They are open on both sides, land and sea, thus blow by blow pressure awaits South Africa’s estuaries if we all don’t act now.
A report released on Friday by the Water Research Commission indicates there is an increase in sea level and sea storms causing loss of estuary habitat due to erosion. An estimated 78% of estuaries are impacted by overfishing, 60% by artificial breaching, 40% by land use development, 34% experience severe pollution pressure, 15% are subject to severe flow modification, while alien or translocated fish occur in 35% of all estuaries.
In addition to increasing human pressure and climate change, South Africa is experiencing an increase in both the duration and frequency of droughts and devasting effects of large floods.
The Swartkops Estuary has a present ecological health indicator of 47 % similar to its natural condition. Back in 2014, a study by Van Niekerk etc al recorded a score of 53%.
The decrease in health can be attributed to nutrient rich freshwater as a result of three upstream Waste Water Treatment Works (WWTWs). According to the report, this has led to an increase in eutrophication and deterioration in health of macrophytes due to extensive mats of Invasive Alien Plants (IAAPs) that are fast growing because of high nutrient input.
Moreover, bait collection and overfishing are also major pressures in the estuary. Due to all these pressures, there has been a decline in birds due to the drying of the salt pans.
Researchers then set out to map different scenarios for the recovery of the Swartkop, which can increase the current score to at least 59%.
Key findings and recommendations of the study include the following:
• Estuary restoration should take place using a socio-ecological systems framework.
• Innovative methods can improve estuary water quality.
• Abandoned salt pans can be used for the treatment of stormwater run-off.
• Sustainable urban drainage systems can improve water quality as shown for the Chatty River
and treatment train implemented in the Markman Canal.
• The size of an artificial wetland must be large enough to cope with the volume of stormwater
inflow, otherwise the wetland can act as a source of nutrients (e.g. Motherwell Canal).
• Estuary primary producers act as important bio-accumulators of metals and nutrient filters.
• Environmental flow and restoration scenarios were used to show the improvement in estuary
health following restoration interventions.