In an Expert Focus article for Waterbriefing, Alan Scrafton, Group Sales and Marketing Manager for leading environmental services provider, Adler and Allan, explains the risks and implications of oxygen depletion, plus best practice for dealing with a common summer problem.

The warm weather we’ve been experiencing this summer is, for most, a welcome change. For still water courses, however - such as lakes and ponds - the hot, dry spell can cause oxygen depletion; a disaster for the aquatic life within these habitats. Warm weather aside, polluting spills are a key contributor at any time of year.

Lack of oxygen or an ‘oxygen crash’ is extremely damaging to fish and other creatures relying on the affected environment, whilst also damaging water quality. Once under way, oxygen depletions are fairly easy to recognise. Partial depletions are characterised by fish hanging at the water surface, or a loss of appetite in ponds where fish are fed – if fish are dead, this means the problem is extremely serious.

Oxygen depletion causes

Warm water: During summer months in deep watercourses (eight feet or greater), the upper four to six feet warms quickly and becomes less dense. Because the upper layer is lighter, it does not mix with the cool, deep water which consequently becomes stagnant; oxygen is depleted and toxic compounds may be produced by bacteria and decaying organic matter.

Algal blooms and decaying organic matter: Algal blooms are one of the primary causes of oxygen depletion and can occur en masse in still, warm waters; in fact this combination of factors is a more likely cause than increased nutrients – commonly a result of high phosphorus levels. The nutrient status of the water simply enables the bloom to grow quicker. If algal blooms are dying this is not necessarily a good thing either - dead and decaying matter will consume oxygen during the rotting process further exacerbating the problem – that goes for any organic matter left to rot.

Polluting spills: A polluting spill, such as plant fertiliser, could in itself cause increased nutrient levels and therefore algae (as mentioned above). Other hazardous liquids such as milk, for example, can also be extremely damaging. A case Adler and Allan dealt with a few years ago, where milk got into the water course from a processing plant, caused the oxygen levels to crash to critical levels within 24 hours, demonstrating how important a quick reaction is in these types of circumstances.

Combatting oxygen depletion

When it comes to protecting the environment, prevention is always better than cure. To minimise the risk of algal blooms taking over, organic silt – often the source of the problem – should be removed. Treatments for oxygen depletion include mechanical aeration and the addition of hydrogen peroxide to the water. Oxygen water testing kits and quality meters are available, enabling continual monitoring and fast action as soon as a problem is detected.

If a waterway is at particular risk of a polluting spill (as per the milk example) then an appropriate spill response procedure should be in place. Spillcare kits, of which Adler and Allan provides, can deliver a good first step in the event of an emergency. Beyond your own efforts, it’s essential to have an emergency spill response and oxygen depletion specialist on call to minimise damage – to oxygen levels and the environment in general – should disaster strike.

Mechanical aeration equipment: Mechanical aeration systems come in two types: aeration re-circulators, which provide flow and de-stratification, and aerator circulators which utilise the Venturi principle to introduce huge columns of air into the aerator slipstream.

Aeration equipment can either be submerged or external to the water. The submerged motor type is capable of being put under water to varying depths – from close to the surface, where they can also help with de-gassing - to up to five metres deep, delivering a more intense re-oxygenating affect. Submerged motor aerators and re-circulators are inconspicuous as well as being silent in operation, so particularly well-suited to rod and line fisheries.

Hydrogen peroxide: Applying hydrogen peroxide to the watercourse is a fast and effective way to boost oxygen levels in an environmental emergency situation, such as following a spill. Hydrogen peroxide is also useful in controlling algal and bacterial growth for open water swimming and immersion sports.

Liquid barley straw can be used, more commonly on a small scale - in a garden pond for example. It provides a slow release of hydrogen peroxide and helps develop the ‘biological maturation’ necessary to keep the eco-system stable.

Rapid response - acting fast is key

Adler and Allan’s extensive experience has shown that acting fast is key - an oxygen crash can prove hugely damaging to wildlife. The provision of emergency oxygen depletion response services, with experts on hand to rapidly assess the situation and deal with incidents plays a key role in minimising the risk. The firm uses a dedicated team of qualified operatives to administer hydrogen peroxide and ecologists in place to continually monitor oxygen and peroxide levels during and after an oxygen depletion solution has been deployed.

For more information about Adler and Allan oxygen depletion systems; including aeration equipment and hydrogen peroxide administration; visit www.adlerandallan.co.uk, or contact: 0800 592 827.