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Plankton dynamics in response to algal blooms in a highly eutrophic estuary in South Africa

  • Authors: Smit, Taryn
  • Date: 2020
  • Subjects: Algal blooms -- South Africa , Estuaries -- South Africa
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49303 , vital:41619
  • Description: The global rise in the incidence of harmful algal blooms in estuaries is a major concern given their importance as a nursery area for a variety of invertebrates and fishes. On the warm-temperate, south-east coast of South Africa, the Sundays Estuary experiences persistent, seasonal HABs due to stable eutrophic conditions. Spring blooms of the dinoflagellate, Heterosigma akashiwo, were recorded for several years in the estuary. This Raphidophyte is known for its consequences in fish and shellfish aquaculture and exhibits harmful properties such as mucilage and reactive oxygen species production. Subsequently, the dissertation investigated larval fish assemblage dynamics, larval prey and predator dynamics and body condition in association with H. akashiwo blooms. HABs mainly altered the water quality within the mesohaline zone in terms of microalgal biomass and dissolved oxygen. Hypereutrophic blooms of H. akashiwo reached 24 996 cells∙mL-1 during the study period. Supersaturated dissolved oxygen concentrations (up to ~13 mg∙L-1 at night and ~21 mg∙L-1 during the day) were recorded during hypereutrophic blooms (> 80 μg∙L-1, ≥ 2781 H. akashiwo cells∙mL-1). Dissolved oxygen differed significantly by bloom state, with the highest dissolved oxygen concentrations. Larval fish density, diversity and community structure variability were lower during hypereutrophic blooms compared to standard blooms and bloom absence, albeit statistically insignificant. Estuarine resident larval density was negatively correlated with dissolved oxygen concentration (P < 0.001). Dominant prey copepod of G. aestuaria larvae, P. hessei, was less abundant and variable during hypereutrophic blooms (mean: 664, range: 4-4301 individuals per m3) compared to standard blooms (mean: 950, range: 2-5237 individuals per m3) and bloom absence (mean: 1182, range: 23-7259 individuals per m3). Although HABs did not appear to drive a mismatch between prey and G. aestuaria larvae, early juvenile larvae made only a small contribution to the assemblage (0.2-1.8%). In terms of predator effects, yolk sac larvae were negatively related to R. terranatalis (P < 0.05). A significant positive relationship was found between prey, P. hessei and G. aestuaria preflexion (P < 0.001), flexion (P < 0.001) and postflexion (P < 0.05) larvae. In a world first, the effects of HABs were investigated on a larval fish species, Gilchristella aestuaria, using biochemical body condition analyses. During severe bloom conditions, G. aestuaria larvae were smaller and the assemblage consisted of mainly early developmental stages (stats). Body condition (RNA per dry weight) was poorest in the presence of hypereutrophic blooms (P < 0.001). A bell-curved relationship between RNA/DW and dissolved oxygen concentration was also produced in a 3-day time-lagged GAM (P < 0.001). In conclusion, hypereutrophic bloom conditions appeared to trigger adult G. aestuaria spawning in the upper mesohaline zone of the estuary in response to heightened primary productivity which occurs during the early bloom stage. However, reductions in copepod abundance (P. hessei) and unfavourable oxygen concentrations interfered with grow-out of G. aestuaria larvae. This research showed that HABs can alter nursery properties to the detriment of G. aestuaria larvae can have serious knock-on effects up the food chain. The loss in abundance of adult, juvenile and larval G. aestuaria, a key forage fish in South African estuaries, has major implications for estuarine food webs, especially in reduced prey availability to juvenile fishes and birds. There is still much to learn about the effects of HABs on the physiological and behavioural aspects on plankton communities worldwide.
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  • Date Issued: 2020

Approaches to detecting and assessing patterns, processes and responses to change in South African estuaries

  • Authors: Van Niekerk, Lara
  • Date: 2018
  • Subjects: Estuaries -- South Africa , Climatic changes -- South Africa
  • Language: English
  • Type: Thesis , Doctoral , PHD
  • Identifier: http://hdl.handle.net/10948/45491 , vital:38621
  • Description: The research presented indicates deep knowledge of estuary pattern-process-function across a broad range of estuary types. This study successfully developed and applied approaches to detect change at varying temporal and spatial scales in South African estuaries. This assessment was based on the physical characteristics of estuaries and predicted or measured change in the drivers of estuary health. This is the first study in the country to review and synthesise the vulnerability of South African estuaries to Climate Change on a regional scale. Through sound scientific approaches this research has advanced our knowledge on complex estuarine systems and made a significant contribution globally to approaches for the conservation and management of estuaries.
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  • Date Issued: 2018

