An assessment of the ecological condition of a wetland on the Lions River floodplain based on soil and vegetation parameters, South Africa

Abstract

Wetlands are increasingly exposed to human activities, resulting in degradation. As the wetland degrades, it loses functionality. In South Africa, wetlands can play an important water-regulating role. This study aims to establish the ecological condition of a historically utilised wetland on the Lions River floodplain in the uMngeni catchment, to provide a guide for the planning and implementation of rehabilitation interventions. A comprehensive assessment of the wetland’s structure was undertaken in 2014, using vegetation and soil parameters, mapped and compared with changes in landuse on the wetland from historical aerial photographs. The study concluded that the wetland’s ecological condition had declined, as a result of historical cultivation and commercial forestry. The wetland vegetation present is still generally aligned with the prevailing hydro-edaphic gradient and soil water regime; however, some areas of the wetland showed a mismatch in the soil water indicators and vegetation wetness indicators (the level of wetness based on vegetation being higher than that showed by the soil), suggesting localised drying out. A moderately high abundance of ruderal indigenous and invasive alien species in 61% of the wetland, particularly the drier areas of the wetland, contributed to the altered ecological condition.

Keywords:

• anthropogenic impacts
• invasive alien plants
• rehabilitation
• soil water regime
• wetland assessments