“Nature has many rules, one of these being that, when any kind of nutrient enters a water course, it won’t just sit there. It will grow something, somehow, some time!”
Surface aeration at Wentworth Bad water leads to fish kill
1.5hp per surface acre for proper aeration. Lake bed aeration is a method of
compressing atmospheric air and pumping it to the lake bottom, allowing it to flow through a series of lake bed positioned ‘air diffusers’, which create micron-sized bubbles that act as an airlift.
The misconception with lake bed aeration is that oxygen is transferred to the water through the bubble. Whereas, in reality, less than 5% of oxygen is transferred this way. As bubbles rise through the water column they expand. Cascading bubbles entrain cold, dense, oxygen starved water below the thermocline and lift it to the surface, allowing the hydrogen sulfide and carbon dioxide gases to escape to atmosphere.
At the same time, oxygen is absorbed into the surface water, and eventually circulated throughout the entire water column. The bottom of the pond
becomes aerobic and metals such as iron are precipitated out of the water, while phosphates are again rendered unavailable for the algae to use as a food source. Unlike surface units, lake bed
aeration uses an unconfined airlift technique, with the amount of energy required to circulate the entire volume of the lake or pond reduced. To size a system using this technique, the entire water volume of the water body is calculated, together with the number of bottom placed diffusers to ‘turnover’ the entire water volume once per day. Your lake or pond, and its fish, depend on oxygen for life. Just like you and me, if the oxygen supply is cut off, for even fifteen minutes, fish die. It does not matter how high the level was earlier in the day, you must be concerned with extremes as well as the chronic low levels that may not necessarily kill the fish, but definitely stress them.
As low oxygen conditions continue, the build up of harmful gasses continues, thermal stratification will become worse and the potential of a deadly mixture, that can result in a fish kill, increases. In a fertile green water pond, algae
will typically draw more oxygen at night than will the fish.
A heavy accumulation of sediment can also draw more oxygen than the fish. This, combined with the green water at night, may result in seeing dead fish spread across your pond in the morning. Here are some actual numbers:
- 1kg of fish will consume about 0.3 grams of oxygen per hour
- Ten thousand litres of ‘green water’ will consume about 190 grams of oxygen per hour
- Sediment oxygen demand for a mucky pond is 2.27 grams per square metre.
- With no mechanical aeration, and relying on the wind, still water rate of oxygenation from the atmosphere at night is about 0.0075 grams per square metre per hour
In summary, if left alone, nature will try to turn your lake or pond into a marshland. You have the ability to slow down and
even reverse that process. An aeration system, be it a display aerator or lake bed system, is the life support for your pond. If your lake or pond has gone ‘bad’, then aeration may be your best rescue solution.
For more information on lake and pond aeration systems contact Hydroscape Ltd. Telephone: 01425 476261 or email:
sales@hydroscape.co.uk
Step into the future
Scotts Professional is now Everris. Same people, same products, new opportunities.
Tel: 01473 201100 | Fax: 01473 830386 | Email:
prof.sales@
everris.com |
www.everris.com 39
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