Determining fPAR and leaf area index of several land cover classes in the Pot River and Tsitsa River catchments of the Eastern Cape, South Africa

Determining the quantum (both annual maxima and minima) and the temporal variation in the leaf area index (LAI), and the fraction of photosynthetically active radiation (fPAR), are three fundamental biophysical characteristics of the plant canopy that should parameterise ecophysiological models of water use (evapotranspiration) and carbon sequestration. Although Earth observation provides values and time series for both these parameters, in-field validation of these values is necessary. Following a very wet summer season, we conducted field surveys of several land cover classes within two quaternary catchments in the Eastern Cape province, South Africa, to determine maximum values of LAI and fPAR that occur within each of these land cover classes. To assist in up-scaling these point measures to the landscape, we present a regression relationship between Landsat 8 NDVI and LAI measured using an Accupar Ceptometer (r2 = 0.92). Peak wet season LAI varied from extremely high (>7.0) under the canopy of invasive black wattle (Acacia mearnsii) trees to ~2.0 under the canopy of a Eucalyptus plantation. Ungrazed native grassland displayed an intermediate LAI value of 3.84. The black wattle stand absorbed 97% of the available PAR, whereas the mature Eucalyptus plantation only absorbed 66% of PAR.Keywords: agroforestry, ecosystem ecology, remote sensin

Exploring the invasion of rangelands by Acacia mearnsii (black wattle): biophysical characteristics and management implications

Australian acacias have spread to many parts of the world. In South Africa, species such as A. mearnsii and A. dealbata are invasive. Consequently, more effort has focused on their clearing. In a context of increasing clearing costs, it is crucial to develop innovative ways of managing invasions. Our aim was to understand the biophysical properties of A. mearnsii in grasslands as they relate to grass production and to explore management implications. Aboveground biomass (AGB) of A. mearnsii was determined using a published allometric equation in invaded grasslands of the northern Eastern Cape, South Africa. The relationships among the A. mearnsii leaf area index (LAI), normalised difference vegetation index (NDVI) and AGB were investigated. The influence of A. mearnsii LAI and terrain slope on grass cover was also investigated. Strong linear relationships between NDVI, LAI and AGB were developed. Acacia mearnsii canopy adversely impacted grass production more than terrain slope (p < 0.05) and when LAI approached 2.1, grass cover dropped to below 10% in infested areas. Reducing A. mearnsii canopy could promote grass production while encouraging carbon sequestration. Given the high AGB and clearing costs, it may be prudent to adopt the ‘novel ecosystems’ approach in managing infested landscapes.Keywords: grassland, invasive plants, landscape ecology, rangeland conditio

Geohydrological conceptualization from a remotely sensed simplified water balance in the sandveld, South Africa

CITATION: Munch, Z. & Gibson, L. A. 2012. Geohydrological conceptualization from a remotely sensed simplified water balance in the sandveld, South Africa. IEEE International Geoscience and Remote Sensing Symposium : Remote Sensing for a Dynamic Earth, 22-27 July, Munich, Germany.The original publication is available http://www.igarss2012.org/Papers/PublicSessionIndex3.asp?Sessionid=1149ENGLISH SUMMARY : The Sandveld (Western Cape, South Africa), located on the Cape West Coast, is characterized by low rainfall and minimal river flows, however despite this limitation, significant aquifer systems are found [1]. The groundwater in the region supports extensive agriculture and supplies towns with water for domestic use. The use of remote sensing can influence the way in which groundwater resources can be managed despite the fact that it is a subsurface resource and therefore cannot be directly measured by remote sensing techniques. The G30F catchment in the Northern Sandveld is reported to be experiencing water stress due to increasing abstraction for domestic water supply and agriculture, particularly potato crops. As suggested by Brunner et al [2], we propose the use of the simplified water balance determined from remote sensing data to estimate recharge and discharge zones within the catchment. Furthermore, we propose that this method is a useful aid in the geohydrological conceptualization of this particular water system. Of particular interest is the use of the recently released MOD16 evapotranspiration (ET) data product together with a precipitation data product, highlighting the ease with which studies of this nature can now be executed.Post printInstitute of Electrical and Electronics Engineer

Measuring and modelling evapotranspiration in a South African grassland : comparison of two improved Penman-Monteith formulations