Present state of macrophytes and responses to management scenarios at the St. Lucia and Mfolozi estuaries

  • Authors: Rautenbach, Kelly
  • Date: 2015
  • Subjects: Aquatic plants -- South Africa , Estuaries -- South Africa , Marine plants -- Ecology -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/3195 , vital:20410
  • Description: The St. Lucia Estuary, the largest estuary in South Africa, has been subject to many natural (a decade long drought) and anthropogenic impacts. A particular mouth manipulation activity, the artificial separation of the Mfolozi River and the St Lucia Estuary in 1952, was done to stop the perceived “silting up” of the estuary, but resulted in a decrease in freshwater supply. The changes in inflows (both fresh and marine) are controlled by management decisions and affect other system parameters such as salinity, water level and turbidity, which influence the distribution of biota. Therefore knowledge on the physico-chemical environment and eco-physiological tolerances of macrophytes will lead to informed future management decisions. The first of the three objectives carried out for this study determined the present state and distribution of the macrophytes of the St. Lucia and Mfolozi estuaries. The macrophyte habitats mapped in 2008 and 2013 were the submerged macrophytes, reeds and sedges, mangroves, grass and shrubs, salt marsh (succulent) and swamp forest. Results indicated that low salinity in the lakes and high water level in 2013 caused die-back or expansion of particular habitats. Submerged macrophytes, in particular Stuckenia pectinata, grows well in water with salinity <15 ppt, therefore this habitat increased by 412 ha (96%) in cover since 2008. Salt marsh decreased by 553 ha (57%) due to inundation. Since 2008 the reeds and sedges increased by 390 ha (in North Lake and the Narrows) due to the salinity decrease. In the Narrows the mangroves decreased by 28 ha (9%) in area cover. This was due to the drought that persisted for so many years, which caused low water levels and non-tidal conditions. The second objective was to determine the present state / health of the mangroves at four sites along the Narrows by assessing sediment condition and population structure of the trees. These results were compared to those obtained in 2010. The total density of Avicennia marina increased since 2010, however this was due to the large increase in seedlings at Site 1, the back channel site. The highest sediment salinity (26 ppt) and porewater salinity (29 ppt) was recorded for this site and these results show that this back channel site was strongly influenced by the open Mfolozi Estuary (increase in marine waters) and tidal conditions at the time of sampling in 2013. The total density of Bruguiera gymnorrhiza decreased, but an increase in adults was recorded at Site 2, the freshwater site. The soil collected from the Bruguiera quadrats was fresher and drier than that of the Avicennia quadrats of Site 2. Lack of seedlings (of both species) was due to the dense stands of Acrostichum aureum (mangrove fern) and Phragmites australis (common reed) and a thick, impenetrable mat of Avicennia pneumatophores. At Sites 3 and 4, the drier sites (where sediment moisture contents were the lowest for all sites at 43 and 42% respectively), seedling and sapling density was low, but adults increased in density since 2010. Recruitment and survival were impacted by the harsh environmental conditions that prevailed prior to 2013 (low water level and non-tidal influence), but adults survived. The results of the test that determined the percentage of aerenchyma of the pneumatophores indicated that waterlogging stress did not affect the aerenchyma of the pneumatophores. However the period of inundation was probably not significant enough to have affected the production of aerenchyma. The third objective formed part of an ongoing study by the Global Environmental Facility (GEF) on the feasibility of linking the Mfolozi River back to the St Lucia Estuary and the responses of these systems to different management scenarios: 1) the “do nothing” scenario; 2) maintain separate Mfolozi and St Lucia mouths representing an open mouth condition; and 3) actively facilitate a single mouth (therefore linking the Mfolozi and St Lucia mouths). Data gathered on the eco-physiological tolerances of the dominant macrophyte species was used to predict the response of the different habitats to these various management scenarios and the results indicated that the best management scenario would be to actively facilitate a single mouth (Scenario 3) as the estuary habitats would increase significantly because of preferred tidal and saline conditions, as this would represent more natural conditions. The results of the study will provide input to recommendations for future “adaptive management” strategies for the Global Environmental Facility (GEF) Project.
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  • Date Issued: 2015

