Oxygen in Your Pond: Are Your Levels up to Par?
|By ED BEAULIEU|
Oxygen is one of—if not the most—vital element on the face of this earth.
Read any science journal or even look it up on the internet and you will not find anyone who will dispute that fact. the truth is that oxygen is vital to many different organisms on earth, not just humans.
Our watery fish friends are no different. they just get the oxygen from a slightly different source than we do. fish and aquatic plants get oxygen from the water; your pond is bursting with life because of the oxygen in and around it.
How does it get there?
Yes, the formula for water is H 2o, but the formula’s oxygen contribution alone isn’t the only oxygen present in your pond. Just because oxygen is a part of the formula doesn’t mean there’s enough of it to sustain aquatic life. the oxygen actually comes from several different sources, but the most common is good old-fashioned absorption. oxygen from the atmosphere is absorbed into the water. Agitation at the surface and splashing (as in a waterfall) increases the absorption of that oxygen into the water because of the expanded surface area created.
Another way that oxygen gets into the water is through aquatic plants, but you certainly can’t rely on aquatic plants to do all the work. It’s a double-edged sword, really. Lots of folks know that plants with submerged foliage can produce massive amounts of oxygen. When the sun shines on them, they use carbon dioxide and produce oxygen. But plants don’t grow much by day, so they store that energy. When they grow at night, they use that stored energy, producing carbon dioxide and using up oxygen. In other words, when nighttime hits, submerged plants (a.k.a. oxygenators) are not your fishes’ friends.
Some of the best oxygenators (also known as submerged aquatics) are fast growing plants with lush foliage that grows under the water line, including anacharis, elodea, and cabomba, as well as a not-so-favorite plant, algae.
Oxygen is essential
Once the oxygen is present in the water, it is used by aquatic plants and animals for respiration. Respiration is a key to their growth and survival. Oxygen is even used by bacteria to help break down dead plant material. So how much oxygen is needed for fish to survive? Minimum levels should be at five parts per million (PPM), allowing the fish to live a few days, but levels of eight PPM would be more desirable. Levels of 11 to 14 PPM are the best. Keeping fish means maintaining a suit able oxygen level. It’s certainly as important as the very water in which they live . . . water is not enough.
Keeping your cool
Pond owners in colder climates always seem to get the short end of the stick in other areas of water gardening, but in the case of oxygen levels in backyard water features, they’ve got a bit of an edge.
In case you don’t remember from Chemistry 101, colder water (under 60° F) dissolves (or carries) more oxygen.
Regardless of whether you’re in a warm or cool climate, you’ll want to be careful with your fish during clean-outs. Putting fish in a tank or tub in the heat of summer for a clean-out can be risky. If you don’t aerate or agitate the tank or vat, or the tank or vat is left in the sun and heating up, your fish may be in danger, due to low oxygen levels. You can simply aerate or agitate water that’s over 75 degrees. An air stone makes this task simple and easy. For a little extra help from Mother Nature, pick a nice, shady spot for the fish to hang out while you do the dirty work!
Where does it go?
Hot weather isn’t the only villain in the dissolved oxygen saga. There are a few common ways that oxygen levels are reduced. The most obvious is fish and plant respiration, which is why it’s so important to make sure you don’t overstock your pond. One inch of fish per square foot of pond is the recommended stocking number, keeping in mind that fish grow and you need to save room for them.
Bacteria are also culprits in oxygen respiration, and beneficial bacteria have especially voracious metabolisms when it comes to consuming oxygen. Your pond’s bacterial flora consumes more oxygen than your fish could ever attempt to. So basically, the very things you need and want in a pond consume the most oxygen. Isn’t that ironic?
Less common ways that may cause dissolved oxygen levels to fall include decaying algae, treatment with chemicals, and the depth of your pond. Algae eats up oxygen as it rots away, consuming massive amounts of the precious element. If your fish are sick, you may also want to keep an eye on the oxygen level of the water. The use of certain chemicals in the pond for treating fish diseases can consume a lot of oxygen. It’s a good idea to agitate the water while treating the fish.
Also, the depth of your pond plays a role in the available oxygen in the pond. Ponds over five feet deep, for example, will have low dissolved oxygen levels at the bottom. This will be true unless there is a means to bring the bottom layer of water to the surface.
Too much of a good thing?
A question still lurks in the back of many a pond owner’s mind. “Is there such a thing as too much oxygen?” The oxygen in a pond is usually at a decent level as long as there is sufficient water movement. A robust waterfall is enough to give a normal residential pond enough oxygen. Generally, oxygen entering the water through its contact with the atmosphere is the only way oxygen mixes with water.
There is an exception to this rule, however. A single, very rare condition can occur where there can be too much oxygen in the water. If fish are kept in a deep pond in full sun, and the bottom of the pond is covered in algae, it is possible that with very clear water, the algae can super-saturate the water column with micro-dissolved oxygen. If there is no shade and no way for fish to leave this water column, then the saturated dissolved oxygen may result in gas bubble disease in fish. One of the reasons that this is very rare is because it would only happen in the warmer months with warmer water, when saturation with oxygen is virtually impossible. In other words, since the water is generally warmer in the summer months, it would be quite odd if this actually happened.
Testing . . . one, two, three
If you catch fish gasping for oxygen at the water, you may want to look into the oxygen level. There are a couple of test kits on the market that can help you find out if your pond is up to par with oxygen.
Finally, don’t forget that ponds are meant to be relaxing oases, providing relief from the troubles of the day. Running out and testing a pond every day is not relaxing. If the oxygen level in the pond is good, there’s no need to try to improve the levels. The fish and plants in the pond get used to their surroundings and have probably already adjusted to the pond’s chemistry. Just remember that favorite pond pets are just like you, living and breathing the same air . . . just a little bit differently!
EdITOR’s NOTE: Ed Beaulieu is chief sustainability officer at Aquascape, Inc. www.aquascapeinc.com.