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How to cite this thesis
Surname, Initial(s). (2012) Title of the thesis or dissertation. PhD. (Chemistry)/ M.Sc. (Physics)/ M.A. (Philosophy)/M.Com. (Finance) etc. [Unpublished]: University of Johannesburg. Retrieved from: https://ujdigispace.uj.ac.za (Accessed: Date).
ECOLOGICAL INTEGRITY OF WESTDENE AND EMMARENTIA DAMS IN JOHANNESBURG
By
LERATO MASETLE
Mini dissertation submitted in partial fulfillment for the degree
Masters In Science (Z O O) in Aquatic Health (Zoology) in the
Faculty of Science UNIVERSITY OF JOHANNESBURG
Supervisor: Prof. Victor Wepener October 2013
i
DECLARATION
I declare that this dissertation is my unaided work being submitted for the degree of
Masters of Science in the University of the Johannesburg, Auckland Park. It has not been submitted elsewhere for any degree or examination. I have acknowledged all the sources of information which have been used in the dissertation.
Signature ______
Date ______Day of ______, 2013
ii
ACKNOWLEDGEMENTS
Special thanks and appreciation to the following persons and organizations:
The University of Johannesburg for allowing me to do this study and for the use of all equipment and facilities necessary for the project.
My supervisor, Prof Victor. Wepener for his professional assistance, guidance and intellectual support throughout the project.
Dr. Richard Greenfield, Dr. Martin Ferreira, and Mr. Wynand Malherbe for their assistance with field work.
Mr. Mkhacani Moses Mathonsi for his assistance in the aquarium.
My family for their ever willing support and guidance, particularly my mother for her support and fine words of encouragement throughout this project.
Praise and glory to my Creator without whom my existence and all that it entails would not have been possible.
iii
A BST R A C T
Urban impoundments play both a recreational and functional role in the urban areas.
From the recreational point of view these impoundments offer aesthetically pleasing environs as well as habitat for aquatic organisms in a built environment. The functional role of impoundments is related to attenuation of storm water run-off that is released into urban water courses. Storm water run-off can have adverse effects on the ecological integrity of aquatic ecosystems. Water quality will influence other physical and biological components of these systems. It is for this reason that the ecological health of impoundments is assessed from an ecotoxicological perspective, focusing on
Westdene and Emmarentia dams in Johannesburg.
It has become common practice to use aquatic biota to assess the impacts of human activities on aquatic ecosystems. This is because animals and plants can provide a long-term integrated reflection of water quality, quantity, habitat quality and other environmental conditions. Water and sediment quality were assessed by applying standard techniques and protocols. Fish were utilized as bioindicator organisms in order to quantify the concentrations of metals available in the dam. Abundance of the macro invertebrate community was also measured. Physico-chemical water analyses were done during each sampling period to assess the water quality against the South
African Water Quality Guidelines.
Ammonia, which can be toxic to aquatic life, remained high in both dams. High phosphate concentration during the low rainfall season in Westdene Dam could result in eutrophication related problems. The microbiological analysis of the water suggests that the main cause of faecal and total coliforms contamination of the impoundments possibly originates from dominant birds, African Sacred Ibis (Threskiornis
iv aethiopicus) and Egyptian Goose (Alopochen aegyptiaca) in the dam and others water birds frequenting the dams.
Abnormally high concentrations of the heavy metals Nickel and Chromium were found in the water body and fish (Clarias gariepinus and Tilapia sparmanii) thus indicating bioavailabity of these metals resulting in bioaccumulation in fish. High concentration of Lead in sediment was recorded and may greatly impact benthic macroinvertebrates population and their habitat.
v
TABLE OF CONTENTS
Declaration ii
Acknowledgements iii
Abstract iv
Table of contents vi
List of tables viii
List of figures ix
CHAPTER 1: INTRODUCTION
1.1 Urban impoundments 1
1.2 Aquatic Health Assessment 2
1.3 Physico-chemical and microbiological water quality properties 2
1.4 Physico-chemical properties of sediment 4
1.5 Metal contamination in run-off from urban areas 5
1.6 Impact of heavy metals on organisms 7
1.7 Organisms impacted by pollution 8
1.8 Metal bioaccumulation in fish 8
1.9 Metal bioaccumulation in feathers 9
Rationale 10
Aim & Objectives 11
C H APT E R 2: MATERIALS AND METHODS
2.1 Field site descriptions 12
2.2 Sampling protocol 15
vi
2.3 Laboratory work/ procedures 15
2.4 Water quality 15
2.5 Microbiological water quality 16
2.6 Physical and chemical properties of sediment 16
2.7 Metal bioaccumulation in fish 18
2.8 Metal bioaccumulation in bird feathers 18
2.9 Macroinvertebrates 19
2.10 Statistical Analyses 19
C H APT E R 3: R ESU L TS
3.1 Water quality 21
3.2 Microbiological water quality analyses 26
3.3 Level of trace metals in water 30
3.4 Metal concentration in sediment 34
3.5 Physical and chemical properties of sediments 37
3.6 Metal concentrations in various fish tissues 39
3.7 Metal concentration in various bird feathers 42
3.8 Macroinvertebrates 43
C H APT E R 4:
Discussion 47
Conclusion 54
REFERENCES 56
vii
LIST OF TABLES
Table1 Classification of organic matter (OM) content in sediment (USEPA,
1991).
Table 2 The classification used for the sediment grain size analysis (Cyrus et
al., 2000).
Table 3 Mean ± and standard error of water quality parameters measured at
three sites in Westdene Dam during the high rainfall sampling period.
Table 4 Mean ± and standard error of water quality parameters measured at
three sites in Westdene Dam during the low rainfall sampling period.
Table 5 Mean ± standard error of water quality parameters measured at three
sites in Emmarentia Dam during the low rainfall sampling period.
Table 6 Physical and chemical characteristics of sediment collected during low
rainfall in Westdene and Emmarentia Dams.
Table 7 Physical and chemical characteristics of sediment collected during
high rainfall in Westdene Dam.
Table 8 Abundance of macroinvertebrates at different sites along the
Emmarentia and Westdene Dam.
LIST OF FIGURES
Figure1 Study area in Gauteng, South Africa showing headwaters of the
Limpopo rising on the Witwatersrand ridge as the Braamfontein Spruit
near the Emmarentia and Westdene dams. (Google Earth Images 2013
Digital Globe)
Figure 2 Total and faecal coliform counts in Westdene Dam during the high
and low rainfall sampling period.
viii
Figure 3 Total and faecal coliform counts in Emmarentia Dam during the low
rainfall sampling period.
Figure 4 Faecal coliform counts in Emmarentia and Westdene Dam during the
low rainfall sampling period.
Figure 5 Dissolved metal concentration at Emmarentia and Westdene Dam
during the high and low rainfall sampling period.
Figure 6 Dissolved metal concentrations at three sites in Westdene Dam during
the high and low rainfall sampling period.
Figure 7 Dissolved metal concentrations at three sites in Emmarentia Dam
during the low rainfall sampling period.
Figure 8 PCA plot showing the dissimilarity among sites in Emmarentia and
Westdene Dam during high and low flow regimes based on the water
quality characteristics.
Figure 9 Sediment metal concentrations in Westdene Dam during the high and
low rainfall sampling period.
Figure 10 Sediment metal concentrations in Emmarentia Dam during the low
rainfall sampling period.
Figure 11 PCA plots showing dissimilarity among sites in Emmarentia and
Westdene Dam during high and low flow regimes based on sediment
characteristics.
Figure 12 Dissolved metal concentrations for the two whole fish species at
Westdene and Emmarentia Dam during the low rainfall sampling
period.
Figure 13 Metal concentrations of various tissues in Banded Tilapia (Tilapia
sparmanii) in Westdene dam during high rainfall.
ix
Figure 14 Metal concentrations of various tissues in Sharptooth Catfish (Clarias
gariepinus) in Westdene dam during high rainfall.
Figure 15 Metal concentrations in feathers of Egyptian geese (Alopochen
aegyptiaca) and Sacred ibis (Threskionis aethiopicus) in Emmarentia
dam during the low rainfall sampling period.
Figure 16 Metal concentrations in feathers of Egyptian geese (Alopochen
aegyptiaca) and Sacred ibis (Threskionis aethiopicus) in Westdene
Dam during the low rainfall sampling period.
Figure 17 RDA plot showing dissimilarity among sites in Emmarentia and
Westdene Dam during with and low flow regimes based on
invertebrate communities.
x
CHAPTER 1 INTRODUCTION
1.1 Urban impoundments
Urban impoundments or dams provide aesthetically pleasing environments for people while serving as habitats for aquatic and terrestrial organisms. Local authorities maintain urban impoundments primarily for storm-water control, as habitats for plants and animals, for the psychological escape it offers city dwellers from the concrete jungle.
Polluted storm-water that runs off the generally impervious surfaces in urban environments and released into dams represents the greatest potential threat to the ecological integrity of these urban ecosystems (Wiechers et al., 1996). Pollutants and toxins from both point and non-point source damage these ecosystems. Typically, the worst offenders are industrial and commercial areas, roads, and high density residential areas. Although sources of specific pollutants may vary widely, motor vehicles are recognized as a major source of pollutants by contributing oils, greases, hydrocarbons and toxic metals (USEPA, 1983).
