Wetlands as early warning (eco)systems for water resource management

Abstract

This paper describes a case study which investigated impacts of a change in catchment land use from natural grassland to commercial forestry on the hydrological regime and distribution of vegetation in a small hillslope seepage wetland near Nottingham Road in the KwaZulu-Natal Midlands. Hydrological modelling was used to estimate the reduction, following afforestation, in surface and subsurface stormflow runoff provided to the wetland by its catchment. Stormflow runoff was shown to have decreased substantially following afforestation, and since the wetland had no input association with a stream or river, its reliance upon surface and subsurface runoff derived from its catchment was considered to be high. Zones of wetness within the wetland were delineated based on edaphic characteristics. Wetland vegetation was classified, using TWINSPAN, into 7 communities. After comparing the edaphic-defined and floristic-defined boundaries of the permanent to semi-permanent wetland zone it was discovered that the area of permanent to semi-permanent wetland vegetation had decreased from its pre-disturbance (edaphic-defined) extent. Implications for water resources management are considered, with particular attention paid to determining the Ecological Reserve for wetlands, and the potential role that wetlands could play in providing an early warning of hydrological change in a catchment.

Keywords: wetland ecology, delineation, water resources management, Ecological Reserve

Water SA Vol. 31(4) 2005: 465-472