Samenvatting

Wetlands are recognised as critical components of blue-green infrastructure, offering flood mitigation and sustainable urban stormwater management solutions. These systems not only regulate water quantity, but also water quality through the natural filtration of pollution and waste water. Wetlands within highly urbanised areas are however increasingly exposed to significant pressures, through both natural and human induced stresses. This review aims to examine the performance of wetlands within the Cape Town area, containing prominent wetlands such as Zeekoevlei, Rietvlei, and the Cape Flats wetlands, all of which form part of conservation areas and play critical roles in biodiversity and urban water management. In addition to thousands of estuaries that all feed into an extensive aquifer system, the area contains over 300 natural and heavily modified wetlands, often referred to as treatment wetlands. Particular focus is therefore placed on their capacity to improve water quality, while exposed to regular hydrological extremes. Consideration is also given to physical changes that reduce wetland treatment capacities. This includes the loss or permanent change to many of these systems through drainage or infilling (to facilitate urban development), stormwater diversion, pollution, social pressures and climate change. This study investigates water quality dynamics across 34 sampling points (within 29 wetlands) over a seven year period. These points provide continuous data consisting of key quality parameters, including E.coli, P04-P, N, DO, NH3, pH, EC, Chl and microscystin (cyanobacteria). Assessment and long-term trend analysis of these parameters, provides critical insights into water quality over time, which also highlights seasonal variations. From the analysis of water quality data, it is evident that pollution levels consistently report above acceptable threshold levels. Temporal trends and pressures from pollution caused by inadequate wastewater treatment, urban run-off and agricultural activities, result in extreme spikes for all of the water quality parameters considered. It is also evident that sampling points in close proximity to informal settlements, that lack basic sanitation services and solid waste management, have a higher vulnerability to deteriorating water quality. Findings reveal that, even though wetlands within this area provide considerable biodiversity and ecosystem services, contamination levels exceed wetland treatment capacities. Although the city’s legislative framework provides for extensive wetland management and conservation strategies, water quality within these areas are likely to further deteriorate if current pressures and land-use management practices are not sufficiently addressed.