Dams serve as reservoirs, which intercept this pollution and the net effect can be: i) a silted-up impoundment; ii) highly polluted water; iii) eutrophication and associated growth of undesirable algae and water weeds; iv) health risks due to faecal pollution; v) unsightly algae, floating debris and bad smells. Problems with increasing population density and the associated increase in pollution could pose risks to both the
1 health of aquatic ecosystems and the health of wildlife and human communities associated with the impoundments (Wiechers et al., 1996).
1.2 Aquatic Health Assessment
Biomonitoring is an important tool in assessing the health of aquatic ecosystems.
Aquatic ecosystem health cannot be measured directly; instead only indicators of health can be measured to assess the "health" status (DWAF, 1995).
One obvious way to estimate the health status of a dam is to use biologic indices. The physiological function, species abundance, population density, and community structure and function of aquatic life are directly influenced by the ecosystem. Many aquatic species such as fish, birds, and benthic macroinvertebrates are common biological indicators of water pollution, which are used in typical assessment indices
(Meng et al., 2009). In addition to biological criteria, physico-chemical and microbiological properties of the aquatic ecosystem are also important in its overall health. Thus, indicators such as water quality and sediment composition are also used to monitor aquatic habitats.
1.3 Physico-chemical and microbiological water quality properties
Water has a natural capacity to integrate physico-chemical and microbiological contaminants without the quality of water deteriorating beyond its value for ecological sustainability and human use (DWAF, 1995). However, large amounts of pollutants from point and non-point sources may result in a deteriorating system.
Monitoring water for salts, nutrients, heavy metals and pathogenic microbes allows
2 for the identification of sources of pollutants as well as the spatial and temporal trends in pollution severity.
Turbidity is the measure of total suspended solids (TSS) in water. The greater the amount of total suspended solids (TSS) in the water, the murkier it appears and the higher the turbidity. Turbidity can alter light penetration, impact benthic habitats and organisms, and also, turbid water is generally unsightly to humans (Moore, 1989;
Michaud, 1991). Conductivity estimates the amount of total dissolved salts, or the total amount of dissolved ions in water. The conductivity of the dam is controlled by the geology or watershed, proximity to roads, the size of the watershed, and other sources of ions to the dam such as pollutants from urban run-off roads, which may
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Minor fractions of the total dissolved solids, nutrients and metals typically have significant negative impacts on streams and dams receiving road run-off water. If soils are washed in the receiving waters, the organic matter in the soil is decomposed by natural aquatic bacteria, which can severely deplete dissolved oxygen concentration, impacting on aquatic life. Dissolved oxygen (DO) is essential for aquatic life. Natural variation in process such as mixing of cold and warm water affects DO concentration. During high rainfall the warmer top of a dam may be oxygen limited due to higher temperature, thus inducing suboptimal conditions for many species in the system (Michaud, 1991, NALMS management guide).
Nutrients required by autotrophic organisms such as inorganic nitrogen and phosphorus, stimulate algal blooms which stifle other organisms. The solubility and biological availability depends on pH which is the measure of acidity or alkalinity of
3 water. When pollution results in higher algal and plant growth, pH levels may increase, as allowed by the buffering capacity of the dam. Although these small changes in pH are not likely to have a direct impact on the aquatic system, they greatly influence the availability and solubility of all chemical forms in the dam and may aggravate the problem with toxic metals (Moore, 1989 and Michaud, 1991).
Heavy metal species accumulate in bed sediments, posing risks to bottom feeding organisms and their predators; bioaccumulate in animal tissues; affect reproduction rates and life spans of aquatic species; and disrupt food chains in aquatic systems
(Harper, 1985).
Major factors affecting microbiological quality of surface waters are discharges from sewage works and run-off from informal settlements (Venter, 1991). Faecal bacterial counts are commonly used to assess the microbiological quality of surface water and faecal coliforms (FC) are the most commonly used bacterial indicator of faecal pollution (DWAF, 1996a). These bacteria are faecal coliforms are indicative of the general hygienic quality of water and potential risk of infectious diseases from water
(Fatoki and Mthabatha, 2001).
1.4 Physico-chemical properties of sediment
Bed sediments are insoluble and chemically inert but contaminants are reactive depending on organic matter and clay amount (Olsen et al., 1982). Once organic contaminants enter the aquatic environment, they rapidly become associated with sediments and suspended particles. (De Groot et al., 1976; Förstner and Wittman,
1979; Honeyman and Santschi, 1988; Huh et al., 1992; Mwanuzi and De Smedt,
1999; Hatje et al., 2003). As a consequence, concentrations of most contaminants in
4 bed sediment and at the sediment water interface usually exceed those in the overlying water column by several orders of magnitude (Horowitz, 1991; Bryan and
Langston, 1992; DaVNDODNLVDQG2¶&RQQRU
Metals generally do not degrade, and with continued input and limited sediment redistribution can accumulate in depositional zones to concentrations high enough to cause toxic effects to aquatic organisms (Chapman, 1989). Bottom sediment does not only act as a sink for anthropogenically introduced metals, but can also be a significant source when agitated. Metals can be remobilised and released from sediment into the overlying water column through natural and anthropogenic disturbance, including bioturbation by benthic invertebrates, storms and dredging
)|UVWQHU 'DVNDODNLV DQG 2¶&RQQRU Long et al., 1995; Goossens and
Zwolsman, 1996; Zoumis et al., 2001; Linge and Oldham, 2002; Eggleton and
Thomas, 2004).
Sediment grain size is a critical factor influencing metal concentrations (Taylor and
McLennan, 1981; Loring, 1990; Kersten and Smedes, 2002; Newman and Watling
2007). Fine-grained sediment such as silt and clay contain a higher metal content in their crystalline structure compared to coarse-grained sediment, such as sand, which is comprised predominantly of low surface area quartz. Sediments may increase their metal concentrations through surface adsorption, and since fine-grained sediments have a higher surface area to mass ratio compared to coarse-grained sediment they often sequester much higher levels of particle-reactive metals than adjacent coarser sediments (Horowitz and Elrick, 1987; Bubb et al., 1991).
5
1.5 Metal contamination from run-off in urban areas
Heavy metals in stormwater run-off result from the operation of motor vehicles, which generate constituents such as fuels, e.g. lead (Pb) and cadmium (Cd), lubricants, e.g. Pb, nickel (Ni), and zinc (Zn), particles from tires or brake lining, e.g.
Cd, chromium (Cr) and Zn and exhaust emissions (Pb, Ni). Heavy metals like Cd, Cr, and Pb may exhibit extreme toxicity even at low concentrations under certain conditions, thus necessitating regular monitoring of sensitive aquatic environments
(Peerzada et al., 1990). The United States Environmental Protection Agency
(USEPA) has classified Cd and Pb as being potentially hazardous and toxic to most forms of life and relatively accessible to aquatic life (DWAF, 1996). In the natural process of biomagnification, minute quantities of metals become part of the various food chains and concentrations become elevated to levels that can prove to be toxic to both human and other living organisms (Ackerfors, 1971; Bryan, 1971; Fatoki and
Mthabatha, 2001; Budambula and Mwachiro, 2006).
During storms the metals are washed into dams (Fatoki, 1993 and Fatoki et al.,
2002). Although the actual quantity of material generated by the operation of motor vehicles is relatively small, the pollution potential is significant since many of these materials are toxic to aquatic life (Harper, 1985). Trace metals are regarded as potential pollutants as they are widely distributed in the environment with sources
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However, the level of these metals in the environment has increased enormously in the past decades as a result of human inputs and activities (Preuss and Kollman, 1974;
Prater, 1975; Merian 1991; Awofolu et al., 2005). The presence of trace metals in aquatic ecosystems has far reaching implications directly to the biota and indirectly to
6 man (Awofolu et al., 2005). Increased urbanization and industrialization has led to an increase in storm water run-off and, thus total pollutants being delivered to dams.
1.6 Impact of some heavy metals on organisms
Cadmium is one of the most toxic elements with reported carcinogenic effects in humans (Goering et al., 1994). It accumulates mainly in the kidney and liver and high concentrations have been found to lead to chronic kidney dysfunction. It induces cell injury and death by interfering with calcium (Ca) regulation in biological systems. It has been found to be toxic to fish and other aquatic organisms (Woodworth and
Pascoe, 1982). Cadmium has been implicated in endocrine disrupting activities, which could pose serious health problems (Stoeppler, 1991). Lead accumulates easily in the living tissue, and is bio-accumulated by benthic bacteria, freshwater plants, invertebrates and fish, though lead does not appear to bio-magnify through the aquatic food web (DWAF, 1996). Chromium is a scarce metal and its natural occurrence in the aquatic ecosystems is very low (Moore and Ramamoorthy, 1984; DWAF, 1996;
Nussey et al., 2000). Both Cr (III) and (VI) are harmful to aquatic organisms, however Chromium (VI) has potentially more negative effects (Brix and DeForest,
2000; Van der Linde, 2006). Freshwater algae and invertebrates are more sensitive to chromium (VI) than fish. Chromium is easily absorbed by gut and body walls (such as shells, gills and mantle) and at higher concentrations it is associated with abnormal enzyme activities, altered blood chemistry, lowered resistance to pathogens, behavioural modifications, disrupted feeding, and osmoregulatory upset (Brix and
DeForest, 2000; Van der Linde, 2006). Cobalt (Co) is classified as essential to life due to its involvement in certain physiological processes, although elevated levels are found to be toxic (Spear, 1981). Essentially it is required for some metabolic activities
7 in organisms, were toxicological effects of large amount of Co include vasodilation, flushing and cardiomyopathy in humans and animals (Teo and Chen, 2001). Nickel is an element of the earth and water (Snodgrass, 1980). Anthropogenic activities can result in Ni discharged into water and air (Galvin, 1996; Nussey 2000). The toxicity of Ni to aquatic life has shown to vary significantly with organism species, pH and water hardness (Birge and Black, 1980; Nussey et al., 2000). Nickel toxicity is generally low (Teo and Chen, 2001), but very high concentrations can cause serious effects.