An application of the choice experiment method to estimate willingness-to-pay for and guide management on estuarine recreational services

  • Authors: Lee, Deborah Ellen
  • Date: 2012
  • Subjects: Estuaries -- South Africa , Estuarine mitigation -- South Africa
  • Language: English
  • Type: Thesis , Masters , MBA
  • Identifier: vital:8864 , http://hdl.handle.net/10948/d1020239
  • Description: Among the world‘s ecosystems, estuaries have the highest total economic value per hectare. They are dynamic coastal biomes that provide a host of different goods and services to the surrounding terrestrial and aquatic environments and the people who utilise them. These goods and services include, inter alia, nursery areas for marine organisms, harvested natural resources (such as fish, shell-fish, bait organisms, reeds and mangroves), flood attenuation, water purification, nutrient and sediment sinks, waste disposal, transport, aesthetic beauty and areas for swimming, boating and fishing. Assessing the condition of estuaries is difficult as their state can change depending on what is being measured. Assessments have been carried out on the health of estuaries in South Africa with the results of these studies being used as inputs to the process of assessing the minimum water supply requirements for each estuary (ecological reserve) in order to maintain or improve its functionality. These ecological reserve requirements are assigned using Resource Directed Measures (RDM). These measures, however, have been criticised for being highly complex and too costly to implement for all South African estuaries within a reasonable time period. Another concern is that the levels of demand for recreational goods and services provided by the estuary are not taken into account when assessing estuarine value. It is important to understand that the use of estuaries for recreational purposes is inextricably linked to their health and sound ecological functioning. Although South African estuaries have been quite well buffered from impacts until only very recently, their use and pressures have escalated faster than what conservation authorities and policy makers have been prepared for over the last couple of decades. There is thus mounting pressure on estuaries as recreational outlets, which, in turn, has led to their functional deterioration as well as deterioration in the quality of the recreational experience as a whole. One implication for management is that more and more trade-offs have to be made in an attempt to balance the conservation and recreational use of estuaries.
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  • Date Issued: 2012

Physico-chemical and microalgal characteristics of the Goukamma Estuary

  • Authors: Kaselowski, Tanja
  • Date: 2012
  • Subjects: Estuarine ecology , Estuaries -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10623 , http://hdl.handle.net/10948/d1011130 , Estuarine ecology , Estuaries -- South Africa
  • Description: Estuaries are intrinsically complex and dynamic ecosystems that display marked spatial and temporal variability. Because estuaries are situated at the receiving end of catchment activities, they are at particular risk of alterations to their natural complexity. The overarching objective of this study was to gain an overview of the abiotic conditions and biotic response of the Goukamma Estuary, a small temporarily open/closed estuary (TOCE) which is situated in a relatively undisturbed catchment in the Southern Cape. Physico-chemical properties drive estuarine ecology, and together with biological indicators, are commonly assessed to determine the present status of an estuary. During the study, physico-chemical parameters reflected great spatial and temporal variability in response to the mouth state over a 13 month period. Parameters ranged within expected limits, as proposed by the conceptual model for water quality of TOCE’s (Snow and Taljaard 2007). Of particular importance was the prominent occurrence of salinity stratification and hypoxic conditions (dissolved oxygen [DO] < 3 mg l-1) during both open and closed mouth states. Data indicated that in the wide and shallow lower reaches, weak stratification gradients were present and oxygenated conditions (DO > 6 mg l-1) were maintained throughout the water column mainly by wind and tidal action. However, stratification increased towards the deeper, channel-like middle and upper reaches of the estuary, followed by a significant reduction in bottom DO concentrations and development of hypoxia and anoxia. Bottom water hypoxia commonly occurs in microtidal estuaries due to the limited influence of mixing forces, mainly by wind and tidal action. The Goukamma Estuary is a channel-like microtidal estuary where stratification effectively limited oxygenation of the bottom water which resulted in frequent occurrence of bottom water hypoxia. During June 2010 when the highest local rainfall (75 mm) was recorded for the region, salinity and DO data showed that this amount of rainfall was insignificant as it did not replenish the water column of oxygen. Only the surface 0.5 m layer was fresh and oxygenated while below this, the water column was completely hypoxic. In an unimpacted state, the Goukamma Estuary is a blackwater system and is expected to be nutrient poor; however, farming activities in the catchment have resulted in elevated nutrient concentrations. This study showed that significantly higher nutrient concentrations were measured in the middle and upper reaches of the estuary, adjacent to cattle farms situated in the floodplain of these reaches. Nutrient concentrations represented mesotrophic (dissolved inorganic nitrogen [DIN] > 500 μg l-1) to eutrophic conditions (dissolved inorganic phosphorus [DIP] > 25 μg l-1). Nutrient input stimulated phytoplankton to attain a significantly high biomass, ranging between 0.3 – 112 μg l-1 (~ 7.7 ± 1.3 μg l-1; n = 128) and 0.8 – 289 μg l-1 (~ 21.1 ± 4.4 μg l-1; n = 80) during the open and closed states, respectively. High organic loads are associated with high oxygen demands which consequently result in hypoxia following decomposition. Exacerbated by natural salinity stratification which effectively limits oxygenation of the water column, unnaturally high nutrient concentrations and coinciding organic loads place the estuary at particular risk of degradation. This study captured key patterns and processes by quantifying salinity, oxygen and nutrient concentrations in addition to biological indicators (phytoplankton biomass and community composition). Considering possible budget constraints, it is recommended that monthly salinity and oxygen concentrations should be monitored as well as seasonal nutrient concentrations. It is also recommended that riparian buffer zones should be established in the middle and upper reaches of the estuary, as these vegetation buffers have been well documented to contribute to nutrient attenuation and improved water quality from agricultural run-off.
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  • Date Issued: 2012

