The cumulative effect of wetland degradation on water quality at a landscape scale.

Abstract

Wetlands have been described as “one of the most globally threatened and important ecosystems”, with most wetlands providing a variety of important ecosystem services, including water quality enhancement. Despite their importance the loss of wetlands is more rapid than that of any other ecosystem, which is of particular concern in South Africa, where many communities are directly and indirectly dependent on wetlands for survival. Two useful wetland assessment tools are currently used in South Africa, but a system that assesses the extent to which wetland ecosystem services (water quality enhancement in particular) are lost as a result of wetland degradation in a landscape context does not currently exist. This study therefore aims to develop a method to determine the cumulative effect of wetland degradation on water quality, which involves the exploration and integration of a number of issues, including land-cover and its effects on water quality, wetland health and its influence on the provision of ecosystem services such as water quality enhancement, and the spatial configuration of wetlands in a landscape, and its effect on water quality at a landscape scale. The method that has been developed is applied to a case study that comprises a quaternary catchment of the upper reaches of the Goukou River Wetlands in the Western Cape of South Africa. Prioritisation criteria are also explored in a series of scenarios, and the criterion and rehabilitation method that gives the best outcome in terms of water quality enhancement is applied to the case study catchment. The workings of the method are scrutinized and benefits and limitations are subsequently highlighted. An important benefit of the methodology is that many previously inadequately explored issues are integrated into a single tool that allows for prioritisation of wetlands for rehabilitation and conservation. This was achieved with South African contexts in mind. Limitations include poor responses by potential questionnaire respondents, while the scope of the study limits the inclusion of detailed aspects which would have further enhanced the accuracy of the tool and of the level of water quality enhancement explored. The methodology that is developed in this research has also not been applied to catchments with good long term water quality data in order to improve its validity. Recommendations for future research are made, which include possible refinement of the system by accounting for factors not included in the current methodology, validation of the system by applying it to a catchment with good water quality data, and the creation of software to make the system easier to use.