1.7 O rganisms impacted by pollution
As a result of water pollution, there are persistent and a wide-reaching stresses on dams leading to an increase in tolerant species and disappearance of sensitive macroinvertebrates, thus spreading to species in the higher trophic levels (Field and
Pitt, 1990; Beyer et al., 2000; Beasley and Kneale, 2004). Therefore aquatic macroinvertebrates can be used for the evaluation of water quality in two ways.
Firstly, the taxonomic diversity of a benthic invertebrate community reflects the water quality conditions, since a high diversity generally indicates a good water quality
(Hynes, 1984). Secondly, specific taxonomic groups can be used as bioindicators, which are characteristics for certain habitat and water quality conditions (Roldàn,
2003).
1.8 Metal bioaccumulation in fish
Fish communities are considered to be an appropriate endpoint for assessing stream or impoundment health because of their high public visibility and their position in food chain. They also provide an integrated view of the impacts of human activities on
8 aquatic systems (Berkman et al., 1986; Karr et al., 1986; Smith et al., 1999; Siligato and Böhmer, 2001) by means of metabolic and biosorption processes (Hodson, 1988;
Carpene et al., 1990; Wicklund-Glynn and Olsson, 1991).
Numerous studies have been conducted in South Africa using fish as bioindicators to study metal exposure in rivers (e.g. Olifants River: Du Preez and Steyn, 1992;
Wepener et al., 1992; Seymour et al., 1995; Du Preez et al., 1997; Marx and Avent-
Oldewage, 1998; Coetzee et al., 2002; Mooi River catchment: van Aardt and
Erdmann, 2004) and dams for water storage (e.g.Witbank Dam: Nussey et al., 2000).
These studies showed that metals are present in relatively high concentrations when compared to the international standards, thus in this study we want to determine what happens in the urban dams.
1.9 Metal bioaccumulation in feathers
Birds have been shown to be particularly useful bioindicators of environmental pollution because they are visible and sensitive to toxins (Burger and Gochfeld,
1995). They therefore give early warnings of environmental stress and are of general interest to the public. Studies in South Africa on the metal concentrations in various tissues of three birds from the metal-polluted Natalspruit wetland have been determined, African Sacred ibis (Threskiornis aethiopicus), Red-Knobbed Coot
Fulica cristata and the Reed Cormorant (Phalacrocorax africanus) (van Eeden and
Schoonbee, 1996). Bird feathers, excrement and eggshells have been used as a non- invasive indicator of metal exposure in birds (Eens et al., 1999; Dauwe et al., 2000;
Vallner et al., 2000; Goutner et al., 2001). Feathers are an important route of
9 excretion for some metals (Braune and Gaskin, 1987a, 1987b), and a significant proportion of the body burden of some metals can be found in feathers.
Rationale
Studies have been done to determine the ecological health of impoundments (such as
Allanson et al., 1990; Bronkhospruit dam, Hartebeespoort dam and Roodeplaat dam;
Thirion, 2000). No data exists for urban impoundments such as the Emmarentia and
Westdene Dams. Therefore, the thrust of this study is to examine the water quality and metal concentration (in both sediments and biota) for two urban impoundments viz. the Emmarentia and Westdene Dams in Johannesburg.
Urban dams are used by surrounding communities and local biota as recreational facilities and habitats to carry out life history functions, albeit in a non-pristine setting. The Westdene and Emmarentia Dams are hubs of biodiversity in all its multiform facets, from humans to the invertebrate life (Visser, 2008). Dams are maintained as integral parts of the community for general-purpose recreation, which are characterized by picnic areas, braai areas (barbeque areas) benches, pathways, and boat launching. Within the dams themselves, many fish and invertebrate species breed providing a food source for the birds and occasionally humans. Both dams are far from natural, as they are located in an urban environment not immune from the industrial and human waste that spews from the engulfing tarmac. However, this does not mean that the dams should be neglected at the expense of more natural ecosystems. All stakeholders, from the vagrant, to the jogger right down to the local
JRYHUQPHQWDXWKRULW\VKRXOGDSSUHFLDWHWKHGDPV¶XWLOLW\WRWKHPVHOYHVVSHFLILFDOO\ and the city of Johannesburg in general (Davie, 2004). A preliminary ecological
10 assessment such as undertaken in this study will enable more rigorous investigations and contribute towards the treatment of urban areas as viable ecological systems, for they are the future upon which most of the world is headed. Thus, a thorough understanding of how they function is warranted.
Aim
To determine the current physical, chemical and biological characteristics of two urban impoundments (dams) to serve as a baseline for further investigation into their ecological health and utility for human recreation.
Objectives
1. Determine the water quality of Westdene and Emmarentia dams and
evaluate it against South African water quality guidelines.
2. Describe the physical and chemical properties of sediments in the two
dams.
3. Determine the status of the macroinvertebrate fauna communities in the
two dams.
4. Quantify the concentrations of metals associated with urban storm water
run-off in aquatic biota of the two dams (fish and bird feathers).
5. Determine the ecological health of the two dams based on physico-
chemical and biological characteristics of these dams.
11
CHAPTER 2 MATERIALS AND METHODS
2.1 Field site descriptions
Johannesburg Metropolitan city has a number of streams that meander through its suburbs, and form the source of two of southern Africa's largest rivers - the Limpopo and the Orange (Wiechers et al., 1996). A large number of small streams, or spruits, trickles through the northern suburbs of the city. Most of the springs from which many of these streams emanate are now covered in concrete and canalized (Visser,
2008).
The Braamfontein Spruit (Figure 1) is largely natural and flows unhindered with parklands on either side. It is the most popular of the city's rivers, providing residents with a much-needed green lung running through the suburbs, which they enjoy, its original state and uses it for leisure activities (Visser, 2008).
The Braamfontein Spruit has two major tributaries: Montgomery and Westdene spruits. This spruit has its origins just above the Westdene Dam. It flows north east below the University of Johannesburg sport grounds, and down through the western and central sections of Melville Koppies, onwards to Emmarentia Dam.
The Westdene and Emmarentia Dams are man-made impoundments located in the north of Johannesburg under the authority of Johannesburg City Council. The
Westdene Dam has a surface area 7 ha and a water volume of 152 000 m3 (Figure 1), while the Emmarentia Dam is 9.7 ha in area with a volume of 250 000 m3 (Figure 1).
Eighty percent of the Westdene catchment comprises low density houses for the affluent while the rest is reserved for park-land. By contrast, the Emmarentia Dam
12 catchment is over 70% park-land and only 30% residential space. Both dams are primarily used for water-based recreation (Wiechers et al., 1996).
13
Figure 1. Study area in Gauteng, South Africa showing headwaters of the Limpopo rising on the Witwatersrand ridge as the Braamfontein Spruit near the Emmarentia and Westdene dams. The background is a false colour digital elevation model draped over a shaded relief map while the picture is the 2013 Digital Globe image from Google Earth.
14
2.2 Sampling protocol
Sampling surveys were conducted in three comparable biophysical sections of both dams: site 1, the inlet; site 2, middle section of the dam and site 3, the outlet at the dam wall. Sampling surveys were conducted during a high rainfall (February, 2006) and low rainfall (October, 2006) period in Westdene Dam, while the Emmarentia
Dam was only sampled during the low rainfall period (October, 2006). The high rainfall period was selected as February (towards the end of the summer rainfall period) and the low rainfall period was selected as October (towards the end of the dry season). The rainfall period is usually associated with high point source pollution resulting from pollutants accumulated at various points in the catchment while conditions are dry.
2.3 Laboratory procedures
Prior to analysis all glassware and plastic containers were soaked in a 2% Contrad soap solution (Merck chemicals) for 24 hours, rinsed with distilled water, soaked in 1
M HCL acid for 24 hours, and rinsed again with distilled water and placed on drying racks for air drying (Giesy and Wiener, 1977).
2.4 Water quality
The water quality variables measured in situ at each site were: conductivity, pH, percentage oxygen saturation and temperature using the Eutech Cyberscan meters.
