No description available.

No description available.

The study area, the KwaZulu-Natal Bight, is an oceanographically important area, which, regardless of having two of the most important fisheries off the east coast of South Africa, has received little research attention regarding its biological functioning. Until now chiefly oceanographic processes have been considered the drivers of this generally oligotrophic system. This study seeks to understand which of three important processes, a topographically induced oceanic upwelling cell near Richards Bay, a cyclonic eddy near Durban, or fluvial fluxes centred around the Thukela River, forces ecological functioning through their nutrient or organic matter input. The overall aim of the thesis is to understand the pelagic and benthic ecosystems of the Bight in terms of these drivers through the use of stable isotope (δ¹³C and δ¹⁵N) analyses of a range of biotic and abiotic samples. These were collected on board of a number of research cruises – forming predominantly part of the larger African Coelacanth Ecosystem Programme suite of studies – in the wet and dry seasons of 2010. Isotopic analyses found distinctions between fluvial and oceanic particulate organic matter and indicate that upwelling was not occurring in either sampling season. Organic matter originating from the Thukela River did not play a significant role in the wet season, although it dominated the planktonic pelagic food web in the dry season. The organic matter of the most productive region in the Bight, the Middle Shelf, was of riverine origin in the dry season, but of indeterminate origin in the wet season when it may have been an artefact of an old upwelling event which had previously occurred to the north of the Bight. There is, however, some evidence suggesting that this organic matter may rather have been of riverine origin, with its δ¹³C signals subsequently having been modified by the diatom bloom occurring there. In the demersal ecosystem, sediment isotopic data show organic matter to be well-mixed throughout the Bight in both seasons, with riverine organic matter dominating most of the Bight except its northern and southern edges, where oceanic organic matter increases in importance. Sediment organic matter (most likely via the macrobenthic biota) was deemed an important food source for demersal animals and omnivory an important feeding strategy. Seasonal studies from 2008 to 2010 in the Thukela Bank area indicate that the demersal animals' stable isotope signatures responded to the seasonal isotopic changes in riverine organic matter, indicating the cross-seasonal importance of this food source to the demersal ecosystem. Parallel methodological studies examined how routine isotopic sample handling procedures could have affected the results of the ecological studies. These studies suggest that i) effects of preservation/fixation methods and the use of dyes are species-dependant; ii) acidification has no effect on zooplankton isotopic signatures, and that iii) drying methods alone and interactively with multiple thawing and refreezing of samples affect the stable isotope values offish muscle tissues. Recommendations are made for further improvements in methodology and considerations to be taken when processing samples. Overall, it is concluded that riverine input to the Bight has a more important biological role than previously thought, and that organic matter from this source is an important driver of ecosystems within the Bight throughout the year for the demersal and pelagic ecosystems. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

The focus of this mini-dissertation is the use of riparian buffer zones to manage nitrate pollution of water resources. Riparian buffer zones are vegetated areas adjacent to streams, lakes and rivers, that are managed to enhance and protect aquatic resources from the adverse impacts of agricultural practices. These zones are recognised globally for their function in water quality amelioration. Despite the growing literature, there is little consensus on how to design, assess and manage these riparian buffer zones specifically for nitrate attenuation. For the purpose of this mini-dissertation, a literature review of world-wide research into the nitrate attenuation efficiencies of riparian buffer zones was undertaken. A database was created using the key information from this literature. Two key processes responsible for immobilising and/or removing nitrate from surface and subsurface flows are generally recognised in the available literature, namely: vegetative uptake and the process of denitrification. A comparison of the available riparian studies indicated that there are similar characteristics in riparian buffer zones that may be responsible for enhancing these key mechanisms. Studies where there was shallow lateral subsurface or uniform surface water delivery pathways, vegetation of close structure and composition, high organic matter in the soils and fluctuating soil surface saturation rates showed the most significant nitrate attenuation efficiencies. The mini-dissertation proposes that these similarities can be used to both assess a riparian landscape for its potential to attenuate nitrate, and to size a riparian buffer zone specifically to meet this function. A set of proposed guidelines based on the findings of the dissertation attempt to illustrate how riparian pollution control recommendations can be achieved. These guidelines are an example of how to assist a farmer or similar landowner in achieving good nitrate removal efficiencies from a riparian buffer zone. The guidelines work through three steps, which help to establish and prioritise management zones, assess each zone's potential for nitrate attenuation, and determine adequate riparian buffer widths for each management zone. A case study was used to illustrate the practical application of the guidelines. Full testing of these guidelines was not within the scope of this mini-dissertation, however the guidelines are an indication of how information regarding riparian function can be applied to a system to determine effective management of water resources. / Thesis (M.Env.Dev.)-University of Natal, Pietermaritzburg, 2002

