Deterioration in the water quality of an urbanised estuary with recommendations for improvement

Abstract

Water quality characteristics of the heavily urbanised and industrialised Swartkops River and Estuary in the Eastern Cape have been the focus of several studies since the 1970s. Overloaded and poorly maintained wastewater treatment works (WWTWs), polluted stormwater runoff and solid waste have all contributed to the deterioration in the water quality of the river and estuary. The objective of this study was to determine the current water quality status of the Swartkops Estuary, by investigating spatial and temporal variability in physico-chemical parameters and phytoplankton biomass and where possiblerelate this to historical water quality data. The present study found evidence suggesting that water is not flushed as efficiently from the upper reaches of the estuary as was previously recorded. Reduced vertical mixing results in strong stratification and persistent eutrophic conditions with phytoplankton blooms (> 20 μg chl a·L−1), extending from the middle reaches to the tidal head of the estuary. The Motherwell Canal was and still is a major source of nitrogen (particularly ammonium) to the estuary, but the Swartkops River is the primary source of phosphorus with excessive inputs from the cumulative effectof three WWTWs upstream. An analysis of historical water quality data in the Swartkops Estuary (1995 to 2013) shows that all recorded dissolved inorganic phosphorus measurements were classified as hypertrophic (> 0.1 mg P·L−1), whereas 41% of dissolved inorganic nitrogen measurements were either mesotrophic or eutrophic. If nutrient removal methods at the three WWTWs were improved and urban runoff into the Motherwell Canal better managed, it is likely that persistent phytoplankton blooms and health risks associated with eutrophication could be reduced.

Molecular Detection and Distribution of Six Medically Important Vibrio spp. in Selected Freshwater and Brackish Water Resources in Eastern Cape Province, South Africa

“…South Africa water resources have been adjudged unprotected (Christine et al, 2013;Colvin et al, 2016) while domesticated and wild animals activities around surface water generally cause contamination of water resources with pathogens (Cabral, 2010;McAllister and Topp, 2012;Decol et al, 2017;Topalcengiz et al, 2017;Liu et al, 2018). Furthermore, domestic wastes from informal settlements along the riverbanks, effluents from overloaded and poorly maintained treatment plants, polluted runoff, and solid wastes that are potential contributors of pathogens to surface water (Fatoki et al, 2001;Chigor et al, 2012;Edokpayi et al, 2017;Adams et al, 2019) were evident at our sampling sites. In addition, droppings from free-range and grazing cows were observed at most of our freshwater sampling sites.…”

Rhizosediments of Salicornia tegetaria Indicate Metal Contamination in the Intertidal Estuary Zone

“…Indeed, Watling and Watling (1982) and Nel et al (2015) both formed the conclusion that pollutants transported into Tippers Creek (Site 4) may be incompletely flushed by tidal action and may have resulted in its build-up over time. Adams et al (2019) recommended Tippers Creek as a long-term metal monitoring site.…”

Salt Marsh Restoration for the Provision of Multiple Ecosystem Services

“…The restoration intervention is to re-create aquatic habitat at an abandoned salt works by routing stormwater run-off from the Motherwell Canal to this site. A network of 14 stormwater drains transport litter, debris, and raw sewage (during infrastructure failures) down a 4.2 km long canal that services the large urbanized Motherwell Township [53]. Although some of the water from the canal enters an artificial wetland before entering the estuary, it is largely ineffective at coping with the high volume of stormwater that is received.…”