Analysis of temporal and spatial changes in major dissolved salts in the Vaal River system over a 40 year period

Abstract

In this study, the fluctuation and variation in salinity composition of the Vaal River and its catchment area was investigated between 1975-2015. Long-term data sets gathered from a 40-year span collected across nine monitoring station in the study catchment area was analysed. The statistical tool applied for the data analysis is the Maucha diagram, as well as the Origin software used in plotting graphs. These graphs revealed several trends and patterns. The graphs and the Maucha diagrams reflected long-time changes in salts composition and concentration in the water of the Vaal River and its catchment area over a 40-year period. From the data analysed, the graphs plotted, and the Maucha diagrams, the salinity of the Vaal River was majorly total alkalinity (TAL) and sulfate (SO4) dominated, with a substantial amount of Calcium (Ca2+). However, the concentration of other salts remained relatively constant during the duration of study. Analysis of 5-year averages of TAL, SO4 and total dissolved solids (TDS) concentration showed that zones and sub-catchment uniquely impacted variation in salinity levels and composition. Furthermore, salinity levels and composition in zones 1 and 4 were greatly impacted by water from the Lesotho Highlands and the Orange River, respectively. The salinity level changes of the Vaal River were mainly attributed to anthropogenic sources such as pollution from (mining) industries, increased urbanisation, economic expansion, paving of roads, increasing population, water transfer in and out of the river’s catchment area and irrigation outflow from agricultural activities. Based on the salinity concentration of the Vaal River and the effect on humans and the environment, routine continuous monitoring and sampling programmes are recommended to be carried out by the National government. This will help to make informed decision on managing the salinity levels of the Vaal River and mitigating any negative attendant consequence of increased salinity.