1.Definition of a Wetland
The National Water Act defines a wetland as land which is transitional between terrestrial and aquatic ecosystems. The water table in a wetland is usually very close to the surface; therefore the land is, at times, covered with shallow water supporting thousands of species, typically adapted to life in saturated soil (Agius, 2010). Wetlands in KwaZulu-Natal vary greatly according to topographic, hydrological and climatic influences. Wetlands can be referred to as swamps, marshes, estuaries, bogs, floodplains, vleis and pans.
The internationally accepted definition of a wetland includes “areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water, the depth of which at low tide does not exceed six meters,” (Dugan, 1993).
There are three unique characteristics that indicate whether an environment is a wetland or not. Firstly there must be a high water table, which acts as a hydrological indicator. Secondly hydric soils must be present, which acts as a pedological indicator. Finally hydrophytic vegetation must grow in the environment, which acts as a botanical indicator (James, 1979).
1.1 Function and Value of Wetlands
Wetlands have many functions and values man increasingly depend upon, due to their exponential population growth. Wetlands have hydrological functions, such as flood attenuation where they form natural floodways, aiding in the transportation of flood waters. Wetlands store water during floods, which is slowly released to downstream areas. Wetlands recharge and discharge ground water and can dissipate erosive forces.
Wetlands improve the quality of water by aiding in the removal of excess nutrients, chemical contaminants, sediments and numerous toxic substances (such as heavy metals and pesticides).
Wetlands also provide a habitat for a broad variety of plants and animals. In Natal 144 wildlife species are dependent on wetlands for their life requirements. Many of the animal species listed as endangered in South Africa are associated to wetlands. Wetlands have high tidal and inland productivity, which provide nutrients and are food sources to many species.
Lastly wetlands have various socio-economic functions which include providing recreational sites for fishing or hunting and they provide educational opportunities for observing and studying nature (Rosenburg, 1993).
2. THREATS TO URBAN WETLAND
The value of wetlands was not realised up until very recently. Prior to this they were not protected by law and therefore were frequently degraded and even destroyed by an increasing and continuous urbanisation and industrialisation of our planet. This damage continues to occur however due to the disregard for the legislation protecting these areas and the ignorance of the possible outcomes of the loss of these wetlands.
2.1 Physical Destruction
There are numerous threats to the sustainability of the wetlands existing today. An ever increasing global population and the resulting outcomes of this is the major hazard for the protraction of these precious regions. It leads to the growth of residential and commercial development which may occur near or over wetlands eventually leading to their destruction from activities such as levelling, dredging, draining, filling, removal of vegetation and restriction of flow in order to create additional land to be used for the purposes of construction (Hendricks, 2004).
2.2 Water Pollution
Human interference in or around wetlands brings about other activities which impact negatively on the wetlands and the ecology within. Pollution from dumping, littering, runoff and untreated stormwater and sewage diversion into a wetland, as well as from public recreational activities, alters the hydrology of the wetland and diminish the water quality. This results in groundwater contamination, poor soil conditions to facilitate vegetation growth, flora and fauna extermination as well as disruption of flow patterns (Agius, 2010 ).
Urbanisation also leads to the exploitation of the resources that wetlands offer. Water is pumped out of the wetland for various purposes such as for potable water and irrigation. These areas are also abundant in minerals and peat which are extracted as well as fish which are harvested excessively. If left unmanaged the sustainability of these wetlands may be at risk. Chemical contamination due to pest control is a secondary effect from these activities which reduces the conditions in which living organisms in the wetland can continue to exist (NSW Department of Natural (Resources, 2008), (MRSC, 2001).
3. WATER QUALITY
Biological communities, such as communities of benthic macroinvertebrates, can change due to habitat degradation, water quality degradation or both. Ecosystems in both rivers and estuaries are affected by water quality variables. These variables could be physical, which include turbidity, temperature and suspensoids; or chemical, which includes toxic and non-toxic variables. Toxic variables being: traces of metal and biocides, and non-toxic variables being: pH, conductivity, nutrients, organic enrichment and dissolved oxygen.
The quality of water can also be affected by the composition of the uMgeni estuary itself. The factors affecting water quality are namely, topography, geology, climate, land use and the type of soil found in the estuary (Eggers, 2007).
4. THE uMNGENI ESTUARY
An estuary, by definition, is a type of wetland located at the crossing point between two environments, viz. marine and fresh water environment, and is the most dynamic and productive ecosystem in the world (Ethekwini Municipality, 2010).
