Dr Sarath Obeysekera 

AI Resources 

Continuous aeration and oxygenation have been successfully used in many countries to improve polluted lakes, although they are usually combined with reducing sewage and nutrient inflows. Aeration alone is not a permanent solution if pollution continues.

Some notable examples are:

1. Germany – Lake Tegel, Berlin
   • Continuous hypolimnetic (deep-water) aeration has been used since the 1970s.
   • Oxygen levels were restored in the deep water, fish populations recovered, and phosphorus release from sediments was significantly reduced.
   • The project is regarded as one of Europe’s successful lake restoration programmes.
2. United States – Onondaga Lake, New York
   • Once one of the most polluted lakes in America due to industrial waste and sewage.
   • Restoration included sewage diversion, phosphorus reduction, dredging, and continuous oxygenation/aeration.
   • Water quality improved dramatically, and many fish species returned.
3. Sweden
   • Several eutrophic lakes have been restored using continuous aeration systems powered by electric compressors.
   • The objective was to prevent oxygen depletion in the bottom waters and reduce internal phosphorus loading.
4. New Zealand – Rotorua Lakes
   • Bubble plume aerators and artificial circulation systems have been installed in some lakes.
   • These systems reduce algal blooms and improve dissolved oxygen, together with catchment nutrient management.

Lessons for Beira Lake

For Beira Lake, continuous solar-powered aeration could be a cost-effective part of the solution. It would:

• Increase dissolved oxygen.
• Reduce foul odours caused by hydrogen sulphide.
• Improve aquatic life.
• Accelerate natural degradation of organic matter.
• Reduce the release of phosphorus from sediments.

However, aeration must be accompanied by:

• Complete interception of sewage and polluted stormwater entering the lake.
• Desilting and dredging where necessary.
• Long-term management of nutrient inputs.

Pumping seawater through the lake to flush it, as has been suggested by some, could transfer contaminated water into the harbour and adjacent coastal waters, potentially affecting the marine environment and Port City. In contrast, continuous aeration treats the lake in situ without exporting pollution.

Given your engineering background and previous role at the SLLRDC, a proposal advocating continuous solar-powered aeration together with interception of sewage inflows and selective dredging would be technically sound and consistent with internationally proven lake restoration practices.

M

Regards

Dr Sarath Obeysekera