CITATION: Gwate, O., et al. 2018. Measuring and modelling evapotranspiration in a South African grassland : comparison of two improved Penman-Monteith formulations. Water SA, 44(3):482-492, doi:10.4314/wsa.v44i3.16.The original publication is available at http://www.wrc.org.zaAccurately measuring evapotranspiration (ET) is important in the context of global atmospheric changes and for use with climate models. Direct ET measurement is costly to apply widely and local calibration and validation of ET models developed elsewhere improves confidence in ET derived from such models. This study sought to compare the performance of the Penman-Monteith-Leuning (PML) and Penman-Monteith-Palmer (PMP) ET models, over mesic grasslands in two study sites in South Africa. The study used routine meteorological data from a scientific-grade automatic weather station (AWS) to apply the PML and PMP models. The PML model was calibrated at one site and validated in both sites. On the other hand, the PMP model does not require calibration and hence it was validated in both sites. The models were validated using ET derived from a large aperture scintillometer (LAS). The PML model performed well at both sites with root mean square error (RMSE) within 20% of the mean daily observed ET (R2 of 0.83 to 0.91). Routine meteorological data were able to reproduce fluxes calculated using micrometeorological techniques and this increased the confidence in the use of data from sparsely distributed AWSs to derive reasonable ET values. The PML model was better able to simulate observed ET compared to the PMP model, since the former models both transpiration and soil evaporation (ES), while the latter only models transpiration. Hence, the PMP model systematically underestimated ET in a context where the leaf area index (LAI) was < 2.5. Model predictions in the grasslands could be improved by incorporating the ES component in the PMP model while the PML model could be improved by careful choice of the number of days to be used in the determination of the fraction of ES.https://www.watersa.net/article/view/6640Publisher's versio

Drowning in data, thirsty for information and starved for understanding: A biodiversity information hub for cooperative environmental monitoring in South Africa

The world is firmly cemented in a notitian age (Latin: notitia, meaning data) – drowning in data, yet thirsty for information and the synthesis of knowledge into understanding. As concerns over biodiversity declines escalate, the volume, diversity and speed at which new environmental and ecological data are generated has increased exponentially. Data availability primes the research and discovery engine driving biodiversity conservation. South Africa (SA) is poised to become a world leader in biodiversity conservation. However, continent-wide resource limitations hamper the establishment of inclusive technologies and robust platforms and tools for biodiversity informatics. In this perspectives piece, we bring together the opinions of 37 co-authors from 20 different departments, across 10 SA universities, 7 national and provincial conservation research agencies, and various institutes and private conservation, research and management bodies, to develop a way forward for biodiversity informatics in SA. We propose the development of a SA Biodiversity Informatics Hub and describe the essential components necessary for its design, implementation and sustainability. We emphasise the importance of developing a culture of cooperation, collaboration and interoperability among custodians of biodiversity data to establish operational workflows for data synthesis. However, our biggest challenges are misgivings around data sharing and multidisciplinary collaboration

The HIV-1 transmission bottleneck

It is well established that most new systemic infections of HIV-1 can be traced back to one or a limited number of founder viruses. Usually, these founders are more closely related to minor HIV-1 populations in the blood of the presumed donor than to more abundant lineages. This has led to the widely accepted idea that transmission selects for viral characteristics that facilitate crossing the mucosal barrier of the recipient’s genital tract, although the specific selective forces or advantages are not completely defined. However, there are other steps along the way to becoming a founder virus at which selection may occur. These steps include the transition from the donor’s general circulation to the genital tract compartment, survival within the transmission fluid, and establishment of a nascent stable local infection in the recipient’s genital tract. Finally, there is the possibility that important narrowing events may also occur during establishment of systemic infection. This is suggested by the surprising observation that the number of founder viruses detected after transmission in intravenous drug users is also limited. Although some of these steps may be heavily selective, others may result mostly in a stochastic narrowing of the available founder pool. Collectively, they shape the initial infection in each recipient

GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2

We describe the observation of GW170104, a gravitational-wave signal produced by the coalescence of a pair of stellar-mass black holes. The signal was measured on January 4, 2017 at 10∶11:58.6 UTC by the twin advanced detectors of the Laser Interferometer Gravitational-Wave Observatory during their second observing run, with a network signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70 000 years. The inferred component black hole masses are 31. 2 + 8.4 − 6.0 M ⊙ and 19. 4 + 5.3 − 5.9 M ⊙ (at the 90% credible level). The black hole spins are best constrained through measurement of the effective inspiral spin parameter, a mass-weighted combination of the spin components perpendicular to the orbital plane, χ eff = − 0.1 2 + 0.21 − 0.30 . This result implies that spin configurations with both component spins positively aligned with the orbital angular momentum are disfavored. The source luminosity distance is 88 0 + 450 − 390     Mpc corresponding to a redshift of z = 0.1 8 + 0.08 − 0.07 . We constrain the magnitude of modifications to the gravitational-wave dispersion relation and perform null tests of general relativity. Assuming that gravitons are dispersed in vacuum like massive particles, we bound the graviton mass to m g ≤ 7.7 × 10 − 23     eV / c 2 . In all cases, we find that GW170104 is consistent with general relativity

Towards land change management using ecosystem dynamics and land cover change in rural Eastern Cape

