Selected soil properties and vegetation composition of five wetland systems on the Maputaland Coastal Plain, Kwazulu-Natal

Abstract

South Africa has a few unique and understudied areas of interest regarding wetlands, of which the Maputaland Coastal Plain (MCP) is one. This is regarded as a large gap in scientific knowledge, especially since firstly, the MCP is regarded as a unique area in terms of biodiversity, geology, social history, and ecosystem variety; and secondly, wetlands are a vulnerable, and yet a greatly important ecosystem type in South Africa. Additionally the wetlands on the aeolian derived sandy soils associated with the MCP are problematic to delineate. Although the wetland delineation guideline of DWAF (2005) gives a list of criteria to aid the delineation process on sandy coastal aquifers, this has never been scientifically reviewed. The aim of this study was to investigate how vegetation and soil properties vary down the topographical slope in various wetland types on the MCP. This was done in order to contribute to the knowledge base and understanding of wetlands in this area, as well as to determine whether differences between zones are significant enough to be used as indicators of wetland boundaries. Soil colour was investigated as a possible new delineation indicator. A section is also devoted to commentary on the current wetland delineation procedure on the MCP. This study shows that wetland types on the MCP are very distinct from each other, and therefore broad statements about the soil and vegetation characteristics of wetlands are discouraged. Three substrate types namely high organic-, duplex-, and sandy substrates dominate wetlands on the MCP. These play a major influential role in the general characteristics and function of the wetland types. Contrary to popular belief, redoximorphic accumulation and -depletions do occur on the MCP, but are often inconsistent in their presence. Chemical soil properties were found not to be good indicators of wetland boundaries on the MCP, although certain patterns can be discerned and applied to determine wetland conditions. The main drivers of wetland vegetation are the wetness- and productivity gradients. A few prominent indicator species can be used for the identification of wetland and non-wetland sites specifically on the MCP. Additionally, a relatively underutilised vegetation assessment procedure called Weighted Averaging was investigated, and can in most cases effectively discern between wetland and non-wetland conditions. This is a useful tool to apply in delineation practices in addition to other indicators. Soil colour can be used to successfully indicate wetland boundaries, and therefore be used as an additional wetland indicator. However, the method requires further testing and refinement for different wetland types. In general the vegetation and soil indicators do not correlate perfectly, and therefore delineation by means of one indicator only is greatly discouraged. An investigation of recommended delineation procedures for the MCP shows that new information on the understanding of wetlands in sandy coastal aquifers urgently needs to be disseminated. Approaches such as that of the USDA-NRCS where regionally specific guidelines are designed to be adapted regularly as new information becomes available, as well as the development of sets of hydric indicators specific to problematic areas, are recommended