Physical and hydrological properties of peatland substrates from different hydrogenetic wetland types on the Maputaland Coastal Plain, South Africa

Abstract

The Maputaland Coastal Plain in KwaZulu-Natal province is home to 60% of all peatlands occurring in South Africa. These ecosystems are increasingly threatened by unsustainable agricultural utilisation, a growing population and climate change. The aim of the study was, therefore, to investigate wetland type characteristic substrates and their physical properties in order to provide more detailed knowledge about the agricultural impact on them. Six study sites were selected and detailed profile descriptions as well as in situ measurements of different physical and hydrological soil parameters were conducted. Soil samples were analysed with laboratory measurements of the saturated hydraulic conductivity, water retention characteristics and hydrophobicity. In addition, the bulk density as well as the organic carbon content were determined. Saturated hydraulic conductivity, hydrophobicity and total water retention capacity were highest for peat derived from wood, which furthermore presented the lowest bulk densities and was found to occur only in channelled and unchannelled valley-bottom wetlands and was absent in interdunal depression wetlands. It was concluded that drainage and clearance of forested valley-bottom wetlands has severe impacts on the physical peat properties. Potential subsidence of low-density peat and consolidation aggravate the danger of flooding and hydrophobicity increases the generation of surface runoff and subsequently the risk of erosion.