Effects of land use change on soil and water quality and plant species composition of Cedara wetlands.

Abstract

Wetlands are vital in the provision of ecosystem services and land use change could affect their functioning and health. Disposal of organic waste slurries on wetlands could result in high nutrient loads, whereas drainage for agriculture, could adversely affect their characteristics, particularly soil properties. The purpose of this study was to assess the effects of land use changes on soil chemical properties, water quality and plant species composition of three wetlands at Cedara. One wetland was used for discharge of sewage effluent and dairy slurry; another was drained using ridge/furrow system and used for pasture production, while the third, undisturbed wetland, was used as the control. A soil survey was carried out to identify soil forms and soil sampling was done on transects at 0–20, 20–40, 40–60 and 60–100 cm depths, and the samples were analysed for pH, clay content, total C and N, CEC, exchangeable K, Ca, Na, Mg, available Mn, Zn, Cu and P. Water samples, taken during different seasons from upstream, midstream and downstream positions, were analysed for quality parameters. Grass species were identified for species composition. Wetland areal extends were greater when soil properties were used to delineate wetland bounderies than when diagnostic plant species were used. The dominant soil form in all wetlands was Katspruit, with Pinedene, Clovelly, Griffin and Hutton on the edges. Soils in all wetlands were acidic, with the drained wetland having higher pH, Ca and Mg concentrations. The dairy/sewage wetland had significantly higher P, Zn and Cu than the ridge/furrow drained wetland while the undisturbed wetland had the least. The undisturbed wetland had higher total C, N and available Mn concentrations than the other two. In the water samples pH, Ca, Mg and P was higher in the ridge/furrow drained wetland than the others. The undisturbed wetland had higher species composition and had more wetland plant species than the other wetlands which mostly had pasture grasses. The findings suggested that land use change will reduce soil C and N and available Mn, and modify the concentrations of available P and micronutrients and bases in the soil, impair water quality and ultimately result in loss of wetland plant species diversity.