example, William et al. (2010 p. 2408) admitted that up to 20% of major rivers in Taiwan had been polluted particularly because of agricultural and industrial activities. As such, wetlands were engineered as alternatives to allow cleaning up of the polluted water bodies. The authors were particular on one of the largest wetlands in the country (Kaoping), which has multi-functions of secondary wastewater polishing and purification of the river. It is, therefore, apparent that artificial wetlands provide the best alternative for cleaning up polluted rivers and enhancing wastewater treatment to improve the quality of water.
Markedly, alteration of the water quality is largely enhanced by the human activities that are unsustainable. The growth and developments in industrial activities and agricultural practices are the main contributes to pollution of wetlands and diminishing water volumes. Morrice et al. (2007 p. 347 delineated various causes of water pollution and alteration of water chemistry, physical, and biological compositions. The authors ascertained that the human activities particularly agriculture, economic developments, atmospheric pollution are the major causes of wetland destruction and degradation. First agriculture result in land use changes as wetlands are converted to agricultural lands because of the increase in the worldwide demand for food (Haidary et al., 2013, p. 2218). The world’s population continues to grow by day and food insufficiency and insecurity is a global menace that inevitably results in conversion of former wetlands into farmlands. The forested areas are also destroyed, which in turn causes a change in the climatic elements that shows domination of droughts and unpredictable rainfall (Birch et al., 2004, p. 461). As a result, a number of wetlands have dried out and others heavily polluted. Additionally, excessive utilization of fertilizers, fungicides, pesticides, rodenticides, and herbicides alters the chemistry of the water particular because of surface runoffs. Karami et al. (2009 p. 3900) also added that there are various factors that cause environmental pollution of wetlands, which include drainage, pollution by wastewater, immethodical hunting, and human encroachment.
According to Birch et al. (2004 p. 459) anthropogenic activities in urban centers generate large volumes of wastes that are often directed to water bodies, which cause wastewater pollution. In fact, the problem is exacerbated by the increase in urbanization and urban sprawl to wetland areas leading to increased volumes and concentration stormwater and sewerage pollutants. The consequence is that the waterways receiving the discharge get polluted with a mix of contaminants including heavy metals from industries, hydrocarbons, oil spillages, and industrial chemicals. Agricultural based industries also release substantial volumes of wastewater contaminated with pathogens, nitrates, phosphates, and other organic matter. Lukacs and Finlayson (2010, p. 598) supplemented that the real effects of water pollution and quality alterations are often felt at the downstream; thus, comparison of the upstream and downstream waters through sampling techniques can be used in providing a rough analysis of the composition and levels of pollution.
It is from Lee et al. (2010 p. 2608) that the authors reveal that it is necessary to focus on non-point and point pollution sources. That is, wetlands can be contaminated by effluents from a specific or point source that is often easy to trace and control. On the other hand, pollutants such as the runoffs from agricultural fields are often dispersed and not easily regulated; thus, known as the non-point sources. The management of water courses including the wetlands demands considerations of various factors including the quality and quantity of water in addition to the land use systems. Murray et al. (2013, p. 132) also added that it is necessary for the water managers and other relevant authorities to monitor strictly the land use changes that affect the local wetlands and advocate for the best remedial measures. The overall idea is to moderate the human activities that have detrimental impacts on the environment. As Birch et al. (2004 p. 462) noted, environmental protection should take into account the effect of human activities on the wetlands, which are considered as the most productive ecosystem in the world. Despite being productive, wetlands are the most fragile ecosystems that are highly vulnerable the exploitative use and unsustainable management systems. As such, the issue of water pollution has changed the quality of water in the wetlands in Australia and urgent remedial measures are needed so as to protect the health of people, fish, and other wildlife living in such ecosystems (Tao 2014, p. 3363).
According to William et al. (2010 p. 2409) a constructed wetland is an artificial engineering design for the purpose of treating polluted waters caused by anthropogenic discharges such as industrial and municipal wastewater. The artificial wetlands are also used for treating of stormwater runoffs from urban centers or agricultural fields. The essence of improving the quality of water uses the same mechanism as the natural wetlands. As Sun et al. (2015 p. 511) mentioned, the wetlands use the natural functions that use of organisms, soil, and vegetation in the purification and removal of the water pollutants. Naturally, the large aquatic plants known as macrophytes, help in breaking down of the impurities in the wastewater so as to remove the pathogens (Shutes 2001 p. 441). The author clarified that there is a range of different plants (the macrophytes) that have the property of breaking down the pollutants in a wetland ecosystem such as the common reed and reedmace. The plants have been found effective in removing the pollutants in a natural wetland; thus, they are planted in an artificial ecosystem to conduct the same purpose.