The response of microalgal biomass and community composition to environmental factors in the Sundays estuary

  • Authors: Kotsedi, Daisy
  • Date: 2011
  • Subjects: Algal blooms -- South Africa -- Sundays River Estuary , Estuaries -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10636 , http://hdl.handle.net/10948/d1013611
  • Description: The Sundays Estuary is permanently open to the sea and has been described as channel-like along its entire length with a narrow intertidal area (mostly less than 5 - 6 m in width). The estuary experiences regular freshwater inflow with large supplies of nutrients, derived from the Orange River transfer scheme and agricultural return flow. In particular, nitrate concentrations are high as a result of fertilisers used in the Sundays River catchment area. The objectives of this study were to measure microalgal biomass and community composition and relate to flow, water quality and other environmental variables. Surveys in August 2006, March 2007, February, June and August 2008 showed that salinity less than 10 percent mostly occurred from 12.5 km from the mouth and this was also where the highest water column chlorophyll a (>20 μg l-1) was found. Different groups of microalgae formed phytoplankton blooms for the different sampling sessions, which were correlated with high chlorophyll a. These included blooms of green algae (August 2006), flagellates (March 2007), dinoflagellates (June 2008) and diatom species (February and August 2008). The dominant diatom (Cyclotella atomus) indicated nutrient-rich conditions. Green algae and diatoms were associated with low salinity water in the upper reaches of the estuary. Flagellates were dominant throughout the estuary particularly when nutrients were low, whereas the dinoflagellate bloom in June 2008 was correlated with high ammonium and pH. Maximum benthic chlorophyll a was found at 12.5 km from the mouth in February, June and August 2008 and was correlated with high sediment organic and moisture content. Benthic diatoms were associated with high temperature whereas some species in June 2008 were associated with high ammonium concentrations. The middle reaches of the estuary characterise a zone of deposition rather than suspension which would favour benthic diatom colonization. Phytoplankton cells settling out on the sediments may account for the high benthic chlorophyll a because maximum water column chlorophyll a was also found in the REI zone (where salinity is less than 10 percent and where high biological activity occurs) in the Sundays Estuary.
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  • Date Issued: 2011

The botanical importance and health of the Bushmans estuary, Eastern Cape, South Africa

