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The desiccated remains of a grunter, one of dozens, on the dry estuary bed of St Lucia. Photo Credit: Amanda Watson
An audacious plan to reverse nearly 60 years of human interference in the ecology of Lake St Lucia shifted into high gear this week. And with the St Lucia estuary in the dire straits it is, not only thanks to the drought but because of human meddling, the return of water from the uMfolozi River to the estuary cannot happen too soon, experts say.
“The artificial separation of the St Lucia and uMfolozi inlets underpins the most significant impacts on the water and salt budget of the lake, and its reversal is key to the sustainability of the system,” Robynne Chrystal wrote in her 2013 thesis for her engineering doctorate at the University of KwaZulu-Natal.
Chrystal notes a separate uMfolozi mouth was dredged open in 1952 to address silting and “to protect sugarcane farms in the uMfolozi floodplain from back-flooding during mouth closures. Since 1952 the management strategy has been to keep the inlets of the uMfolozi and St Lucia separate.”
With its natural feed cut off, the reduction to about 30% of the 325km2 of the lake’s surface area has had a devastating effect on local marine lifecycles. The prawn industry has already shut down, and the desiccated remains of starving grunter fish and mollusks litter the estuary’s sandy beach. “iSimangaliso has three estuarine coastal lakes within the park, where there are only four or five in the country. It’s also our biggest estuary at between 70-90km long,” says estuarine ecologist Nicky Forbes.
Standing on the jetty at Catalina Bay in iSimangaliso, the dry estuary bed is about two metres below our feet. The nceme – a type of grass favoured for weaving into baskets – is dry and withered. Fresh hippo spoor crisscross the bed, evidence of one of the largest populations in the country searching for less saline water.
“The estuary is very wide and very shallow, which makes for a very high evaporation rate,” Forbes explains. Aside from the obvious problems of evaporation, the increase in salinity to toxic levels is another. Sea water is constituted of 35 grams of salt to a litre of water. “At one stage it would have been at about 15 parts per thousand. Now it is about 250 parts per thousand in the remaining water.”
As the carcasses of fish and shells show, little survives these conditions. iSimangiliso Wetland Park CEO Andrew Zaloumis said an initial spend of R10 million – courtesy of grant money from the Global Environmental Facility and the World Bank – will see nearly 100 000 cubic metres of nearly 65 years’ worth of dredging, dumped into the estuary to close off the feed from the uMfolozi, reduced to slurry and pumped back into the ocean by Cyclone Engineering Projects.
After the initial work, there’s another R20 million to continue if the progress is good and the work done to specifications, Zaloumis says. It is key to remember the St Lucia estuarine system bed is below sea level, which means once opened, the uMfolozi River will continue to obey physics by flowing from a high point to a low point.
Forbes noted the mouth of the estuary will also be opened to mean sea level, which will allow for the crossover area between sea and freshwater lake to return to normality, which will encourage marine life to return to normal.