Notably, the artificially designed wetlands emulate the features of the natural ecosystems. Shutes (2001 p. 441) explained the mechanisms and processes that happen in the natural wetlands. The author revealed that the natural macrophytes had large biomass both at the roots and leaves, where the roots have a dense system of the underground rhizome. The tissues in the subsurface grow both vertically and horizontally to form a dense and extensive matrix that allow high uptake of nutrients from the soil. Additionally, the plants have hollow tissues that transfer air from the leaves down to the roots; thus, allowing aerobic breakdown of the soil nutrients, which are often the pollutants removed from the water. The aerobic microorganisms thrive underneath the plants, and there robust reproduction enhances removal of the pollutants. Moreover, anaerobic microorganisms are found in the underlying soil; hence, allowing the breakdown of the organic pollutants even without the presence of oxygen.
Vymazal (2010 p. 530) also supported the concept by admitting that the engineering system of the artificial wetlands is just meant to copy the mechanism of the natural wetlands to allow treatment or purification of polluted water. The process involves an assemblage of the different microbial organism, wetland soils, and vegetation that helps infiltration of the contaminated water. Vymazal (2010 p. 531) supplemented that constructed wetlands are engineered to take advantages of the mechanisms and processes that happen in a natural ecosystem; however, in a more controllable environment. Therefore, it is easy to regulate and monitor the effectiveness and efficiencies of the constructed wetlands. It is because of the ability to control the constructed wetlands in terms of inputs and outputs which make them very efficient at removing suspended solids and organic matters. Nevertheless, the constructed wetlands may have less efficiency in removal of nitrogen and phosphorus, particularly if not well maintained (Kovacic et al., 2000, p. 1263).
William et al. (2010, p. 2408) noted that wetlands are complex environments that are designed to contain shallow waters and are dominated by water-loving vegetation known as hydrophytic plants. The design process ensures that the wetlands are shallow and highly vegetated to enhance the activities of sedimentation, biological uptake of nutrients, and fine filtration to remove the water pollutants. Markedly, the wetlands are made up of an inlet zone that is also known as a sedimentation basin to remove the coarse sediments (Radcliffe 2010, p.792). They also have a macrophyte zone that is shallow and extensively covered with the hydrophytic vegetation to enhance uptake of soluble pollutants and remove fine particles from the water stream. The macrophytes are prevented from scouring by a bypass channel. Evidently, the constructed wetlands are useful in the removal of concentrated soluble pollutants which cannot be done well other means. Birch et al. (2004, p. 460) added that depending on the design and maintenance, the constructed wetlands can be used for attenuation of storm events and reduce the velocity of water flow.
Conventionally, the constructed wetlands are ‘man-made ecosystems’ designed to ensure proper treatment of wastewater by removing the pollutants based on the natural processes of bio-filtration and biodegradation. The natural processes are also used in controlling and maintaining the efficiency of the artificial wetlands. Markedly, the main purpose of constructing the wetlands in Australia is to maintain the values and functions that were provided by the destroyed wetlands. As aforementioned, the natural wetlands have been under threat due to food insecurity that promotes conversion of wetland into farmlands, and other human activities such as industrialization, urbanization, which are enhanced by the rapid growth of human population (Bagalwa 2006, p. 140). The worsening climate also affects the quality and quantity of wetland waters; thus, making artificial wetlands imperative alternative for removing the dangerous sediments and other pollutants from the wastewaters. In summation, constructed wetlands have multiple functions and roles including but not limited to reducing the flow of stormwaters, providing habitat for diverse species of plants and animals, recharging the underground water, and improving water quality.