Additional water samples were collected in triplicate at each site in 1: l acid washed polyethelene bottles and transported back to the laboratory on ice, for freezing and further analysis. Frozen water samples were thawed to room temperature and a Merck
Spectroquant Spectrophotometer was used to analyse samples for the following
15 chemical variables: ammonium, chloride, chemical oxygen demand (COD), nitrite, nitrate, phosphorus, and sulphates. For the analyses of metals, samples were filtered through a 0.45 µm Millipore membrane filter and acidified with 1M ultrapure nitric acid. All samples were stored in 15 ml acid washed polypropylene vials and refrigerated until analysis (Bervoets and Blust, 2003).
2.5 Microbiological water quality
Water samples, collected in sterile water bottles from each site in triplicate, were used to perform the faecal and total coliforms counts using the standard membrane filtration method. Two agar media, m-FC and m-Endo, were used for faecal coliforms and total coliform counts respectively. The 100 ml water sample was filtered through a 0.45 µm Millipore membrane filter. M-(QGRDJDUSODWHVZHUHLQFXEDWHGDWÛ&IRU
24 hours while m-)& DJDU SODWHV ZHUH LQFXEDWHG DW Û& IRU KRXUV ':$)
1992).
2.6 Physical and chemical properties of sediment
Sediment samples were collected in triplicate from all three sites in each dam. The upper 5 cm of the substrate was collected and placed in polyethylene honey jars.
Samples were refrigerated until further analysis. Samples were allowed to defrost and sediment was dried in an oven at 60oC for 24 hours to a constant weight. A known mass of sediment was incinerated for six hours at 600oC to determine the organic content. The percentage organic content (Table 1) was classified according to the
USEPA (1991).
16
Table1: Classification of organic matter (OM) content in sediment (US. EPA, 1991)
% OM Class
< 0.05% Very low
0.05 - 1% Low
1 - 2 % Moderately low
2 - 4% Medium
>4% High
The remaining dried sediment was used to determine the grain size composition of each sample. An Endecott sieve system was used with various sieves, ranging from 53 to 4000 µm. The characterizations of the particle sizes were carried out according to the method described by Cyrus et al. (2000) (Table 2).
Table 2. The classification used for the sediment grain size analysis (Cyrus et al.,
2000)
Size (µm) Classification
> 40000 µm Gravel
4000 µm - 2000 µm Very coarse sand
2000 µm - 500 µm Coarse sand
500 µm - 212 µm Medium sand
212 µm - 53 µm Very fine sand
< 53 µm Clay
17
2.7 Metal bioaccumulation in fish
Fish were collected by means of electroshocking, gill nets and seine nets in both dams. Two fish species were sampled, i.e. the Banded Tilapia (Tilapia sparrmanii) and the African Sharptooth Catfish (Clarias gariepinus). Juvenile fish were frozen for whole fish analyses. The larger specimens were dissected on a polyethylene dissection board, using clean stainless steel tools. Muscle, gill filaments, fat and liver tissues were removed and placed in pre-cleaned polyproylene Falcon tubes and frozen until further analysis. Thawed tissue samples were placed in 50 ml pre-weighed polypropylene vials to determine wet mass. They were then dried in a 60 ÛC oven to a constant weight. After the dry tissue weight was determined, tissue samples were then digested in an acid solution (5 ml ultra pure HNO3 (65%):0.2 ml H2O2 (50%)) for 12 hours. Further digestion was performed by heating the samples in a microwave oven during four consecutive steps of 5 minutes at 200, 300, 400, and 500 W (Blust et al.,
1988). The digested samples were the diluted in 1% HNO3 (AR) , Indium internal standard was added to correct for interference from high-dissolved solids and metal concentrations were determined using a Thermo-Elemental UltraMass 700 inductive coupled plasma mass spectrophotometer (ICP-MS).
2.8 Metal bioaccumulation in bird feathers
Feather samples were collected from the bird islands situated in both dams. In addition feathers were plucked from the breast area of African Sacred Ibis
(Threskiornis aethiopicus) and Egyptian Goose (Alopochen aegyptiaca) carcasses found on the islands. The feathers were washed alternately with MQ water and 1 M acetone. The process was repeated three times to remove any externally bound metals.
Samples were then transferred to pre-weighed polypropylene vials and dried in an
18 oven for 24 hours at 60 ÛC (Eens et al., 1999; Dauwe et al., 2002). The feathers were then acidified with 1:1 mixture of HNO3 (70%) and H2O2 (30%) and left to stand at room temperature for 24 hours. The digestion was completed with the microwave
(1000W) destruction procedure (Blust et al., 1998). Samples were digested for 5 minutes at each following power levels: 200, 300, 400, and 500 W. The samples were then diluted 50 times and stored in a dark at room temperature until analysis. The metal content of all samples were measured using a Thermo-Elemental UltraMass
(700 ICP-MS).
2.9 Macroinvertebrates
Invertebrates were sampled using a standard sweep net (30 x 30 x 30 cm net with 1 mm meshed nylon netting). At all the sites one common biotope, i.e. marginal vegetation was sampled. Marginal vegetation sampling consisted of sweeping the vegetation for a distance of at least 5 m (Malherbe et al., 2010). The invertebrate samples were preserved in 10% neutrally buffered formalin solution with the vital stain Rose Bengal. The samples were taken to the laboratory for identification and enumeration. The organisms were identified to family level using relevant keys, under a stereomicroscope.
2.10 Statistical Analyses
The graphical representations were performed using GraphPad Prism and the data are reported as mean (±) and standard error. The variations in spatial and temporal metal concentrations were tested by one-way analysis of variance (ANOVA), considering site and rainfall periods as variables. Data were tested for normality and homogeneity of variance using Kolmogrov-6PLUQRII DQG /HYHQH¶V WHVWV UHVSHFWLYHO\ :KHQ the
19
ANOVA revealed significant differences, post-hoc multiple comparisons were carried out using the appropriate test (i.e. Scheffé test for equal and Dunnette T3 test for unequal variances) test to identify the significant differences between sites and rainfall. The significance level was taken as p<0.05. All physic-chemical parameters measured in both water and sediment were analysed using Principle Component
Analysis (PCA) (ter Braak and Prentice, 1988). The relationship between invertebrate abundance and diversity and environmental parameters was determined using
Redundancy Analysis (RDA) (CANOCO - ter Braak and Smilauer, 1998). A RDA is derivative of a PCA with one additional feature. The values entered into the analysis are not the original data but the best-fit values estimated from a multiple linear regression between each variable in turn and a second matrix of environmental data.
20
C H APT E R 3 R ESU L TS
3.1 Water quality
The water quality results for Westdene Dam (Tables 3 and 4) were mostly within the target water quality range (TWQR) for both recreational use (DWAF 1996a) and aquatic ecosystems (DWAF 1996b) during both the sampling surveys. The only exceptions were for oxygen saturation (during the low rainfall sampling survey at sites 1 and 2) and for ammonia, which was greater than 0.015 mg/l at all the sites. The
TWQR for recreational use of non-contact water is not available. On a temporal scale pH, oxygen saturation, ammonium, COD, nitrite and phosphate concentrations, were higher in the low rainfall period. By contrast conductivity, chloride and nitrate concentrations were higher during the high rainfall survey. There were differences between the sites in the high rainfall period; i.e. conductivity in site 1, oxygen saturation in site 3 and COD in site 3, were significantly higher (p<0.05). In the low rainfall; conductivity in site 1, oxygen saturation in site 2 and COD in site 3 were significantly higher (p<0.05) in Westdene Dam.
For Emmarentia Dam (Table 5) the water quality variables at all the sites, with the
H[FHSWLRQ RI DPPRQLD ZHUH ZLWKLQ WKH 7:45¶V Once again ammonia concentrations were greater than 0.015 mg/l at all the sites. There were also
21 differences between sites; COD, nitrates in site 3 and chloride in site 2, were significantly higher (p<0.05) than site 1.
Water quality for the duration of the low rainfall period between the two dams; pH, phosphates and COD in Westdene Dam were significantly higher (p<0.05). In
Emmarentia dam conductivity and nitrates were significantly higher (p<0.05).
22
Table 3. Mean ± standard error of water quality parameters measured at three sites in Westdene Dam during the high rainfall sampling period.