  • Authors: Jafta, Nolusindiso
  • Date: 2010
  • Subjects: Estuaries -- South Africa , Bushmans river estuary , Estuarine ecology -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10614 , http://hdl.handle.net/10948/1255 , Estuaries -- South Africa , Bushmans river estuary , Estuarine ecology -- South Africa
  • Description: The Bushmans Estuary is one of the few permanently open estuaries in the Eastern Cape that is characterized by large intertidal salt marshes. Freshwater inflow to the estuary has decreased as a result of abstraction by more than 30 weirs and farm dams in the catchment. The mean annual run-off is naturally low (38 x 106 m3 y-1) and thus abstraction and reduction of freshwater inflow to the estuary is expected to cause a number of changes. The aims of this study were to determine the current health/status of the estuary based on the macrophytes and microalgae and identify monitoring indicators for the East London Department of Water Affairs, River Health Programme. Changes in the estuary over time were determined from available historical data which were compared with present data. This analysis showed that under normal average conditions freshwater inflow to the estuary is very low, less that 0.02 m3 s-1 most of the time. Under these conditions the estuary is in a homogenous marine state. Vertical and horizontal salinity gradients only form when high rainfall and run-off occurs (> 5 m3.s-1). Salinity gradients from 30.1 PSU at the mouth to 2.2 PSU in the upper reaches were measured in 2006 after a high flow event. However the estuary quickly reverted back to its homogenous condition within weeks after this flood. This study showed that freshwater inflow increased nutrient input to the estuary. Total oxidised nitrogen (TOxN) and soluble reactive phosphorus (SRP) concentrations were higher in August 2006, after the flood, than during the other low flow sampling sessions. TOxN decreased from a mean concentration of 21.6 μM in 2006 to 1.93 μM in February 2009. SRP decreased from 55.3 μM to 0.2 μM respectively. With the increased nutrient availability, the response in the estuary was an increase in phytoplankton biomass. After the 2006 floods the average water column chlorophyll-a was 9.0 μg l-1, while in the low freshwater inflow years it ranged from 2.1 to 4.8 μg l-1. The composition of the phytoplankton community was always dominated by flagellates and then diatoms, with higher cell numbers in the nutrient-enriched 2006 period. Although the water column nutrient data indicated that the estuary was oligotrophic, benthic microalgal biomass (11.9-16.1 μg.g-1) in the intertidal zone was comparable with nutrient rich estuaries. Benthic species indicative of polluted conditions were found (Nitzschia frustulum, Navicula gregaria, Navicula cryptotenelloides). These benthic species were found at the sites where wastewater / sewage seepage had occurred. Benthic diatom species also indicated freshwater inflow. During the high flow period in 2006 the dominant diatoms were fresh to brackish species that were strongly associated with the high concentrations of TOxN and SRP (Tryblionella constricta, Diploneis smithii, Hippodonta cf. gremainii, and Navicula species). During the freshwater limited period of 2008 and 2009 the benthic diatom species shifted to a group responding to the high salinity, ammonium and silicate concentrations. The species in this group were Nitzschia flexa, Navicula tenneloides, Diploneis elliptica, Amphora subacutiuscula and Nitzschia coarctata. Ordination results showed that the epiphytic diatom species responded to different environmental variables in the different years. Most of the species in 2008/2009 were associated with high salinity, temperature, dissolved oxygen, ammonium and silicate concentrations while the response was towards TOxN and SRP in 2006. The dominant species were Cocconeis placentula v euglyphyta in 2006; Nitzschia frustulum in 2008; and Synedra spp in 2009. The average biomass of the epiphytes was significantly lower in May 2008 than in both August 2006 and February 2009; 88.0 + 17.7 mg.m-2, 1.7 + 0.8 mg.m-2, and 61.8 + 14.4 mg.m-2 respectively. GIS mapping of past and present aerial photographs showed that submerged macrophyte (Zostera capensis) cover in 1966 and 1973 was less than that mapped for 2004. Salt marsh also increased its cover over time, from 86.9 ha in 1966 to 126 ha in 2004, colonizing what were bare sandy areas. Long-term monitoring of the health of the Bushmans Estuary should focus on salinity (as an indicator of inflow or deprivation of freshwater), benthic diatom identification and macrophyte distribution and composition (for the detection of pollution input), and bathymetric surveys (for shallowing of the estuary due to sedimentation).
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  • Date Issued: 2010

Valuing preferences for freshwater inflows into selected Western and Southern Cape estuaries

