“The sulphide levels are very, very high, as is the organic matter level. I am still waiting for results on heavy metals which should come tomorrow (Mar 9), and the pH level is quite neutral,” Dr Vipawee Dummee told The Phuket News today (Mar 8).
“The black muddiness level has not changed at all since the release of the wastewater into the bay two weeks ago,” she noted.
“For levels of organic matter, we compared South Patong, which is Tri Trang, to Northern Patong. The organic matter of Tri Trang was 2-6 times higher than that of northern Patong.
“Sulphide at Northern Patong was not detected (below 1 milligram per kilogram) while South Patong has a value of 3-17 mg/kg, which is very high, indicating that there is organic spoilage on the seafloor,” she said.
“Wastewater, which contains settleable solids, fine particles and organic matter, which is especially fiber from human manure, becomes a mud-like sediment.
“This muddy coating does not get washed away and does not dissolve in water. We do not know whether maybe the upcoming monsoon season will wash it away,” she added.
“Also, due to chemicals in wastewater from municipalities such as washing excrement and so on, including nitrogen and phosphorous, which are the same in fertilisers, goes into natural water and causes algae blooms which float on top of the water. This has occurred at Patong several times before.
“But when the nitrogen and phosphorus mix with the sediment which has sunken on the seafloor, it will cause the growth of blue and green algae which covers the sea floor.
“Eggs or larvae need to settle on the seafloor, such as prawns, crabs and coral,” Dr Vipawee explained.
“The algae will die and decompose but it will continue to grow back. It is expected that within this year, many populations of sea species will be rendered unable to reproduce due to algae covering the entire seabed.
“The result depends on the rate of oxygen that penetrates into the seafloor. Oxygen reduces the amount of sulphide.
“Organic matter will be decomposed by bacteria, and if there is oxygen, it has no effect. but if there is not enough oxygen, organic matter will turn into sulphide, which is toxic,” she explained.
“The mud layer is the barrier, it blocks oxygen at the top.
“In the short term, there is no noticeable effect from the untreated sewage. There has been some coral bleaching, but right now the coral is already beginning to recover, so there is no sufficient damage,” said Dr Vipawee,
On Feb 23 Dr Vipawee told The Phuket News that the soft corals, which are Mushroom Leather corals or Sarcophyton sp, covering an area of about one rai were being damaged. (See story here).
“The bleaching is starting to occur when small parts of the raw sewage drop onto the corals. It is blenching right now,” she had said.
Dr Vipawee updated The Phuket News that this morning (Mar 8), the Mushroom Leather Corals are already “doing better”.
“We are at ease with the short term effects. There are no surprises for now. But it is the long term effect that could be dangerous to the marine life.
“Many people are unaware that Patong Bay has an abundant marine life, equal to around Koh Khai for example. There is this notion that Patong Bay is just rocks and sand, that is wrong. There is a lot of life. We need to look after it better.
“For example today, we discovered that there is a new population of hundreds of giant clams in Patong Bay,” she noted.
“These clams were not previously thought to not exist in this area any more. They are able to close their shell when there is harmful matter in the water and survive. The tide moves the wastewater away, and then they re-open.”