Riparian systems perform many critical ecological functions and services. Riparian areas are in urgent need of rehabilitation to restore their natural functioning. In order to successfully implement rehabilitation efforts in riparian areas, a management plan for rehabilitation is required. An important facet of a management plan would be the assessment of riparian habitat quality. The aim of this study is to produce a riparian habitat assessment approach that would be helpful in developing a rehabilitation management plan. The approach needs to assess habitat from a landscape scale through to a site scale, be concise, user friendly, effective and be able to be used by all land managers. It must also allow for the identification of areas of high asset value that will be prioritised for rehabilitation efforts. Existing local and international habitat assessment methodologies reviewed did not satisfactorily meet all the above objectives. Accordingly, a new methodology for riparian habitat assessment was developed, consisting of a 3-leve1 approach which assesses habitat from a landscape scale (macroscale assessment), a reach scale (intermediate-scale assessment) and at a site scale (microscale assessment). The approach was tested in a case study of the Rivers Bend farm in the Nkwaleni Valley, KwaZulu-Natal, South Africa. The developed methodology allows for an assessment technique of riparian areas that now explicitly includes landscape attributes, local characteristics of the river system (reach scale) and site scale level of assessment. Both the macroscale and the microscale assessments produced spatial representations of asset values within the study area. These areas were prioritised for rehabilitation efforts. Although these assessments produced results for identifying asset sites, the scoring· systems did not reflect the changes in habitat quality with enough detail. It is recommended that the characteristics determining the quality ratings and the scoring systems of these assessments be reassessed. The intermediate-scale assessment produced relevant stream profiles and gradient classes, but the application of the assessment did not successful1y delineate the river into homogenous segments. Further study is required to better integrate the 3-levels of the developed methodology. / Thesis (M.Env.Dev.)-University of Natal, Pietermaritzburg, 2001.

The KwaZulu-Natal Bight is an important area along the South African east coast, stretching 160 km north from Scottsburgh to St Lucia (Lutjeharms et al., 2000). The Bight is of interest to the region as the area contains some distinct physical features, which are presumed to drive the ecological functioning of the shelf ecosystem through their role in nutrient sources. These include the Tugela River, the second largest river in South Africa in terms of outflow, and the Agulhas Current that forms an outer border at the edge of the continental shelf. Phytoplankton interacts with the majority of essential ecological networks and therefore greatly influences marine ecosystems. To this end, it is necessary to understand their ecophysiological rate processes – particularly those that are influenced by the dominant nutrient inputs to the Bight. The overall aim of this project is therefore to provide an insight into the sources of nutrients driving phytoplankton productivity in the Bight. Synoptic surveys were conducted to provide an indication of the distribution of Total Suspended Solids (TSS), Particulate Organic Matter (POM) and phytoplankton in the Bight, while focussed experiments used stable isotopes to examine the rate processes involving C and N acquisition, as well as sources of N available in the surface water. Concentration of particulate organic phosphorus and nitrogen were found to be higher in the wet season when compared to the dry season. During the wet season a large variation in chlorophyll-a fluorescence was observed across the Bight, while natural abundance isotope data indicated a seasonal change in the nutrient source available. For the wet season nutrient concentration varied with site and depth, however uptake rates (μg N.1ˉ¹.hˉ¹) measured using ¹⁵N tracer additions were not significantly different with site and depth. Alternatively, the dry season showed a significant difference between site in surface waters. In the wet season the mid shelf area had the highest uptake rate and phytoplankton biomass while the Richards Bay north site dominated, with regard to the previously mentioned factors, in the dry season. At the time of the experiments, neither the Durban eddy nor the upwelling cell were present, and hypotheses regarding the importance of these physical features in driving phytoplankton nutrient acquisition could not be assessed. However, a notable difference in uptake rate between the wet and dry seasons was observed, and this difference is likely due to the fluvial sources of nutrients from the Tugela and many other rivers entering the KZN coast, which are absent during the dry season. The results indicate that terrestrial nutrient sources play a major role in influencing nutrient concentrations on the Bight, and hence influence the nearshore ecosystem of the region. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.

