Abstract
This study aimed to link land cover/use change to water quality in an important water supply coastal catchment. The approach followed a spatial and temporal analysis of historical catchment land use change to assess how changes influenced water quality and river flow in the Touws and Duiwe Rivers, southwestern Cape, South Africa. Each sub-catchment has unique characteristics which influence land use and water quality and the purpose was to analyse each one separately. Historical water quality and flow analysis were based on the records available (Duiwe River: 1998–2013; Touws River: 1980–2013) together with rainfall data. Records were analysed to detect trends over time, which were linked to changes in land use activities. Agriculture intensified rapidly in the Duiwe River catchment with most arable land cultivated by 1960 and water storage as farm dams escalating. Concentrations of nutrients and electrical conductivity were higher in the Duiwe River than in the more natural Touws River, and were positively correlated to river flows. Mean values for total nitrogen and electrical conductivity were 0.03 mg/L and 16.7 mg/L, respectively, in the Touws River and 0.25 mg/L and 127 mg/L, respectively, in the Duiwe River. Nutrient concentrations decreased in the Duiwe River after 2006 as fertilizer applications to pastures were reduced. The South African Target Water Quality Ranges were exceeded at times and in the Touws catchment this appears to have been due to extensive fires. For instance, sodium concentrations reached a maximum of 1 874.5 mg/L in 1996 compared to a usual average concentration of 20.8 mg/L where the guidelines are between 0 and100 mg/L. The link between land cover/use and water quality was demonstrated and when spatial heterogeneity of the catchments was altered by human or natural events, this was reflected in changes in the water quality. Keywords : land cover, spatial analysis, sub-catchment scale
Highlights
Water is a limited resource and water quality deterioration is a major threat to water resources in Southern Africa, given the prevalence of natural climatically-driven water scarcity
This study focuses on land cover/use and how it has changed on a sub-catchment scale and within a buffer zone of two mainstem rivers, the Touws and Duiwe, thereby influencing water quality and flows, in an important water supply coastal catchment
The study demonstrates the link between land cover/use and water quality and the role of temporal and spatial scales in understanding the influence of land cover and management of land use activities on water quality
Summary
Water is a limited resource and water quality deterioration is a major threat to water resources in Southern Africa, given the prevalence of natural climatically-driven water scarcity. National-scale assessments of water resources showed that freshwater and estuarine ecosystems are highly threatened by intense land use pressures escalating from river source to sea (Nel et al, 2011). The cumulative impacts from freshwater systems are received by coastal ecosystems and the effects of land cover change can negatively impact productivity, biodiversity and ecological functioning of these ecosystems (Lemley et al, 2014). Managers are realising that their strategies need to extend further inland to include the impacts on water quality and flow in rivers feeding these systems (Lemley et al, 2014). An understanding of the influence of land use and management within a catchment is required to assess the impact of non-point source pollution on water quality. The management of land use activities can play a role, e.g., altering river channels or changing the imperviousness of a surface (Brummer et al, 2016) so surface water discharge increases or decreases (Royall, 2013) altering the flow in rivers and groundwater and affecting the physical, chemical and biological processes in the receiving water bodies (Tong and Chen, 2002)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
