College of Agriculture, Engineering and Science

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An assessment of the potential impacts of climate variability on sugarcane production across Southern Africa.
(2023) Ngcobo, Simphiwe Innocent.; Jewitt, Graham Paul Wyndham.; Hill, Trevor Raymond.; Archer, Emma.
The scale and extent of changes to demographic, economic and environmental systems exacerbated by human activities have been rapid and pervasive enough that it has been established that a new geologic era termed the Anthropocene has already begun. One of the most critical and challenging consequences of the Anthropocene has been the accelerated release of greenhouse gases leading to global warming and, consequently, climate change (CC), which has impacted hydrological responses and available water resources by increasing surface temperatures and altering precipitation patterns across spatio-temporal scales. These changes have exacerbated the vulnerability of various systems that sustain livelihoods, placing them at high risk of collapse. One of these systems is sugarcane production, which is a crucially important agricultural activity in many parts of the world, including southern Africa. There is a consensus that as a region, southern Africa will be subjected to amplified hydrological impacts which will affect the sugarcane production landscape. Further the expansion and intensification of sugarcane production across southern Africa is highly likely due, in part, to the recognition of the economic and social importance of this activity for supporting livelihoods. Sugarcane yields have been declining over the past 25 years in the region because of the increased frequency of climatic extremes. Literature reviews showed that by amplifying precipitation variability, climate change will increase the exposure and vulnerability of sugarcane to water stress and will have a devastating impact on yields. However, knowledge gaps remain regarding climate change impacts on water resources and sugarcane yields. Further, few studies have addressed the vulnerability and adaptation potential of sugarcane production at sufficient spatio-temporal scales. To address these knowledge gaps, an initial review was conducted to understand the dynamics between global change and water resources across southern Africa. The review showed that although global drivers are intricately related, their water resources impacts are highly complex, indirectly coupled and spatially and temporally sensitive. Having established a general perspective of the impacts of global change in southern Africa, the multi-scale drivers of sugarcane production were analysed using of a frequency analysis. This approach allowed the determination of proximate and ultimate drivers in the uMngeni, uMlaas, and Umvoti catchments in South Africa, the Ubombo catchment in eSwatini, the Shire catchment in Malawi and the Kilombero catchment in Tanzania. The frequency analysis provided quantitative descriptions of the water resource impacts of sugarcane production across southern Africa. Applying a relationship between observed sugarcane yields and future low, medium, and high production scenarios, this study developed water use estimates for sugarcane over multiple growing cycles. Results indicated that ultimate drivers play