Saturday, July 23, 2011

How to get rid of your seemingly unstoppable pond algae

Excessive growth of algae (aka algal bloom or eutrophication) is not a new problem in Singapore. You can sometimes see a canal or even a reservoir taking on an unnatural greenish or bluish tinge. For the aquarium hobbyist, it is just as tough a nut to crack as the algae is removed physically, chemically or biologically, only to return with fresh vigour after a while, seeminlgly impossible to kill.

Figure: "Orange" algae in stream in Chinese Garden (Apr 2011)

 Figure: Pond badly overgrown with "green" algae at Sungei Buloh Wetland Reserve (SBWR) (Mar 2011)

Figure: Another shot of the same pond in SBWR (Mar 2011)

With a sprinkling of scientific principles, here are my sentiments on curbing this tough guy.

First: scoping out your opponent
Find out who this tough guy really is. Algae comes in all sorts of flavours, from red, green, blue-green, brown to diatoms and dinoflagellates. To really nail it down to species level, you will need molecular techniques in well equipped labs. Since most of us do not have access to such high powered stuff, we will have to settle on visual examination under microscope. (I agree that most of us do not have a microscope stashed away at home either but at least most schools should have a few to play with.)
 Figure: Microcystis spp under 10x magnification

Figure: Anabaena sp under 10x magnification

Once you have an idea of your guy, check out his characteristics. How does he grow? What are his most important nutrients? Which nutrient is the limiting one? In the case of the above 2 algae, they normally bloom in an excess of phosphorus usually in the form of phosphate.

Second: scoping out your water
Hey, this is water quality blog so yes, you have to check out your water quality. The standard parameters include: dissolved oxygen (DO), electrical conductivity (EC), turbidity, pH, alkalinity, hardness, nitrate, ammonia, phosphate, biochemical oxygen demand (BOD), chemical oxygen demand (COD). Feel free to add more if you have the resources but the above should be a good starting point. Throw in chlorophyll a (a chemical found in algae) if you think you are up to it.

Go through your water quality data. Is there anything wrong besides the algae you observe? Anything amiss could point to some systemic problem that might have triggered the algal bloom. Following the above examples of Microcystis and Anabaena, the phosphate level is likely to be elevated.

Comparative studiesUnfortunately, it is hard to define what is meant by elevated in a natural environment impacted by numerous uncontrollable factors. One way is to make comparisons. Ideally, you should compare the same variable against time i.e. what was the phosphate level 1 year, 5 years, 10 years ago. Unfortunately, almost no one in Singapore (short of PUB in their reservoirs) does regular long term water quality monitoring (WQM) of their water bodies.

The alternative is to compare against a nearby "clean" water body. Since it is algae free, does it have a lower phosphate level?

Third: scope out your environment
Assuming you have discovered elevated phosphate level in your algae infested pond, ask: where does it come from? What are the sources of water flowing into your pond? Does surface run-off carry fertilisers from your next door vegetable farm neighbour into your pond?

You may have to check historical records too as your pond  may be sitting on an old farming area. If your pond sediment is choked full of phosphate from chicken waste from the previous chicken farm, you will have to get rid of the sediment.

I am all for long term solutions so learning the source of problem and tackling it at the source has always been my principle.

Fourth: ACT
As mentioned earlier, you may have the option of physical, chemical and biological methods.

Drain your pond and dredge out your sediment if it is the source of phosphate. You may also mechanically remove your algae via nets and filters

Add alum or other chemicals (there are quite a few exotic ones in the market now) to bind the phosphate in your water into solid form and remove the solids.

By the nature of their operations (e.g. nature parks), some organisations are reluctant to use physical and chemical methods. Biological methods like phytoremediation appears appealing because of their naturalness. Yet, they may not pack the punch necessary to remove the nutrient (e.g. phosphate) sufficiently.
Other actions
Naturally, if the source of nutrient appears to come from your surroundings, you probably to get your neighbours into the picture to discuss ways to resolve your problem.

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