The role of beneficial bacteria in maintaining a healthy pond.
Bacteria fulfil so many vital roles in shaping life on earth that we are still discovering new ways in which they affect the world we live in.
They are so adaptable that they are found in every ecosystem on the planet and even as man makes new niches or materials, it is never long before bacteria have colonised them and started to break them down as a source of energy.
Bacteria are both man’s ally and enemy, performing beneficial roles such as breaking down waste and making antibiotics while others invade living organisms causing diseases such as tuberculosis and even anthrax.
It is not long after being introduced to koi keeping that we soon discover the two types of role that bacteria can play in our hobby. Those that cause diseases such as ulcers, septicaemia and fin rot and the beneficial bacteria that colonise filters to help keep our water quality balanced.
We are all probably guilty to a certain degree of dumbing-down the impact that bacteria have on a koi pond. We are happy to give bacteria the credit of managing the nitrogen cycle in our ponds, breaking ammonia down into nitrite and then into nitrate – but nothing much else on top of that. But this is merely the tip of the iceberg when considering the breadth of influence that these backroom boys have in maintaining both our ponds and our koi in tip-top condition.
The ‘bio’ in biofilter is actually credited to bacteria – the biological means by which the water is filtered. When we manage our ponds so that the water quality is maintained, what we are actually doing is providing the pond so that it is suitable for bacteria to thrive in so that they can maintain the pond’s stability by processing the vast array of waste products produced in a pond. So what makes bacteria so good at what they do?
Bacteria – What are they?
Bacteria are microscopic organisms that were first discovered in the late 17th century. They are generally between 0.5 and 1.5(m in length(1/10000th of a cm) and can be seen through a high powered light microscope. They live as single cells or as colonies and can live off a wide range of food including either organic and inorganic materials (such as iron, sulphur and even concrete) They reproduce asexually by budding off other bacteria, taking with them a copy of the DNA. This process can take as little as 10 minutes enabling bacteria to colonise new areas very rapidly.
Bacterial Functions in a pond.
The bacterial breakdown of toxic ammonia into nitrites and then nitrates is at the top of every koi keeper’s list when discussing the roles that bacteria play in maintaining a koi pond. This is because ammonia is a direct threat to our koi and we have test kits readily available that can measure how well our filter are coping with the breakdown of ammonia into nitrite.
But the extent to which bacterial activity plays a part in determining the quality of our pond environment is far greater than the nitrogen cycle this and by appreciating the needs of other beneficial bacteria, we can assist them as well to maintain as natural a pond environment as possible.
Heterotrophic bacteria.
Food items that bacteria breakdown can be divided into 2 groups – those that are organic (i.e. contain carbon and are the product of life) and those that are inorganic (such as simple compounds containing nitrogen, sulphur and phosphorous etc). Heterotrophic bacteria are concerned with the first group of compounds and are like you and I in that they will digest these compounds so they can absorb the soluble nutrients. Heterotrophic bacteria have a much greater role to play in a mud pond compared to a koi pond as the environment is typically organically rich. Mud ponds will readily accumulate organic matter in a silty, soft pond bottom – and these bacteria proliferate in such an environment, exploiting the settled organic matter.
Heterotrophic bacteria
Are often described as mineralising bacteria as they breakdown the complex organic molecules into their simple building blocks (or minerals). These same bacteria will accumulate in a settlement or vortex chamber where there is a high concentration of organic matter. Heterotrophic bacteria demand a great deal of oxygen from the water, something that is directly proportional to the amount of organic matter available (both solid and dissolved in the water). While this does not pose such a problem in a lightly stocked, balanced clay pond, an intensively stocked koi pond could soon become stressed if DO levels start to decline. It is advisable to keep dissolved organic carbon and particulate organic matter to a minimum in a koi pond by regular purges of mechanical filters and the installation of a protein skimmer to removed DOC.
Although heterotrophic bacteria are very obliging and will soon get to work on available organic matter, this could actually have an overall negative effect on the pond and you should keep their workload to a minimum.
When things go wrong.
If for any reason, organic matter is allowed to accumulate, or if excessive amounts of food are offered, then the resulting population explosion of heterotrophic bacteria would soon lead to other problems. Because bacteria are simple, single-celled organisms, they digest organic matter by releasing their digestive enzymes into the surrounding pond water, absorbing the products of digestion through their cell walls. They will do this while being attached to adjacent hard surfaces close to the organic matter (if not the organic matter itself). Consequently, when there is an abundance of organic matter the pond can soon deteriorate to resemble a stomach and intestine, releasing lots of CO2, methane, ammonia with the enzyme cocktail resulting in an acidifying and oxygen-depleted environment. This change in the pond water cannot be tolerated by higher organisms, including koi and would soon result in koi gasping at the surface.
Autotrophic bacteria.
hese bacteria gain energy from the chemical bonds that make up inorganic compounds such as ammonia, phosphate and sulphates. Many different bacteria (besides the well documented Nitrosomonas and Nitrobacter) are involved in the breakdown of nitrogenous compounds in a koi pond. Other bacteria include Nitrocystis and Nitrosogloea (besides others) each exploiting their own particular niche. Where no filter exists in a mud pond, these bacteria will coat exposed hard surfaces including the microscopic particles of clay suspended in the water, representing a huge (yet natural) fluidised bed filter. Their requirements in a clay pond are the same as we provide for them in a filter system – oxygenated water and the supply and removal of waste products.
Just as there is a plethora of bacteria that process nitrogenous waste, there are also bacteria whose niche is the breakdown of other inorganic compounds such as sulphates and phosphates. In the same way that nitrifying bacteria gain energy from processing nitrogenous compounds, sulphur bacteria (often identified with the prefix Thio) and phosphate loving bacteria act as middle men, processing and recycling these nutrients that are vital to a ponds wider ecology and stability. These are not as familiar to us as nitrifying bacteria as the consequences of them underperforming are not as catastrophic. Nevertheless, we need to be aware that these and many other types of bacteria are at the heart of the all recycling of nutrients in a pond environment, and other bioprocesses are reliant on the regular throughput of products by these bacteria.
What’s in the slime?
You will have noticed that it doesn’t take long for a bacterial slime to coat anything that is placed in a pond. Bacteria will soon become attached to and colonise a hard surface, secreting a slime onto that surface that eventually even covers themselves. Research has shown that bacteria actually take and absorb their ‘food’ be it organic or inorganic as it absorbs into this slimy zoogloeal film. This living slime coat has a lifecycle of its own, and gets thicker and deeper over time. In fact, it becomes attractive to heterotrophic bacteria that target it as a source of food. Eventually, the film becomes so thick that the bacteria closest to the hard surface die off, causing the film to drop off, leaving space for a new colonisation.
Bacteria are the ultimate reprocessors and are the middlemen involved in processing the full range of organic and inorganic compounds in a pond. In fact, so fundamental is their role in the management of the earth’s environments that biodegradable products are only biodegradable because of bacteria.
Bacteria play a far greater role in maintaining good water quality than simply processing ammonia into nitrate, to the extent that when we say we are managing a koi pond, in effect we are providing the correct conditions for those bacteria to manage our pond’s environment for us.
