Algal Toxins in Water Supplies: It won’t happen here… or… will it?

19 August 2014

A couple of posts ago I mentioned the incident in Toledo (Ohio) that caused many to padlock (figuratively) their taps and take to their computers about the topic of algal toxins.  An article of a couple of days ago speculates whether water supplies in the Philadelphia area are even likely to produce toxic blue-green algal blooms. Based on experience I would hesitate to make such a sweeping statement.  Here are just three examples of why I say this:

Water quality can change suddenly and without warning...

Water quality can change suddenly and without warning…

Many years ago, shortly after taking up a position as Hydrobiologist for the City of Cape Town, I was taken on a tour of the reservoirs supplying raw potable water to the City, most of these dams some distance inland from the metropolitan area.  The newest and largest of these was broad and relatively shallow and located on a substrate somewhat rich in geological phosphorus.  This caused me to ask the official from the Department of Water Affairs whether or not his department was concerned about the risk of cyanobacterial blooms.  The reply was something to the effect that this would never be a problem as the local waters are rich in humic acids, creating an environment unsuitable for the development of blue-green algal blooms (this was about the same time that the National Regulator, in a spectacular flurry of idiocy, decreed that eutrophication would never become a real problem issue in South Africa! – mainly because a report that said it would had been hidden away).

Needless to say, the aforementioned reservoir produced a beautiful bloom of Anabaena solitaria a couple of years later and this organism has become a common component of the dam ever since, resulting in the need to remove (thankfully) just the taste and odour compound geosmin.

A couple of years later I was asked to investigate a massive stock death on a farm in the southern Cape – an area where the waters are very stained with humics and the ambient pH levels can be as low as 4 !  Some 400 pregnant milk cows died horrible deaths within a short distance of the tank of water they drank from.  Despite the low pH, the cyanobacterium involved in this case, an Oscillatoria species, had formed mats in the cement walls of the tank, creating an environment that was buffered against the acidity by the limestone.

In the third case, I undertook regular monitoring at the second-largest reservoir furthest from Cape Town, an off-channel impoundment that was designed to be fed by two canals, bringing water from two very different river systems.  The bulk supply originated from a very clean source – and sustained the dam in good condition, apart from seasonal blooms of the filamentous diatom Aulacosiera granulata – which did little more than hinder the engineers attempts to form a good floc in the treatment works.   The second river system drained an agricultural area and was known to be of low quality – resulting in myself and others warning against it being used to top up the reservoir.  Needless to day the water quality declined rapidly following the introduction of  this source, cyanobacterial- fuelled chlorophyll concentrations rose rapidly year on year and the toxin and taste and odour problems commenced.

So, moral of this little tale is quite small issues can demonstrably alter water quality, leading rapidly to a very unpleasant situation.  It is, therefore, somewhat reckless to lead the public, and officials for that matter, to believe that a problem like toxic algal blooms won’t occur in a particular waterbody.  All it takes is for an often very subtle threshold to be breached.

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