Browsing by Author "Rivers-Moore, Nicholas Andrew."

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Development of a connectivity index to assess aquatic macroinvertebrate species vulnerability to thermal change : a case study in KwaZulu-Natal Province.
(2015) Ramulifho, Pfananani Anania.; Rivers-Moore, Nicholas Andrew.; Dallas, Helen.
Connectivity of river systems is a critical ecological component affecting not only the integrity of aquatic systems but also freshwater species’ habitat, community structure, migration and other life activities such as feeding rate and reproduction. Connectivity is a product of longitudinal and lateral conditions of rivers that in turn impact on flow and water temperature time series patterns (temporal connectivity). No comprehensive connectivity index of rivers has previously been developed for South Africa’s KwaZulu-Natal Province. The aims of this study were to develop a connectivity index for selected main rivers in KwaZulu-Natal, where free-flowing rivers represent full connectivity, and to assess quaternary catchments which would most be vulnerable to the impacts of increased water temperatures in response to climate change in terms of aquatic biota. A connectivity index at quaternary catchment scale was developed for main rivers in KZN based on in-stream barriers, land cover fragmentation and small dams density. The temporal dimension of connectivity involved an examination of stream flow and water temperature changes at selected stations based on comparisons of data from before and after construction of in-stream barriers. Temporal connectivity was incorporated into the longitudinal connectivity index score using the concept of reset distance. Reset distance was calculated based on mean daily flow volumes and the distance between impoundments at each of the selected quaternary catchments. Based on these assessments, catchments likely to be most vulnerable to species community changes were detected as a function of connectivity of rivers and slope gradient of streams. The assumption was that aquatic macroinvertebrate species are likely to be most impacted by rapid thermal change (based on temperature lapse rates) in the high altitude catchments particularly where such rivers have reduced connectivity. The uMngeni catchment emerged with the most disconnected river in the province due to its closely located in-stream barriers and long distance recovery potential of flow. The quaternary catchment with lowest lateral connectivity also occurred within the uMngeni catchment. It is concluded that catchment management authorities should consider both connectivity and vulnerability (climate change) assessments of river systems as a tool negotiating for sustainable conservation plan of aquatic species and ecological integrity of rivers.
Modelling the likelihood of wetland occurrence in KwaZulu-Natal, South Africa : a Bayesian approach.
(2014) Hiestermann, Jens.; Mutanga, Onisimo.; Rivers-Moore, Nicholas Andrew.
Global trends of transformation and loss of wetlands to other land uses has deleterious effects on surrounding ecosystems, and there is a resultant increasing need for improved mapping of wetlands. This is because wetland conservation and management depends on accurate spatial representation of these systems. Current approaches to mapping wetlands through the classification of satellite imagery typically under-represent actual wetland area, and the importance of ancillary data in improving the accuracy in mapping wetlands is recognized. This study uses likelihood estimates of wetland occurrence in KwaZulu-Natal (KZN), South Africa, using a number of environmental surrogate predictors (such as slope, rainfall, soil properties etc.). Using statistical information from a set of mutually independent environmental variables in known wetland areas, conditional probabilities were derived through a Bayesian network (BN) from which a raster layer of wetland probability was created. The layer represents the likelihood of wetlands occurring in a specific area according to the statistical conditional probability of the wetland determinants. Probability values of 80% and greater also accounted for approximately 6% of the KZN area (5 520 km²), which is substantially more than the previously documented wetland area in KZN (4% of the KZN area or 4 200 km²). Using an independent test dataset, Receiver Operating Characteristic (ROC) curves with the Area Under Curve (AUC) analysis verified that the final model output predicted wetland area well (AUC 0.853). Based on visual comparisons between the probability layer and ground verified wetland systems, it was shown that high wetland probability areas in the final output correlated well with previously highlighted major wetland and wetland-rich areas in KZN. Assessment of the final probability values indicated that the higher the probability values, the higher the accuracy in predicting wetland occurrence in a landscape setting, irrespective of the wetland area. It was concluded that the layer derived from predictor layers in a BN has the potential to improve the accuracy of the KZN wetland layer by serving as valuable ancillary data. Application of the final probability layer could extend into the development of updated spatial freshwater conservation plans, potentially predicting the historical wetland extents, and as input into the land cover classification process. Keywords: ancillary data, Bayesian network, GIS, modelling, probability, wetland mapping.
