The ecosystem has been revitalised after Lake St Lucia and the uMfolozi River were relinked 18 months ago. Picture: iSimangaliso
The ecosystem has been revitalised after Lake St Lucia and the uMfolozi River were relinked 18 months ago. Picture: iSimangaliso

Lake St Lucia regenerating life

By VIVIEN VAN DER SANDT Time of article published Dec 27, 2013

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Durban - Lake St Lucia has changed the course imposed by history, which could have seen the massive estuary dying, by bouncing back towards its natural state and once again attracting sea and bird life.

The regeneration of the World Heritage Site began after it was relinked with the uMfolozi River 18 months ago. At the time water was pushed into the estuary for two months, iSimangaliso said.

For 62 years before that, the lake and the river had been kept separate by former managements of the St Lucia wetland area, in the belief that sediments carried by the uMfolozi posed a threat to the lake. However, the Isimangaliso Authority implemented a new ecological strategy, relinking it with the uMfolozi River in July last year.

Now the river runs back into Lake St Lucia, and scientific researchers are seeing positive results. These include a return to salinities more typical of an estuary, and the reappearance of fish and prawns which can now enter the lake from the sea. During last summer the lake system hosted 50 000 birds, almost half of which were migratory wading birds attracted by the rich food in the intertidal habitats at the mouth and other shoreline areas of the lake.

The lake is again functioning as a “nursery area” for sea life, allowing marine migrants to complete their estuarine-dependent life cycles.

The revitalised ecosystem has also attracted bird life. Last summer, the intertidal habitats at the mouth and other shoreline areas of the lake hosted a large number and variety of migratory wading birds attracted by the rich food resources present in the area.

“Because the uMfolozi River provides about 60 percent of the lake’s fresh water, the separation of the two systems deprived the lake of a significant inflow of fresh water,” explained iSimangaliso Wetland Park chief executive, Andrew Zaloumis.

“The loss of the uMfolozi (through it being diverted years ago) also altered the movement of sediments in the mouth area and affected the natural opening and closing of the St Lucia mouth.

“The implications of (the former) management approach became evident during the drought of 2001-2010, the worst in living memory. During this period, the lessening of the uMfolozi’s influence on the estuarine and marine environments caused the St Lucia mouth to close, with detrimental effects on the marine, estuarine and lake ecosystems.”

During that time the estuary became four separate bodies of water, disconnected from the lower estuary,” he said.

“Now, for the first time in a decade, the salinity gradient in the system is more typical of estuarine conditions, with low salinities in the upper estuary (Lister’s Point and Fani’s Island) and more marine conditions within the lower estuary (Narrows).

The changes can be seen in graphs compiled by researchers. In an estuary, salinities are usually higher near the mouth where the sea has the greatest influence and lower at the head of an estuary. At Lake St Lucia, this was not the pattern in the past.

“The results of recent multi-disciplinary science (studies) undertaken under the auspices of iSimangaliso have given us a better understanding of the uMfolozi’s hydrological and ecological importance,” said Zaloumis.

“The uMfolozi influences the opening and closing of the St Lucia mouth, the system’s overall water and salinity balance, and the movement of marine and river sediments which are a natural component of the estuarine environment.

“Following the joining of the two systems, modelling exercises suggest that the estuary will be open to the sea more often than it will be closed, and that the uMfolozi River exerts a necessary influence on the overall health of the St Lucia system.”

He said iSimangaliso remained committed to the new strategy, which also provides for the management of the estuary with minimum intervention.

“While it is likely that the mouth will continue to move northwards during summer, the dynamic impacts of river flow and wave action mean that the mouth could be positioned anywhere between Maphelane and St Lucia.

“Studies that refine our understanding of the lake are well under way. These will also propose management interventions that reflect this improved understanding. Our goal is to restore the long-term hydrological and ecological functioning of Lake St Lucia.”

He said the iSimangaliso Authority would continue to monitor the situation and investigations were well under way to find a long-term solution to the hydrological and ecological issues facing the estuary system. The multi-disciplinary study is supported by the iSimangaliso Global Environment Facility project.

iSimangaliso Wetland Park was listed as a world heritage site in 1999 for several outstanding universal values, a key component being its ecosystems and ecological processes that include the unique Lake St Lucia system.

 

Wetland supports variety of life

According to the Ramsar Convention on Wetlands, the area covered is 155 500 hectares, consisting of several principal habitat types.

It supports the largest estuarine prawn nursery area in South Africa and is an important migratory bird staging area, feeding ground for flamingos, and spawning and nursery area for many of the 82 species of fish supported.

It is also a breeding area for crocodiles. Large mammals include hippos and black rhino. Human activities have included cattle grazing, slash and burn cultivation, and the planting of (pine trees). The site is an important recreational area offering many facilities and activities. The site was threatened by large-scale mining for heavy metals, but spared. - Daily News

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