Study begun into causes of swarming at Bedok Reservoir
Lim Yan Liang Straits Times 10 Mar 12;
IT IS likely that the midge infestation that hit Bedok Reservoir twice since 2011 was due to a combination of environmental factors that wreaked havoc on the eco-system there. That is what experts as well as the authorities have said, although they were quick to add that more time was needed to study the problem.
Rainfall, temperature, wind direction and changes in water quality, such as the amount of nutrients, could all have added up to cause the midge swarming, said the National Environment Agency (NEA) and national water agency PUB.
But they could not conclusively determine as yet the cause of it, said a spokesman representing both agencies.
The issue was raised in Parliament on Tuesday by Aljunied GRC MP Low Thia Khiang, who pressed the Ministry for Environment and Water Resources repeatedly for a progress update as well as long-term solutions.
The green and blue flies made their appearances at Bedok Reservoir in large numbers in January last year and this year, causing inconveniences to residents and businesses.
Senior Minister of State for the Environment and Water Resources Grace Fu said the government had commissioned a three-year study to look into the problem.
The study, which began in January this year, involves researchers from the National University of Singapore's Tropical Marine Science Institute and Department of Biological Sciences; entomologists from NEA's Environmental Health Institute as well as an overseas midge expert.
They have been tasked to identify the species involved, investigate if the infestation is related to weather or water quality changes, and suggest potential solutions. Residents may have to live with the problem for a while - PUB and NEA say the team has to collect at least two years of data in order to understand what the triggers are.
While some residents speculated that the appearance of midges might be linked to the rainy season, none could explain why they only started becoming a problem two years ago when the reservoir itself is more than 25 years old.
'I've lived here for 20 years and this wasn't a serious problem till two years ago,' said Madam Huang Chew Hong, a shop owner at Bedok Reservoir Road. NEA and PUB said unlike reservoirs like MacRitchie which are located in protected catchment areas with mature eco-systems more than a century old, Bedok Reservoir is man-made and constructed from a former sand quarry.
'Being an urbanised reservoir, the eco-system at Bedok Reservoir may not be adequately balanced or established, and there may not be sufficient predators to feed on and control the midge populations,' said the spokesman.
The midge infestations did result in a jump in spider and swift numbers, both predators that feed on midges. PUB said it is looking into planting flora that can attract such predators to act as a long-term biological control method.
Professor Peter Cranston, the expert involved in the study, told The Straits Times in January that one possible reason for the scale of the infestation here was the onset of heavy rain, which washed nutrients from the soil into the reservoir. This in turn caused the algae in them to bloom, boosting the number of midges as their larvae feed on algae.
Another possible reason for the infestations might be warmer temperatures more conducive to algal growth, said Pestbuster Rentokil Initial technical manager Lim Min Hui.
When contacted, Mr Low said the focus should be on the water eco-system, since that is where midge breeding occurs. He also felt more could have been done sooner.
'I would have expected the study to have at least commenced in early 2011 when swarming occurred, if not earlier,' he said.
Interim measures such as scrubbing of the reservoir wall and removal of plants near the bank to reduce breeding should have been implemented, he said.
An NEA-PUB task force continues to fog reservoir grounds three times and apply larvicide five times a week.
Additional reporting by Chow Jia Ying and Chong Ning Qian