According to Lukacs and Finlayson (2010), the constructed wetlands are majorly used for purification of wastewater by integrating chemical and biophysical processes, which the same in natural ecosystems. The major advantage of the constructed wetlands is that they allow regulation, monitoring, and controlling of the treatment process by regulating the inputs and outputs in the systems (Radcliffe 2010, p.793). Depending on the design, the wetlands can remove various types of pollutants including suspended and dissolved organic matter, biological wastes, such as coliforms (Escherichia coli) and other pathogenic organisms. Landers and Knuth (1991 p. 150) revealed that wetlands are important in the management of water quality by assimilating nutrients mainly from the agricultural fields. The essence of removing the pollutants is to increase the water quality; hence, increasing the usefulness of the resource. Water is an essential resource for humans, animals, and plants, and its essentiality is only high if not polluted. In a nutshell, the purpose of constructing the wetlands is to deliver and distribute healthy water for human use and avoid harm to the aquatic animals (Yu et al. 2015, p. 100). Additionally, the wetland removes biodegradable pollutants from the soil; thus, helping in maintain the quality and fertility of the soil, which is an essential medium for food production. Notably, making the water free from harmful pollutants enhance economic, social, environmental health.
Blanca et al. (2012, p. 238) analyzed the suspended solids found in pollutants and found that they contain organic and inorganic materials; particular if the water is sourced from industries and sanitaria. However, Bagalwa (2006, p. 139) disagreed that artificial wetlands are inefficient in removing nitrogen and phosphorus as pollutants, particularly if the wetlands are not well designed. As noted, the effectiveness and efficiency of the wetlands depend on a variety of factors such as wetland site, wetland categories, wetland area, and hydrology (Chavan, Dennett, and Marchand 2008, p. 240).
Dandenong Creek Catchment is situated in the southeast part of Melbourne, which is found along the north-eastern shores of Port Phillip Bay (Dobbie and Green 2013, p. 144). The catchment stretches to about 881km2 of farmland, forest, urban areas, and reclaimed swamps. The differentiation in the land uses has occurred due to human encroachments, which have particularly led to destruction and conversion of a land use system to another. For example, the quest for food production has resulted in cutting down of large tracts of forests to pave the way for agricultural practices. The upper part of the catchment is dominated by forested land that offers a good habitat for wild animals and plants. Fortunately, the local authority in charge of the catchment area has in the recent past tightened the policies of cutting down of trees, which to some extent has limited the destruction of the forested section. Notably, the anthropogenic activities are majorly carried on the middle and lower parts of the catchment, which has a rich history since the 1800s and has led to the draining of a swamp called Carrum Carrum and construction of river Patterson. According to Dobbie and Green (2013, p. 145), the catchment has many waterways which include the Dandenong, Kananook, Eumemmerring, Blind, Monbulk, Corthanwarrabul, and Ferny Creeks. Notably, the essential role of the Dandenong Creek Catchment is to improve the safety and quality of water in addition to reducing the volume of water litters and sediments. The catchment also offers a unique recreational site that source revenue to the local authorities and translates to economic developments in Australia. Additionally, to provides habitat for wild plants and animals in addition to offering other ecosystem services.
Markedly, the literature review entailed a systematic evaluation and comparison of different works that relate to the topic of the study. First, the review starts with giving information about wetlands and water qualities. The chapter reveals that the quality of water is a fundamental consideration that must be made when using the resource in order to avoid harmful effects on people, animals, and plants. It is noted that water is a critical resource; thus, its quality and safety should be maintained. Unfortunately, the world ecosystems including wetlands are under serious threat due to unsustainable human activities. As a result of mechanization, industrialization, and increase in agricultural activities, the natural ecosystems have been under intense pressure. The literature review also shows that wetlands are the most productive, but at the same time the most vulnerable ecosystems. Consequently, much of the world’s wetlands have been destroyed or seriously polluted. As such, the remedial measure is to construct artificial wetlands to help in maintaining the quality of water through emulating the processes taking place in natural ecosystems.
Notably, constructed wetlands are designed as the natural wetlands to permit purification, removal, trapping, or filtration of water pollutants. The point is that the constructed wetlands help in removing water contaminants such as suspended organic matter, inorganic substances, nutrients, pathogens, and other water contaminants through the process of biodegradation and bio-filtration. Just as the natural wetlands, the constructed ones have a macrophytic zone that has dense plantations of hydrophytic plants to enhance the biodegradation of pollutants. The main advantage of constructing the wetlands is because they allow maintained and controlled technique of treating wastewater; hence, providing the possibility of monitoring the efficiency of improving water quality.
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