Historical land use change and its influence on stream ecosystems and water quality (#119)
The southern Cape region, Western Cape, South Africa, is an area of focus as it occurs in a climatic transition zone between the winter and summer rainfall, making it vulnerable to climate change. The area has been exposed to several natural disasters, e.g. floods, droughts and sea storm surges, which are predicted to worsen as the climate becomes warmer. The study area occurs in the Duiwe River catchment on the Kleinkeurbooms and Duiwe River. Agriculture is the main land use and water user with an increase in population growth. As the demand for water increases the availability and quality is affected. The history of the area plays an important role in understanding impacts on the river systems both in terms of water quality and fluvial change. A catchment scale land use/cover change detection analysis (1936-2013) was performed together with time series precipitation, flow and water quality data. Land cover mapping showed that by 1959 irrigated pastures became the dominant land cover and irrigated vegetables increased threefold. Irrigated vegetables and irrigated pastures reached their maximum extent in 1966 as dairy farming became the main industry with the upper catchment dominated by Pinus species plantations. The impact of agricultural abstractions are substantial and has changed the flow character of the Duiwe River in its lower reaches from perennial to non-perennial flow at times. Invasive alien plants, mainly Acacia species have also impacted the aquatic ecosystem by reducing river flows and invading riparian zones causing banks to destabilise and erode.