The effects of population growth on the groundwater quality of a sandy rural catchment

Abstract

Maputaland is a natural environment situated along the northeast coast of South Africa. Within this area a small section of about 8000 ha was studied with respect to the quality of water from incoming rainfall, the groundwater, the streams and lakes to the outflow through the small Mgobezeleni Estuary. The study area is a representative sample of the Maputaland Coastal Plain that runs from the Lake St Lucia World Heritage site to the Mozambican border. All the water in the area emanates from rainfall with no rivers flowing into the area. Projects initiated from the 1960s by the government in order to improve the welfare of the local population have resulted in a large influx of people, both residents and tourists. The population in the catchment is made up of a relatively small local population that has risen from almost zero in 1970 to about 15 000 in 2015. There is a large annual visiting population of up to 250 000 that is economically valuable to the small resident population. The result is that accommodation facilities have increased together with the necessary infrastructure of water supplies and sewage facilities. The groundwater quality indicates that the sewage facilities are impacting the nitrogen and phosphorus concentrations but that these levels are not present in the lakes into which the groundwater flows. The presence of large amounts of fringing macrophytes in one lake and a high density of cyanophyte microalgae (or cyanobacteria) in the other indicates that sewage pollution is the cause. However, the lakes appear to be removing much of the sewage pollution because the estuary water below the lakes has a high quality. These data suggest that similar pollution might adversely affect other areas of Maputaland, which have a growing tourist population attracted to the Maputaland game parks.