the most dominant role in the expansion of sugarcane production within each catchment. Drawing from this analysis, a methodology of assessing yield declines was developed based on a yield gap analysis using the AquaCrop crop growth model. The results were used to develop recommendations to mitigate yield declines by offering safeguards for the sugarcane industry against climatic extremes. Modelling results suggested that yield trends can be attributed to existing crop management approaches instead of prevailing hydroclimatic regimes. The importance of recognising the vulnerability and adaptation potential in sugarcane production was highlighted in this study. It was concluded that if sugarcane growers are to adapt to the effects of extreme climatic events, they must consider shifting crop management approaches and be proactively included in related research. This research highlighted the importance of addressing the interactions between activities that drive land use change, such as sugarcane production, and the current impacts of climatic extremes on water resources. This is important in rapidly developing regions and climate change hotspots such as southern Africa. The development of innovative adaptation policies that will safeguard the already-pressured water resources and secure the sustainability of sugarcane production will become increasingly important under an altered climate. Iqoqa. Isikali nobungako boguquko lwezibalo zabantu, ezomnotho, kanye nezinhlelo zemvelo osekonakaliswe imisebenzi yabantu sekwenyuke kakhulu futhi kwasabalala ngokwanele kangangokuthi sekuphakanyiswe ukuthi isikhathi sokwakheka esisha somhlaba nezinto esibizwa nge-Anthropocene sesivele siqalile. Omunye yemiphumela emanzonzo futhi enezinkinga ye-Anthropocene seyibe ukukhuphuka ngesivinini esikhulu sokukhipha isisi esikhishwa umhlaba nokuholelele ekushiseni kakhulu komhlaba futhi, okuholele, ekuguqukeni kwesimo sezulu, iclimate change (CC), nosekube nemithelela ekuphenduleni okusebenza ngamanzi kanye nemisuka yamanzi ekhona ngokwenyusa amazinga okushisa angaphezulu futhi kwashintsha izindlela zokwehla kwemvula kuzo zonke izindawo ezahlukene lapho kwenzeka khona. Lezi zinguquko sezidlondlobalise ukungabi namandla kwezindlela eziningi ezigcina izimpilo zabantu, ngokuzibeka engcupheni enkulu ukuthi zifadalale. Enye yalezi zindlela umkhiqizo womoba, ongomunye umsebenzi obalulekile kakhulu kwezolimo ezingxenyeni eziningi zomhlaba, okubalwa kuzo imazansi le-Afrika. Kunokuvumelana okukhona ukuthi njengesifunda, imazansi kuzomele ibhekane nesimo somthelela wokusebenza kwamanzi esidlondlobele kakhulu nesizoba nomthelela emkhakheni wokukhiqiza umoba. Okunye futhi, kuyacaca ukuthi ukukhula kanye namandla okukhiqizwa kukamoba kuzo zonke izindawo ezimazansi ne-Afrika zingaba kakhulu ngenxa, yokunye kwakho, ukukhomba ezomnotho kanye nokubaluleka kwenhlalo yabantu, kwalesi senzeko ukwesekela izimpilo zabantu. Izivuno seziya ngokwehla esikhathini esiyiminyaka engama-25 edlule esifundeni njengomphumela wokwenyuka njalo kwezimo zezulu ezimanzonzo. Ukubuyekezwa kwemibhalo kuveze ukuthi ukwenyuka nokuhleleka kokwehla kwemvula, i-CC izokhuphula ukungabi namandla komoba, okuya engcindezini yamanzi futhi kuzoba nomthelela omubi kakhulu ezivunweni. Yize noma kunjalo, amagebe olwazi asekhona mayelana nemithelela