Structural and functional attributes of Heuweltjies in the fynbos and succulent Karoo biomes: the interaction of termites, vegetation and geochemistry

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dc.contributor.advisorJacobs, Shayne Martinen_ZA
dc.contributor.advisorMiller, Jodie A.en_ZA
dc.contributor.advisorFrancis, Michele Louiseen_ZA
dc.contributor.advisorClarke, Catherine E.en_ZA
dc.contributor.advisorCrous, Casparus J.en_ZA
dc.contributor.authorVermonti, Nicolaen_ZA
dc.contributor.otherStellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.en_ZA
dc.date.accessioned2022-03-09T08:11:29Z
dc.date.accessioned2022-04-29T09:32:17Z
dc.date.available2022-03-09T08:11:29Z
dc.date.available2022-04-29T09:32:17Z
dc.date.issued2022-04
dc.descriptionThesis (MScConsEcol)--Stellenbosch University, 2022.en_ZA
dc.description.abstractENGLISH ABSTRACT: The structural and functional attributes of heuweltjies in the Fynbos and Succulent Karoo biomes were studied with the aim of investigating the interaction amongst vegetation, termites, and geochemistry on heuweltjies found across the West Coast of South Africa. This study takes a multi-disciplinary approach to determine possible sources of salinity in the biotic community, that can be considered inputs into heuweltjie mound soils. Heuweltjie vegetation communities were found to host different plant species that were structured differently and consisted of different plant functional types. These differences occurred between heuweltjies found in the Fynbos and Succulent Karoo, and among the centre, slope, and off areas of the heuweltjie mound. Anthropogenic disturbance such as grazing was also found to bring about changes in the structure of the vegetation communities. A subsample of the most common plant species growing in these communities were found to host variable concentrations of plant tissue ions, with sodium, magnesium, and potassium as the major ions found in higher concentrations, in the species growing on the mounds. These plants are suspected to have an important role in maintaining, but not causing the higher ion concentrations which are seen in central heuweltjie soils, as these plants could take up ions through their roots into their tissues and return them when abscission or senescence occurs. This creates a feedback loop with the soil environment. Where soils are saline, halophytic plants would be expected to form part of this cycle. Two external sources of salt were identified as viable contributors to the accumulation of salts that are associated with heuweltjie mounds. Aerosols deposited on the outer surfaces of the plants were identified to have a marine source of sodium, magnesium, and sulphate. Calcium deposits were enriched compared with seawater ion ratios. The foraging activities of Microhodotermes viator and foraging rodents were the second external source investigated to assess their impact on heuweltjie soils, using stable δ13C and δ15N isotope analysis. An evaluation was made of the plants that most likely were targeted by termites and rodents, using observations and δ13C. It appeared that termites collect live plant material nearby to their foraging holes, with the exception of any succulent plant species in the Fynbos, or stem and leaf succulents in the Succulent Karoo. This study shows that calcium oxalate crystals (whewellite CaC2O4·H2O) are present in plant tissues on centre mound soils as well as in the plant material collected by termites and rodents while weddellite (Ca(C2O4)·2H2O) was present but only in the centre mound plants of the Fynbos. This suggests that the heuweltjies may be suitable environments for the oxalate-carbonate pathway to take place, in which decomposition of calcium oxalate in plant material leads to the precipitation of calcite in the surrounding soil and provides a possible explanation for the calcite enrichment common in heuweltjie centres. Plant material was also found to be a source of pentahydrite (MgSO4.5H20), halite (NaCl), sylvite (KCl) and sodium oxalate (Na2C2O4). The impact that M. viator has on salt dynamics of heuweltjie centre mound soils was assessed in more detail. Ion input estimations due to M. viator foraging, were made using plant material input rates of 0.08 g per minute per foraging hole, on one heuweltjie. If foraging occurred for an hour every day, the ions with the highest estimated inputs per year were found to be calcium with 18 g (Fynbos) and 42 g (S. Karoo), and sodium 4 g (Fynbos) and 45 g (S. Karoo). Considering the estimated age of heuweltjies (4000 to 30 000 years old), total calcium inputs could range from 74 kg to 522 kg in the heuweltjies at the Fynbos site, and the Succulent Karoo estimates could be between 166 kg to 1 ton, for just one foraging hole. These estimates could be at five times more per heuweltjie when considering the number of possible foraging holes, the termites use. Concentrations of calcium in the plant washes were found in levels four to twenty times higher than what Midgely et at. (2012) had previously been suggested would be needed to form the calcite layer, exclusively from sources of precipitation. Considering the contributions from the plant material along with the external deposits a calcrete layer of 0.25m wide could viably be formed in less than 3600 years. This study found, quantified, and presented evidence, that the foraging action of termites and deposition of marine aerosols, are both considerable inputs into the salt dynamics of heuweltjie centre mound soils.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.en_ZA
dc.description.versionMastersen_ZA
dc.format.extentxii, 195 pages : illustrations (some color)en_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/124782
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectHeuweltjies -- South Africa -- Karooen_ZA
dc.subjectTermitesen_ZA
dc.subjectSalten_ZA
dc.subjectCalciteen_ZA
dc.subjectVegetation communitiesen_ZA
dc.subjectFynbos -- South Africa -- Karooen_ZA
dc.subjectSucculent Karooen_ZA
dc.subjectPlants -- Effect of minerals onen_ZA
dc.subjectPlants -- Effect of salt onen_ZA
dc.subjectPlants -- Effect of calcium onen_ZA
dc.subjectUCTDen_ZA
dc.titleStructural and functional attributes of Heuweltjies in the fynbos and succulent Karoo biomes: the interaction of termites, vegetation and geochemistryen_ZA
dc.typeThesisen_ZA
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