Thesis (PhD)--Stellenbosch University, 2019.ENGLISH ABSTRACT: Land cover change, triggered by natural and anthropogenic land use change, affects ecosystem services provided by grasslands. Woody encroachment into the grasslands is a threat to function and productivity of rangelands, and threaten rural livelihoods, intensified by rising CO2 levels associated with climate change. Processes of change can only effectively be identified after spatial land transition has been revealed and patterns of change quantified. Accurately quantifying the rates and extent of land cover change is the first step in relating underlying land use processes and the environmental effects thereof to land cover change trajectories involving grassland transformation. The study aims to demonstrate how land cover change, in particular woody encroachment influences landscape functions provided by grasslands in the Eastern Cape. The study seeks to determine how accurately land cover transformation can be quantified and modelled using existing datasets that may contain map error and raises the question how the error pattern can affect modelling of future evapotranspiration and carbon storage. A further question is how the drivers of change vary between regions under different land tenure, i.e. dualistic or commercial systems. Systematic land cover change analysis and future land change modelling were used to characterise land cover change trajectories and flows in the landscape. Flows were described using (1) an indicator-based approach, and (2) intensity analysis and change budget. Hypothetical map error was determined for observed and modelled land cover maps. Overall change was partitioned into quantity, exchange and shift disagreement and intensity. The change budget was computed both at catchment and local level. Map error was further investigated using a local geographically weighted method. Local geographically weighted correspondence matrices were constructed to determine spatially explicit probabilities of change and error at catchment level and per land cover class. By consulting the overall allocation difference maps, hotspots of change and probable error were identified for further investigation. Trends in remote sensing-derived biophysical variables were analysed to determine how land cover change would affect the surface energy budget and the carbon cycle, as proxies for water use and rangeland productivity. Primary drivers of landscape modification comprised rangeland degradation, woody encroachment, urbanisation, increased dryland cultivation and commercial afforestation, with the latter concentrated in the commercial catchment. Though grassland persistence still dominated land cover in the landscape, catchments under dualistic land tenure experienced steeper declines in the grassland area. Woody encroachment was also found predominantly in these catchments. Overall accuracy for the input land cover maps were reported as >80%, equating to theoretical land cover change accuracy of 67–72%. Landscape change varied between 18% and 42%, with 19% estimated from direct overlay of land cover maps with 30 m resolution pixels. By applying a multi-resolution aggregation technique, the study showed that lower resolution input data would identify less change in the landscape, mainly because the allocation error diminishes at lower resolutions. For higher change accuracies and reliability, the accuracy of input land cover maps would have to be increased. Hypothetical map error in observed land cover change maps were found to be higher in catchments under dualistic tenure for gaining transitions, whereas losing transitions showed higher error in catchments practicing commercial farming. The hypothetical error accounted for almost 50% of the reported change. The modelled land cover change showed higher allocation disagreement, suggesting that the land change model was not very reliable, particularly for the commercial catchment. Analysis of remotely sensed data products such as albedo, net primary production and evapotranspiration, in combination with land cover change data has led to better understanding of the landscape of the catchments. Though grasslands are predicted to decrease in favour of woody invasive plant species and cultivated land, this study predicted a decrease of 12% and 6% respectively in net carbon storage and water use by vegetation. Information from multiple sources, in both quality and type, were integrated to better understand rangeland productivity degradation and to compare the impact of climate versus land management in the different catchments. Quantifying changes in biophysical parameters can assist scientists and managers in addressing global challenges.AFRIKAANSE OPSOMMING: Verandering in grondbedekking wat deur natuurlike en antropogeniese verandering in grondgebruik veroorsaak word, beïnvloed die ekostelseldienste wat deur grasvelde gelewer word. Houtagtige indringing van die grasvelde is ʼn bedreiging vir die funksionering en produktiwiteit van weivelde en bedreig landelike lewensbestaan. Hierdie proses word aangehelp deur die toenemende CO2-vlakke wat met klimaatsverandering verband hou. Prosesse van verandering kan eers effektief geïdentifiseer word nadat ruimtelike landoorgang geopenbaar is en patrone van verandering gekwantifiseer is. Die akkurate kwantifisering van die trajek en omvang van grondbedekkingsverandering is die eerste stap om die onderliggende prosesse vir grondgebruik en die omgewingseffekte daarvan aan grondbedekkingstrajeksies te koppel. Laasgenoemde hou direkte verband met die transformasie van grasveld. Hierdie studie het ten doel om te demonstreer hoe grondbedekkingsverandering, veral deur houtagtige indringerplante, die landskapfunksies wat grasvelde in die Oos-Kaap verrig beïnvloed. Die studie poog om te bepaal hoe akkuraat die transformasie van grondbedekking met bestaande datastelle, wat kaartfoute bevat, gekwantifiseer en gemodeller kan word. Daar is onsekerheid oor hoe die foutpatrone in die datastelle die modellering van toekomstige evapotranspirasie en koolstofopberging kan beïnvloed. 'n Verdere navorsingsvraag is hoe die drywers van verandering tussen streke onder verskillende grondbesit, te wete dualistiese of kommersiële stelsels, wissel. Sistematiese ontleding van grondbedekking en toekomstige modellering is gebruik om die trajek en vloei van grondverandering in die landskap te beskryf. Vloei is beskryf met behulp van (1) 'n aanwyser-gebaseerde benadering, en (2) intensiteitsanalise en veranderingsbegroting. Hipotetiese kaartfoute is vir waargenome en gemodelleerde grondbedekkingskaarte bepaal. Algehele verandering is in kwantiteit, wissel en verskuiwingsverskille en intensiteit opgedeel. Die veranderingsbegroting is per opvanggebied sowel as op plaaslike vlak bereken. Kaartfoute is verder met behulp van 'n plaaslike geografies-geweegde metode ondersoek. Plaaslike geografies-geweegde korrespondensie-matrikse is opgestel om ruimtelik-sensitiewe waarskynlikhede vir veranderinge en foute per opvanggebied en grondbedekkingklas te bepaal. Die totale toekenningsverskilkaarte is geraadpleeg om brandpunte van verandering en waarskynlike foute vir verdere ondersoek te identifiseer. Die tendense in biofisiese veranderlikes wat vanaf afstandswaarneming afgely is, is ontleed om te bepaal hoe verandering in grondbedekking die oppervlakte-energiebegroting en die koolstofsiklus, wat watergebruik en graslandproduktiwiteit verteenwoordig, sou beïnvloed. Die resultate het getoon dat weiveldagteruitgang, houtagtige indringing, verstedeliking, verhoogde droëlandverbouing en kommersiële bosbou, met laasgenoemde gekonsentreer in die kommersiële opvanggebied, die primêre drywers van grondbedekkingsverandering was. Alhoewel grasland grondbedekking die landskap steeds oorheers, het dit in opvanggebiede onder dualistiese grondbesit afgeneem. Houtagtige indringing is hoofsaaklik in hierdie opvanggebiede opgemerk. Die algehele akkuraatheid van die inset grondbedekkingskaarte is as >80% gerapporteer, wat teoreties in die konteks van grondbedekkingverandering aan 67-72% gelykstaande is. Landskapverandering het tussen 18% en 42% gewissel, met 19% wat op direkte oorleg van 30 m resolusie grondbedekkingskaarte geraam is. 'n Multi-resolusie-samevoegingstegniek het getoon dat laer resolusie-insetdata minder verandering in die landskap identifiseer, hoofsaaklik omdat die toewysingsfout by laer resolusies verminder. Die akkuraatheid van grondbedekkingskaarte sal verhoog moet word om die akkuraatheid en betroubaarheid van veranderinge te verbeter. Daar is bevind dat hipotetiese kaartfoute in waargenome grondebedekkingsveranderingskaarte hoër was in opvanggebiede onder dualistiese bestuur vir grondbedekkingsklasse wat toegeneem het, terwyl in die kommersiële opgevanggebied groter foute in grondbedekkingsklasse met afnemende oorgange opgetel is. Die hipotetiese fout was verantwoordelik vir byna 50% van die gemelde verandering. Die gemodelleerde gronddekkingverandering het 'n groter toewysigingsverskil getoon, wat daarop dui dat die grondbedekkingsveranderingsmodel nie baie betroubaar was nie, veral nie vir die kommersiële opvanggebied nie. Analise van afstandswaarnemingsdataprodukte soos albedo, netto primêre produksie en evapotranspirasie, in kombinasie met grondbedekkingsveranderingsdata, het gelei tot 'n beter begrip van die landskap in die opvanggebiede. Alhoewel die voorspelling is dat grasvelde ten gunste van houtagtige indringerplantspesies en bewerkte lande sal afneem, het hierdie studie slegs 'n afname van onderskeidelik 12% en 6% in die netto koolstofopberging en watergebruik deur plantegroei voorspel. Inligting uit verskeie bronne, beide in kwaliteit en tipe, is geïntegreer om die agteruitgang van die landskapproduktiwiteit beter te verstaan en om die impak van klimaat op grondbestuur in die verskillende opvanggebiede te vergelyk. Die kwantifisering van veranderinge in biofisiese parameters kan wetenskaplikes en bestuurders help om wêreldwye uitdagings die hoof te bied.Doctora

