Thursday, January 14, 2010

Some thoughts on the fish kill at Pasir Ris

I must admit I have not been following the news about the recent fish kill at Pasir Ris as close as I should have. But thanks to Ria, her blog posts quickly brought me up to speed on the sequence of events. Here are the links with further links inside the webpages.
  1. Dead fish patrol: Pasir Ris
  2. Any dead fish at Changi?
From all accounts, the situation appeared to be a classic case of eutrophication. Put simply, eutrophication is an excessive growth of algae (sometimes, the term plankton is used though they are not the same) caused by the introduction of nutrients into an ecosystem. Depending on the type of algae, the nutrients may be nitrate, phosphate, silica or others.

Without further information from AVA (or NEA which was strangely silent in this whole episode) about the kind of algae (or "plankton" as given in the media) in the seas off Pasir Ris, I can only surmise that nitrate and ammonia (which can degrade to nitrate) are the probably culprits. In general, seawater is limited by nitrogen so once a sudden excessive input of nitrogen (in the form of nitrate or ammonia) rushes in, the algae immediately makes the best of this bonanza to multiply.

Nitrate is commonly found in fertilisers (yes, it is good for plants too!) and sewage (an decomposition product of ammonia). The question is: who was releasing these fertilisers or sewage? One suggestion was the incidental heavy rains have washed fertilisers or sewage into the sea. Of course, the question remains: where did these fertilisers and sewage come from?

Algae grows fast but they die fast too. Dead algae is major bad news as they decompose, using up dissolved oxygen (DO) in the water. Since many marine organims can only breathe DO, they are in trouble. However, marine organisms are not created equally. Some are more hardy than others since they need less DO to survive.

Wouldn't oxygen from the air replenish the loss of DO in seawater? Yes, it would but the rate of replenishment lags far behind the rate of DO usage in decompostion. Imagine lots and lots of algae dying and taking up DO. Atmospheric oxygen wouldn't have a chance!














Figure: Eutrophication at Botanic Garden (Nov 08). The greenish water is a dead giveaway.
Monitoring by AVA
According to AVA, regular monitoring was in place even before the recent fish kill event (Straits Times Forum 11 Jan 10). When the fish kill occurred, its staff was monitoring daily.

It will be great if AVA can reveal more about its regular monitoring programme - how regular? where are the monitoring stations? What kind of data are collected? For its daily monitoring during the fish kill episode, in addition to the above questions, can AVA reveal the following - what kind of algae was detected in the bloom? Was there a spike in the nutrient levels? What kind of nutrients? What is the trend for DO during the monitoring period?

What about NEA? It has many water sampling stations along the coast. Can their data shed any light on the fish kill? For that matter, NEA has never elaborated on its monitoring programme either i.e. kind of data collected, frequency of collection. Its water quality results have never been in the public domain (except for bits and pieces in its annual report.) (That goes the same for PUB. Have you ever tried requesting for a copy of the analysis report of the tap water that goes to your house?)

Figure: NEA sampling stations in both inland and coastal waters (taken from NEA website a few years back as it no longer could be found currently)

For some reason, water quality data are considered confidential in Singapore. Do such data constitute an issue of national security? Or are the agencies concerned about a vulnerability in their legal position?

Check out the extensive data placed online by the Environmental Protection Department (EPD) of Hong Kong.

Or the data compiled by USGS (U.S. Geological Survey) for the USA.

3 comments:

ria said...

Thank you! For this very enlightening explanation of the situation!

It is indeed frustrating that there is so little information released on what has been learnt about the incident.

Gardeners said...

thrice, once in East Coast road, once in Ang Mo kio and another time in Jurong, I suffered fish death in fish tanks and fish ponds when I added tap water into the tanks and ponds. These had happened in the last 2 years and prior to that it had not happened in last 20 years I had been keeping fish. For the East Coast case, I called in PUB to check the water quality but was never given the test results. The officer just tell me that although the water is not safe for fishes, their job is just to make sure it is safe for people and not for fish. ???

KCK said...

Gardeners: We are unlike in the U.S. where water companies are obliged to provide water quality test results to their consumers upon request.

Perhaps PUB is more of a government agency than a business entity so customer may not be king.