Variable Site TWQR Recreational S1 S2 S3 use Aquatic Ecosystem
Temperature (oC) 17.8 ± 0.048 18.1 ± 0.051 16.7 ± 0.046 n/a >2oC /10% of reference value pH 7.22 ± 0.033 7.37 ± 0.021 7.9 ± 0.100 n/a >0.5% - 5% of reference value Conductivity (µS/cm) 407 ± 0.010 389 ± 0.053 385 ± 0.051 n/a >15% of reference value Oxygen (mg/l) 7.25 ± 0.005 7.48 ± 0.005 10.2 ± 0.111 n/a n/a
Oxygen saturation (%) 93 ± 0.574 95.1 ± 0.050 126 ± 0.571 n/a 80% -120% saturation COD (mg/l) 6 ± 1.735 9 ± 0.571 2.8 ± 2.173 n/a n/a Ammonium (mg/l) 0.02 ± 0.015 0.05 ± 0.005 0.05 ± 0.01 n/a n/a
Nitrate (mg/l) 4.5 ± 1.581 4 ± 0.322 4.6 ± 0.203 n/a >15% of reference value Nitrite (mg/l) 0.03 ± 0.005 0.02 ± 0.001 0.02 ± 0.001 n/a >15% of reference value Chloride (mg/l) 11 ± 0.571 10 ± 0.571 9 ± 0.001 n/a n/a Phosphate (mg/l) 0.03 ± 0.005 0.02 ± 0.005 0.04 ± 0.005 n/a >15% of reference value Sulphate (mg/l) 13 ± 0.011 11 ± 1.000 10 ± 0.571 n/a n/a Faecal Coliforms (cfu/100ml) 72 ± 7.022 323 ± 21.503 76 ± 8.624 of no concern n/a Total Coliforms (cfu/100ml) 51 ± 8.182 211 ± 21.011 52 ± 1.000 of no concern n/a
23
Table 4. Mean ± standard error of water quality parameters measured at three sites in Westdene Dam during the low rainfall sampling period. Variable Site TWQR S1 S2 S3 Recreational use Aquatic Ecosystem
Temperature (oC) 13.5 ± 0.051 12.2 ± 0.051 10.5 ± 0.053 n/a >2oC /10% of reference value pH 9.3 ± 0.073 9.8 ± 0.071 9.2 ± 0.081 n/a >0.5% /5% of reference value Conductivity (µS/cm) 288 ± 0.584 256 ± 0.573 243 ± 0.571 n/a >15% of reference value Oxygen (mg/l) 7.25 ± 0.011 8.78 ± 0.011 6.17 ± 0.013 n/a n/a Oxygen saturation (%) 131.3 ± 0.051 151.8 ± 0.173 107.8 ± 0.053 n/a 80% -120% saturation COD (mg/l) 16 ± 1.733 19 ± 0.574 20 ± 2.311 n/a n/a Ammonium (mg/l) 0.08 ± 0.061 0.15 ± 0.001 0.49 ± 0.011 n/a n/a Nitrate (mg/l) 2.4 ± 0.464 1.9 ± 0.051 1 ± 0.751 n/a >15% of reference value Nitrite (mg/l) 0.04 ± 0.005 0.05 ± 0.001 0.07±0.011 n/a >15% of reference value Chloride (mg/l) 5 ± 0.571 5 ± 0.001 5 ± 0.001 n/a n/a Phosphate (mg/l) 0.08 ± 0.001 0.12 ± 0.005 0.09 ± 0.001 n/a >15% of reference value Sulphate (mg/l) 10 ± 0.572 12 ± 0.001 13 ± 0.574 n/a n/a Faecal Coliforms (cfu/100ml) 27 ± 4.584 316 ± 91.911 29 ± 6.012 of no concern n/a Total Coliforms (cfu/100ml) 16 ± 10.013 191 ± 45.232 16 ± 2.011 of no concern n/a
24
Table 5. Mean ± standard error of water quality parameters measured at three sites in Emmarentia Dam during the low rainfall sampling period. Variable Site TWQR S1 S2 S3 Recreational use Aquatic Ecosystem
Temperature (oC) 12.5 ± 0.051 11.6 ± 0.005 12.1 ± 0.001 n/a >2oC /10% of reference value pH 6.38 ± 0.011 6.51 ± 0.005 6.47 ± 0.001 n/a >0.5% /5% of reference value Conductivity (µS/cm) 295 ± 0.001 305 ± 0.571 302 ± 0.572 n/a >15% of reference value Oxygen (mg/l) 10.27 ± 0.011 11.09 ± 0.005 11.09 ± 0.005 n/a n/a Oxygen saturation (%) 106 ± 0.571 108.8 ± 0.101 107.1 ± 0.01 n/a 80% -120% saturation COD (mg/l) 12 ± 1.733 8 ± 1.151 14 ± 0.572 n/a n/a Ammonium (mg/l) 0.18 ± 0.02 0.14 ± 0.017 0.18 ± 0.02 n/a n/a Nitrate (mg/l) 2.3 ± 1.521 2 ± 2.301 12 ± 2.313 n/a >15% of reference value Nitrite (mg/l) 0.02 ± 0.001 0.02 ± 0.001 0.02 ± 0.001 n/a >15% of reference value Chloride (mg/l) 5 ± 0.571 7 ± 0.571 5 ± 1.151 n/a n/a Phosphate (mg/l) 0.03 ± 0.005 0.02 ± 0.001 0.02 ± 0.005 n/a >15% of reference value Sulphate (mg/l) 13 ± 0.571 12 ± 2.641 13 ± 3.632 n/a n/a Faecal Coliforms (cfu/100ml) 233 ± 32.712 109 ± 7.571 76 ± 6.001 of no concern n/a Total Coliforms (cfu/100ml) 85 ± 3.601 128 ± 2.511 19 ± 9.501 of no concern n/a
25
3.2 Microbiological water quality analyses
The coliform counts in both dams were highest at sites adjacent to the bird island. In
Westdene Dam during both sampling surveys, faecal coliforms (FC) and total coliforms (TC) at site 2 were higher than site 1 and site 3 (Figure 2). In general the high rainfall period had higher plate counts than the low rainfall survey and FC counts were higher than TC counts (Figure 2). The FC and TC counts at site 1 and site 3 were significantly higher (p<0.05) during the low rainfall period than the high rainfall survey (Figure 2). The Emmarentia Dam FC counts were highest at site 1, while the
TC counts were highest at site 2 (Figure 3). The TC and FC concentrations were higher in Westdene Dam than Emmarentia Dam during the corresponding sampling surveys (Figure 4).
26
Figure 2. Total and faecal coliform counts in Westdene Dam during the high and low rainfall sampling period. Bars represent mean ± standard errors of three replicate samples taken per site. Bars with asterisks indicate significant differences between surveys at a site. Bars with a common superscript indicate significant differences between sites during a sample survey.
27
Figure 3. Total and faecal coliform counts in Emmarentia Dam during the low rainfall sampling period. Bars represent mean ± standard errors of three replicate samples taken per site.
28
Figure 4. Faecal coliform and Total coliform counts in Emmarentia and Westdene
Dam during the low rainfall sampling period. Bars represent mean ± standard errors of three replicate samples taken per site.
29
3.3 Level of trace metals in water
High levels of Ni were detected in both dams (Figure 5), at all sites in all sampling surveys and it was significantly higher (p<0.05) in Westdene Dam during the high flow period. Concentrations of Cd, Cr, Co and Pb were lower than SA guideline for
Aquatic Ecosystems TWQR (DWAF, 1996). While high levels of Cd at site 2, Co at site 1 and Pb at site 1 were observed in Westdene Dam during the high rainfall period
(Figure 5). In Emmarentia Dam high levels of Cr at site 1 and Pb at site 2 during the low rainfall period was also observed.
Figure 5. Dissolved metal concentration (mean ± standard error in µg.l-1) in water at both dams during the high and low rainfall sampling period. (WHF- Westdene Dam
High-rain Flow, WLF- Westdene Dam Low-rainfall and ELF- Emmarentia Dam
Low-rainfall flow)
30
A 3 B
) 0.06
-1 High rainfall ) -1 g. l g. 2 Low rainfall P
g. l 0.04 P
1 0.02 Cr content Cr( content Co Co content (
0 0.00 S1 S1 S2 S2 S3 S3 S1 S1 S2 S2 S3 S3
C D 20 0.4 ) ) -1 -1 15 0.3 g. l g. l g. P P 10 0.2
5 0.1 Cd Cd content ( Ni content ( Ni content
0 0.0 S1 S1 S2 S2 S3 S3 S1 S1 S2 S2 S3 S3
E 0.10 )
-1 0.08 g. l P 0.06
0.04
0.02 Pb Pb content (
0.00 S1 S1 S2 S2 S3 S3
Figure 6. Dissolved metal concentrations (mean ± standard error in µg.l-1) in water at three sites in Westdene Dam during the high (open bars) and low (solid bars) rainfall sampling period.
31
A B 4 0.015 ) ) -1 -1 3 g. l g. g. l g. 0.010 P P
2
0.005 1 Cr ( content Co content ( content Co
0 0.000 S1 S2 S3 S1 S2 S3
C D 20 0.04 ) ) -1
15 -1 0.03 g. l g. P g. l g. P 10 0.02
5 0.01 Ni content ( Ni content Cd content ( content Cd 0 0.00 S1 S2 S3 S1 S2 S3
E 0.4 ) -1 0.3 g. l g. P
0.2
0.1 Pb content (
0.0 S1 S2 S3
Figure 7. Dissolved metal concentrations (mean ± standard error in µg.l-1) at three sites in Emmarentia Dam during the low rainfall sampling period.
32
The PCA plot of the water quality and metal concentrations describes 99.20% of variation in data, where 88.25 is displayed on the first axis, while 10.95% is displayed on the second axis (Figure 8). There is separation of sites on Westdene and
Emmarentia Dams. In a biplot each arrow points in a direction of steepest increase of values for the corresponding variable. The angles between arrows indicate the correlation between the variables: the approximated correlation is positive when the angle is acute and negative when the angle is larger than 90 degrees. The length of the arrow is a measure of fit for the variables. For sampling sites the distance between symbols in the figure approximates the dissimilarity of their water physico-chemical characteristics, measured by their Euclidean distance.
