BY TAN CHENG LI
Foul flows: A proliferation of algae — most likely caused by raw or partially treated sewage — has coloured the sullage green. This drain on Pulau Perhentian Kecil discharges straight into the sea. — Filepic
Sewage pollution is slowly marring the coral reefs of Pulau Perhentian in Terengganu.
THE coral reefs of Pulau Perhentian are slowly losing their hues. Instead of a riot of colours that come from healthy coral polyps, they are now increasingly being covered by dull, brown algae.
These marine plants occur naturally on reefs but if there are excessive nutrients in the water, such as from fertiliser and sewage, they will proliferate and crowd out other reef organisms.
A report by Reef Check Malaysia (RCM) says the average algae cover of 10.6% over the last five years at Perhentian is far higher than the national average, which in 2010 was 3.3%.
Once widespread, the algae cover can no longer be kept under control by algae-grazing fish (and other herbivorous organisms). It then takes over the reef, smothering and killing corals. It also reduces the clean surface available for recruitment of new corals on rock and old dead corals, hindering the recovery of reefs. Algae-dominated reefs are less diverse and less productive than coral-dominated reefs, and they lose much of their value, particularly for tourism
RCM says there has been a marked decline in the area of hard corals in Perhentian since 2009, to just 36% (“fair” condition) in 2011. The decline coincides with a period of consistently high (though fluctuating) levels of algae on the reefs.
Given the absence of other sources of nutrient – there are no industries or farms on the island, plus it is 20km from the nearest river on the mainland – the likely trigger of the algae growth is sewage pollution.
A study by Environmental Resources Management (which was engaged by RCM) has indicated sewage pollution around Perhentian. Of the 13 resorts surveyed, only two were found to have adequate sewage treatment systems that operate according to discharge limits. Eight resorts have systems that require maintenance and refurbishment (generally involving desludging), while three have systems that require complete upgrades.
However, the ERM study discovered poor maintenance of septic tanks, with only one resort reporting that sludge is transported back to the mainland for treatment. Some operators have never desludged their septic tanks. Those which do, routinely discharge sludge directly to sea or land.
“It is considered highly likely that this is contributing to the spread of algae on the coral reefs, which, if not reversed, could significantly damage the reefs in the next few years,” says RCM.
It, however, does not support the plan for a central sewage plant for the island. The reasons: there is limited water and electricity supply to run the facility; the lack of flat land for a large installation; resorts are far apart and to connect them to the plant, sewage pipes will have to traverse the channel between the islands; and the considerable disruptions to terrestrial ecosystems during installation of pipework as the islands are hilly. Also, many resorts are located on rented land with very short rental terms (usually only two years). There would be significant difficulties in negotiating between land owner and resort operator regarding costs of installation.
As an alternative to a large, centralised sewage treatment plant, RCM proposes improving the existing septic tank systems by regular desludging and better maintenance. It says septic tanks, if properly designed and maintained, can be adequate in preventing sewage pollution. Representatives of Indah Water Konsortium (IWK), who visited the island in February 2012, agreed too that a desludging operation is a better option than constructing a full-scale plant.
Other East Coast islands are suffering from sewage pollution similar to Perhentian’s. No detailed survey of sewage treatment systems is available for the islands but RCM personnel, who regularly visit these places for surveys and other programmes, have observed poor sewage infrastructure. In Pulau Tioman, owners of two resorts more than 20 years old said they have never desludged their septic tanks. Water quality sampling by RCM in 2009 at 11 sites in Tioman found several sites to be highly contaminated with coliform bacteria, indicative of sewage pollution. Levels were particularly high at Salang village, which has several large resorts, but lacks adequate sewage treatment facilities. In Pulau Redang, a stream in a resort area regularly has odours related to sewage pollution. In Pulau Aur, reefs near three resorts are covered with algae.
RCM suggests that IWK investigate the possibility of providing a mobile septic tank desludging facility to service the resorts on all East Coast islands. It says providing such a facility should be viewed not as a cost but as an investment in protecting coral reefs, which are the foundation of the economies on the islands, bringing in an estimated revenue of RM360mil annually.
Source: The Star