  • Authors: Akoto, William
  • Date: 2009
  • Subjects: Estuarine ecology -- South Africa , Freshwater ecology -- South Africa , Estuaries -- South Africa
  • Language: English
  • Type: Thesis , Masters , MCom
  • Identifier: vital:8992 , http://hdl.handle.net/10948/915 , Estuarine ecology -- South Africa , Freshwater ecology -- South Africa , Estuaries -- South Africa
  • Description: An estuary is the last stage of a river. It is where the river meets the sea. Estuaries are one of the most significant features of the South African coastline. In recent years, South Africa has witnessed an increase in the demand for freshwater for both industrial and domestic purposes. At the same time, there has been a gradual deterioration of river systems and their catchments. To add to this, there has been a gradual reduction in the amount of recorded rainfall, which is the primary source of freshwater for rivers. This has resulted in decreased freshwater inflow into estuaries, a situation which poses a serious threat to the biological functioning of these estuaries and the services rendered to its recreational users. A deterioration of estuary services reduces the yield for subsistence households and their appeal for recration. This study uses the contingent valuation method as its primary methodology to elicit users' willingness-to-pay to reduce the negative impacts of reduced freshwater inflow into selected western and southern Cape estuaries. Eight estuaries were selected for this study; the Breede, Duiwenhoks, Great Berg, Kleinemond West, Mhlathuze, Swartvlei and Olifants estuaries. The contingent valuation (CV) method is widely used for studies of this nature because of its ability to capture active, passive and non-use values. The CV method involves directly asking people how much they would be willing to pay for specific environmental services. In this case, users were asked what they would be willing to pay to sustain freshwater inflows into selected estuaries in order to prevent the negative impacts of reduced inflows. The travel cost method (TCM) was uesed to generate an alternative comparative set of values for the purposes of convergence testing. This is because convergence testing is highly desirable as a validity test for CV estimates.
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  • Date Issued: 2009

Phytoplankton chlorophyll a concentration and community structure in two temporarily open/closed estuaries in the Eastern Cape, South Africa

