This point was raised during a lecture given on Monday by Dr David Le Maitre, of the CSIR Natural Resources and the Environment Unit in Stellenbosch.
He estimates that the Duiwe River's flow has been reduced by about 86%. This has altered the flushing of the Langvlei and Bo-Langvlei lakes and has probably increased the accumulation of nutrients, chemicals (pesticides) and sediments. The extensive invasion of alien trees have compounded the problem.
The lakes, including Langvlei, Bo-Langvlei and Rondevlei, are interconnected and situated along the N2 in Wilderness to the south of the Hoekwil, Touwsranten and Woodville areas where a lot of water is extracted for agricultural activities, including cattle farming, wheat and vegetable growing.
He was sharing his expertise as guest lecturer during a BTech Nature Conservation Fresh Water Management class while speaking on the topic 'Developing an approach to assessing the impacts of land-use on river water quality'.
He gave a PowerPoint presentation showing preliminary findings of a model he has developed. A more in-depth study, with systematic water sampling and monitoring, is underway to confirm these findings.
Problem solving
In reply to a question as to what can be done about the situation, he said there was a need to bring everyone who had interests in the water quality in the lakes and rivers together, to discuss the problems and identify solutions. The aim of these discussions should be to find ways to ensure that water quality was improved and the rivers and lakes conserved for the benefit of all its inhabitants and tourists.
Dr Le Maitre is currently working on projects looking at the relationship between biodiversity, ecosystem service generation and benefit flows, focusing on water and land productivity; and modelling impacts of invasive alien plant species on water resources, biodiversity and rangelands in South Africa. This is for use in prioritising species and catchments for control measures.
Dr Le Maitre is a plant ecologist specialising in conservation biology, invasion ecology of Cape fynbos vegetation and also has expertise in assessing the hydrological and ecological impacts of invading alien plants and the dynamics of invasion processes.
Touw River healthy
On the upside, Dr Le Maitre said the Touw River showed a 100% healthy flow, which means that SANParks' Ebb and Flow site and Wilderness had the benefit of enjoying good water quality. This is because there is relatively little human activity in the catchment of this river.
The Wilderness lake system as seen on Google Earth shows The Serpentine River, Island Lake, Langlvei and Rondevlei from left.
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