Figure 1. Aerial photograph of uMngeni River leading to uMngeni Estuary and out into the Indian ocean (Ethekwini Municipality, 2010)
Figure 2. Photograph of uMngeni Estuary (Ethekwini Municipality, 2010)
4.1 Description of the uMngeni Estuary
The uMngeni Estuary supported by the uMngeni River, which carries water from the Inanda Dam, flows into the Indian Ocean at Durban as depicted in Figure 1 (The River Health Programme, 2002). The uMngeni Estuary is a 230 ha, structurally modified, permanently open estuary which can be viewed in Figure 2. One of uMngeni Estuary’s most eye catching features is its Beachwood Mangrove, located on the northern bank – the fifth largest mangrove in South Africa (Ethekwini Municipality, 2010). The uMngeni Estuary is of both ecological and recreational importance – providing marine animals with a habitat as well as allowing for human sporting activities such as angling (South African River Health Programme, 2004). The mouth of this estuary, being permanently open, gives rise to a high salinity gradient, which brings about a diverse fish population. It houses 24 taxa of benthic macro-invertebrates, with polychaete Capitella capitata being the most prominent – a type of indicator species which detects organic pollution. There is also an abundance of birds at the estuary (Ethekwini Municipality, 2010).
4.2 Threats to the uMngeni Estuary
The uMngeni Estuary, like many other natural water sites, are susceptible to threats. Currently, the state of this estuary is classified as “highly degraded” by the eThekwini Municipality. uMngeni Estuary is situated in the eThekwini Municipal Area, an area home to a third of KwaZulu-Natal’s population; however, this population occupies only 1% of the province’s land area, creating a population over load and the need for urban expansion. Expansions along the coastal regions disrupt the estuarine environment causing degradation (Ethekwini Municipality, 2010). Other more serious threats include: canalisation of the uMngeni River, this results in the removal of habitats in the estuary region; the Inanda Dam regulating the flow of water, thus preventing the natural supply of sand entering to the river resulting in silting and the closing of the estuary; eutrophication as a result of nutrient additions; chemical and organic pollutants; invasive alien plant species and direct resource exploitation due to sand mining and over fishing (South African River Health Programme, 2004).
4.3 Reasons for Restoration
It is of importance that the uMngeni Estuary be restored to good condition for it is viewed as a biodiversity asset, providing key ecosystem services such as nursery area for fisheries, flood abatement, biodiversity refuge protection and recreation. Being located adjacent to Moses Mabhida Stadium and at the northern end of Durban’s beachfront, it is a zone of recreational activities as well as a tourist “hot spot” and it is therefore crucial that the condition of the estuary be enhanced to promote tourism and economic growth in South Africa. In addition, a good quality estuary would offer the local community, as well as visitors, the opportunity to engage in nature based activities in an urban landscape (ECO Systems, 2010).
5. POSSIBLE RESTORATION PROCEDURES
A damaged or degraded wetland is by no means useless or irreparable. In fact in many countries throughout the world damaged wetlands have successfully been restored such as the Tidal Wetlands at East Trinity, Cairns, Australia (Agius, 2010). After decades of being subjected to noxious sulphuric acid runoff, scientists were able to reverse the effects by gradually allowing sea water into the wetland using existing floodgates.
5.1 Considerations when Attempting Restoration
According to the Parks and Recreation Board for the City of New York, the key points to focus on when attempting the restoration of any wetland are the re-establishment of appropriate hydrological systems, soils and indigenous vegetation (Parks and Recreation, 2010). This can be achieved by a number of acts to undo the negative effects that were previously impacting upon the wetland. These acts include fill removal, fresh soil placement, invasive plant eradication and indigenous plant restoration, erosion control, stormwater, runoff and pollution management (Parks and Recreation, 2010).
5.2 Possible Mitigation Measures to Aid Restoration
Fill removal and soil replacement aims at land alterations that will assist in reforming previous ecologic conditions that existed within the wetland. The eradication or control of alien plants and the restoration of indigenous plants also assist with this revitalization. Stormwater, runoff and pollution can be eliminated and managed however long term pollution elimination can only be achieved through the efforts of the surrounding residents and industrialists. These people should understand the value of a wetland and therefore why conservation is crucial in order for them to behave in manner that does not result in further pollution (Casagrande, 1997).
During the restoration process it would be extremely beneficial to utilise indicators so as to monitor the quality of the water and thus the condition of the wetland as a whole. In this way the progress or lack thereof can be noted and this may give an idea of the way in which to proceed with the restoration process.
