Vegetation-induced, subsurface precipitation of carbonate as an aggradational process in the permanent swamps of the Okavango (delta) fan, Botswana

McCarthy, T. S.; Ellery, W.N.; Ellery, Karen

doi:10.1016/0009-2541(93)90105-r

Cited by 100 publications

(70 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As the trees transpire they leave dissolved solutes behind resulting in salinity increase in the groundwater. As a result of this, salt accumulations occur underneath islands and minimize surface water salinity (McCarthy et al 1994). Similar processes are beginning to be identified in other sub-tropical major wetlands, such as the Everglades (e.g., Wetzel et al 2005, Sullivan et al 2010.…”

Section: Introductionmentioning

confidence: 85%

“…Ecosystem services performed by riparian tree species include primary production which produces food, nutrient cycling (Murkin 1998) and water purification through the process of evapotranspiration (McCarthy et al 1994). Riparian tree species hold the soil together through their roots which helps to reduce erosion due to floods (Carter 1996).…”

Section: Introductionmentioning

confidence: 99%

“…Riparian habitats serve as corridors and connecting elements which help to maintain regional diversity (Naiman et al 1993). In the Okavango Delta, though, riparian tree habitats are frequently fragmented by floodplains and channels (McCarthy et al 1994, Gumbricht et al 2004). Although they do not form continuous corridors, they are also significant in maintaining local diversity.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Spatial variation of population size structure of selected riparian tree species in the Okavango Delta, Botswana

Tsheboeng¹,

Murray-Hudson²

2013

Biodivers. Ecol.

View full text Add to dashboard Cite

Abstract:Transpiration by riparian trees in the Okavango Delta (Botswana) creates a salinity gradient which facilitates continuous water movement from the swamps to the islands. This leads to salt accumulations underneath islands which minimizes surface water salinity. The aim of this study was to investigate spatial variation in population size structure of riparian tree species in the Delta. It was hypothesized that riparian tree population structure will vary spatially due to different hydrological conditions. Riparian vegetation was surveyed in Boro, Santawani, Moremi, Vumbura and Seronga from a total of 75 plots measuring 20m x 50m. Species chosen for this study in terms of their dominance were Croton megalobotrys Müll. Arg, Philenoptera violacea (Klotzsch) Schrire, Diospyros mespiliformis Hochst. Ex A.DC and Acacia nigrescens Oliv. Diameter at breast height (dbh) was measured for tree individuals with stem diameter >2.5cm. Linear regression analysis was used to infer population size class distribution of each species. Croton megalobotrys Müll. Arg showed a reverse J size class distribution (SCD) pattern in Boro, Santawani and Vumbura while it showed a bell shaped pattern in Moremi. Philenoptera violacea (Klotzsch) Schrire showed an irregular size class distribution pattern with some missing size classes in Boro and Santawani while it showed a reversed J shaped size class distribution pattern with more individuals in the lower size classes in Vumbura. Diospyros mespiliformis Hochst. Ex A.DC showed a U shaped SCD pattern in Boro and irregular pattern in Seronga and Vumbura. Acacia nigrescens Oliv showed irregular SCD pattern with some missing size classes in Boro and Santawani and reverse J shaped SCD pattern with more individuals in the lower size classes in Seronga.Keywords: diameter at breast hight (dbh); Okavango; recruitment; size class distribution (SCD); species.Variação espacial da estrutura de tamanho da população de espécies selecionadas de árvores ribeirinhas no delta do Okavango, Botsuana Resumo: A transpiração de árvores ribeirinhas no delta do Okavango, Botsuana, cria um gradiente de salinidade que facilita o movimento contínuo de água dos pântanos para as ilhas. Isto leva a acumulações de sal debaixo das ilhas que minimizam a salinidade da água de superfície. O objetivo deste estudo foi investigar a variação espacial na estrutura de tamanho da população de espécies de árvores ribeirinhas no delta. Postula-se que a estrutura da população de árvores ribeirinhas irá variar espacialmente devido à diferentes condições hidrológicas. A vegetação ribeirinha foi monitorada em Boro, Santawani, Moremi, Vumbura e Seronga de um total de 75 terrenos de 20m x 50m. As espécies escolhidas para esse estudo, em termos de sua posição dominante foram Croton megalobotrys Müll. Arg, Philenoptera violacea (Klotzsch) Schrire, Diospyros mespiliformis Hochst. Ex A.DC e Acacia nigrescens Oliv. O diâmetro à altura do peito (DBH) foi medido em arbóreas com diâmetro do caule maior que 2.5 cm. A análise de regressão linear f...

show abstract

Section: Introductionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Spatial variation of population size structure of selected riparian tree species in the Okavango Delta, Botswana

Tsheboeng¹,

Murray-Hudson²

2013

Biodivers. Ecol.