yokuguquka kwesimo sezulu emisukeni yamanzi kanye nezivuno zomoba. Okunye futhi, imibhalo embalwa ikubukile ukungabi namandla kanye nokukwazi ukuhambisana nomkhiqizo womoba ngokwanele ezindaweni ezahlukene. Ukubhekana nalezi zikhala zolwazi, ukubuyekezwa kokuqala kwenziwa ukuqonda ubukhephukhephu phakathi kokuguquka kwesimo sezulu kanye nemisuka yamanzi kuzo zonke izindawo ezisemazansi ne-Afrika. Ukubuyekeza kwaveza ukuthi yize noma izimo ezihola inhlanganisela yomhlaba wonke zihlobene, imisuka yamanzi yabo inomthelela omkhulu, ngokuhambisana okungaqondile futhi okuyingxenye futhi okwesikhashana ukuzwelana nesimo. Emva kokuhlanganisa ukuqonda okwejwayelekile ngemithelela yokuguquka kwesimo sezulu emazansi ne-Afrika, izimo eziyimbangela eziningi ezithinteka ekukhiqizweni komoba zahlaziywa ngokusebenzisa ukuhlaziya kwesibalomvama. Le ndlela ivumela ukukhomba izimbangela ezihlobene futhi ezinesigqi emithonjeni elawula ngamanzi yaseMngeni, eMlaas, kanye naseMvoti eNingizimu Afrika, umthombo olawula amanzi wase-Ubombo eSwatini, umthombo olawula amanzi waseShire eMalawi kanye nomthombo olawula amanzi waseKilombero eTanzania. Ukuhlaziya kwezibalomvama kwanikeza izincazelo zezinombolo nemithelela yomsuka wamanzi wokukhiqiza umoba kuzo zonke izindawo ezisemazansi ne-Afrika. Ukusebenzisa ubudlelwane phakathi kwezivuno zomoba ezabukwa kanye nobuphansi besikhathi esizayo, iphakathi nendawo, kanye nokuphakama kwezihlandla zomkhiqizo, lolu cwaningo luqambe izihlawumbiselo zokusetshenziswa kwamanzi emobeni ngesikhathi eziningi zokukhula kwawo. Imiphumela iveze ukuthi izimbangela eziyizo zibamba iqhaza elikhulu kakhulu ekwandiseni umkhiqizo womoba emthonjeni wokusebenzisa amanzi ngamunye. Ukuthatha kulokhu kuhlaziya, indlela yokuhlola eveza ukwehla yaqanjwa ngenxa yokuhlaziya kwesikhala somphumela ngokusebenzisa isifanekiso sokukhula kwesivuno i-AquaCrop. Imiphumela yasetshenziswa ukuqamba izincomo zokulwisana nokwehla kwemiphumela ngokunikeza izindlela zokuqapha umkhakha womoba uma kubukwa izimo zesimo sezulu ezimanzonzo. Imiphumela yokufanisa iveze ukuthi umgudu wemiphumela ungahlotshaniswa nezindlela zokwenganyelwa kwesivuno okukhona njengokuphikisana nezindlela ezihambelana nokuguquka kwesimo sezulu esinamanzi, ukubaluleka kokukhomba ukungabi namandla kanye nokukwazi ukumelana nesimo emkhiqizweni womoba kwavezwa obala kulolu cwaningo. Kwaphethwa ngokuthi abatshali bomoba kumele bahlangabezane nemithelela yezigameko zokuguquka kwezimo zezulu ezimanzonzo, kumele babuke ukuthi bangaguqula izindlela zokwenganyelwa kwesivuno futhi bazimisele ukuzibandakanya ocwaningweni oluhlobene. Lolu cwaningo luveze ukubaluleka kokubhekana nokuxhumana phakathi kwezinto ezenziwayo eziqhuba uguquko lokusebenzisa umhlaba, ezifana nomkhiqizo womoba, kanye nemithelela yamanje yokuguquka kwesimo sezulu ephakeme emisukweni yamanzi. Lokhu kubalulekile ezifundeni ezithuthuka ngesivinini ezivama emazansi ne-Afrika. Ukuthuthuka kwemibono emisha yezinqubomgomo zokulwisana nesimo ezizoqapha imisuka yamanzi esivele icindezelekile futhi zigcine ukuqinisekisa ukulondolozeka komkhiqizo womoba, kuzoba into ebaluleke kakhulu ngaphansi kwesimo sezulu esesiguqukile.
Physiological responses of a South African high-latitude coral community to global warming.
(2021) Hanekom, Tanja.; Porter, Sean Nixon.; Sshleyer, Michael Henry.