Assessment of GIS-interpolation techniques for groundwater evaluation : a case study of the Sandveld, Western Cape, South Africa

Thesis (MSc)--University of Stellenbosch, 2004ENGLISH ABSTRACT: The Sandveld, a potato growing area of the Western Cape is subject to significant groundwater abstraction for both municipal and agriculture purposes. The climate is arid and sensitive and important ecosystems in the area are showing varying degrees of impact. Management measures are needed to ensure ongoing sustainable development of the area. In this study, different interpolation techniques were evaluated to calculate values for unsampled variables rainfall and groundwater elevation. Local deterministic techniques as well as geostatistical techniques were used. It was found that geostatistical techniques, especially with collateral information, such as topography, provided a more accurate result. For environmental studies of this nature, Kriging is recommended as interpolation technique. The underlying data will determine the selection of the particular type of Kriging. Data was extracted from a customized relational database, geoMon, used for data capture, retrieval, processing and reporting. Ease of data extraction facilitated analysis. The interpolated grids were applied in two scenarios: Recharge calculations and quantification as well as a new classification approach according to Resource Directed Measures (RDM). Management classes were defined based on GIS-derived data.AFRIKAANSE OPSOMMING: Die Sandveld, ‘n aartappelverbouingsgebied in die Wes-Kaap, ondergaan aansienlike grondwateronttrekking vir beide munisipale sowel as landbou doeleindes. Die klimaat is dor en droog en sensitiewe en belangrike ekosisteme in die area ondervind wisselende impakvlakke. Bestuursmaatreëls word benodig om volhoubare ontwikkeling van die area te verseker. In hierdie studie is verskillende interpolasie tegnieke om onbekende waardes vir veranderlikes gebruik in grondwater evaluasie te bereken, evalueer. Lokale deterministiese tegnieke sowel as geostatistiese tegnieke is gebruik. Geostatistiese tegnieke, veral gebruik saam met addisionele inligting soos topografie, bereken meer akkurate resultate. Vir omgewingsstudies van hierdie aard, word Kriging aanbeveel as interpolasie tegniek. Eienskappe van die onderliggende data word gebruik om die tipe Kriging aan te dui. Data is onttrek uit ‘n gebruikersaangepaste databasis, geoMon, wat gebruik is vir datavaslegging, onttrekking, prosessering en verslaggewing. Die gemak waarmee data onttrek kon word het analise vergemaklik. Geïnterpoleerde data is gebruik vir grondwateraanvullingsberekeninge en -kwantifisering sowel as ‘n nuwe benadering tot klassifikasie volgens hulpbron gerigte maatreëls. Bestuursklasse gebaseer op GIS-afgeleide data, is gedefinieer