6. BIO-MONITORING AND RESTORATION
Human activities are continuing to increase yearly and this is placing pressure on wetlands. Many wetlands have already been destroyed due to urban and agricultural development. The remaining wetlands need to be monitored so that they remain functional. Efficient and accurate techniques are essential for the assessment of a wetland. There are four major factors in wetland degradation namely: altered water regime, habitat modification, pollutants and exotic species.
Monitoring may be defined as the collection and analysis of environmental data
(Biological, chemical, and/or physical) over a sufficient period of time and frequency to
determine the status or trend in one or more environmental parameters or characteristics toward meeting a management objective (Cale. 2004).
Wetlands are sensitive and need to be constantly monitored to remain balanced.
Monitoring wetlands provides information on the Biotic Integrity which is defined as “the ability to support and maintain a balanced, integrated, adaptive community of organisms having a species composition, diversity and functional organization comparable to that of natural habitat of the region.” (Garner 2002).
6.1 Types of Monitoring Methods
Digital change detection is used to spot visual changes over a landscape. Aerial photos are captured via satellite or aircraft. Images taken at different times are observed and changes in vegetation are noted any suspicious findings prompt further investigations.
Chemical and physical monitoring gives useful insight into the state of the water with the wetland. Samples of water are gathered and properties such as water depth, dissolved oxygen content, biochemical oxygen demand (BOD), ph levels, temperature and turbidity are determined and analysed to establish the status of the wetland. Toxicity tests are carried out in laboratories whereby a sample is taken from the wetland then screened and compared to that of controlled water to check for toxicity. Chemical monitoring provides information on toxic compounds but cannot provide early warnings (Michael 2010).
Biological Monitoring uses the responses of living organisms to determine the state of a wetland. Living organisms such as Algae, benthic macro invertebrates, vertebrates, phytoplankton etc are used as indicators of the wetland’s status these organisms are sensitive to change. Changes in their reproduction, growth, behavior etc are observed which gives insight with regards to what’s happening in that environment. Samples of these living organisms are taken and analyzed. Early warning systems can be developed whereby organisms from site are kept in a special on site laboratory and receive flow from the actual site, these organisms are monitored over time to note any behavioral and physical changes induced by anthropogenic stress. Early detection is key to restoring a balanced environment (NAVFAC, 2004).
6.2 Monitoring Restoration
Monitoring methods are not only useful for early detection they also aid in monitoring restoration processes. During restoration monitoring techniques can be used to collect data on soil, nutrient levels, plant and animal growth etc ,this data would indicate whether or not the restoration is successful. The restoration process must be under constant monitoring to ensure success.
Bio-monitoring, by definition, is a technique used to check the health of an aquatic ecosystem by using the density and relative abundance of resident organisms as an indicator (Day, J., 2000).
According to Rosenberg and Resh (1993), the “ideal’ indicator should have the following characteristics:
The indicator should be a taxonomically sound and be identifiable with ease
The indicator should have a wide spread population distribution
The indicator should be numerically abundant
The body size of the indicator should be large
The ecological requirements of the indicator should be known
Indicator should be suitable for the use in laboratory studies
7.1 Programmes Implementing Bio-monitoring
To increase the awareness and knowledge on the state of aquatic ecosystems across South Africa, The Department of Water Affairs (DWA) developed a programme, known as the National Aquatic Ecosystem Bio-monitoring Programme (NAEBP), for monitoring the health of aquatic ecosystems. This programme was later renamed the River Health Programme (RHP), which focused on the implementation and maintenance of bio-monitoring across South Africa. The RHP use invertebrates as one of the many organisms used for bio-monitoring (WRC, 2002).
7.2 South African Scoring System
Scoring Systems are used to allocate scores to different biotic groups, based on the organism’s sensitivity to pollution and environmental stress. For example, stoneflies and mayflies have high scores based on their abundance and presence. The South African Scoring System, better known as the SASS4, is based on macro-invertebrates, where taxa are assigned sensitivity scores according to their responsiveness to changes in the water quality. All biotopes are sampled to obtain an accurate reflection of the communities of macro-invertebrates and their corresponding sensitivities to deteriorating water quality. The sensitivity scores for all the communities are summed to give the sample score. The Average Score per Taxon (ASPT) is found by dividing the sample score with the number of communities found (Graham, M., 1998).
