Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Storing soil organic carbon (SOC) is a possible way of reducing atmospheric
CO2 and potentially mitigating the effects of global warming. This study looks
at soil carbon stocks, the sampling methodology and modelling of soil organic
carbon in indigenous forests, wetlands, grasslands and pine plantations in
Woodbush in the North-Eastern escarpment of Limpopo Province, South
Africa. Dominant Pine species planted in Woodbush are Pinus patula, Pinus
elliotti and Pinus taeda. Woodbush plantation was selected as study area
because it provided easy access to all the ecosystems that were to be
studied. All ecosystems in Woodbush are located in such a way that it was
easy to compare them, as they existed under similar environmental and
climatic conditions. The climatic conditions of Woodbush promote
accumulation of SOC due to relatively higher precipitation and cooler
temperatures than most parts of Limpopo Province.
Five transects were made: two in indigenous forests and three in plantations.
Only the surface (0-7 cm) layer was sampled with a distance of 20 m between
sampling points. Transects were not made in grasslands and wetlands
because of the patchy occurrence of these ecosystems. In addition to
transects, eight 1ha plots, two in each ecosystem, were sampled. Surface (0-
7 cm depth) samples were collected on a grid of 20 x 20 m in each sampling
plot. Two soil profile pits were sampled in each sampling plot, with samples
being taken at 5, 10, 15, 20 30, 40, 50 60, 75 and 100 cm depth.
The average carbon stocks per hectare of land to a soil depth of 100 cm were
as follows: 71 t.ha-1 in wetlands, 28 t.ha-1 in grasslands, 64 t.ha-1in indigenous forests, and 46 t.ha-1 in pine plantations. Although wetlands sequestered large
amounts of SOC per hectare, their relative contribution to carbon
sequestration was low because of the relatively small area (87.2 ha) they
occupy in the study area (and in South Africa).
Prediction models for vertical distribution of SOC were developed using
STATISTICA 6.0 for each ecosystem in order to estimate the carbon stocks to
a depth of 100 cm based on SOC content and soil bulk density of the surface
samples. These models were developed from observed values in soil profiles
for each ecosystem.
SOC content and carbon stocks were analyzed using GIS (ARCVIEW). The
GIS analysis was aimed at assessing the effect of topography, elevation, soil
type, and vegetation on accumulation and distribution of SOC stocks. Most
shallow Inanda soils were distributed at elevations between 1545 m and
1777 m, and on a gentle slope in the Northern aspect of the mountain. Deep
Inanda soils were found mostly in the lower elevation range of 967 m and
1545 m on moderate slopes. Deep and shallow Inanda soils were found on
the southern aspect.
Deep Kranskop soils are evenly distributed and mostly found at an elevation
range of between 1080 and 1430 m on gentle slopes, while at an elevation
range of between 1430 and 1780 m, they were found on moderate slopes.
Deep soils had higher SOC stocks than shallow soils and soils in the southern
aspects had higher SOC stocks than in the northern aspects. / AFRIKAANSE OPSOMMING: Die berging van grond organiese koolstof is ‘n moontlike manier om
atmosferiese koolsuurgas (CO2) te verminder en dus om die invloed van
globale verwarming te versag. In hierdie studie was die grond-koolstof
voorraad bestudeer, asook die metodologie van die monsterneming en
modellering van organiese grond-koolstof van inheemse woude, vleie,
grasvelde en denneplantasies. Die studie was uitgevoer op Woodbush
plantasie gele op die Noord-Oosterlike platorand van die Limpopo Provinsie,
Suid-Afrika. Die algemeenste dennespesies in Woodbush is Pinus patula,
Pinus elliotti en Pinus taeda. Die Woodbush plantasie was gekies as
studiegebied omdat dit oor al die ekosisteme wat bestudeer moet word,
beskik. Die ekosisteme in Woodbush is naby mekaar en dus maklik
vergelykbaar want die omgewings- en klimaatstoestande is eenders. Die
klimaatstoestande van Woodbush bevorder die akkumulasie van grond
organiese koolstof omdat die reënval hoër en die temperature laer is as in die
meeste ander dele van die Limpopo Provinsie.
Vyf dwarssnitte was gemaak, twee in inheemse woude en drie in plantasies.
Monsters was net uit die grondoppervlak laag geneem (7 cm) met 20 m
tussen monsterpunte. Dwarssnitte was nie in grasvelde en vleie gemaak nie
want hierdie sisteme is te gelokaliseerd. Monsters was ook geneem in agt 1
ha persele, twee in elke ekosisteem. Oppervlakmonsters (tot ‘n diepte van
7 cm) is op ‘n ruitnet van 20 x 20 m uit elke perseel versamel. Monsters was
verder ook geneem uit twee profielgate per perseel, op dieptes 5, 10, 15, 20,
30, 40, 50, 60, 75 en 100 cm. Die gemiddelde koolstof voorraad per hektaar, op ‘n gronddiepte van 100 cm,
was as volg: 71 t.ha –1 in vleie, 28 t.ha-1 in grasvelde, 64 t.ha-1 in inheemse
woude en 46 t.ha-1 in denneplantasies. Alhoewel vleie groot hoeveelhede
grond organiese koolstof akkumuleer, is hulle bydrae tot koolstof akkumulasie
laag want hulle beslaan ‘n klein oppervlak binne die studiegebied (87.2 ha)
asook klein oppervlaktes binne Suid-Afrika.
Voorspellingsmodelle vir die vertikale verspreiding van grondkoolstof was met
die gebruik van STATISTICA 6.0 ontwikkel ten einde te skat wat die
koolstofvoorrraad op ‘n diepte van 100 cm was. Die skattings was gebaseer
op organiese grondkoolstofinhoud en die gronddigtheid van
oppervlakmonsters. Hierdie modelle was ontwikkel vanaf die waargenome
waardes van grondprofiele vir elke ekosisteem.
Die organiese koolstofinhoud van die grond en die koolstofvoorraad is ontleed
met behulp van GIS (ARCVIEW). Die GIS ontleding was daarop gemik om die
effek van topografie, hoogte bo seespiëel, grondtipe en plantegroei, op die
akkumulasie en verspreiding van organiese grondkoolstof, te beraam. Die
meeste vlak Inanda grondvorms kom voor tussen 1545 m en 1777 m bo
seespiëel, asook op effens steil hellings op die Noordelike berghang. Die
diep Inanda grondvorms is geleë op laer hoogtes bo seespiëel, gewoonlik
tussen 967 en 1545 m, op effens steil hellings. Beide diep en vlak Inanda
gronde word gevind op die suidelike berghang.
Diep Kranskop gronde is eweredig versprei en word gewoonlik tussen 1080
en 1430 m bo seespiëel, op effens steil hellings, gevind. Dit kom ook voor op
matig steil hellings, tussen 1430 en 1780 m bo seespiëel. Daar is meer organiese koolstof in diep grond as in vlak grond en meer in gronde teen die
suidelike hang as op die noordelike hang.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16392 |
| Date | 12 1900 |
| Creators | Mongwe, Hlamalani Godfrey |
| Contributors | Rozanov, A., Fey, M. V., University of Stellenbosch. Faculty of Agrisciences. Dept. of Soil Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xv, 163 leaves : ill. |
| Rights | University of Stellenbosch |
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