View full text Add to dashboard Cite

show abstract

“…Once an island nucleus has thus formed, it grows by chemical precipitation, a process driven by the high evapotranspiration by trees on island fringes. The growth of islands is believed to occur by expansion in the soil within the vegetated fringes as a result of the precipitation of calcium carbonate and silica from the groundwater as the salinity of the water rises due to evapotranspirational loss of groundwater (McCarthy et al, 1993a). Evapotranspiration of groundwater also leads to a build-up of the more soluble salts and ultimately the formation of salt crusts (trona) on the islands.…”

Section: Study Areamentioning

confidence: 99%

“…The region is characterized by extremely low local relief, with a maximum relief of no more than 2 to 3 m (e.g. McCarthy et al, 1993a;Gumbricht et al, 2001). The average relief is much lower, and in kilometre-long transects, the standard deviation on elevation is typically around 50 cm.…”

Section: Introductionmentioning

confidence: 99%

The micro‐topography of the wetlands of the Okavango Delta, Botswana

Gumbricht

McCarthy

Bauer

2004

Earth Surf Processes Landf

View full text Add to dashboard Cite

The surface of the 40 000 km 2 Okavango alluvial fan is remarkably smooth, and almost everywhere lies within two to three metres of a perfectly smooth theoretical surface. Deviations from this perfect surface give rise to islands in the Okavango wetlands. This microtopography was mapped by assigning empirical elevations to remotely sensed vegetation community classes, based on the observation that vegetation is very sensitive to small, local differences in elevation. Even though empirical, the method produces fairly accurate results. The technique allows estimation of depths of inundation and therefore will be applicable even when high resolution radar altimetry becomes available. The micro-topography has arisen as a result of clastic sedimentation in distributary channels, which produces local relief of less than two metres, and more importantly as a result of chemical precipitation in island soils, which produces similar local relief. The micro-topography is, therefore, an expression of the non-random sedimentation taking place on the fan. Volume calculations of islands extracted from the micro-topography, combined with estimates of current sediment influx, suggest that the land surface of the wetland may only be a few tens of thousands of years old. Constant switching of water distribution, driven by local aggradation, has distributed sediment widely. Mass balance calculations suggest that over a period of c. 150 000 years all of the fan would at one time or other have been inundated, and thus subject to sedimentation. Coalescing of islands over time results in net aggradation of the fan surface. The amount of vertical aggradation on islands and in channels is restricted by the water depth. Restricted vertical relief, in turn, maximizes the distribution of water, limiting its average depth. Aggradation in the permanent swamps occurs predominantly by clastic sedimentation. Rates of aggradation here are very similar to those in the seasonal swamps, maintaining the overall gradient, possibly because of the operation of a feedback loop between the two. The limited amount of local aggradation arising from both clastic and chemical sedimentation, combined with constant changes in water distribution, has resulted in a near-perfect conical surface over the fan. In addition to providing information on sedimentary processes, the micro-topography has several useful hydrological applications. Copyright

show abstract

The role of biota in the initiation and growth of islands on the floodplain of the Okavango alluvial fan, Botswana

McCarthy

Ellery

Dangerfield

1998

Earth Surf. Process. Landforms

View full text Add to dashboard Cite

A group of islands of varying size on the floodplain of the Okavango alluvial fan, were studied to establish the processes which lead to the initiation and growth of islands. It was found that islands are initiated by the mound-building activities of the termite Macrotermes michaelseni. These termites import fine grained materials to use as a mortar for the construction of epigeal mounds. Their activities create a topographic feature, raised above the level of seasonal flooding, and also change the physical properties and nutrient status of the mound soil. Shrubs and trees are able to colonize these mounds, which results in increased transpiration. As a result, precipitation of calcite and silica from the shallow ground water occurs preferentially beneath the mounds, resulting in vertical and especially lateral growth, causing island expansion.

show abstract

Vegetation-induced, subsurface precipitation of carbonate as an aggradational process in the permanent swamps of the Okavango (delta) fan, Botswana

Cited by 100 publications

References 10 publications

Spatial variation of population size structure of selected riparian tree species in the Okavango Delta, Botswana

Spatial variation of population size structure of selected riparian tree species in the Okavango Delta, Botswana

The micro‐topography of the wetlands of the Okavango Delta, Botswana

The role of biota in the initiation and growth of islands on the floodplain of the Okavango alluvial fan, Botswana

Contact Info

Product

Resources

About