7.3 Habitat Assessments Aiding Bio-monitoring
For bio-monitoring to reflect the true condition of the river and estuary, a habitat assessment must be performed. An assessment of the habitat integrity must be performed before the assessment of the biotic integrity. A habitat assessment will aid the bio-monitoring in numerous ways, including finding appropriate sampling sites, provides basic information that will help interpret the bio-monitoring results and will help identify constraints on the potential of a site. The SASS4 recognizes 3 habitat assessment guides which could be used, namely, the Habitat Assessment Matrix (HAM) which looks at the impact of physical habitat degradation using a SASS score, the habitat assessment (HABS1) in which habitats are assessed based on biotopes used for sampling and Habitat Quality Index (HQI) which is very similar to the HAM (WRC, 2002).
8. BENTHIC MACRO-INVERTEBRATES
Benthic macro invertebrates (benthic = bottom, macro = large and invertebrates = animal without backbones) are animals without backbones that are larger than ? millimetre – a photograph of benthic macro-invertebrates can be viewed in Figure 3 below. These animals live in sediment, debris plants etc for at least part of their life. Benthic macro invertebrates include crustaceans such as crayfish, such as clams and snails, aquatic worms and the immature forms of aquatic insects such as stonefly and mayfly nymphs (DNR 2004).
Figure 3. Photograph of Benthic Macro-invertebrates
Benthic macro invertebrates are widespread and can live on all bottom types. They are found in wetlands, lakes ponds etc. most benthic species can be found the whole year round but numbers intensify during spring just before the reproductive season. Benthic macro invertebrates easily move around with the currents or by flying. Many species undergo metamorphosis then reproduce. Most of their lives are spent in water (Rosenburg,1993).
These organisms are an invaluable tool with regards to wetland monitoring and bio-assessments in general. When placed in harmful environments these organisms display “tell tale” responses, these responses help conservationists identify problems in the wetland.
8.1 Characteristics That Aid in Bio-Assessments
Benthic macro invertebrates have characteristic that aid in bio-assessments.
uThey are well dispersed and occur in most wetlands.
uShow different reactions to different types of pollution and other adverse effects.
uHigh life ps
uSampling of Benthic macro invertebrates is simple , does not require heavy equipment
The observation of benthic macro invertebrates provides important information that will prolong wetland health and increase sustainability. Their behaviour and availability aids conservationists to develop early warning signs and save wetlands.
9. THE USE OF BENTHIC MACRO-INVERTEBRATES IN BIO-MONITORING
Benthic macro-invertebrates possess all the ideal characteristics of a bio-monitoring indicator, as listed above by Rosenberg and Resh (1993). Benthic macro-invertebrates have been documented as one of the most valuable tools for bio-monitoring aquatic ecosystems and are widely chosen to evaluate the quality of surface waters. The types of bio-monitoring using benthic macro-invertebrates include surveillance and to ensure compliance (Richard, 2010).Surveillance surveys could be taken before and after the environmental impact or could also be taken to see whether water resource management techniques are effective or not. Benthic macro-invertebrates could be used to ensure immediate environmental requirements are met or used to control and monitor long term water quality (Townsend 1980).
9.1 Sensitivity of Benthic Macro-invertebrates to Environmental Stress
According to Rosenberg and Resh (1993), benthic macro-invertebrate display certain reactions, that are both biochemical and physiological, when confronted by an adverse environment. Exposure to impacted environments could even lead to deformities. Jeffrey and Madden (1991) found that other macro invertebrates have also had negative side effects, such as a decrease in the case building ability of the Agapetus fuscipes, a decline in the feeding rate of the amphipod Gammarus pulex and a change in the reproductive behaviour of the midge Chironomus riparius. Salanki (1986) noted that the populations of the macro invertebrates tend to drift down stream of the water body when faced with chemo-physical changes. Therefore the most common indicators of environmental stress in macro invertebrates are the changes in their growth, survival, population distributions and reproduction.
9.2 Advantages of Using Benthic Macro-invertebrates in Bio-monitoring
In this literature review benthic macro-invertebrates have been chosen as the biological indicator in the uMngeni Estuary, over other forms on macro invertebrates for numerous reasons. They occur and can survive in almost all types of habitats. There are various taxa of benthic macro-invertebrates that range in sensitivity to all kinds of environmental stresses and pollutants. Benthic macro-invertebrates are sedentary by nature, making it easier for them to pick up on approaching pollutants. Their life cycles are long enough to detect exposure to pollution and environmental stress, and the population will not recuperate so quickly that the harm will go undetected. Sampling the Benthic macro-invertebrates is a simple procedure and does not require complicated devices on site (WRC 2002).