Agriculture contributes significantly to national and global greenhouse gas (GHG) inventories but there is considerable control over management decisions and changes in production methods could lead to a significant reduction and possible mitigation of emissions from the sector. For example, conservation tillage practices have been suggested as a method of sequestering atmospheric carbon dioxide (CO2), however, many questions remain unanswered regarding the short-term efficacy of the production method and knowledge gaps exist regarding possible interactions with essential nutrient cycles, and the production of non-CO2 GHGs, such as nitrous oxide (N2O). Between autumn 2005 and 2009, a micrometeorological flux system was used to determine net CO2 and N2O exchange from an annual cropping system situated on clay soil in the Red River Valley of southern Manitoba. Four plots (4-ha each) were independently evaluated and planted to corn in 2006 and faba bean in 2007; in 2008, two spring wheat plots were monitored. As well, during the non-growing season in 2006-2007 following corn harvest, a second micrometeorological flux system capable of simultaneously measuring stable C isotopologue (12CO2 and 13CO2) fluxes was operated at the site. Tillage intensity and crop management practices were examined for their influence on GHG emissions. Significant inter-annual variability in CO2 and N2O fluxes as a function of crop and related management activities was observed. Tillage intensity did not affect GHG emissions from the site. After accounting for harvest removals, the net ecosystem C budgets were 510 (source), 3140 (source) and -480 (sink) kg C/ha/year for the three respective crop years, summing to a three-year loss of 3170 kg C/ha. Stable C isotope flux measurements during the non-growing season following corn harvest indicated that approximately 70 % and 20 – 30 % of the total respiration flux originated from crop residue C during the fall of 2006 and spring of 2007, respectively. The N2O emissions at the site further exacerbated the net global warming potential of this annual agroecosystem.

Although rather inconspicuous on healthy coral reefs, macroalgae form the basis of coral food webs. Today, macroalgae are generally increasing and many reefs undergo transitions from coral to macroalgal dominance resulting from e.g. enhanced nutrient loading or increased fishing. This thesis aims to investigate the relative importance of top-down and bottom-up regulation, and different herbivore types, on macroalgal distribution, fecundity and community composition on coral reefs. Papers I and II indicate that macroalgal abundance in a coral reef system is largely governed by top-down regulation through grazing by herbivores, while bottom-up regulation through enhanced nutrient availability rather influence algal species composition. Paper II also shows that these regulating effects are not as evident in an area with relatively strong water motion, suggesting that impacts of anthropogenic disturbance may be site-specific. Paper III shows that herbivory is an important factor influencing macroalgal growth and subsequent reproduction. Furthermore, Paper IV and V conclude that efficiency in removing macroalgal biomass is dependent on the type of dominant herbivore, where sea urchins seem to be more effective than fish. Paper IV indicates a seasonal variation in macroalgal biomass and distribution in a small geographic scale but with relatively high temporal resolution. Paper V on the other hand shows these same effects, but with a focus on geographic variation, including a large part of the East African region, as well as between year temporal variations in Kenya. Together, results from the two latter studies indicate that herbivory by fish may not be able to prevent a macroalgal bloom in a degraded system where substrate availability for algal colonization is high, but that it may still facilitate coral recovery over time. Thus, a large algal biomass may not necessarily indicate a reef beyond the possibility of recovery. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 4: Manuscript. Paper 5: Manuscript.</p>

Acid mine drainage (AMD) is a significant environmental issue worldwide, which often causes severe contamination and marked species losses in receiving streams. However, little is known about how this stress alters food webs and ecosystem function. I conducted a literature review, which revealed that AMD-impacted streams generally had depauperate benthic communities dominated by a few tolerant species and impaired ecosystem processes. Next, using survey and experimental-based approaches, I investigated food web structure and energy flow in these highly stressed streams, which typically have low pH (< 3), high concentrations of dissolved metals (Al, Fe), and substrata coated with metal hydroxide precipitates, on the South Island, New Zealand. Inputs of AMD caused substantial loss of consumers and reduced the overall number of links between species generating small and simplified food webs, with few invertebrates and no fish. Comparative analysis of food webs from a survey of 20 streams with either anthropogenic or natural sources of acidity and metals, indicated that anthropogenic sources had a stronger negative effect on food web properties (size, food chain length, number of links); an effect driven primarily by differences in consumer diversity and diet. However, the presence of fewer trophic levels and reduced trophic diversity (detected using isotopic metrics), were common structural attributes in AMD-impacted webs along a pH gradient, regardless of impact level. Furthermore, complementary dietary analyses of consumer gut contents and stable isotope signatures (δ13C and 15N) confirmed that primary consumers fed generally on basal resources and that there were few predatory interactions, which reflected low densities of small-bodied chironomids. This suggests that food quantity was unlikely to limit primary consumers but that reduced prey availability may be an additional stressor for predators. In these radically re-structured food webs, trophic bottlenecks were generated at the primary consumer level and energy flow to higher consumers was disrupted. However, streams still retained some limited function, including slow leaf litter breakdown, which provided detrital resources and supported the small food webs. Overall, my findings have furthered our understanding of these highly stressed stream ecosystems by providing new insights into interactions among species and trophic levels that structure food webs and enable function.