The health of the world’s coral reefs is deteriorating rapidly due to global climate change and increasing localised anthropogenic stressors. The substantial benefits resulting from coral reef ecosystems, economically and ecologically, requires that research be conducted on their responses to rising sea temperatures driven by climate change. Millions of people depend on the natural resources that coral reefs provide, whether for food or eco-tourism, trade and other indirect sources of income. Although South African coral reef communities lie within a long-established marine protected area, the iSimangaliso Wetland Park World Heritage Site, this status does not preclude them from being affected by the potential effects of global warming. Therefore, the objective of this study was to quantify several physiological parameters, including net community calcification (total alkalinity), growth (dimension and weight) and photosynthetic efficiency in the hard coral Acropora appressa, the soft coral Sinularia brassica and ‘live rock’ under local historical-average (24.4°C), future (26.9°C) and bleaching-threshold (28.8°C) temperatures indicative of climate change conditions projected at Sodwana Bay. Corals and live rock were exposed to the three different temperature treatments during a 10-week long mesocosm experiment that consisted of three phases: the initial phase during which temperatures were increased from 24.4°C over four weeks to reach setpoints of 26.9°C (future) and 28.8°C (bleaching threshold), respectively; the middle phase during which temperatures were held stable at each treatment’s setpoint for the proceeding four weeks; and the final phase during which a further 1°C increase was done over two weeks in the bleaching-threshold treatment to simulate an extreme warming scenario. An initial increase in size was evident in both coral species exposed to the historical-average control temperature and the future temperature projected for Sodwana Bay in 2100 by the representative concentration pathway (RCP) 4.5 climate change scenario. Although the growth trends of both species persisted in the control treatment, the overall linear growth of A. appressa was lower under the RCP 4.5 climate change temperature scenario and bleaching-threshold temperature relative to the control temperature. While no significant treatment effects were found, a decrease in the linear extension of A. appressa was evident at the end of the experiment at the bleaching-threshold temperature relative to the control temperature. Continuous growth trends were evident in the control and RCP 4.5 climate change scenario for S. brassica, however a reduction in diameter after 5 weeks was apparent in the bleaching-threshold treatment. A gradual increase in buoyant weight of A. appressa was evident across all treatments and experimental phases, with a slower growth rate only apparent towards the end of the experiment in the bleaching-threshold treatment. The buoyant weight of S. brassica decreased up until the start of the middle phase in the control treatment and RCP 4.5 treatment. However, an increasing trend in the weight of S. brassica was measured in the same two treatments from the end of the middle phase until the experiment concluded. Contrastingly, the weight of S. brassica in the bleaching-threshold treatment continued to decrease throughout the course of the experiment. Pulse-amplitude modulated fluorometry measurements of the photosynthetic efficiency of both A. appressa and S. brassica were lower under the temperature conditions projected by the RCP 4.5 scenario and by the bleaching-threshold temperature, relative to the historical-average control temperature. Contrastingly, live rock showed no significant differences in photosynthetic efficiency among the different temperature treatments. On average, total alkalinity levels were higher under future temperature conditions projected by the RCP 4.5 temperature scenario and by the bleaching-threshold temperature, relative to the control temperature, indicating suppressed net community calcification. Suppressed net community calcification was particularly evident during (week 6) and at the end (week 8) of the middle phase of the experiment. The experiment revealed that exposure to temperatures equivalent to those projected by the RCP 4.5 climate change scenario in 2100 and the local bleaching threshold are likely to be deleterious to high-latitude corals and coral reef communities in South Africa: buoyant weight and dimension, as well as photosynthetic efficiency were negatively affected in both species of coral and net community calcification was supressed under the two future climate scenarios of warming. Due to the location of Sodwana Bay reefs, the results indicate that calcification processes will be an essential physiological response to consider under global warming conditions. However, as high-latitude reef areas generally fared better during recent bleaching conditions, these reefs can be utilised to improve climate-change projection models. Such model improvements can guide climate policymakers in enhanced conservation efforts that will further stakeholder engagement and outreach. Accordingly, urgent action is needed to reduce greenhouse gas emissions to minimise the effects of global warming on coral reef communities as much as possible. Such efforts will further help to attain the 2°C Paris Climate Agreement and improve socioeconomic development for the management of reefs.
Polyhydroxyalkanoate production by Bacillus thuringiensis: an aspect of biorefining pulp and paper mill sludge.
(2021) Singh, Sarisha.; Govinden, Roshini.; Sithole, Bishop Bruce.; Lekha, Prabashni.; Permaul, Kugenthiren.
