Lake St Lucia on road to recovery

THANKS to good summer rains and proactive measures instituted 18 months ago when the uMfolozi River was encouraged to re-link to Lake St Lucia, the iSimangaliso Wetland Park ecosystems are showing highly promising results.

A media release issued last week indicated ‘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’.

‘The joining of the two systems marks the end of a management approach which has kept them separate for the last 62 years, in the belief that sediments carried by the uMfolozi posed a threat to the lake,’ said iSimangaliso CEO, Andrew Zaloumis.

‘Because the uMfolozi River provides about 60% of the lake’s fresh water, the separation of the two systems deprived the lake of a significant inflow of fresh water.

‘The loss of the uMfolozi also altered the movement of sediments in the mouth area and affected the natural opening and closing of the St Lucia mouth.

‘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.

‘The exciting changes being recorded as a result indicate that natural processes are being restored and that the estuary is recovering.’

Rainfall

A total of 1505 mm of rain was received in St Lucia town over the past year (October 2012 – October 2013.

Good rains (540 mm) fell during the spring and summer of late 2012 and early 2013 with this trend continuing through autumn and winter 2013 (270mm and 150 mm respectively).

The first two months of spring 2013 yielded good rains with 185 mm recorded at St Lucia, and the trend continues.

Good rains have also fallen in the five river catchments that flow into the lake.

This has resulted in significant changes to the current ecological state of the whole Lake St Lucia system which stretches for 70 km from Maphelane in the south to the uMkhuze swamps in the north.

Water levels

The strongly flowing rivers have resulted in dramatic and sustained increases in the water levels throughout the lake system.

The uMfolozi has remained consistently joined to the Lake St Lucia system; its high water volume entering Lake St Lucia for over 14 months for the first time in 60 years.

The lake system is now one continuous water body from the mouth area near Maphelane to the uMkhuze wetlands in the north.

Water levels in the system are high and above mean sea level.

This increase in water volume has resulted in a change in living conditions for the plants and animals and has significantly increased habitat diversity and functionality throughout the system.

Mouth state

Because of the outflows from the uMfolozi River and the tidal currents, the estuary mouth has remained open since September 2012 creating a direct connection between the Lake St Lucia system and the sea via the beach spillway for the past 15 months.

Tidal exchange of water occurs during the high spring tides and even some of the higher neap tides, allowing both river and seawater to enter the estuary.