During both flow regimes site 2 in Westdene Dam showed some degree of similarity and Emmarentia Dam site 1 and site 2 are dominated by high faecal and total coliforms, Pb, and Co concentrations. The phosphates, sulphates, chlorides, nitrates, oxygen levels, COD, conductivity, Cd, Cr, and Ni concentrations are the variables contributing to the similarity of water quality parameters at Westdene Dam site 1 and site 3 during the high rainfall. In Westdene Dam site 1, site 3 and Emmarentia Dam site 3 is dominated by high level of nitrites and ammonium in the low rainfall sampling period.
33
0.6 Nitrites W1LF Ammonium W3LF wCr COD E3LF T pH Suphates Phosphates wNi O% Nitrates wCd Conductivity W1HF Chloride O mg/l W3HF
wCo E1LF E2LF wPb -0.6 FC W2LF W2HF TC
-1.5 1.0 Figure 8. PCA plot showing the dissimilarity among sites in both dams during high (sites with suffix ±H) and low flow (sites with suffix ±L) regimes based on the water quality characteristics.
3.4 Metal concentration in sediment
In Emmarentia Dam Ni and Cr were significantly high (p<0.05) in concentrations in
all three sites during the low rainfall survey. Whereas Co, Cd and Pb (p<0.05)
concentrations were significantly lower in all three sites, except for Pb at site 1 which
had highest concentration (Figure 10).
There were significant differences in concentrations of Cr, Co, Ni, and Pb in
Westdene Dam surface sediments between the two flow periods (p<0.05). There
were also significant spatial variations in concentrations of Cr, Co, Ni, and Pb in the
sediment (Figure 9). During the low rainfall period Cr, Ni, and Pb concentrations
were highest at site 1. During the high rainfall period Cr, Co, Ni concentrations were
highest at site 3 except for Pb at site 1.
34
B ab A ab 1200 25000 * * 1100 ) )
-1 1000 -1 20000 900 g.g
g.g 800 P P 15000 700 600 10000 500 400 b 300 a b 5000 a
Co content ( 200 Cr content Cr( content 100 0 0 S1 S2 S3 S1 S2 S3
C ab D 14 7000 * 13
) 12 )
6000 -1
-1 11 10 5000 g.g g.g
P 9 P 4000 b 8 7 3000 6 a 5 2000 4 3 Ni content ( Ni content 1000 Cd ( content 2 1 0 0 S1 S2 S3 S1 S2 S3
ab E * 30000 a ) -1
g.g 20000 P
10000
Pb Pb content ( b 0 S1 S2 S3
Figure 9. Sediment metal concentrations (µg.g-1 dry mass) in Westdene Dam during the high (open bars) and low (solid bars) rainfall sampling period. Bars represent mean ± standard errors of three replicate samples taken per site. Bars with asterisks indicate significant differences between surveys at a site. Bars with a common superscript indicate significant difference between sites during a sample survey.
35
A B 450 30000
) 400 ) -1
-1 350 g.g
g.g 300 20000 P P 250 200 10000 150 100 Co content ( content Co Cr content ( 50 0 0 S1 S2 S3 S1 S2 S3
C D 11 5000 10 ) ) -1 9
-1 4000 8 g.g g.g P 7 P 3000 6 5 2000 4 3 1000 2 Ni content ( Cd content ( 1 0 0 S1 S2 S3 S1 S2 S3
E 70000
) 60000 -1 50000 g.g P 40000 30000 20000
Pb content ( 10000 0 S1 S2 S3
Figure 10. Sediment metal concentrations (µg.g-1 dry mass) in Emmarentia Dam during the low rainfall sampling period. Bars represent mean ± standard errors of three replicate samples taken per site.
36
3.5 Physical and chemical properties of sediments
Analysis of sediment characteristics for both dams in the low rainfall regime indicated that moisture content ranged between 21.4% and 32.9% (Table 6 and 7). In the high rainfall the moisture content increased to range from 22.6% to 37.3% in Westdene
Dam (Table 7) and the organic content ranged between 4.2% and 7%. The organic content of the sediment sample during the low rainfall in both dams ranged from 0.7% to 6.1% (Table 6). The grain size in both sampling periods in Westdene Dam is generally dominated by medium sands, except during the low rainfall site 3. During the high rainfall survey sites 2 and 3 were dominated by clay and medium sand in
Emmarentia Dam, while during the low rainfall the grain size was dominated by coarse sands (Table 6 and 7).
Table 6. Physical and chemical composition of sediment collected during low rainfall survey in Westdene and Emmarentia dams.
Variables (%) WS1 WS2 WS3 ES1 ES2 ES3 Moisture content 26.6 27.2 21.4 32.9 21.6 26.3 Organic content 3.1 4.6 6.1 0.7 4.3 2.7 Gravel 0 0 1.6 2.7 0 9.9 Very coarse sand 4.3 6.9 20.1 12.6 2.5 18 Coarse sand 32.7 27.8 17.7 43.2 32.1 33 Medium sand 50.5 51 24.2 29.5 46.8 28.7 Very fine sand 3.4 2 9.7 7.6 15.5 7.7 Clay 8.8 12.1 26.4 4.2 3 2.5
37
Table 7. Physical and chemical composition of sediment collected during high rainfall survey in Westdene Dam.
Variables (%) WS1 WS2 WS3
Moisture content 22.6 28.7 37.3
Organic content 7 4.2 6.1
Gravel 0 0 1.6
Very coarse sand 4.4 6.9 20.9
Coarse sand 32.9 28 18.3
Medium sand 50.8 51.3 25.1
Very fine sand 3.4 2 10.1
Clay 0.7 38.4 16.9
PCA plot (Figure 11) displays the dissimilarity among the sites on both dams during low and high rainfall based on sediment characteristics. This plot describes 98.8% of variation in the data, where 75.6% is displayed on the first axis, while 23.2% is displayed on the second axis. The sediment in Emmarentia Dam is dominated by high percentages of gravel in site1 and site 3. Very fine sands are distinctive of Westdene
Dam site 3 in the high rainfall and high moisture content, coarse sand in site 3 in the low rainfall. During both surveys in Westdene Dam site 1 and site 2 and Emmarentia
Dam site 2 was dominated by high organic content, medium sands and clay.
38
Figure 11. PCA plots showing dissimilarity among sites in both dams during high
(sites with suffix ±H) and low flow (sites with suffix ±L) regimes based on sediment characteristics.
3.6 Metal bioaccumulation in whole fish and tissues
The bioaccumulation of metals (Cr, Co, Ni, Cd and Pb) in whole juveniles of the two fish species are shown in Figure 12, with Ni being the highest in concentration in both species (Figure 13 and 14). The order of bioaccumulation for both dams during the low rainfall period was the same with the highest concentrations being Ni followed by
Cr, Pb, Co and Cd in decreasing concentrations (Figure 13).
Gills, liver and muscle tissues of T. sparmanii were analysed to evaluate metal bioaccumulation patterns in tissues. The liver had the highest concentrations of all
39 metals except Pb while muscles had the lowest metal bioaccumulation (Figure 13).
The trend for Pb bioaccumulation in tissues was gill, liver and muscles in decreasing concentrations (Figure 13). For C. gariepinus, adipose tissue was analysed in addition to the other tissues. The order for tissue metal bioaccumulation in this species was gills, muscle, liver and adipose for Ni, Cr and Co. Whereas for Pb, the concentration pattern was gills, liver, muscle and adipose; while for Cd the order was muscle, liver, gills and adipose in decreasing order (Figure. 14). l
Figure 12. Metal bioaccumulation (mean ± standard error µg.g-1 dry mass) for whole fish species at Westdene Dam (solid bars) and Emmarentia Dam (open bars) during the low rainfall sampling period.
40
25000
) Gills -1 20000 Liver g.g
P Muscle 15000
10000
5000 Metal content ( content Metal 0 Cr Co Ni Cd Pb
Figure 13. Metal bioaccumulation (mean ± standard error µg.g-1 dry mass) of various tissues in Tilapia sparmanii in Westdene dam during the high rainfall sampling period.
4500
) Liver
-1 4000 3500 Muscle g.g
P 3000 Adipose 2500 Gills 2000 1500 1000 500 Metal content ( content Metal 0 Cr Co Ni Cd Pb
Figure 14. Metal bioaccumulation (mean ± standard error µg.g-1 dry mass) of various tissues in Clarias gariepinus in Westdene dam during high rainfall sampling period. 41
3.7 Metal bioaccumulation in bird feathers
The results of the metal content in the feathers are summarized in Figures 17 and 18.
All values are represented as mean ± standard error in µg.g-1 dry mass and significant differences were determined using analysis of variance (ANOVA) and t-test. General patterns of the metal bioaccumulation in bird species at both dams for low rainfall survey revealed high Cr, Ni, and Pb concentrations, with low Co and Cd concentrations. There were no significant differences (p< 0.05) in metal concentration among the bird species. Both bird species from Westdene Dam had the highest metal content in comparison to Emmarentia Dam.