Refining prediction accuracy for pest blackfly outbreaks using Bayesian networks, Orange River, Northern Cape, South Africa.
(2018) Naidoo, Sashin.; Hill, Trevor Raymond.; Rivers-Moore, Nicholas Andrew.
Construction of dams, impoundments and Inter-Basin Transfer schemes (IBTs) along the Orange River are aimed to provide useable water for multiple sectors. However, operation of these water schemes had led to changes in flow regimes, seston concentrations and water temperatures, which has led to an escalation of pest blackfly (S.chutteri) outbreaks along the lower to middle reaches of the Orange River. Pest blackfly bite livestock, poultry and humans asthey require a blood meal to complete ovarian development. During outbreak periods, livestock farming and the grape industries are affected negatively by pest blackflies along the Orange River. The blackfly control programme has been operating for over twenty years, and aims to control blackfly outbreaks by applying larvicides along the Orange River. Although this programme is in place, periodic outbreaks occur and losses in livestock and productivity can amount to an estimated R300 million during an outbreak (2013). Therefore, other methods should need to be integrated with this programme to achieve blackfly control. Predictive modelling was identified as a method to assist the blackfly problem. Being able to predict when, where and the severity of an outbreak, will assist management in control planning. Bayesian network (Bn) models were identified as a suitable predictive model,as multiple variables can be used in understanding the cause and effects of a response variable.The aim of the research was to refine prediction accuracy of blackfly outbreaks along the middle to lower reaches of the Orange River, using Bns. Fourteen sites were sampled along the Orange River, for which abiotic and biotic data were collected during four sampling periods. These data were used in assisting quantitative components of the Bns, whilst the qualitative components were based of previous Bns with additions on new nodes that were identified as affecting blackfly outbreaks. Water temperature data showed that sites were split into two distinct groupings, for which Bns were constructed.These were termed the upper and lower stream models. The upper stream model had the higher outbreak probabilities, whilst it was predicted for both models that summer would be the season most likely for an outbreak to occur. The species most likely to cause an outbreak was identified to be either S.chutteri or S.damnosum, with switching in dominance throughout sampling periods potentially due to switching in seston concentrations. Future outbreak probabilities based on scenarios of increased discharge and water temperatures indicate that the blackfly problem is likely to worsen, with increases in discharge resulting in greater habitat availability for pest species and increases in water temperature resulting in shorter life cycles and more rapid reproduction.The Bns constructed show promise in assisting management as blackfly outbreak probabilities were refined on a spatial and temporal scale along the middle to lower reaches of the Orange River.
Role of water temperature variability in structuring aquatic macroinvertebrate communities : case study on the Keurbooms and Kowie Rivers, South Africa.
(2011) Eady, Bruce Robert.; Hill, Trevor Raymond.; Rivers-Moore, Nicholas Andrew.