9.3 Disadvantages of Using Benthic Macro-Invertebrates in Bio-monitoring
However, according to Rosenberg and Resh (1993), there are disadvantages to using benthic macro-invertebrates in bio-monitoring. There are certain environmental impacts that do not affect benthic macro-invertebrates. Water quality is not the only factor that effects their population distribution and abundance, the natural conditions of the habitat in which they live also plays an important role. Their population abundance and distribution varies across the seasonal changes, which can cause sampling problems. Fortunately, the problems discussed can be overcome with proper knowledge of the habitat predilections, life history and drift patterns.
10. Role Benthic Macro-invertebrates Will Play in Monitoring and Conserving uMngeni Estuary
10.1 Characteristics of the Benthic Macro-invertebrate Population that Indicates the Health Status of the Estuary
The surveillance of benthic macro-invertebrate communities, focusing on taxonomic composition and richness, is the most sensitive tool for effectively detecting changes in aquatic ecosystems, like the uMngeni Estuary. Therefore it is more beneficial to analyse the entire population of invertebrates as a whole rather than looking at individual taxa. Population characteristics, that could be used to detect environmental changes, include richness, diversity and interactions as a functional community. Community functions include productivity processes, decomposition and fluxes in nutrients and energy (Williams, 1990)
10.2How Feeding Groups Are Linked To the Composition of the Estuary
The analysis of the size and characteristics of various feeding groups of benthic macro-invertebrates can be linked to certain aquatic conditions and can give insight into the nature and composition of the estuary. According to Townsend (1980), these macro-invertebrates can be categorized into 4 major feeding groups, namely, grazers which feed of algae, shredders which feed of large particles of plant matter, collectors which feed on fine particles on the stream bed or filtering through the water and predators which feed on invertebrates, fish and other aquatic animals. Therefore if an unnatural increase in the number of grazers were found during the bio-monitoring, it could be concluded that there is an abnormal growth of algae in the estuary that could be due to an environmental stress or pollutant.
10.3. The Distribution of the Various Types of Benthic Macro-Invertebrates Along the uMngeni River Into the Estuary
The benthic macro-invertebrate population distribution in terms of the various feeding groups, with regards to the uMngeni River supplying the uMngeni Estuary, will be as follows. The upper part of the river will have course particulate organic matter. Here large population groups of shredders and predators can be found. In the middle reaches of the river, finer material can be found supporting collectors and grazers. In the lower reaches of the river and estuary the material found will be very fine and tend to settle as the current slows down. Here predominantly grazers can be. However the population distribution down the river into the estuary can be influenced by many abiotic factors, such as oxygen, current, substratum, concentration of dissolved chemicals and temperature. All these factors must be taken into consideration during the testing phase.
10.4. The Effectiveness of Using Benthic Macro-Invertebrates in Bio-Monitoring
Using benthic macro-invertebrates in bio-monitoring is one of the most effective ways to indicate an environmental impact. For example if toxins are flowing through the water of the river, a chemical investigation would not reflect the exact impacts as the toxins would be quickly washed downstream and out of the estuary. However there would be radical changes to the benthic macro-invertebrate populations for quite some time, even after the toxins have gone (Graham 1998). An investigation determined by Muirhead-Thomson (1987), showed that a community of benthic macro-invertebrates took 2 to 3 week to recover from the application of the insecticide, methoxychlor. This would give researchers ample time to find the exact impacts of a pollutant or environmental stress if implemented along the uMngeni River and into the estuary.
11. AREAS OF CONCENTRATION
Different species of invertebrates can be located at specific areas throughout the estuary as discussed in the previous section. It is therefore important to know which region of the wetland would be of particular significance in achieving the goal of restoration. The overall state of the water quality of the uMngeni Estuary is especially dependant on the condition of the freshwater being provided by the uMngeni River. It would thus be prudent to pay attention to the benthic macro-invertebrates that exist at the point where river and estuary meet and even further up along the river as well. In this way it may determined if considerable degradation is occurring before the water even enters the wetland. By monitoring and enhancing the condition of water in the river the quality of the water in the estuary can be enhanced (South African River Health Programme, 2004). Ultimately a large number of concentration areas should be chosen so as to obtain a general idea of the state of the estuary and whether conditions are improving or declining.
The uMngeni Estuary is an invaluable ecosystem in the Durban area that if left unprotected will be destroyed by pollution and exploitation. It is essential that efforts be made to restore this environmental treasure to a naturally functioning wetland devoid of human impaction. In correlation with the restoration procedure the utilisation of a bio-monitoring process is extremely useful in determining wether conditions in the wetland are improving. The most indicative organisms in bio-monitoring are benthic macro-invertebrates and for this reason their use in attempting to restore the uMngeni estuary would be of great benefit and worth to its survival.
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