The substantial success of plastic as a material is owed to its unparalleled designs with unique properties and proved versatility in an extensive range of applications. Unfortunately, the reliance on single-use plastic commodities consequently results in the incorrect disposal and accumulation of this waste at staggering rates in our environment and landfill sites. In this regard, there is a vested interest in replacing petrochemical plastics with natural, biodegradable plastics (bioplastics). Of the many natural polymers available, microbially synthesized polyhydroxyalkanoates (PHAs) have gained popularity. Eco-friendly PHA-based bioplastics are characteristically as robust and as durable as their oil-based equivalents. Pulp and paper mill sludge (PPMS) is another solid waste stream that is predominantly disposed of via landfilling. The environmentally hazardous gases and leachate emitted from PPMS together with limited landfill space availability and the implementation of strict waste management legislation may not make landfilling practicable in the future. However, this carbohydrate-rich biomass has favorable traits that make it applicable as a feedstock for microbial biomass and PHA production. Hence, in the interest of addressing the issues mentioned above, this study aimed to beneficiate PPMS into PHAs by applying it as the sole feedstock for microbial cell proliferation and subsequent PHA production. Presently, to the best of the author’s knowledge, there are no reports on PHA production as a route for valorization of PPMS from South African pulp and paper mills. Thus, the novelty of the present study is marked by the unique ways of incorporating PPMS as a low-cost substrate as well as the various fermentative strategies navigated to enhance both microbial cell biomass and PHA productivity. In the present study, it was established that Bacillus thuringiensis had promising PHA-producing capability. The strain synthesized a copolymer and terpolymer using untreated (raw) neutral semi-sulphite chemical pulping and cardboard recycling mill (NSSC-CR) and prehydrolysis kraft and kraft pulping mill (PHKK) PPMS in a consolidated bioprocessing fermentation. A separate hydrolysis and fermentation strategy was pursued whereby a glucose-rich hydrolyzate was obtained from enzymolysis of PPMS and subsequently utilized in a cyclic fed-batch fermentation (CFBF) strategy to obtained enhanced yields of cell biomass and PHAs. Response surface methodology (RSM) was first implemented to optimize the conditions for enzymatic saccharification of de-ashed PHKK PPMS. The optimized variables were; pH 4.89; 51°C; hydrolysis time 22.9 h; 30 U/g β-glucosidase and 60 U/g cellulase; and 6.4% of dried de-ashed PPMS fiber resulting in a hydrolyzate comprising of 48.27% glucose. Thereafter, CFBF was pursued where the glucose-rich hydrolyzate was employed as the sole carbon source for cell proliferation and PHA production. The statistically optimized fermentation conditions to obtain high cell density biomass (OD600 of 2.42) were; 8.77 g L-1 yeast extract; 66.63% hydrolyzate (v/v); a fermentation pH of 7.18; and an incubation time of 27.22 h. The CFBF comprised of three cycles and after the third cyclic event, maximum cell biomass (20.99 g L-1) and PHA concentration (14.28 g L-1) were achieved. This cyclic strategy yielded an almost 3-fold increase in biomass concentration and a 4-fold increase in PHA concentration compared with batch fermentation. The properties of the synthesized PHAs were similar to commercial polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV) and also displayed slightly higher thermostability and lower crystallinity compared with commercial PHB and PHBV. This is the first report detailing the proof of concept of using PPMS from South African pulp and paper making mills for cell biomass and PHA production by B. thuringiensis. In addition, this study reports on the practicality and novelty of utilizing PPMS either in its raw, untreated state or as enzymatically saccharified glucose-rich hydrolyzate as cheap substrates applicable for both cell biomass and PHA production using different fermentation strategies. Finally, to the best of our knowledge, this is also the first report that has successfully applied B. thuringiensis in a CFBF strategy coupled with glucose-rich hydrolyzate as the sole carbon source for the production of high cell density biomass and enhanced PHA production. From this study, it is intended that innovative insights and prospective solutions to valorizing pulp and paper mill sludge are provided, whilst simultaneously generating a value-added product.

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