4000 ) -1
g.g 3000 P
2000
1000 Metal content ( content Metal 0 Cr Co Ni Cd Pb
Figure 15. Metal concentrations (mean ± standard error µg.g-1 dry mass) in feathers of
Alopochen aegyptiaca (open bars) and Threskiornis aethiopicus (solid bar) in
Emmarentia Dam during the low rainfall sampling period.
42
7000 )
-1 6000 g.g
P 5000 4000 3000 2000 1000 Metal content ( content Metal 0 Cr Co Ni Cd Pb
Figure 16. Metal concentrations (mean ± standard error µg.g-1 dry mass) in feathers of
Alopochen aegyptiaca (open bars) and Threskiornis aethiopicus is (solid bar) in
Westdene Dam during the low rainfall sampling period.
3.8 Macroinvertebrates
In Westdene Dam 11 taxa comprised of 210 individuals were recorded in high rainfall period (Table 8), and 5 taxa of 184 individuals were recorded in low rainfall period
(Table 8). Eight taxa and 149 individuals were also recorded in Emmarentia Dam.
The highest taxa abundance was observed in Westdene Dam for the sampling site 1, followed by site 2 and site 3 (Table 8) during high rainfall period. Mollusca and
Diptera were represented by the dominant Planorbidae family with highest abundance recorded in site 1 and site 2, and Chironomidae with highest abundance in site 2.
During the low rainfall period, Hirudinae, Chironomidae and Coenagrionidae were dominant families present in all sites, with Chironomidae being more abundant in site
3 and site 2 (Table 8). In Emmarentia Dam Ancylidae, Physidae, Chironomidae and
43
Coenagrionidae individuals were present at all three sites. Ancylidae were the most abundant at site 2 and Chironomidae highest at site 1(Table 8).
RDA plot (Figure 17) displays the dissimilarity among the sites on both dams during high and low rainfall based on invertebrates characteristics. This plot describes 64.6% of the variation in the data, where 36.1% is displayed on the first axis, while 28.5% is displayed on the second axis. It is evident from the results that the environmental variables that had a significant influence (p<0.05) on the invertebrate groupings were sediment characteristics, that is course and medium sand, whilst temperature (i.e. flow period), nitrites and mud content had conditional effects on the invertebrate community structures.
44
Figure 17. RDA plot showing dissimilarity among sites in both dams during (sites with suffx ±H) and low flow (sites with suffix ±L) regimes based on invertebrate communities.
45
Table 8. Abundance of macroinvertebrates at different sites in the Emmarentia and Westdene Dams
Westdene Westdene Emmarentia High rainfall Low rainfall Low rainfall
Order Family Site 1 Site 2 Site 3 Site 1 Site 2 Site 3 Site 1 Site 2 Site 3 Mollusca Ancylidae _ 1 _ _ _ _ 8 15 13 Lymnaeidae 6 1 _ _ _ _ 3 _ 15 Physidae 5 _ _ _ _ _ 2 2 4 Planorbidae 27 6 22 5 4 _ 5 _ 14 Sphaeriidae ______6 _ _ Annelida Hirudinae 11 _ _ 2 7 9 _ _ _ Oligochaeta 11 12 _ _ 8 7 _ _ _ Diptera Chironomidae 15 33 8 17 45 58 19 3 14 Ceratopogonidae 12 14 5 _ _ _ 2 2 _ Zygoptera Coenagrionidae 7 _ _ 7 10 5 4 13 5 Hemiptera Belostomatidae 4 6 2 ______Coleoptera Dysticidae 1 _ 1 ______
Total number of families 10 7 2 4 5 4 8 5 6
Abundance 99 73 38 31 74 79 49 35 65
46
C H APT E R 4 DISC USSI O NS
4.1 Water quality
The high oxygen saturation during low rainfall could be ascribed to the fact that oxygen is more soluble in colder water than in warmer water and that metabolic processes (e.g. respiration) of aquatic organisms are slower in winter than in summer and therefore need less oxygen during winter for biochemical reactions (Vos and Roos, 2005). Ammonia remained high in both dams which can be toxic to aquatic life, although ammonia exists primarily as
+ NH4 in water, a fraction of ammonia can also be present as disassociated NH4OH or free ammonia (Wetzel, 1983). This fraction is pH and temperature dependant and as temperature and pH rises so the proportion of NH4OH increases and the toxicity to aquatic life increases
(Freeman et al., 2000). However in this study the pH was fairly neutral and therefore the percentage of toxic ammonia is expected to be fairly low. High phosphate concentration (>
0.05 mg/l) during the low rainfall in Westdene Dam could result in eutrophication related problems. It has been shown that at phosphates concentrations of 0.05 mg/l, there is response from phytoplankton (Freeman et al., 2000). Phosphates will stimulate the growth of plankton and aquatic plants, which provide food for fish. This may cause an increase in the fish population and improve the overall water quality. However, elevated concentrations of phosphates will lead to algal blooms and result in detrimental consequences such as odors and discolouration of water interfering with recreational and aesthetic water uses.
4.2 Microbiological water quality analyses
In Westdene Dam during the high rainfall period, high FC and TC counts were encountered at all sites. This is due to the fact that considerable faecal debris may have accumulated in storm water collecting pipes between transient storm events, highly contaminated storm
47 flows may result. Since high rainfall events have a potential to cause greater peak non-point source faecal loading in impoundments than low rain fall period (Tunnicliff and Brickler,
1984). The survey indicated that high bacterial counts were primarily restricted to site 2, a site were many water birds reside and their droppings result in faecal contamination in the surrounding water body (Venter, 1991). Water birds inhabiting the water can contaminate the water through direct defecation (Nevondo and Cloete, 1999). In low rainfall FC and TC counts were noticeably low at all three sites in comparison to high rainfall. Greenfield (2004) concluded in the study of the Nyl River wetland system that TC numbers increased with rainfall events as bacteria entered the system via the Nylstroom/Modimolle sewage treatment works and agricultural runoff. In the river catchments of the North West Province (Wose
Kinge and Mbewe, 2012) increased FC and TC contamination were found in all catchments.
Significantly high levels of FC and TC were observed during the summer season in the study.
Although site 2 FC and TC showed higher concentration than site 1 and site 3, attributable to water birds residing at site and their faecal matter contamining the water surrounding the site.
A high FC count in site 1 and TC counts in site 2 in Emmarentia Dam during low rainfall was a cause of faecal contamination by water birds in the residing sites. Although studies have shown water birds are known to be an important nonpoint source of faecal contamination of surface waters (Alderisio and DeLuca, 1999; Geldreich and Kenner, 1969; Hussong et al.,
1979; Kirschner et al., 2004; Ricca and Cooney, 1998), their contribution to faecal pollution is mostly difficult to estimate. Thus a holistic approach for evaluating the performance of faecal indicator bacteria in all sites should be determined in relation between feces production and input of faecal indicator bacteria into aquatic systems by water birds (Kirschner et al.,
2004).
The level of trace metals at both dams can be related to non-point source. High concentrations of Ni (14.57 µg/l) were detected at all three sites during both sampling
48 surveys. There is no TWQR for trace metals in water for recreational use (DWAF, 1996e).
The levels of Cr (2.81 µg/l) were within TWQR range (DWAF, 1996a). In the study done on the Vaal River system (Vaal dam and Vaal River Barrage) show Pb and Ni concentrations were below the detection limit in water (0.1 mg/l) and (50 mg/l) (Crafford and Avent-
Oldewage, 2010). Low Cr concentrations were also below detection limits (Crafford and
Avent-Oldewage, 2011).
The seasonal variation of the dissolved metal concentrations within the water bodies of the two dams were measured and the highest metal concentrations were recorded in the low rainfall survey. In a study reported by De Klerk et al., (2012) of four reed pans on the
Mpumalanga Highveld dissolved metals concentrations such as Ni and Cr there was a seasonal differences with regard to metal concentrations found in water. Winter and Spring yielded the highest metal concentrations while lowest metal concentrations occurred during
Summer. Thus higher metal concentrations continue to be associated with low rainfall period.
4.3 Metal concentrations in sediment
Metal concentrations were highest during high rainfall in Westdene Dam indicating a strong seasonal variation in metal content. This variation in surface sediments may be a consequence of storm water runoff charged with dissolved metals from road surfaces. However,
Emmarentia Dam during the low rainfall period had higher concentrations of metals than the high rainfall in Westdene Dam. No data were collected for the high rainfall and thus no direct comparisons were possible. Higher metal content in Emmarentia Dam were probably due to a greater catchment area since the Dam is the outlet for two major streams in the
Braamfontein spruit catchment whereas Westdene Dam only drains a single stream. Seasonal variations of sediment in endorheic reed pans on the Mpumalanga Highveld (De Klerk et al.,
2012) were found to have metal concentrations higher than those recorded in overlying water,
49 as is the case with Emmarentia and Westdene Dams. This is because metals are introduced into the sediment by physical, chemical and biological processes which are able to accumulate metals overtime (Tessier and Campbell, 1987; ANZECC and ARMCANZ, 2000).