  • Authors: Gama, Phumelele Thuthuka
  • Date: 2008
  • Subjects: Estuarine ecology -- South Africa , Chlorophyll -- South Africa , Estuaries -- South Africa , Phytoplankton populations -- South Africa
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:10621 , http://hdl.handle.net/10948/707 , Estuarine ecology -- South Africa , Chlorophyll -- South Africa , Estuaries -- South Africa , Phytoplankton populations -- South Africa
  • Description: River flow is important in controlling phytoplankton distribution in estuaries. Data on the effect of river inflow on phytoplankton distribution patterns in temporarily open/closed estuaries is lacking. This study investigated the influence of river inflow on size-fractionated phytoplankton biomass (Chl a), community composition and environmental parameters measured monthly over three years in two temporarily open/closed estuaries in the Eastern Cape, South Africa. A once-off primary production study over an annual cycle was completed in the Van Stadens and Maitland estuaries. The study monitored physical, chemical and biological characteristics in both estuaries to examine the effects of changes in environmental factors and river inflow. Daily sampling of physico-chemical and biological variables from river to sea was carried out in the Van Stadens to investigate short-time scale effects of changes in environmental factors and river inflow on the phytoplankton biomass. Five and three stations in the main channel of the Van Stadens and Maitland estuaries respectively were sampled at 0.5 m below the water surface and 0.5 m above the sediment surface for biological and chemical variables and at the surface, 0.25 m and every 0.5 m thereafter for physical parameters. Five stations adjacent to the main channel along the estuary were monitored for groundwater macronutrient concentrations and five additional sites located within the upper catchment of the Van Stadens River were sampled on a quarterly basis over two years. Both estuaries were characterised by distinct hydrological conditions, an overwash, an open, a closed and a semi-closed mouth phase. Flooding in the Maitland and Van Stadens estuaries in 2001 and 2002 caused sediment scour, altered channel morphology and brought about breaching of the mouth. Flood driven mouth-breaching events occurred three and four times in each of the estuaries during the study. The mouth stayed open 20 – 25 percent and was closed 60 – 65 percent of the time. In the Van Stadens the closed overwash mouth condition occurred approximately 10 – 20 percent of the time while in the Maitland it occurred less with the semi-closed mouth condition occurring 10 – 20 percent of the time. Incidents related to mouth opening not associated with strong river floods occurred approximately 10 – 15 percent of the time, although in the Maitland a semi-closed mouth state persisted more frequently than in the Van Stadens Estuary. During flooding events salinity dropped to low levels (< 5 psu) but soon recovered to brackish conditions when river flow was reduced and marine water penetrated deep upstream. Reduction in river flow combined with marine sediment deposition resulted in the closure of the mouth. During closed mouth conditions strong onshore storm surges and spring high tides introduced marine water through overwash that kept salinity high. In both estuaries salinity showed a negative correlation with rainfall (R2 = 0.12), indicative of the strong influence of marine overwash that kept salinity high thus masking the influence of freshwater. High rainfall in the Van Stadens Estuary caused high levels of turbidity that reduced light penetration at depth. Light attenuation was positively correlated with the high rainfall (R 2 = 0.26) suggesting that increased turbidity was linked to rainfall induced discharge. In contrast, in the Maitland Estuary light attenuation did not show any correlation with increased rainfall possibly because of the reduced water depth and increased euphotic zone following the floods in 2002. High river inflow introduced macronutrients in both estuaries such that dissolved inorganic phosphates (DIP) and dissolved inorganic nitrogen (DIN) concentrations in the Van Stadens Estuary were strongly correlated with rainfall (R2 = 0.78 and 0.57 respectively). In the Maitland Estuary DIP and DIN concentrations remained significantly higher (p < 0.05) compared to that in the Van Stadens suggesting that the Maitland catchment contributed greater nutrient input into the estuary and may be associated with farming activities. Phytoplankton chlorophyll a (Chl a) ranged from 0.8 – 13.9 μg L-1 in the Van Stadens and in the Maitland Estuary from 5.3 – 138 μg L-1 during the 3-year study. During the open mouth condition Chl a biomass and primary production ranged from 5.4 – 52.9 μg Chl a L-1 and 1.2 – 11.7 mg C m-2 d-1 in the Maitland and in the Van Stadens from 1.6 – 9.8 μg Chl a L-1 and 1.2 - 14 mg C m-2 d-1 respectively. Maximum annual primary production in the Maitland and Van Stadens estuaries was 8.8 and 5.1 g C m-2 y-1 respectively. When the mouth was open in the Van Stadens Estuary the microphytoplankton (> 20 μm) accounted for > 65 percent of the Chl a, whereas during closed mouth conditions they accounted for about 55 percent of the Chl a biomass. Chlorophytes became the dominant taxon in the dry summer months but were replaced by cryptophytes and dinoflagellates during the wet season. When nutrient concentrations were low during low flow conditions in the Van Stadens Estuary mixotrophic microphytoplankton became an important fraction of the water column together with phototrophic dinoflagellates and cryptophytes. In the Maitland large sized chlorophytes were the dominant taxa in late spring and summer seasons and made up more than 80 percent of the cell numbers. In the Maitland before the floods in 2002 cyanophytes were the dominant group in late spring contributing more than 75 percent in cell abundance. Data from the short-term study in the Van Stadens Estuary showed similarities and differences in the Chl a response to increased river inflow. High river inflow initially reduced Chl a biomass followed by a recovery period of a couple of days compared to a 8 – 10 week recovery period in studies monitored over seasonal and annual temporal scales. The responses may be dissimilar but help to illustrate that there are similar response patterns to environmental forcing necessary to support phytoplankton biomass at different temporal scales. This study has demonstrated that flooding events caused by strong river flow cause breaching of the mouth, a reduction in salinity and marked nutrient input. Although the causes of flooding can be similar in both estuaries the resultant effects are varied and can alter the ability of the estuary to retain water. This study was able to demonstrate that the supply of macronutrients from the catchment was strongly correlated with rainfall (R2 = 0.67) and that phytoplankton growth mainly depended on an allochthonous source of macronutrients although internal supplies could be critical at times in controlling microalgal biomass.
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  • Date Issued: 2008

The value of freshwater inflows into the Kowie, Kromme and Nahoon Estuaries

  • Authors: Sale, Michael Charles
  • Date: 2007
  • Subjects: Estuaries -- South Africa , Freshwater ecology -- South Africa
  • Language: English
  • Type: Thesis , Masters , MCom
  • Identifier: vital:9003 , http://hdl.handle.net/10948/599 , http://hdl.handle.net/10948/d1011689 , Estuaries -- South Africa , Freshwater ecology -- South Africa
  • Description: An estuary can be defined as a partially enclosed, coastal body of water which is either permanently or periodically open to the sea and within which there is a measurable variation of salinity due to the mixture of sea water with fresh water derived from land drainage. Estuaries are extremely important environmental assets and the management of them is dependent on the active involvement of the people whose livelihoods depend on them. There have been steady decreases in freshwater inflows into them during the past century due to abstraction of river water for human consumption and alien tree and plant infestations. Due to these decreases in freshwater inflows, many estuaries have become smaller and are providing reduced recreational services to users, such as boaters, fishermen and birders. This reduction in recreational service provision has adverse economic consequences. The scale of these consequences have become of great interest to river catchment planners. Of particular interest is the value of the freshwater inflows into estuaries relative to other abstractions of this water. The value referred to here is in terms of the environmental services yielded to recreational users. From a management perspective, it is desirable that these marginal values be compared with marginal cost values of this water in its best alternative use in order to guide the allocation of inflows into the respective estuaries. The aim of this study is to place a monetary value on this freshwater inflow at the Kowie, Kromme and Nahoon estuaries. Due to the fact that the freshwater flowing into estuaries is not a traded good, an alternative method to market price must be used to value it. The method of valuation used in this study is the contingent valuation method. The contingent valuation method (CVM) is a survey technique which asks individuals to place values upon changes to environmental assets. The questionnaires used in the surveys differed slightly. The one administered at the Nahoon Estuary was revised in the light of experience gained at the administration of the ones at the Kowie and the Kromme estuaries. Some questions in the latter two surveys were found to be confusing to the respondents and were made clearer and some of the questions were found to yield little extra information and were scrapped from the Nahoon Estuary survey.
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  • Date Issued: 2007