Water temperature is a critical factor affecting the abundance and richness of freshwater stream aquatic macroinvertebrate communities. Variable seasonal river temperature patterns are a critical factor in maintaining temporal segregation in aquatic invertebrate communities, allowing for resource partitioning and preventing competitive exclusions, while spatial differences in water temperatures permit zonation of species. This research investigated whether the degree of predictability in a stream’s water temperature profile may provide some indication of the degree of structure and functional predictability of macroinvertebrate communities. Quarterly aquatic macroinvertebrate sampling over a single year along the longitudinal axes of two river systems, Keurbooms River in the southern Cape, and the Kowie River in the Eastern Cape, were undertaken as the core component of this research. The two river systems shared similar ecoregions and profile zones, however were expected to differ in their thermal variability, based on the hydrological index and flow regimes for their respective quaternary catchments. Hourly water temperature data were collected at each sampling site from data loggers installed at five paired sites on each stream system. The aquatic biotopes sampled were in close proximity to the loggers. Multivariate analysis techniques were performed on the macroinvertebrate and water temperature data. Macroinvertebrate taxon richness was greater on the perennial Keurbooms than the non-perennial Kowie River where, on a seasonal basis, taxon richness increased from winter to autumn on both systems. Macroinvertebrate species turnover throughout the seasons was higher for sites having lower water temperature predictability values than sites with higher predictability values. This trend was more apparent on the Keurbooms with a less variable flow regime. Temporal species turnover differed between sites and streams, where reduced seasonal flows transformed the more dominant aquatic biotopes from stones-in-current into standing pools. Findings included aquatic macroinvertebrates responding typically in a predictable manner to changing conditions in their environment, where water temperature and flow varied. The findings of this research demonstrate that macroinvertebrate taxa do respond in a predictable manner to changes in their environment. This was particularly evident in relation to variability in water temperature and flow.
Water temperature and fish distribution in the Sabie River system : towards the development of an adaptive management tool.
(2003) Rivers-Moore, Nicholas Andrew.; Jewitt, Graham Paul Wyndham.
Water temperatures are a fundamental water quality component, and a key abiotic determinant of fish distribution patterns in rivers. A river 's thermal regime is the product of a multitude of thermal drivers and buffers interacting at different temporal and spatial scales, including, inter alia, air temperatures, flow volumes (including groundwater flows and lateral inputs from tributaries), channel geomorphology and riparian vegetation. "Healthy" river systems are self-sustaining, with adequate thermal variability to maintain biotic diversity. Temporal variability of flow volumes and water temperatures, and how these change along the longitudinal axis of a river, contribute towards a rivers "signature". Rivers that have had their signatures altered through anthropogenic impacts may no longer be sustainable, and require varying levels of management. Successful river management should include a quantification of these signatures , a definition of the "desired" state which management aims to achieve, associated "thresholds" of change or concern, and monitoring programmes. Such an approach requires flexibility and adaptability, as well as appropriate tools being available to natural resource managers. Indices, the utility of which are enhanced when included in predicative modelling systems, are a common means of assessing system variability and change. The degree of confidence placed in such tools depends on the level of fundamental science, and the degree of system understanding, underpinning them. This research contributes to the understanding of the ecological significance . of water temperatures in variable semi-arid river systems, using the Sabie River (Mpumalanga, South Africa) as a case study, and indices derived from biological indicators (Chiloglanis , Pisces: Mochokidae) to quantify the effects of cumulative changes in heat units against a hypothesised critical water temperature threshold. Hourly water temperatures for 20002002 collected at nine sites in the main rivers of the Sabie catchment, together with biannual surveys of relative abundances and community patterns of fish collected using standard electrofishing techniques, were used to provide the basis for a modelling system which aims to provide river managers with a tool for quantifying changes to the thermal regime of the Sabie River. This modelling system consisted of a suite of pragmatic models, including multiple linear regression models for simulating daily maximum water temperatures, and simple cause-and-effect relationships between biological indices (change In condition factor and change in the ratio of relative abundances of two species of Chiloglanis) and annual metrics of time-of-exposure to heat stress. It was concluded that changes in the thermal regimes of the rivers in the Sabie catchment are likely to lead to changes in fish distribution patterns, and a decline in river health. Inherent system variability suggests that management decisions will be made in the face considerable uncertainty. Indirect management of water temperatures may be possible through maintenance of flow volumes and flow variability. However, the most appropriate management approach for maintaining fish diversity within these rivers is to ensure that obstacles to fish migration are minimized, to maximise the ability of river biota to respond to thermal changes, by accessing suitable alternative habitats or refugia. Future research should focus on extending the time series of water temperatures from such river systems, and further understanding the drivers and buffers contributing to the thermal regimes of variable semi-arid river systems in South Africa. Additional testing of the validity of the hypothesized relationships between abiotic processes underpinning biotic patterns should be undertaken.