Sediment analysis may provide important geographical information on contaminant inputs into an aquatic ecosystem (Long and Chapman, 1985). There was significant spatial variation of Cr (p<0.01) and Ni (p<0.01) in both dams during the sampling surveys. Crafford and
Avent-Oldewage (2010 and 2011) found Ni and Pb concentrations in sediment were below detection limits (9mg/g and 0.5mg/g) while low concentrations of Cr were recorded in a study done on the Vaal River system.
4.4 Physical and chemical properties of sediments
The physical and chemical properties of sediments are known to influence toxicity and are used to aid in the interpretation of sediment quality assessments (USEPA, 2001). During high and low rainfall survey organic content ranged from medium to high, except at site 1 in
Emmarentia Dam the sediments organic content was low. The results for both dams indicate organic content is medium to high. The sediment grain size analysis showed a combination of medium and coarse sand. The low level of mud found in this study is an indication that there is erosion occurring with large amount of sediment transportation. This is substantiated by study which was done by CRUZ (2000) and Malherbe (2006) showing that the sediment grain size in different systems consisted of mostly coarse sand during the high rainfall period and during low rainfall it changed to a combination of coarse and medium sand.
4.5 Metal concentrations in various fish tissues
Metal contamination of aquatic ecosystems has long been recognized as a serious pollution problem. Metals, released into surface water tend to accumulate in the sediments through
50 adsorption and precipitation processes. It can be reintroduced into water in a bio-available form with changing water quality conditions to fish which absorbs it from the water by means of gills or epithelial tissues and concentrates in the body (Wren et al., 1983). The ability off each tissue to either regulate or accumulate metals can be directly related to total amount of metal accumulated in that specific tissue. Furthermore, physiological differences and position of each tissue in the fish can also influence the bioaccumulation of a particular metal (Kotze,
1997). Clarias gariepinus and T. sparrmanii accumulated heavy metals in the sequence Ni >
Cr > Pb > Cd > Co. In the study, metal concentrations in different tissues were variable, but in C. gariepinus it was clear that the highest concentrations were recorded in the gills followed by muscle, liver and adipose tissues. In T. sparrmanii highest concentrations were found in liver tissues followed by gills and muscle.
Fish are known to accumulate Ni in different tissues, when they are exposed to elevated levels in their environment (Van Hoof and Nauwerlaers, 1984; Vos and Hovens, 1986;
Nussey et al., 2000). Nickel bioaccumulated in all tissues, and the data indicated gills as the most concentrated in both species, followed by muscle, liver, adipose in C. gariepinus and followed by liver and muscle in T. sparmanii. Therefore, gills are the main site for absorption of Ni from surrounding medium. It should be remembered that gills play an important role in the secrection of metals, probably via secretion of mucus (Heath, 1991). Nickel concentrations found in fish species in Emmarentia and Westdene Dams were higher than those concentration found at other localities in the upper Olifants River catchment, e.g. between 9 to 71 µg.g-1 dry mass (Barhoorn, 1996; Coetzee, 1996; Kotze, 1997). The second highest levels of Ni occurred in the liver of T. sparrmanii and muscle of C. gariepinus.
Experimental bioaccumulation studies conducted on carp (Cyprinus carpio) showed the order
51 of Ni accumulation was gills>liver>muscle during sublethal exposures, compared to G>M>L during lethal exposure (Sreedevi et al., 1992).
All the tissues of T. sparrmanii accumulated higher level of Cr than those of C. gariepinus.
The liver was the major site for Cr accumulation (3979.5 µg.g-1) followed by gills and muscles, were gills were major site of Cr accumulation (1173.4 µg.g-1), as was also observed in T. sparrmanii and C. gariepinus by Nussey et al., (2000).
4.6 Metal concentration in various bird feathers
Bioaccumulation of trace metals varied between Alopochen aegyptiaca and Threskiornis aethiopicus, where a highest concentration of Ni and Cr was observed in both species at
Emmarentia Dam and Westdene Dam. The values were mostly higher than values obtained for feathers of weavers (Ploceus velatus) in Gauteng and North West Province (Meyer, 2005) and Great Tits (Parus major) in Belgium (Janssens et al., 2001). This shows there is pollution of trace metals in both dams.
The levels of Cd were in the same range as in the feathers of weavers (Meyer, 2005) and
Sand Martins (Riparia riparia) from Hungary (Vallner et al., 2000). The Cd values obtained from Emmarentia and Westdene dams were higher and similar to values recorded 2002 and
2005 at Rietvlei and Roodekrans. The metal concentrations in this study also correspond to values along the pollution gradient for Great Tit feathers (Janssens et al., 2001). The Co values were higher than values obtained in the feathers of weavers in Gauteng and North
West province. In this study Cr was mostly higher than values obtained from Rietvlei 2002.
Nickel concentrations were higher than Great Tits feathers from pollution sites in Belgium
(Janssens et al., 2001) and feathers of weavers in Gauteng and North West province. This might show there is Ni pollution in both dams of this study. High metal concentrations of Pb were recorded and were higher than Rietvlei 2002 and similar to Great tits of feathers at
52 polluted site in Belgium (Dauwe et al., 2002). High metal concentrations of Ni and Cr in both dams are an indication of Ni and Cr pollution occurring at all sites.
4.7 Macroinvertebrates
Aquatic biota integrates and reflects changes in their environment. Assessment of biological communities, like aquatic macroinvertebrates, can be used to present an integrated measurement of the integrity of an aquatic resource (Harper 1985). Aquatic macroinvertebrates are aquatic insects (or the different life stages of insects), crabs, shrimps, leeches, etc. found in dams, lakes, streams, rivers, ponds, wetlands, etc. Resident aquatic macroinvertebrates are good, short term indicators of ecological integrity because they integrate the effects of physical and chemical changes. They are adapted to live within certain environmental conditions and changes within this environment may adversely affect community composition and abundance. Integration of biological indicators (like aquatic macroinvertebrates) with chemical- and physical indicators will ultimately provide information on ecological status of the impoundment (Hill, 2005).
In this study the numbers of benthic macroinvertebrate taxa recorded in Westdene Dam at high rainfall survey, highest invertebrate abundance, richness and diversity were found at the inlet of storm water runoff at site 1 with the most tolerant taxa. As is the case at Goedever
Wachting se Pan in Mpumalanga that had the highest invertebrate taxa richness recorded (De
Klerk, 2009).
The nature of impoundments and the habitats they create has an effect on the benthic invertebratecommunity composition and diversity as it creates a more or less homogenous environment. In both Dams taxa recorded, was dominated by Chironomidae. The dipterans, notably the family Chironomidae, have been found to dominate the communities and show
53 no habitat restriction (Ogbeibu and Oribhabor, 2002). There was a significant reduction of taxa in the low rainfall in comparison to high rainfall in Westdene Dam. This is due to increase in productivity during warm seasons, which leads to a regeneration of plants and animals during this period (Dallas and Day, 1993). As it was evident in the study of Reed pans in Mpumalanga (De Klerk, et al., 2012) showed a definite seasonal variation in the number of taxa, with lower number of taxa occurring in winter and spring, compared to summer and autumn. In this study a distinction can be seen between high and low rainfall.
RDA showed sediment characteristics combined with seasonal variability (temperature) played a role in distribution and abundance of benthos. Such as diversity occurring during high rainfall with more tolerant invertebrates (e.g. Ceratopogonidae, Dysticidae and
Planorbidae) and driving variables appears to be conductivity, chlorides and temperature. In the low rainfall the driving variables are pH, nitrites and phosphorous with Chironomidae being the dominant taxa in Westdene dam, whereas oxygen is one of the main physico- chemical variables responsible for different community structure such as Sphaeriidae and
Ancylidae. In these sites high levels of nutrients they lead to disappearance of invertebrates taxa that are sensitive taxa, such as Baetidae and dominance of tolerant taxa (De Klerk,
2009).
CONCLUSIONS AND RECOMMENDATIONS
The physical and chemical parameters of water in Emmarentia and Westdene Dams indicate that both dams have acceptable water quality for non-recreational uses. The high concentrations of phosphates and nitrates should however be of concern for aquatic health in the dams. There is a danger that increasing concentrations of these macronutrients could result in mesotrophic to eutrophic conditions. Also, there were high concentrations of fecal matter on the bird islands at both dams, which may pose a threat to humans if the dams are
54 used for recreational activities. The macroinvertebrate community structures in both dams were dominated by species tolerant of high levels of nutrients and degraded water quality such as Chironomidae. Both dams had high concentrations of Ni, Cr and Pb in water and sediment which were also detected in fish and bird feathers. The high levels of these metals could potentially pose a threat to the aquatic health in these systems.
The results from this study shows the systems are already being impacted and provides a baseline against which further degradation or even improvement can be evaluated. The study can contribute as a guideline to educate people to a more correct use of the urban impoundment.
To improve the aquatic health of the two dams the following recommendations are suggested;
x The community and stakeholders affected in the surrounding area need to advocate
pollution prevention measures to reduce the introduction of pollutants to the
environment, such as control and physical removal of paper, plastic, glass, algae, and
hyacinths.
x This study should be continued with further bioassessments (such as sediment,
macroinvertebrate sampling and bioaccumulation) biannually during high and low
rainfall periods.
x Chemical monitoring of the water quality should be done monthly at all sites to
determine pollution impacts.
55
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