A preliminary investigation of the ecology of the Larger Kleinmond River Estuary, Bathurst District

  • Authors: Brown, Alexander Claude, 1931-2005
  • Date: 1953
  • Subjects: Kleinemonde River Estuary (South Africa) , Estuaries -- South Africa , Estuarine ecology -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5904 , http://hdl.handle.net/10962/d1014611
  • Description: Introduction. On the coast of the Bathurst Division, Eastern Cape Province, some 42 miles south- east of Grahamstown, lie two estuaries opening within a few yards of one another. These are known as the Kleinemonde. This paper embodies the results of an ecological survey of the fauna of the Larger Kleinmond Estuary. The chief concern has been the aquatic fauna but animals living along the banks have also been dealt with as far as possible, as have the birds. This is the second of South Africa's blind estuaries to be studied, the Klein River, Hermanus, having been investigated in 1947-49 by workers from the University of Cape Town. Though common in South Africa, blind estuaries are rare in parts of the world such as Europe, and present an almost entirely new field of research for the ecologist. It is hoped, therefore, that the investigation of the Kleinmond Estuary and a comparison with the results obtained from the Klein River, Hermanus, will add to our knowledge of this subject and be of service to future investigators. The history of the Kleimnond River is worthy of mention, for the lagoon was not always blind and shallow. The early maps of the 1820 settlers show the river as a navigable stream; sailing vessels anchored out at sea and sent lighters up what was then known as the Lydendoch River to collect fresh meat. The area at the mouth of the river was called Port Jessie. In these early days the region abounded with game. Hippo and elephant were common. the former inhabiting deep pools in the upper reaches of the river; pools which have since completely silted up. Constant ploughing of the slopes adjoining the river has caused vast amounts of soil to be washed by rains into the stream, and today what was within living memory a deep, clear stream is a shallow, blind and muddy river, a reflection of man's destructive methods of farming. These changes must have had a far-reaching effect on the fauna of the estuary; an effect about which we can, alas, only speculate. It is perhaps significant that though rich in numbers, the fauna is poor in species, tunicates and echinoderms being apparently entirely absent. The work involved in this survey was undertaken between September 1952 and November 1953, under the direction of Professor J . Omer-Cooper of Rhodes University, frequent and regular visits being made to the estuary. The entire month of February, 1953, was spent on the shore of the lagoon, so that animals could be observed over a continuous period. The starting date of the survey was particularly fortunate, as on September 28th, 1952, the river came down in flood and broke through the sand-bar separating the lagoon from the sea. The work thus began at a definite point in the estuarine cycle, the importance of which it is hoped to show.
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  • Date Issued: 1953

South African estuaries in the Anthropocene

  • Authors: Perissinotto, Renzo
  • Subjects: Estuaries -- South Africa , Geology, Stratigraphic -- Anthropocene , f-sa
  • Language: English
  • Type: text , Lectures
  • Identifier: http://hdl.handle.net/10948/20977 , vital:29424
  • Description: In the new geological epoch of total human dominance of the planet, already widely referred to as the “Anthropocene”, estuaries are among the most vulnerable ecosystems to the changes that man’s activities have imposed on the coastal zone. For the non-specialist, an estuary is a “semi-enclosed coastal body of water, which has a permanent or temporary connection with the open sea, and within which sea water is diluted with fresh water from land drainage”.
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