Timber industry linked to St Lucia woes
THE crippling drought and indirect effects from sugar farming have both been blamed for drying up Africa’s largest estuarine lake – yet the timber industry may also be linked to the recent drop in water levels at Lake St Lucia.
This estuarine lake system depends on a mixture of fresh water from rivers, rain and groundwater, as well as salty water from the sea.
Over the past several months the surface area of the lake has shrunk by nearly 70%, mainly because of poor rain and the high temperatures that have increased evaporation levels in the heartland of South Africa’s first World Heritage Site.
Decades of sugar-cane farming along the Mfolozi flood plain has also been identified as a significant contributor to the drop in water levels, owing to the diversion of river water that once fed Lake St Lucia.
Now it appears that tree plantations on the western shores of the lake may also play some part in exacerbating the critical water shortage in one of the country’s biggest nursery grounds for sea fish, prawns and other marine species.
Numerous studies going back several decades have cautioned that commercial timber growing, especially of gum trees from Australia, sucks up large volumes of groundwater.
Some of the earliest warnings date back to the 1960s when the Kriel Commission of Inquiry voiced concern about timber plantations and the need to ensure that the lake’s water supply was protected against further commercial tree plantations in the five river catchments feeding the lake.
In 1991, University of Zululand hydrologist Brian Rawlins calculated that 25 000ha of deep-rooted pine and gum trees planted around the lake could reduce groundwater inflow into Lake St Lucia by as much as 30% – but only during extreme dry periods.
Although about 16 000ha of these plantations have been gradually removed over the last 15 years, the SiyaQhubeka Forests group still has almost 15 000ha of plantations along the Western shores section of the park.
Mondi, the 65% majority shareholder of the SiyaQhubeka plantations, has acknowledged its responsibility to mitigate the negative impacts of timber farming, but noted that the low water levels at St Lucia have been exacerbated by extreme drought, several years of below-average rainfall and “gross modification” of several river catchments feeding the lake.
Nevertheless, recent studies by University of the Free State hydrologist Claudia Brites showed that gum trees in the Mondi/SiyaQhubeka plantation at Nyalazi on the western shores lowered the groundwater table by almost 16m over a period of 13 years – almost 1m each year. Prof Bruce Kelbe, from the University of Zululand’s hydrology department, conducted a report for the Water Research Commission in 2010, suggesting that commercial forests on the western shores were having a significant effect on groundwater discharge into the lake.
He reported that the importance of groundwater flow to the lake in years of normal rainfall was negligible. But when there was a drought, as in 2004-2005, groundwater became the “only source of freshwater” into the lake and played an important role in diluting high salinity levels.
Kelbe’s report also illustrated the importance of groundwater flows in the Siyaya estuary at Mtunzini, noting that timber plantations in the Siyaya catchment had completely dried up the estuary after sugar plantations were replaced with gum trees in the 1990s. Before that, he said, neither the Siyaya or Manzamnyama streams had stopped flowing.
During the 2004-2005 drought, aerial photographs revealed groundwater flowing down the beaches along the eastern shores of Lake St Lucia, helping to dilute high salinity levels and provide areas of refuge for freshwater species.
In her 2013 study on the environmental impacts of timber plantations on Lake St Lucia, Brites concluded that each gum tree used at least 16 litres of water each day in SiyaQhubeka plantations on the lake’s western shores.
Her study suggested that these gum trees used more than twice as much groundwater compared to nearby indigenous vegetation.
Balanced against this evidence of water depletion by the timber industry, however, there is also clear evidence that human modification to other river catchments – especially the Mfolozi River – have played a major role in starving the lake of fresh water.
A recent scientific review by the Water Research Commission suggests that: “There is now little doubt that St Lucia will be unable to survive as a World Heritage Site unless it obtains Mfolozi River water (especially during droughts).
In this review, former Ezemvelo KZN Wildlife ecologist Ricky Taylor said the decision to separate the mouth of the Mfolozi River from the Lake St Lucia estuary in 1952 was a “pivotal point” in the recent history of the lake.
“Without Mfolozi water, there is insufficient freshwater during drought periods to sustain the St Lucia ecosystem in the state that it used to be in under those same conditions. The longer and more severe the drought, the greater the ecosystem changes that occur.”
Estuarine specialist Professor Anthony “Ticky” Forbes commented that the time for talking was over.
Now it was time for action to start restoring the lake’s ecological health.
“What has happened at St Lucia can only be described as a national estuarine catastrophe,” he said, noting that the shallow-water prawn fishery around the Tugela Banks had collapsed and there had also been a reduction in the number of migrant sea fish able to use St Lucia as a nursery ground.