Spatial and temporal analysis of the nitrate concentrations in groundwater for South Africa

Abstract

The aims of this investigation was to create an updated view of the nitrate distribution for the country, to identify whether there are any gaps or significant changes in the distribution of nitrate concentration over the sampling record and identify areas where nitrate pollution occurs as an ecological hazard for priority research and remediation. Data was sourced from the national groundwater database for the entire country for the period up until 2008. Previous maps used data pre-1990 and up to 2001. Additional nitrate data was sourced to supplement the NGDB data. The data was evaluated using excel pivot tables, and maps plotted using ArcMAP. Maps of the total count representing the total number of points sampled and their densities for South Africa, as well as the minimum, maximum and average nitrate concentration for the various decades were used to evaluate the extent and duration of nitrate pollution in South Africa. The nitrate concentrations were overlayed on the geological or hydroterrains and land cover for South Africa to investigate if there are links between lithology, land cover and nitrate concentrations. Comparison of maps compiled for different periods indicate that the Western Cape now has elevated nitrate levels, possibly associated with agricultural stock farming. The Northern Cape Province, in particular the Kalahari has elevated nitrate levels, but a distinct lack of recent sampling may mask the extent of the current spatial distribution of nitrate concentrations. The scarcity of sampling points within urban centres makes it difficult for pollution monitoring and control to take place.